colour temperature

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 56 insertions, 0 deletions

diff --git a/src/colour.py b/src/colour.py
new file mode 100644
index 0000000..df5b38d
--- /dev/null
+++ b/src/colour.py
@@ -0,0 +1,56 @@
+#!/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/>.
+
+
+def linear_to_standard(*colour):
+    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):
+    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):
+    return [Y * x / y, Y, Y * (1 - x - y) / y]
+
+def ciexyz_to_ciexyy(X, Y, Z):
+    p = -Y / X
+    q = 1 + Y / X
+    y = 1 / (p / 2 + (p ** 2 / 4 - q) ** 0.5)
+    x = X * y / Y
+    return [x, y, Y]
+
+def ciexyz_to_linear(X, Y, Z):
+    r = 3.2406 * X - 1.5372 * Y - 0.4986 * Z
+    g = -0.9689 * X + 1.8758 * Y + 0.0415 * Z
+    b = 0.0557 * X - 0.2040 * Y + 1.0570 * Z
+    return [r, g, b]
+
+def linear_to_ciexyz(r, g, b):
+    X = 0.4124 * r + 0.3576 * g + 0.1805 * b
+    Y = 0.2126 * r + 0.7152 * g + 0.0722 * b
+    Z = 0.0193 * r + 0.1192 * g + 1.9502 * b
+    return [X, Y, Z]
+
+def to_ciexyy(r, g, b):
+    (r, g, b) = standard_to_linear(r, g, b)
+    (X, Y, Z) = linear_to_ciexyz(r, g, b)
+    return ciexyz_to_ciexyy(X, Y, Z)
+
+def to_srgb(x, y, Y):
+    (X, Y, Z) = ciexyy_to_ciexyz(x, y, Y)
+    (r, g, b) = ciexyz_to_linear(X, Y, Z)
+    return linear_to_standard(r, g, b)
+