[libcamera-devel,v4,1/2] ipa: Create a camera sensor helper class

12601 diff mbox series

Setting analogue gain for a specific sensor is not a straightforward
operation, as one needs to know how the gain is calculated for it.

This commit introduces a new camera sensor helper in libipa which aims
to solve this specific issue.
It is based on the MIPI alliance Specification for Camera Command Set
and implements, for now, only the analogue "Global gain" mode.

Is makes it possible to only have 4 parameters to store per sensor, and
the gain calculation is then done identically for all of them. This
commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
ov5693.

Adding a new sensor is pretty straightforward as one only needs to
implement the sub-class for it and register that class to the
CameraSensorHelperFactory.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
---
 src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
 src/ipa/libipa/camera_sensor_helper.h   |  88 +++++++
 src/ipa/libipa/meson.build              |   2 +
 3 files changed, 408 insertions(+)
 create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
 create mode 100644 src/ipa/libipa/camera_sensor_helper.h

Hello Jean-Michel,

On Tue, Jun 15, 2021 at 03:35:33PM +0200, Jean-Michel Hautbois wrote:
> Setting analogue gain for a specific sensor is not a straightforward
> operation, as one needs to know how the gain is calculated for it.
>
> This commit introduces a new camera sensor helper in libipa which aims
> to solve this specific issue.
> It is based on the MIPI alliance Specification for Camera Command Set
> and implements, for now, only the analogue "Global gain" mode.
>
> Is makes it possible to only have 4 parameters to store per sensor, and
> the gain calculation is then done identically for all of them. This
> commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
> ov5693.
>
> Adding a new sensor is pretty straightforward as one only needs to
> implement the sub-class for it and register that class to the
> CameraSensorHelperFactory.

Well, the commit message seems to suggest this will onle serve for
gain calculations, while my understanding is that it will support more
sensor-specific parameter calculations.

What about
- One paragraph that briefly explains that sensor specific
  computations are required

- One paragraph that says that initially only gain calculation is
  supported and how

- One last paragraph that says that helpers for the X,Y,Z sensors are
  created in this patch

>
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
> ---
>  src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>  src/ipa/libipa/camera_sensor_helper.h   |  88 +++++++
>  src/ipa/libipa/meson.build              |   2 +
>  3 files changed, 408 insertions(+)
>  create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
>  create mode 100644 src/ipa/libipa/camera_sensor_helper.h
>
> diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
> new file mode 100644
> index 00000000..cd996b2c
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -0,0 +1,318 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.cpp - Helper class providing camera information

Helper class that performs sensor-specific paramter computations

> + */
> +#include "camera_sensor_helper.h"
> +
> +#include <map>

is map used ?
I see std::unique_ptr<> and std::vector<> (also std::string but
<string> is included by the header file

> +
> +#include "libcamera/internal/log.h"
> +
> +/**
> + * \file camera_sensor_helper.h
> + * \brief Helper class for each sensor

I would repeat the above description

> + *
> + * Each camera sensor supported by libcamera may need specific information to
> + * be sent (analogue gain is sensor dependant for instance).

Computation of sensor configuration parameters is a sensor specific
operation. Each CameraHelper derived class computes the value of
configuration parameters, for example the analogue gain value, using
sensor-specific functions and constants.

What do you think ?

> + *
> + * Every subclass of CameraSensorHelper shall be registered with libipa using
> + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(CameraSensorHelper)
> +
> +namespace ipa {
> +
> +/**
> + * \class CameraSensorHelper
> + * \brief Compute sensor tuning parameters using sensor-specific constants

Base class for computing ...

> + *
> + * CameraSensorHelper instances are unique and sensor dependant.

CameraSensorHelper derived class instances are sensor specific. Each
supported sensor will have an associated base class defined.

> + */
> +
> +/**
> + * \brief Construct a CameraSensorHelper instance
> + *
> + * The CameraSensorHelper instances shall never be constructed manually, but always

CameraSensorHelper derived class instances...

> + * through the CameraSensorHelperFactory::create() method.
> + */
> +CameraSensorHelper::CameraSensorHelper()
> +{
> +}
> +
> +CameraSensorHelper::~CameraSensorHelper()
> +{
> +}
> +
> +/**
> + * CameraSensorHelper::GainCode(double gain)
> + * \brief Compute gain code from the analogue gain value

analogue gain absolute value
> + * \param[in] gain The real gain to pass
> + * \return the gain code to pass to V4l2
> + *
> + * This function aims to abstract the calculation of the gain letting the IPA
> + * use the real gain for its estimations.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + */
> +uint32_t CameraSensorHelper::GainCode(double gain) const

function names start with lowercase

> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +

Rouge \t

> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
> +}
> +
> +/**
> + * CameraSensorHelper::Gain
> + * \brief Compute the real gain from the V4l2 subdev control gain

s/real/absolute ? not sure...

control gain code ?

> + * \param[in] gainCode The V4l2 subdev control gain
> + * \return The real gain
> + *
> + * This function aims to abstract the calculation of the gain letting the IPA
> + * use the real gain for its estimations. It is the counterpart of the function
> + * CameraSensorHelper::getGainCode.

now called GainCode

> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + */
> +double CameraSensorHelper::Gain(uint32_t gainCode) const
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +
> +	return (analogueGainConstants_.m0 * gainCode + analogueGainConstants_.c0) /
> +	       (analogueGainConstants_.m1 * gainCode + analogueGainConstants_.c1);
> +}
> +
> +/**
> + * \enum CameraSensorHelper::AnalogueGainType
> + * \brief Specify the Gain mode supported by the sensor

.. the gain calculation modes as defined by the MIPI ...

> + *
> + * Describes the image sensor analogue Gain capabilities.

It's more about two different ways to calculate the gain value

> + * Two modes are possible, depending on the sensor: Global and Alternate.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainLinear
> + * \brief Sensor supports linear gain

Gain is computed using linear gain estimation ?
Or something along these line (what I mean is that this should
describe the gain calculation mode algorithm, not what the sensor
supports).

> + *
> + * The relationship between the integer Gain parameter and the resulting Gain
> + * multiplier is given by the following equation:
> + *
> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
> + *
> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> + * image-sensor-specific constants exposed by the sensor.

s/exposed by/of/

> + * These constants are static parameters, and for any given image sensor either
> + * m0 or m1 shall be zero.
> + *
> + * The full Gain equation therefore reduces to either:
> + *
> + * \f$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainExponential
> + * \brief Sensor supports exponential gain (introduced in CCS v1.1)

Same comment as above

> + *
> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also available.
> + * If the image sensor supports it, then the global analogue Gain can be controlled
> + * by linear and exponential gain formula:
> + *
> + * \f$gain = analogLinearGainGlobal * 2^{analogExponentialGainGlobal}\f$
> + * \todo not implemented in libipa
> + */
> +
> +/**
> + * \struct CameraSensorHelper::AnalogueGainConstants
> + * \brief Analogue gain constants used for gain calculation
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::type
> + * \brief Analogue gain coding type

"Analogue gain calculation mode" ?

So this should be of type enum AnalogueGainType not uint16 ?

> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m0
> + * \brief Constant used in the analogue Gain control coding/decoding

s/Gain control/Gain

Gain is spelled with capital G in many places, I guess it's
intentional then

> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c0
> + * \brief Constant used in the analogue Gain control coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m1
> + * \brief Constant used in the analogue Gain control coding/decoding
> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c1
> + * \brief Constant used in the analogue Gain control coding/decoding
> + */

same comment for these three

> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants_
> + * \brief The analogue gain parameters used for calculation
> + *
> + * The analogue gain is calculated through a formula, and its parameters are
> + * sensor specific. Use this variable to store the values at init time.
> + *
> + */
> +
> +/**
> + * \class CameraSensorHelperFactory
> + * \brief Registration of CameraSensorHelperFactory classes and creation of instances
> + *
> + * To facilitate discovery and instantiation of CameraSensorHelper classes, the
> + * CameraSensorHelperFactory class maintains a registry of camera sensor helper
> + * classes. Each CameraSensorHelper subclass shall register itself using the
> + * REGISTER_CAMERA_SENSOR_HELPER() macro, which will create a corresponding
> + * instance of a CameraSensorHelperFactory subclass and register it with the
> + * static list of factories.
> + */
> +
> +/**
> + * \brief Construct a camera sensor helper factory
> + * \param[in] name Name of the camera sensor helper class
> + *
> + * Creating an instance of the factory registers it with the global list of
> + * factories, accessible through the factories() function.
> + *
> + * The factory \a name is used for debug purpose and shall be unique.
> + */
> +CameraSensorHelperFactory::CameraSensorHelperFactory(const std::string name)
> +	: name_(name)
> +{
> +	registerType(this);
> +}
> +
> +/**
> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
> + *
> + * \return A unique pointer to a new instance of the CameraSensorHelper subclass
> + * corresponding to the factory
> + */
> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create(const std::string &name)
> +{
> +	std::vector<CameraSensorHelperFactory *> &factories =
> +		CameraSensorHelperFactory::factories();
> +
> +	for (CameraSensorHelperFactory *factory : factories) {
> +		if (name != factory->name_)
> +			continue;
> +
> +		CameraSensorHelper *helper = factory->createInstance();
> +		return std::unique_ptr<CameraSensorHelper>(helper);
> +	}

Empty line maybe ?

> +	return nullptr;
> +}
> +
> +/**
> + * \brief Add a camera sensor helper class to the registry
> + * \param[in] factory Factory to use to construct the camera sensor helper
> + *
> + * The caller is responsible to guarantee the uniqueness of the camera sensor helper
> + * name.
> + */
> +void CameraSensorHelperFactory::registerType(CameraSensorHelperFactory *factory)
> +{
> +	std::vector<CameraSensorHelperFactory *> &factories = CameraSensorHelperFactory::factories();
> +
> +	factories.push_back(factory);
> +}
> +
> +/**
> + * \brief Retrieve the list of all camera sensor helper factories
> + *
> + * The static factories map is defined inside the function to ensures it gets
> + * initialized on first use, without any dependency on link order.
> + *
> + * \return The list of camera sensor helper factories
> + */
> +std::vector<CameraSensorHelperFactory *> &CameraSensorHelperFactory::factories()
> +{
> +	static std::vector<CameraSensorHelperFactory *> factories;
> +	return factories;
> +}
> +
> +/**
> + * CameraSensorHelperFactory::createInstance()
> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
> + *
> + * This virtual function is implemented by the REGISTER_CAMERA_SENSOR_HELPER()
> + * macro. It creates a camera sensor helper instance associated with the camera
> + * sensor model.
> + *
> + * \return A pointer to a newly constructed instance of the CameraSensorHelper
> + * subclass corresponding to the factory
> + */
> +
> +/**
> + * \def REGISTER_CAMERA_SENSOR_HELPER
> + * \brief Register a camera sensor helper with the camera sensor helper factory
> + * \param[in] name Sensor model name used to register the class
> + * \param[in] helper Class name of CameraSensorHelper derived class to register
> + *
> + * Register a CameraSensorHelper subclass with the factory and make it available to
> + * try and match devices.
> + */
> +
> +/**
> + * \class CameraSensorHelperImx219
> + * \brief Create and give helpers for the imx219 sensor
> + */
> +class CameraSensorHelperImx219 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperImx219()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> +
> +/**
> + * \class CameraSensorHelperOv5670
> + * \brief Create and give helpers for the ov5670 sensor
> + */
> +class CameraSensorHelperOv5670 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5670()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> +
> +/**
> + * \class CameraSensorHelperOv5693
> + * \brief Create and give helpers for the ov5693 sensor
> + */
> +class CameraSensorHelperOv5693 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5693()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */

Nice!

> diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
> new file mode 100644
> index 00000000..ea7558d3
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.h
> @@ -0,0 +1,88 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.h - Helper class providing camera information

To be algined with the .cpp file comment if you change it

> + */
> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +
> +#include <stdint.h>
> +
> +#include <string>

You need to include vector (I have a compilation error for this)
> +
> +#include <libcamera/class.h>
> +#include <libcamera/object.h>

object.h can be removed

> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +class CameraSensorHelper;

What's this for ?

> +
> +class CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelper();
> +	virtual ~CameraSensorHelper();

Can these be = default ?

> +
> +	uint32_t GainCode(double gain) const;
> +	double Gain(uint32_t gainCode) const;

Should these be virtual if a subclass need to override them ?

> +
> +protected:
> +	enum AnalogueGainType {
> +		AnalogueGainLinear = 0,
> +		AnalogueGainExponential = 2,

Does 0 and 2 come from the CCS specs ?

> +	};
> +
> +	struct AnalogueGainConstants {
> +		uint16_t type;
> +		int16_t m0;
> +		int16_t c0;
> +		int16_t m1;
> +		int16_t c1;
> +	};
> +
> +	AnalogueGainConstants analogueGainConstants_;
> +
> +private:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
> +};
> +
> +class CameraSensorHelperFactory
> +{
> +public:
> +	CameraSensorHelperFactory(const std::string name);
> +	virtual ~CameraSensorHelperFactory() = default;
> +
> +	static std::unique_ptr<CameraSensorHelper> create(const std::string &name);
> +
> +	static void registerType(CameraSensorHelperFactory *factory);
> +	static std::vector<CameraSensorHelperFactory *> &factories();
> +
> +private:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)
> +	virtual CameraSensorHelper *createInstance() = 0;
> +
> +	std::string name_;
> +};
> +
> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)               \
> +class helper##Factory final : public CameraSensorHelperFactory    \
> +{                                                                 \
> +public:                                                           \
> +	helper##Factory() : CameraSensorHelperFactory(name) {} \
> +								  \
> +private:                                                          \
> +	CameraSensorHelper *createInstance()                      \
> +	{                                                         \
> +		return new helper();                          \
> +	}                                                         \
> +};                                                                \
> +static helper##Factory global_##helper##Factory;
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> +
> +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
> diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
> index 038fc490..dc90542c 100644
> --- a/src/ipa/libipa/meson.build
> +++ b/src/ipa/libipa/meson.build
> @@ -2,11 +2,13 @@
>
>  libipa_headers = files([
>      'algorithm.h',
> +    'camera_sensor_helper.h',
>      'histogram.h'
>  ])
>
>  libipa_sources = files([
>      'algorithm.cpp',
> +    'camera_sensor_helper.cpp',
>      'histogram.cpp'
>  ])

Mostly minors, good job, almost there from my side :)
Bear with me a little more for the documentation comments, take
whatever you consider appropriate in.

Thanks
  j

>
> --
> 2.30.2
>

Hi Jacopo,

On 18/06/2021 12:15, Jacopo Mondi wrote:
> Hello Jean-Michel,
> 
> On Tue, Jun 15, 2021 at 03:35:33PM +0200, Jean-Michel Hautbois wrote:
>> Setting analogue gain for a specific sensor is not a straightforward
>> operation, as one needs to know how the gain is calculated for it.
>>
>> This commit introduces a new camera sensor helper in libipa which aims
>> to solve this specific issue.
>> It is based on the MIPI alliance Specification for Camera Command Set
>> and implements, for now, only the analogue "Global gain" mode.
>>
>> Is makes it possible to only have 4 parameters to store per sensor, and
>> the gain calculation is then done identically for all of them. This
>> commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
>> ov5693.
>>
>> Adding a new sensor is pretty straightforward as one only needs to
>> implement the sub-class for it and register that class to the
>> CameraSensorHelperFactory.
> 
> Well, the commit message seems to suggest this will onle serve for
> gain calculations, while my understanding is that it will support more
> sensor-specific parameter calculations.
> 
> What about
> - One paragraph that briefly explains that sensor specific
>   computations are required
> 
> - One paragraph that says that initially only gain calculation is
>   supported and how
> 
> - One last paragraph that says that helpers for the X,Y,Z sensors are
>   created in this patch
> 

Reworded as:
    ipa: Create a camera sensor helper class

    For various sensor operations, it may be needed to do sensor specific
    computations, like analogue gain or vertical blanking.

    This commit introduces a new camera sensor helper in libipa which aims
    to solve this specific issue.
    It is based on the MIPI alliance Specification for Camera Command Set
    and implements, for now, only the analogue "Global gain" mode.
    Setting analogue gain for a specific sensor is not a straightforward
    operation, as one needs to know how the gain is calculated for it.

    Three helpers are created in this patch: imx219, ov5670 and ov5693.

    Adding a new sensor is pretty straightforward as one only needs to
    implement the sub-class for it and register that class to the
    CameraSensorHelperFactory.

Please tel me if it is ok for you :-).


>>
>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
>> ---
>>  src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>>  src/ipa/libipa/camera_sensor_helper.h   |  88 +++++++
>>  src/ipa/libipa/meson.build              |   2 +
>>  3 files changed, 408 insertions(+)
>>  create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
>>  create mode 100644 src/ipa/libipa/camera_sensor_helper.h
>>
>> diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
>> new file mode 100644
>> index 00000000..cd996b2c
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
>> @@ -0,0 +1,318 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.cpp - Helper class providing camera information
> 
> Helper class that performs sensor-specific paramter computations
> 
>> + */
>> +#include "camera_sensor_helper.h"
>> +
>> +#include <map>
> 
> is map used ?
> I see std::unique_ptr<> and std::vector<> (also std::string but
> <string> is included by the header file
> 
>> +
>> +#include "libcamera/internal/log.h"
>> +
>> +/**
>> + * \file camera_sensor_helper.h
>> + * \brief Helper class for each sensor
> 
> I would repeat the above description
> 
>> + *
>> + * Each camera sensor supported by libcamera may need specific information to
>> + * be sent (analogue gain is sensor dependant for instance).
> 
> Computation of sensor configuration parameters is a sensor specific
> operation. Each CameraHelper derived class computes the value of
> configuration parameters, for example the analogue gain value, using
> sensor-specific functions and constants.
> 
> What do you think ?
> 
>> + *
>> + * Every subclass of CameraSensorHelper shall be registered with libipa using
>> + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
>> + */
>> +
>> +namespace libcamera {
>> +
>> +LOG_DEFINE_CATEGORY(CameraSensorHelper)
>> +
>> +namespace ipa {
>> +
>> +/**
>> + * \class CameraSensorHelper
>> + * \brief Compute sensor tuning parameters using sensor-specific constants
> 
> Base class for computing ...
> 
>> + *
>> + * CameraSensorHelper instances are unique and sensor dependant.
> 
> CameraSensorHelper derived class instances are sensor specific. Each
> supported sensor will have an associated base class defined.
> 
>> + */
>> +
>> +/**
>> + * \brief Construct a CameraSensorHelper instance
>> + *
>> + * The CameraSensorHelper instances shall never be constructed manually, but always
> 
> CameraSensorHelper derived class instances...
> 
>> + * through the CameraSensorHelperFactory::create() method.
>> + */
>> +CameraSensorHelper::CameraSensorHelper()
>> +{
>> +}
>> +
>> +CameraSensorHelper::~CameraSensorHelper()
>> +{
>> +}
>> +
>> +/**
>> + * CameraSensorHelper::GainCode(double gain)
>> + * \brief Compute gain code from the analogue gain value
> 
> analogue gain absolute value
>> + * \param[in] gain The real gain to pass
>> + * \return the gain code to pass to V4l2
>> + *
>> + * This function aims to abstract the calculation of the gain letting the IPA
>> + * use the real gain for its estimations.
>> + *
>> + * The parameters come from the MIPI Alliance Camera Specification for
>> + * Camera Command Set (CCS).
>> + */
>> +uint32_t CameraSensorHelper::GainCode(double gain) const
> 
> function names start with lowercase
> 
>> +{
>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
> 
> Rouge \t
> 
>> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
>> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
>> +}
>> +
>> +/**
>> + * CameraSensorHelper::Gain
>> + * \brief Compute the real gain from the V4l2 subdev control gain
> 
> s/real/absolute ? not sure...
> 
> control gain code ?
> 
>> + * \param[in] gainCode The V4l2 subdev control gain
>> + * \return The real gain
>> + *
>> + * This function aims to abstract the calculation of the gain letting the IPA
>> + * use the real gain for its estimations. It is the counterpart of the function
>> + * CameraSensorHelper::getGainCode.
> 
> now called GainCode
> 
>> + *
>> + * The parameters come from the MIPI Alliance Camera Specification for
>> + * Camera Command Set (CCS).
>> + */
>> +double CameraSensorHelper::Gain(uint32_t gainCode) const
>> +{
>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
>> +	return (analogueGainConstants_.m0 * gainCode + analogueGainConstants_.c0) /
>> +	       (analogueGainConstants_.m1 * gainCode + analogueGainConstants_.c1);
>> +}
>> +
>> +/**
>> + * \enum CameraSensorHelper::AnalogueGainType
>> + * \brief Specify the Gain mode supported by the sensor
> 
> .. the gain calculation modes as defined by the MIPI ...
> 
>> + *
>> + * Describes the image sensor analogue Gain capabilities.
> 
> It's more about two different ways to calculate the gain value
> 

It is the way it is described in the MIPI specification, I simple
copy/pasted this one ;-).

>> + * Two modes are possible, depending on the sensor: Global and Alternate.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainLinear
>> + * \brief Sensor supports linear gain
> 
> Gain is computed using linear gain estimation ?
> Or something along these line (what I mean is that this should
> describe the gain calculation mode algorithm, not what the sensor
> supports).
> 
>> + *
>> + * The relationship between the integer Gain parameter and the resulting Gain
>> + * multiplier is given by the following equation:
>> + *
>> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
>> + *
>> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
>> + * image-sensor-specific constants exposed by the sensor.
> 
> s/exposed by/of/
> 
>> + * These constants are static parameters, and for any given image sensor either
>> + * m0 or m1 shall be zero.
>> + *
>> + * The full Gain equation therefore reduces to either:
>> + *
>> + * \f$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainExponential
>> + * \brief Sensor supports exponential gain (introduced in CCS v1.1)
> 
> Same comment as above
> 
>> + *
>> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also available.
>> + * If the image sensor supports it, then the global analogue Gain can be controlled
>> + * by linear and exponential gain formula:
>> + *
>> + * \f$gain = analogLinearGainGlobal * 2^{analogExponentialGainGlobal}\f$
>> + * \todo not implemented in libipa
>> + */
>> +
>> +/**
>> + * \struct CameraSensorHelper::AnalogueGainConstants
>> + * \brief Analogue gain constants used for gain calculation
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::type
>> + * \brief Analogue gain coding type
> 
> "Analogue gain calculation mode" ?
> 
> So this should be of type enum AnalogueGainType not uint16 ?
> 
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m0
>> + * \brief Constant used in the analogue Gain control coding/decoding
> 
> s/Gain control/Gain
> 
> Gain is spelled with capital G in many places, I guess it's
> intentional then
> 
>> + *
>> + * Note: either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c0
>> + * \brief Constant used in the analogue Gain control coding/decoding
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m1
>> + * \brief Constant used in the analogue Gain control coding/decoding
>> + *
>> + * Note: either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c1
>> + * \brief Constant used in the analogue Gain control coding/decoding
>> + */
> 
> same comment for these three
> 
>> +
>> +/**
>> + * \var CameraSensorHelper::analogueGainConstants_
>> + * \brief The analogue gain parameters used for calculation
>> + *
>> + * The analogue gain is calculated through a formula, and its parameters are
>> + * sensor specific. Use this variable to store the values at init time.
>> + *
>> + */
>> +
>> +/**
>> + * \class CameraSensorHelperFactory
>> + * \brief Registration of CameraSensorHelperFactory classes and creation of instances
>> + *
>> + * To facilitate discovery and instantiation of CameraSensorHelper classes, the
>> + * CameraSensorHelperFactory class maintains a registry of camera sensor helper
>> + * classes. Each CameraSensorHelper subclass shall register itself using the
>> + * REGISTER_CAMERA_SENSOR_HELPER() macro, which will create a corresponding
>> + * instance of a CameraSensorHelperFactory subclass and register it with the
>> + * static list of factories.
>> + */
>> +
>> +/**
>> + * \brief Construct a camera sensor helper factory
>> + * \param[in] name Name of the camera sensor helper class
>> + *
>> + * Creating an instance of the factory registers it with the global list of
>> + * factories, accessible through the factories() function.
>> + *
>> + * The factory \a name is used for debug purpose and shall be unique.
>> + */
>> +CameraSensorHelperFactory::CameraSensorHelperFactory(const std::string name)
>> +	: name_(name)
>> +{
>> +	registerType(this);
>> +}
>> +
>> +/**
>> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
>> + *
>> + * \return A unique pointer to a new instance of the CameraSensorHelper subclass
>> + * corresponding to the factory
>> + */
>> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create(const std::string &name)
>> +{
>> +	std::vector<CameraSensorHelperFactory *> &factories =
>> +		CameraSensorHelperFactory::factories();
>> +
>> +	for (CameraSensorHelperFactory *factory : factories) {
>> +		if (name != factory->name_)
>> +			continue;
>> +
>> +		CameraSensorHelper *helper = factory->createInstance();
>> +		return std::unique_ptr<CameraSensorHelper>(helper);
>> +	}
> 
> Empty line maybe ?
> 
>> +	return nullptr;
>> +}
>> +
>> +/**
>> + * \brief Add a camera sensor helper class to the registry
>> + * \param[in] factory Factory to use to construct the camera sensor helper
>> + *
>> + * The caller is responsible to guarantee the uniqueness of the camera sensor helper
>> + * name.
>> + */
>> +void CameraSensorHelperFactory::registerType(CameraSensorHelperFactory *factory)
>> +{
>> +	std::vector<CameraSensorHelperFactory *> &factories = CameraSensorHelperFactory::factories();
>> +
>> +	factories.push_back(factory);
>> +}
>> +
>> +/**
>> + * \brief Retrieve the list of all camera sensor helper factories
>> + *
>> + * The static factories map is defined inside the function to ensures it gets
>> + * initialized on first use, without any dependency on link order.
>> + *
>> + * \return The list of camera sensor helper factories
>> + */
>> +std::vector<CameraSensorHelperFactory *> &CameraSensorHelperFactory::factories()
>> +{
>> +	static std::vector<CameraSensorHelperFactory *> factories;
>> +	return factories;
>> +}
>> +
>> +/**
>> + * CameraSensorHelperFactory::createInstance()
>> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
>> + *
>> + * This virtual function is implemented by the REGISTER_CAMERA_SENSOR_HELPER()
>> + * macro. It creates a camera sensor helper instance associated with the camera
>> + * sensor model.
>> + *
>> + * \return A pointer to a newly constructed instance of the CameraSensorHelper
>> + * subclass corresponding to the factory
>> + */
>> +
>> +/**
>> + * \def REGISTER_CAMERA_SENSOR_HELPER
>> + * \brief Register a camera sensor helper with the camera sensor helper factory
>> + * \param[in] name Sensor model name used to register the class
>> + * \param[in] helper Class name of CameraSensorHelper derived class to register
>> + *
>> + * Register a CameraSensorHelper subclass with the factory and make it available to
>> + * try and match devices.
>> + */
>> +
>> +/**
>> + * \class CameraSensorHelperImx219
>> + * \brief Create and give helpers for the imx219 sensor
>> + */
>> +class CameraSensorHelperImx219 : public CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelperImx219()
>> +	{
>> +		analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256, 256 };
>> +	}
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
>> +
>> +/**
>> + * \class CameraSensorHelperOv5670
>> + * \brief Create and give helpers for the ov5670 sensor
>> + */
>> +class CameraSensorHelperOv5670 : public CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelperOv5670()
>> +	{
>> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
>> +	}
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
>> +
>> +/**
>> + * \class CameraSensorHelperOv5693
>> + * \brief Create and give helpers for the ov5693 sensor
>> + */
>> +class CameraSensorHelperOv5693 : public CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelperOv5693()
>> +	{
>> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
>> +	}
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
>> +
>> +} /* namespace ipa */
>> +
>> +} /* namespace libcamera */
> 
> Nice!
> 
>> diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
>> new file mode 100644
>> index 00000000..ea7558d3
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.h
>> @@ -0,0 +1,88 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.h - Helper class providing camera information
> 
> To be algined with the .cpp file comment if you change it
> 
>> + */
>> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +
>> +#include <stdint.h>
>> +
>> +#include <string>
> 
> You need to include vector (I have a compilation error for this)
>> +
>> +#include <libcamera/class.h>
>> +#include <libcamera/object.h>
> 
> object.h can be removed
> 
>> +
>> +namespace libcamera {
>> +
>> +namespace ipa {
>> +
>> +class CameraSensorHelper;
> 
> What's this for ?
> 
>> +
>> +class CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelper();
>> +	virtual ~CameraSensorHelper();
> 
> Can these be = default ?
> 
>> +
>> +	uint32_t GainCode(double gain) const;
>> +	double Gain(uint32_t gainCode) const;
> 
> Should these be virtual if a subclass need to override them ?
> 
>> +
>> +protected:
>> +	enum AnalogueGainType {
>> +		AnalogueGainLinear = 0,
>> +		AnalogueGainExponential = 2,
> 
> Does 0 and 2 come from the CCS specs ?
> 
>> +	};
>> +
>> +	struct AnalogueGainConstants {
>> +		uint16_t type;
>> +		int16_t m0;
>> +		int16_t c0;
>> +		int16_t m1;
>> +		int16_t c1;
>> +	};
>> +
>> +	AnalogueGainConstants analogueGainConstants_;
>> +
>> +private:
>> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
>> +};
>> +
>> +class CameraSensorHelperFactory
>> +{
>> +public:
>> +	CameraSensorHelperFactory(const std::string name);
>> +	virtual ~CameraSensorHelperFactory() = default;
>> +
>> +	static std::unique_ptr<CameraSensorHelper> create(const std::string &name);
>> +
>> +	static void registerType(CameraSensorHelperFactory *factory);
>> +	static std::vector<CameraSensorHelperFactory *> &factories();
>> +
>> +private:
>> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)
>> +	virtual CameraSensorHelper *createInstance() = 0;
>> +
>> +	std::string name_;
>> +};
>> +
>> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)               \
>> +class helper##Factory final : public CameraSensorHelperFactory    \
>> +{                                                                 \
>> +public:                                                           \
>> +	helper##Factory() : CameraSensorHelperFactory(name) {} \
>> +								  \
>> +private:                                                          \
>> +	CameraSensorHelper *createInstance()                      \
>> +	{                                                         \
>> +		return new helper();                          \
>> +	}                                                         \
>> +};                                                                \
>> +static helper##Factory global_##helper##Factory;
>> +
>> +} /* namespace ipa */
>> +
>> +} /* namespace libcamera */
>> +
>> +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
>> diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
>> index 038fc490..dc90542c 100644
>> --- a/src/ipa/libipa/meson.build
>> +++ b/src/ipa/libipa/meson.build
>> @@ -2,11 +2,13 @@
>>
>>  libipa_headers = files([
>>      'algorithm.h',
>> +    'camera_sensor_helper.h',
>>      'histogram.h'
>>  ])
>>
>>  libipa_sources = files([
>>      'algorithm.cpp',
>> +    'camera_sensor_helper.cpp',
>>      'histogram.cpp'
>>  ])
> 
> Mostly minors, good job, almost there from my side :)
> Bear with me a little more for the documentation comments, take
> whatever you consider appropriate in.
> 
> Thanks
>   j
> 
>>
>> --
>> 2.30.2
>>