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 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