"""Conversion functions between RGB and other color systems. | |
This modules provides two functions for each color system ABC: | |
rgb_to_abc(r, g, b) --> a, b, c | |
abc_to_rgb(a, b, c) --> r, g, b | |
All inputs and outputs are triples of floats in the range [0.0...1.0] | |
(with the exception of I and Q, which covers a slightly larger range). | |
Inputs outside the valid range may cause exceptions or invalid outputs. | |
Supported color systems: | |
RGB: Red, Green, Blue components | |
YIQ: Luminance, Chrominance (used by composite video signals) | |
HLS: Hue, Luminance, Saturation | |
HSV: Hue, Saturation, Value | |
""" | |
# References: | |
# http://en.wikipedia.org/wiki/YIQ | |
# http://en.wikipedia.org/wiki/HLS_color_space | |
# http://en.wikipedia.org/wiki/HSV_color_space | |
__all__ = ["rgb_to_yiq","yiq_to_rgb","rgb_to_hls","hls_to_rgb", | |
"rgb_to_hsv","hsv_to_rgb"] | |
# Some floating point constants | |
ONE_THIRD = 1.0/3.0 | |
ONE_SIXTH = 1.0/6.0 | |
TWO_THIRD = 2.0/3.0 | |
# YIQ: used by composite video signals (linear combinations of RGB) | |
# Y: perceived grey level (0.0 == black, 1.0 == white) | |
# I, Q: color components | |
def rgb_to_yiq(r, g, b): | |
y = 0.30*r + 0.59*g + 0.11*b | |
i = 0.60*r - 0.28*g - 0.32*b | |
q = 0.21*r - 0.52*g + 0.31*b | |
return (y, i, q) | |
def yiq_to_rgb(y, i, q): | |
r = y + 0.948262*i + 0.624013*q | |
g = y - 0.276066*i - 0.639810*q | |
b = y - 1.105450*i + 1.729860*q | |
if r < 0.0: | |
r = 0.0 | |
if g < 0.0: | |
g = 0.0 | |
if b < 0.0: | |
b = 0.0 | |
if r > 1.0: | |
r = 1.0 | |
if g > 1.0: | |
g = 1.0 | |
if b > 1.0: | |
b = 1.0 | |
return (r, g, b) | |
# HLS: Hue, Luminance, Saturation | |
# H: position in the spectrum | |
# L: color lightness | |
# S: color saturation | |
def rgb_to_hls(r, g, b): | |
maxc = max(r, g, b) | |
minc = min(r, g, b) | |
# XXX Can optimize (maxc+minc) and (maxc-minc) | |
l = (minc+maxc)/2.0 | |
if minc == maxc: | |
return 0.0, l, 0.0 | |
if l <= 0.5: | |
s = (maxc-minc) / (maxc+minc) | |
else: | |
s = (maxc-minc) / (2.0-maxc-minc) | |
rc = (maxc-r) / (maxc-minc) | |
gc = (maxc-g) / (maxc-minc) | |
bc = (maxc-b) / (maxc-minc) | |
if r == maxc: | |
h = bc-gc | |
elif g == maxc: | |
h = 2.0+rc-bc | |
else: | |
h = 4.0+gc-rc | |
h = (h/6.0) % 1.0 | |
return h, l, s | |
def hls_to_rgb(h, l, s): | |
if s == 0.0: | |
return l, l, l | |
if l <= 0.5: | |
m2 = l * (1.0+s) | |
else: | |
m2 = l+s-(l*s) | |
m1 = 2.0*l - m2 | |
return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD)) | |
def _v(m1, m2, hue): | |
hue = hue % 1.0 | |
if hue < ONE_SIXTH: | |
return m1 + (m2-m1)*hue*6.0 | |
if hue < 0.5: | |
return m2 | |
if hue < TWO_THIRD: | |
return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0 | |
return m1 | |
# HSV: Hue, Saturation, Value | |
# H: position in the spectrum | |
# S: color saturation ("purity") | |
# V: color brightness | |
def rgb_to_hsv(r, g, b): | |
maxc = max(r, g, b) | |
minc = min(r, g, b) | |
v = maxc | |
if minc == maxc: | |
return 0.0, 0.0, v | |
s = (maxc-minc) / maxc | |
rc = (maxc-r) / (maxc-minc) | |
gc = (maxc-g) / (maxc-minc) | |
bc = (maxc-b) / (maxc-minc) | |
if r == maxc: | |
h = bc-gc | |
elif g == maxc: | |
h = 2.0+rc-bc | |
else: | |
h = 4.0+gc-rc | |
h = (h/6.0) % 1.0 | |
return h, s, v | |
def hsv_to_rgb(h, s, v): | |
if s == 0.0: | |
return v, v, v | |
i = int(h*6.0) # XXX assume int() truncates! | |
f = (h*6.0) - i | |
p = v*(1.0 - s) | |
q = v*(1.0 - s*f) | |
t = v*(1.0 - s*(1.0-f)) | |
i = i%6 | |
if i == 0: | |
return v, t, p | |
if i == 1: | |
return q, v, p | |
if i == 2: | |
return p, v, t | |
if i == 3: | |
return p, q, v | |
if i == 4: | |
return t, p, v | |
if i == 5: | |
return v, p, q | |
# Cannot get here |