# Source code for colorsys

```
"""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
#
# There are a great many versions of the constants used in these formulae.
# The ones in this library uses constants from the FCC version of NTSC.

[docs]def rgb_to_yiq(r, g, b):
y = 0.30*r + 0.59*g + 0.11*b
i = 0.74*(r-y) - 0.27*(b-y)
q = 0.48*(r-y) + 0.41*(b-y)
return (y, i, q)

[docs]def yiq_to_rgb(y, i, q):
# r = y + (0.27*q + 0.41*i) / (0.74*0.41 + 0.27*0.48)
# b = y + (0.74*q - 0.48*i) / (0.74*0.41 + 0.27*0.48)
# g = y - (0.30*(r-y) + 0.11*(b-y)) / 0.59

r = y + 0.9468822170900693*i + 0.6235565819861433*q
g = y - 0.27478764629897834*i - 0.6356910791873801*q
b = y - 1.1085450346420322*i + 1.7090069284064666*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

[docs]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

[docs]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

[docs]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

[docs]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

```