[libcamera-devel,v4,4/7] libcamera: colorspace: Rectify the ColorSpace::Srgb preset

17253 diff mbox series

Rectify the ColorSpace::Srgb to denote that it does not use
any Y'Cbcr encoding and uses full range.

The kernel on the other hand, recommends to use Rec601 as the encoding
for V4L2_COLORSPACE_SRGB. It is not very explicit but it can be
inferred that the kernel assumes V4L2_COLORSPACE_SRGB is a YUV-encoded
one. However, when the data is in RGB, no encoding is required (and
this is denoted by YcbcrEncoding::None in libcamera).

Hence, to be clear on the libcamera colorspace API, rectify the
ColorSpace::Srgb preset to use YcbcrEncoding::None and full range.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
---
 src/libcamera/color_space.cpp | 18 ++++++++++--------
 src/libcamera/v4l2_device.cpp |  7 +++++--
 2 files changed, 15 insertions(+), 10 deletions(-)

On Tue, Aug 30, 2022 at 01:17:22PM +0530, Umang Jain via libcamera-devel wrote:
> Rectify the ColorSpace::Srgb to denote that it does not use
> any Y'Cbcr encoding and uses full range.
> 
> The kernel on the other hand, recommends to use Rec601 as the encoding
> for V4L2_COLORSPACE_SRGB. It is not very explicit but it can be
> inferred that the kernel assumes V4L2_COLORSPACE_SRGB is a YUV-encoded
> one. However, when the data is in RGB, no encoding is required (and
> this is denoted by YcbcrEncoding::None in libcamera).
> 
> Hence, to be clear on the libcamera colorspace API, rectify the
> ColorSpace::Srgb preset to use YcbcrEncoding::None and full range.
> 
> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>

> ---
>  src/libcamera/color_space.cpp | 18 ++++++++++--------
>  src/libcamera/v4l2_device.cpp |  7 +++++--
>  2 files changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/src/libcamera/color_space.cpp b/src/libcamera/color_space.cpp
> index 944d0e98..ec34620a 100644
> --- a/src/libcamera/color_space.cpp
> +++ b/src/libcamera/color_space.cpp
> @@ -49,8 +49,13 @@ namespace libcamera {
>   * - <a href="https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/colorspaces-details.html#col-bt2020">Rec.2020</a>
>   *
>   * Note that there is no guarantee of a 1:1 mapping between color space names
> - * and definitions in libcamera and V4L2. A notable difference is that the sYCC
> - * libcamera color space is called JPEG in V4L2 due to historical reasons.
> + * and definitions in libcamera and V4L2. Two notable differences are
> + *
> + * - The sRGB libcamera color space is defined for RGB formats only with no
> + *   Y'CbCr encoding and a full quantization range, while the V4L2 SRGB color
> + *   space has a Y'CbCr encoding and a limited quantization range.
> + * - The sYCC libcamera color space is called JPEG in V4L2 due to historical
> + *   reasons.
>   *
>   * \todo Define the color space fully in the libcamera API to avoid referencing
>   * V4L2
> @@ -138,16 +143,13 @@ const ColorSpace ColorSpace::Raw = {
>  };
>  
>  /**
> - * \brief A constant representing the sRGB color space
> - *
> - * This is identical to the sYCC color space except that the Y'CbCr
> - * range is limited rather than full.
> + * \brief A constant representing the sRGB color space (RGB formats only)
>   */
>  const ColorSpace ColorSpace::Srgb = {
>  	Primaries::Rec709,
>  	TransferFunction::Srgb,
> -	YcbcrEncoding::Rec601,
> -	Range::Limited
> +	YcbcrEncoding::None,
> +	Range::Full
>  };
>  
>  /**
> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> index 301620f8..1d899657 100644
> --- a/src/libcamera/v4l2_device.cpp
> +++ b/src/libcamera/v4l2_device.cpp
> @@ -746,7 +746,11 @@ void V4L2Device::eventAvailable()
>  
>  static const std::map<uint32_t, ColorSpace> v4l2ToColorSpace = {
>  	{ V4L2_COLORSPACE_RAW, ColorSpace::Raw },
> -	{ V4L2_COLORSPACE_SRGB, ColorSpace::Srgb },
> +	{ V4L2_COLORSPACE_SRGB, {
> +		ColorSpace::Primaries::Rec709,
> +		ColorSpace::TransferFunction::Srgb,
> +		ColorSpace::YcbcrEncoding::Rec601,
> +		ColorSpace::Range::Limited } },
>  	{ V4L2_COLORSPACE_JPEG, ColorSpace::Sycc },
>  	{ V4L2_COLORSPACE_SMPTE170M, ColorSpace::Smpte170m },
>  	{ V4L2_COLORSPACE_REC709, ColorSpace::Rec709 },
> @@ -772,7 +776,6 @@ static const std::map<uint32_t, ColorSpace::Range> v4l2ToRange = {
>  
>  static const std::vector<std::pair<ColorSpace, v4l2_colorspace>> colorSpaceToV4l2 = {
>  	{ ColorSpace::Raw, V4L2_COLORSPACE_RAW },
> -	{ ColorSpace::Srgb, V4L2_COLORSPACE_SRGB },
>  	{ ColorSpace::Sycc, V4L2_COLORSPACE_JPEG },
>  	{ ColorSpace::Smpte170m, V4L2_COLORSPACE_SMPTE170M },
>  	{ ColorSpace::Rec709, V4L2_COLORSPACE_REC709 },
> -- 
> 2.37.2
>