libcamera/vivid.git - libcamera pipeline handler for VIVID

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2021, Google Inc.
 *
 * Helper class that performs sensor-specific
 * parameter computations
 */
#include "camera_sensor_helper.h"

#include <cmath>
#include <limits>

#include <libcamera/base/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
 *
 * Instances derived from CameraSensorHelper class are sensor-specific.
 * Each supported sensor will have an associated base class defined.
 */

/**
 * \fn CameraSensorHelper::CameraSensorHelper()
 * \brief Construct a CameraSensorHelper instance
 *
 * CameraSensorHelper derived class instances shall never be constructed
 * manually but always through the CameraSensorHelperFactoryBase::create()
 * function.
 */

/**
 * \fn CameraSensorHelper::blackLevel()
 * \brief Fetch the black level of the sensor
 *
 * This function returns the black level of the sensor scaled to a 16bit pixel
 * width. If it is unknown an empty optional is returned.
 *
 * \todo Fill the blanks and add pedestal values for all supported sensors. Once
 * done, drop the std::optional<>.
 *
 * Black levels are typically the result of the following phenomena:
 * - Pedestal added by the sensor to pixel values. They are typically fixed,
 *   sometimes programmable and should be reported in datasheets (but
 *   documentation is not always available).
 * - Dark currents and other physical effects that add charge to pixels in the
 *   absence of light. Those can depend on the integration time and the sensor
 *   die temperature, and their contribution to pixel values depend on the
 *   sensor gains.
 *
 * The pedestal is usually the value with the biggest contribution to the
 * overall black level. In most cases it is either known before or in rare cases
 * (there is not a single driver with such a control in the linux kernel) can be
 * queried from the sensor. This function provides that fixed, known value.
 *
 * \return The black level of the sensor, or std::nullopt if not known
 */

/**
 * \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.
 *
 * \return The gain code to pass to V4L2
 */
uint32_t CameraSensorHelper::gainCode(double gain) const
{
	const AnalogueGainConstants &k = gainConstants_;

	switch (gainType_) {
	case AnalogueGainLinear:
		ASSERT(k.linear.m0 == 0 || k.linear.m1 == 0);

		return (k.linear.c0 - k.linear.c1 * gain) /
		       (k.linear.m1 * gain - k.linear.m0);

	case AnalogueGainExponential:
		ASSERT(k.exp.a != 0 && k.exp.m != 0);

		return std::log2(gain / k.exp.a) / k.exp.m;

	default:
		ASSERT(false);
		return 0;
	}
}

/**
 * \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.
 *
 * \return The real gain
 */
double CameraSensorHelper::gain(uint32_t gainCode) const
{
	const AnalogueGainConstants &k = gainConstants_;
	double gain = static_cast<double>(gainCode);

	switch (gainType_) {
	case AnalogueGainLinear:
		ASSERT(k.linear.m0 == 0 || k.linear.m1 == 0);

		return (k.linear.m0 * gain + k.linear.c0) /
		       (k.linear.m1 * gain + k.linear.c1);

	case AnalogueGainExponential:
		ASSERT(k.exp.a != 0 && k.exp.m != 0);

		return k.exp.a * std::exp2(k.exp.m * gain);

	default:
		ASSERT(false);
		return 0.0;
	}
}

/**
 * \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: Linear and Exponential.
 */

/**
 * \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 expressed using an exponential model
 *
 * The relationship between the integer gain parameter and the resulting gain
 * multiplier is given by the following equation:
 *
 * \f$gain = a \cdot 2^{m \cdot x}\f$
 *
 * Where 'x' is the gain control parameter, and 'a' and 'm' are image
 * sensor-specific constants.
 *
 * This is a subset of the MIPI CCS exponential gain model with the linear
 * factor 'a' being a constant, but with the exponent being configurable
 * through the 'm' coefficient.
 *
 * When the gain is expressed in dB, 'a' is equal to 1 and 'm' to
 * \f$log_{2}{10^{\frac{1}{20}}}\f$.
 */

/**
 * \struct CameraSensorHelper::AnalogueGainLinearConstants
 * \brief Analogue gain constants for the linear gain model
 *
 * \var CameraSensorHelper::AnalogueGainLinearConstants::m0
 * \brief Constant used in the linear gain coding/decoding
 *
 * \note Either m0 or m1 shall be zero.
 *
 * \var CameraSensorHelper::AnalogueGainLinearConstants::c0
 * \brief Constant used in the linear gain coding/decoding
 *
 * \var CameraSensorHelper::AnalogueGainLinearConstants::m1
 * \brief Constant used in the linear gain coding/decoding
 *
 * \note Either m0 or m1 shall be zero.
 *
 * \var CameraSensorHelper::AnalogueGainLinearConstants::c1
 * \brief Constant used in the linear gain coding/decoding
 */

/**
 * \struct CameraSensorHelper::AnalogueGainExpConstants
 * \brief Analogue gain constants for the exponential gain model
 *
 * \var CameraSensorHelper::AnalogueGainExpConstants::a
 * \brief Constant used in the exponential gain coding/decoding
 *
 * \var CameraSensorHelper::AnalogueGainExpConstants::m
 * \brief Constant used in the exponential gain coding/decoding
 */

/**
 * \struct CameraSensorHelper::AnalogueGainConstants
 * \brief Analogue gain model constants
 *
 * This union stores the constants used to calculate the analogue gain. The
 * CameraSensorHelper::gainType_ variable selects which union member is valid.
 *
 * \var CameraSensorHelper::AnalogueGainConstants::linear
 * \brief Constants for the linear gain model
 *
 * \var CameraSensorHelper::AnalogueGainConstants::exp
 * \brief Constants for the exponential gain model
 */

/**
 * \var CameraSensorHelper::blackLevel_
 * \brief The black level of the sensor
 * \sa CameraSensorHelper::blackLevel()
 */

/**
 * \var CameraSensorHelper::gainType_
 * \brief The analogue gain model type
 */

/**
 * \var CameraSensorHelper::gainConstants_
 * \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 CameraSensorHelperFactoryBase
 * \brief Base class for camera sensor helper factories
 *
 * The CameraSensorHelperFactoryBase class is the base of all specializations of
 * the CameraSensorHelperFactory class template. It implements the factory
 * registration, maintains a registry of factories, and provides access to the
 * registered factories.
 */

/**
 * \brief Construct a camera sensor helper factory base
 * \param[in] name Name of the camera sensor helper class
 *
 * Creating an instance of the factory base registers it with the global list of
 * factories, accessible through the factories() function.
 *
 * The factory \a name is used to look up factories and shall be unique.
 */
CameraSensorHelperFactoryBase::CameraSensorHelperFactoryBase(const std::string name)
	: name_(name)
{
	registerType(this);
}

/**
 * \brief Create an instance of the CameraSensorHelper corresponding to
 * a named factory
 * \param[in] name Name of the factory
 *
 * \return A unique pointer to a new instance of the CameraSensorHelper subclass
 * corresponding to the named factory or a null pointer if no such factory
 * exists
 */
std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactoryBase::create(const std::string &name)
{
	const std::vector<CameraSensorHelperFactoryBase *> &factories =
		CameraSensorHelperFactoryBase::factories();

	for (const CameraSensorHelperFactoryBase *factory : factories) {
		if (name != factory->name_)
			continue;

		return factory->createInstance();
	}


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