import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

toolkit/components/places/ColorConversion.js

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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Given a color in the Lab space, return its chroma (colorfulness,
+ * saturation).
+ *
+ * @param lab
+ *        The lab color to get the chroma from
+ *
+ * @return A number greater than zero that measures chroma in the image
+ */
+function labChroma(lab) {
+  return Math.sqrt(Math.pow(lab.a, 2) + Math.pow(lab.b, 2));
+}
+
+/**
+ * Given the RGB components of a color as integers from 0-255, return the
+ * color in the XYZ color space.
+ *
+ * @return An object with x, y, z properties holding those components of the
+ *         color in the XYZ color space.
+ */
+function rgb2xyz(r, g, b) {
+  r /= 255;
+  g /= 255;
+  b /= 255;
+
+  // assume sRGB
+  r = r > 0.04045 ? Math.pow(((r + 0.055) / 1.055), 2.4) : (r / 12.92);
+  g = g > 0.04045 ? Math.pow(((g + 0.055) / 1.055), 2.4) : (g / 12.92);
+  b = b > 0.04045 ? Math.pow(((b + 0.055) / 1.055), 2.4) : (b / 12.92);
+
+  return {
+    x: ((r * 0.4124) + (g * 0.3576) + (b * 0.1805)) * 100,
+    y: ((r * 0.2126) + (g * 0.7152) + (b * 0.0722)) * 100,
+    z: ((r * 0.0193) + (g * 0.1192) + (b * 0.9505)) * 100
+  };
+}
+
+/**
+ * Given the RGB components of a color as integers from 0-255, return the
+ * color in the Lab color space.
+ *
+ * @return An object with lightness, a, b properties holding those components
+ *         of the color in the Lab color space.
+ */
+function rgb2lab(r, g, b) {
+  let xyz = rgb2xyz(r, g, b),
+        x = xyz.x / 95.047,
+        y = xyz.y / 100,
+        z = xyz.z / 108.883;
+
+  x = x > 0.008856 ? Math.pow(x, 1/3) : (7.787 * x) + (16 / 116);
+  y = y > 0.008856 ? Math.pow(y, 1/3) : (7.787 * y) + (16 / 116);
+  z = z > 0.008856 ? Math.pow(z, 1/3) : (7.787 * z) + (16 / 116);
+
+  return {
+    lightness: (116 * y) - 16,
+    a:  500 * (x - y),
+    b:  200 * (y - z)
+  };
+}