libcamera: ipa: simple: Make gamma adjustable

The gamma value is fixed in software ISP.  Let's make it adjustable,
similarly to contrast and saturation, and report it in metadata.

Reviewed-by: Robert Mader <robert.mader@collabora.com>
Reviewed-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/simple/algorithms/adjust.cpp

@@ -23,6 +23,7 @@ LOG_DEFINE_CATEGORY(IPASoftAdjust)
 
 int Adjust::init(IPAContext &context, [[maybe_unused]] const YamlObject &tuningData)
 {
+	context.ctrlMap[&controls::Gamma] = ControlInfo(0.1f, 10.0f, kDefaultGamma);
 	context.ctrlMap[&controls::Contrast] = ControlInfo(0.0f, 2.0f, 1.0f);
 	if (context.ccmEnabled)
 		context.ctrlMap[&controls::Saturation] = ControlInfo(0.0f, 2.0f, 1.0f);
@@ -32,6 +33,7 @@ int Adjust::init(IPAContext &context, [[maybe_unused]] const YamlObject &tuningD
 int Adjust::configure(IPAContext &context,
 		      [[maybe_unused]] const IPAConfigInfo &configInfo)
 {
+	context.activeState.knobs.gamma = kDefaultGamma;
 	context.activeState.knobs.contrast = std::optional<double>();
 	context.activeState.knobs.saturation = std::optional<double>();
 
@@ -43,6 +45,12 @@ void Adjust::queueRequest(typename Module::Context &context,
 			  [[maybe_unused]] typename Module::FrameContext &frameContext,
 			  const ControlList &controls)
 {
+	const auto &gamma = controls.get(controls::Gamma);
+	if (gamma.has_value()) {
+		context.activeState.knobs.gamma = gamma.value();
+		LOG(IPASoftAdjust, Debug) << "Setting gamma to " << gamma.value();
+	}
+
 	const auto &contrast = controls.get(controls::Contrast);
 	if (contrast.has_value()) {
 		context.activeState.knobs.contrast = contrast;
@@ -83,6 +91,7 @@ void Adjust::prepare(IPAContext &context,
 		     IPAFrameContext &frameContext,
 		     [[maybe_unused]] DebayerParams *params)
 {
+	frameContext.gamma = context.activeState.knobs.gamma;
 	frameContext.contrast = context.activeState.knobs.contrast;
 
 	if (!context.ccmEnabled)
@@ -105,6 +114,9 @@ void Adjust::process([[maybe_unused]] IPAContext &context,
 		     [[maybe_unused]] const SwIspStats *stats,
 		     ControlList &metadata)
 {
+	const auto &gamma = frameContext.gamma;
+	metadata.set(controls::Gamma, gamma);
+
 	const auto &contrast = frameContext.contrast;
 	if (contrast)
 		metadata.set(controls::Contrast, contrast.value());

src/ipa/simple/algorithms/adjust.h

@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 /*
- * Copyright (C) 2024-2025, Red Hat Inc.
+ * Copyright (C) 2024-2026, Red Hat Inc.
  *
  * Color correction matrix
  */
@@ -19,6 +19,8 @@ namespace libcamera {
 
 namespace ipa::soft::algorithms {
 
+constexpr float kDefaultGamma = 2.2f;
+
 class Adjust : public Algorithm
 {
 public:

src/ipa/simple/algorithms/lut.cpp

@@ -18,6 +18,8 @@
 
 #include "simple/ipa_context.h"
 
+#include "adjust.h"
+
 namespace libcamera {
 
 LOG_DEFINE_CATEGORY(IPASoftLut)
@@ -27,8 +29,6 @@ namespace ipa::soft::algorithms {
 int Lut::configure(IPAContext &context,
 		   [[maybe_unused]] const IPAConfigInfo &configInfo)
 {
-	/* Gamma value is fixed */
-	context.configuration.gamma = 1.0 / 2.2;
 	updateGammaTable(context);
 
 	return 0;
@@ -37,6 +37,7 @@ int Lut::configure(IPAContext &context,
 void Lut::updateGammaTable(IPAContext &context)
 {
 	const auto blackLevel = context.activeState.blc.level;
+	const auto gamma = 1.0 / context.activeState.knobs.gamma;
 	const auto contrast = context.activeState.knobs.contrast.value_or(1.0);
 	/* Convert 0..2 to 0..infinity; avoid actual inifinity at tan(pi/2) */
 	double contrastExp = tan(std::clamp(contrast * M_PI_4, 0.0, M_PI_2 - 0.00001));
@@ -52,8 +53,7 @@ void Lut::updateGammaTable(IPAContext &context)
 				normalized = 0.5 * std::pow(normalized / 0.5, contrastExp);
 			else
 				normalized = 1.0 - 0.5 * std::pow((1.0 - normalized) / 0.5, contrastExp);
-			gammaTable[i] = UINT8_MAX *
-					std::pow(normalized, context.configuration.gamma);
+			gammaTable[i] = UINT8_MAX * std::pow(normalized, gamma);
 		}
 		/*
 		 * Due to CCM operations, the table lookup may reach indices below the black
@@ -65,6 +65,7 @@ void Lut::updateGammaTable(IPAContext &context)
 			  gammaTable[blackIndex]);
 	}
 
+	context.activeState.gamma.gamma = gamma;
 	context.activeState.gamma.blackLevel = blackLevel;
 	context.activeState.gamma.contrastExp = contrastExp;
 }
@@ -131,7 +132,7 @@ void Lut::prepare(IPAContext &context,
 		context.activeState.matrixChanged = false;
 	}
 
-	params->gamma = context.configuration.gamma;
+	params->gamma = context.activeState.gamma.gamma;
 	params->contrastExp = context.activeState.gamma.contrastExp;
 }
 

src/ipa/simple/ipa_context.h

@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 /*
- * Copyright (C) 2024-2025 Red Hat, Inc.
+ * Copyright (C) 2024-2026 Red Hat, Inc.
  *
  * Simple pipeline IPA Context
  */
@@ -25,7 +25,6 @@ namespace libcamera {
 namespace ipa::soft {
 
 struct IPASessionConfiguration {
-	float gamma;
 	struct {
 		int32_t exposureMin, exposureMax;
 		double againMin, againMax, again10, againMinStep;
@@ -58,6 +57,7 @@ struct IPAActiveState {
 	struct {
 		std::array<double, kGammaLookupSize> gammaTable;
 		uint8_t blackLevel;
+		float gamma;
 		double contrast;
 		double contrastExp;
 	} gamma;
@@ -66,6 +66,7 @@ struct IPAActiveState {
 	bool matrixChanged = false;
 
 	struct {
+		float gamma;
 		/* 0..2 range, 1.0 = normal */
 		std::optional<double> contrast;
 		std::optional<float> saturation;
@@ -85,6 +86,7 @@ struct IPAFrameContext : public FrameContext {
 		double blue;
 	} gains;
 
+	float gamma;
 	std::optional<double> contrast;
 	std::optional<float> saturation;
 };