| """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 |