Lib/colorsys.py

   1 # Conversion functions between RGB and other color systems.
   2 #
   3 # Define two functions for each color system XYZ:
   4 #   rgb_to_xyz(r, g, b) --> x, y, z
   5 #   xyz_to_rgb(x, y, z) --> r, g, b
   6 # All inputs and outputs are triples of floats in the range [0.0...1.0].
   7 # Inputs outside this range may cause exceptions or invalid outputs.
   8 #
   9 # Supported color systems:
  10 # RGB: Red, Green, Blue components
  11 # YIQ: used by composite video signals
  12 # HLS: Hue, Luminance, S???
  13 # HSV: Hue, Saturation, Value(?)
  14 #
  15 # References:
  16 # XXX Where's the literature?
  17
  18
  19 # Some floating point constants
  20
  21 ONE_THIRD = 1.0/3.0
  22 ONE_SIXTH = 1.0/6.0
  23 TWO_THIRD = 2.0/3.0
  24
  25
  26 # YIQ: used by composite video signals (linear combinations of RGB)
  27 # Y: perceived grey level (0.0 == black, 1.0 == white)
  28 # I, Q: color components
  29
  30 def rgb_to_yiq(r, g, b):
  31     y = 0.30*r + 0.59*g + 0.11*b
  32     i = 0.60*r - 0.28*g - 0.32*b
  33     q = 0.21*r - 0.52*g + 0.31*b
  34     return (y, i, q)
  35
  36 def yiq_to_rgb(y, i, q):
  37     r = y + 0.948262*i + 0.624013*q
  38     g = y - 0.276066*i - 0.639810*q
  39     b = y - 1.105450*i + 1.729860*q
  40     if r < 0.0: r = 0.0
  41     if g < 0.0: g = 0.0
  42     if b < 0.0: b = 0.0
  43     if r > 1.0: r = 1.0
  44     if g > 1.0: g = 1.0
  45     if b > 1.0: b = 1.0
  46     return (r, g, b)
  47
  48
  49 # HLS: Hue, Luminance, S???
  50 # H: position in the spectrum
  51 # L: ???
  52 # S: ???
  53
  54 def rgb_to_hls(r, g, b):
  55     maxc = max(r, g, b)
  56     minc = min(r, g, b)
  57     # XXX Can optimize (maxc+minc) and (maxc-minc)
  58     l = (minc+maxc)/2.0
  59     if minc == maxc: return 0.0, l, 0.0
  60     if l <= 0.5: s = (maxc-minc) / (maxc+minc)
  61     else: s = (maxc-minc) / (2.0-maxc-minc)
  62     rc = (maxc-r) / (maxc-minc)
  63     gc = (maxc-g) / (maxc-minc)
  64     bc = (maxc-b) / (maxc-minc)
  65     if r == maxc: h = bc-gc
  66     elif g == maxc: h = 2.0+rc-bc
  67     else: h = 4.0+gc-rc
  68     h = (h/6.0) % 1.0
  69     return h, l, s
  70
  71 def hls_to_rgb(h, l, s):
  72     if s == 0.0: return l, l, l
  73     if l <= 0.5: m2 = l * (1.0+s)
  74     else: m2 = l+s-(l*s)
  75     m1 = 2.0*l - m2
  76     return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD))
  77
  78 def _v(m1, m2, hue):
  79     hue = hue % 1.0
  80     if hue < ONE_SIXTH: return m1 + (m2-m1)*hue*6.0
  81     if hue < 0.5: return m2
  82     if hue < TWO_THIRD: return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0
  83     return m1
  84
  85
  86 # HSV: Hue, Saturation, Value(?)
  87 # H: position in the spectrum
  88 # S: ???
  89 # V: ???
  90
  91 def rgb_to_hsv(r, g, b):
  92     maxc = max(r, g, b)
  93     minc = min(r, g, b)
  94     v = maxc
  95     if minc == maxc: return 0.0, 0.0, v
  96     s = (maxc-minc) / maxc
  97     rc = (maxc-r) / (maxc-minc)
  98     gc = (maxc-g) / (maxc-minc)
  99     bc = (maxc-b) / (maxc-minc)
 100     if r == maxc: h = bc-gc
 101     elif g == maxc: h = 2.0+rc-bc
 102     else: h = 4.0+gc-rc
 103     h = (h/6.0) % 1.0
 104     return h, s, v
 105
 106 def hsv_to_rgb(h, s, v):
 107     if s == 0.0: return v, v, v
 108     i = int(h*6.0) # XXX assume int() truncates!
 109     f = (h*6.0) - i
 110     p = v*(1.0 - s)
 111     q = v*(1.0 - s*f)
 112     t = v*(1.0 - s*(1.0-f))
 113     if i%6 == 0: return v, t, p
 114     if i == 1: return q, v, p
 115     if i == 2: return p, v, t
 116     if i == 3: return p, q, v
 117     if i == 4: return t, p, v
 118     if i == 5: return v, p, q
 119     # Cannot get here