New module 'colorsys' implements conversions between different color systems.

Lib/colorsys.py

+# Conversion functions between RGB and other color systems.
+#
+# Define two functions for each color system XYZ:
+#   rgb_to_xyz(r, g, b) --> x, y, z
+#   xyz_to_rgb(x, y, z) --> r, g, b
+# All inputs and outputs are triples of floats in the range [0.0...1.0].
+# Inputs outside this range may cause exceptions or invalid outputs.
+#
+# Supported color systems:
+# RGB: Red, Green, Blue components
+# YIQ: used by composite video signals
+# HLS: Hue, Luminance, S???
+# HSV: Hue, Saturation, Value(?)
+#
+# References:
+# XXX Where's the literature?
+
+
+# Some floating point constants
+
+ONE_THIRD = 1.0/3.0
+ONE_SIXTH = 1.0/6.0
+TWO_THIRD = 2.0/3.0
+
+
+# YIQ: used by composite video signals (linear combinations of RGB)
+# Y: perceived grey level (0.0 == black, 1.0 == white)
+# I, Q: color components
+
+def rgb_to_yiq(r, g, b):
+    y = 0.30*r + 0.59*g + 0.11*b
+    i = 0.60*r - 0.28*g - 0.32*b
+    q = 0.21*r - 0.52*g + 0.31*b
+    return (y, i, q)
+
+def yiq_to_rgb(y, i, q):
+    r = y + 0.948262*i + 0.624013*q
+    g = y - 0.276066*i - 0.639810*q
+    b = y - 1.105450*i + 1.729860*q
+    if r < 0.0: r = 0.0
+    if g < 0.0: g = 0.0
+    if b < 0.0: b = 0.0
+    if r > 1.0: r = 1.0
+    if g > 1.0: g = 1.0
+    if b > 1.0: b = 1.0
+    return (r, g, b)
+
+
+# HLS: Hue, Luminance, S???
+# H: position in the spectrum
+# L: ???
+# S: ???
+
+def rgb_to_hls(r, g, b):
+    maxc = max(r, g, b)
+    minc = min(r, g, b)
+    # XXX Can optimize (maxc+minc) and (maxc-minc)
+    l = (minc+maxc)/2.0
+    if minc == maxc: return 0.0, l, 0.0
+    if l <= 0.5: s = (maxc-minc) / (maxc+minc)
+    else: s = (maxc-minc) / (2.0-maxc-minc)
+    rc = (maxc-r) / (maxc-minc)
+    gc = (maxc-g) / (maxc-minc)
+    bc = (maxc-b) / (maxc-minc)
+    if r == maxc: h = bc-gc
+    elif g == maxc: h = 2.0+rc-bc
+    else: h = 4.0+gc-rc
+    h = (h/6.0) % 1.0
+    return h, l, s
+
+def hls_to_rgb(h, l, s):
+    if s == 0.0: return l, l, l
+    if l <= 0.5: m2 = l * (1.0+s)
+    else: m2 = l+s-(l*s)
+    m1 = 2.0*l - m2
+    return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD))
+
+def _v(m1, m2, hue):
+    hue = hue % 1.0
+    if hue < ONE_SIXTH: return m1 + (m2-m1)*hue*6.0
+    if hue < 0.5: return m2
+    if hue < TWO_THIRD: return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0
+    return m1
+
+
+# HSV: Hue, Saturation, Value(?)
+# H: position in the spectrum
+# S: ???
+# V: ???
+
+def rgb_to_hsv(r, g, b):
+    maxc = max(r, g, b)
+    minc = min(r, g, b)
+    v = maxc
+    if minc == maxc: return 0.0, 0.0, v
+    s = (maxc-minc) / maxc
+    rc = (maxc-r) / (maxc-minc)
+    gc = (maxc-g) / (maxc-minc)
+    bc = (maxc-b) / (maxc-minc)
+    if r == maxc: h = bc-gc
+    elif g == maxc: h = 2.0+rc-bc
+    else: h = 4.0+gc-rc
+    h = (h/6.0) % 1.0
+    return h, s, v
+
+def hsv_to_rgb(h, s, v):
+    if s == 0.0: return v, v, v
+    i = int(h*6.0) # XXX assume int() truncates!
+    f = (h*6.0) - i
+    p = v*(1.0 - s)
+    q = v*(1.0 - s*f)
+    t = v*(1.0 - s*(1.0-f))
+    if i%6 == 0: return v, t, p
+    if i == 1: return q, v, p
+    if i == 2: return p, v, t
+    if i == 3: return p, q, v
+    if i == 4: return t, p, v
+    if i == 5: return v, p, q
+    # Cannot get here