ipa: libipa: Add lsc polynomial class

Add a basic class to represent polynomials as specified in the DNG spec
for vignetting correction.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/libipa/lsc_polynomial.cpp

@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Ideas On Board
+ *
+ * Polynomial class to represent lens shading correction
+ */
+
+#include "lsc_polynomial.h"
+
+#include <libcamera/base/log.h>
+
+/**
+ * \file lsc_polynomial.h
+ * \brief LscPolynomial class
+ */
+
+namespace libcamera {
+
+LOG_DEFINE_CATEGORY(LscPolynomial)
+
+namespace ipa {
+
+/**
+ * \class LscPolynomial
+ * \brief Class for handling even polynomials used in lens shading correction
+ *
+ * Shading artifacts of camera lenses can be modeled using even radial
+ * polynomials. This class implements a polynomial with 5 coefficients which
+ * follows the definition of the FixVignetteRadial opcode in the Adobe DNG
+ * specification.
+ */
+
+/**
+ * \fn LscPolynomial::LscPolynomial(double cx = 0.0, double cy = 0.0, double k0 = 0.0,
+		      double k1 = 0.0, double k2 = 0.0, double k3 = 0.0,
+		      double k4 = 0.0)
+ * \brief Construct a polynomial using the given coefficients
+ * \param cx Center-x relative to the image in normalized coordinates (0..1)
+ * \param cy Center-y relative to the image in normalized coordinates (0..1)
+ * \param k0 Coefficient of the polynomial
+ * \param k1 Coefficient of the polynomial
+ * \param k2 Coefficient of the polynomial
+ * \param k3 Coefficient of the polynomial
+ * \param k4 Coefficient of the polynomial
+ */
+
+/**
+ * \fn LscPolynomial::sampleAtNormalizedPixelPos(double x, double y)
+ * \brief Sample the polynomial at the given normalized pixel position
+ *
+ * This functions samples the polynomial at the given pixel position divided by
+ * the value returned by getM().
+ *
+ * \param x x position in normalized coordinates
+ * \param y y position in normalized coordinates
+ * \return The sampled value
+ */
+
+/**
+ * \fn LscPolynomial::getM()
+ * \brief Get the value m as described in the dng specification
+ *
+ * Returns m according to dng spec. m represents the Euclidean distance
+ * (in pixels) from the optical center to the farthest pixel in the
+ * image.
+ *
+ * \return The sampled value
+ */
+
+/**
+ * \fn LscPolynomial::setReferenceImageSize(const Size &size)
+ * \brief Set the reference image size
+ *
+ * Set the reference image size that is used for subsequent calls to getM() and
+ * sampleAtNormalizedPixelPos()
+ *
+ * \param size The size of the reference image
+ */
+
+} // namespace ipa
+} // namespace libcamera

src/ipa/libipa/lsc_polynomial.h

@@ -0,0 +1,105 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Ideas On Board
+ *
+ * Helper for radial polynomial used in lens shading correction.
+ */
+#pragma once
+
+#include <algorithm>
+#include <array>
+#include <assert.h>
+#include <cmath>
+
+#include <libcamera/base/log.h>
+#include <libcamera/base/span.h>
+
+#include "libcamera/internal/yaml_parser.h"
+
+namespace libcamera {
+
+LOG_DECLARE_CATEGORY(LscPolynomial)
+
+namespace ipa {
+
+class LscPolynomial
+{
+public:
+	LscPolynomial(double cx = 0.0, double cy = 0.0, double k0 = 0.0,
+		      double k1 = 0.0, double k2 = 0.0, double k3 = 0.0,
+		      double k4 = 0.0)
+		: cx_(cx), cy_(cy), cnx_(0), cny_(0),
+		  coefficients_({ k0, k1, k2, k3, k4 })
+	{
+	}
+
+	double sampleAtNormalizedPixelPos(double x, double y) const
+	{
+		double dx = x - cnx_;
+		double dy = y - cny_;
+		double r = sqrt(dx * dx + dy * dy);
+		double res = 1.0;
+		for (unsigned int i = 0; i < coefficients_.size(); i++) {
+			res += coefficients_[i] * std::pow(r, (i + 1) * 2);
+		}
+		return res;
+	}
+
+	double getM() const
+	{
+		double cpx = imageSize_.width * cx_;
+		double cpy = imageSize_.height * cy_;
+		double mx = std::max(cpx, std::fabs(imageSize_.width - cpx));
+		double my = std::max(cpy, std::fabs(imageSize_.height - cpy));
+
+		return sqrt(mx * mx + my * my);
+	}
+
+	void setReferenceImageSize(const Size &size)
+	{
+		assert(!size.isNull());
+		imageSize_ = size;
+
+		/* Calculate normalized centers */
+		double m = getM();
+		cnx_ = (size.width * cx_) / m;
+		cny_ = (size.height * cy_) / m;
+	}
+
+private:
+	double cx_;
+	double cy_;
+	double cnx_;
+	double cny_;
+	std::array<double, 5> coefficients_;
+
+	Size imageSize_;
+};
+
+} /* namespace ipa */
+
+#ifndef __DOXYGEN__
+
+template<>
+struct YamlObject::Getter<ipa::LscPolynomial> {
+	std::optional<ipa::LscPolynomial> get(const YamlObject &obj) const
+	{
+		std::optional<double> cx = obj["cx"].get<double>();
+		std::optional<double> cy = obj["cy"].get<double>();
+		std::optional<double> k0 = obj["k0"].get<double>();
+		std::optional<double> k1 = obj["k1"].get<double>();
+		std::optional<double> k2 = obj["k2"].get<double>();
+		std::optional<double> k3 = obj["k3"].get<double>();
+		std::optional<double> k4 = obj["k4"].get<double>();
+
+		if (!(cx && cy && k0 && k1 && k2 && k3 && k4))
+			LOG(LscPolynomial, Error)
+				<< "Polynomial is missing a parameter";
+
+		return ipa::LscPolynomial(*cx, *cy, *k0, *k1, *k2, *k3, *k4);
+	}
+};
+
+#endif
+
+} /* namespace libcamera */

src/ipa/libipa/meson.build

@@ -8,6 +8,7 @@ libipa_headers = files([
     'fc_queue.h',
     'histogram.h',
     'interpolator.h',
+    'lsc_polynomial.h',
     'matrix.h',
     'module.h',
     'pwl.h',
@@ -22,6 +23,7 @@ libipa_sources = files([
     'fc_queue.cpp',
     'histogram.cpp',
     'interpolator.cpp',
+    'lsc_polynomial.cpp',
     'matrix.cpp',
     'module.cpp',
     'pwl.cpp',