ipa: rkisp1: Introduce AGC

Now that we have IPAContext and Algorithm, we can implement a simple AGC
based on the IPU3 one. It is very similar, except that there is no
histogram used for an inter quantile mean. The RkISP1 is returning a 5x5
array (for V10) of luminance means. Estimating the relative luminance is
thus a simple mean of all the blocks already calculated by the ISP.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/rkisp1/algorithms/agc.cpp

@@ -0,0 +1,285 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Ideas On Board
+ *
+ * agc.cpp - AGC/AEC mean-based control algorithm
+ */
+
+#include "agc.h"
+
+#include <algorithm>
+#include <chrono>
+#include <cmath>
+
+#include <libcamera/base/log.h>
+
+#include <libcamera/ipa/core_ipa_interface.h>
+
+/**
+ * \file agc.h
+ */
+
+namespace libcamera {
+
+using namespace std::literals::chrono_literals;
+
+namespace ipa::rkisp1::algorithms {
+
+/**
+ * \class Agc
+ * \brief A mean-based auto-exposure algorithm
+ */
+
+LOG_DEFINE_CATEGORY(RkISP1Agc)
+
+/* Limits for analogue gain values */
+static constexpr double kMinAnalogueGain = 1.0;
+static constexpr double kMaxAnalogueGain = 8.0;
+
+/* \todo Honour the FrameDurationLimits control instead of hardcoding a limit */
+static constexpr utils::Duration kMaxShutterSpeed = 60ms;
+
+/* Number of frames to wait before calculating stats on minimum exposure */
+static constexpr uint32_t kNumStartupFrames = 10;
+
+/*
+ * Relative luminance target.
+ *
+ * It's a number that's chosen so that, when the camera points at a grey
+ * target, the resulting image brightness is considered right.
+ *
+ * \todo Why is the value different between IPU3 and RkISP1 ?
+ */
+static constexpr double kRelativeLuminanceTarget = 0.4;
+
+Agc::Agc()
+	: frameCount_(0), filteredExposure_(0s)
+{
+}
+
+/**
+ * \brief Configure the AGC given a configInfo
+ * \param[in] context The shared IPA context
+ * \param[in] configInfo The IPA configuration data
+ *
+ * \return 0
+ */
+int Agc::configure(IPAContext &context,
+		   [[maybe_unused]] const IPACameraSensorInfo &configInfo)
+{
+	/* Configure the default exposure and gain. */
+	context.frameContext.agc.gain = std::max(context.configuration.agc.minAnalogueGain, kMinAnalogueGain);
+	context.frameContext.agc.exposure = 10ms / context.configuration.sensor.lineDuration;
+
+	/*
+	 * According to the RkISP1 documentation:
+	 * - versions < V12 have RKISP1_CIF_ISP_AE_MEAN_MAX_V10 entries,
+	 * - versions >= V12 have RKISP1_CIF_ISP_AE_MEAN_MAX_V12 entries.
+	 */
+	if (context.configuration.hw.revision < RKISP1_V12)
+		numCells_ = RKISP1_CIF_ISP_AE_MEAN_MAX_V10;
+	else
+		numCells_ = RKISP1_CIF_ISP_AE_MEAN_MAX_V12;
+
+	/* \todo Use actual frame index by populating it in the frameContext. */
+	frameCount_ = 0;
+	return 0;
+}
+
+/**
+ * \brief Apply a filter on the exposure value to limit the speed of changes
+ * \param[in] exposureValue The target exposure from the AGC algorithm
+ *
+ * The speed of the filter is adaptive, and will produce the target quicker
+ * during startup, or when the target exposure is within 20% of the most recent
+ * filter output.
+ *
+ * \return The filtered exposure
+ */
+utils::Duration Agc::filterExposure(utils::Duration exposureValue)
+{
+	double speed = 0.2;
+
+	/* Adapt instantly if we are in startup phase. */
+	if (frameCount_ < kNumStartupFrames)
+		speed = 1.0;
+
+	/*
+	 * If we are close to the desired result, go faster to avoid making
+	 * multiple micro-adjustments.
+	 * \todo Make this customisable?
+	 */
+	if (filteredExposure_ < 1.2 * exposureValue &&
+	    filteredExposure_ > 0.8 * exposureValue)
+		speed = sqrt(speed);
+
+	filteredExposure_ = speed * exposureValue +
+			    filteredExposure_ * (1.0 - speed);
+
+	LOG(RkISP1Agc, Debug) << "After filtering, exposure " << filteredExposure_;
+
+	return filteredExposure_;
+}
+
+/**
+ * \brief Estimate the new exposure and gain values
+ * \param[inout] frameContext The shared IPA frame Context
+ * \param[in] yGain The gain calculated on the current brightness level
+ */
+void Agc::computeExposure(IPAContext &context, double yGain)
+{
+	IPASessionConfiguration &configuration = context.configuration;
+	IPAFrameContext &frameContext = context.frameContext;
+
+	/* Get the effective exposure and gain applied on the sensor. */
+	uint32_t exposure = frameContext.sensor.exposure;
+	double analogueGain = frameContext.sensor.gain;
+
+	utils::Duration minShutterSpeed = configuration.agc.minShutterSpeed;
+	utils::Duration maxShutterSpeed = std::min(configuration.agc.maxShutterSpeed,
+						   kMaxShutterSpeed);
+
+	double minAnalogueGain = std::max(configuration.agc.minAnalogueGain,
+					  kMinAnalogueGain);
+	double maxAnalogueGain = std::min(configuration.agc.maxAnalogueGain,
+					  kMaxAnalogueGain);
+
+	/* Consider within 1% of the target as correctly exposed. */
+	if (std::abs(yGain - 1.0) < 0.01)
+		return;
+
+	/* extracted from Rpi::Agc::computeTargetExposure. */
+
+	/* Calculate the shutter time in seconds. */
+	utils::Duration currentShutter = exposure * configuration.sensor.lineDuration;
+
+	/*
+	 * Update the exposure value for the next computation using the values
+	 * of exposure and gain really used by the sensor.
+	 */
+	utils::Duration effectiveExposureValue = currentShutter * analogueGain;
+
+	LOG(RkISP1Agc, Debug) << "Actual total exposure " << currentShutter * analogueGain
+			      << " Shutter speed " << currentShutter
+			      << " Gain " << analogueGain
+			      << " Needed ev gain " << yGain;
+
+	/*
+	 * Calculate the current exposure value for the scene as the latest
+	 * exposure value applied multiplied by the new estimated gain.
+	 */
+	utils::Duration exposureValue = effectiveExposureValue * yGain;
+
+	/* Clamp the exposure value to the min and max authorized. */
+	utils::Duration maxTotalExposure = maxShutterSpeed * maxAnalogueGain;
+	exposureValue = std::min(exposureValue, maxTotalExposure);
+	LOG(RkISP1Agc, Debug) << "Target total exposure " << exposureValue
+			      << ", maximum is " << maxTotalExposure;
+
+	/*
+	 * Divide the exposure value as new exposure and gain values.
+	 * \todo estimate if we need to desaturate
+	 */
+	exposureValue = filterExposure(exposureValue);
+
+	/*
+	 * Push the shutter time up to the maximum first, and only then
+	 * increase the gain.
+	 */
+	utils::Duration shutterTime = std::clamp<utils::Duration>(exposureValue / minAnalogueGain,
+								  minShutterSpeed, maxShutterSpeed);
+	double stepGain = std::clamp(exposureValue / shutterTime,
+				     minAnalogueGain, maxAnalogueGain);
+	LOG(RkISP1Agc, Debug) << "Divided up shutter and gain are "
+			      << shutterTime << " and "
+			      << stepGain;
+
+	/* Update the estimated exposure and gain. */
+	frameContext.agc.exposure = shutterTime / configuration.sensor.lineDuration;
+	frameContext.agc.gain = stepGain;
+}
+
+/**
+ * \brief Estimate the relative luminance of the frame with a given gain
+ * \param[in] ae The RkISP1 statistics and ISP results
+ * \param[in] gain The gain to apply to the frame
+ *
+ * This function estimates the average relative luminance of the frame that
+ * would be output by the sensor if an additional \a gain was applied.
+ *
+ * The estimation is based on the AE statistics for the current frame. Y
+ * averages for all cells are first multiplied by the gain, and then saturated
+ * to approximate the sensor behaviour at high brightness values. The
+ * approximation is quite rough, as it doesn't take into account non-linearities
+ * when approaching saturation. In this case, saturating after the conversion to
+ * YUV doesn't take into account the fact that the R, G and B components
+ * contribute differently to the relative luminance.
+ *
+ * \todo Have a dedicated YUV algorithm ?
+ *
+ * The values are normalized to the [0.0, 1.0] range, where 1.0 corresponds to a
+ * theoretical perfect reflector of 100% reference white.
+ *
+ * More detailed information can be found in:
+ * https://en.wikipedia.org/wiki/Relative_luminance
+ *
+ * \return The relative luminance
+ */
+double Agc::estimateLuminance(const rkisp1_cif_isp_ae_stat *ae,
+			      double gain)
+{
+	double ySum = 0.0;
+
+	/* Sum the averages, saturated to 255. */
+	for (unsigned int aeCell = 0; aeCell < numCells_; aeCell++)
+		ySum += std::min(ae->exp_mean[aeCell] * gain, 255.0);
+
+	/* \todo Weight with the AWB gains */
+
+	return ySum / numCells_ / 255;
+}
+
+/**
+ * \brief Process RkISP1 statistics, and run AGC operations
+ * \param[in] context The shared IPA context
+ * \param[in] stats The RKISP1 statistics and ISP results
+ *
+ * Identify the current image brightness, and use that to estimate the optimal
+ * new exposure and gain for the scene.
+ */
+void Agc::process(IPAContext &context, const rkisp1_stat_buffer *stats)
+{
+	const rkisp1_cif_isp_stat *params = &stats->params;
+	ASSERT(stats->meas_type & RKISP1_CIF_ISP_STAT_AUTOEXP);
+
+	const rkisp1_cif_isp_ae_stat *ae = &params->ae;
+
+	/*
+	 * Estimate the gain needed to achieve a relative luminance target. To
+	 * account for non-linearity caused by saturation, the value needs to be
+	 * estimated in an iterative process, as multiplying by a gain will not
+	 * increase the relative luminance by the same factor if some image
+	 * regions are saturated.
+	 */
+	double yGain = 1.0;
+	double yTarget = kRelativeLuminanceTarget;
+
+	for (unsigned int i = 0; i < 8; i++) {
+		double yValue = estimateLuminance(ae, yGain);
+		double extra_gain = std::min(10.0, yTarget / (yValue + .001));
+
+		yGain *= extra_gain;
+		LOG(RkISP1Agc, Debug) << "Y value: " << yValue
+				      << ", Y target: " << yTarget
+				      << ", gives gain " << yGain;
+		if (extra_gain < 1.01)
+			break;
+	}
+
+	computeExposure(context, yGain);
+	frameCount_++;
+}
+
+} /* namespace ipa::rkisp1::algorithms */
+
+} /* namespace libcamera */

src/ipa/rkisp1/algorithms/agc.h

@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Ideas On Board
+ *
+ * agc.h - RkISP1 AGC/AEC mean-based control algorithm
+ */
+
+#pragma once
+
+#include <linux/rkisp1-config.h>
+
+#include <libcamera/base/utils.h>
+
+#include <libcamera/geometry.h>
+
+#include "algorithm.h"
+
+namespace libcamera {
+
+struct IPACameraSensorInfo;
+
+namespace ipa::rkisp1::algorithms {
+
+class Agc : public Algorithm
+{
+public:
+	Agc();
+	~Agc() = default;
+
+	int configure(IPAContext &context, const IPACameraSensorInfo &configInfo) override;
+	void process(IPAContext &context, const rkisp1_stat_buffer *stats) override;
+
+private:
+	void computeExposure(IPAContext &Context, double yGain);
+	utils::Duration filterExposure(utils::Duration exposureValue);
+	double estimateLuminance(const rkisp1_cif_isp_ae_stat *ae, double gain);
+
+	uint64_t frameCount_;
+
+	uint32_t numCells_;
+
+	utils::Duration filteredExposure_;
+};
+
+} /* namespace ipa::rkisp1::algorithms */
+} /* namespace libcamera */

src/ipa/rkisp1/algorithms/meson.build

@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: CC0-1.0
 
 rkisp1_ipa_algorithms = files([
+    'agc.cpp',
 ])

src/ipa/rkisp1/ipa_context.cpp

@@ -56,6 +56,21 @@ namespace libcamera::ipa::rkisp1 {
  */
 
 /**
+ * \var IPASessionConfiguration::agc
+ * \brief AGC parameters configuration of the IPA
+ *
+ * \var IPASessionConfiguration::agc.minShutterSpeed
+ * \brief Minimum shutter speed supported with the configured sensor
+ *
+ * \var IPASessionConfiguration::agc.maxShutterSpeed
+ * \brief Maximum shutter speed supported with the configured sensor
+ *
+ * \var IPASessionConfiguration::agc.minAnalogueGain
+ * \brief Minimum analogue gain supported with the configured sensor
+ *
+ * \var IPASessionConfiguration::agc.maxAnalogueGain
+ * \brief Maximum analogue gain supported with the configured sensor
+ *
  * \var IPASessionConfiguration::hw
  * \brief RkISP1-specific hardware information
  *
@@ -63,4 +78,39 @@ namespace libcamera::ipa::rkisp1 {
  * \brief Hardware revision of the ISP
  */
 
+/**
+ * \var IPASessionConfiguration::sensor
+ * \brief Sensor-specific configuration of the IPA
+ *
+ * \var IPASessionConfiguration::sensor.lineDuration
+ * \brief Line duration in microseconds
+ */
+
+/**
+ * \var IPAFrameContext::agc
+ * \brief Context for the Automatic Gain Control algorithm
+ *
+ * The exposure and gain determined are expected to be applied to the sensor
+ * at the earliest opportunity.
+ *
+ * \var IPAFrameContext::agc.exposure
+ * \brief Exposure time expressed as a number of lines
+ *
+ * \var IPAFrameContext::agc.gain
+ * \brief Analogue gain multiplier
+ *
+ * The gain should be adapted to the sensor specific gain code before applying.
+ */
+
+/**
+ * \var IPAFrameContext::sensor
+ * \brief Effective sensor values
+ *
+ * \var IPAFrameContext::sensor.exposure
+ * \brief Exposure time expressed as a number of lines
+ *
+ * \var IPAFrameContext::sensor.gain
+ * \brief Analogue gain multiplier
+ */
+
 } /* namespace libcamera::ipa::rkisp1 */

src/ipa/rkisp1/ipa_context.h

@@ -10,17 +10,39 @@
 
 #include <linux/rkisp1-config.h>
 
+#include <libcamera/base/utils.h>
+
 namespace libcamera {
 
 namespace ipa::rkisp1 {
 
 struct IPASessionConfiguration {
+	struct {
+		utils::Duration minShutterSpeed;
+		utils::Duration maxShutterSpeed;
+		double minAnalogueGain;
+		double maxAnalogueGain;
+	} agc;
+
+	struct {
+		utils::Duration lineDuration;
+	} sensor;
+
 	struct {
 		rkisp1_cif_isp_version revision;
 	} hw;
 };
 
 struct IPAFrameContext {
+	struct {
+		uint32_t exposure;
+		double gain;
+	} agc;
+
+	struct {
+		uint32_t exposure;
+		double gain;
+	} sensor;
 };
 
 struct IPAContext {

src/ipa/rkisp1/rkisp1.cpp

@@ -25,6 +25,7 @@
 
 #include <libcamera/internal/mapped_framebuffer.h>
 
+#include "algorithms/agc.h"
 #include "algorithms/algorithm.h"
 #include "libipa/camera_sensor_helper.h"
 
@@ -34,6 +35,8 @@ namespace libcamera {
 
 LOG_DEFINE_CATEGORY(IPARkISP1)
 
+using namespace std::literals::chrono_literals;
+
 namespace ipa::rkisp1 {
 
 class IPARkISP1 : public IPARkISP1Interface
@@ -66,16 +69,13 @@ private:
 
 	/* Camera sensor controls. */
 	bool autoExposure_;
-	uint32_t exposure_;
 	uint32_t minExposure_;
 	uint32_t maxExposure_;
-	uint32_t gain_;
 	uint32_t minGain_;
 	uint32_t maxGain_;
 
 	/* revision-specific data */
 	rkisp1_cif_isp_version hwRevision_;
-	unsigned int hwAeMeanMax_;
 	unsigned int hwHistBinNMax_;
 	unsigned int hwGammaOutMaxSamples_;
 	unsigned int hwHistogramWeightGridsSize_;
@@ -95,13 +95,11 @@ int IPARkISP1::init(const IPASettings &settings, unsigned int hwRevision)
 	/* \todo Add support for other revisions */
 	switch (hwRevision) {
 	case RKISP1_V10:
-		hwAeMeanMax_ = RKISP1_CIF_ISP_AE_MEAN_MAX_V10;
 		hwHistBinNMax_ = RKISP1_CIF_ISP_HIST_BIN_N_MAX_V10;
 		hwGammaOutMaxSamples_ = RKISP1_CIF_ISP_GAMMA_OUT_MAX_SAMPLES_V10;
 		hwHistogramWeightGridsSize_ = RKISP1_CIF_ISP_HISTOGRAM_WEIGHT_GRIDS_SIZE_V10;
 		break;
 	case RKISP1_V12:
-		hwAeMeanMax_ = RKISP1_CIF_ISP_AE_MEAN_MAX_V12;
 		hwHistBinNMax_ = RKISP1_CIF_ISP_HIST_BIN_N_MAX_V12;
 		hwGammaOutMaxSamples_ = RKISP1_CIF_ISP_GAMMA_OUT_MAX_SAMPLES_V12;
 		hwHistogramWeightGridsSize_ = RKISP1_CIF_ISP_HISTOGRAM_WEIGHT_GRIDS_SIZE_V12;
@@ -126,6 +124,9 @@ int IPARkISP1::init(const IPASettings &settings, unsigned int hwRevision)
 		return -ENODEV;
 	}
 
+	/* Construct our Algorithms */
+	algorithms_.push_back(std::make_unique<algorithms::Agc>());
+
 	return 0;
 }
 
@@ -167,11 +168,9 @@ int IPARkISP1::configure([[maybe_unused]] const IPACameraSensorInfo &info,
 
 	minExposure_ = itExp->second.min().get<int32_t>();
 	maxExposure_ = itExp->second.max().get<int32_t>();
-	exposure_ = minExposure_;
 
 	minGain_ = itGain->second.min().get<int32_t>();
 	maxGain_ = itGain->second.max().get<int32_t>();
-	gain_ = minGain_;
 
 	LOG(IPARkISP1, Info)
 		<< "Exposure: " << minExposure_ << "-" << maxExposure_
@@ -183,6 +182,26 @@ int IPARkISP1::configure([[maybe_unused]] const IPACameraSensorInfo &info,
 	/* Set the hardware revision for the algorithms. */
 	context_.configuration.hw.revision = hwRevision_;
 
+	context_.configuration.sensor.lineDuration = info.lineLength * 1.0s / info.pixelRate;
+
+	/*
+	 * When the AGC computes the new exposure values for a frame, it needs
+	 * to know the limits for shutter speed and analogue gain.
+	 * As it depends on the sensor, update it with the controls.
+	 *
+	 * \todo take VBLANK into account for maximum shutter speed
+	 */
+	context_.configuration.agc.minShutterSpeed = minExposure_ * context_.configuration.sensor.lineDuration;
+	context_.configuration.agc.maxShutterSpeed = maxExposure_ * context_.configuration.sensor.lineDuration;
+	context_.configuration.agc.minAnalogueGain = camHelper_->gain(minGain_);
+	context_.configuration.agc.maxAnalogueGain = camHelper_->gain(maxGain_);
+
+	for (auto const &algo : algorithms_) {
+		int ret = algo->configure(context_, info);
+		if (ret)
+			return ret;
+	}
+
 	return 0;
 }
 
@@ -227,6 +246,11 @@ void IPARkISP1::processEvent(const RkISP1Event &event)
 			reinterpret_cast<rkisp1_stat_buffer *>(
 				mappedBuffers_.at(bufferId).planes()[0].data());
 
+		context_.frameContext.sensor.exposure =
+			event.sensorControls.get(V4L2_CID_EXPOSURE).get<int32_t>();
+		context_.frameContext.sensor.gain =
+			camHelper_->gain(event.sensorControls.get(V4L2_CID_ANALOGUE_GAIN).get<int32_t>());
+
 		updateStatistics(frame, stats);
 		break;
 	}
@@ -271,44 +295,12 @@ void IPARkISP1::queueRequest(unsigned int frame, rkisp1_params_cfg *params,
 void IPARkISP1::updateStatistics(unsigned int frame,
 				 const rkisp1_stat_buffer *stats)
 {
-	const rkisp1_cif_isp_stat *params = &stats->params;
 	unsigned int aeState = 0;
 
-	if (stats->meas_type & RKISP1_CIF_ISP_STAT_AUTOEXP) {
+	for (auto const &algo : algorithms_)
-		const rkisp1_cif_isp_ae_stat *ae = &params->ae;
+		algo->process(context_, stats);
 
-		const unsigned int target = 60;
+	setControls(frame);
-
-		unsigned int value = 0;
-		unsigned int num = 0;
-		for (unsigned int i = 0; i < hwAeMeanMax_; i++) {
-			if (ae->exp_mean[i] <= 15)
-				continue;
-
-			value += ae->exp_mean[i];
-			num++;
-		}
-		value /= num;
-
-		double factor = (double)target / value;
-
-		if (frame % 3 == 0) {
-			double exposure;
-
-			exposure = factor * exposure_ * gain_ / minGain_;
-			exposure_ = std::clamp<uint64_t>((uint64_t)exposure,
-							 minExposure_,
-							 maxExposure_);
-
-			exposure = exposure / exposure_ * minGain_;
-			gain_ = std::clamp<uint64_t>((uint64_t)exposure,
-						     minGain_, maxGain_);
-
-			setControls(frame + 1);
-		}
-
-		aeState = fabs(factor - 1.0f) < 0.05f ? 2 : 1;
-	}
 
 	metadataReady(frame, aeState);
 }
@@ -318,9 +310,12 @@ void IPARkISP1::setControls(unsigned int frame)
 	RkISP1Action op;
 	op.op = ActionV4L2Set;
 
+	uint32_t exposure = context_.frameContext.agc.exposure;
+	uint32_t gain = camHelper_->gainCode(context_.frameContext.agc.gain);
+
 	ControlList ctrls(ctrls_);
-	ctrls.set(V4L2_CID_EXPOSURE, static_cast<int32_t>(exposure_));
+	ctrls.set(V4L2_CID_EXPOSURE, static_cast<int32_t>(exposure));
-	ctrls.set(V4L2_CID_ANALOGUE_GAIN, static_cast<int32_t>(gain_));
+	ctrls.set(V4L2_CID_ANALOGUE_GAIN, static_cast<int32_t>(gain));
 	op.sensorControls = ctrls;
 
 	queueFrameAction.emit(frame, op);