ipa: ipu3: Remove bespoke AGC functions from IPU3

Now that the IPU3's Agc is derived from MeanLuminanceAgc we can
delete all the unecessary bespoke functions.

Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>
Signed-off-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

2 files changed, 3 insertions, 251 deletions

diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
index b1ba27fe..c9b5548c 100644
--- a/src/ipa/ipu3/algorithms/agc.cpp
+++ b/src/ipa/ipu3/algorithms/agc.cpp
@@ -56,20 +56,6 @@ static constexpr utils::Duration kMaxShutterSpeed = 60ms;
 /* Histogram constants */
 static constexpr uint32_t knumHistogramBins = 256;
 
-/* Target value to reach for the top 2% of the histogram */
-static constexpr double kEvGainTarget = 0.5;
-
-/* 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.
- */
-static constexpr double kRelativeLuminanceTarget = 0.16;
-
 Agc::Agc()
 	: minShutterSpeed_(0s), maxShutterSpeed_(0s)
 {
@@ -125,8 +111,6 @@ int Agc::configure(IPAContext &context,
 	activeState.agc.gain = minAnalogueGain_;
 	activeState.agc.exposure = 10ms / configuration.sensor.lineDuration;
 
-	frameCount_ = 0;
-
 	context.activeState.agc.constraintMode = constraintModes().begin()->first;
 	context.activeState.agc.exposureMode = exposureModeHelpers().begin()->first;
 
@@ -138,42 +122,6 @@ int Agc::configure(IPAContext &context,
 	return 0;
 }
 
-/**
- * \brief Estimate the mean value of the top 2% of the histogram
- * \param[in] stats The statistics computed by the ImgU
- * \param[in] grid The grid used to store the statistics in the IPU3
- * \return The mean value of the top 2% of the histogram
- */
-double Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
-			      const ipu3_uapi_grid_config &grid) const
-{
-	/* Initialise the histogram array */
-	uint32_t hist[knumHistogramBins] = { 0 };
-
-	for (unsigned int cellY = 0; cellY < grid.height; cellY++) {
-		for (unsigned int cellX = 0; cellX < grid.width; cellX++) {
-			uint32_t cellPosition = cellY * stride_ + cellX;
-
-			const ipu3_uapi_awb_set_item *cell =
-				reinterpret_cast<const ipu3_uapi_awb_set_item *>(
-					&stats->awb_raw_buffer.meta_data[cellPosition]
-				);
-
-			uint8_t gr = cell->Gr_avg;
-			uint8_t gb = cell->Gb_avg;
-			/*
-			 * Store the average green value to estimate the
-			 * brightness. Even the overexposed pixels are
-			 * taken into account.
-			 */
-			hist[(gr + gb) / 2]++;
-		}
-	}
-
-	/* Estimate the quantile mean of the top 2% of the histogram. */
-	return Histogram(Span<uint32_t>(hist)).interQuantileMean(0.98, 1.0);
-}
-
 Histogram Agc::parseStatistics(const ipu3_uapi_stats_3a *stats,
 			       const ipu3_uapi_grid_config &grid)
 {
@@ -208,122 +156,8 @@ Histogram Agc::parseStatistics(const ipu3_uapi_stats_3a *stats,
 }
 
 /**
- * \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(IPU3Agc, 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 based on the relative luminance target
- * \param[in] iqMeanGain The gain calculated based on the relative luminance target
- */
-void Agc::computeExposure(IPAContext &context, IPAFrameContext &frameContext,
-			  double yGain, double iqMeanGain)
-{
-	const IPASessionConfiguration &configuration = context.configuration;
-	/* Get the effective exposure and gain applied on the sensor. */
-	uint32_t exposure = frameContext.sensor.exposure;
-	double analogueGain = frameContext.sensor.gain;
-
-	/* Use the highest of the two gain estimates. */
-	double evGain = std::max(yGain, iqMeanGain);
-
-	/* Consider within 1% of the target as correctly exposed */
-	if (utils::abs_diff(evGain, 1.0) < 0.01)
-		LOG(IPU3Agc, Debug) << "We are well exposed (evGain = "
-				    << evGain << ")";
-
-	/* 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(IPU3Agc, Debug) << "Actual total exposure " << currentShutter * analogueGain
-			    << " Shutter speed " << currentShutter
-			    << " Gain " << analogueGain
-			    << " Needed ev gain " << evGain;
-
-	/*
-	 * Calculate the current exposure value for the scene as the latest
-	 * exposure value applied multiplied by the new estimated gain.
-	 */
-	utils::Duration exposureValue = effectiveExposureValue * evGain;
-
-	/* Clamp the exposure value to the min and max authorized */
-	utils::Duration maxTotalExposure = maxShutterSpeed_ * maxAnalogueGain_;
-	exposureValue = std::min(exposureValue, maxTotalExposure);
-	LOG(IPU3Agc, Debug) << "Target total exposure " << exposureValue
-			    << ", maximum is " << maxTotalExposure;
-
-	/*
-	 * Filter the exposure.
-	 * \todo estimate if we need to desaturate
-	 */
-	exposureValue = filterExposure(exposureValue);
-
-	/*
-	 * Divide the exposure value as new exposure and gain values.
-	 *
-	 * 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(IPU3Agc, Debug) << "Divided up shutter and gain are "
-			    << shutterTime << " and "
-			    << stepGain;
-}
-
-/**
  * \brief Estimate the relative luminance of the frame with a given gain
- * \param[in] frameContext The shared IPA frame context
- * \param[in] grid The grid used to store the statistics in the IPU3
- * \param[in] stats The IPU3 statistics and ISP results
- * \param[in] gain The gain to apply to the frame
- * \return The relative luminance
- *
- * This function estimates the average relative luminance of the frame that
- * would be output by the sensor if an additional \a gain was applied.
+ * \param[in] gain The gain to apply in estimating luminance
  *
  * The estimation is based on the AWB statistics for the current frame. Red,
  * green and blue averages for all cells are first multiplied by the gain, and
@@ -338,42 +172,9 @@ void Agc::computeExposure(IPAContext &context, IPAFrameContext &frameContext,
  *
  * More detailed information can be found in:
  * https://en.wikipedia.org/wiki/Relative_luminance
+ *
+ * \return The relative luminance of the frame
  */
-double Agc::estimateLuminance(IPAActiveState &activeState,
-			      const ipu3_uapi_grid_config &grid,
-			      const ipu3_uapi_stats_3a *stats,
-			      double gain)
-{
-	double redSum = 0, greenSum = 0, blueSum = 0;
-
-	/* Sum the per-channel averages, saturated to 255. */
-	for (unsigned int cellY = 0; cellY < grid.height; cellY++) {
-		for (unsigned int cellX = 0; cellX < grid.width; cellX++) {
-			uint32_t cellPosition = cellY * stride_ + cellX;
-
-			const ipu3_uapi_awb_set_item *cell =
-				reinterpret_cast<const ipu3_uapi_awb_set_item *>(
-					&stats->awb_raw_buffer.meta_data[cellPosition]
-				);
-			const uint8_t G_avg = (cell->Gr_avg + cell->Gb_avg) / 2;
-
-			redSum += std::min(cell->R_avg * gain, 255.0);
-			greenSum += std::min(G_avg * gain, 255.0);
-			blueSum += std::min(cell->B_avg * gain, 255.0);
-		}
-	}
-
-	/*
-	 * Apply the AWB gains to approximate colours correctly, use the Rec.
-	 * 601 formula to calculate the relative luminance, and normalize it.
-	 */
-	double ySum = redSum * activeState.awb.gains.red * 0.299
-		    + greenSum * activeState.awb.gains.green * 0.587
-		    + blueSum * activeState.awb.gains.blue * 0.114;
-
-	return ySum / (grid.height * grid.width) / 255;
-}
-
 double Agc::estimateLuminance(double gain) const
 {
 	double redSum = 0, greenSum = 0, blueSum = 0;
@@ -407,42 +208,6 @@ void Agc::process(IPAContext &context, [[maybe_unused]] const uint32_t frame,
 		  const ipu3_uapi_stats_3a *stats,
 		  ControlList &metadata)
 {
-	/*
-	 * Estimate the gain needed to have the proportion of pixels in a given
-	 * desired range. iqMean is the mean value of the top 2% of the
-	 * cumulative histogram, and we want it to be as close as possible to a
-	 * configured target.
-	 */
-	double iqMean = measureBrightness(stats, context.configuration.grid.bdsGrid);
-	double iqMeanGain = kEvGainTarget * knumHistogramBins / iqMean;
-
-	/*
-	 * 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(context.activeState,
-						  context.configuration.grid.bdsGrid,
-						  stats, yGain);
-		double extraGain = std::min(10.0, yTarget / (yValue + .001));
-
-		yGain *= extraGain;
-		LOG(IPU3Agc, Debug) << "Y value: " << yValue
-				    << ", Y target: " << yTarget
-				    << ", gives gain " << yGain;
-		if (extraGain < 1.01)
-			break;
-	}
-
-	computeExposure(context, frameContext, yGain, iqMeanGain);
-	frameCount_++;
-
 	Histogram hist = parseStatistics(stats, context.configuration.grid.bdsGrid);
 	rGain_ = context.activeState.awb.gains.red;
 	gGain_ = context.activeState.awb.gains.blue;
diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
index 1d6855a9..762cc072 100644
--- a/src/ipa/ipu3/algorithms/agc.h
+++ b/src/ipa/ipu3/algorithms/agc.h
@@ -38,29 +38,16 @@ public:
 		     ControlList &metadata) override;
 
 private:
-	double measureBrightness(const ipu3_uapi_stats_3a *stats,
-				 const ipu3_uapi_grid_config &grid) const;
-	utils::Duration filterExposure(utils::Duration currentExposure);
-	void computeExposure(IPAContext &context, IPAFrameContext &frameContext,
-			     double yGain, double iqMeanGain);
-	double estimateLuminance(IPAActiveState &activeState,
-				 const ipu3_uapi_grid_config &grid,
-				 const ipu3_uapi_stats_3a *stats,
-				 double gain);
 	double estimateLuminance(double gain) const override;
 	Histogram parseStatistics(const ipu3_uapi_stats_3a *stats,
 				  const ipu3_uapi_grid_config &grid);
 
-	uint64_t frameCount_;
-
 	utils::Duration minShutterSpeed_;
 	utils::Duration maxShutterSpeed_;
 
 	double minAnalogueGain_;
 	double maxAnalogueGain_;
 
-	utils::Duration filteredExposure_;
-
 	uint32_t stride_;
 	double rGain_;
 	double gGain_;