[libcamera-devel] [PATCH v6 1/2] ipa: Create a camera sensor helper class

[Jean-Michel Hautbois]

Hi Kieran,

On 24/06/2021 14:46, Kieran Bingham wrote:
> Hi JM,
> 
> On 22/06/2021 10:45, Jean-Michel Hautbois wrote:
>> 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.
>>
>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
>> Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
>> ---
>>  src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>>  src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
>>  src/ipa/libipa/meson.build              |   2 +
>>  3 files changed, 407 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..a114ee73
>> --- /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 that performs sensor-specific parameter computations
>> + */
>> +#include "camera_sensor_helper.h"
>> +
>> +#include "libcamera/internal/log.h"
>> +
>> +/**
>> + * \file camera_sensor_helper.h
>> + * \brief Helper class that performs sensor-specific parameter computations
>> + *
>> + * 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.
>> + *
>> + * 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 Base class for computing sensor tuning parameters using sensor-specific constants
>> + *
>> + * CameraSensorHelper derived class instances are sensor specific. Each
>> + * supported sensor will have an associated base class defined.
>> + */
>> +
>> +/**
>> + * \brief Construct a CameraSensorHelper instance
>> + *
>> + * CameraSensorHelper derived class instances shall never be constructed manually
>> + * but always through the CameraSensorHelperFactory::create() method.
>> + */
>> +
>> +/**
>> + * \brief Compute gain code from the analogue gain absolute value
>> + * \param[in] gain The real gain to pass
>> + *
>> + * 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).
>> + *
>> + * \return The gain code to pass to V4l2
>> + */
>> +uint32_t CameraSensorHelper::gainCode(double gain) const
>> +{
>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> 
> This doesn't need brackets around the two comparisons.
> 
> The == takes precedence over the || so those are evaluated before the
> logical OR.
> 
> https://en.cppreference.com/w/cpp/language/operator_precedence
> 
> I personally don't mind over-scoping though, as it helps make sure
> things are clear when order of precedence isn't always in peoples minds.
> 

I like it that way to ease reading :-).

> 
>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
>> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
>> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
>> +}
>> +
>> +/**
>> + * \brief Compute the real gain from the V4l2 subdev control gain code
>> + * \param[in] gainCode The V4l2 subdev control 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::gainCode.
>> + *
>> + * The parameters come from the MIPI Alliance Camera Specification for
>> + * Camera Command Set (CCS).
>> + *
>> + * \return The real gain
>> + */
>> +double CameraSensorHelper::gain(uint32_t gainCode) const
>> +{
>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> 
> Same,
> 
>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
>> +	return (analogueGainConstants_.m0 * static_cast<double>(gainCode) + analogueGainConstants_.c0) /
>> +	       (analogueGainConstants_.m1 * static_cast<double>(gainCode) + analogueGainConstants_.c1);
> 
> We're at v6, so I assume those calculations have been verified by now?
> 
> In particular all the type promotions ...
> 

Which are a pain... :-p but in our case it should be ok as far as I can
tell...
Would you prefer to see explicit conversions before the return ?

> 
>> +}
>> +
>> +/**
>> + * \enum CameraSensorHelper::AnalogueGainType
>> + * \brief the gain calculation modes as defined by the MIPI CCS
>> + *
>> + * Describes the image sensor analogue gain capabilities.
>> + * Two modes are possible, depending on the sensor: Global and Alternate.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainLinear
>> + * \brief Gain is computed using linear gain estimation
>> + *
>> + * 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 of 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
>> + * \brief Gain is computed using exponential gain estimation (introduced in CCS v1.1)
>> + *
>> + * 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 calculation mode
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m0
>> + * \brief Constant used in the analogue Gain coding/decoding
>> + *
>> + * \note either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c0
>> + * \brief Constant used in the analogue gain coding/decoding
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m1
>> + * \brief Constant used in the analogue gain coding/decoding
>> + *
>> + * \note either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c1
>> + * \brief Constant used in the analogue gain 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
>> + * \param[in] name Name of 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;
>> +}
>> +
>> +/**
>> + * \fn 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
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelperFactory::name_
>> + * \brief The name of 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)
> 
> If these will grow, should we have one file per camera sensor helper to
> split these out ?
> 
> Or is that overkill for the moment? I guess it can be broken out later
> when new features are added that would make the scale increase.
> 
> 
> Other than that, I don't want to block this series for things that can
> continue in development so:
> 
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> 
> and I'll let you decide if it should be split now or later.
> 

Thank you... I won't split it now, but it will be in a short notice
probably ;-).

> --
> Kieran
> 
> 
> 
>> +
>> +/**
>> + * \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 */
>> diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
>> new file mode 100644
>> index 00000000..c43e4bf6
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.h
>> @@ -0,0 +1,87 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.h - Helper class that performs sensor-specific parameter computations
>> + */
>> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +
>> +#include <stdint.h>
>> +
>> +#include <memory>
>> +#include <string>
>> +#include <vector>
>> +
>> +#include <libcamera/class.h>
>> +
>> +namespace libcamera {
>> +
>> +namespace ipa {
>> +
>> +class CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelper() = default;
>> +	virtual ~CameraSensorHelper() = default;
>> +
>> +	virtual uint32_t gainCode(double gain) const;
>> +	virtual double gain(uint32_t gainCode) const;
>> +
>> +protected:
>> +	enum AnalogueGainType {
>> +		AnalogueGainLinear = 0,
>> +		AnalogueGainExponential = 2,
>> +	};
>> +
>> +	struct AnalogueGainConstants {
>> +		AnalogueGainType 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();
>> +
>> +protected:
>> +	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'
>>  ])
>>  
>>