ipa: rpi: agc: Use channel constraints in the AGC algorithm

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@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

src/ipa/rpi/controller/rpi/agc.cpp

@@ -39,6 +39,7 @@ 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());
 	}
@@ -58,6 +59,8 @@ int Agc::read(const libcamera::YamlObject &params)
 		return -1;
 	}
 
+	channelTotalExposures_.resize(channelData_.size(), 0s);
+
 	return 0;
 }
 
@@ -236,16 +239,22 @@ static void getDelayedChannelIndex(Metadata *metadata, const char *message, unsi
 	}
 }
 
-static void setCurrentChannelIndex(Metadata *metadata, const char *message, unsigned int channelIndex)
+static libcamera::utils::Duration
+setCurrentChannelIndexGetExposure(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)
@@ -310,8 +319,11 @@ void Agc::process(StatisticsPtr &stats, Metadata *imageMetadata)
 		LOG(RPiAgc, Debug) << "process: channel " << channelIndex << " not seen yet";
 	}
 
-	channelData.channel.process(stats, deviceStatus, imageMetadata);
-	setCurrentChannelIndex(imageMetadata, "process: no AGC status found", channelIndex);
+	channelData.channel.process(stats, deviceStatus, imageMetadata, channelTotalExposures_);
+	auto dur = setCurrentChannelIndexGetExposure(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();

src/ipa/rpi/controller/rpi/agc.h

@@ -55,6 +55,7 @@ private:
 	std::vector<AgcChannelData> channelData_;
 	std::vector<unsigned int> activeChannels_;
 	unsigned int index_; /* index into the activeChannels_ */
+	AgcChannelTotalExposures channelTotalExposures_;
 };
 
 } /* namespace RPiController */

src/ipa/rpi/controller/rpi/agc_channel.cpp

@@ -493,7 +493,9 @@ void AgcChannel::prepare(Metadata *imageMetadata)
 	}
 }
 
-void AgcChannel::process(StatisticsPtr &stats, DeviceStatus const &deviceStatus, Metadata *imageMetadata)
+void AgcChannel::process(StatisticsPtr &stats, DeviceStatus const &deviceStatus,
+			 Metadata *imageMetadata,
+			 const AgcChannelTotalExposures &channelTotalExposures)
 {
 	frameCount_++;
 	/*
@@ -513,11 +515,16 @@ void AgcChannel::process(StatisticsPtr &stats, DeviceStatus const &deviceStatus,
 	/* The results have to be filtered so as not to change too rapidly. */
 	filterExposure();
 	/*
-	 * 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.
+	 * 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 desaturate = applyDigitalGain(gain, targetY);
+	bool channelBound = applyChannelConstraints(channelTotalExposures);
+	/*
+	 * Some of the exposure has to be applied as digital gain, so work out
+	 * 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, channelBound);
 	/*
 	 * The last thing is to divide up the exposure value into a shutter time
 	 * and analogue gain, according to the current exposure mode.
@@ -794,7 +801,44 @@ 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 or no exposure available- 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) << "Constraint applies";
+			channelBound = true;
+		} else
+			LOG(RPiAgc, Debug) << "Constraint 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);
@@ -814,8 +858,8 @@ 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;

src/ipa/rpi/controller/rpi/agc_channel.h

@@ -21,6 +21,8 @@
 
 namespace RPiController {
 
+using AgcChannelTotalExposures = std::vector<libcamera::utils::Duration>;
+
 struct AgcMeteringMode {
 	std::vector<double> weights;
 	int read(const libcamera::YamlObject &params);
@@ -95,7 +97,8 @@ public:
 	void disableAuto();
 	void switchMode(CameraMode const &cameraMode, Metadata *metadata);
 	void prepare(Metadata *imageMetadata);
-	void process(StatisticsPtr &stats, DeviceStatus const &deviceStatus, Metadata *imageMetadata);
+	void process(StatisticsPtr &stats, DeviceStatus const &deviceStatus, Metadata *imageMetadata,
+		     const AgcChannelTotalExposures &channelTotalExposures);
 
 private:
 	bool updateLockStatus(DeviceStatus const &deviceStatus);
@@ -107,7 +110,8 @@ 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);