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"""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.

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)

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

def rgb_to_hls(r, g, b):

maxc = max(r, g, b)

minc = min(r, g, b)

sumc = (maxc+minc)

rangec = (maxc-minc)

l = sumc/2.0

if minc == maxc:

return 0.0, l, 0.0

if l <= 0.5:

s = rangec / sumc

else:

s = rangec / (2.0-maxc-minc) # Not always 2.0-sumc: gh-106498.

rc = (maxc-r) / rangec

gc = (maxc-g) / rangec

bc = (maxc-b) / rangec

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)

rangec = (maxc-minc)

v = maxc

if minc == maxc:

return 0.0, 0.0, v

s = rangec / maxc

rc = (maxc-r) / rangec

gc = (maxc-g) / rangec

bc = (maxc-b) / rangec

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

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