1"""Conversion functions between RGB and other color systems. 2 3This modules provides two functions for each color system ABC: 4 5 rgb_to_abc(r, g, b) --> a, b, c 6 abc_to_rgb(a, b, c) --> r, g, b 7 8All inputs and outputs are triples of floats in the range [0.0...1.0] 9(with the exception of I and Q, which covers a slightly larger range). 10Inputs outside the valid range may cause exceptions or invalid outputs. 11 12Supported color systems: 13RGB: Red, Green, Blue components 14YIQ: Luminance, Chrominance (used by composite video signals) 15HLS: Hue, Luminance, Saturation 16HSV: Hue, Saturation, Value 17""" 18 19# References: 20# http://en.wikipedia.org/wiki/YIQ 21# http://en.wikipedia.org/wiki/HLS_color_space 22# http://en.wikipedia.org/wiki/HSV_color_space 23 24__all__ = ["rgb_to_yiq","yiq_to_rgb","rgb_to_hls","hls_to_rgb", 25 "rgb_to_hsv","hsv_to_rgb"] 26 27# Some floating point constants 28 29ONE_THIRD = 1.0/3.0 30ONE_SIXTH = 1.0/6.0 31TWO_THIRD = 2.0/3.0 32 33# YIQ: used by composite video signals (linear combinations of RGB) 34# Y: perceived grey level (0.0 == black, 1.0 == white) 35# I, Q: color components 36# 37# There are a great many versions of the constants used in these formulae. 38# The ones in this library uses constants from the FCC version of NTSC. 39 40def rgb_to_yiq(r, g, b): 41 y = 0.30*r + 0.59*g + 0.11*b 42 i = 0.74*(r-y) - 0.27*(b-y) 43 q = 0.48*(r-y) + 0.41*(b-y) 44 return (y, i, q) 45 46def yiq_to_rgb(y, i, q): 47 # r = y + (0.27*q + 0.41*i) / (0.74*0.41 + 0.27*0.48) 48 # b = y + (0.74*q - 0.48*i) / (0.74*0.41 + 0.27*0.48) 49 # g = y - (0.30*(r-y) + 0.11*(b-y)) / 0.59 50 51 r = y + 0.9468822170900693*i + 0.6235565819861433*q 52 g = y - 0.27478764629897834*i - 0.6356910791873801*q 53 b = y - 1.1085450346420322*i + 1.7090069284064666*q 54 55 if r < 0.0: 56 r = 0.0 57 if g < 0.0: 58 g = 0.0 59 if b < 0.0: 60 b = 0.0 61 if r > 1.0: 62 r = 1.0 63 if g > 1.0: 64 g = 1.0 65 if b > 1.0: 66 b = 1.0 67 return (r, g, b) 68 69 70# HLS: Hue, Luminance, Saturation 71# H: position in the spectrum 72# L: color lightness 73# S: color saturation 74 75def rgb_to_hls(r, g, b): 76 maxc = max(r, g, b) 77 minc = min(r, g, b) 78 sumc = (maxc+minc) 79 rangec = (maxc-minc) 80 l = sumc/2.0 81 if minc == maxc: 82 return 0.0, l, 0.0 83 if l <= 0.5: 84 s = rangec / sumc 85 else: 86 s = rangec / (2.0-sumc) 87 rc = (maxc-r) / rangec 88 gc = (maxc-g) / rangec 89 bc = (maxc-b) / rangec 90 if r == maxc: 91 h = bc-gc 92 elif g == maxc: 93 h = 2.0+rc-bc 94 else: 95 h = 4.0+gc-rc 96 h = (h/6.0) % 1.0 97 return h, l, s 98 99def hls_to_rgb(h, l, s): 100 if s == 0.0: 101 return l, l, l 102 if l <= 0.5: 103 m2 = l * (1.0+s) 104 else: 105 m2 = l+s-(l*s) 106 m1 = 2.0*l - m2 107 return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD)) 108 109def _v(m1, m2, hue): 110 hue = hue % 1.0 111 if hue < ONE_SIXTH: 112 return m1 + (m2-m1)*hue*6.0 113 if hue < 0.5: 114 return m2 115 if hue < TWO_THIRD: 116 return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0 117 return m1 118 119 120# HSV: Hue, Saturation, Value 121# H: position in the spectrum 122# S: color saturation ("purity") 123# V: color brightness 124 125def rgb_to_hsv(r, g, b): 126 maxc = max(r, g, b) 127 minc = min(r, g, b) 128 v = maxc 129 if minc == maxc: 130 return 0.0, 0.0, v 131 s = (maxc-minc) / maxc 132 rc = (maxc-r) / (maxc-minc) 133 gc = (maxc-g) / (maxc-minc) 134 bc = (maxc-b) / (maxc-minc) 135 if r == maxc: 136 h = bc-gc 137 elif g == maxc: 138 h = 2.0+rc-bc 139 else: 140 h = 4.0+gc-rc 141 h = (h/6.0) % 1.0 142 return h, s, v 143 144def hsv_to_rgb(h, s, v): 145 if s == 0.0: 146 return v, v, v 147 i = int(h*6.0) # XXX assume int() truncates! 148 f = (h*6.0) - i 149 p = v*(1.0 - s) 150 q = v*(1.0 - s*f) 151 t = v*(1.0 - s*(1.0-f)) 152 i = i%6 153 if i == 0: 154 return v, t, p 155 if i == 1: 156 return q, v, p 157 if i == 2: 158 return p, v, t 159 if i == 3: 160 return p, q, v 161 if i == 4: 162 return t, p, v 163 if i == 5: 164 return v, p, q 165 # Cannot get here 166