ipa: rkisp1: Introduce AWB

The RkISP1 ISP calculates a mean value for Y, Cr and Cb at each frame.
There is a RGB mode which could theoretically give us the values for R,
G and B directly, but it seems to be failing right now.

Convert those values into R, G and B and estimate the gain to apply in a
grey world.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Tested-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/ipa/rkisp1/algorithms/awb.cpp

@@ -0,0 +1,178 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021-2022, Ideas On Board
+ *
+ * awb.cpp - AWB control algorithm
+ */
+
+#include "awb.h"
+
+#include <algorithm>
+#include <cmath>
+
+#include <libcamera/base/log.h>
+
+#include <libcamera/ipa/core_ipa_interface.h>
+
+/**
+ * \file awb.h
+ */
+
+namespace libcamera {
+
+namespace ipa::rkisp1::algorithms {
+
+/**
+ * \class Awb
+ * \brief A Grey world white balance correction algorithm
+ */
+
+LOG_DEFINE_CATEGORY(RkISP1Awb)
+
+/**
+ * \copydoc libcamera::ipa::Algorithm::configure
+ */
+int Awb::configure(IPAContext &context,
+		   const IPACameraSensorInfo &configInfo)
+{
+	context.frameContext.awb.gains.red = 1.0;
+	context.frameContext.awb.gains.blue = 1.0;
+	context.frameContext.awb.gains.green = 1.0;
+
+	/*
+	 * Define the measurement window for AWB as a centered rectangle
+	 * covering 3/4 of the image width and height.
+	 */
+	context.configuration.awb.measureWindow.h_offs = configInfo.outputSize.width / 8;
+	context.configuration.awb.measureWindow.v_offs = configInfo.outputSize.height / 8;
+	context.configuration.awb.measureWindow.h_size = 3 * configInfo.outputSize.width / 4;
+	context.configuration.awb.measureWindow.v_size = 3 * configInfo.outputSize.height / 4;
+
+	return 0;
+}
+
+uint32_t Awb::estimateCCT(double red, double green, double blue)
+{
+	/* Convert the RGB values to CIE tristimulus values (XYZ) */
+	double X = (-0.14282) * (red) + (1.54924) * (green) + (-0.95641) * (blue);
+	double Y = (-0.32466) * (red) + (1.57837) * (green) + (-0.73191) * (blue);
+	double Z = (-0.68202) * (red) + (0.77073) * (green) + (0.56332) * (blue);
+
+	/* Calculate the normalized chromaticity values */
+	double x = X / (X + Y + Z);
+	double y = Y / (X + Y + Z);
+
+	/* Calculate CCT */
+	double n = (x - 0.3320) / (0.1858 - y);
+	return 449 * n * n * n + 3525 * n * n + 6823.3 * n + 5520.33;
+}
+
+/**
+ * \copydoc libcamera::ipa::Algorithm::prepare
+ */
+void Awb::prepare(IPAContext &context, rkisp1_params_cfg *params)
+{
+	params->others.awb_gain_config.gain_green_b = 256 * context.frameContext.awb.gains.green;
+	params->others.awb_gain_config.gain_blue = 256 * context.frameContext.awb.gains.blue;
+	params->others.awb_gain_config.gain_red = 256 * context.frameContext.awb.gains.red;
+	params->others.awb_gain_config.gain_green_r = 256 * context.frameContext.awb.gains.green;
+
+	/* Update the gains. */
+	params->module_cfg_update |= RKISP1_CIF_ISP_MODULE_AWB_GAIN;
+
+	/* If we already have configured the gains and window, return. */
+	if (context.frameContext.frameCount > 0)
+		return;
+
+	/* Configure the gains to apply. */
+	params->module_en_update |= RKISP1_CIF_ISP_MODULE_AWB_GAIN;
+	/* Update the ISP to apply the gains configured. */
+	params->module_ens |= RKISP1_CIF_ISP_MODULE_AWB_GAIN;
+
+	/* Configure the measure window for AWB. */
+	params->meas.awb_meas_config.awb_wnd = context.configuration.awb.measureWindow;
+	/*
+	 * Measure Y, Cr and Cb means.
+	 * \todo RGB is not working, the kernel seems to not configure it ?
+	 */
+	params->meas.awb_meas_config.awb_mode = RKISP1_CIF_ISP_AWB_MODE_YCBCR;
+	/* Reference Cr and Cb. */
+	params->meas.awb_meas_config.awb_ref_cb = 128;
+	params->meas.awb_meas_config.awb_ref_cr = 128;
+	/* Y values to include are between min_y and max_y only. */
+	params->meas.awb_meas_config.min_y = 16;
+	params->meas.awb_meas_config.max_y = 250;
+	/* Maximum Cr+Cb value to take into account for awb. */
+	params->meas.awb_meas_config.max_csum = 250;
+	/* Minimum Cr and Cb values to take into account. */
+	params->meas.awb_meas_config.min_c = 16;
+	/* Number of frames to use to estimate the mean (0 means 1 frame). */
+	params->meas.awb_meas_config.frames = 0;
+
+	/* Update AWB measurement unit configuration. */
+	params->module_cfg_update |= RKISP1_CIF_ISP_MODULE_AWB;
+	/* Make sure the ISP is measuring the means for the next frame. */
+	params->module_en_update |= RKISP1_CIF_ISP_MODULE_AWB;
+	params->module_ens |= RKISP1_CIF_ISP_MODULE_AWB;
+}
+
+/**
+ * \copydoc libcamera::ipa::Algorithm::process
+ */
+void Awb::process([[maybe_unused]] IPAContext &context, const rkisp1_stat_buffer *stats)
+{
+	const rkisp1_cif_isp_stat *params = &stats->params;
+	const rkisp1_cif_isp_awb_stat *awb = &params->awb;
+	IPAFrameContext &frameContext = context.frameContext;
+
+	/* Get the YCbCr mean values */
+	double yMean = awb->awb_mean[0].mean_y_or_g;
+	double crMean = awb->awb_mean[0].mean_cr_or_r;
+	double cbMean = awb->awb_mean[0].mean_cb_or_b;
+
+	/*
+	 * Convert from YCbCr to RGB.
+	 * The hardware uses the following formulas:
+	 * Y = 16 + 0.2500 R + 0.5000 G + 0.1094 B
+	 * Cb = 128 - 0.1406 R - 0.2969 G + 0.4375 B
+	 * Cr = 128 + 0.4375 R - 0.3750 G - 0.0625 B
+	 *
+	 * The inverse matrix is thus:
+	 * [[1,1636, -0,0623,  1,6008]
+	 *  [1,1636, -0,4045, -0,7949]
+	 *  [1,1636,  1,9912, -0,0250]]
+	 */
+	yMean -= 16;
+	cbMean -= 128;
+	crMean -= 128;
+	double redMean = 1.1636 * yMean - 0.0623 * cbMean + 1.6008 * crMean;
+	double greenMean = 1.1636 * yMean - 0.4045 * cbMean - 0.7949 * crMean;
+	double blueMean = 1.1636 * yMean + 1.9912 * cbMean - 0.0250 * crMean;
+
+	/* Estimate the red and blue gains to apply in a grey world. */
+	double redGain = greenMean / (redMean + 1);
+	double blueGain = greenMean / (blueMean + 1);
+
+	/* Filter the values to avoid oscillations. */
+	double speed = 0.2;
+	redGain = speed * redGain + (1 - speed) * frameContext.awb.gains.red;
+	blueGain = speed * blueGain + (1 - speed) * frameContext.awb.gains.blue;
+
+	/*
+	 * Gain values are unsigned integer value, range 0 to 4 with 8 bit
+	 * fractional part.
+	 */
+	frameContext.awb.gains.red = std::clamp(redGain, 0.0, 1023.0 / 256);
+	frameContext.awb.gains.blue = std::clamp(blueGain, 0.0, 1023.0 / 256);
+	/* Hardcode the green gain to 1.0. */
+	frameContext.awb.gains.green = 1.0;
+
+	frameContext.awb.temperatureK = estimateCCT(redMean, greenMean, blueMean);
+
+	LOG(RkISP1Awb, Debug) << "Gain found for red: " << context.frameContext.awb.gains.red
+			      << " and for blue: " << context.frameContext.awb.gains.blue;
+}
+
+} /* namespace ipa::rkisp1::algorithms */
+
+} /* namespace libcamera */

src/ipa/rkisp1/algorithms/awb.h

@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021-2022, Ideas On Board
+ *
+ * awb.h - AWB control algorithm
+ */
+
+#pragma once
+
+#include <linux/rkisp1-config.h>
+
+#include "algorithm.h"
+
+namespace libcamera {
+
+namespace ipa::rkisp1::algorithms {
+
+class Awb : public Algorithm
+{
+public:
+	Awb() = default;
+	~Awb() = default;
+
+	int configure(IPAContext &context, const IPACameraSensorInfo &configInfo) override;
+	void prepare(IPAContext &context, rkisp1_params_cfg *params) override;
+	void process(IPAContext &context, const rkisp1_stat_buffer *stats) override;
+
+private:
+	uint32_t estimateCCT(double red, double green, double blue);
+};
+
+} /* namespace ipa::rkisp1::algorithms */
+} /* namespace libcamera */

src/ipa/rkisp1/algorithms/meson.build

@@ -2,5 +2,6 @@
 
 rkisp1_ipa_algorithms = files([
     'agc.cpp',
+    'awb.cpp',
     'blc.cpp',
 ])

src/ipa/rkisp1/ipa_context.cpp

@@ -81,6 +81,14 @@ namespace libcamera::ipa::rkisp1 {
  * \brief Hardware revision of the ISP
  */
 
+/**
+ * \var IPASessionConfiguration::awb
+ * \brief AWB parameters configuration of the IPA
+ *
+ * \var IPASessionConfiguration::awb.measureWindow
+ * \brief AWB measure window
+ */
+
 /**
  * \var IPASessionConfiguration::sensor
  * \brief Sensor-specific configuration of the IPA
@@ -105,6 +113,26 @@ namespace libcamera::ipa::rkisp1 {
  * The gain should be adapted to the sensor specific gain code before applying.
  */
 
+/**
+ * \var IPAFrameContext::awb
+ * \brief Context for the Automatic White Balance algorithm
+ *
+ * \struct IPAFrameContext::awb.gains
+ * \brief White balance gains
+ *
+ * \var IPAFrameContext::awb.gains.red
+ * \brief White balance gain for R channel
+ *
+ * \var IPAFrameContext::awb.gains.green
+ * \brief White balance gain for G channel
+ *
+ * \var IPAFrameContext::awb.gains.blue
+ * \brief White balance gain for B channel
+ *
+ * \var IPAFrameContext::awb.temperatureK
+ * \brief Estimated color temperature
+ */
+
 /**
  * \var IPAFrameContext::sensor
  * \brief Effective sensor values

src/ipa/rkisp1/ipa_context.h

@@ -12,6 +12,8 @@
 
 #include <libcamera/base/utils.h>
 
+#include <libcamera/geometry.h>
+
 namespace libcamera {
 
 namespace ipa::rkisp1 {
@@ -25,6 +27,10 @@ struct IPASessionConfiguration {
 		struct rkisp1_cif_isp_window measureWindow;
 	} agc;
 
+	struct {
+		struct rkisp1_cif_isp_window measureWindow;
+	} awb;
+
 	struct {
 		utils::Duration lineDuration;
 	} sensor;
@@ -40,6 +46,16 @@ struct IPAFrameContext {
 		double gain;
 	} agc;
 
+	struct {
+		struct {
+			double red;
+			double green;
+			double blue;
+		} gains;
+
+		double temperatureK;
+	} awb;
+
 	struct {
 		uint32_t exposure;
 		double gain;

src/ipa/rkisp1/rkisp1.cpp

@@ -27,6 +27,7 @@
 
 #include "algorithms/agc.h"
 #include "algorithms/algorithm.h"
+#include "algorithms/awb.h"
 #include "algorithms/blc.h"
 #include "libipa/camera_sensor_helper.h"
 
@@ -121,6 +122,7 @@ int IPARkISP1::init(const IPASettings &settings, unsigned int hwRevision)
 
 	/* Construct our Algorithms */
 	algorithms_.push_back(std::make_unique<algorithms::Agc>());
+	algorithms_.push_back(std::make_unique<algorithms::Awb>());
 	algorithms_.push_back(std::make_unique<algorithms::BlackLevelCorrection>());
 
 	return 0;