1 """Conversion functions between RGB and other color systems. 2 3 This 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 8 All 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). 10 Inputs outside the valid range may cause exceptions or invalid outputs. 11 12 Supported color systems: 13 RGB: Red, Green, Blue components 14 YIQ: Luminance, Chrominance (used by composite video signals) 15 HLS: Hue, Luminance, Saturation 16 HSV: 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 29 ONE_THIRD = 1.0/3.0 30 ONE_SIXTH = 1.0/6.0 31 TWO_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 def rgb_to_yiq(r, g, b): 38 y = 0.30*r + 0.59*g + 0.11*b 39 i = 0.60*r - 0.28*g - 0.32*b 40 q = 0.21*r - 0.52*g + 0.31*b 41 return (y, i, q) 42 43 def yiq_to_rgb(y, i, q): 44 r = y + 0.948262*i + 0.624013*q 45 g = y - 0.276066*i - 0.639810*q 46 b = y - 1.105450*i + 1.729860*q 47 if r < 0.0: 48 r = 0.0 49 if g < 0.0: 50 g = 0.0 51 if b < 0.0: 52 b = 0.0 53 if r > 1.0: 54 r = 1.0 55 if g > 1.0: 56 g = 1.0 57 if b > 1.0: 58 b = 1.0 59 return (r, g, b) 60 61 62 # HLS: Hue, Luminance, Saturation 63 # H: position in the spectrum 64 # L: color lightness 65 # S: color saturation 66 67 def rgb_to_hls(r, g, b): 68 maxc = max(r, g, b) 69 minc = min(r, g, b) 70 # XXX Can optimize (maxc+minc) and (maxc-minc) 71 l = (minc+maxc)/2.0 72 if minc == maxc: 73 return 0.0, l, 0.0 74 if l <= 0.5: 75 s = (maxc-minc) / (maxc+minc) 76 else: 77 s = (maxc-minc) / (2.0-maxc-minc) 78 rc = (maxc-r) / (maxc-minc) 79 gc = (maxc-g) / (maxc-minc) 80 bc = (maxc-b) / (maxc-minc) 81 if r == maxc: 82 h = bc-gc 83 elif g == maxc: 84 h = 2.0+rc-bc 85 else: 86 h = 4.0+gc-rc 87 h = (h/6.0) % 1.0 88 return h, l, s 89 90 def hls_to_rgb(h, l, s): 91 if s == 0.0: 92 return l, l, l 93 if l <= 0.5: 94 m2 = l * (1.0+s) 95 else: 96 m2 = l+s-(l*s) 97 m1 = 2.0*l - m2 98 return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD)) 99 100 def _v(m1, m2, hue): 101 hue = hue % 1.0 102 if hue < ONE_SIXTH: 103 return m1 + (m2-m1)*hue*6.0 104 if hue < 0.5: 105 return m2 106 if hue < TWO_THIRD: 107 return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0 108 return m1 109 110 111 # HSV: Hue, Saturation, Value 112 # H: position in the spectrum 113 # S: color saturation ("purity") 114 # V: color brightness 115 116 def rgb_to_hsv(r, g, b): 117 maxc = max(r, g, b) 118 minc = min(r, g, b) 119 v = maxc 120 if minc == maxc: 121 return 0.0, 0.0, v 122 s = (maxc-minc) / maxc 123 rc = (maxc-r) / (maxc-minc) 124 gc = (maxc-g) / (maxc-minc) 125 bc = (maxc-b) / (maxc-minc) 126 if r == maxc: 127 h = bc-gc 128 elif g == maxc: 129 h = 2.0+rc-bc 130 else: 131 h = 4.0+gc-rc 132 h = (h/6.0) % 1.0 133 return h, s, v 134 135 def hsv_to_rgb(h, s, v): 136 if s == 0.0: 137 return v, v, v 138 i = int(h*6.0) # XXX assume int() truncates! 139 f = (h*6.0) - i 140 p = v*(1.0 - s) 141 q = v*(1.0 - s*f) 142 t = v*(1.0 - s*(1.0-f)) 143 i = i%6 144 if i == 0: 145 return v, t, p 146 if i == 1: 147 return q, v, p 148 if i == 2: 149 return p, v, t 150 if i == 3: 151 return p, q, v 152 if i == 4: 153 return t, p, v 154 if i == 5: 155 return v, p, q 156 # Cannot get here 157
