ipa: libipa: Add Lux helper

Add a Lux helper to libipa that does the estimation of the lux level
given gain, exposure, and luminance histogram. The helper also
handles reading the reference values from the tuning file. These are
expected to be common operations of lux algorithm modules in IPAs, and
is modeled/copied from Raspberry Pi.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Isaac Scott <isaac.scott@ideasonboard.com>

3 files changed, 225 insertions, 0 deletions

diff --git a/src/ipa/libipa/lux.cpp b/src/ipa/libipa/lux.cpp
new file mode 100644
index 00000000..bae8198f
--- /dev/null
+++ b/src/ipa/libipa/lux.cpp
@@ -0,0 +1,181 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2019, Raspberry Pi Ltd
+ * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
+ *
+ * Helper class that implements lux estimation
+ */
+#include "lux.h"
+
+#include <algorithm>
+#include <chrono>
+
+#include <libcamera/base/log.h>
+
+#include "libcamera/internal/yaml_parser.h"
+
+#include "histogram.h"
+
+/**
+ * \file lux.h
+ * \brief Helper class that implements lux estimation
+ *
+ * Estimating the lux level of an image is a common operation that can for
+ * instance be used to adjust the target Y value in AGC or for Bayesian AWB
+ * estimation.
+ */
+
+namespace libcamera {
+
+using namespace std::literals::chrono_literals;
+
+LOG_DEFINE_CATEGORY(Lux)
+
+namespace ipa {
+
+/**
+ * \class Lux
+ * \brief Class that implements lux estimation
+ *
+ * IPAs that wish to use lux estimation should create a Lux algorithm module
+ * that lightly wraps this module by providing the platform-specific luminance
+ * histogram. The Lux entry in the tuning file must then precede the algorithms
+ * that depend on the estimated lux value.
+ */
+
+/**
+ * \var Lux::binSize_
+ * \brief The maximum count of each bin
+ */
+
+/**
+ * \var Lux::referenceExposureTime_
+ * \brief The exposure time of the reference image, in microseconds
+ */
+
+/**
+ * \var Lux::referenceAnalogueGain_
+ * \brief The analogue gain of the reference image
+ */
+
+/**
+ * \var Lux::referenceDigitalGain_
+ * \brief The analogue gain of the reference image
+ */
+
+/**
+ * \var Lux::referenceY_
+ * \brief The measured luminance of the reference image, out of the bin size
+ *
+ * \sa binSize_
+ */
+
+/**
+ * \var Lux::referenceLux_
+ * \brief The estimated lux level of the reference image
+ */
+
+/**
+  * \brief Construct the Lux helper module
+  * \param[in] binSize The maximum count of each bin
+  */
+Lux::Lux(unsigned int binSize)
+	: binSize_(binSize)
+{
+}
+
+/**
+ * \brief Parse tuning data
+ * \param[in] tuningData The YamlObject representing the tuning data
+ *
+ * This function parses yaml tuning data for the common Lux module. It requires
+ * reference exposure time, analogue gain, digital gain, and lux values.
+ *
+ * \code{.unparsed}
+ * algorithms:
+ *   - Lux:
+ *       referenceExposureTime: 10000
+ *       referenceAnalogueGain: 4.0
+ *       referenceDigitalGain: 1.0
+ *       referenceY: 12000
+ *       referenceLux: 1000
+ * \endcode
+ *
+ * \return 0 on success or a negative error code
+ */
+int Lux::parseTuningData(const YamlObject &tuningData)
+{
+	auto value = tuningData["referenceExposureTime"].get<double>();
+	if (!value) {
+		LOG(Lux, Error) << "Missing tuning parameter: "
+				<< "'referenceExposureTime'";
+		return -EINVAL;
+	}
+	referenceExposureTime_ = *value * 1.0us;
+
+	value = tuningData["referenceAnalogueGain"].get<double>();
+	if (!value) {
+		LOG(Lux, Error) << "Missing tuning parameter: "
+				<< "'referenceAnalogueGain'";
+		return -EINVAL;
+	}
+	referenceAnalogueGain_ = *value;
+
+	value = tuningData["referenceDigitalGain"].get<double>();
+	if (!value) {
+		LOG(Lux, Error) << "Missing tuning parameter: "
+				<< "'referenceDigitalGain'";
+		return -EINVAL;
+	}
+	referenceDigitalGain_ = *value;
+
+	value = tuningData["referenceY"].get<double>();
+	if (!value) {
+		LOG(Lux, Error) << "Missing tuning parameter: "
+				<< "'referenceY'";
+		return -EINVAL;
+	}
+	referenceY_ = *value;
+
+	value = tuningData["referenceLux"].get<double>();
+	if (!value) {
+		LOG(Lux, Error) << "Missing tuning parameter: "
+				<< "'referenceLux'";
+		return -EINVAL;
+	}
+	referenceLux_ = *value;
+
+	return 0;
+}
+
+/**
+ * \brief Estimate lux given runtime values
+ * \param[in] exposureTime Exposure time applied to the frame
+ * \param[in] aGain Analogue gain applied to the frame
+ * \param[in] dGain Digital gain applied to the frame
+ * \param[in] yHist Histogram from the ISP statistics
+ *
+ * Estimate the lux given the exposure time, gain, and histogram.
+ *
+ * \return Estimated lux value
+ */
+double Lux::estimateLux(utils::Duration exposureTime,
+			double aGain, double dGain,
+			const Histogram &yHist) const
+{
+	double currentY = yHist.interQuantileMean(0, 1);
+	double exposureTimeRatio = referenceExposureTime_ / exposureTime;
+	double aGainRatio = referenceAnalogueGain_ / aGain;
+	double dGainRatio = referenceDigitalGain_ / dGain;
+	double yRatio = currentY * (binSize_ / yHist.bins()) / referenceY_;
+
+	double estimatedLux = exposureTimeRatio * aGainRatio * dGainRatio *
+			      yRatio * referenceLux_;
+
+	LOG(Lux, Debug) << "Estimated lux " << estimatedLux;
+	return estimatedLux;
+}
+
+} /* namespace ipa */
+
+} /* namespace libcamera */
diff --git a/src/ipa/libipa/lux.h b/src/ipa/libipa/lux.h
new file mode 100644
index 00000000..93ca6479
--- /dev/null
+++ b/src/ipa/libipa/lux.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2019, Raspberry Pi Ltd
+ * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
+ *
+ * Helper class that implements lux estimation
+ */
+
+#pragma once
+
+#include <libcamera/base/utils.h>
+
+namespace libcamera {
+
+class YamlObject;
+
+namespace ipa {
+
+class Histogram;
+
+class Lux
+{
+public:
+	Lux(unsigned int binSize);
+
+	int parseTuningData(const YamlObject &tuningData);
+	double estimateLux(utils::Duration exposureTime,
+			   double aGain, double dGain,
+			   const Histogram &yHist) const;
+
+private:
+	unsigned int binSize_;
+	utils::Duration referenceExposureTime_;
+	double referenceAnalogueGain_;
+	double referenceDigitalGain_;
+	double referenceY_;
+	double referenceLux_;
+};
+
+} /* namespace ipa */
+
+} /* namespace libcamera */
diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
index a7f16ff6..f2b2f4be 100644
--- a/src/ipa/libipa/meson.build
+++ b/src/ipa/libipa/meson.build
@@ -11,6 +11,7 @@ libipa_headers = files([
     'histogram.h',
     'interpolator.h',
     'lsc_polynomial.h',
+    'lux.h',
     'module.h',
     'pwl.h',
     'vector.h',
@@ -27,6 +28,7 @@ libipa_sources = files([
     'histogram.cpp',
     'interpolator.cpp',
     'lsc_polynomial.cpp',
+    'lux.cpp',
     'module.cpp',
     'pwl.cpp',
     'vector.cpp',