libcamera: software_isp: Move exposure+gain to an algorithm module

This is the last step to fully convert software ISP to Algorithm-based
processing.

The newly introduced frameContext.sensor parameters are set, and the
updated code moved, before calling Algorithm::process() to have the
values up-to-date in stats processing.

Resolves software ISP TODO #10.

Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

8 files changed, 228 insertions, 137 deletions

diff --git a/src/ipa/simple/algorithms/agc.cpp b/src/ipa/simple/algorithms/agc.cpp
new file mode 100644
index 00000000..783dfb8b
--- /dev/null
+++ b/src/ipa/simple/algorithms/agc.cpp
@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Red Hat Inc.
+ *
+ * Exposure and gain
+ */
+
+#include "agc.h"
+
+#include <stdint.h>
+
+#include <libcamera/base/log.h>
+
+namespace libcamera {
+
+LOG_DEFINE_CATEGORY(IPASoftExposure)
+
+namespace ipa::soft::algorithms {
+
+/*
+ * The number of bins to use for the optimal exposure calculations.
+ */
+static constexpr unsigned int kExposureBinsCount = 5;
+
+/*
+ * The exposure is optimal when the mean sample value of the histogram is
+ * in the middle of the range.
+ */
+static constexpr float kExposureOptimal = kExposureBinsCount / 2.0;
+
+/*
+ * The below value implements the hysteresis for the exposure adjustment.
+ * It is small enough to have the exposure close to the optimal, and is big
+ * enough to prevent the exposure from wobbling around the optimal value.
+ */
+static constexpr float kExposureSatisfactory = 0.2;
+
+Agc::Agc()
+{
+}
+
+void Agc::updateExposure(IPAContext &context, double exposureMSV)
+{
+	/*
+	 * kExpDenominator of 10 gives ~10% increment/decrement;
+	 * kExpDenominator of 5 - about ~20%
+	 */
+	static constexpr uint8_t kExpDenominator = 10;
+	static constexpr uint8_t kExpNumeratorUp = kExpDenominator + 1;
+	static constexpr uint8_t kExpNumeratorDown = kExpDenominator - 1;
+
+	double next;
+	int32_t &exposure = context.activeState.agc.exposure;
+	double &again = context.activeState.agc.again;
+
+	if (exposureMSV < kExposureOptimal - kExposureSatisfactory) {
+		next = exposure * kExpNumeratorUp / kExpDenominator;
+		if (next - exposure < 1)
+			exposure += 1;
+		else
+			exposure = next;
+		if (exposure >= context.configuration.agc.exposureMax) {
+			next = again * kExpNumeratorUp / kExpDenominator;
+			if (next - again < context.configuration.agc.againMinStep)
+				again += context.configuration.agc.againMinStep;
+			else
+				again = next;
+		}
+	}
+
+	if (exposureMSV > kExposureOptimal + kExposureSatisfactory) {
+		if (exposure == context.configuration.agc.exposureMax &&
+		    again > context.configuration.agc.againMin) {
+			next = again * kExpNumeratorDown / kExpDenominator;
+			if (again - next < context.configuration.agc.againMinStep)
+				again -= context.configuration.agc.againMinStep;
+			else
+				again = next;
+		} else {
+			next = exposure * kExpNumeratorDown / kExpDenominator;
+			if (exposure - next < 1)
+				exposure -= 1;
+			else
+				exposure = next;
+		}
+	}
+
+	exposure = std::clamp(exposure, context.configuration.agc.exposureMin,
+			      context.configuration.agc.exposureMax);
+	again = std::clamp(again, context.configuration.agc.againMin,
+			   context.configuration.agc.againMax);
+
+	LOG(IPASoftExposure, Debug)
+		<< "exposureMSV " << exposureMSV
+		<< " exp " << exposure << " again " << again;
+}
+
+void Agc::process(IPAContext &context,
+		  [[maybe_unused]] const uint32_t frame,
+		  [[maybe_unused]] IPAFrameContext &frameContext,
+		  const SwIspStats *stats,
+		  [[maybe_unused]] ControlList &metadata)
+{
+	/*
+	 * Calculate Mean Sample Value (MSV) according to formula from:
+	 * https://www.araa.asn.au/acra/acra2007/papers/paper84final.pdf
+	 */
+	const auto &histogram = stats->yHistogram;
+	const unsigned int blackLevelHistIdx =
+		context.activeState.blc.level / (256 / SwIspStats::kYHistogramSize);
+	const unsigned int histogramSize =
+		SwIspStats::kYHistogramSize - blackLevelHistIdx;
+	const unsigned int yHistValsPerBin = histogramSize / kExposureBinsCount;
+	const unsigned int yHistValsPerBinMod =
+		histogramSize / (histogramSize % kExposureBinsCount + 1);
+	int exposureBins[kExposureBinsCount] = {};
+	unsigned int denom = 0;
+	unsigned int num = 0;
+
+	for (unsigned int i = 0; i < histogramSize; i++) {
+		unsigned int idx = (i - (i / yHistValsPerBinMod)) / yHistValsPerBin;
+		exposureBins[idx] += histogram[blackLevelHistIdx + i];
+	}
+
+	for (unsigned int i = 0; i < kExposureBinsCount; i++) {
+		LOG(IPASoftExposure, Debug) << i << ": " << exposureBins[i];
+		denom += exposureBins[i];
+		num += exposureBins[i] * (i + 1);
+	}
+
+	float exposureMSV = (denom == 0 ? 0 : static_cast<float>(num) / denom);
+	updateExposure(context, exposureMSV);
+}
+
+REGISTER_IPA_ALGORITHM(Agc, "Agc")
+
+} /* namespace ipa::soft::algorithms */
+
+} /* namespace libcamera */
diff --git a/src/ipa/simple/algorithms/agc.h b/src/ipa/simple/algorithms/agc.h
new file mode 100644
index 00000000..ad5fca9f
--- /dev/null
+++ b/src/ipa/simple/algorithms/agc.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Red Hat Inc.
+ *
+ * Exposure and gain
+ */
+
+#pragma once
+
+#include "algorithm.h"
+
+namespace libcamera {
+
+namespace ipa::soft::algorithms {
+
+class Agc : public Algorithm
+{
+public:
+	Agc();
+	~Agc() = default;
+
+	void process(IPAContext &context, const uint32_t frame,
+		     IPAFrameContext &frameContext,
+		     const SwIspStats *stats,
+		     ControlList &metadata) override;
+
+private:
+	void updateExposure(IPAContext &context, double exposureMSV);
+};
+
+} /* namespace ipa::soft::algorithms */
+
+} /* namespace libcamera */
diff --git a/src/ipa/simple/algorithms/meson.build b/src/ipa/simple/algorithms/meson.build
index f575611e..37a2eb53 100644
--- a/src/ipa/simple/algorithms/meson.build
+++ b/src/ipa/simple/algorithms/meson.build
@@ -2,6 +2,7 @@
 
 soft_simple_ipa_algorithms = files([
     'awb.cpp',
+    'agc.cpp',
     'blc.cpp',
     'lut.cpp',
 ])
diff --git a/src/ipa/simple/data/uncalibrated.yaml b/src/ipa/simple/data/uncalibrated.yaml
index 893a0b92..3f147112 100644
--- a/src/ipa/simple/data/uncalibrated.yaml
+++ b/src/ipa/simple/data/uncalibrated.yaml
@@ -6,4 +6,5 @@ algorithms:
   - BlackLevel:
   - Awb:
   - Lut:
+  - Agc:
 ...
diff --git a/src/ipa/simple/ipa_context.cpp b/src/ipa/simple/ipa_context.cpp
index 5fa492cb..3f94bbeb 100644
--- a/src/ipa/simple/ipa_context.cpp
+++ b/src/ipa/simple/ipa_context.cpp
@@ -78,6 +78,17 @@ namespace libcamera::ipa::soft {
  */
 
 /**
+ * \var IPAActiveState::agc
+ * \brief Context for the AGC algorithm
+ *
+ * \var IPAActiveState::agc.exposure
+ * \brief Current exposure value
+ *
+ * \var IPAActiveState::agc.again
+ * \brief Current analog gain value
+ */
+
+/**
  * \var IPAActiveState::gamma
  * \brief Context for gamma in the Colors algorithm
  *
diff --git a/src/ipa/simple/ipa_context.h b/src/ipa/simple/ipa_context.h
index cf1ef3fd..3519f20f 100644
--- a/src/ipa/simple/ipa_context.h
+++ b/src/ipa/simple/ipa_context.h
@@ -18,6 +18,10 @@ namespace ipa::soft {
 
 struct IPASessionConfiguration {
 	float gamma;
+	struct {
+		int32_t exposureMin, exposureMax;
+		double againMin, againMax, againMinStep;
+	} agc;
 };
 
 struct IPAActiveState {
@@ -31,6 +35,11 @@ struct IPAActiveState {
 		double blue;
 	} gains;
 
+	struct {
+		int32_t exposure;
+		double again;
+	} agc;
+
 	static constexpr unsigned int kGammaLookupSize = 1024;
 	struct {
 		std::array<double, kGammaLookupSize> gammaTable;
@@ -39,6 +48,10 @@ struct IPAActiveState {
 };
 
 struct IPAFrameContext : public FrameContext {
+	struct {
+		uint32_t exposure;
+		double gain;
+	} sensor;
 };
 
 struct IPAContext {
diff --git a/src/ipa/simple/soft_simple.cpp b/src/ipa/simple/soft_simple.cpp
index 60310a8e..b28c7039 100644
--- a/src/ipa/simple/soft_simple.cpp
+++ b/src/ipa/simple/soft_simple.cpp
@@ -34,23 +34,6 @@ LOG_DEFINE_CATEGORY(IPASoft)
 
 namespace ipa::soft {
 
-/*
- * The number of bins to use for the optimal exposure calculations.
- */
-static constexpr unsigned int kExposureBinsCount = 5;
-
-/*
- * The exposure is optimal when the mean sample value of the histogram is
- * in the middle of the range.
- */
-static constexpr float kExposureOptimal = kExposureBinsCount / 2.0;
-
-/*
- * The below value implements the hysteresis for the exposure adjustment.
- * It is small enough to have the exposure close to the optimal, and is big
- * enough to prevent the exposure from wobbling around the optimal value.
- */
-static constexpr float kExposureSatisfactory = 0.2;
 /* Maximum number of frame contexts to be held */
 static constexpr uint32_t kMaxFrameContexts = 16;
 
@@ -58,8 +41,7 @@ class IPASoftSimple : public ipa::soft::IPASoftInterface, public Module
 {
 public:
 	IPASoftSimple()
-		: params_(nullptr), stats_(nullptr),
-		  context_({ {}, {}, { kMaxFrameContexts } })
+		: context_({ {}, {}, { kMaxFrameContexts } })
 	{
 	}
 
@@ -92,11 +74,6 @@ private:
 
 	/* Local parameter storage */
 	struct IPAContext context_;
-
-	int32_t exposureMin_, exposureMax_;
-	int32_t exposure_;
-	double againMin_, againMax_, againMinStep_;
-	double again_;
 };
 
 IPASoftSimple::~IPASoftSimple()
@@ -207,20 +184,23 @@ int IPASoftSimple::configure(const IPAConfigInfo &configInfo)
 	const ControlInfo &exposureInfo = sensorInfoMap_.find(V4L2_CID_EXPOSURE)->second;
 	const ControlInfo &gainInfo = sensorInfoMap_.find(V4L2_CID_ANALOGUE_GAIN)->second;
 
-	exposureMin_ = exposureInfo.min().get<int32_t>();
-	exposureMax_ = exposureInfo.max().get<int32_t>();
-	if (!exposureMin_) {
+	context_.configuration.agc.exposureMin = exposureInfo.min().get<int32_t>();
+	context_.configuration.agc.exposureMax = exposureInfo.max().get<int32_t>();
+	if (!context_.configuration.agc.exposureMin) {
 		LOG(IPASoft, Warning) << "Minimum exposure is zero, that can't be linear";
-		exposureMin_ = 1;
+		context_.configuration.agc.exposureMin = 1;
 	}
 
 	int32_t againMin = gainInfo.min().get<int32_t>();
 	int32_t againMax = gainInfo.max().get<int32_t>();
 
 	if (camHelper_) {
-		againMin_ = camHelper_->gain(againMin);
-		againMax_ = camHelper_->gain(againMax);
-		againMinStep_ = (againMax_ - againMin_) / 100.0;
+		context_.configuration.agc.againMin = camHelper_->gain(againMin);
+		context_.configuration.agc.againMax = camHelper_->gain(againMax);
+		context_.configuration.agc.againMinStep =
+			(context_.configuration.agc.againMax -
+			 context_.configuration.agc.againMin) /
+			100.0;
 	} else {
 		/*
 		 * The camera sensor gain (g) is usually not equal to the value written
@@ -232,13 +212,14 @@ int IPASoftSimple::configure(const IPAConfigInfo &configInfo)
 		 * the AGC algorithm (abrupt near one edge, and very small near the
 		 * other) we limit the range of the gain values used.
 		 */
-		againMax_ = againMax;
+		context_.configuration.agc.againMax = againMax;
 		if (!againMin) {
 			LOG(IPASoft, Warning)
 				<< "Minimum gain is zero, that can't be linear";
-			againMin_ = std::min(100, againMin / 2 + againMax / 2);
+			context_.configuration.agc.againMin =
+				std::min(100, againMin / 2 + againMax / 2);
 		}
-		againMinStep_ = 1.0;
+		context_.configuration.agc.againMinStep = 1.0;
 	}
 
 	for (auto const &algo : algorithms()) {
@@ -247,9 +228,12 @@ int IPASoftSimple::configure(const IPAConfigInfo &configInfo)
 			return ret;
 	}
 
-	LOG(IPASoft, Info) << "Exposure " << exposureMin_ << "-" << exposureMax_
-			   << ", gain " << againMin_ << "-" << againMax_
-			   << " (" << againMinStep_ << ")";
+	LOG(IPASoft, Info)
+		<< "Exposure " << context_.configuration.agc.exposureMin << "-"
+		<< context_.configuration.agc.exposureMax
+		<< ", gain " << context_.configuration.agc.againMin << "-"
+		<< context_.configuration.agc.againMax
+		<< " (" << context_.configuration.agc.againMinStep << ")";
 
 	return 0;
 }
@@ -284,6 +268,12 @@ void IPASoftSimple::processStats(const uint32_t frame,
 				 const ControlList &sensorControls)
 {
 	IPAFrameContext &frameContext = context_.frameContexts.get(frame);
+
+	frameContext.sensor.exposure =
+		sensorControls.get(V4L2_CID_EXPOSURE).get<int32_t>();
+	int32_t again = sensorControls.get(V4L2_CID_ANALOGUE_GAIN).get<int32_t>();
+	frameContext.sensor.gain = camHelper_ ? camHelper_->gain(again) : again;
+
 	/*
 	 * Software ISP currently does not produce any metadata. Use an empty
 	 * ControlList for now.
@@ -294,37 +284,6 @@ void IPASoftSimple::processStats(const uint32_t frame,
 	for (auto const &algo : algorithms())
 		algo->process(context_, frame, frameContext, stats_, metadata);
 
-	/* \todo Switch to the libipa/algorithm.h API someday. */
-
-	/*
-	 * Calculate Mean Sample Value (MSV) according to formula from:
-	 * https://www.araa.asn.au/acra/acra2007/papers/paper84final.pdf
-	 */
-	const uint8_t blackLevel = context_.activeState.blc.level;
-	const unsigned int blackLevelHistIdx =
-		blackLevel / (256 / SwIspStats::kYHistogramSize);
-	const unsigned int histogramSize =
-		SwIspStats::kYHistogramSize - blackLevelHistIdx;
-	const unsigned int yHistValsPerBin = histogramSize / kExposureBinsCount;
-	const unsigned int yHistValsPerBinMod =
-		histogramSize / (histogramSize % kExposureBinsCount + 1);
-	int exposureBins[kExposureBinsCount] = {};
-	unsigned int denom = 0;
-	unsigned int num = 0;
-
-	for (unsigned int i = 0; i < histogramSize; i++) {
-		unsigned int idx = (i - (i / yHistValsPerBinMod)) / yHistValsPerBin;
-		exposureBins[idx] += stats_->yHistogram[blackLevelHistIdx + i];
-	}
-
-	for (unsigned int i = 0; i < kExposureBinsCount; i++) {
-		LOG(IPASoft, Debug) << i << ": " << exposureBins[i];
-		denom += exposureBins[i];
-		num += exposureBins[i] * (i + 1);
-	}
-
-	float exposureMSV = static_cast<float>(num) / denom;
-
 	/* Sanity check */
 	if (!sensorControls.contains(V4L2_CID_EXPOSURE) ||
 	    !sensorControls.contains(V4L2_CID_ANALOGUE_GAIN)) {
@@ -332,70 +291,14 @@ void IPASoftSimple::processStats(const uint32_t frame,
 		return;
 	}
 
-	exposure_ = sensorControls.get(V4L2_CID_EXPOSURE).get<int32_t>();
-	int32_t again = sensorControls.get(V4L2_CID_ANALOGUE_GAIN).get<int32_t>();
-	again_ = camHelper_ ? camHelper_->gain(again) : again;
-
-	updateExposure(exposureMSV);
-
 	ControlList ctrls(sensorInfoMap_);
 
-	ctrls.set(V4L2_CID_EXPOSURE, exposure_);
+	auto &againNew = context_.activeState.agc.again;
+	ctrls.set(V4L2_CID_EXPOSURE, context_.activeState.agc.exposure);
 	ctrls.set(V4L2_CID_ANALOGUE_GAIN,
-		  static_cast<int32_t>(camHelper_ ? camHelper_->gainCode(again_) : again_));
+		  static_cast<int32_t>(camHelper_ ? camHelper_->gainCode(againNew) : againNew));
 
 	setSensorControls.emit(ctrls);
-
-	LOG(IPASoft, Debug) << "exposureMSV " << exposureMSV
-			    << " exp " << exposure_ << " again " << again_
-			    << " black level " << static_cast<unsigned int>(blackLevel);
-}
-
-void IPASoftSimple::updateExposure(double exposureMSV)
-{
-	/*
-	 * kExpDenominator of 10 gives ~10% increment/decrement;
-	 * kExpDenominator of 5 - about ~20%
-	 */
-	static constexpr uint8_t kExpDenominator = 10;
-	static constexpr uint8_t kExpNumeratorUp = kExpDenominator + 1;
-	static constexpr uint8_t kExpNumeratorDown = kExpDenominator - 1;
-
-	double next;
-
-	if (exposureMSV < kExposureOptimal - kExposureSatisfactory) {
-		next = exposure_ * kExpNumeratorUp / kExpDenominator;
-		if (next - exposure_ < 1)
-			exposure_ += 1;
-		else
-			exposure_ = next;
-		if (exposure_ >= exposureMax_) {
-			next = again_ * kExpNumeratorUp / kExpDenominator;
-			if (next - again_ < againMinStep_)
-				again_ += againMinStep_;
-			else
-				again_ = next;
-		}
-	}
-
-	if (exposureMSV > kExposureOptimal + kExposureSatisfactory) {
-		if (exposure_ == exposureMax_ && again_ > againMin_) {
-			next = again_ * kExpNumeratorDown / kExpDenominator;
-			if (again_ - next < againMinStep_)
-				again_ -= againMinStep_;
-			else
-				again_ = next;
-		} else {
-			next = exposure_ * kExpNumeratorDown / kExpDenominator;
-			if (exposure_ - next < 1)
-				exposure_ -= 1;
-			else
-				exposure_ = next;
-		}
-	}
-
-	exposure_ = std::clamp(exposure_, exposureMin_, exposureMax_);
-	again_ = std::clamp(again_, againMin_, againMax_);
 }
 
 std::string IPASoftSimple::logPrefix() const
diff --git a/src/libcamera/software_isp/TODO b/src/libcamera/software_isp/TODO
index 8eeede46..a50db668 100644
--- a/src/libcamera/software_isp/TODO
+++ b/src/libcamera/software_isp/TODO
@@ -199,16 +199,6 @@ Yes, because, well... all the other IPAs were doing that...
 
 ---
 
-10. Switch to libipa/algorithm.h API in processStats
-
->> void IPASoftSimple::processStats(const ControlList &sensorControls)
->>
-> Do you envision switching to the libipa/algorithm.h API at some point ?
-
-At some point, yes.
-
----
-
 13. Improve black level and colour gains application
 
 I think the black level should eventually be moved before debayering, and