[PATCH v1 05/11] libipa: Add grey world AWB algorithm

[Stefan Klug]

Add the grey world algorithm that is currently used in rkisp1 to libipa.
No changes in functionality were made.

Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
---
 src/ipa/libipa/awb_grey.cpp | 114 ++++++++++++++++++++++++++++++++++++
 src/ipa/libipa/awb_grey.h   |  35 +++++++++++
 src/ipa/libipa/meson.build  |   2 +
 3 files changed, 151 insertions(+)
 create mode 100644 src/ipa/libipa/awb_grey.cpp
 create mode 100644 src/ipa/libipa/awb_grey.h

diff --git a/src/ipa/libipa/awb_grey.cpp b/src/ipa/libipa/awb_grey.cpp
new file mode 100644
index 000000000000..192a7cf3834a
--- /dev/null
+++ b/src/ipa/libipa/awb_grey.cpp
@@ -0,0 +1,114 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024 Ideas on Board Oy
+ *
+ * Base class for bayesian AWB algorithm
+ */
+
+#include "awb_grey.h"
+
+#include <cmath>
+
+#include <libcamera/base/log.h>
+#include <libcamera/control_ids.h>
+
+#include "colours.h"
+
+using namespace libcamera::controls;
+
+/**
+ * \file awb_grey.h
+ * \brief Implementation of a grey world AWB algorithm
+ */
+
+namespace libcamera {
+
+LOG_DECLARE_CATEGORY(Awb)
+namespace ipa {
+
+/**
+ * \class AwbGrey
+ * \brief A Grey world auto white balance algorithm
+ */
+
+/**
+ * \brief Initialize the algorithm with the given tuning data
+ * \param[in] tuningData The tuning data for the algorithm
+ *
+ * Load the colour temperature curve from the tuning data. If there is no tuning
+ * data available, continue with a warning. Manual colour temperature will not
+ * work in that case.
+ *
+ * \return 0 on success, a negative error code otherwise
+ */
+int AwbGrey::init(const YamlObject &tuningData)
+{
+	Interpolator<Vector<double, 2>> gains;
+	int ret = gains.readYaml(tuningData["colourGains"], "ct", "gains");
+	if (ret < 0)
+		LOG(Awb, Warning)
+			<< "Failed to parse 'colourGains' "
+			<< "parameter from tuning file; "
+			<< "manual colour temperature will not work properly";
+	else
+		colourGainCurve_ = gains;
+
+	return 0;
+}
+
+/**
+ * \brief Calculate awb data from the given statistics
+ * \param[in] stats The statistics to use for the calculation
+ * \param[in] lux The lux value of the scene
+ *
+ * Estimates the colour temperature based on the coulours::estimateCCT function.
+ * The gains are calculated purely based on the RGB means provided by the \a
+ * stats. The colour temperature is not taken into account when calculating the
+ * gains.
+ *
+ * The \a lux parameter is not used in this algorithm.
+ *
+ * \return The awb result
+ */
+AwbResult AwbGrey::calculateAwb(const AwbStats &stats, [[maybe_unused]] int lux)
+{
+	AwbResult result;
+	auto means = stats.getRGBMeans();
+	result.colourTemperature = estimateCCT(means);
+
+	/*
+	 * Estimate the red and blue gains to apply in a grey world. The green
+	 * gain is hardcoded to 1.0. Avoid divisions by zero by clamping the
+	 * divisor to a minimum value of 1.0.
+	 */
+	result.gains.r() = means.g() / std::max(means.r(), 1.0);
+	result.gains.g() = 1.0;
+	result.gains.b() = means.g() / std::max(means.b(), 1.0);
+	return result;
+}
+
+/**
+ * \brief Compute white balance gains from a colour temperature
+ * \param[in] colourTemperature The colour temperature in Kelvin
+ *
+ * Compute the white balance gains from a \a colourTemperature. This function
+ * does not take any statistics into account. It simply interpolates the colour
+ * gains configured in the colour temperature curve.
+ *
+ * \return The colour gains if a colour temperature curve is available,
+ * [1, 1, 1] otherwise.
+ */
+RGB<double> AwbGrey::gainsFromColourTemperature(double colourTemperature)
+{
+	if (!colourGainCurve_) {
+		LOG(Awb, Error) << "No gains defined";
+		return RGB<double>({ 1.0, 1.0, 1.0 });
+	}
+
+	auto gains = colourGainCurve_->getInterpolated(colourTemperature);
+	return { { gains[0], 1.0, gains[0] } };
+}
+
+} /* namespace ipa */
+
+} /* namespace libcamera */
diff --git a/src/ipa/libipa/awb_grey.h b/src/ipa/libipa/awb_grey.h
new file mode 100644
index 000000000000..6eda8e5498fb
--- /dev/null
+++ b/src/ipa/libipa/awb_grey.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024 Ideas on Board Oy
+ *
+ * AWB grey world algorithm
+ */
+
+#pragma once
+
+#include "libcamera/internal/yaml_parser.h"
+
+#include "awb.h"
+#include "interpolator.h"
+#include "vector.h"
+
+namespace libcamera {
+
+namespace ipa {
+
+class AwbGrey : public AwbAlgorithm
+{
+public:
+	AwbGrey() = default;
+
+	int init(const YamlObject &tuningData) override;
+	AwbResult calculateAwb(const AwbStats &stats, int lux) override;
+	RGB<double> gainsFromColourTemperature(double coulourTemperature) override;
+
+private:
+	std::optional<Interpolator<Vector<double, 2>>> colourGainCurve_;
+};
+
+} /* namespace ipa */
+
+} /* namespace libcamera */
diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
index 03e879c5834f..c550a6eb45b6 100644
--- a/src/ipa/libipa/meson.build
+++ b/src/ipa/libipa/meson.build
@@ -3,6 +3,7 @@
 libipa_headers = files([
     'agc_mean_luminance.h',
     'algorithm.h',
+    'awb_grey.h',
     'awb.h',
     'camera_sensor_helper.h',
     'colours.h',
@@ -21,6 +22,7 @@ libipa_headers = files([
 libipa_sources = files([
     'agc_mean_luminance.cpp',
     'algorithm.cpp',
+    'awb_grey.cpp',
     'awb.cpp',
     'camera_sensor_helper.cpp',
     'colours.cpp',
-- 
2.43.0