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0d89e351e1
r878@spiff: Fredrik | 2005-11-12 14:37:22 +0100 minor docstring and comment tweaks (wikipedia might not be the ultimate reference, but it's a lot better than "XXX" ;-)
127 lines
3.4 KiB
Python
127 lines
3.4 KiB
Python
"""Conversion functions between RGB and other color systems.
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This modules provides two functions for each color system ABC:
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rgb_to_abc(r, g, b) --> a, b, c
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abc_to_rgb(a, b, c) --> r, g, b
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All inputs and outputs are triples of floats in the range [0.0...1.0]
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(with the exception of I and Q, which covers a slightly larger range).
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Inputs outside the valid range may cause exceptions or invalid outputs.
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Supported color systems:
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RGB: Red, Green, Blue components
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YIQ: Luminance, Chrominance (used by composite video signals)
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HLS: Hue, Luminance, Saturation
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HSV: Hue, Saturation, Value
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"""
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# References:
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# http://en.wikipedia.org/wiki/YIQ
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# http://en.wikipedia.org/wiki/HLS_color_space
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# http://en.wikipedia.org/wiki/HSV_color_space
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__all__ = ["rgb_to_yiq","yiq_to_rgb","rgb_to_hls","hls_to_rgb",
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"rgb_to_hsv","hsv_to_rgb"]
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# Some floating point constants
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ONE_THIRD = 1.0/3.0
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ONE_SIXTH = 1.0/6.0
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TWO_THIRD = 2.0/3.0
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# YIQ: used by composite video signals (linear combinations of RGB)
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# Y: perceived grey level (0.0 == black, 1.0 == white)
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# I, Q: color components
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def rgb_to_yiq(r, g, b):
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y = 0.30*r + 0.59*g + 0.11*b
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i = 0.60*r - 0.28*g - 0.32*b
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q = 0.21*r - 0.52*g + 0.31*b
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return (y, i, q)
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def yiq_to_rgb(y, i, q):
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r = y + 0.948262*i + 0.624013*q
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g = y - 0.276066*i - 0.639810*q
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b = y - 1.105450*i + 1.729860*q
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if r < 0.0: r = 0.0
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if g < 0.0: g = 0.0
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if b < 0.0: b = 0.0
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if r > 1.0: r = 1.0
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if g > 1.0: g = 1.0
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if b > 1.0: b = 1.0
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return (r, g, b)
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# HLS: Hue, Luminance, Saturation
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# H: position in the spectrum
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# L: color lightness
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# S: color saturation
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def rgb_to_hls(r, g, b):
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maxc = max(r, g, b)
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minc = min(r, g, b)
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# XXX Can optimize (maxc+minc) and (maxc-minc)
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l = (minc+maxc)/2.0
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if minc == maxc: return 0.0, l, 0.0
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if l <= 0.5: s = (maxc-minc) / (maxc+minc)
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else: s = (maxc-minc) / (2.0-maxc-minc)
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rc = (maxc-r) / (maxc-minc)
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gc = (maxc-g) / (maxc-minc)
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bc = (maxc-b) / (maxc-minc)
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if r == maxc: h = bc-gc
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elif g == maxc: h = 2.0+rc-bc
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else: h = 4.0+gc-rc
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h = (h/6.0) % 1.0
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return h, l, s
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def hls_to_rgb(h, l, s):
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if s == 0.0: return l, l, l
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if l <= 0.5: m2 = l * (1.0+s)
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else: m2 = l+s-(l*s)
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m1 = 2.0*l - m2
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return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD))
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def _v(m1, m2, hue):
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hue = hue % 1.0
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if hue < ONE_SIXTH: return m1 + (m2-m1)*hue*6.0
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if hue < 0.5: return m2
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if hue < TWO_THIRD: return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0
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return m1
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# HSV: Hue, Saturation, Value
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# H: position in the spectrum
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# S: color saturation ("purity")
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# V: color brightness
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def rgb_to_hsv(r, g, b):
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maxc = max(r, g, b)
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minc = min(r, g, b)
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v = maxc
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if minc == maxc: return 0.0, 0.0, v
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s = (maxc-minc) / maxc
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rc = (maxc-r) / (maxc-minc)
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gc = (maxc-g) / (maxc-minc)
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bc = (maxc-b) / (maxc-minc)
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if r == maxc: h = bc-gc
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elif g == maxc: h = 2.0+rc-bc
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else: h = 4.0+gc-rc
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h = (h/6.0) % 1.0
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return h, s, v
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def hsv_to_rgb(h, s, v):
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if s == 0.0: return v, v, v
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i = int(h*6.0) # XXX assume int() truncates!
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f = (h*6.0) - i
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p = v*(1.0 - s)
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q = v*(1.0 - s*f)
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t = v*(1.0 - s*(1.0-f))
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if i%6 == 0: return v, t, p
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if i == 1: return q, v, p
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if i == 2: return p, v, t
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if i == 3: return p, q, v
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if i == 4: return t, p, v
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if i == 5: return v, p, q
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# Cannot get here
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