[libcamera-devel,1/1] libcamera: controls: Add DigitalGain control
diff mbox series

Message ID 20201027141246.4708-2-david.plowman@raspberrypi.com
State Superseded
Headers show
Series
  • DigitalGain control
Related show

Commit Message

David Plowman Oct. 27, 2020, 2:12 p.m. UTC 
This control reports the global digital gain applied by the pipeline
as a whole, after capturing a raw image from the sensor.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
---
 src/libcamera/control_ids.yaml | 11 +++++++++++
 1 file changed, 11 insertions(+)

Comments

Kieran Bingham Nov. 16, 2020, 10:40 a.m. UTC | #1 
Hi David,

On 27/10/2020 14:12, David Plowman wrote:
> This control reports the global digital gain applied by the pipeline
> as a whole, after capturing a raw image from the sensor.
> 
> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> ---
>  src/libcamera/control_ids.yaml | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> index c8874fa9..e6362c74 100644
> --- a/src/libcamera/control_ids.yaml
> +++ b/src/libcamera/control_ids.yaml
> @@ -530,4 +530,15 @@ controls:
>          This control is only present when the pipeline supports scaling. Its
>          maximum valid value is given by the properties::ScalerCropMaximum
>          property, and the two can be used to implement digital zoom.
> +
> +  - DigitalGain:
> +      type: float
> +      description: |
> +        Global digital gain value applied to the image during all the
> +        processing steps after capturing the image from the sensor. Any raw
> +        images, therefore, will not include this gain, but the final images
> +        output by the imaging pipeline as a whole will include it.
> +
> +        This control is intended to report the value used by the image
> +        processing pipeline.


If this is a per-stream thing anyway, I guess it will then be up to
pipeline handlers to set this to the appropriate value for each stream
when it completes. The fact that this value would not be applicable to a
RAW stream makes me think it certainly should be a per-stream metadata
style value.


I'd hope this could be handled by a common helper in that instance so it
doesn't get left out of some pipeline handlers, but included in some,
and become inconsistent. Not yet sure how we can handle that, but that
will be a core issue anyway.


I wonder if we should mark this somehow as read-only, at least until we
determine that someone needs to set it.

We could introduce a control property between type: and description:
  read-only: true


Otherwise, I see no objections currently. I think we're just waiting on
top-level thoughts from Laurent. (And perhaps per-stream controls, but
that brings it's own questions )

Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>


>  ...
>
Jacopo Mondi Nov. 23, 2020, 8:58 a.m. UTC | #2 
Hi Kieran,

On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> Hi David,
>
> On 27/10/2020 14:12, David Plowman wrote:
> > This control reports the global digital gain applied by the pipeline
> > as a whole, after capturing a raw image from the sensor.
> >
> > Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > ---
> >  src/libcamera/control_ids.yaml | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > index c8874fa9..e6362c74 100644
> > --- a/src/libcamera/control_ids.yaml
> > +++ b/src/libcamera/control_ids.yaml
> > @@ -530,4 +530,15 @@ controls:
> >          This control is only present when the pipeline supports scaling. Its
> >          maximum valid value is given by the properties::ScalerCropMaximum
> >          property, and the two can be used to implement digital zoom.
> > +
> > +  - DigitalGain:
> > +      type: float
> > +      description: |
> > +        Global digital gain value applied to the image during all the
> > +        processing steps after capturing the image from the sensor. Any raw
> > +        images, therefore, will not include this gain, but the final images
> > +        output by the imaging pipeline as a whole will include it.
> > +
> > +        This control is intended to report the value used by the image
> > +        processing pipeline.
>
>
> If this is a per-stream thing anyway, I guess it will then be up to
> pipeline handlers to set this to the appropriate value for each stream
> when it completes. The fact that this value would not be applicable to a
> RAW stream makes me think it certainly should be a per-stream metadata
> style value.
>
>
> I'd hope this could be handled by a common helper in that instance so it
> doesn't get left out of some pipeline handlers, but included in some,
> and become inconsistent. Not yet sure how we can handle that, but that
> will be a core issue anyway.
>
>
> I wonder if we should mark this somehow as read-only, at least until we
> determine that someone needs to set it.
>
> We could introduce a control property between type: and description:
>   read-only: true

Isn't a read-only control just a metadata ?

Wouldn't it be enough for a pipeline that does not support changing
the control value from applications not reporting it in the list of
supported Camera's controls, but only report it as part of a completed
request's metadata ?

Thanks
  j

>
>
> Otherwise, I see no objections currently. I think we're just waiting on
> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> that brings it's own questions )
>
> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
>
>
> >  ...
> >
>
> --
> Regards
> --
> Kieran
> _______________________________________________
> libcamera-devel mailing list
> libcamera-devel@lists.libcamera.org
> https://lists.libcamera.org/listinfo/libcamera-devel
Kieran Bingham Nov. 23, 2020, 9:17 a.m. UTC | #3 
Hi Jacopo,

On 23/11/2020 08:58, Jacopo Mondi wrote:
> Hi Kieran,
> 
> On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
>> Hi David,
>>
>> On 27/10/2020 14:12, David Plowman wrote:
>>> This control reports the global digital gain applied by the pipeline
>>> as a whole, after capturing a raw image from the sensor.
>>>
>>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
>>> ---
>>>  src/libcamera/control_ids.yaml | 11 +++++++++++
>>>  1 file changed, 11 insertions(+)
>>>
>>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
>>> index c8874fa9..e6362c74 100644
>>> --- a/src/libcamera/control_ids.yaml
>>> +++ b/src/libcamera/control_ids.yaml
>>> @@ -530,4 +530,15 @@ controls:
>>>          This control is only present when the pipeline supports scaling. Its
>>>          maximum valid value is given by the properties::ScalerCropMaximum
>>>          property, and the two can be used to implement digital zoom.
>>> +
>>> +  - DigitalGain:
>>> +      type: float
>>> +      description: |
>>> +        Global digital gain value applied to the image during all the
>>> +        processing steps after capturing the image from the sensor. Any raw
>>> +        images, therefore, will not include this gain, but the final images
>>> +        output by the imaging pipeline as a whole will include it.
>>> +
>>> +        This control is intended to report the value used by the image
>>> +        processing pipeline.
>>
>>
>> If this is a per-stream thing anyway, I guess it will then be up to
>> pipeline handlers to set this to the appropriate value for each stream
>> when it completes. The fact that this value would not be applicable to a
>> RAW stream makes me think it certainly should be a per-stream metadata
>> style value.
>>
>>
>> I'd hope this could be handled by a common helper in that instance so it
>> doesn't get left out of some pipeline handlers, but included in some,
>> and become inconsistent. Not yet sure how we can handle that, but that
>> will be a core issue anyway.
>>
>>
>> I wonder if we should mark this somehow as read-only, at least until we
>> determine that someone needs to set it.
>>
>> We could introduce a control property between type: and description:
>>   read-only: true
> 
> Isn't a read-only control just a metadata ?
> 
> Wouldn't it be enough for a pipeline that does not support changing
> the control value from applications not reporting it in the list of
> supported Camera's controls, but only report it as part of a completed
> request's metadata ?

Ah, yes of course - because if the control is not listed as supported it
won't be there to set in the first place! I forgot about that.

So - indeed, no requirement to mark anything as read-only. That will be
implicit.

--
Kieran


> 
> Thanks
>   j
> 
>>
>>
>> Otherwise, I see no objections currently. I think we're just waiting on
>> top-level thoughts from Laurent. (And perhaps per-stream controls, but
>> that brings it's own questions )
>>
>> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
>>
>>
>>>  ...
>>>
>>
>> --
>> Regards
>> --
>> Kieran
>> _______________________________________________
>> libcamera-devel mailing list
>> libcamera-devel@lists.libcamera.org
>> https://lists.libcamera.org/listinfo/libcamera-devel
David Plowman Nov. 24, 2020, 8:28 a.m. UTC | #4 
Hi everyone

Sounds like we're happy enough from the point of view of this thing
being read-only (for Raspberry Pi at least). Would anyone want any
changes to the wording? Perhaps the final sentence/paragraph might now
be better as

"This control is present in a request's ControlList only if the
pipeline supports setting the value. Even when it cannot be set by an
application, the pipeline may still report the actual value used in
the metadata returned with completed requests."

Any other thoughts?

Thanks
David

On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
<kieran.bingham@ideasonboard.com> wrote:
>
> Hi Jacopo,
>
> On 23/11/2020 08:58, Jacopo Mondi wrote:
> > Hi Kieran,
> >
> > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> >> Hi David,
> >>
> >> On 27/10/2020 14:12, David Plowman wrote:
> >>> This control reports the global digital gain applied by the pipeline
> >>> as a whole, after capturing a raw image from the sensor.
> >>>
> >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> >>> ---
> >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> >>>  1 file changed, 11 insertions(+)
> >>>
> >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> >>> index c8874fa9..e6362c74 100644
> >>> --- a/src/libcamera/control_ids.yaml
> >>> +++ b/src/libcamera/control_ids.yaml
> >>> @@ -530,4 +530,15 @@ controls:
> >>>          This control is only present when the pipeline supports scaling. Its
> >>>          maximum valid value is given by the properties::ScalerCropMaximum
> >>>          property, and the two can be used to implement digital zoom.
> >>> +
> >>> +  - DigitalGain:
> >>> +      type: float
> >>> +      description: |
> >>> +        Global digital gain value applied to the image during all the
> >>> +        processing steps after capturing the image from the sensor. Any raw
> >>> +        images, therefore, will not include this gain, but the final images
> >>> +        output by the imaging pipeline as a whole will include it.
> >>> +
> >>> +        This control is intended to report the value used by the image
> >>> +        processing pipeline.
> >>
> >>
> >> If this is a per-stream thing anyway, I guess it will then be up to
> >> pipeline handlers to set this to the appropriate value for each stream
> >> when it completes. The fact that this value would not be applicable to a
> >> RAW stream makes me think it certainly should be a per-stream metadata
> >> style value.
> >>
> >>
> >> I'd hope this could be handled by a common helper in that instance so it
> >> doesn't get left out of some pipeline handlers, but included in some,
> >> and become inconsistent. Not yet sure how we can handle that, but that
> >> will be a core issue anyway.
> >>
> >>
> >> I wonder if we should mark this somehow as read-only, at least until we
> >> determine that someone needs to set it.
> >>
> >> We could introduce a control property between type: and description:
> >>   read-only: true
> >
> > Isn't a read-only control just a metadata ?
> >
> > Wouldn't it be enough for a pipeline that does not support changing
> > the control value from applications not reporting it in the list of
> > supported Camera's controls, but only report it as part of a completed
> > request's metadata ?
>
> Ah, yes of course - because if the control is not listed as supported it
> won't be there to set in the first place! I forgot about that.
>
> So - indeed, no requirement to mark anything as read-only. That will be
> implicit.
>
> --
> Kieran
>
>
> >
> > Thanks
> >   j
> >
> >>
> >>
> >> Otherwise, I see no objections currently. I think we're just waiting on
> >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> >> that brings it's own questions )
> >>
> >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> >>
> >>
> >>>  ...
> >>>
> >>
> >> --
> >> Regards
> >> --
> >> Kieran
> >> _______________________________________________
> >> libcamera-devel mailing list
> >> libcamera-devel@lists.libcamera.org
> >> https://lists.libcamera.org/listinfo/libcamera-devel
>
> --
> Regards
> --
> Kieran
Jacopo Mondi Nov. 24, 2020, 8:43 a.m. UTC | #5 
Hi David,

On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> Hi everyone
>
> Sounds like we're happy enough from the point of view of this thing
> being read-only (for Raspberry Pi at least). Would anyone want any
> changes to the wording? Perhaps the final sentence/paragraph might now
> be better as
>
> "This control is present in a request's ControlList only if the
> pipeline supports setting the value. Even when it cannot be set by an
> application, the pipeline may still report the actual value used in
> the metadata returned with completed requests."

I don't think it it necessary. It is implied that if a pipeline
handler does not support changing the digital gain it should not
expose it a one of the Camera's controls.

Likewise, if it is something that applications should be informed of,
it will be reported via metadata.

I think we're good to go, except for the point that we've left
floating about having this a single value or a per-channel value.

I'm trying to get a feeling how this would be reported by your ISP. I
see in example you have two per-channel values for the ColourGains
control. Is this anyway related ?

>
> Any other thoughts?
>
> Thanks
> David
>
> On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
> <kieran.bingham@ideasonboard.com> wrote:
> >
> > Hi Jacopo,
> >
> > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > Hi Kieran,
> > >
> > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > >> Hi David,
> > >>
> > >> On 27/10/2020 14:12, David Plowman wrote:
> > >>> This control reports the global digital gain applied by the pipeline
> > >>> as a whole, after capturing a raw image from the sensor.
> > >>>
> > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > >>> ---
> > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > >>>  1 file changed, 11 insertions(+)
> > >>>
> > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > >>> index c8874fa9..e6362c74 100644
> > >>> --- a/src/libcamera/control_ids.yaml
> > >>> +++ b/src/libcamera/control_ids.yaml
> > >>> @@ -530,4 +530,15 @@ controls:
> > >>>          This control is only present when the pipeline supports scaling. Its
> > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > >>>          property, and the two can be used to implement digital zoom.
> > >>> +
> > >>> +  - DigitalGain:
> > >>> +      type: float
> > >>> +      description: |
> > >>> +        Global digital gain value applied to the image during all the
> > >>> +        processing steps after capturing the image from the sensor. Any raw
> > >>> +        images, therefore, will not include this gain, but the final images
> > >>> +        output by the imaging pipeline as a whole will include it.
> > >>> +
> > >>> +        This control is intended to report the value used by the image
> > >>> +        processing pipeline.
> > >>
> > >>
> > >> If this is a per-stream thing anyway, I guess it will then be up to
> > >> pipeline handlers to set this to the appropriate value for each stream
> > >> when it completes. The fact that this value would not be applicable to a
> > >> RAW stream makes me think it certainly should be a per-stream metadata
> > >> style value.
> > >>
> > >>
> > >> I'd hope this could be handled by a common helper in that instance so it
> > >> doesn't get left out of some pipeline handlers, but included in some,
> > >> and become inconsistent. Not yet sure how we can handle that, but that
> > >> will be a core issue anyway.
> > >>
> > >>
> > >> I wonder if we should mark this somehow as read-only, at least until we
> > >> determine that someone needs to set it.
> > >>
> > >> We could introduce a control property between type: and description:
> > >>   read-only: true
> > >
> > > Isn't a read-only control just a metadata ?
> > >
> > > Wouldn't it be enough for a pipeline that does not support changing
> > > the control value from applications not reporting it in the list of
> > > supported Camera's controls, but only report it as part of a completed
> > > request's metadata ?
> >
> > Ah, yes of course - because if the control is not listed as supported it
> > won't be there to set in the first place! I forgot about that.
> >
> > So - indeed, no requirement to mark anything as read-only. That will be
> > implicit.
> >
> > --
> > Kieran
> >
> >
> > >
> > > Thanks
> > >   j
> > >
> > >>
> > >>
> > >> Otherwise, I see no objections currently. I think we're just waiting on
> > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > >> that brings it's own questions )
> > >>
> > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > >>
> > >>
> > >>>  ...
> > >>>
> > >>
> > >> --
> > >> Regards
> > >> --
> > >> Kieran
> > >> _______________________________________________
> > >> libcamera-devel mailing list
> > >> libcamera-devel@lists.libcamera.org
> > >> https://lists.libcamera.org/listinfo/libcamera-devel
> >
> > --
> > Regards
> > --
> > Kieran
David Plowman Nov. 24, 2020, 10:15 a.m. UTC | #6 
Hi Jacopo

You're right, there's a relationship there. ColourGains obviously
gives you the red and blue gains determined by the AWB usually. You
might get the values 1.6 and 2.0 (for red and blue)

In our case, if we report a single "global gain" value you can kind of
imagine it as the green gain, where the colour gains were normalised
for a green gain of 1. So if the global gain was 1.25, then the actual
RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
1.25, 2.5).

In the per-channel case I guess you'd be reporting these 3 numbers
directly. For me this duplicates information that's already in the
ColourGains, and it seems to muddle things up a bit. Imagine you had a
pipeline that lets you set a global gain - you'd have to query the
current white balance and work out all three numbers and set them. But
then you've set the white balance as well. Or maybe we do something
special so that you haven't? You see why it confuses me! So on balance
I'm with the single value approach, though I could live either way.

Thanks!
David

On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
>
> Hi David,
>
> On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > Hi everyone
> >
> > Sounds like we're happy enough from the point of view of this thing
> > being read-only (for Raspberry Pi at least). Would anyone want any
> > changes to the wording? Perhaps the final sentence/paragraph might now
> > be better as
> >
> > "This control is present in a request's ControlList only if the
> > pipeline supports setting the value. Even when it cannot be set by an
> > application, the pipeline may still report the actual value used in
> > the metadata returned with completed requests."
>
> I don't think it it necessary. It is implied that if a pipeline
> handler does not support changing the digital gain it should not
> expose it a one of the Camera's controls.
>
> Likewise, if it is something that applications should be informed of,
> it will be reported via metadata.
>
> I think we're good to go, except for the point that we've left
> floating about having this a single value or a per-channel value.
>
> I'm trying to get a feeling how this would be reported by your ISP. I
> see in example you have two per-channel values for the ColourGains
> control. Is this anyway related ?
>
> >
> > Any other thoughts?
> >
> > Thanks
> > David
> >
> > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
> > <kieran.bingham@ideasonboard.com> wrote:
> > >
> > > Hi Jacopo,
> > >
> > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > Hi Kieran,
> > > >
> > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > >> Hi David,
> > > >>
> > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > >>> This control reports the global digital gain applied by the pipeline
> > > >>> as a whole, after capturing a raw image from the sensor.
> > > >>>
> > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > >>> ---
> > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > >>>  1 file changed, 11 insertions(+)
> > > >>>
> > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > >>> index c8874fa9..e6362c74 100644
> > > >>> --- a/src/libcamera/control_ids.yaml
> > > >>> +++ b/src/libcamera/control_ids.yaml
> > > >>> @@ -530,4 +530,15 @@ controls:
> > > >>>          This control is only present when the pipeline supports scaling. Its
> > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > >>>          property, and the two can be used to implement digital zoom.
> > > >>> +
> > > >>> +  - DigitalGain:
> > > >>> +      type: float
> > > >>> +      description: |
> > > >>> +        Global digital gain value applied to the image during all the
> > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > >>> +        images, therefore, will not include this gain, but the final images
> > > >>> +        output by the imaging pipeline as a whole will include it.
> > > >>> +
> > > >>> +        This control is intended to report the value used by the image
> > > >>> +        processing pipeline.
> > > >>
> > > >>
> > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > >> pipeline handlers to set this to the appropriate value for each stream
> > > >> when it completes. The fact that this value would not be applicable to a
> > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > >> style value.
> > > >>
> > > >>
> > > >> I'd hope this could be handled by a common helper in that instance so it
> > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > >> will be a core issue anyway.
> > > >>
> > > >>
> > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > >> determine that someone needs to set it.
> > > >>
> > > >> We could introduce a control property between type: and description:
> > > >>   read-only: true
> > > >
> > > > Isn't a read-only control just a metadata ?
> > > >
> > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > the control value from applications not reporting it in the list of
> > > > supported Camera's controls, but only report it as part of a completed
> > > > request's metadata ?
> > >
> > > Ah, yes of course - because if the control is not listed as supported it
> > > won't be there to set in the first place! I forgot about that.
> > >
> > > So - indeed, no requirement to mark anything as read-only. That will be
> > > implicit.
> > >
> > > --
> > > Kieran
> > >
> > >
> > > >
> > > > Thanks
> > > >   j
> > > >
> > > >>
> > > >>
> > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > >> that brings it's own questions )
> > > >>
> > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > >>
> > > >>
> > > >>>  ...
> > > >>>
> > > >>
> > > >> --
> > > >> Regards
> > > >> --
> > > >> Kieran
> > > >> _______________________________________________
> > > >> libcamera-devel mailing list
> > > >> libcamera-devel@lists.libcamera.org
> > > >> https://lists.libcamera.org/listinfo/libcamera-devel
> > >
> > > --
> > > Regards
> > > --
> > > Kieran
Jacopo Mondi Nov. 24, 2020, 11:28 a.m. UTC | #7 
Hi David,

On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
> Hi Jacopo
>
> You're right, there's a relationship there. ColourGains obviously
> gives you the red and blue gains determined by the AWB usually. You
> might get the values 1.6 and 2.0 (for red and blue)
>
> In our case, if we report a single "global gain" value you can kind of
> imagine it as the green gain, where the colour gains were normalised
> for a green gain of 1. So if the global gain was 1.25, then the actual
> RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
> 1.25, 2.5).

That's a really helpful explanation for me, thanks

>
> In the per-channel case I guess you'd be reporting these 3 numbers
> directly. For me this duplicates information that's already in the
> ColourGains, and it seems to muddle things up a bit. Imagine you had a
> pipeline that lets you set a global gain - you'd have to query the
> current white balance and work out all three numbers and set them. But
> then you've set the white balance as well. Or maybe we do something
> special so that you haven't? You see why it confuses me! So on balance
> I'm with the single value approach, though I could live either way.

I see. With the above explanation I really see why a single global
value is probably enough.

My question is now: are the above notions (blue/red gains normalized
on a green value of 1, how global gain is used to obtain per-channel
gains etc) standard knowledge I'm lacking, or:

1) It's worth to describe them in the control documentation as they're
"standard" and won't change per-pipeline
2) They might differe per-pipeline and they need to be
described in the pipeline model documentation ?
3) It is assumed the reader knows she's dealing with

Thanks
   j

>
> Thanks!
> David
>
> On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
> >
> > Hi David,
> >
> > On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > > Hi everyone
> > >
> > > Sounds like we're happy enough from the point of view of this thing
> > > being read-only (for Raspberry Pi at least). Would anyone want any
> > > changes to the wording? Perhaps the final sentence/paragraph might now
> > > be better as
> > >
> > > "This control is present in a request's ControlList only if the
> > > pipeline supports setting the value. Even when it cannot be set by an
> > > application, the pipeline may still report the actual value used in
> > > the metadata returned with completed requests."
> >
> > I don't think it it necessary. It is implied that if a pipeline
> > handler does not support changing the digital gain it should not
> > expose it a one of the Camera's controls.
> >
> > Likewise, if it is something that applications should be informed of,
> > it will be reported via metadata.
> >
> > I think we're good to go, except for the point that we've left
> > floating about having this a single value or a per-channel value.
> >
> > I'm trying to get a feeling how this would be reported by your ISP. I
> > see in example you have two per-channel values for the ColourGains
> > control. Is this anyway related ?
> >
> > >
> > > Any other thoughts?
> > >
> > > Thanks
> > > David
> > >
> > > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
> > > <kieran.bingham@ideasonboard.com> wrote:
> > > >
> > > > Hi Jacopo,
> > > >
> > > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > > Hi Kieran,
> > > > >
> > > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > > >> Hi David,
> > > > >>
> > > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > > >>> This control reports the global digital gain applied by the pipeline
> > > > >>> as a whole, after capturing a raw image from the sensor.
> > > > >>>
> > > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > > >>> ---
> > > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > > >>>  1 file changed, 11 insertions(+)
> > > > >>>
> > > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > > >>> index c8874fa9..e6362c74 100644
> > > > >>> --- a/src/libcamera/control_ids.yaml
> > > > >>> +++ b/src/libcamera/control_ids.yaml
> > > > >>> @@ -530,4 +530,15 @@ controls:
> > > > >>>          This control is only present when the pipeline supports scaling. Its
> > > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > > >>>          property, and the two can be used to implement digital zoom.
> > > > >>> +
> > > > >>> +  - DigitalGain:
> > > > >>> +      type: float
> > > > >>> +      description: |
> > > > >>> +        Global digital gain value applied to the image during all the
> > > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > > >>> +        images, therefore, will not include this gain, but the final images
> > > > >>> +        output by the imaging pipeline as a whole will include it.
> > > > >>> +
> > > > >>> +        This control is intended to report the value used by the image
> > > > >>> +        processing pipeline.
> > > > >>
> > > > >>
> > > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > > >> pipeline handlers to set this to the appropriate value for each stream
> > > > >> when it completes. The fact that this value would not be applicable to a
> > > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > > >> style value.
> > > > >>
> > > > >>
> > > > >> I'd hope this could be handled by a common helper in that instance so it
> > > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > > >> will be a core issue anyway.
> > > > >>
> > > > >>
> > > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > > >> determine that someone needs to set it.
> > > > >>
> > > > >> We could introduce a control property between type: and description:
> > > > >>   read-only: true
> > > > >
> > > > > Isn't a read-only control just a metadata ?
> > > > >
> > > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > > the control value from applications not reporting it in the list of
> > > > > supported Camera's controls, but only report it as part of a completed
> > > > > request's metadata ?
> > > >
> > > > Ah, yes of course - because if the control is not listed as supported it
> > > > won't be there to set in the first place! I forgot about that.
> > > >
> > > > So - indeed, no requirement to mark anything as read-only. That will be
> > > > implicit.
> > > >
> > > > --
> > > > Kieran
> > > >
> > > >
> > > > >
> > > > > Thanks
> > > > >   j
> > > > >
> > > > >>
> > > > >>
> > > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > > >> that brings it's own questions )
> > > > >>
> > > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > > >>
> > > > >>
> > > > >>>  ...
> > > > >>>
> > > > >>
> > > > >> --
> > > > >> Regards
> > > > >> --
> > > > >> Kieran
> > > > >> _______________________________________________
> > > > >> libcamera-devel mailing list
> > > > >> libcamera-devel@lists.libcamera.org
> > > > >> https://lists.libcamera.org/listinfo/libcamera-devel
> > > >
> > > > --
> > > > Regards
> > > > --
> > > > Kieran
David Plowman Nov. 24, 2020, 12:40 p.m. UTC | #8 
Hi Jacopo

Thanks for the reply. More discussion below...

On Tue, 24 Nov 2020 at 11:28, Jacopo Mondi <jacopo@jmondi.org> wrote:
>
> Hi David,
>
> On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
> > Hi Jacopo
> >
> > You're right, there's a relationship there. ColourGains obviously
> > gives you the red and blue gains determined by the AWB usually. You
> > might get the values 1.6 and 2.0 (for red and blue)
> >
> > In our case, if we report a single "global gain" value you can kind of
> > imagine it as the green gain, where the colour gains were normalised
> > for a green gain of 1. So if the global gain was 1.25, then the actual
> > RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
> > 1.25, 2.5).
>
> That's a really helpful explanation for me, thanks
>
> >
> > In the per-channel case I guess you'd be reporting these 3 numbers
> > directly. For me this duplicates information that's already in the
> > ColourGains, and it seems to muddle things up a bit. Imagine you had a
> > pipeline that lets you set a global gain - you'd have to query the
> > current white balance and work out all three numbers and set them. But
> > then you've set the white balance as well. Or maybe we do something
> > special so that you haven't? You see why it confuses me! So on balance
> > I'm with the single value approach, though I could live either way.
>
> I see. With the above explanation I really see why a single global
> value is probably enough.
>
> My question is now: are the above notions (blue/red gains normalized
> on a green value of 1, how global gain is used to obtain per-channel
> gains etc) standard knowledge I'm lacking, or:
>
> 1) It's worth to describe them in the control documentation as they're
> "standard" and won't change per-pipeline
> 2) They might differe per-pipeline and they need to be
> described in the pipeline model documentation ?
> 3) It is assumed the reader knows she's dealing with

Difficult. I can't really see too many other ways of defining it, but
you know, pipelines all have their nuances. You probably can't
guarantee that what I described is completely "standard".

A slightly more qualitative definition seems OK to me - the amount of
linear gain applied by the pipeline to all pixels (in addition to the
colour gains). Particular pipelines might feel they need to document
it more carefully if there are any complications in how they deal with
it.

Best regards
David

>
> Thanks
>    j
>
> >
> > Thanks!
> > David
> >
> > On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > >
> > > Hi David,
> > >
> > > On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > > > Hi everyone
> > > >
> > > > Sounds like we're happy enough from the point of view of this thing
> > > > being read-only (for Raspberry Pi at least). Would anyone want any
> > > > changes to the wording? Perhaps the final sentence/paragraph might now
> > > > be better as
> > > >
> > > > "This control is present in a request's ControlList only if the
> > > > pipeline supports setting the value. Even when it cannot be set by an
> > > > application, the pipeline may still report the actual value used in
> > > > the metadata returned with completed requests."
> > >
> > > I don't think it it necessary. It is implied that if a pipeline
> > > handler does not support changing the digital gain it should not
> > > expose it a one of the Camera's controls.
> > >
> > > Likewise, if it is something that applications should be informed of,
> > > it will be reported via metadata.
> > >
> > > I think we're good to go, except for the point that we've left
> > > floating about having this a single value or a per-channel value.
> > >
> > > I'm trying to get a feeling how this would be reported by your ISP. I
> > > see in example you have two per-channel values for the ColourGains
> > > control. Is this anyway related ?
> > >
> > > >
> > > > Any other thoughts?
> > > >
> > > > Thanks
> > > > David
> > > >
> > > > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
> > > > <kieran.bingham@ideasonboard.com> wrote:
> > > > >
> > > > > Hi Jacopo,
> > > > >
> > > > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > > > Hi Kieran,
> > > > > >
> > > > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > > > >> Hi David,
> > > > > >>
> > > > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > > > >>> This control reports the global digital gain applied by the pipeline
> > > > > >>> as a whole, after capturing a raw image from the sensor.
> > > > > >>>
> > > > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > > > >>> ---
> > > > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > > > >>>  1 file changed, 11 insertions(+)
> > > > > >>>
> > > > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > > > >>> index c8874fa9..e6362c74 100644
> > > > > >>> --- a/src/libcamera/control_ids.yaml
> > > > > >>> +++ b/src/libcamera/control_ids.yaml
> > > > > >>> @@ -530,4 +530,15 @@ controls:
> > > > > >>>          This control is only present when the pipeline supports scaling. Its
> > > > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > > > >>>          property, and the two can be used to implement digital zoom.
> > > > > >>> +
> > > > > >>> +  - DigitalGain:
> > > > > >>> +      type: float
> > > > > >>> +      description: |
> > > > > >>> +        Global digital gain value applied to the image during all the
> > > > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > > > >>> +        images, therefore, will not include this gain, but the final images
> > > > > >>> +        output by the imaging pipeline as a whole will include it.
> > > > > >>> +
> > > > > >>> +        This control is intended to report the value used by the image
> > > > > >>> +        processing pipeline.
> > > > > >>
> > > > > >>
> > > > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > > > >> pipeline handlers to set this to the appropriate value for each stream
> > > > > >> when it completes. The fact that this value would not be applicable to a
> > > > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > > > >> style value.
> > > > > >>
> > > > > >>
> > > > > >> I'd hope this could be handled by a common helper in that instance so it
> > > > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > > > >> will be a core issue anyway.
> > > > > >>
> > > > > >>
> > > > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > > > >> determine that someone needs to set it.
> > > > > >>
> > > > > >> We could introduce a control property between type: and description:
> > > > > >>   read-only: true
> > > > > >
> > > > > > Isn't a read-only control just a metadata ?
> > > > > >
> > > > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > > > the control value from applications not reporting it in the list of
> > > > > > supported Camera's controls, but only report it as part of a completed
> > > > > > request's metadata ?
> > > > >
> > > > > Ah, yes of course - because if the control is not listed as supported it
> > > > > won't be there to set in the first place! I forgot about that.
> > > > >
> > > > > So - indeed, no requirement to mark anything as read-only. That will be
> > > > > implicit.
> > > > >
> > > > > --
> > > > > Kieran
> > > > >
> > > > >
> > > > > >
> > > > > > Thanks
> > > > > >   j
> > > > > >
> > > > > >>
> > > > > >>
> > > > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > > > >> that brings it's own questions )
> > > > > >>
> > > > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > > > >>
> > > > > >>
> > > > > >>>  ...
> > > > > >>>
> > > > > >>
> > > > > >> --
> > > > > >> Regards
> > > > > >> --
> > > > > >> Kieran
> > > > > >> _______________________________________________
> > > > > >> libcamera-devel mailing list
> > > > > >> libcamera-devel@lists.libcamera.org
> > > > > >> https://lists.libcamera.org/listinfo/libcamera-devel
> > > > >
> > > > > --
> > > > > Regards
> > > > > --
> > > > > Kieran
Jacopo Mondi Nov. 25, 2020, 9:03 p.m. UTC | #9 
Hi David,
    I tried proposing a new version based on the outcome of our
discussion

Please see below

On Tue, Nov 24, 2020 at 12:40:38PM +0000, David Plowman wrote:
> Hi Jacopo
>
> Thanks for the reply. More discussion below...
>
> On Tue, 24 Nov 2020 at 11:28, Jacopo Mondi <jacopo@jmondi.org> wrote:
> >
> > Hi David,
> >
> > On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
> > > Hi Jacopo
> > >
> > > You're right, there's a relationship there. ColourGains obviously
> > > gives you the red and blue gains determined by the AWB usually. You
> > > might get the values 1.6 and 2.0 (for red and blue)
> > >
> > > In our case, if we report a single "global gain" value you can kind of
> > > imagine it as the green gain, where the colour gains were normalised
> > > for a green gain of 1. So if the global gain was 1.25, then the actual
> > > RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
> > > 1.25, 2.5).
> >
> > That's a really helpful explanation for me, thanks
> >
> > >
> > > In the per-channel case I guess you'd be reporting these 3 numbers
> > > directly. For me this duplicates information that's already in the
> > > ColourGains, and it seems to muddle things up a bit. Imagine you had a
> > > pipeline that lets you set a global gain - you'd have to query the
> > > current white balance and work out all three numbers and set them. But
> > > then you've set the white balance as well. Or maybe we do something
> > > special so that you haven't? You see why it confuses me! So on balance
> > > I'm with the single value approach, though I could live either way.
> >
> > I see. With the above explanation I really see why a single global
> > value is probably enough.
> >
> > My question is now: are the above notions (blue/red gains normalized
> > on a green value of 1, how global gain is used to obtain per-channel
> > gains etc) standard knowledge I'm lacking, or:
> >
> > 1) It's worth to describe them in the control documentation as they're
> > "standard" and won't change per-pipeline
> > 2) They might differe per-pipeline and they need to be
> > described in the pipeline model documentation ?
> > 3) It is assumed the reader knows she's dealing with
>
> Difficult. I can't really see too many other ways of defining it, but
> you know, pipelines all have their nuances. You probably can't
> guarantee that what I described is completely "standard".
>
> A slightly more qualitative definition seems OK to me - the amount of
> linear gain applied by the pipeline to all pixels (in addition to the
> colour gains). Particular pipelines might feel they need to document
> it more carefully if there are any complications in how they deal with
> it.
>
> Best regards
> David
>
> >
> > Thanks
> >    j
> >
> > >
> > > Thanks!
> > > David
> > >
> > > On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > >
> > > > Hi David,
> > > >
> > > > On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > > > > Hi everyone
> > > > >
> > > > > Sounds like we're happy enough from the point of view of this thing
> > > > > being read-only (for Raspberry Pi at least). Would anyone want any
> > > > > changes to the wording? Perhaps the final sentence/paragraph might now
> > > > > be better as
> > > > >
> > > > > "This control is present in a request's ControlList only if the
> > > > > pipeline supports setting the value. Even when it cannot be set by an
> > > > > application, the pipeline may still report the actual value used in
> > > > > the metadata returned with completed requests."
> > > >
> > > > I don't think it it necessary. It is implied that if a pipeline
> > > > handler does not support changing the digital gain it should not
> > > > expose it a one of the Camera's controls.
> > > >
> > > > Likewise, if it is something that applications should be informed of,
> > > > it will be reported via metadata.
> > > >
> > > > I think we're good to go, except for the point that we've left
> > > > floating about having this a single value or a per-channel value.
> > > >
> > > > I'm trying to get a feeling how this would be reported by your ISP. I
> > > > see in example you have two per-channel values for the ColourGains
> > > > control. Is this anyway related ?
> > > >
> > > > >
> > > > > Any other thoughts?
> > > > >
> > > > > Thanks
> > > > > David
> > > > >
> > > > > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
> > > > > <kieran.bingham@ideasonboard.com> wrote:
> > > > > >
> > > > > > Hi Jacopo,
> > > > > >
> > > > > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > > > > Hi Kieran,
> > > > > > >
> > > > > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > > > > >> Hi David,
> > > > > > >>
> > > > > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > > > > >>> This control reports the global digital gain applied by the pipeline
> > > > > > >>> as a whole, after capturing a raw image from the sensor.
> > > > > > >>>
> > > > > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > > > > >>> ---
> > > > > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > > > > >>>  1 file changed, 11 insertions(+)
> > > > > > >>>
> > > > > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > > > > >>> index c8874fa9..e6362c74 100644
> > > > > > >>> --- a/src/libcamera/control_ids.yaml
> > > > > > >>> +++ b/src/libcamera/control_ids.yaml
> > > > > > >>> @@ -530,4 +530,15 @@ controls:
> > > > > > >>>          This control is only present when the pipeline supports scaling. Its
> > > > > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > > > > >>>          property, and the two can be used to implement digital zoom.
> > > > > > >>> +
> > > > > > >>> +  - DigitalGain:
> > > > > > >>> +      type: float
> > > > > > >>> +      description: |
> > > > > > >>> +        Global digital gain value applied to the image during all the
> > > > > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > > > > >>> +        images, therefore, will not include this gain, but the final images
> > > > > > >>> +        output by the imaging pipeline as a whole will include it.
> > > > > > >>> +
> > > > > > >>> +        This control is intended to report the value used by the image
> > > > > > >>> +        processing pipeline.

  - DigitalGain:
      type: float
      description: |
        Digital gain value applied during the processing steps applied
        to the image as captured from the sensor.

        The global digital gain factor is applied to all the colour channels
        of the RAW image. Different pipeline models are free to
        specify how the global gain factor applies to each separate
        channel.

        If an imaging pipeline applies digital gain in distinct
        processing steps, this value indicates their total sum.
        Pipelines are free to decide how to adjust each processing
        step to respect the received gain factor and shall report
        their total value in the request metadata.

However this deferring to each pipeline model documentation makes me
wonder if expressing per-channel values would make things more
explicit...

Feel free to take in what you consider appropriate.

> > > > > > >>
> > > > > > >>
> > > > > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > > > > >> pipeline handlers to set this to the appropriate value for each stream
> > > > > > >> when it completes. The fact that this value would not be applicable to a
> > > > > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > > > > >> style value.
> > > > > > >>
> > > > > > >>
> > > > > > >> I'd hope this could be handled by a common helper in that instance so it
> > > > > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > > > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > > > > >> will be a core issue anyway.
> > > > > > >>
> > > > > > >>
> > > > > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > > > > >> determine that someone needs to set it.
> > > > > > >>
> > > > > > >> We could introduce a control property between type: and description:
> > > > > > >>   read-only: true
> > > > > > >
> > > > > > > Isn't a read-only control just a metadata ?
> > > > > > >
> > > > > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > > > > the control value from applications not reporting it in the list of
> > > > > > > supported Camera's controls, but only report it as part of a completed
> > > > > > > request's metadata ?
> > > > > >
> > > > > > Ah, yes of course - because if the control is not listed as supported it
> > > > > > won't be there to set in the first place! I forgot about that.
> > > > > >
> > > > > > So - indeed, no requirement to mark anything as read-only. That will be
> > > > > > implicit.
> > > > > >
> > > > > > --
> > > > > > Kieran
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > Thanks
> > > > > > >   j
> > > > > > >
> > > > > > >>
> > > > > > >>
> > > > > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > > > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > > > > >> that brings it's own questions )
> > > > > > >>
> > > > > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > > > > >>
> > > > > > >>
> > > > > > >>>  ...
> > > > > > >>>
> > > > > > >>
> > > > > > >> --
> > > > > > >> Regards
> > > > > > >> --
> > > > > > >> Kieran
> > > > > > >> _______________________________________________
> > > > > > >> libcamera-devel mailing list
> > > > > > >> libcamera-devel@lists.libcamera.org
> > > > > > >> https://lists.libcamera.org/listinfo/libcamera-devel
> > > > > >
> > > > > > --
> > > > > > Regards
> > > > > > --
> > > > > > Kieran
David Plowman Nov. 26, 2020, 9:50 a.m. UTC | #10 
Hi Jacopo

Thanks for the update on this.

On Wed, 25 Nov 2020 at 21:02, Jacopo Mondi <jacopo@jmondi.org> wrote:
>
> Hi David,
>     I tried proposing a new version based on the outcome of our
> discussion
>
> Please see below
>
> On Tue, Nov 24, 2020 at 12:40:38PM +0000, David Plowman wrote:
> > Hi Jacopo
> >
> > Thanks for the reply. More discussion below...
> >
> > On Tue, 24 Nov 2020 at 11:28, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > >
> > > Hi David,
> > >
> > > On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
> > > > Hi Jacopo
> > > >
> > > > You're right, there's a relationship there. ColourGains obviously
> > > > gives you the red and blue gains determined by the AWB usually. You
> > > > might get the values 1.6 and 2.0 (for red and blue)
> > > >
> > > > In our case, if we report a single "global gain" value you can kind of
> > > > imagine it as the green gain, where the colour gains were normalised
> > > > for a green gain of 1. So if the global gain was 1.25, then the actual
> > > > RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
> > > > 1.25, 2.5).
> > >
> > > That's a really helpful explanation for me, thanks
> > >
> > > >
> > > > In the per-channel case I guess you'd be reporting these 3 numbers
> > > > directly. For me this duplicates information that's already in the
> > > > ColourGains, and it seems to muddle things up a bit. Imagine you had a
> > > > pipeline that lets you set a global gain - you'd have to query the
> > > > current white balance and work out all three numbers and set them. But
> > > > then you've set the white balance as well. Or maybe we do something
> > > > special so that you haven't? You see why it confuses me! So on balance
> > > > I'm with the single value approach, though I could live either way.
> > >
> > > I see. With the above explanation I really see why a single global
> > > value is probably enough.
> > >
> > > My question is now: are the above notions (blue/red gains normalized
> > > on a green value of 1, how global gain is used to obtain per-channel
> > > gains etc) standard knowledge I'm lacking, or:
> > >
> > > 1) It's worth to describe them in the control documentation as they're
> > > "standard" and won't change per-pipeline
> > > 2) They might differe per-pipeline and they need to be
> > > described in the pipeline model documentation ?
> > > 3) It is assumed the reader knows she's dealing with
> >
> > Difficult. I can't really see too many other ways of defining it, but
> > you know, pipelines all have their nuances. You probably can't
> > guarantee that what I described is completely "standard".
> >
> > A slightly more qualitative definition seems OK to me - the amount of
> > linear gain applied by the pipeline to all pixels (in addition to the
> > colour gains). Particular pipelines might feel they need to document
> > it more carefully if there are any complications in how they deal with
> > it.
> >
> > Best regards
> > David
> >
> > >
> > > Thanks
> > >    j
> > >
> > > >
> > > > Thanks!
> > > > David
> > > >
> > > > On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > > >
> > > > > Hi David,
> > > > >
> > > > > On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > > > > > Hi everyone
> > > > > >
> > > > > > Sounds like we're happy enough from the point of view of this thing
> > > > > > being read-only (for Raspberry Pi at least). Would anyone want any
> > > > > > changes to the wording? Perhaps the final sentence/paragraph might now
> > > > > > be better as
> > > > > >
> > > > > > "This control is present in a request's ControlList only if the
> > > > > > pipeline supports setting the value. Even when it cannot be set by an
> > > > > > application, the pipeline may still report the actual value used in
> > > > > > the metadata returned with completed requests."
> > > > >
> > > > > I don't think it it necessary. It is implied that if a pipeline
> > > > > handler does not support changing the digital gain it should not
> > > > > expose it a one of the Camera's controls.
> > > > >
> > > > > Likewise, if it is something that applications should be informed of,
> > > > > it will be reported via metadata.
> > > > >
> > > > > I think we're good to go, except for the point that we've left
> > > > > floating about having this a single value or a per-channel value.
> > > > >
> > > > > I'm trying to get a feeling how this would be reported by your ISP. I
> > > > > see in example you have two per-channel values for the ColourGains
> > > > > control. Is this anyway related ?
> > > > >
> > > > > >
> > > > > > Any other thoughts?
> > > > > >
> > > > > > Thanks
> > > > > > David
> > > > > >
> > > > > > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
> > > > > > <kieran.bingham@ideasonboard.com> wrote:
> > > > > > >
> > > > > > > Hi Jacopo,
> > > > > > >
> > > > > > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > > > > > Hi Kieran,
> > > > > > > >
> > > > > > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > > > > > >> Hi David,
> > > > > > > >>
> > > > > > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > > > > > >>> This control reports the global digital gain applied by the pipeline
> > > > > > > >>> as a whole, after capturing a raw image from the sensor.
> > > > > > > >>>
> > > > > > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > > > > > >>> ---
> > > > > > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > > > > > >>>  1 file changed, 11 insertions(+)
> > > > > > > >>>
> > > > > > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > > > > > >>> index c8874fa9..e6362c74 100644
> > > > > > > >>> --- a/src/libcamera/control_ids.yaml
> > > > > > > >>> +++ b/src/libcamera/control_ids.yaml
> > > > > > > >>> @@ -530,4 +530,15 @@ controls:
> > > > > > > >>>          This control is only present when the pipeline supports scaling. Its
> > > > > > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > > > > > >>>          property, and the two can be used to implement digital zoom.
> > > > > > > >>> +
> > > > > > > >>> +  - DigitalGain:
> > > > > > > >>> +      type: float
> > > > > > > >>> +      description: |
> > > > > > > >>> +        Global digital gain value applied to the image during all the
> > > > > > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > > > > > >>> +        images, therefore, will not include this gain, but the final images
> > > > > > > >>> +        output by the imaging pipeline as a whole will include it.
> > > > > > > >>> +
> > > > > > > >>> +        This control is intended to report the value used by the image
> > > > > > > >>> +        processing pipeline.
>
>   - DigitalGain:
>       type: float
>       description: |
>         Digital gain value applied during the processing steps applied
>         to the image as captured from the sensor.
>
>         The global digital gain factor is applied to all the colour channels
>         of the RAW image. Different pipeline models are free to
>         specify how the global gain factor applies to each separate
>         channel.
>
>         If an imaging pipeline applies digital gain in distinct
>         processing steps, this value indicates their total sum.
>         Pipelines are free to decide how to adjust each processing
>         step to respect the received gain factor and shall report
>         their total value in the request metadata.
>
> However this deferring to each pipeline model documentation makes me
> wonder if expressing per-channel values would make things more
> explicit...
>
> Feel free to take in what you consider appropriate.

Yes, this is all so difficult, we just need to make a decision,
really. Per-channel values work for me, but only because we're not
going to let people set them. As a read-only thing, it seems a bit
easier to understand/explain. We could ignore the question of setting
a global digital gain until someone wants to do it (maybe no one ever
will...).

What do you think?

Thanks!
David

>
> > > > > > > >>
> > > > > > > >>
> > > > > > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > > > > > >> pipeline handlers to set this to the appropriate value for each stream
> > > > > > > >> when it completes. The fact that this value would not be applicable to a
> > > > > > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > > > > > >> style value.
> > > > > > > >>
> > > > > > > >>
> > > > > > > >> I'd hope this could be handled by a common helper in that instance so it
> > > > > > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > > > > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > > > > > >> will be a core issue anyway.
> > > > > > > >>
> > > > > > > >>
> > > > > > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > > > > > >> determine that someone needs to set it.
> > > > > > > >>
> > > > > > > >> We could introduce a control property between type: and description:
> > > > > > > >>   read-only: true
> > > > > > > >
> > > > > > > > Isn't a read-only control just a metadata ?
> > > > > > > >
> > > > > > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > > > > > the control value from applications not reporting it in the list of
> > > > > > > > supported Camera's controls, but only report it as part of a completed
> > > > > > > > request's metadata ?
> > > > > > >
> > > > > > > Ah, yes of course - because if the control is not listed as supported it
> > > > > > > won't be there to set in the first place! I forgot about that.
> > > > > > >
> > > > > > > So - indeed, no requirement to mark anything as read-only. That will be
> > > > > > > implicit.
> > > > > > >
> > > > > > > --
> > > > > > > Kieran
> > > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > Thanks
> > > > > > > >   j
> > > > > > > >
> > > > > > > >>
> > > > > > > >>
> > > > > > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > > > > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > > > > > >> that brings it's own questions )
> > > > > > > >>
> > > > > > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > > > > > >>
> > > > > > > >>
> > > > > > > >>>  ...
> > > > > > > >>>
> > > > > > > >>
> > > > > > > >> --
> > > > > > > >> Regards
> > > > > > > >> --
> > > > > > > >> Kieran
> > > > > > > >> _______________________________________________
> > > > > > > >> libcamera-devel mailing list
> > > > > > > >> libcamera-devel@lists.libcamera.org
> > > > > > > >> https://lists.libcamera.org/listinfo/libcamera-devel
> > > > > > >
> > > > > > > --
> > > > > > > Regards
> > > > > > > --
> > > > > > > Kieran
Jacopo Mondi Nov. 26, 2020, 10:25 a.m. UTC | #11 
Hi David,

On Thu, Nov 26, 2020 at 09:50:05AM +0000, David Plowman wrote:
> Hi Jacopo
>
> Thanks for the update on this.
>
> On Wed, 25 Nov 2020 at 21:02, Jacopo Mondi <jacopo@jmondi.org> wrote:
> >
> > Hi David,
> >     I tried proposing a new version based on the outcome of our
> > discussion
> >
> > Please see below
> >
> > On Tue, Nov 24, 2020 at 12:40:38PM +0000, David Plowman wrote:
> > > Hi Jacopo
> > >
> > > Thanks for the reply. More discussion below...
> > >
> > > On Tue, 24 Nov 2020 at 11:28, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > >
> > > > Hi David,
> > > >
> > > > On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
> > > > > Hi Jacopo
> > > > >
> > > > > You're right, there's a relationship there. ColourGains obviously
> > > > > gives you the red and blue gains determined by the AWB usually. You
> > > > > might get the values 1.6 and 2.0 (for red and blue)
> > > > >
> > > > > In our case, if we report a single "global gain" value you can kind of
> > > > > imagine it as the green gain, where the colour gains were normalised
> > > > > for a green gain of 1. So if the global gain was 1.25, then the actual
> > > > > RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
> > > > > 1.25, 2.5).
> > > >
> > > > That's a really helpful explanation for me, thanks
> > > >
> > > > >
> > > > > In the per-channel case I guess you'd be reporting these 3 numbers
> > > > > directly. For me this duplicates information that's already in the
> > > > > ColourGains, and it seems to muddle things up a bit. Imagine you had a
> > > > > pipeline that lets you set a global gain - you'd have to query the
> > > > > current white balance and work out all three numbers and set them. But
> > > > > then you've set the white balance as well. Or maybe we do something
> > > > > special so that you haven't? You see why it confuses me! So on balance
> > > > > I'm with the single value approach, though I could live either way.
> > > >
> > > > I see. With the above explanation I really see why a single global
> > > > value is probably enough.
> > > >
> > > > My question is now: are the above notions (blue/red gains normalized
> > > > on a green value of 1, how global gain is used to obtain per-channel
> > > > gains etc) standard knowledge I'm lacking, or:
> > > >
> > > > 1) It's worth to describe them in the control documentation as they're
> > > > "standard" and won't change per-pipeline
> > > > 2) They might differe per-pipeline and they need to be
> > > > described in the pipeline model documentation ?
> > > > 3) It is assumed the reader knows she's dealing with
> > >
> > > Difficult. I can't really see too many other ways of defining it, but
> > > you know, pipelines all have their nuances. You probably can't
> > > guarantee that what I described is completely "standard".
> > >
> > > A slightly more qualitative definition seems OK to me - the amount of
> > > linear gain applied by the pipeline to all pixels (in addition to the
> > > colour gains). Particular pipelines might feel they need to document
> > > it more carefully if there are any complications in how they deal with
> > > it.
> > >
> > > Best regards
> > > David
> > >
> > > >
> > > > Thanks
> > > >    j
> > > >
> > > > >
> > > > > Thanks!
> > > > > David
> > > > >
> > > > > On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > > > >
> > > > > > Hi David,
> > > > > >
> > > > > > On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > > > > > > Hi everyone
> > > > > > >
> > > > > > > Sounds like we're happy enough from the point of view of this thing
> > > > > > > being read-only (for Raspberry Pi at least). Would anyone want any
> > > > > > > changes to the wording? Perhaps the final sentence/paragraph might now
> > > > > > > be better as
> > > > > > >
> > > > > > > "This control is present in a request's ControlList only if the
> > > > > > > pipeline supports setting the value. Even when it cannot be set by an
> > > > > > > application, the pipeline may still report the actual value used in
> > > > > > > the metadata returned with completed requests."
> > > > > >
> > > > > > I don't think it it necessary. It is implied that if a pipeline
> > > > > > handler does not support changing the digital gain it should not
> > > > > > expose it a one of the Camera's controls.
> > > > > >
> > > > > > Likewise, if it is something that applications should be informed of,
> > > > > > it will be reported via metadata.
> > > > > >
> > > > > > I think we're good to go, except for the point that we've left
> > > > > > floating about having this a single value or a per-channel value.
> > > > > >
> > > > > > I'm trying to get a feeling how this would be reported by your ISP. I
> > > > > > see in example you have two per-channel values for the ColourGains
> > > > > > control. Is this anyway related ?
> > > > > >
> > > > > > >
> > > > > > > Any other thoughts?
> > > > > > >
> > > > > > > Thanks
> > > > > > > David
> > > > > > >
> > > > > > > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
> > > > > > > <kieran.bingham@ideasonboard.com> wrote:
> > > > > > > >
> > > > > > > > Hi Jacopo,
> > > > > > > >
> > > > > > > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > > > > > > Hi Kieran,
> > > > > > > > >
> > > > > > > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > > > > > > >> Hi David,
> > > > > > > > >>
> > > > > > > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > > > > > > >>> This control reports the global digital gain applied by the pipeline
> > > > > > > > >>> as a whole, after capturing a raw image from the sensor.
> > > > > > > > >>>
> > > > > > > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > > > > > > >>> ---
> > > > > > > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > > > > > > >>>  1 file changed, 11 insertions(+)
> > > > > > > > >>>
> > > > > > > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > > > > > > >>> index c8874fa9..e6362c74 100644
> > > > > > > > >>> --- a/src/libcamera/control_ids.yaml
> > > > > > > > >>> +++ b/src/libcamera/control_ids.yaml
> > > > > > > > >>> @@ -530,4 +530,15 @@ controls:
> > > > > > > > >>>          This control is only present when the pipeline supports scaling. Its
> > > > > > > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > > > > > > >>>          property, and the two can be used to implement digital zoom.
> > > > > > > > >>> +
> > > > > > > > >>> +  - DigitalGain:
> > > > > > > > >>> +      type: float
> > > > > > > > >>> +      description: |
> > > > > > > > >>> +        Global digital gain value applied to the image during all the
> > > > > > > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > > > > > > >>> +        images, therefore, will not include this gain, but the final images
> > > > > > > > >>> +        output by the imaging pipeline as a whole will include it.
> > > > > > > > >>> +
> > > > > > > > >>> +        This control is intended to report the value used by the image
> > > > > > > > >>> +        processing pipeline.
> >
> >   - DigitalGain:
> >       type: float
> >       description: |
> >         Digital gain value applied during the processing steps applied
> >         to the image as captured from the sensor.
> >
> >         The global digital gain factor is applied to all the colour channels
> >         of the RAW image. Different pipeline models are free to
> >         specify how the global gain factor applies to each separate
> >         channel.
> >
> >         If an imaging pipeline applies digital gain in distinct
> >         processing steps, this value indicates their total sum.
> >         Pipelines are free to decide how to adjust each processing
> >         step to respect the received gain factor and shall report
> >         their total value in the request metadata.
> >
> > However this deferring to each pipeline model documentation makes me
> > wonder if expressing per-channel values would make things more
> > explicit...
> >
> > Feel free to take in what you consider appropriate.
>
> Yes, this is all so difficult, we just need to make a decision,
> really. Per-channel values work for me, but only because we're not
> going to let people set them. As a read-only thing, it seems a bit
> easier to understand/explain. We could ignore the question of setting
> a global digital gain until someone wants to do it (maybe no one ever
> will...).
>
> What do you think?

I think that once we have a pipeline that supports per-channel
digital gains we will introduce 'DigitalGains' as an array control,
deprectate this one, and keep supporting it in pipelines that exposed
it (through an internal helper maybe) not to break applications that
made use of it.

It's hard for me to have a firm idea without a real use case, but one
thing that presses me is not to mention this control is read only in
its definition. If that's the case for RPi just report it in metadata
only, but let's not restrict other platforms.

Do you think in the next iteration you will include reporting this
control from the pipeline too ? if I'm not mistaken this version
contains the control definition only.

Thanks
  j


>
> Thanks!
> David
>
> >
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > > > > > > >> pipeline handlers to set this to the appropriate value for each stream
> > > > > > > > >> when it completes. The fact that this value would not be applicable to a
> > > > > > > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > > > > > > >> style value.
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >> I'd hope this could be handled by a common helper in that instance so it
> > > > > > > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > > > > > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > > > > > > >> will be a core issue anyway.
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > > > > > > >> determine that someone needs to set it.
> > > > > > > > >>
> > > > > > > > >> We could introduce a control property between type: and description:
> > > > > > > > >>   read-only: true
> > > > > > > > >
> > > > > > > > > Isn't a read-only control just a metadata ?
> > > > > > > > >
> > > > > > > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > > > > > > the control value from applications not reporting it in the list of
> > > > > > > > > supported Camera's controls, but only report it as part of a completed
> > > > > > > > > request's metadata ?
> > > > > > > >
> > > > > > > > Ah, yes of course - because if the control is not listed as supported it
> > > > > > > > won't be there to set in the first place! I forgot about that.
> > > > > > > >
> > > > > > > > So - indeed, no requirement to mark anything as read-only. That will be
> > > > > > > > implicit.
> > > > > > > >
> > > > > > > > --
> > > > > > > > Kieran
> > > > > > > >
> > > > > > > >
> > > > > > > > >
> > > > > > > > > Thanks
> > > > > > > > >   j
> > > > > > > > >
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > > > > > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > > > > > > >> that brings it's own questions )
> > > > > > > > >>
> > > > > > > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >>>  ...
> > > > > > > > >>>
> > > > > > > > >>
> > > > > > > > >> --
> > > > > > > > >> Regards
> > > > > > > > >> --
> > > > > > > > >> Kieran
> > > > > > > > >> _______________________________________________
> > > > > > > > >> libcamera-devel mailing list
> > > > > > > > >> libcamera-devel@lists.libcamera.org
> > > > > > > > >> https://lists.libcamera.org/listinfo/libcamera-devel
> > > > > > > >
> > > > > > > > --
> > > > > > > > Regards
> > > > > > > > --
> > > > > > > > Kieran
Laurent Pinchart Nov. 26, 2020, 10:49 a.m. UTC | #12 
Hello,

On Mon, Nov 23, 2020 at 09:17:33AM +0000, Kieran Bingham wrote:
> On 23/11/2020 08:58, Jacopo Mondi wrote:
> > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> >> On 27/10/2020 14:12, David Plowman wrote:
> >>> This control reports the global digital gain applied by the pipeline
> >>> as a whole, after capturing a raw image from the sensor.
> >>>
> >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> >>> ---
> >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> >>>  1 file changed, 11 insertions(+)
> >>>
> >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> >>> index c8874fa9..e6362c74 100644
> >>> --- a/src/libcamera/control_ids.yaml
> >>> +++ b/src/libcamera/control_ids.yaml
> >>> @@ -530,4 +530,15 @@ controls:
> >>>          This control is only present when the pipeline supports scaling. Its
> >>>          maximum valid value is given by the properties::ScalerCropMaximum
> >>>          property, and the two can be used to implement digital zoom.
> >>> +
> >>> +  - DigitalGain:
> >>> +      type: float
> >>> +      description: |
> >>> +        Global digital gain value applied to the image during all the
> >>> +        processing steps after capturing the image from the sensor. Any raw
> >>> +        images, therefore, will not include this gain, but the final images
> >>> +        output by the imaging pipeline as a whole will include it.
> >>> +
> >>> +        This control is intended to report the value used by the image
> >>> +        processing pipeline.
> >>
> >> If this is a per-stream thing anyway, I guess it will then be up to
> >> pipeline handlers to set this to the appropriate value for each stream
> >> when it completes. The fact that this value would not be applicable to a
> >> RAW stream makes me think it certainly should be a per-stream metadata
> >> style value.
> >>
> >> I'd hope this could be handled by a common helper in that instance so it
> >> doesn't get left out of some pipeline handlers, but included in some,
> >> and become inconsistent. Not yet sure how we can handle that, but that
> >> will be a core issue anyway.
> >>
> >> I wonder if we should mark this somehow as read-only, at least until we
> >> determine that someone needs to set it.
> >>
> >> We could introduce a control property between type: and description:
> >>   read-only: true
> > 
> > Isn't a read-only control just a metadata ?
> > 
> > Wouldn't it be enough for a pipeline that does not support changing
> > the control value from applications not reporting it in the list of
> > supported Camera's controls, but only report it as part of a completed
> > request's metadata ?
> 
> Ah, yes of course - because if the control is not listed as supported it
> won't be there to set in the first place! I forgot about that.
> 
> So - indeed, no requirement to mark anything as read-only. That will be
> implicit.

There could still be value in specifying this in the yaml file, to
document which controls are meant to be read-only. Instead of writing
"This control is read-only" or "This control is meant to be used in
metadata only", a read-only property (I'm sure we'll bikeshed the name,
maybe "type: metadata" would be better) would allow compile-time and
runtime sanity checks. That's not a prerequisite for this patch though.

> >> Otherwise, I see no objections currently. I think we're just waiting on
> >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> >> that brings it's own questions )
> >>
> >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> >>
> >>>  ...
> >>>
> >>
> >> --
> >> Regards
> >> --
> >> Kieran
> >> _______________________________________________
> >> libcamera-devel mailing list
> >> libcamera-devel@lists.libcamera.org
> >> https://lists.libcamera.org/listinfo/libcamera-devel
> 
> -- 
> Regards
> --
> Kieran
> _______________________________________________
> libcamera-devel mailing list
> libcamera-devel@lists.libcamera.org
> https://lists.libcamera.org/listinfo/libcamera-devel
Kieran Bingham Nov. 26, 2020, 10:52 a.m. UTC | #13 
Hi Laurent,

On 26/11/2020 10:49, Laurent Pinchart wrote:
> Hello,
> 
> On Mon, Nov 23, 2020 at 09:17:33AM +0000, Kieran Bingham wrote:
>> On 23/11/2020 08:58, Jacopo Mondi wrote:
>>> On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
>>>> On 27/10/2020 14:12, David Plowman wrote:
>>>>> This control reports the global digital gain applied by the pipeline
>>>>> as a whole, after capturing a raw image from the sensor.
>>>>>
>>>>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
>>>>> ---
>>>>>  src/libcamera/control_ids.yaml | 11 +++++++++++
>>>>>  1 file changed, 11 insertions(+)
>>>>>
>>>>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
>>>>> index c8874fa9..e6362c74 100644
>>>>> --- a/src/libcamera/control_ids.yaml
>>>>> +++ b/src/libcamera/control_ids.yaml
>>>>> @@ -530,4 +530,15 @@ controls:
>>>>>          This control is only present when the pipeline supports scaling. Its
>>>>>          maximum valid value is given by the properties::ScalerCropMaximum
>>>>>          property, and the two can be used to implement digital zoom.
>>>>> +
>>>>> +  - DigitalGain:
>>>>> +      type: float
>>>>> +      description: |
>>>>> +        Global digital gain value applied to the image during all the
>>>>> +        processing steps after capturing the image from the sensor. Any raw
>>>>> +        images, therefore, will not include this gain, but the final images
>>>>> +        output by the imaging pipeline as a whole will include it.
>>>>> +
>>>>> +        This control is intended to report the value used by the image
>>>>> +        processing pipeline.
>>>>
>>>> If this is a per-stream thing anyway, I guess it will then be up to
>>>> pipeline handlers to set this to the appropriate value for each stream
>>>> when it completes. The fact that this value would not be applicable to a
>>>> RAW stream makes me think it certainly should be a per-stream metadata
>>>> style value.
>>>>
>>>> I'd hope this could be handled by a common helper in that instance so it
>>>> doesn't get left out of some pipeline handlers, but included in some,
>>>> and become inconsistent. Not yet sure how we can handle that, but that
>>>> will be a core issue anyway.
>>>>
>>>> I wonder if we should mark this somehow as read-only, at least until we
>>>> determine that someone needs to set it.
>>>>
>>>> We could introduce a control property between type: and description:
>>>>   read-only: true
>>>
>>> Isn't a read-only control just a metadata ?
>>>
>>> Wouldn't it be enough for a pipeline that does not support changing
>>> the control value from applications not reporting it in the list of
>>> supported Camera's controls, but only report it as part of a completed
>>> request's metadata ?
>>
>> Ah, yes of course - because if the control is not listed as supported it
>> won't be there to set in the first place! I forgot about that.
>>
>> So - indeed, no requirement to mark anything as read-only. That will be
>> implicit.
> 
> There could still be value in specifying this in the yaml file, to
> document which controls are meant to be read-only. Instead of writing
> "This control is read-only" or "This control is meant to be used in
> metadata only", a read-only property (I'm sure we'll bikeshed the name,
> maybe "type: metadata" would be better) would allow compile-time and
> runtime sanity checks. That's not a prerequisite for this patch though.

I don't actually think this has to be a read-only control though.

I can imagine this being an enabled control that will allow increasing
the gain of an image (without affecting colour balance).

To me - this is the same as AnalogueGain but applied at the ISP rather
than the sensor right ?

--
Kieran


> 
>>>> Otherwise, I see no objections currently. I think we're just waiting on
>>>> top-level thoughts from Laurent. (And perhaps per-stream controls, but
>>>> that brings it's own questions )
>>>>
>>>> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
>>>>
>>>>>  ...
>>>>>
>>>>
>>>> --
>>>> Regards
>>>> --
>>>> Kieran
>>>> _______________________________________________
>>>> libcamera-devel mailing list
>>>> libcamera-devel@lists.libcamera.org
>>>> https://lists.libcamera.org/listinfo/libcamera-devel
>>
>> -- 
>> Regards
>> --
>> Kieran
>> _______________________________________________
>> libcamera-devel mailing list
>> libcamera-devel@lists.libcamera.org
>> https://lists.libcamera.org/listinfo/libcamera-devel
>
Kieran Bingham Nov. 26, 2020, 10:57 a.m. UTC | #14 
Hi Jacopo, David,

On 26/11/2020 10:25, Jacopo Mondi wrote:
> Hi David,
> 
> On Thu, Nov 26, 2020 at 09:50:05AM +0000, David Plowman wrote:
>> Hi Jacopo
>>
>> Thanks for the update on this.
>>
>> On Wed, 25 Nov 2020 at 21:02, Jacopo Mondi <jacopo@jmondi.org> wrote:
>>>
>>> Hi David,
>>>     I tried proposing a new version based on the outcome of our
>>> discussion
>>>
>>> Please see below
>>>
>>> On Tue, Nov 24, 2020 at 12:40:38PM +0000, David Plowman wrote:
>>>> Hi Jacopo
>>>>
>>>> Thanks for the reply. More discussion below...
>>>>
>>>> On Tue, 24 Nov 2020 at 11:28, Jacopo Mondi <jacopo@jmondi.org> wrote:
>>>>>
>>>>> Hi David,
>>>>>
>>>>> On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
>>>>>> Hi Jacopo
>>>>>>
>>>>>> You're right, there's a relationship there. ColourGains obviously
>>>>>> gives you the red and blue gains determined by the AWB usually. You
>>>>>> might get the values 1.6 and 2.0 (for red and blue)
>>>>>>
>>>>>> In our case, if we report a single "global gain" value you can kind of
>>>>>> imagine it as the green gain, where the colour gains were normalised
>>>>>> for a green gain of 1. So if the global gain was 1.25, then the actual
>>>>>> RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
>>>>>> 1.25, 2.5).
>>>>>
>>>>> That's a really helpful explanation for me, thanks
>>>>>
>>>>>>
>>>>>> In the per-channel case I guess you'd be reporting these 3 numbers
>>>>>> directly. For me this duplicates information that's already in the
>>>>>> ColourGains, and it seems to muddle things up a bit. Imagine you had a
>>>>>> pipeline that lets you set a global gain - you'd have to query the
>>>>>> current white balance and work out all three numbers and set them. But
>>>>>> then you've set the white balance as well. Or maybe we do something
>>>>>> special so that you haven't? You see why it confuses me! So on balance
>>>>>> I'm with the single value approach, though I could live either way.
>>>>>
>>>>> I see. With the above explanation I really see why a single global
>>>>> value is probably enough.
>>>>>
>>>>> My question is now: are the above notions (blue/red gains normalized
>>>>> on a green value of 1, how global gain is used to obtain per-channel
>>>>> gains etc) standard knowledge I'm lacking, or:
>>>>>
>>>>> 1) It's worth to describe them in the control documentation as they're
>>>>> "standard" and won't change per-pipeline
>>>>> 2) They might differe per-pipeline and they need to be
>>>>> described in the pipeline model documentation ?
>>>>> 3) It is assumed the reader knows she's dealing with
>>>>
>>>> Difficult. I can't really see too many other ways of defining it, but
>>>> you know, pipelines all have their nuances. You probably can't
>>>> guarantee that what I described is completely "standard".
>>>>
>>>> A slightly more qualitative definition seems OK to me - the amount of
>>>> linear gain applied by the pipeline to all pixels (in addition to the
>>>> colour gains). Particular pipelines might feel they need to document
>>>> it more carefully if there are any complications in how they deal with
>>>> it.
>>>>
>>>> Best regards
>>>> David
>>>>
>>>>>
>>>>> Thanks
>>>>>    j
>>>>>
>>>>>>
>>>>>> Thanks!
>>>>>> David
>>>>>>
>>>>>> On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
>>>>>>>
>>>>>>> Hi David,
>>>>>>>
>>>>>>> On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
>>>>>>>> Hi everyone
>>>>>>>>
>>>>>>>> Sounds like we're happy enough from the point of view of this thing
>>>>>>>> being read-only (for Raspberry Pi at least). Would anyone want any
>>>>>>>> changes to the wording? Perhaps the final sentence/paragraph might now
>>>>>>>> be better as
>>>>>>>>
>>>>>>>> "This control is present in a request's ControlList only if the
>>>>>>>> pipeline supports setting the value. Even when it cannot be set by an
>>>>>>>> application, the pipeline may still report the actual value used in
>>>>>>>> the metadata returned with completed requests."
>>>>>>>
>>>>>>> I don't think it it necessary. It is implied that if a pipeline
>>>>>>> handler does not support changing the digital gain it should not
>>>>>>> expose it a one of the Camera's controls.
>>>>>>>
>>>>>>> Likewise, if it is something that applications should be informed of,
>>>>>>> it will be reported via metadata.
>>>>>>>
>>>>>>> I think we're good to go, except for the point that we've left
>>>>>>> floating about having this a single value or a per-channel value.
>>>>>>>
>>>>>>> I'm trying to get a feeling how this would be reported by your ISP. I
>>>>>>> see in example you have two per-channel values for the ColourGains
>>>>>>> control. Is this anyway related ?
>>>>>>>
>>>>>>>>
>>>>>>>> Any other thoughts?
>>>>>>>>
>>>>>>>> Thanks
>>>>>>>> David
>>>>>>>>
>>>>>>>> On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
>>>>>>>> <kieran.bingham@ideasonboard.com> wrote:
>>>>>>>>>
>>>>>>>>> Hi Jacopo,
>>>>>>>>>
>>>>>>>>> On 23/11/2020 08:58, Jacopo Mondi wrote:
>>>>>>>>>> Hi Kieran,
>>>>>>>>>>
>>>>>>>>>> On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
>>>>>>>>>>> Hi David,
>>>>>>>>>>>
>>>>>>>>>>> On 27/10/2020 14:12, David Plowman wrote:
>>>>>>>>>>>> This control reports the global digital gain applied by the pipeline
>>>>>>>>>>>> as a whole, after capturing a raw image from the sensor.
>>>>>>>>>>>>
>>>>>>>>>>>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
>>>>>>>>>>>> ---
>>>>>>>>>>>>  src/libcamera/control_ids.yaml | 11 +++++++++++
>>>>>>>>>>>>  1 file changed, 11 insertions(+)
>>>>>>>>>>>>
>>>>>>>>>>>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
>>>>>>>>>>>> index c8874fa9..e6362c74 100644
>>>>>>>>>>>> --- a/src/libcamera/control_ids.yaml
>>>>>>>>>>>> +++ b/src/libcamera/control_ids.yaml
>>>>>>>>>>>> @@ -530,4 +530,15 @@ controls:
>>>>>>>>>>>>          This control is only present when the pipeline supports scaling. Its
>>>>>>>>>>>>          maximum valid value is given by the properties::ScalerCropMaximum
>>>>>>>>>>>>          property, and the two can be used to implement digital zoom.
>>>>>>>>>>>> +
>>>>>>>>>>>> +  - DigitalGain:
>>>>>>>>>>>> +      type: float
>>>>>>>>>>>> +      description: |
>>>>>>>>>>>> +        Global digital gain value applied to the image during all the
>>>>>>>>>>>> +        processing steps after capturing the image from the sensor. Any raw
>>>>>>>>>>>> +        images, therefore, will not include this gain, but the final images
>>>>>>>>>>>> +        output by the imaging pipeline as a whole will include it.
>>>>>>>>>>>> +
>>>>>>>>>>>> +        This control is intended to report the value used by the image
>>>>>>>>>>>> +        processing pipeline.
>>>
>>>   - DigitalGain:
>>>       type: float
>>>       description: |
>>>         Digital gain value applied during the processing steps applied
>>>         to the image as captured from the sensor.
>>>
>>>         The global digital gain factor is applied to all the colour channels
>>>         of the RAW image. Different pipeline models are free to
>>>         specify how the global gain factor applies to each separate
>>>         channel.
>>>
>>>         If an imaging pipeline applies digital gain in distinct
>>>         processing steps, this value indicates their total sum.
>>>         Pipelines are free to decide how to adjust each processing
>>>         step to respect the received gain factor and shall report
>>>         their total value in the request metadata.
>>>
>>> However this deferring to each pipeline model documentation makes me
>>> wonder if expressing per-channel values would make things more
>>> explicit...
>>>
>>> Feel free to take in what you consider appropriate.
>>
>> Yes, this is all so difficult, we just need to make a decision,
>> really. Per-channel values work for me, but only because we're not
>> going to let people set them. As a read-only thing, it seems a bit
>> easier to understand/explain. We could ignore the question of setting
>> a global digital gain until someone wants to do it (maybe no one ever
>> will...).
>>
>> What do you think?
> 
> I think that once we have a pipeline that supports per-channel
> digital gains we will introduce 'DigitalGains' as an array control,

That's called colour balance isn't it ?

To me - DigitalGain is analogous to AnalogueGain - and would be expected
to not affect the colour balance.

If you want to control colour balance, that's manipulating the channels
independently, which we have a control for already.


In my opinion, DigitalGain could potentially be something that an
application might set, or even that an IPA might set indicating - "I
want to increase the gain/brightness of the whole image (either beyond
the capability of the AnalogueGain, or if the AnalogueGain can not be
changed)".

And it would be an effect that is /after/ colour balance has occurred.
Perhaps it might be important to declare specifically that the
DigitalGain is a factor applied after any balance gains...

--
Kieran



> deprectate this one, and keep supporting it in pipelines that exposed
> it (through an internal helper maybe) not to break applications that
> made use of it.
> 
> It's hard for me to have a firm idea without a real use case, but one
> thing that presses me is not to mention this control is read only in
> its definition. If that's the case for RPi just report it in metadata
> only, but let's not restrict other platforms.
> 
> Do you think in the next iteration you will include reporting this
> control from the pipeline too ? if I'm not mistaken this version
> contains the control definition only.
> 
> Thanks
>   j
> 
> 
>>
>> Thanks!
>> David
>>
>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> If this is a per-stream thing anyway, I guess it will then be up to
>>>>>>>>>>> pipeline handlers to set this to the appropriate value for each stream
>>>>>>>>>>> when it completes. The fact that this value would not be applicable to a
>>>>>>>>>>> RAW stream makes me think it certainly should be a per-stream metadata
>>>>>>>>>>> style value.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> I'd hope this could be handled by a common helper in that instance so it
>>>>>>>>>>> doesn't get left out of some pipeline handlers, but included in some,
>>>>>>>>>>> and become inconsistent. Not yet sure how we can handle that, but that
>>>>>>>>>>> will be a core issue anyway.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> I wonder if we should mark this somehow as read-only, at least until we
>>>>>>>>>>> determine that someone needs to set it.
>>>>>>>>>>>
>>>>>>>>>>> We could introduce a control property between type: and description:
>>>>>>>>>>>   read-only: true
>>>>>>>>>>
>>>>>>>>>> Isn't a read-only control just a metadata ?
>>>>>>>>>>
>>>>>>>>>> Wouldn't it be enough for a pipeline that does not support changing
>>>>>>>>>> the control value from applications not reporting it in the list of
>>>>>>>>>> supported Camera's controls, but only report it as part of a completed
>>>>>>>>>> request's metadata ?
>>>>>>>>>
>>>>>>>>> Ah, yes of course - because if the control is not listed as supported it
>>>>>>>>> won't be there to set in the first place! I forgot about that.
>>>>>>>>>
>>>>>>>>> So - indeed, no requirement to mark anything as read-only. That will be
>>>>>>>>> implicit.
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> Kieran
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Thanks
>>>>>>>>>>   j
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Otherwise, I see no objections currently. I think we're just waiting on
>>>>>>>>>>> top-level thoughts from Laurent. (And perhaps per-stream controls, but
>>>>>>>>>>> that brings it's own questions )
>>>>>>>>>>>
>>>>>>>>>>> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>>  ...
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> Regards
>>>>>>>>>>> --
>>>>>>>>>>> Kieran
>>>>>>>>>>> _______________________________________________
>>>>>>>>>>> libcamera-devel mailing list
>>>>>>>>>>> libcamera-devel@lists.libcamera.org
>>>>>>>>>>> https://lists.libcamera.org/listinfo/libcamera-devel
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> Regards
>>>>>>>>> --
>>>>>>>>> Kieran
David Plowman Nov. 26, 2020, 11:07 a.m. UTC | #15 
Hi Jacopo

Yes, I'll submit a v2 with the text you had earlier, and I'll add an
patch where the Raspberry Pi IPAs fill it in.

Thanks!
David

On Thu, 26 Nov 2020 at 10:25, Jacopo Mondi <jacopo@jmondi.org> wrote:
>
> Hi David,
>
> On Thu, Nov 26, 2020 at 09:50:05AM +0000, David Plowman wrote:
> > Hi Jacopo
> >
> > Thanks for the update on this.
> >
> > On Wed, 25 Nov 2020 at 21:02, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > >
> > > Hi David,
> > >     I tried proposing a new version based on the outcome of our
> > > discussion
> > >
> > > Please see below
> > >
> > > On Tue, Nov 24, 2020 at 12:40:38PM +0000, David Plowman wrote:
> > > > Hi Jacopo
> > > >
> > > > Thanks for the reply. More discussion below...
> > > >
> > > > On Tue, 24 Nov 2020 at 11:28, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > > >
> > > > > Hi David,
> > > > >
> > > > > On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
> > > > > > Hi Jacopo
> > > > > >
> > > > > > You're right, there's a relationship there. ColourGains obviously
> > > > > > gives you the red and blue gains determined by the AWB usually. You
> > > > > > might get the values 1.6 and 2.0 (for red and blue)
> > > > > >
> > > > > > In our case, if we report a single "global gain" value you can kind of
> > > > > > imagine it as the green gain, where the colour gains were normalised
> > > > > > for a green gain of 1. So if the global gain was 1.25, then the actual
> > > > > > RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
> > > > > > 1.25, 2.5).
> > > > >
> > > > > That's a really helpful explanation for me, thanks
> > > > >
> > > > > >
> > > > > > In the per-channel case I guess you'd be reporting these 3 numbers
> > > > > > directly. For me this duplicates information that's already in the
> > > > > > ColourGains, and it seems to muddle things up a bit. Imagine you had a
> > > > > > pipeline that lets you set a global gain - you'd have to query the
> > > > > > current white balance and work out all three numbers and set them. But
> > > > > > then you've set the white balance as well. Or maybe we do something
> > > > > > special so that you haven't? You see why it confuses me! So on balance
> > > > > > I'm with the single value approach, though I could live either way.
> > > > >
> > > > > I see. With the above explanation I really see why a single global
> > > > > value is probably enough.
> > > > >
> > > > > My question is now: are the above notions (blue/red gains normalized
> > > > > on a green value of 1, how global gain is used to obtain per-channel
> > > > > gains etc) standard knowledge I'm lacking, or:
> > > > >
> > > > > 1) It's worth to describe them in the control documentation as they're
> > > > > "standard" and won't change per-pipeline
> > > > > 2) They might differe per-pipeline and they need to be
> > > > > described in the pipeline model documentation ?
> > > > > 3) It is assumed the reader knows she's dealing with
> > > >
> > > > Difficult. I can't really see too many other ways of defining it, but
> > > > you know, pipelines all have their nuances. You probably can't
> > > > guarantee that what I described is completely "standard".
> > > >
> > > > A slightly more qualitative definition seems OK to me - the amount of
> > > > linear gain applied by the pipeline to all pixels (in addition to the
> > > > colour gains). Particular pipelines might feel they need to document
> > > > it more carefully if there are any complications in how they deal with
> > > > it.
> > > >
> > > > Best regards
> > > > David
> > > >
> > > > >
> > > > > Thanks
> > > > >    j
> > > > >
> > > > > >
> > > > > > Thanks!
> > > > > > David
> > > > > >
> > > > > > On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > > > > >
> > > > > > > Hi David,
> > > > > > >
> > > > > > > On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > > > > > > > Hi everyone
> > > > > > > >
> > > > > > > > Sounds like we're happy enough from the point of view of this thing
> > > > > > > > being read-only (for Raspberry Pi at least). Would anyone want any
> > > > > > > > changes to the wording? Perhaps the final sentence/paragraph might now
> > > > > > > > be better as
> > > > > > > >
> > > > > > > > "This control is present in a request's ControlList only if the
> > > > > > > > pipeline supports setting the value. Even when it cannot be set by an
> > > > > > > > application, the pipeline may still report the actual value used in
> > > > > > > > the metadata returned with completed requests."
> > > > > > >
> > > > > > > I don't think it it necessary. It is implied that if a pipeline
> > > > > > > handler does not support changing the digital gain it should not
> > > > > > > expose it a one of the Camera's controls.
> > > > > > >
> > > > > > > Likewise, if it is something that applications should be informed of,
> > > > > > > it will be reported via metadata.
> > > > > > >
> > > > > > > I think we're good to go, except for the point that we've left
> > > > > > > floating about having this a single value or a per-channel value.
> > > > > > >
> > > > > > > I'm trying to get a feeling how this would be reported by your ISP. I
> > > > > > > see in example you have two per-channel values for the ColourGains
> > > > > > > control. Is this anyway related ?
> > > > > > >
> > > > > > > >
> > > > > > > > Any other thoughts?
> > > > > > > >
> > > > > > > > Thanks
> > > > > > > > David
> > > > > > > >
> > > > > > > > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
> > > > > > > > <kieran.bingham@ideasonboard.com> wrote:
> > > > > > > > >
> > > > > > > > > Hi Jacopo,
> > > > > > > > >
> > > > > > > > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > > > > > > > Hi Kieran,
> > > > > > > > > >
> > > > > > > > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > > > > > > > >> Hi David,
> > > > > > > > > >>
> > > > > > > > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > > > > > > > >>> This control reports the global digital gain applied by the pipeline
> > > > > > > > > >>> as a whole, after capturing a raw image from the sensor.
> > > > > > > > > >>>
> > > > > > > > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > > > > > > > >>> ---
> > > > > > > > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > > > > > > > >>>  1 file changed, 11 insertions(+)
> > > > > > > > > >>>
> > > > > > > > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > > > > > > > >>> index c8874fa9..e6362c74 100644
> > > > > > > > > >>> --- a/src/libcamera/control_ids.yaml
> > > > > > > > > >>> +++ b/src/libcamera/control_ids.yaml
> > > > > > > > > >>> @@ -530,4 +530,15 @@ controls:
> > > > > > > > > >>>          This control is only present when the pipeline supports scaling. Its
> > > > > > > > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > > > > > > > >>>          property, and the two can be used to implement digital zoom.
> > > > > > > > > >>> +
> > > > > > > > > >>> +  - DigitalGain:
> > > > > > > > > >>> +      type: float
> > > > > > > > > >>> +      description: |
> > > > > > > > > >>> +        Global digital gain value applied to the image during all the
> > > > > > > > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > > > > > > > >>> +        images, therefore, will not include this gain, but the final images
> > > > > > > > > >>> +        output by the imaging pipeline as a whole will include it.
> > > > > > > > > >>> +
> > > > > > > > > >>> +        This control is intended to report the value used by the image
> > > > > > > > > >>> +        processing pipeline.
> > >
> > >   - DigitalGain:
> > >       type: float
> > >       description: |
> > >         Digital gain value applied during the processing steps applied
> > >         to the image as captured from the sensor.
> > >
> > >         The global digital gain factor is applied to all the colour channels
> > >         of the RAW image. Different pipeline models are free to
> > >         specify how the global gain factor applies to each separate
> > >         channel.
> > >
> > >         If an imaging pipeline applies digital gain in distinct
> > >         processing steps, this value indicates their total sum.
> > >         Pipelines are free to decide how to adjust each processing
> > >         step to respect the received gain factor and shall report
> > >         their total value in the request metadata.
> > >
> > > However this deferring to each pipeline model documentation makes me
> > > wonder if expressing per-channel values would make things more
> > > explicit...
> > >
> > > Feel free to take in what you consider appropriate.
> >
> > Yes, this is all so difficult, we just need to make a decision,
> > really. Per-channel values work for me, but only because we're not
> > going to let people set them. As a read-only thing, it seems a bit
> > easier to understand/explain. We could ignore the question of setting
> > a global digital gain until someone wants to do it (maybe no one ever
> > will...).
> >
> > What do you think?
>
> I think that once we have a pipeline that supports per-channel
> digital gains we will introduce 'DigitalGains' as an array control,
> deprectate this one, and keep supporting it in pipelines that exposed
> it (through an internal helper maybe) not to break applications that
> made use of it.
>
> It's hard for me to have a firm idea without a real use case, but one
> thing that presses me is not to mention this control is read only in
> its definition. If that's the case for RPi just report it in metadata
> only, but let's not restrict other platforms.
>
> Do you think in the next iteration you will include reporting this
> control from the pipeline too ? if I'm not mistaken this version
> contains the control definition only.
>
> Thanks
>   j
>
>
> >
> > Thanks!
> > David
> >
> > >
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > > > > > > > >> pipeline handlers to set this to the appropriate value for each stream
> > > > > > > > > >> when it completes. The fact that this value would not be applicable to a
> > > > > > > > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > > > > > > > >> style value.
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >> I'd hope this could be handled by a common helper in that instance so it
> > > > > > > > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > > > > > > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > > > > > > > >> will be a core issue anyway.
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > > > > > > > >> determine that someone needs to set it.
> > > > > > > > > >>
> > > > > > > > > >> We could introduce a control property between type: and description:
> > > > > > > > > >>   read-only: true
> > > > > > > > > >
> > > > > > > > > > Isn't a read-only control just a metadata ?
> > > > > > > > > >
> > > > > > > > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > > > > > > > the control value from applications not reporting it in the list of
> > > > > > > > > > supported Camera's controls, but only report it as part of a completed
> > > > > > > > > > request's metadata ?
> > > > > > > > >
> > > > > > > > > Ah, yes of course - because if the control is not listed as supported it
> > > > > > > > > won't be there to set in the first place! I forgot about that.
> > > > > > > > >
> > > > > > > > > So - indeed, no requirement to mark anything as read-only. That will be
> > > > > > > > > implicit.
> > > > > > > > >
> > > > > > > > > --
> > > > > > > > > Kieran
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > Thanks
> > > > > > > > > >   j
> > > > > > > > > >
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > > > > > > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > > > > > > > >> that brings it's own questions )
> > > > > > > > > >>
> > > > > > > > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >>>  ...
> > > > > > > > > >>>
> > > > > > > > > >>
> > > > > > > > > >> --
> > > > > > > > > >> Regards
> > > > > > > > > >> --
> > > > > > > > > >> Kieran
> > > > > > > > > >> _______________________________________________
> > > > > > > > > >> libcamera-devel mailing list
> > > > > > > > > >> libcamera-devel@lists.libcamera.org
> > > > > > > > > >> https://lists.libcamera.org/listinfo/libcamera-devel
> > > > > > > > >
> > > > > > > > > --
> > > > > > > > > Regards
> > > > > > > > > --
> > > > > > > > > Kieran
Laurent Pinchart Nov. 26, 2020, 11:25 a.m. UTC | #16 
Hi Kieran,

On Thu, Nov 26, 2020 at 10:52:43AM +0000, Kieran Bingham wrote:
> On 26/11/2020 10:49, Laurent Pinchart wrote:
> > On Mon, Nov 23, 2020 at 09:17:33AM +0000, Kieran Bingham wrote:
> >> On 23/11/2020 08:58, Jacopo Mondi wrote:
> >>> On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> >>>> On 27/10/2020 14:12, David Plowman wrote:
> >>>>> This control reports the global digital gain applied by the pipeline
> >>>>> as a whole, after capturing a raw image from the sensor.
> >>>>>
> >>>>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> >>>>> ---
> >>>>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> >>>>>  1 file changed, 11 insertions(+)
> >>>>>
> >>>>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> >>>>> index c8874fa9..e6362c74 100644
> >>>>> --- a/src/libcamera/control_ids.yaml
> >>>>> +++ b/src/libcamera/control_ids.yaml
> >>>>> @@ -530,4 +530,15 @@ controls:
> >>>>>          This control is only present when the pipeline supports scaling. Its
> >>>>>          maximum valid value is given by the properties::ScalerCropMaximum
> >>>>>          property, and the two can be used to implement digital zoom.
> >>>>> +
> >>>>> +  - DigitalGain:
> >>>>> +      type: float
> >>>>> +      description: |
> >>>>> +        Global digital gain value applied to the image during all the
> >>>>> +        processing steps after capturing the image from the sensor. Any raw
> >>>>> +        images, therefore, will not include this gain, but the final images
> >>>>> +        output by the imaging pipeline as a whole will include it.
> >>>>> +
> >>>>> +        This control is intended to report the value used by the image
> >>>>> +        processing pipeline.
> >>>>
> >>>> If this is a per-stream thing anyway, I guess it will then be up to
> >>>> pipeline handlers to set this to the appropriate value for each stream
> >>>> when it completes. The fact that this value would not be applicable to a
> >>>> RAW stream makes me think it certainly should be a per-stream metadata
> >>>> style value.
> >>>>
> >>>> I'd hope this could be handled by a common helper in that instance so it
> >>>> doesn't get left out of some pipeline handlers, but included in some,
> >>>> and become inconsistent. Not yet sure how we can handle that, but that
> >>>> will be a core issue anyway.
> >>>>
> >>>> I wonder if we should mark this somehow as read-only, at least until we
> >>>> determine that someone needs to set it.
> >>>>
> >>>> We could introduce a control property between type: and description:
> >>>>   read-only: true
> >>>
> >>> Isn't a read-only control just a metadata ?
> >>>
> >>> Wouldn't it be enough for a pipeline that does not support changing
> >>> the control value from applications not reporting it in the list of
> >>> supported Camera's controls, but only report it as part of a completed
> >>> request's metadata ?
> >>
> >> Ah, yes of course - because if the control is not listed as supported it
> >> won't be there to set in the first place! I forgot about that.
> >>
> >> So - indeed, no requirement to mark anything as read-only. That will be
> >> implicit.
> > 
> > There could still be value in specifying this in the yaml file, to
> > document which controls are meant to be read-only. Instead of writing
> > "This control is read-only" or "This control is meant to be used in
> > metadata only", a read-only property (I'm sure we'll bikeshed the name,
> > maybe "type: metadata" would be better) would allow compile-time and
> > runtime sanity checks. That's not a prerequisite for this patch though.
> 
> I don't actually think this has to be a read-only control though.
> 
> I can imagine this being an enabled control that will allow increasing
> the gain of an image (without affecting colour balance).
> 
> To me - this is the same as AnalogueGain but applied at the ISP rather
> than the sensor right ?

Yes, this doesn't necessarily have to be read-only, my comment was about
general handling of read-only controls, not this specific one.

> >>>> Otherwise, I see no objections currently. I think we're just waiting on
> >>>> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> >>>> that brings it's own questions )
> >>>>
> >>>> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> >>>>
> >>>>>  ...
Laurent Pinchart Nov. 26, 2020, 12:42 p.m. UTC | #17 
Hi David,

On Tue, Nov 24, 2020 at 12:40:38PM +0000, David Plowman wrote:
> On Tue, 24 Nov 2020 at 11:28, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
> > > Hi Jacopo
> > >
> > > You're right, there's a relationship there. ColourGains obviously
> > > gives you the red and blue gains determined by the AWB usually. You
> > > might get the values 1.6 and 2.0 (for red and blue)
> > >
> > > In our case, if we report a single "global gain" value you can kind of
> > > imagine it as the green gain, where the colour gains were normalised
> > > for a green gain of 1. So if the global gain was 1.25, then the actual
> > > RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
> > > 1.25, 2.5).
> >
> > That's a really helpful explanation for me, thanks
> >
> > > In the per-channel case I guess you'd be reporting these 3 numbers
> > > directly. For me this duplicates information that's already in the
> > > ColourGains, and it seems to muddle things up a bit. Imagine you had a
> > > pipeline that lets you set a global gain - you'd have to query the
> > > current white balance and work out all three numbers and set them. But
> > > then you've set the white balance as well. Or maybe we do something
> > > special so that you haven't? You see why it confuses me! So on balance
> > > I'm with the single value approach, though I could live either way.
> >
> > I see. With the above explanation I really see why a single global
> > value is probably enough.
> >
> > My question is now: are the above notions (blue/red gains normalized
> > on a green value of 1, how global gain is used to obtain per-channel
> > gains etc) standard knowledge I'm lacking, or:
> >
> > 1) It's worth to describe them in the control documentation as they're
> > "standard" and won't change per-pipeline
> > 2) They might differe per-pipeline and they need to be
> > described in the pipeline model documentation ?
> > 3) It is assumed the reader knows she's dealing with
> 
> Difficult. I can't really see too many other ways of defining it, but
> you know, pipelines all have their nuances. You probably can't
> guarantee that what I described is completely "standard".

This is really what I'd like to address :-)

Have you seen the "libcamera: camera: Document the camera and pipeline
model" patch (which is now in the master branch) ? It's the very first
step in standardizing a logical pipeline model that pipeline handlers
need to confirm to.

In a nutshell, the idea is that libcamera needs to standardize the
behaviour of cameras as seen from applications in order to make
applications portable. To do so, we define a logical pipeline model that
describes the processing operations performed by the camera, from the
pixel array to the captured image.

Hardware platforms differ in the feature they support and how they
implement them, so most operations in the pipeline model are optional.
Furthermore, there's no requirement to have the hardware performing
those operations in the same order, or more generically in the same way,
as the logical model mandates, as long as the visible effect from an
application point of view is the same. Pipeline handlers are responsible
for exposing the standard logical model and mapping it to device
features.

I expect that not all devices will be able to expose the same pipeline
model, so we will need to support multiple options, with a way for the
pipeline handlers to report which options apply to the cameras they
handle. This can be reported through properties or through other means.
We already support this, albeit implicitly: pipeline handlers that don't
support some of the processing operations simply don't expose the
corresponding controls. I expect we will also need properties to report
the order of operations, when different orders lead to different results
and all need to be supported. This should however remain the exception
rather than the rule.

I would like to expand the pipeline model documentation to include
colour processing, and I think digital gain really fits here. We can
still apply your patch (or the next version of it) before finalizing
documentation of the colour processing in the pipeline model, but
controls will then likely change soon after, which would require
adapting your applications. It may end up causing more pain than gain.

As you have more experience than me in this area, I wonder if you could
help reviewing an initial proposal ? I envision the following
sensitivity and colour-related operations, in order.

- Total gain in the sensor, made of analog and/or digital gain. This
  applies to all images, RAW and processed, and to all channels. If
  auto-exposure is enabled, the control value is ignored. The actual
  value is always reported in metadata.

  Questions:

   - Should we mandate that pipeline handlers and IPAs prioritize analog
     gain before applying digital gain ?

   - Can there be use cases for per-channel sensor-side gains ? In most
     cases I expect the white balance to be applied in the ISP, but will
     that always be the case ? What if auto-white-balance is disabled,
     and the user sets manual per-channel gains, could there be a reason
     to apply them in the sensor ?

- Digital gain on the ISP side (a.k.a. "post-RAW sensitivity boost" in
  Android). This applies to processed images only, and to all channels.
  If auto-exposure is enabled, the control value is ignored. The actual
  value is always reported in metadata.

  Questions:

  - Should this be renamed ? "Digital gain" can be confused with the
    digital gain in the sensor. A name that captures the fact that the
    gain is applied on processed images only may be better (I don't like
    the Android name too much, but it handles this issue).

- Per-channel gains. This is currently handled as red and blue gains,
  with the green gains being hardcoded to 1.0.

  Questions:

  - Should we change this ? I see two potential issues:

    - Not all systems may use a Bayer colour filter array, so other
      gains may be needed (I'm thinking about RGBW patterns for
      instance, or any other from
      https://en.wikipedia.org/wiki/Color_filter_array).

    - Hardcoding the green gains to 1.0 means that we will have an
      "average" gain different than 1.0 in most cases. This will
      effectively change the sensitivity of the camera, and should be
      taken into account to compute the ISO value. Applications could do
      so, but I wonder if we shouldn't mandate that the "average" gain
      remains 1.0, with the "sensitivity boost" being handled by the
      digital gain control only. How to compute the "average" gain is an
      interesting problem here, as I expect it will need to take a full
      colour model into account.

- Demosaicing. This shouldn't apply any gain.

- RGB-to-RGB colour transformation matrix.

  Questions:

  - Similarly to the per-channel gains, should we require that this
    matrix applies no gain (i.e. the sum of elements in a line should be
    1.0) ?

- RGB-to-YUV colour encoding matrix.

  Questions:

  - Similarly to the RGB-to-RGB matrix, should we forbid gains ?

Is there any other colour processing operation I have missed ?

> A slightly more qualitative definition seems OK to me - the amount of
> linear gain applied by the pipeline to all pixels (in addition to the
> colour gains). Particular pipelines might feel they need to document
> it more carefully if there are any complications in how they deal with
> it.
>
> > > On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > > On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > > > > Hi everyone
> > > > >
> > > > > Sounds like we're happy enough from the point of view of this thing
> > > > > being read-only (for Raspberry Pi at least). Would anyone want any
> > > > > changes to the wording? Perhaps the final sentence/paragraph might now
> > > > > be better as
> > > > >
> > > > > "This control is present in a request's ControlList only if the
> > > > > pipeline supports setting the value. Even when it cannot be set by an
> > > > > application, the pipeline may still report the actual value used in
> > > > > the metadata returned with completed requests."
> > > >
> > > > I don't think it it necessary. It is implied that if a pipeline
> > > > handler does not support changing the digital gain it should not
> > > > expose it a one of the Camera's controls.
> > > >
> > > > Likewise, if it is something that applications should be informed of,
> > > > it will be reported via metadata.
> > > >
> > > > I think we're good to go, except for the point that we've left
> > > > floating about having this a single value or a per-channel value.
> > > >
> > > > I'm trying to get a feeling how this would be reported by your ISP. I
> > > > see in example you have two per-channel values for the ColourGains
> > > > control. Is this anyway related ?
> > > >
> > > > > Any other thoughts?
> > > > >
> > > > > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham wrote:
> > > > > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > > > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > > > > >>> This control reports the global digital gain applied by the pipeline
> > > > > > >>> as a whole, after capturing a raw image from the sensor.
> > > > > > >>>
> > > > > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > > > > >>> ---
> > > > > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > > > > >>>  1 file changed, 11 insertions(+)
> > > > > > >>>
> > > > > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > > > > >>> index c8874fa9..e6362c74 100644
> > > > > > >>> --- a/src/libcamera/control_ids.yaml
> > > > > > >>> +++ b/src/libcamera/control_ids.yaml
> > > > > > >>> @@ -530,4 +530,15 @@ controls:
> > > > > > >>>          This control is only present when the pipeline supports scaling. Its
> > > > > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > > > > >>>          property, and the two can be used to implement digital zoom.
> > > > > > >>> +
> > > > > > >>> +  - DigitalGain:
> > > > > > >>> +      type: float
> > > > > > >>> +      description: |
> > > > > > >>> +        Global digital gain value applied to the image during all the
> > > > > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > > > > >>> +        images, therefore, will not include this gain, but the final images
> > > > > > >>> +        output by the imaging pipeline as a whole will include it.
> > > > > > >>> +
> > > > > > >>> +        This control is intended to report the value used by the image
> > > > > > >>> +        processing pipeline.
> > > > > > >>
> > > > > > >>
> > > > > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > > > > >> pipeline handlers to set this to the appropriate value for each stream
> > > > > > >> when it completes. The fact that this value would not be applicable to a
> > > > > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > > > > >> style value.
> > > > > > >>
> > > > > > >>
> > > > > > >> I'd hope this could be handled by a common helper in that instance so it
> > > > > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > > > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > > > > >> will be a core issue anyway.
> > > > > > >>
> > > > > > >>
> > > > > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > > > > >> determine that someone needs to set it.
> > > > > > >>
> > > > > > >> We could introduce a control property between type: and description:
> > > > > > >>   read-only: true
> > > > > > >
> > > > > > > Isn't a read-only control just a metadata ?
> > > > > > >
> > > > > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > > > > the control value from applications not reporting it in the list of
> > > > > > > supported Camera's controls, but only report it as part of a completed
> > > > > > > request's metadata ?
> > > > > >
> > > > > > Ah, yes of course - because if the control is not listed as supported it
> > > > > > won't be there to set in the first place! I forgot about that.
> > > > > >
> > > > > > So - indeed, no requirement to mark anything as read-only. That will be
> > > > > > implicit.
> > > > > >
> > > > > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > > > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > > > > >> that brings it's own questions )
> > > > > > >>
> > > > > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > > > > >>
> > > > > > >>>  ...
David Plowman Nov. 26, 2020, 7:04 p.m. UTC | #18 
Hi Laurent

Thanks for sending me this discussion, I agree it's an important
topic. Perhaps I can add a few rambling thoughts here and there, and
also try to answer your questions. Obviously my answers are rather
influenced by the Broadcom pipeline, and also the logical Raspberry Pi
view that we put on top of it!

On Thu, 26 Nov 2020 at 12:42, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi David,
>
> On Tue, Nov 24, 2020 at 12:40:38PM +0000, David Plowman wrote:
> > On Tue, 24 Nov 2020 at 11:28, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
> > > > Hi Jacopo
> > > >
> > > > You're right, there's a relationship there. ColourGains obviously
> > > > gives you the red and blue gains determined by the AWB usually. You
> > > > might get the values 1.6 and 2.0 (for red and blue)
> > > >
> > > > In our case, if we report a single "global gain" value you can kind of
> > > > imagine it as the green gain, where the colour gains were normalised
> > > > for a green gain of 1. So if the global gain was 1.25, then the actual
> > > > RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
> > > > 1.25, 2.5).
> > >
> > > That's a really helpful explanation for me, thanks
> > >
> > > > In the per-channel case I guess you'd be reporting these 3 numbers
> > > > directly. For me this duplicates information that's already in the
> > > > ColourGains, and it seems to muddle things up a bit. Imagine you had a
> > > > pipeline that lets you set a global gain - you'd have to query the
> > > > current white balance and work out all three numbers and set them. But
> > > > then you've set the white balance as well. Or maybe we do something
> > > > special so that you haven't? You see why it confuses me! So on balance
> > > > I'm with the single value approach, though I could live either way.
> > >
> > > I see. With the above explanation I really see why a single global
> > > value is probably enough.
> > >
> > > My question is now: are the above notions (blue/red gains normalized
> > > on a green value of 1, how global gain is used to obtain per-channel
> > > gains etc) standard knowledge I'm lacking, or:
> > >
> > > 1) It's worth to describe them in the control documentation as they're
> > > "standard" and won't change per-pipeline
> > > 2) They might differe per-pipeline and they need to be
> > > described in the pipeline model documentation ?
> > > 3) It is assumed the reader knows she's dealing with
> >
> > Difficult. I can't really see too many other ways of defining it, but
> > you know, pipelines all have their nuances. You probably can't
> > guarantee that what I described is completely "standard".
>
> This is really what I'd like to address :-)
>
> Have you seen the "libcamera: camera: Document the camera and pipeline
> model" patch (which is now in the master branch) ? It's the very first
> step in standardizing a logical pipeline model that pipeline handlers
> need to confirm to.
>
> In a nutshell, the idea is that libcamera needs to standardize the
> behaviour of cameras as seen from applications in order to make
> applications portable. To do so, we define a logical pipeline model that
> describes the processing operations performed by the camera, from the
> pixel array to the captured image.
>
> Hardware platforms differ in the feature they support and how they
> implement them, so most operations in the pipeline model are optional.
> Furthermore, there's no requirement to have the hardware performing
> those operations in the same order, or more generically in the same way,
> as the logical model mandates, as long as the visible effect from an
> application point of view is the same. Pipeline handlers are responsible
> for exposing the standard logical model and mapping it to device
> features.
>
> I expect that not all devices will be able to expose the same pipeline
> model, so we will need to support multiple options, with a way for the
> pipeline handlers to report which options apply to the cameras they
> handle. This can be reported through properties or through other means.
> We already support this, albeit implicitly: pipeline handlers that don't
> support some of the processing operations simply don't expose the
> corresponding controls. I expect we will also need properties to report
> the order of operations, when different orders lead to different results
> and all need to be supported. This should however remain the exception
> rather than the rule.
>
> I would like to expand the pipeline model documentation to include
> colour processing, and I think digital gain really fits here. We can
> still apply your patch (or the next version of it) before finalizing
> documentation of the colour processing in the pipeline model, but
> controls will then likely change soon after, which would require
> adapting your applications. It may end up causing more pain than gain.
>
> As you have more experience than me in this area, I wonder if you could
> help reviewing an initial proposal ? I envision the following
> sensitivity and colour-related operations, in order.
>
> - Total gain in the sensor, made of analog and/or digital gain. This
>   applies to all images, RAW and processed, and to all channels. If
>   auto-exposure is enabled, the control value is ignored. The actual
>   value is always reported in metadata.

I agree that we obviously need to know the analogue gain applied by
the sensor. Optionally there might be digital gain in the sensor too.
In many respects I'd quite like to see controls like this:

SensorGain - this is the combined gain applied by the sensor, analogue
and digital (if any).
SensorDigitalGain - this is optional and can be used if the sensor
applies any digital gain.

The reason for this is that applications can simply look for the
SensorGain and ignore anything else. Mostly they won't care if the
gain was analogue or digital. I'd certainly not want application code
to be forced to go checking for SensorDigitalGain when it won't
usually be there. Even when a sensor has applied digital gain, I think
that reporting the SensorDigitalGain information, while helpful,
should be optional. (To be honest I've never seen sensor digital gain
used.)

I would just add that, when AGC is enabled, setting the gain still
makes sense. You still need the AGC (well, AEC/AGC) to control the
shutter speed to give you those fixed ISO captures. Similarly, there's
no reason not to let an application fix the shutter speed and let the
AGC vary the gain.

>
>   Questions:
>
>    - Should we mandate that pipeline handlers and IPAs prioritize analog
>      gain before applying digital gain ?

I can't really see any reason to mandate this. It would be normal, I
agree, and it would probably be helpful to see it reported in the
metadata if digital gain has been used, but I don't really see a need
to force any particular behaviour.

>
>    - Can there be use cases for per-channel sensor-side gains ? In most
>      cases I expect the white balance to be applied in the ISP, but will
>      that always be the case ? What if auto-white-balance is disabled,
>      and the user sets manual per-channel gains, could there be a reason
>      to apply them in the sensor ?

Again, I've never seen sensor-side per channel gains myself, though
you'd be brave to assert that no one will ever use them. I don't see
AWB being disabled as a reason to use them. If you want to fix the
colour gains, there's no reason not to do it in the ISP.

However, it seems reasonable to me to leave it up to the pipeline
handler and its IPAs. If someone wants to set fixed colour gains
(effectively stop the AWB), and the pipeline handler wants to do it by
setting them in the sensor, good luck to them!

>
> - Digital gain on the ISP side (a.k.a. "post-RAW sensitivity boost" in
>   Android). This applies to processed images only, and to all channels.
>   If auto-exposure is enabled, the control value is ignored. The actual
>   value is always reported in metadata.
>
>   Questions:
>
>   - Should this be renamed ? "Digital gain" can be confused with the
>     digital gain in the sensor. A name that captures the fact that the
>     gain is applied on processed images only may be better (I don't like
>     the Android name too much, but it handles this issue).

"Post-RAW sensitivity boost" sounds execrable. Just my opinion,
though! I'd be happy with DigitalGain (on its own) being the gain in
the ISP, and SensorDigitalGain (if present) being the digital gain in
the sensor, but I know opinions will vary! IspDigitalGain? IspGain?
PipelineDigitalGain? PipelineGain?

>
> - Per-channel gains. This is currently handled as red and blue gains,
>   with the green gains being hardcoded to 1.0.
>
>   Questions:
>
>   - Should we change this ? I see two potential issues:
>
>     - Not all systems may use a Bayer colour filter array, so other
>       gains may be needed (I'm thinking about RGBW patterns for
>       instance, or any other from
>       https://en.wikipedia.org/wiki/Color_filter_array).

So I think red and blue gains alone are OK, even with something like
an RGBW filter. Finding white balance is a problem of finding a single
2D point in a plane, giving you (for example) red and blue gains. With
an RGBW filter, I'd expect the AWB calibration process would tell you
what to do with the W pixels once you've been told where in this space
you are.

I'm assuming other primaries (e.g. CMYK) or multi-spectral images are
out of scope!

>
>     - Hardcoding the green gains to 1.0 means that we will have an
>       "average" gain different than 1.0 in most cases. This will
>       effectively change the sensitivity of the camera, and should be
>       taken into account to compute the ISO value. Applications could do
>       so, but I wonder if we shouldn't mandate that the "average" gain
>       remains 1.0, with the "sensitivity boost" being handled by the
>       digital gain control only. How to compute the "average" gain is an
>       interesting problem here, as I expect it will need to take a full
>       colour model into account.

My experience has been as follows. The sensor manufacturer will tell
you that an image with analogue gain of 1 corresponds to an ISO of
(for example) 40. The OEM will then want you to white balance this
image properly and then for it to come out of the system with an ISO
of 40. Yet the RGB colour gains you have applied might actually have
been (1.5, 1.0, 2.0). So perhaps the green gain is really the thing
that corresponds to a "global gain", it's certainly the one with most
effect.

Note further that you can *never* apply any gains less than 1. If you
do, any saturated pixels will become unsaturated, so if you applied
RGB gains like (0.8, 1.0, 1.6) all your bright whites would go cyan.
The upshot is that you have to apply (1.0, 1.25, 2.0) instead (scale
everything up by 1 / 0.8 = 1.25). So in this case, what is the "global
gain"? Is it 1.25? Does that mean your ISO (which you might have
thought was 40) is now 1.25*40 = 50? Maybe. For me, this is probably
OK if you don't let people set the global gain.

Buf if you do, I think there are further problems. What happens if
your user says "I don't want any global gain, so I'll set it to 1". Do
you let the whites go cyan? Or force it to be 1.25 instead so that all
values between 1 and 1.25 have no effect? Or maybe you always include
an extra gain of 1 / 0.8 (in this case), so that we can still call the
good values (1.0, 1.25, 2.0) a "global gain of 1"? Tricky questions.

I end up in a place, therefore, where I feel you kind of have to let
pipelines do what they want. I think we can still maintain the
following:

* Handling the two colour gains (normalised to a green gain of 1) seems fine.
* You should be able to query and set the colour gains (effectively,
the white balance).
* You should ideally be able to query the "global gain". It gives you
some idea of the "effective gain" (in some vague sense) applied to all
pixels. You can use it to scale your ISO estimates, for example.
* If a pipeline wants to let you set the global gain, there's a bit of
a question as to what it really means!

>
> - Demosaicing. This shouldn't apply any gain.

Agree.

>
> - RGB-to-RGB colour transformation matrix.
>
>   Questions:
>
>   - Similarly to the per-channel gains, should we require that this
>     matrix applies no gain (i.e. the sum of elements in a line should be
>     1.0) ?

Agree. Even if a pipeline actually mixes its gains and colour matrix
together, there's no reason not to present them as separate things
externally.

>
> - RGB-to-YUV colour encoding matrix.
>
>   Questions:
>
>   - Similarly to the RGB-to-RGB matrix, should we forbid gains ?

I think so.

>
> Is there any other colour processing operation I have missed ?

Some pipelines have relatively sophisticated lookup tables for
fine-tuning colours, but I don't think those concern anything we've
discussed here.

I think that's everything. Sorry if it's a bit long in places!

David

>
> > A slightly more qualitative definition seems OK to me - the amount of
> > linear gain applied by the pipeline to all pixels (in addition to the
> > colour gains). Particular pipelines might feel they need to document
> > it more carefully if there are any complications in how they deal with
> > it.
> >
> > > > On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > > > On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > > > > > Hi everyone
> > > > > >
> > > > > > Sounds like we're happy enough from the point of view of this thing
> > > > > > being read-only (for Raspberry Pi at least). Would anyone want any
> > > > > > changes to the wording? Perhaps the final sentence/paragraph might now
> > > > > > be better as
> > > > > >
> > > > > > "This control is present in a request's ControlList only if the
> > > > > > pipeline supports setting the value. Even when it cannot be set by an
> > > > > > application, the pipeline may still report the actual value used in
> > > > > > the metadata returned with completed requests."
> > > > >
> > > > > I don't think it it necessary. It is implied that if a pipeline
> > > > > handler does not support changing the digital gain it should not
> > > > > expose it a one of the Camera's controls.
> > > > >
> > > > > Likewise, if it is something that applications should be informed of,
> > > > > it will be reported via metadata.
> > > > >
> > > > > I think we're good to go, except for the point that we've left
> > > > > floating about having this a single value or a per-channel value.
> > > > >
> > > > > I'm trying to get a feeling how this would be reported by your ISP. I
> > > > > see in example you have two per-channel values for the ColourGains
> > > > > control. Is this anyway related ?
> > > > >
> > > > > > Any other thoughts?
> > > > > >
> > > > > > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham wrote:
> > > > > > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > > > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > > > > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > > > > > >>> This control reports the global digital gain applied by the pipeline
> > > > > > > >>> as a whole, after capturing a raw image from the sensor.
> > > > > > > >>>
> > > > > > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > > > > > >>> ---
> > > > > > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > > > > > >>>  1 file changed, 11 insertions(+)
> > > > > > > >>>
> > > > > > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > > > > > >>> index c8874fa9..e6362c74 100644
> > > > > > > >>> --- a/src/libcamera/control_ids.yaml
> > > > > > > >>> +++ b/src/libcamera/control_ids.yaml
> > > > > > > >>> @@ -530,4 +530,15 @@ controls:
> > > > > > > >>>          This control is only present when the pipeline supports scaling. Its
> > > > > > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > > > > > >>>          property, and the two can be used to implement digital zoom.
> > > > > > > >>> +
> > > > > > > >>> +  - DigitalGain:
> > > > > > > >>> +      type: float
> > > > > > > >>> +      description: |
> > > > > > > >>> +        Global digital gain value applied to the image during all the
> > > > > > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > > > > > >>> +        images, therefore, will not include this gain, but the final images
> > > > > > > >>> +        output by the imaging pipeline as a whole will include it.
> > > > > > > >>> +
> > > > > > > >>> +        This control is intended to report the value used by the image
> > > > > > > >>> +        processing pipeline.
> > > > > > > >>
> > > > > > > >>
> > > > > > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > > > > > >> pipeline handlers to set this to the appropriate value for each stream
> > > > > > > >> when it completes. The fact that this value would not be applicable to a
> > > > > > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > > > > > >> style value.
> > > > > > > >>
> > > > > > > >>
> > > > > > > >> I'd hope this could be handled by a common helper in that instance so it
> > > > > > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > > > > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > > > > > >> will be a core issue anyway.
> > > > > > > >>
> > > > > > > >>
> > > > > > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > > > > > >> determine that someone needs to set it.
> > > > > > > >>
> > > > > > > >> We could introduce a control property between type: and description:
> > > > > > > >>   read-only: true
> > > > > > > >
> > > > > > > > Isn't a read-only control just a metadata ?
> > > > > > > >
> > > > > > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > > > > > the control value from applications not reporting it in the list of
> > > > > > > > supported Camera's controls, but only report it as part of a completed
> > > > > > > > request's metadata ?
> > > > > > >
> > > > > > > Ah, yes of course - because if the control is not listed as supported it
> > > > > > > won't be there to set in the first place! I forgot about that.
> > > > > > >
> > > > > > > So - indeed, no requirement to mark anything as read-only. That will be
> > > > > > > implicit.
> > > > > > >
> > > > > > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > > > > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > > > > > >> that brings it's own questions )
> > > > > > > >>
> > > > > > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > > > > > >>
> > > > > > > >>>  ...
>
> --
> Regards,
>
> Laurent Pinchart
Laurent Pinchart Dec. 20, 2020, 1:37 a.m. UTC | #19 
Hi David,

On Thu, Nov 26, 2020 at 07:04:13PM +0000, David Plowman wrote:
> Hi Laurent
> 
> Thanks for sending me this discussion, I agree it's an important
> topic. Perhaps I can add a few rambling thoughts here and there, and
> also try to answer your questions. Obviously my answers are rather
> influenced by the Broadcom pipeline, and also the logical Raspberry Pi
> view that we put on top of it!

That's the added value, providing a view point from a real use case :-)

> On Thu, 26 Nov 2020 at 12:42, Laurent Pinchart wrote:
> > On Tue, Nov 24, 2020 at 12:40:38PM +0000, David Plowman wrote:
> > > On Tue, 24 Nov 2020 at 11:28, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > > On Tue, Nov 24, 2020 at 10:15:25AM +0000, David Plowman wrote:
> > > > > Hi Jacopo
> > > > >
> > > > > You're right, there's a relationship there. ColourGains obviously
> > > > > gives you the red and blue gains determined by the AWB usually. You
> > > > > might get the values 1.6 and 2.0 (for red and blue)
> > > > >
> > > > > In our case, if we report a single "global gain" value you can kind of
> > > > > imagine it as the green gain, where the colour gains were normalised
> > > > > for a green gain of 1. So if the global gain was 1.25, then the actual
> > > > > RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
> > > > > 1.25, 2.5).
> > > >
> > > > That's a really helpful explanation for me, thanks
> > > >
> > > > > In the per-channel case I guess you'd be reporting these 3 numbers
> > > > > directly. For me this duplicates information that's already in the
> > > > > ColourGains, and it seems to muddle things up a bit. Imagine you had a
> > > > > pipeline that lets you set a global gain - you'd have to query the
> > > > > current white balance and work out all three numbers and set them. But
> > > > > then you've set the white balance as well. Or maybe we do something
> > > > > special so that you haven't? You see why it confuses me! So on balance
> > > > > I'm with the single value approach, though I could live either way.
> > > >
> > > > I see. With the above explanation I really see why a single global
> > > > value is probably enough.
> > > >
> > > > My question is now: are the above notions (blue/red gains normalized
> > > > on a green value of 1, how global gain is used to obtain per-channel
> > > > gains etc) standard knowledge I'm lacking, or:
> > > >
> > > > 1) It's worth to describe them in the control documentation as they're
> > > > "standard" and won't change per-pipeline
> > > > 2) They might differe per-pipeline and they need to be
> > > > described in the pipeline model documentation ?
> > > > 3) It is assumed the reader knows she's dealing with
> > >
> > > Difficult. I can't really see too many other ways of defining it, but
> > > you know, pipelines all have their nuances. You probably can't
> > > guarantee that what I described is completely "standard".
> >
> > This is really what I'd like to address :-)
> >
> > Have you seen the "libcamera: camera: Document the camera and pipeline
> > model" patch (which is now in the master branch) ? It's the very first
> > step in standardizing a logical pipeline model that pipeline handlers
> > need to confirm to.
> >
> > In a nutshell, the idea is that libcamera needs to standardize the
> > behaviour of cameras as seen from applications in order to make
> > applications portable. To do so, we define a logical pipeline model that
> > describes the processing operations performed by the camera, from the
> > pixel array to the captured image.
> >
> > Hardware platforms differ in the feature they support and how they
> > implement them, so most operations in the pipeline model are optional.
> > Furthermore, there's no requirement to have the hardware performing
> > those operations in the same order, or more generically in the same way,
> > as the logical model mandates, as long as the visible effect from an
> > application point of view is the same. Pipeline handlers are responsible
> > for exposing the standard logical model and mapping it to device
> > features.
> >
> > I expect that not all devices will be able to expose the same pipeline
> > model, so we will need to support multiple options, with a way for the
> > pipeline handlers to report which options apply to the cameras they
> > handle. This can be reported through properties or through other means.
> > We already support this, albeit implicitly: pipeline handlers that don't
> > support some of the processing operations simply don't expose the
> > corresponding controls. I expect we will also need properties to report
> > the order of operations, when different orders lead to different results
> > and all need to be supported. This should however remain the exception
> > rather than the rule.
> >
> > I would like to expand the pipeline model documentation to include
> > colour processing, and I think digital gain really fits here. We can
> > still apply your patch (or the next version of it) before finalizing
> > documentation of the colour processing in the pipeline model, but
> > controls will then likely change soon after, which would require
> > adapting your applications. It may end up causing more pain than gain.
> >
> > As you have more experience than me in this area, I wonder if you could
> > help reviewing an initial proposal ? I envision the following
> > sensitivity and colour-related operations, in order.
> >
> > - Total gain in the sensor, made of analog and/or digital gain. This
> >   applies to all images, RAW and processed, and to all channels. If
> >   auto-exposure is enabled, the control value is ignored. The actual
> >   value is always reported in metadata.
> 
> I agree that we obviously need to know the analogue gain applied by
> the sensor. Optionally there might be digital gain in the sensor too.
> In many respects I'd quite like to see controls like this:
> 
> SensorGain - this is the combined gain applied by the sensor, analogue
> and digital (if any).
> SensorDigitalGain - this is optional and can be used if the sensor
> applies any digital gain.
> 
> The reason for this is that applications can simply look for the
> SensorGain and ignore anything else. Mostly they won't care if the
> gain was analogue or digital. I'd certainly not want application code
> to be forced to go checking for SensorDigitalGain when it won't
> usually be there. Even when a sensor has applied digital gain, I think
> that reporting the SensorDigitalGain information, while helpful,
> should be optional. (To be honest I've never seen sensor digital gain
> used.)

Sounds like a good idea to me.

> I would just add that, when AGC is enabled, setting the gain still
> makes sense. You still need the AGC (well, AEC/AGC) to control the
> shutter speed to give you those fixed ISO captures. Similarly, there's
> no reason not to let an application fix the shutter speed and let the
> AGC vary the gain.

Fully agreed, semi-manual modes are important to support.

On a side note, would you happen to have any recommendation for any good
reading material covering the concept of ISO speed and exposure index ?

> >   Questions:
> >
> >    - Should we mandate that pipeline handlers and IPAs prioritize analog
> >      gain before applying digital gain ?
> 
> I can't really see any reason to mandate this. It would be normal, I
> agree, and it would probably be helpful to see it reported in the
> metadata if digital gain has been used, but I don't really see a need
> to force any particular behaviour.

The reasons why I'm considering mandating a particular behaviour is to
give guidelines to both application developers and pipeline handler
developers. From a pipeline handler point of view, giving clear
guidelines would help ensuring a more consistent behaviour across
different platforms. From an application point of view, a more
consistent behaviour means better portability. Obviously there's a
balance to be found here, the more we mandate a particular behaviour,
the higher the risk a platform won't be able to support it. It would
also restrict innovation to some extent.

Maybe a good middleground would be to specify a recommended behaviour
for pipeline handlers, with an invitation to discuss any proposed
departure from that behaviour ?

> >    - Can there be use cases for per-channel sensor-side gains ? In most
> >      cases I expect the white balance to be applied in the ISP, but will
> >      that always be the case ? What if auto-white-balance is disabled,
> >      and the user sets manual per-channel gains, could there be a reason
> >      to apply them in the sensor ?
> 
> Again, I've never seen sensor-side per channel gains myself, though

They seem to be fairly common in camera sensors, but probably not
commonly used.

> you'd be brave to assert that no one will ever use them. I don't see
> AWB being disabled as a reason to use them. If you want to fix the
> colour gains, there's no reason not to do it in the ISP.

Colour gains in the ISP (especially when the ISP operates in memory to
memory mode) are much easier to synchronize, so that's what I would also
use. When AWB is disabled, synchronizing gains to a particular frame is
less of an issue, so that's why I thought setting them on the sensor
would be less of a problem in that case. But thinking about it, the user
could change the gains over time... And one could use staggered writes
to handle colour gains in the sensor the same way as the analog gain and
exposure time.

> However, it seems reasonable to me to leave it up to the pipeline
> handler and its IPAs. If someone wants to set fixed colour gains
> (effectively stop the AWB), and the pipeline handler wants to do it by
> setting them in the sensor, good luck to them!

:-)

> >
> > - Digital gain on the ISP side (a.k.a. "post-RAW sensitivity boost" in
> >   Android). This applies to processed images only, and to all channels.
> >   If auto-exposure is enabled, the control value is ignored. The actual
> >   value is always reported in metadata.
> >
> >   Questions:
> >
> >   - Should this be renamed ? "Digital gain" can be confused with the
> >     digital gain in the sensor. A name that captures the fact that the
> >     gain is applied on processed images only may be better (I don't like
> >     the Android name too much, but it handles this issue).
> 
> "Post-RAW sensitivity boost" sounds execrable. Just my opinion,

I fully agree, I don't like the name either.

> though! I'd be happy with DigitalGain (on its own) being the gain in
> the ISP, and SensorDigitalGain (if present) being the digital gain in
> the sensor, but I know opinions will vary! IspDigitalGain? IspGain?
> PipelineDigitalGain? PipelineGain?

I'll add naming to my todo list, to be handled as part of a big rename
execise when we'll stabilize the API. I think it's safe to say we won't
go for the Android name :-)

> > - Per-channel gains. This is currently handled as red and blue gains,
> >   with the green gains being hardcoded to 1.0.
> >
> >   Questions:
> >
> >   - Should we change this ? I see two potential issues:
> >
> >     - Not all systems may use a Bayer colour filter array, so other
> >       gains may be needed (I'm thinking about RGBW patterns for
> >       instance, or any other from
> >       https://en.wikipedia.org/wiki/Color_filter_array).
> 
> So I think red and blue gains alone are OK, even with something like
> an RGBW filter. Finding white balance is a problem of finding a single
> 2D point in a plane, giving you (for example) red and blue gains. With
> an RGBW filter, I'd expect the AWB calibration process would tell you
> what to do with the W pixels once you've been told where in this space
> you are.
> 
> I'm assuming other primaries (e.g. CMYK) or multi-spectral images are
> out of scope!

For now :-)

> >     - Hardcoding the green gains to 1.0 means that we will have an
> >       "average" gain different than 1.0 in most cases. This will
> >       effectively change the sensitivity of the camera, and should be
> >       taken into account to compute the ISO value. Applications could do
> >       so, but I wonder if we shouldn't mandate that the "average" gain
> >       remains 1.0, with the "sensitivity boost" being handled by the
> >       digital gain control only. How to compute the "average" gain is an
> >       interesting problem here, as I expect it will need to take a full
> >       colour model into account.
> 
> My experience has been as follows. The sensor manufacturer will tell
> you that an image with analogue gain of 1 corresponds to an ISO of
> (for example) 40. The OEM will then want you to white balance this
> image properly and then for it to come out of the system with an ISO
> of 40. Yet the RGB colour gains you have applied might actually have
> been (1.5, 1.0, 2.0). So perhaps the green gain is really the thing
> that corresponds to a "global gain", it's certainly the one with most
> effect.
> 
> Note further that you can *never* apply any gains less than 1. If you
> do, any saturated pixels will become unsaturated, so if you applied
> RGB gains like (0.8, 1.0, 1.6) all your bright whites would go cyan.
> The upshot is that you have to apply (1.0, 1.25, 2.0) instead (scale
> everything up by 1 / 0.8 = 1.25). So in this case, what is the "global
> gain"? Is it 1.25? Does that mean your ISO (which you might have
> thought was 40) is now 1.25*40 = 50? Maybe. For me, this is probably
> OK if you don't let people set the global gain.
> 
> Buf if you do, I think there are further problems. What happens if
> your user says "I don't want any global gain, so I'll set it to 1". Do
> you let the whites go cyan? Or force it to be 1.25 instead so that all
> values between 1 and 1.25 have no effect? Or maybe you always include
> an extra gain of 1 / 0.8 (in this case), so that we can still call the
> good values (1.0, 1.25, 2.0) a "global gain of 1"? Tricky questions.
> 
> I end up in a place, therefore, where I feel you kind of have to let
> pipelines do what they want. I think we can still maintain the
> following:
> 
> * Handling the two colour gains (normalised to a green gain of 1) seems fine.
> * You should be able to query and set the colour gains (effectively,
> the white balance).
> * You should ideally be able to query the "global gain". It gives you
> some idea of the "effective gain" (in some vague sense) applied to all
> pixels. You can use it to scale your ISO estimates, for example.
> * If a pipeline wants to let you set the global gain, there's a bit of
> a question as to what it really means!

Thanks for your input. This is a bit tricky, especially the "does it
mean the ISO is 50" question. This will probably require more thoughts.

> > - Demosaicing. This shouldn't apply any gain.
> 
> Agree.
> 
> > - RGB-to-RGB colour transformation matrix.
> >
> >   Questions:
> >
> >   - Similarly to the per-channel gains, should we require that this
> >     matrix applies no gain (i.e. the sum of elements in a line should be
> >     1.0) ?
> 
> Agree. Even if a pipeline actually mixes its gains and colour matrix
> together, there's no reason not to present them as separate things
> externally.

Exactly. I think the pipeline model should preclude gains from being
applied in the RGB-to-RGB matrix, but mapping gains from the pipeline
model to the hardware is the responsibility of the pipeline handler.

> > - RGB-to-YUV colour encoding matrix.
> >
> >   Questions:
> >
> >   - Similarly to the RGB-to-RGB matrix, should we forbid gains ?
> 
> I think so.
> 
> > Is there any other colour processing operation I have missed ?
> 
> Some pipelines have relatively sophisticated lookup tables for
> fine-tuning colours, but I don't think those concern anything we've
> discussed here.

Yes, beside per-component gamma tables, there are also cubic lookup
tables. In theory you could apply any type of gain there, but I don't
think they should be included in the gains discussion.

> I think that's everything. Sorry if it's a bit long in places!

Not at all! It's all great input, than you very much.

> > > A slightly more qualitative definition seems OK to me - the amount of
> > > linear gain applied by the pipeline to all pixels (in addition to the
> > > colour gains). Particular pipelines might feel they need to document
> > > it more carefully if there are any complications in how they deal with
> > > it.
> > >
> > > > > On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo@jmondi.org> wrote:
> > > > > > On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > > > > > > Hi everyone
> > > > > > >
> > > > > > > Sounds like we're happy enough from the point of view of this thing
> > > > > > > being read-only (for Raspberry Pi at least). Would anyone want any
> > > > > > > changes to the wording? Perhaps the final sentence/paragraph might now
> > > > > > > be better as
> > > > > > >
> > > > > > > "This control is present in a request's ControlList only if the
> > > > > > > pipeline supports setting the value. Even when it cannot be set by an
> > > > > > > application, the pipeline may still report the actual value used in
> > > > > > > the metadata returned with completed requests."
> > > > > >
> > > > > > I don't think it it necessary. It is implied that if a pipeline
> > > > > > handler does not support changing the digital gain it should not
> > > > > > expose it a one of the Camera's controls.
> > > > > >
> > > > > > Likewise, if it is something that applications should be informed of,
> > > > > > it will be reported via metadata.
> > > > > >
> > > > > > I think we're good to go, except for the point that we've left
> > > > > > floating about having this a single value or a per-channel value.
> > > > > >
> > > > > > I'm trying to get a feeling how this would be reported by your ISP. I
> > > > > > see in example you have two per-channel values for the ColourGains
> > > > > > control. Is this anyway related ?
> > > > > >
> > > > > > > Any other thoughts?
> > > > > > >
> > > > > > > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham wrote:
> > > > > > > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > > > > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > > > > > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > > > > > > >>> This control reports the global digital gain applied by the pipeline
> > > > > > > > >>> as a whole, after capturing a raw image from the sensor.
> > > > > > > > >>>
> > > > > > > > >>> Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
> > > > > > > > >>> ---
> > > > > > > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > > > > > > >>>  1 file changed, 11 insertions(+)
> > > > > > > > >>>
> > > > > > > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > > > > > > >>> index c8874fa9..e6362c74 100644
> > > > > > > > >>> --- a/src/libcamera/control_ids.yaml
> > > > > > > > >>> +++ b/src/libcamera/control_ids.yaml
> > > > > > > > >>> @@ -530,4 +530,15 @@ controls:
> > > > > > > > >>>          This control is only present when the pipeline supports scaling. Its
> > > > > > > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > > > > > > >>>          property, and the two can be used to implement digital zoom.
> > > > > > > > >>> +
> > > > > > > > >>> +  - DigitalGain:
> > > > > > > > >>> +      type: float
> > > > > > > > >>> +      description: |
> > > > > > > > >>> +        Global digital gain value applied to the image during all the
> > > > > > > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > > > > > > >>> +        images, therefore, will not include this gain, but the final images
> > > > > > > > >>> +        output by the imaging pipeline as a whole will include it.
> > > > > > > > >>> +
> > > > > > > > >>> +        This control is intended to report the value used by the image
> > > > > > > > >>> +        processing pipeline.
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > > > > > > >> pipeline handlers to set this to the appropriate value for each stream
> > > > > > > > >> when it completes. The fact that this value would not be applicable to a
> > > > > > > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > > > > > > >> style value.
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >> I'd hope this could be handled by a common helper in that instance so it
> > > > > > > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > > > > > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > > > > > > >> will be a core issue anyway.
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > > > > > > >> determine that someone needs to set it.
> > > > > > > > >>
> > > > > > > > >> We could introduce a control property between type: and description:
> > > > > > > > >>   read-only: true
> > > > > > > > >
> > > > > > > > > Isn't a read-only control just a metadata ?
> > > > > > > > >
> > > > > > > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > > > > > > the control value from applications not reporting it in the list of
> > > > > > > > > supported Camera's controls, but only report it as part of a completed
> > > > > > > > > request's metadata ?
> > > > > > > >
> > > > > > > > Ah, yes of course - because if the control is not listed as supported it
> > > > > > > > won't be there to set in the first place! I forgot about that.
> > > > > > > >
> > > > > > > > So - indeed, no requirement to mark anything as read-only. That will be
> > > > > > > > implicit.
> > > > > > > >
> > > > > > > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > > > > > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > > > > > > >> that brings it's own questions )
> > > > > > > > >>
> > > > > > > > >> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> > > > > > > > >>
> > > > > > > > >>>  ...

Patch
diff mbox series 

diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
index c8874fa9..e6362c74 100644
--- a/src/libcamera/control_ids.yaml
+++ b/src/libcamera/control_ids.yaml
@@ -530,4 +530,15 @@  controls:
         This control is only present when the pipeline supports scaling. Its
         maximum valid value is given by the properties::ScalerCropMaximum
         property, and the two can be used to implement digital zoom.
+
+  - DigitalGain:
+      type: float
+      description: |
+        Global digital gain value applied to the image during all the
+        processing steps after capturing the image from the sensor. Any raw
+        images, therefore, will not include this gain, but the final images
+        output by the imaging pipeline as a whole will include it.
+
+        This control is intended to report the value used by the image
+        processing pipeline.
 ...