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 # 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 40 def 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 46 def 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 75 def rgb_to_hls(r, g, b): 76 maxc = max(r, g, b) 77 minc = min(r, g, b) 78 # XXX Can optimize (maxc+minc) and (maxc-minc) 79 l = (minc+maxc)/2.0 80 if minc == maxc: 81 return 0.0, l, 0.0 82 if l <= 0.5: 83 s = (maxc-minc) / (maxc+minc) 84 else: 85 s = (maxc-minc) / (2.0-maxc-minc) 86 rc = (maxc-r) / (maxc-minc) 87 gc = (maxc-g) / (maxc-minc) 88 bc = (maxc-b) / (maxc-minc) 89 if r == maxc: 90 h = bc-gc 91 elif g == maxc: 92 h = 2.0+rc-bc 93 else: 94 h = 4.0+gc-rc 95 h = (h/6.0) % 1.0 96 return h, l, s 97 98 def hls_to_rgb(h, l, s): 99 if s == 0.0: 100 return l, l, l 101 if l <= 0.5: 102 m2 = l * (1.0+s) 103 else: 104 m2 = l+s-(l*s) 105 m1 = 2.0*l - m2 106 return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD)) 107 108 def _v(m1, m2, hue): 109 hue = hue % 1.0 110 if hue < ONE_SIXTH: 111 return m1 + (m2-m1)*hue*6.0 112 if hue < 0.5: 113 return m2 114 if hue < TWO_THIRD: 115 return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0 116 return m1 117 118 119 # HSV: Hue, Saturation, Value 120 # H: position in the spectrum 121 # S: color saturation ("purity") 122 # V: color brightness 123 124 def rgb_to_hsv(r, g, b): 125 maxc = max(r, g, b) 126 minc = min(r, g, b) 127 v = maxc 128 if minc == maxc: 129 return 0.0, 0.0, v 130 s = (maxc-minc) / maxc 131 rc = (maxc-r) / (maxc-minc) 132 gc = (maxc-g) / (maxc-minc) 133 bc = (maxc-b) / (maxc-minc) 134 if r == maxc: 135 h = bc-gc 136 elif g == maxc: 137 h = 2.0+rc-bc 138 else: 139 h = 4.0+gc-rc 140 h = (h/6.0) % 1.0 141 return h, s, v 142 143 def hsv_to_rgb(h, s, v): 144 if s == 0.0: 145 return v, v, v 146 i = int(h*6.0) # XXX assume int() truncates! 147 f = (h*6.0) - i 148 p = v*(1.0 - s) 149 q = v*(1.0 - s*f) 150 t = v*(1.0 - s*(1.0-f)) 151 i = i%6 152 if i == 0: 153 return v, t, p 154 if i == 1: 155 return q, v, p 156 if i == 2: 157 return p, v, t 158 if i == 3: 159 return p, q, v 160 if i == 4: 161 return t, p, v 162 if i == 5: 163 return v, p, q 164 # Cannot get here 165
