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#!/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
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