#!/usr/bin/env python3 # Copyright © 2014 Mattias Andrée (maandree@member.fsf.org) # # This program is free software: you can redistribute it and/or modify # it under the terms of the GNU Affero General Public License as published by # the Free Software Foundation, either version 3 of the License, or # (at your option) any later version. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU Affero General Public License for more details. # # You should have received a copy of the GNU Affero General Public License # along with this program. If not, see <http://www.gnu.org/licenses/>. # This module implements functions from convertions between colour spaces # and comparion of colours def linear_to_standard(*colour): ''' Convert [0, 1] linear RGB to [0, 1] sRGB @param colour:*float The red component, the green component, and the blue component @return :[float, float, float] The red, green and blue components ''' return [12.92 * c if c <= 0.0031308 else (1 + 0.055) * c ** (1 / 2.4) - 0.055 for c in colour] def standard_to_linear(*colour): ''' Convert [0, 1] sRGB to [0, 1] linear RGB @param colour:*float The red component, the green component, and the blue component @return :[float, float, float] The red, green and blue components ''' return [c / 12.92 if c <= 0.04045 else ((c + 0.055) / (1 + 0.055)) ** 2.4 for c in colour] def ciexyy_to_ciexyz(x, y, Y): ''' Convert CIE xyY to CIE XYZ @param x:float The x parameter @param y:float The y parameter @param Y:float The Y parameter @return :[float, float, float] The X, Y and Z parameters ''' return [Y if y == 0 else Y * x / y, Y, Y if y == 0 else Y * (1 - x - y) / y] def ciexyz_to_ciexyy(X, Y, Z): ''' Convert CIE XYZ to CIE xyY @param X:float The X parameter @param Y:float The Y parameter @param Z:float The Z parameter @return :[float, float, float] The x, y and Y parameters ''' s = X + Y + Z return [X / s, Y / s, Y] if not s == 0 else [0, 0, 0] def matrix_mul_vector(matrix, vector): ''' Multiplies a matrix with a vector @param matrix:list<list<int>> The matrix @param vector:list<int> The vector @return :list<int> The resulting vector ''' return [sum([r * v for r, v in zip(row, vector)]) for row in matrix] ciexyz_to_linear_matrix = [[ 3.240450, -1.537140, -0.4985320], [-0.969266, 1.876010, 0.0415561], [0.0556434, -0.204026, 1.0572300]] ''' Multiplication matrix to convert from CIE xyY to linear RGB ''' def ciexyz_to_linear(X, Y, Z): ''' Convert CIE XYZ to [0, 1] linear RGB @param X:float The X parameter @param Y:float The Y parameter @param Z:float The Z parameter @return :[float, float, float] The red, green and blue components ''' return matrix_mul_vector(ciexyz_to_linear_matrix, [X, Y, Z]) linear_to_ciexyz_matrix = [[0.4124564, 0.3575761, 0.1804375], [0.2126729, 0.7151522, 0.0721750], [0.0193339, 0.1191920, 0.9503041]] ''' Multiplication matrix to convert from linear RGB to CIE xyY ''' def linear_to_ciexyz(r, g, b): ''' Convert [0, 1] linear RGB to CIE XYZ @param r:float The red component @param g:float The green component @param b:float The blue component @return :[float, float, float] The X, Y and Z parameters ''' return matrix_mul_vector(linear_to_ciexyz_matrix, [r, g, b]) def srgb_to_ciexyy(r, g, b): ''' Convert [0, 1] sRGB to CIE xyY @param r:float The red component @param g:float The green component @param b:float The blue component @return :[float, float, float] The x, y and Y parameters ''' if r == g == b == 0: return (0.312857, 0.328993, 0) return ciexyz_to_ciexyy(*linear_to_ciexyz(*standard_to_linear(r, g, b))) def ciexyy_to_srgb(x, y, Y): ''' Convert CIE xyY to [0, 1] sRGB @param x:float The x parameter @param y:float The y parameter @param Y:float The Y parameter @return :[float, float, float] The red, green and blue components ''' return linear_to_standard(*ciexyz_to_linear(*ciexyy_to_ciexyz(x, y, Y))) def ciexyz_to_cielab(x, y, z): ''' Convert from CIE XYZ to CIE L*a*b* @param x:float The X parameter @param y:float The Y parameter @param z:float The Z parameter @return :[float, float, float] The L*, a* and b* components ''' x /= 0.95047 z /= 1.08883 f = lambda c : c ** 1 / 3 if c > 0.00885642 else (7.78 + 703 / 99900) * c + 0.1379310 l = 116 * f(y) - 16 a = 500 * (f(x) - f(y)) b = 200 * (f(y) - f(z)) return (l, a, b) def cielab_to_xiexyz(l, a, b): ''' Convert from CIE L*a*b* to CIE XYZ @param l:float The L* parameter @param a:float The a* parameter @param b:float The b* parameter @return :[float, float, float] The X, Y and Z components ''' y = (l + 16) / 116 x = a / 500 + y z = y - b / 200 f = lambda c : c ** 3 if c ** 3 > 0.00885642 else (c - 0.1379310) / (7.78 + 703 / 99900) return [f(c) * m for c, m in zip((x, y, z), (0.95047, 1, 1.08883))] def delta_e(a, b): ''' Convert the distance (∆E*_ab) between two [0, 1] sRGB colours @param a:(float, float, float) The first colour @param b:(float, float, float) The second colour @return :float The difference ''' standard_to_cielab = lambda x : ciexyz_to_cielab(*linear_to_ciexyz(*standard_to_linear(*a))) return sum([(c1 - c2) ** 2 for c1, c2 in zip(standard_to_cielab(a), standard_to_cielab(b))]) ** 0.5