libcamera: software_isp: Move color mappings out of debayering

Constructing the color mapping tables is related to stats rather than
debayering, where they are applied.  Let's move the corresponding code
to stats processing.

The same applies to the auxiliary gamma table.  As the gamma value is
currently fixed and used in a single place, with the temporary exception
mentioned below, there is no need to share it anywhere anymore.

It's necessary to initialize SoftwareIsp::debayerParams_ to default
values.  These initial values are used for the first two frames, before
they are changed based on determined stats.  To avoid sharing the gamma
value constant in artificial ways, we use 0.5 directly in the
initialization.  This all is not a particularly elegant thing to do,
such a code belongs conceptually to the similar code in stats
processing, but doing better is left for larger refactoring.

This is a preliminary step towards building this functionality on top of
libipa/algorithm.h, which should follow.

Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Andrei Konovalov <andrey.konovalov.ynk@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 42 insertions, 9 deletions

diff --git a/src/ipa/simple/soft_simple.cpp b/src/ipa/simple/soft_simple.cpp
index dbbeabbf..92095e59 100644
--- a/src/ipa/simple/soft_simple.cpp
+++ b/src/ipa/simple/soft_simple.cpp
@@ -5,6 +5,7 @@
  * Simple Software Image Processing Algorithm module
  */
 
+#include <cmath>
 #include <numeric>
 #include <stdint.h>
 #include <sys/mman.h>
@@ -84,6 +85,10 @@ private:
 	ControlInfoMap sensorInfoMap_;
 	BlackLevel blackLevel_;
 
+	static constexpr unsigned int kGammaLookupSize = 1024;
+	std::array<uint8_t, kGammaLookupSize> gammaTable_;
+	int lastBlackLevel_ = -1;
+
 	int32_t exposureMin_, exposureMax_;
 	int32_t exposure_;
 	double againMin_, againMax_, againMinStep_;
@@ -246,7 +251,6 @@ void IPASoftSimple::processStats(const ControlList &sensorControls)
 	if (ignoreUpdates_ > 0)
 		blackLevel_.update(histogram);
 	const uint8_t blackLevel = blackLevel_.get();
-	params_->blackLevel = blackLevel;
 
 	/*
 	 * Black level must be subtracted to get the correct AWB ratios, they
@@ -263,13 +267,42 @@ void IPASoftSimple::processStats(const ControlList &sensorControls)
 	/*
 	 * Calculate red and blue gains for AWB.
 	 * Clamp max gain at 4.0, this also avoids 0 division.
+	 * Gain: 128 = 0.5, 256 = 1.0, 512 = 2.0, etc.
 	 */
-	params_->gainR = sumR <= sumG / 4 ? 1024 : 256 * sumG / sumR;
-	params_->gainB = sumB <= sumG / 4 ? 1024 : 256 * sumG / sumB;
-
+	const unsigned int gainR = sumR <= sumG / 4 ? 1024 : 256 * sumG / sumR;
+	const unsigned int gainB = sumB <= sumG / 4 ? 1024 : 256 * sumG / sumB;
 	/* Green gain and gamma values are fixed */
-	params_->gainG = 256;
-	params_->gamma = 0.5;
+	constexpr unsigned int gainG = 256;
+
+	/* Update the gamma table if needed */
+	if (blackLevel != lastBlackLevel_) {
+		constexpr float gamma = 0.5;
+		const unsigned int blackIndex = blackLevel * kGammaLookupSize / 256;
+		std::fill(gammaTable_.begin(), gammaTable_.begin() + blackIndex, 0);
+		const float divisor = kGammaLookupSize - blackIndex - 1.0;
+		for (unsigned int i = blackIndex; i < kGammaLookupSize; i++)
+			gammaTable_[i] = UINT8_MAX *
+					 std::pow((i - blackIndex) / divisor, gamma);
+
+		lastBlackLevel_ = blackLevel;
+	}
+
+	for (unsigned int i = 0; i < DebayerParams::kRGBLookupSize; i++) {
+		constexpr unsigned int div =
+			DebayerParams::kRGBLookupSize * DebayerParams::kGain10 /
+			kGammaLookupSize;
+		unsigned int idx;
+
+		/* Apply gamma after gain! */
+		idx = std::min({ i * gainR / div, (kGammaLookupSize - 1) });
+		params_->red[i] = gammaTable_[idx];
+
+		idx = std::min({ i * gainG / div, (kGammaLookupSize - 1) });
+		params_->green[i] = gammaTable_[idx];
+
+		idx = std::min({ i * gainB / div, (kGammaLookupSize - 1) });
+		params_->blue[i] = gammaTable_[idx];
+	}
 
 	setIspParams.emit();
 
@@ -290,7 +323,7 @@ void IPASoftSimple::processStats(const ControlList &sensorControls)
 	 * https://www.araa.asn.au/acra/acra2007/papers/paper84final.pdf
 	 */
 	const unsigned int blackLevelHistIdx =
-		params_->blackLevel / (256 / SwIspStats::kYHistogramSize);
+		blackLevel / (256 / SwIspStats::kYHistogramSize);
 	const unsigned int histogramSize =
 		SwIspStats::kYHistogramSize - blackLevelHistIdx;
 	const unsigned int yHistValsPerBin = histogramSize / kExposureBinsCount;
@@ -338,8 +371,8 @@ void IPASoftSimple::processStats(const ControlList &sensorControls)
 
 	LOG(IPASoft, Debug) << "exposureMSV " << exposureMSV
 			    << " exp " << exposure_ << " again " << again_
-			    << " gain R/B " << params_->gainR << "/" << params_->gainB
-			    << " black level " << params_->blackLevel;
+			    << " gain R/B " << gainR << "/" << gainB
+			    << " black level " << static_cast<unsigned int>(blackLevel);
 }
 
 void IPASoftSimple::updateExposure(double exposureMSV)