home *** CD-ROM | disk | FTP | other *** search
- """Conversion functions between RGB and other color systems.
-
- This modules provides two functions for each color system ABC:
-
- rgb_to_abc(r, g, b) --> a, b, c
- abc_to_rgb(a, b, c) --> 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
-