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