[libcamera-devel] [PATCH v2 5/5] ipa: raspberrypi: Normalise region sums to 16-bits

[Naushir Patuck]

The VC4 ISP uses a pipeline bit-depth of 13-bits. The AGC algorithm needs to
know this bit-depth when computing the Y value for the image.

Instead of hardcoding the VC4 bit-depth in the AGC source code, normalise all
region sums to 16-bits when filling the Statistics structure. AWB and ALSC are
agnostic about pipeline depth, so do not need changing.

Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
---
 src/ipa/raspberrypi/controller/rpi/agc.cpp | 10 ++++------
 src/ipa/raspberrypi/raspberrypi.cpp        | 16 ++++++++++------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/src/ipa/raspberrypi/controller/rpi/agc.cpp b/src/ipa/raspberrypi/controller/rpi/agc.cpp
index a7f0e954407d..e400e478162f 100644
--- a/src/ipa/raspberrypi/controller/rpi/agc.cpp
+++ b/src/ipa/raspberrypi/controller/rpi/agc.cpp
@@ -28,8 +28,6 @@ LOG_DEFINE_CATEGORY(RPiAgc)
 
 #define NAME "rpi.agc"
 
-static constexpr unsigned int PipelineBits = 13; /* seems to be a 13-bit pipeline */
-
 int AgcMeteringMode::read(const libcamera::YamlObject &params)
 {
 	const YamlObject &yamlWeights = params["weights"];
@@ -592,9 +590,9 @@ static double computeInitialY(StatisticsPtr &stats, AwbStatus const &awb,
 	double rSum = 0, gSum = 0, bSum = 0, pixelSum = 0;
 	for (unsigned int i = 0; i < stats->agcRegions.numRegions(); i++) {
 		auto &region = stats->agcRegions.get(i);
-		double rAcc = std::min<double>(region.val.rSum * gain, ((1 << PipelineBits) - 1) * region.counted);
-		double gAcc = std::min<double>(region.val.gSum * gain, ((1 << PipelineBits) - 1) * region.counted);
-		double bAcc = std::min<double>(region.val.bSum * gain, ((1 << PipelineBits) - 1) * region.counted);
+		double rAcc = std::min<double>(region.val.rSum * gain, ((1 << 16) - 1) * region.counted);
+		double gAcc = std::min<double>(region.val.gSum * gain, ((1 << 16) - 1) * region.counted);
+		double bAcc = std::min<double>(region.val.bSum * gain, ((1 << 16) - 1) * region.counted);
 		rSum += rAcc * weights[i];
 		gSum += gAcc * weights[i];
 		bSum += bAcc * weights[i];
@@ -607,7 +605,7 @@ static double computeInitialY(StatisticsPtr &stats, AwbStatus const &awb,
 	double ySum = rSum * awb.gainR * .299 +
 		      gSum * awb.gainG * .587 +
 		      bSum * awb.gainB * .114;
-	return ySum / pixelSum / (1 << PipelineBits);
+	return ySum / pixelSum / (1 << 16);
 }
 
 /*
diff --git a/src/ipa/raspberrypi/raspberrypi.cpp b/src/ipa/raspberrypi/raspberrypi.cpp
index 44527357243d..ac1875d203ae 100644
--- a/src/ipa/raspberrypi/raspberrypi.cpp
+++ b/src/ipa/raspberrypi/raspberrypi.cpp
@@ -1132,11 +1132,15 @@ RPiController::StatisticsPtr IPARPi::fillStatistics(bcm2835_isp_stats *stats) co
 	/* RGB histograms are not used, so do not populate them. */
 	statistics->yHist = std::move(RPiController::Histogram(stats->hist[0].g_hist, NUM_HISTOGRAM_BINS));
 
+	/*
+	 * All region sums are based on a 13-bit pipeline bit-depth. Normalise
+	 * this to 16-bits for the AGC/AWB/ALSC algorithms.
+	 */
 	statistics->awbRegions.init({ DEFAULT_AWB_REGIONS_X, DEFAULT_AWB_REGIONS_Y });
 	for (i = 0; i < statistics->awbRegions.numRegions(); i++)
-		statistics->awbRegions.set(i, { { stats->awb_stats[i].r_sum,
-						  stats->awb_stats[i].g_sum,
-						  stats->awb_stats[i].b_sum },
+		statistics->awbRegions.set(i, { { stats->awb_stats[i].r_sum << 3,
+						  stats->awb_stats[i].g_sum << 3,
+						  stats->awb_stats[i].b_sum << 3 },
 						stats->awb_stats[i].counted,
 						stats->awb_stats[i].notcounted });
 
@@ -1146,9 +1150,9 @@ RPiController::StatisticsPtr IPARPi::fillStatistics(bcm2835_isp_stats *stats) co
 	 */
 	statistics->agcRegions.init(15);
 	for (i = 0; i < statistics->agcRegions.numRegions(); i++)
-		statistics->agcRegions.set(i, { { stats->agc_stats[i].r_sum,
-						  stats->agc_stats[i].g_sum,
-						  stats->agc_stats[i].b_sum },
+		statistics->agcRegions.set(i, { { stats->agc_stats[i].r_sum << 3,
+						  stats->agc_stats[i].g_sum << 3,
+						  stats->agc_stats[i].b_sum << 3 },
 						stats->agc_stats[i].counted,
 						stats->awb_stats[i].notcounted });
 
-- 
2.25.1