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diff --git a/src/ipa/libipa/colours.cpp b/src/ipa/libipa/colours.cpp
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+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2024, Ideas on Board Oy
+ *
+ * libipa miscellaneous colour helpers
+ */
+
+#include "colours.h"
+
+#include <algorithm>
+#include <cmath>
+
+namespace libcamera {
+
+namespace ipa {
+
+/**
+ * \file colours.h
+ * \brief Functions to reduce code duplication between IPA modules
+ */
+
+/**
+ * \brief Estimate luminance from RGB values following ITU-R BT.601
+ * \param[in] rgb The RGB value
+ *
+ * This function estimates a luminance value from a triplet of Red, Green and
+ * Blue values, following the formula defined by ITU-R Recommendation BT.601-7
+ * which can be found at https://www.itu.int/rec/R-REC-BT.601
+ *
+ * \return The estimated luminance value
+ */
+double rec601LuminanceFromRGB(const RGB<double> &rgb)
+{
+	static const Vector<double, 3> rgb2y{{
+		0.299, 0.587, 0.114
+	}};
+
+	return rgb.dot(rgb2y);
+}
+
+/**
+ * \brief Estimate correlated colour temperature from RGB color space input
+ * \param[in] rgb The RGB value
+ *
+ * This function estimates the correlated color temperature RGB color space
+ * input. In physics and color science, the Planckian locus or black body locus
+ * is the path or locus that the color of an incandescent black body would take
+ * in a particular chromaticity space as the black body temperature changes.
+ *
+ * If a narrow range of color temperatures is considered (those encapsulating
+ * daylight being the most practical case) one can approximate the Planckian
+ * locus in order to calculate the CCT in terms of chromaticity coordinates.
+ *
+ * More detailed information can be found in:
+ * https://en.wikipedia.org/wiki/Color_temperature#Approximation
+ *
+ * \return The estimated color temperature
+ */
+uint32_t estimateCCT(const RGB<double> &rgb)
+{
+	/*
+	 * Convert the RGB values to CIE tristimulus values (XYZ) and divide by
+	 * the sum of X, Y and Z to calculate the CIE xy chromaticity.
+	 */
+	static const Matrix<double, 3, 3> rgb2xyz({
+		-0.14282, 1.54924, -0.95641,
+		-0.32466, 1.57837, -0.73191,
+		-0.68202, 0.77073,  0.56332
+	});
+
+	Vector<double, 3> xyz = rgb2xyz * rgb;
+	xyz /= xyz.sum();
+
+	/* Calculate CCT */
+	double n = (xyz.x() - 0.3320) / (0.1858 - xyz.y());
+	return 449 * n * n * n + 3525 * n * n + 6823.3 * n + 5520.33;
+}
+
+} /* namespace ipa */
+
+} /* namespace libcamera */