[libcamera-devel,v3,1/2] ipa: Create a camera sensor helper class

12561 diff mbox series

Setting analogue gain for a specific sensor is not a straghtforward
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 straightfoward 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 | 319 ++++++++++++++++++++++++
 src/ipa/libipa/camera_sensor_helper.h   |  88 +++++++
 src/ipa/libipa/meson.build              |   2 +
 3 files changed, 409 insertions(+)
 create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
 create mode 100644 src/ipa/libipa/camera_sensor_helper.h

Hi JM

On 11/06/2021 08:03, Jean-Michel Hautbois wrote:
> Setting analogue gain for a specific sensor is not a straghtforward

s/straghtforward/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 straightfoward as one only needs to

s/straightfoward/straightforward/

> 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 | 319 ++++++++++++++++++++++++
>  src/ipa/libipa/camera_sensor_helper.h   |  88 +++++++
>  src/ipa/libipa/meson.build              |   2 +
>  3 files changed, 409 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..4e50ee53
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -0,0 +1,319 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.cpp - Helper class providing camera information
> + */
> +#include "camera_sensor_helper.h"
> +
> +#include <map>
> +
> +#include "libcamera/internal/log.h"
> +
> +/**
> + * \file camera_sensor_helper.h
> + * \brief Helper class for each sensor
> + *
> + * Each camera sensor supported by libcamera may need specific informations to

s/informations/information/


> + * be sent (analogue gain is sensor dependant for instance).
> + *
> + * 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
> + *
> + * CameraSensorHelper instances are unique and sensor dependant.
> + */
> +
> +/**
> + * \brief Construct a CameraSensorHelper instance
> + * \param[in] name The sensor model name
> + *
> + * The CameraSensorHelper instances shall never be constructed manually, but always
> + * through the CameraSensorHelperFactory::create() method.
> + */
> +CameraSensorHelper::CameraSensorHelper()
> +{
> +}
> +
> +CameraSensorHelper::~CameraSensorHelper()
> +{
> +}

Do these need to be implemented if they're empty ? (Or are they
placeholders so they can be populated later? But if that's the case they
could be added when needed...

> +
> +/**
> + * CameraSensorHelper::GainCode(double gain)
> + * \brief Compute gain code from the analogue gain 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
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +	
> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
> +}
> +
> +/**
> + * CameraSensorHelper::Gain
> + * \brief Compute the real gain from the V4l2 subdev control gain
> + * \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.
> + *
> + * 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
> + *
> + * Describes the image sensor analog Gain capabilities.
> + * Two modes are possible, depending on the sensor: Global and Alternate.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainLinear
> + * \brief Sensor supports linear gain
> + *
> + * 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.
> + * 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

This mixes Analogue and Analog below. We should at least be consistent
in the spelling type used.

Same in many places.


> + * \brief Sensor supports exponential gain (introduced in CCS v1.1)
> + *
> + * Starting with CCS v1.1, Alternate Global Analog Gain is also available.
> + * If the image sensor supports it, then the global analog 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
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m0
> + * \brief Constant used in the analog Gain control coding/decoding
> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c0
> + * \brief Constant used in the analog Gain control coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m1
> + * \brief Constant used in the analog Gain control coding/decoding
> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c1
> + * \brief Constant used in the analog Gain control coding/decoding
> + */
> +
> +/**
> + * \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);
> +	}
> +	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)


This is a lot of code for what so far is a table. I assume there will be
more complex requirements on the class though so I think it's ok.


> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
> new file mode 100644
> index 00000000..cc486be8
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.h
> @@ -0,0 +1,88 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */

Why is this BSD-2 instead of LGPL-2.1-or-later?

Is this specifically derived from RPi code?
In which case should that be mentioned in the Copyright?

Same for the .cpp I think.


> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.h - Helper class providing camera information
> + */
> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +
> +#include <stdint.h>
> +
> +#include <string>
> +
> +#include <libcamera/class.h>
> +#include <libcamera/object.h>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +class CameraSensorHelper;
> +
> +class CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelper();
> +	virtual ~CameraSensorHelper();
> +
> +	uint32_t GainCode(double gain) const;
> +	double Gain(uint32_t gainCode) const;
> +
> +protected:
> +	enum AnalogueGainType {
> +		AnalogueGainLinear = 0,
> +		AnalogueGainExponential = 2,
> +	};
> +
> +	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'
>  ])
>  
>

Hi Kieran,

On 11/06/2021 11:53, Kieran Bingham wrote:
> Hi JM
> 
> On 11/06/2021 08:03, Jean-Michel Hautbois wrote:
>> Setting analogue gain for a specific sensor is not a straghtforward
> 
> s/straghtforward/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 straightfoward as one only needs to
> 
> s/straightfoward/straightforward/
> 
>> 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 | 319 ++++++++++++++++++++++++
>>  src/ipa/libipa/camera_sensor_helper.h   |  88 +++++++
>>  src/ipa/libipa/meson.build              |   2 +
>>  3 files changed, 409 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..4e50ee53
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
>> @@ -0,0 +1,319 @@
>> +/* SPDX-License-Identifier: BSD-2-Clause */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.cpp - Helper class providing camera information
>> + */
>> +#include "camera_sensor_helper.h"
>> +
>> +#include <map>
>> +
>> +#include "libcamera/internal/log.h"
>> +
>> +/**
>> + * \file camera_sensor_helper.h
>> + * \brief Helper class for each sensor
>> + *
>> + * Each camera sensor supported by libcamera may need specific informations to
> 
> s/informations/information/
> 
> 
>> + * be sent (analogue gain is sensor dependant for instance).
>> + *
>> + * 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
>> + *
>> + * CameraSensorHelper instances are unique and sensor dependant.
>> + */
>> +
>> +/**
>> + * \brief Construct a CameraSensorHelper instance
>> + * \param[in] name The sensor model name
>> + *
>> + * The CameraSensorHelper instances shall never be constructed manually, but always
>> + * through the CameraSensorHelperFactory::create() method.
>> + */
>> +CameraSensorHelper::CameraSensorHelper()
>> +{
>> +}
>> +
>> +CameraSensorHelper::~CameraSensorHelper()
>> +{
>> +}
> 
> Do these need to be implemented if they're empty ? (Or are they
> placeholders so they can be populated later? But if that's the case they
> could be added when needed...
> 
>> +
>> +/**
>> + * CameraSensorHelper::GainCode(double gain)
>> + * \brief Compute gain code from the analogue gain 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
>> +{
>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +	
>> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
>> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
>> +}
>> +
>> +/**
>> + * CameraSensorHelper::Gain
>> + * \brief Compute the real gain from the V4l2 subdev control gain
>> + * \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.
>> + *
>> + * 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
>> + *
>> + * Describes the image sensor analog Gain capabilities.
>> + * Two modes are possible, depending on the sensor: Global and Alternate.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainLinear
>> + * \brief Sensor supports linear gain
>> + *
>> + * 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.
>> + * 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
> 
> This mixes Analogue and Analog below. We should at least be consistent
> in the spelling type used.
> 
> Same in many places.
> 
> 
>> + * \brief Sensor supports exponential gain (introduced in CCS v1.1)
>> + *
>> + * Starting with CCS v1.1, Alternate Global Analog Gain is also available.
>> + * If the image sensor supports it, then the global analog 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
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m0
>> + * \brief Constant used in the analog Gain control coding/decoding
>> + *
>> + * Note: either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c0
>> + * \brief Constant used in the analog Gain control coding/decoding
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m1
>> + * \brief Constant used in the analog Gain control coding/decoding
>> + *
>> + * Note: either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c1
>> + * \brief Constant used in the analog Gain control coding/decoding
>> + */
>> +
>> +/**
>> + * \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);
>> +	}
>> +	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)
> 
> 
> This is a lot of code for what so far is a table. I assume there will be
> more complex requirements on the class though so I think it's ok.
> 

Thanks for all the remarks :-).
Indeed the helper aims to do more than just calculate an analogue gain :-).

> 
>> +
>> +} /* namespace ipa */
>> +
>> +} /* namespace libcamera */
>> diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
>> new file mode 100644
>> index 00000000..cc486be8
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.h
>> @@ -0,0 +1,88 @@
>> +/* SPDX-License-Identifier: BSD-2-Clause */
> 
> Why is this BSD-2 instead of LGPL-2.1-or-later?
> 
> Is this specifically derived from RPi code?
> In which case should that be mentioned in the Copyright?
> 
> Same for the .cpp I think.
> 

It is more coming from PipelineHandler :-).
I changed it to LGPL-2.1-or-later to be consistent with the other IPA
classes.

> 
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.h - Helper class providing camera information
>> + */
>> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +
>> +#include <stdint.h>
>> +
>> +#include <string>
>> +
>> +#include <libcamera/class.h>
>> +#include <libcamera/object.h>
>> +
>> +namespace libcamera {
>> +
>> +namespace ipa {
>> +
>> +class CameraSensorHelper;
>> +
>> +class CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelper();
>> +	virtual ~CameraSensorHelper();
>> +
>> +	uint32_t GainCode(double gain) const;
>> +	double Gain(uint32_t gainCode) const;
>> +
>> +protected:
>> +	enum AnalogueGainType {
>> +		AnalogueGainLinear = 0,
>> +		AnalogueGainExponential = 2,
>> +	};
>> +
>> +	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'
>>  ])
>>  
>>
>

On 14/06/2021 09:51, Jean-Michel Hautbois wrote:
> Hi Kieran,
> 
> On 11/06/2021 11:53, Kieran Bingham wrote:
>> Hi JM
>>
>> On 11/06/2021 08:03, Jean-Michel Hautbois wrote:
>>> Setting analogue gain for a specific sensor is not a straghtforward
>>
>> s/straghtforward/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 straightfoward as one only needs to
>>
>> s/straightfoward/straightforward/
>>
>>> 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 | 319 ++++++++++++++++++++++++
>>>  src/ipa/libipa/camera_sensor_helper.h   |  88 +++++++
>>>  src/ipa/libipa/meson.build              |   2 +
>>>  3 files changed, 409 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..4e50ee53
>>> --- /dev/null
>>> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
>>> @@ -0,0 +1,319 @@
>>> +/* SPDX-License-Identifier: BSD-2-Clause */
>>> +/*
>>> + * Copyright (C) 2021, Google Inc.
>>> + *
>>> + * camera_sensor_helper.cpp - Helper class providing camera information
>>> + */
>>> +#include "camera_sensor_helper.h"
>>> +
>>> +#include <map>
>>> +
>>> +#include "libcamera/internal/log.h"
>>> +
>>> +/**
>>> + * \file camera_sensor_helper.h
>>> + * \brief Helper class for each sensor
>>> + *
>>> + * Each camera sensor supported by libcamera may need specific informations to
>>
>> s/informations/information/
>>
>>
>>> + * be sent (analogue gain is sensor dependant for instance).
>>> + *
>>> + * 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
>>> + *
>>> + * CameraSensorHelper instances are unique and sensor dependant.
>>> + */
>>> +
>>> +/**
>>> + * \brief Construct a CameraSensorHelper instance
>>> + * \param[in] name The sensor model name
>>> + *
>>> + * The CameraSensorHelper instances shall never be constructed manually, but always
>>> + * through the CameraSensorHelperFactory::create() method.
>>> + */
>>> +CameraSensorHelper::CameraSensorHelper()
>>> +{
>>> +}
>>> +
>>> +CameraSensorHelper::~CameraSensorHelper()
>>> +{
>>> +}
>>
>> Do these need to be implemented if they're empty ? (Or are they
>> placeholders so they can be populated later? But if that's the case they
>> could be added when needed...
>>

I think you need those as you call them through
CameraSensorHelperFactory, and if you don't, then you will have
something like :
symbol lookup error: /usr/lib/x86_64-linux-gnu/libcamera/ipa_ipu3.so:
undefined symbol:
libcamera::ipa::CameraSensorHelperFactory::create(std::__1::basic_string<char,
std::__1::char_traits<char>, std::__1::allocator<char> > const&)

Even if I suppose we may have them declared by another mean ?

>>> +
>>> +/**
>>> + * CameraSensorHelper::GainCode(double gain)
>>> + * \brief Compute gain code from the analogue gain 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
>>> +{
>>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
>>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>>> +	
>>> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
>>> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
>>> +}
>>> +
>>> +/**
>>> + * CameraSensorHelper::Gain
>>> + * \brief Compute the real gain from the V4l2 subdev control gain
>>> + * \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.
>>> + *
>>> + * 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
>>> + *
>>> + * Describes the image sensor analog Gain capabilities.
>>> + * Two modes are possible, depending on the sensor: Global and Alternate.
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainLinear
>>> + * \brief Sensor supports linear gain
>>> + *
>>> + * 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.
>>> + * 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
>>
>> This mixes Analogue and Analog below. We should at least be consistent
>> in the spelling type used.
>>
>> Same in many places.
>>
>>
>>> + * \brief Sensor supports exponential gain (introduced in CCS v1.1)
>>> + *
>>> + * Starting with CCS v1.1, Alternate Global Analog Gain is also available.
>>> + * If the image sensor supports it, then the global analog 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
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainConstants::m0
>>> + * \brief Constant used in the analog Gain control coding/decoding
>>> + *
>>> + * Note: either m0 or m1 shall be zero.
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainConstants::c0
>>> + * \brief Constant used in the analog Gain control coding/decoding
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainConstants::m1
>>> + * \brief Constant used in the analog Gain control coding/decoding
>>> + *
>>> + * Note: either m0 or m1 shall be zero.
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainConstants::c1
>>> + * \brief Constant used in the analog Gain control coding/decoding
>>> + */
>>> +
>>> +/**
>>> + * \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);
>>> +	}
>>> +	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)
>>
>>
>> This is a lot of code for what so far is a table. I assume there will be
>> more complex requirements on the class though so I think it's ok.
>>
> 
> Thanks for all the remarks :-).
> Indeed the helper aims to do more than just calculate an analogue gain :-).
> 
>>
>>> +
>>> +} /* namespace ipa */
>>> +
>>> +} /* namespace libcamera */
>>> diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
>>> new file mode 100644
>>> index 00000000..cc486be8
>>> --- /dev/null
>>> +++ b/src/ipa/libipa/camera_sensor_helper.h
>>> @@ -0,0 +1,88 @@
>>> +/* SPDX-License-Identifier: BSD-2-Clause */
>>
>> Why is this BSD-2 instead of LGPL-2.1-or-later?
>>
>> Is this specifically derived from RPi code?
>> In which case should that be mentioned in the Copyright?
>>
>> Same for the .cpp I think.
>>
> 
> It is more coming from PipelineHandler :-).
> I changed it to LGPL-2.1-or-later to be consistent with the other IPA
> classes.
> 
>>
>>> +/*
>>> + * Copyright (C) 2021, Google Inc.
>>> + *
>>> + * camera_sensor_helper.h - Helper class providing camera information
>>> + */
>>> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>>> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>>> +
>>> +#include <stdint.h>
>>> +
>>> +#include <string>
>>> +
>>> +#include <libcamera/class.h>
>>> +#include <libcamera/object.h>
>>> +
>>> +namespace libcamera {
>>> +
>>> +namespace ipa {
>>> +
>>> +class CameraSensorHelper;
>>> +
>>> +class CameraSensorHelper
>>> +{
>>> +public:
>>> +	CameraSensorHelper();
>>> +	virtual ~CameraSensorHelper();
>>> +
>>> +	uint32_t GainCode(double gain) const;
>>> +	double Gain(uint32_t gainCode) const;
>>> +
>>> +protected:
>>> +	enum AnalogueGainType {
>>> +		AnalogueGainLinear = 0,
>>> +		AnalogueGainExponential = 2,
>>> +	};
>>> +
>>> +	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'
>>>  ])
>>>  
>>>
>>