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: r = 0.0
  48     if g < 0.0: g = 0.0
  49     if b < 0.0: b = 0.0
  50     if r > 1.0: r = 1.0
  51     if g > 1.0: g = 1.0
  52     if b > 1.0: b = 1.0
  53     return (r, g, b)
  54
  55
  56 # HLS: Hue, Luminance, Saturation
  57 # H: position in the spectrum
  58 # L: color lightness
  59 # S: color saturation
  60
  61 def rgb_to_hls(r, g, b):
  62     maxc = max(r, g, b)
  63     minc = min(r, g, b)
  64     # XXX Can optimize (maxc+minc) and (maxc-minc)
  65     l = (minc+maxc)/2.0
  66     if minc == maxc: return 0.0, l, 0.0
  67     if l <= 0.5: s = (maxc-minc) / (maxc+minc)
  68     else: s = (maxc-minc) / (2.0-maxc-minc)
  69     rc = (maxc-r) / (maxc-minc)
  70     gc = (maxc-g) / (maxc-minc)
  71     bc = (maxc-b) / (maxc-minc)
  72     if r == maxc: h = bc-gc
  73     elif g == maxc: h = 2.0+rc-bc
  74     else: h = 4.0+gc-rc
  75     h = (h/6.0) % 1.0
  76     return h, l, s
  77
  78 def hls_to_rgb(h, l, s):
  79     if s == 0.0: return l, l, l
  80     if l <= 0.5: m2 = l * (1.0+s)
  81     else: m2 = l+s-(l*s)
  82     m1 = 2.0*l - m2
  83     return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD))
  84
  85 def _v(m1, m2, hue):
  86     hue = hue % 1.0
  87     if hue < ONE_SIXTH: return m1 + (m2-m1)*hue*6.0
  88     if hue < 0.5: return m2
  89     if hue < TWO_THIRD: return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0
  90     return m1
  91
  92
  93 # HSV: Hue, Saturation, Value
  94 # H: position in the spectrum
  95 # S: color saturation ("purity")
  96 # V: color brightness
  97
  98 def rgb_to_hsv(r, g, b):
  99     maxc = max(r, g, b)
 100     minc = min(r, g, b)
 101     v = maxc
 102     if minc == maxc: return 0.0, 0.0, v
 103     s = (maxc-minc) / maxc
 104     rc = (maxc-r) / (maxc-minc)
 105     gc = (maxc-g) / (maxc-minc)
 106     bc = (maxc-b) / (maxc-minc)
 107     if r == maxc: h = bc-gc
 108     elif g == maxc: h = 2.0+rc-bc
 109     else: h = 4.0+gc-rc
 110     h = (h/6.0) % 1.0
 111     return h, s, v
 112
 113 def hsv_to_rgb(h, s, v):
 114     if s == 0.0: return v, v, v
 115     i = int(h*6.0) # XXX assume int() truncates!
 116     f = (h*6.0) - i
 117     p = v*(1.0 - s)
 118     q = v*(1.0 - s*f)
 119     t = v*(1.0 - s*(1.0-f))
 120     i = i%6
 121     if i == 0: return v, t, p
 122     if i == 1: return q, v, p
 123     if i == 2: return p, v, t
 124     if i == 3: return p, q, v
 125     if i == 4: return t, p, v
 126     if i == 5: return v, p, q
 127     # Cannot get here