"""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](with the exception of I and Q, which covers a slightly larger range).Inputs outside the valid range may cause exceptions or invalid outputs. Supported color systems:RGB: Red, Green, Blue componentsYIQ: Luminance, Chrominance (used by composite video signals)HLS: Hue, Luminance, SaturationHSV: Hue, Saturation, Value""" # References:# http://en.wikipedia.org/wiki/YIQ# http://en.wikipedia.org/wiki/HLS_color_space# http://en.wikipedia.org/wiki/HSV_color_space __all__ = ["rgb_to_yiq","yiq_to_rgb","rgb_to_hls","hls_to_rgb",           "rgb_to_hsv","hsv_to_rgb"] # Some floating point constants ONE_THIRD = 1.0/3.0ONE_SIXTH = 1.0/6.0TWO_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, Saturation# H: position in the spectrum# L: color lightness# S: color saturation 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: color saturation ("purity")# V: color brightness 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