"""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 components YIQ: Luminance, Chrominance (used by composite video signals) HLS: Hue, Luminance, Saturation HSV: 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 = 1.0/3.0 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 # # There are a great many versions of the constants used in these formulae. # The ones in this library uses constants from the FCC version of NTSC. def rgb_to_yiq(r, g, b): y = 0.30*r + 0.59*g + 0.11*b i = 0.74*(r-y) - 0.27*(b-y) q = 0.48*(r-y) + 0.41*(b-y) return (y, i, q) def yiq_to_rgb(y, i, q): # r = y + (0.27*q + 0.41*i) / (0.74*0.41 + 0.27*0.48) # b = y + (0.74*q - 0.48*i) / (0.74*0.41 + 0.27*0.48) # g = y - (0.30*(r-y) + 0.11*(b-y)) / 0.59 r = y + 0.9468822170900693*i + 0.6235565819861433*q g = y - 0.27478764629897834*i - 0.6356910791873801*q b = y - 1.1085450346420322*i + 1.7090069284064666*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)) i = i%6 if i == 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