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-"""Conversion functions between RGB and other color systems.
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-
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-This modules provides two functions for each color system ABC:
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-
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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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-
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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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-
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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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-
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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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-
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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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-
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-# Some floating point constants
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-
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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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-
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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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-#
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-# There are a great many versions of the constants used in these formulae.
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-# The ones in this library uses constants from the FCC version of NTSC.
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-
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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 = 0.74*(r-y) - 0.27*(b-y)
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- q = 0.48*(r-y) + 0.41*(b-y)
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- return (y, i, q)
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-
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-def yiq_to_rgb(y, i, q):
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- # r = y + (0.27*q + 0.41*i) / (0.74*0.41 + 0.27*0.48)
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- # b = y + (0.74*q - 0.48*i) / (0.74*0.41 + 0.27*0.48)
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- # g = y - (0.30*(r-y) + 0.11*(b-y)) / 0.59
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-
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- r = y + 0.9468822170900693*i + 0.6235565819861433*q
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- g = y - 0.27478764629897834*i - 0.6356910791873801*q
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- b = y - 1.1085450346420322*i + 1.7090069284064666*q
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-
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- if r < 0.0:
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- r = 0.0
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- if g < 0.0:
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- g = 0.0
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- if b < 0.0:
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- b = 0.0
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- if r > 1.0:
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- r = 1.0
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- if g > 1.0:
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- g = 1.0
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- if b > 1.0:
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- b = 1.0
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- return (r, g, b)
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-
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-
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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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-
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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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- sumc = (maxc+minc)
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- rangec = (maxc-minc)
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- l = sumc/2.0
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- if minc == maxc:
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- return 0.0, l, 0.0
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- if l <= 0.5:
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- s = rangec / sumc
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- else:
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- s = rangec / (2.0-maxc-minc) # Not always 2.0-sumc: gh-106498.
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- rc = (maxc-r) / rangec
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- gc = (maxc-g) / rangec
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- bc = (maxc-b) / rangec
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- if r == maxc:
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- h = bc-gc
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- elif g == maxc:
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- h = 2.0+rc-bc
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- else:
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- h = 4.0+gc-rc
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- # h = (h/6.0) % 1.0
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- h = h / 6.0
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- h = h - int(h)
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- return h, l, s
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-
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-def hls_to_rgb(h, l, s):
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- if s == 0.0:
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- return l, l, l
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- if l <= 0.5:
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- m2 = l * (1.0+s)
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- else:
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- 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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-
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-def _v(m1, m2, hue):
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- # hue = hue % 1.0
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- hue = hue - int(hue)
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- if hue < ONE_SIXTH:
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- return m1 + (m2-m1)*hue*6.0
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- if hue < 0.5:
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- return m2
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- if hue < TWO_THIRD:
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- return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0
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- return m1
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-
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-
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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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-
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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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- rangec = (maxc-minc)
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- v = maxc
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- if minc == maxc:
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- return 0.0, 0.0, v
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- s = rangec / maxc
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- rc = (maxc-r) / rangec
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- gc = (maxc-g) / rangec
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- bc = (maxc-b) / rangec
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- if r == maxc:
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- h = bc-gc
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- elif g == maxc:
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- h = 2.0+rc-bc
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- else:
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- h = 4.0+gc-rc
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- # h = (h/6.0) % 1.0
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- h = h / 6.0
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- h = h - int(h)
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- return h, s, v
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-
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-def hsv_to_rgb(h, s, v):
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- if s == 0.0:
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- 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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- i = i%6
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- if i == 0:
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- return v, t, p
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- if i == 1:
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- return q, v, p
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- if i == 2:
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- return p, v, t
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- if i == 3:
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- return p, q, v
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- if i == 4:
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- return t, p, v
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- if i == 5:
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- return v, p, q
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- # Cannot get here
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