libcamera: src: ipa: raspberrypi: agc: Improve AE locked logic

Previously we required that the sensor absolutely reaches the target
exposure, but this can fail if frame rates or analogue gains are
limited. Instead insist only that we get several frames with the same
exposure time, analogue gain and that the algorithm's target exposure
hasn't changed either.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

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

@@ -154,6 +154,7 @@ Agc::Agc(Controller *controller)
 	: AgcAlgorithm(controller), metering_mode_(nullptr),
 	  exposure_mode_(nullptr), constraint_mode_(nullptr),
 	  frame_count_(0), lock_count_(0),
+	  last_target_exposure_(0.0),
 	  ev_(1.0), flicker_period_(0.0),
 	  fixed_shutter_(0), fixed_analogue_gain_(0.0)
 {
@@ -162,6 +163,7 @@ Agc::Agc(Controller *controller)
 	// it's not been calculated yet (i.e. Process hasn't yet run).
 	memset(&status_, 0, sizeof(status_));
 	status_.ev = ev_;
+	memset(&last_device_status_, 0, sizeof(last_device_status_));
 }
 
 char const *Agc::Name() const
@@ -262,8 +264,6 @@ void Agc::SwitchMode([[maybe_unused]] CameraMode const &camera_mode,
 
 void Agc::Prepare(Metadata *image_metadata)
 {
-	int lock_count = lock_count_;
-	lock_count_ = 0;
 	status_.digital_gain = 1.0;
 	fetchAwbStatus(image_metadata); // always fetch it so that Process knows it's been done
 
@@ -287,31 +287,10 @@ void Agc::Prepare(Metadata *image_metadata)
 				LOG(RPiAgc, Debug) << "Use digital_gain " << status_.digital_gain;
 				LOG(RPiAgc, Debug) << "Effective exposure " << actual_exposure * status_.digital_gain;
 				// Decide whether AEC/AGC has converged.
-				// Insist AGC is steady for MAX_LOCK_COUNT
+				updateLockStatus(device_status);
-				// frames before we say we are "locked".
-				// (The hard-coded constants may need to
-				// become customisable.)
-				if (status_.target_exposure_value) {
-#define MAX_LOCK_COUNT 3
-					double err = 0.10 * status_.target_exposure_value + 200;
-					if (actual_exposure <
-						    status_.target_exposure_value + err &&
-					    actual_exposure >
-						    status_.target_exposure_value - err)
-						lock_count_ =
-							std::min(lock_count + 1,
-								 MAX_LOCK_COUNT);
-					else if (actual_exposure <
-							 status_.target_exposure_value + 1.5 * err &&
-						 actual_exposure >
-							 status_.target_exposure_value - 1.5 * err)
-						lock_count_ = lock_count;
-					LOG(RPiAgc, Debug) << "Lock count: " << lock_count_;
-				}
 			}
 		} else
-			LOG(RPiAgc, Debug) << Name() << ": no device metadata";
+			LOG(RPiAgc, Warning) << Name() << ": no device metadata";
-		status_.locked = lock_count_ >= MAX_LOCK_COUNT;
 		image_metadata->Set("agc.status", status_);
 	}
 }
@@ -342,6 +321,43 @@ void Agc::Process(StatisticsPtr &stats, Metadata *image_metadata)
 	writeAndFinish(image_metadata, desaturate);
 }
 
+void Agc::updateLockStatus(DeviceStatus const &device_status)
+{
+	const double ERROR_FACTOR = 0.10; // make these customisable?
+	const int MAX_LOCK_COUNT = 5;
+	// Reset "lock count" when we exceed this multiple of ERROR_FACTOR
+	const double RESET_MARGIN = 1.5;
+
+	// Add 200us to the exposure time error to allow for line quantisation.
+	double exposure_error = last_device_status_.shutter_speed * ERROR_FACTOR + 200;
+	double gain_error = last_device_status_.analogue_gain * ERROR_FACTOR;
+	double target_error = last_target_exposure_ * ERROR_FACTOR;
+
+	// Note that we don't know the exposure/gain limits of the sensor, so
+	// the values we keep requesting may be unachievable. For this reason
+	// we only insist that we're close to values in the past few frames.
+	if (device_status.shutter_speed > last_device_status_.shutter_speed - exposure_error &&
+	    device_status.shutter_speed < last_device_status_.shutter_speed + exposure_error &&
+	    device_status.analogue_gain > last_device_status_.analogue_gain - gain_error &&
+	    device_status.analogue_gain < last_device_status_.analogue_gain + gain_error &&
+	    status_.target_exposure_value > last_target_exposure_ - target_error &&
+	    status_.target_exposure_value < last_target_exposure_ + target_error)
+		lock_count_ = std::min(lock_count_ + 1, MAX_LOCK_COUNT);
+	else if (device_status.shutter_speed < last_device_status_.shutter_speed - RESET_MARGIN * exposure_error ||
+		 device_status.shutter_speed > last_device_status_.shutter_speed + RESET_MARGIN * exposure_error ||
+		 device_status.analogue_gain < last_device_status_.analogue_gain - RESET_MARGIN * gain_error ||
+		 device_status.analogue_gain > last_device_status_.analogue_gain + RESET_MARGIN * gain_error ||
+		 status_.target_exposure_value < last_target_exposure_ - RESET_MARGIN * target_error ||
+		 status_.target_exposure_value > last_target_exposure_ + RESET_MARGIN * target_error)
+		lock_count_ = 0;
+
+	last_device_status_ = device_status;
+	last_target_exposure_ = status_.target_exposure_value;
+
+	LOG(RPiAgc, Debug) << "Lock count updated to " << lock_count_;
+	status_.locked = lock_count_ == MAX_LOCK_COUNT;
+}
+
 static void copy_string(std::string const &s, char *d, size_t size)
 {
 	size_t length = s.copy(d, size - 1);

src/ipa/raspberrypi/controller/rpi/agc.hpp

@@ -82,6 +82,7 @@ public:
 	void Process(StatisticsPtr &stats, Metadata *image_metadata) override;
 
 private:
+	void updateLockStatus(DeviceStatus const &device_status);
 	AgcConfig config_;
 	void housekeepConfig();
 	void fetchCurrentExposure(Metadata *image_metadata);
@@ -111,6 +112,8 @@ private:
 	ExposureValues filtered_; // these values are filtered towards target
 	AgcStatus status_;
 	int lock_count_;
+	DeviceStatus last_device_status_;
+	double last_target_exposure_;
 	// Below here the "settings" that applications can change.
 	std::string metering_mode_name_;
 	std::string exposure_mode_name_;