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
37def 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
43def 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
67def 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
90def 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
100def _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
116def 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
135def 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