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