[libcamera-devel] [PATCH v2 5/5] ipa: rpi: agc: Use channel constraints in the AGC algorithm

David Plowman david.plowman at raspberrypi.com
Wed Aug 23 14:09:15 CEST 2023


Whenever we run Agc::process(), we store the most recent total
exposure requested for each channel.

With these values we can apply the channel constraints after
time-filtering the requested total exposure, but before working out
how much digital gain is needed.

Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
Reviewed-by: Naushir Patuck <naush at raspberrypi.com>
---
 src/ipa/rpi/controller/rpi/agc.cpp         | 21 ++++--
 src/ipa/rpi/controller/rpi/agc.h           |  1 +
 src/ipa/rpi/controller/rpi/agc_channel.cpp | 75 +++++++++++++++++++---
 src/ipa/rpi/controller/rpi/agc_channel.h   |  8 ++-
 4 files changed, 88 insertions(+), 17 deletions(-)

diff --git a/src/ipa/rpi/controller/rpi/agc.cpp b/src/ipa/rpi/controller/rpi/agc.cpp
index 7e627bba..3c730d4c 100644
--- a/src/ipa/rpi/controller/rpi/agc.cpp
+++ b/src/ipa/rpi/controller/rpi/agc.cpp
@@ -40,6 +40,7 @@ int Agc::read(const libcamera::YamlObject &params)
 	 */
 	if (!params.contains("channels")) {
 		LOG(RPiAgc, Debug) << "Single channel only";
+		channelTotalExposures_.resize(1, 0s);
 		channelData_.emplace_back();
 		return channelData_.back().channel.read(params, getHardwareConfig());
 	}
@@ -59,6 +60,8 @@ int Agc::read(const libcamera::YamlObject &params)
 		return -1;
 	}
 
+	channelTotalExposures_.resize(channelData_.size(), 0s);
+
 	return 0;
 }
 
@@ -234,15 +237,21 @@ static void getChannelIndex(Metadata *metadata, const char *message, unsigned in
 		LOG(RPiAgc, Debug) << message;
 }
 
-static void setChannelIndex(Metadata *metadata, const char *message, unsigned int channelIndex)
+static libcamera::utils::Duration
+setChannelIndex(Metadata *metadata, const char *message, unsigned int channelIndex)
 {
 	std::unique_lock<RPiController::Metadata> lock(*metadata);
 	AgcStatus *status = metadata->getLocked<AgcStatus>("agc.status");
-	if (status)
+	libcamera::utils::Duration dur = 0s;
+
+	if (status) {
 		status->channel = channelIndex;
-	else
+		dur = status->totalExposureValue;
+	} else
 		/* This does happen at startup, otherwise it would be a Warning or Error. */
 		LOG(RPiAgc, Debug) << message;
+
+	return dur;
 }
 
 void Agc::prepare(Metadata *imageMetadata)
@@ -306,8 +315,10 @@ void Agc::process(StatisticsPtr &stats, Metadata *imageMetadata)
 		/* Can also happen when new channels start. */
 		LOG(RPiAgc, Debug) << "process: channel " << channelIndex << " not seen yet";
 
-	channelData.channel.process(stats, &deviceStatus, imageMetadata);
-	setChannelIndex(imageMetadata, "process: no AGC status found", channelIndex);
+	channelData.channel.process(stats, &deviceStatus, imageMetadata, channelTotalExposures_);
+	auto dur = setChannelIndex(imageMetadata, "process: no AGC status found", channelIndex);
+	if (dur)
+		channelTotalExposures_[channelIndex] = dur;
 
 	/* And onto the next channel for the next call. */
 	index_ = (index_ + 1) % activeChannels_.size();
diff --git a/src/ipa/rpi/controller/rpi/agc.h b/src/ipa/rpi/controller/rpi/agc.h
index 2eed2bab..e301c5cb 100644
--- a/src/ipa/rpi/controller/rpi/agc.h
+++ b/src/ipa/rpi/controller/rpi/agc.h
@@ -54,6 +54,7 @@ private:
 	std::vector<AgcChannelData> channelData_;
 	std::vector<unsigned int> activeChannels_;
 	unsigned int index_; /* index into the activeChannels_ */
+	AgcChannelTotalExposures channelTotalExposures_;
 };
 
 } /* namespace RPiController */
diff --git a/src/ipa/rpi/controller/rpi/agc_channel.cpp b/src/ipa/rpi/controller/rpi/agc_channel.cpp
index 44198c2c..54fd08e8 100644
--- a/src/ipa/rpi/controller/rpi/agc_channel.cpp
+++ b/src/ipa/rpi/controller/rpi/agc_channel.cpp
@@ -175,6 +175,11 @@ readConstraintModes(std::map<std::string, AgcConstraintMode> &constraintModes,
 
 int AgcChannelConstraint::read(const libcamera::YamlObject &params)
 {
+	auto channelValue = params["channel"].get<unsigned int>();
+	if (!channelValue)
+		return -EINVAL;
+	channel = *channelValue;
+
 	std::string boundString = params["bound"].get<std::string>("");
 	transform(boundString.begin(), boundString.end(),
 		  boundString.begin(), ::toupper);
@@ -184,10 +189,10 @@ int AgcChannelConstraint::read(const libcamera::YamlObject &params)
 	}
 	bound = boundString == "UPPER" ? Bound::UPPER : Bound::LOWER;
 
-	auto value = params["factor"].get<double>();
-	if (!value)
+	auto factorValue = params["factor"].get<double>();
+	if (!factorValue)
 		return -EINVAL;
-	factor = *value;
+	factor = *factorValue;
 
 	return 0;
 }
@@ -231,6 +236,7 @@ int AgcConfig::read(const libcamera::YamlObject &params)
 		ret = readChannelConstraints(channelConstraints, params["channel_constraints"]);
 		if (ret)
 			return ret;
+		LOG(RPiAgc, Info) << "Read " << channelConstraints.size() << " channel constraints";
 	}
 
 	ret = yTarget.read(params["y_target"]);
@@ -489,7 +495,9 @@ void AgcChannel::prepare(Metadata *imageMetadata)
 	}
 }
 
-void AgcChannel::process(StatisticsPtr &stats, const DeviceStatus *deviceStatus, Metadata *imageMetadata)
+void AgcChannel::process(StatisticsPtr &stats, const DeviceStatus *deviceStatus,
+			 Metadata *imageMetadata,
+			 const AgcChannelTotalExposures &channelTotalExposures)
 {
 	frameCount_++;
 	/*
@@ -508,12 +516,17 @@ void AgcChannel::process(StatisticsPtr &stats, const DeviceStatus *deviceStatus,
 	computeTargetExposure(gain);
 	/* The results have to be filtered so as not to change too rapidly. */
 	filterExposure();
+	/*
+	 * We may be asked to limit the exposure using other channels. If another channel
+	 * determines our upper bound we may want to know this later.
+	 */
+	bool channelBound = applyChannelConstraints(channelTotalExposures);
 	/*
 	 * Some of the exposure has to be applied as digital gain, so work out
-	 * what that is. This function also tells us whether it's decided to
-	 * "desaturate" the image more quickly.
+	 * what that is. It also tells us whether it's trying to desaturate the image
+	 * more quickly, which can only happen when another channel is not limiting us.
 	 */
-	bool desaturate = applyDigitalGain(gain, targetY);
+	bool desaturate = applyDigitalGain(gain, targetY, channelBound);
 	/*
 	 * The last thing is to divide up the exposure value into a shutter time
 	 * and analogue gain, according to the current exposure mode.
@@ -792,7 +805,49 @@ void AgcChannel::computeTargetExposure(double gain)
 	LOG(RPiAgc, Debug) << "Target totalExposure " << target_.totalExposure;
 }
 
-bool AgcChannel::applyDigitalGain(double gain, double targetY)
+bool AgcChannel::applyChannelConstraints(const AgcChannelTotalExposures &channelTotalExposures)
+{
+	bool channelBound = false;
+	LOG(RPiAgc, Debug)
+		<< "Total exposure before channel constraints " << filtered_.totalExposure;
+
+	for (const auto &constraint : config_.channelConstraints) {
+		LOG(RPiAgc, Debug)
+			<< "Check constraint: channel " << constraint.channel << " bound "
+			<< (constraint.bound == AgcChannelConstraint::Bound::UPPER ? "UPPER" : "LOWER")
+			<< " factor " << constraint.factor;
+		if (constraint.channel >= channelTotalExposures.size() ||
+		    !channelTotalExposures[constraint.channel]) {
+			LOG(RPiAgc, Debug) << "no such channel - skipped";
+			continue;
+		}
+
+		if (channelTotalExposures[constraint.channel] == 0s) {
+			LOG(RPiAgc, Debug) << "zero exposure - skipped";
+			continue;
+		}
+
+		libcamera::utils::Duration limitExposure =
+			channelTotalExposures[constraint.channel] * constraint.factor;
+		LOG(RPiAgc, Debug) << "Limit exposure " << limitExposure;
+		if ((constraint.bound == AgcChannelConstraint::Bound::UPPER &&
+		     filtered_.totalExposure > limitExposure) ||
+		    (constraint.bound == AgcChannelConstraint::Bound::LOWER &&
+		     filtered_.totalExposure < limitExposure)) {
+			filtered_.totalExposure = limitExposure;
+			LOG(RPiAgc, Debug) << "Applies";
+			channelBound = true;
+		} else
+			LOG(RPiAgc, Debug) << "Does not apply";
+	}
+
+	LOG(RPiAgc, Debug)
+		<< "Total exposure after channel constraints " << filtered_.totalExposure;
+
+	return channelBound;
+}
+
+bool AgcChannel::applyDigitalGain(double gain, double targetY, bool channelBound)
 {
 	double minColourGain = std::min({ awb_.gainR, awb_.gainG, awb_.gainB, 1.0 });
 	ASSERT(minColourGain != 0.0);
@@ -812,8 +867,8 @@ bool AgcChannel::applyDigitalGain(double gain, double targetY)
 	 * quickly (and we then approach the correct value more quickly from
 	 * below).
 	 */
-	bool desaturate = targetY > config_.fastReduceThreshold &&
-			  gain < sqrt(targetY);
+	bool desaturate = !channelBound &&
+			  targetY > config_.fastReduceThreshold && gain < sqrt(targetY);
 	if (desaturate)
 		dg /= config_.fastReduceThreshold;
 	LOG(RPiAgc, Debug) << "Digital gain " << dg << " desaturate? " << desaturate;
diff --git a/src/ipa/rpi/controller/rpi/agc_channel.h b/src/ipa/rpi/controller/rpi/agc_channel.h
index 446125ef..c3f701eb 100644
--- a/src/ipa/rpi/controller/rpi/agc_channel.h
+++ b/src/ipa/rpi/controller/rpi/agc_channel.h
@@ -19,6 +19,8 @@
 
 namespace RPiController {
 
+using AgcChannelTotalExposures = std::vector<libcamera::utils::Duration>;
+
 struct AgcMeteringMode {
 	std::vector<double> weights;
 	int read(const libcamera::YamlObject &params);
@@ -93,7 +95,8 @@ public:
 	void disableAuto();
 	void switchMode(CameraMode const &cameraMode, Metadata *metadata);
 	void prepare(Metadata *imageMetadata);
-	void process(StatisticsPtr &stats, const DeviceStatus *deviceStatus, Metadata *imageMetadata);
+	void process(StatisticsPtr &stats, const DeviceStatus *deviceStatus, Metadata *imageMetadata,
+		     const AgcChannelTotalExposures &channelTotalExposures);
 
 private:
 	bool updateLockStatus(DeviceStatus const &deviceStatus);
@@ -105,7 +108,8 @@ private:
 			 double &gain, double &targetY);
 	void computeTargetExposure(double gain);
 	void filterExposure();
-	bool applyDigitalGain(double gain, double targetY);
+	bool applyChannelConstraints(const AgcChannelTotalExposures &channelTotalExposures);
+	bool applyDigitalGain(double gain, double targetY, bool channelBound);
 	void divideUpExposure();
 	void writeAndFinish(Metadata *imageMetadata, bool desaturate);
 	libcamera::utils::Duration limitShutter(libcamera::utils::Duration shutter);
-- 
2.30.2



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