Lib/colorsys.py

   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