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920dae64 AT |
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 | Inputs outside this range may cause exceptions or invalid outputs. | |
10 | ||
11 | Supported color systems: | |
12 | RGB: Red, Green, Blue components | |
13 | YIQ: used by composite video signals | |
14 | HLS: Hue, Luminance, Saturation | |
15 | HSV: Hue, Saturation, Value | |
16 | """ | |
17 | # References: | |
18 | # XXX Where's the literature? | |
19 | ||
20 | __all__ = ["rgb_to_yiq","yiq_to_rgb","rgb_to_hls","hls_to_rgb", | |
21 | "rgb_to_hsv","hsv_to_rgb"] | |
22 | ||
23 | # Some floating point constants | |
24 | ||
25 | ONE_THIRD = 1.0/3.0 | |
26 | ONE_SIXTH = 1.0/6.0 | |
27 | TWO_THIRD = 2.0/3.0 | |
28 | ||
29 | ||
30 | # YIQ: used by composite video signals (linear combinations of RGB) | |
31 | # Y: perceived grey level (0.0 == black, 1.0 == white) | |
32 | # I, Q: color components | |
33 | ||
34 | def rgb_to_yiq(r, g, b): | |
35 | y = 0.30*r + 0.59*g + 0.11*b | |
36 | i = 0.60*r - 0.28*g - 0.32*b | |
37 | q = 0.21*r - 0.52*g + 0.31*b | |
38 | return (y, i, q) | |
39 | ||
40 | def yiq_to_rgb(y, i, q): | |
41 | r = y + 0.948262*i + 0.624013*q | |
42 | g = y - 0.276066*i - 0.639810*q | |
43 | b = y - 1.105450*i + 1.729860*q | |
44 | if r < 0.0: r = 0.0 | |
45 | if g < 0.0: g = 0.0 | |
46 | if b < 0.0: b = 0.0 | |
47 | if r > 1.0: r = 1.0 | |
48 | if g > 1.0: g = 1.0 | |
49 | if b > 1.0: b = 1.0 | |
50 | return (r, g, b) | |
51 | ||
52 | ||
53 | # HLS: Hue, Luminance, S??? | |
54 | # H: position in the spectrum | |
55 | # L: ??? | |
56 | # S: ??? | |
57 | ||
58 | def rgb_to_hls(r, g, b): | |
59 | maxc = max(r, g, b) | |
60 | minc = min(r, g, b) | |
61 | # XXX Can optimize (maxc+minc) and (maxc-minc) | |
62 | l = (minc+maxc)/2.0 | |
63 | if minc == maxc: return 0.0, l, 0.0 | |
64 | if l <= 0.5: s = (maxc-minc) / (maxc+minc) | |
65 | else: s = (maxc-minc) / (2.0-maxc-minc) | |
66 | rc = (maxc-r) / (maxc-minc) | |
67 | gc = (maxc-g) / (maxc-minc) | |
68 | bc = (maxc-b) / (maxc-minc) | |
69 | if r == maxc: h = bc-gc | |
70 | elif g == maxc: h = 2.0+rc-bc | |
71 | else: h = 4.0+gc-rc | |
72 | h = (h/6.0) % 1.0 | |
73 | return h, l, s | |
74 | ||
75 | def hls_to_rgb(h, l, s): | |
76 | if s == 0.0: return l, l, l | |
77 | if l <= 0.5: m2 = l * (1.0+s) | |
78 | else: m2 = l+s-(l*s) | |
79 | m1 = 2.0*l - m2 | |
80 | return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD)) | |
81 | ||
82 | def _v(m1, m2, hue): | |
83 | hue = hue % 1.0 | |
84 | if hue < ONE_SIXTH: return m1 + (m2-m1)*hue*6.0 | |
85 | if hue < 0.5: return m2 | |
86 | if hue < TWO_THIRD: return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0 | |
87 | return m1 | |
88 | ||
89 | ||
90 | # HSV: Hue, Saturation, Value(?) | |
91 | # H: position in the spectrum | |
92 | # S: ??? | |
93 | # V: ??? | |
94 | ||
95 | def rgb_to_hsv(r, g, b): | |
96 | maxc = max(r, g, b) | |
97 | minc = min(r, g, b) | |
98 | v = maxc | |
99 | if minc == maxc: return 0.0, 0.0, v | |
100 | s = (maxc-minc) / maxc | |
101 | rc = (maxc-r) / (maxc-minc) | |
102 | gc = (maxc-g) / (maxc-minc) | |
103 | bc = (maxc-b) / (maxc-minc) | |
104 | if r == maxc: h = bc-gc | |
105 | elif g == maxc: h = 2.0+rc-bc | |
106 | else: h = 4.0+gc-rc | |
107 | h = (h/6.0) % 1.0 | |
108 | return h, s, v | |
109 | ||
110 | def hsv_to_rgb(h, s, v): | |
111 | if s == 0.0: return v, v, v | |
112 | i = int(h*6.0) # XXX assume int() truncates! | |
113 | f = (h*6.0) - i | |
114 | p = v*(1.0 - s) | |
115 | q = v*(1.0 - s*f) | |
116 | t = v*(1.0 - s*(1.0-f)) | |
117 | if i%6 == 0: return v, t, p | |
118 | if i == 1: return q, v, p | |
119 | if i == 2: return p, v, t | |
120 | if i == 3: return p, q, v | |
121 | if i == 4: return t, p, v | |
122 | if i == 5: return v, p, q | |
123 | # Cannot get here |