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| 1 | +# Conversion functions between RGB and other color systems. |
| 2 | +# |
| 3 | +# Define two functions for each color system XYZ: |
| 4 | +# rgb_to_xyz(r, g, b) --> x, y, z |
| 5 | +# xyz_to_rgb(x, y, z) --> r, g, b |
| 6 | +# All inputs and outputs are triples of floats in the range [0.0...1.0]. |
| 7 | +# Inputs outside this range may cause exceptions or invalid outputs. |
| 8 | +# |
| 9 | +# Supported color systems: |
| 10 | +# RGB: Red, Green, Blue components |
| 11 | +# YIQ: used by composite video signals |
| 12 | +# HLS: Hue, Luminance, S??? |
| 13 | +# HSV: Hue, Saturation, Value(?) |
| 14 | +# |
| 15 | +# References: |
| 16 | +# XXX Where's the literature? |
| 17 | + |
| 18 | + |
| 19 | +# Some floating point constants |
| 20 | + |
| 21 | +ONE_THIRD = 1.0/3.0 |
| 22 | +ONE_SIXTH = 1.0/6.0 |
| 23 | +TWO_THIRD = 2.0/3.0 |
| 24 | + |
| 25 | + |
| 26 | +# YIQ: used by composite video signals (linear combinations of RGB) |
| 27 | +# Y: perceived grey level (0.0 == black, 1.0 == white) |
| 28 | +# I, Q: color components |
| 29 | + |
| 30 | +def rgb_to_yiq(r, g, b): |
| 31 | + y = 0.30*r + 0.59*g + 0.11*b |
| 32 | + i = 0.60*r - 0.28*g - 0.32*b |
| 33 | + q = 0.21*r - 0.52*g + 0.31*b |
| 34 | + return (y, i, q) |
| 35 | + |
| 36 | +def yiq_to_rgb(y, i, q): |
| 37 | + r = y + 0.948262*i + 0.624013*q |
| 38 | + g = y - 0.276066*i - 0.639810*q |
| 39 | + b = y - 1.105450*i + 1.729860*q |
| 40 | + if r < 0.0: r = 0.0 |
| 41 | + if g < 0.0: g = 0.0 |
| 42 | + if b < 0.0: b = 0.0 |
| 43 | + if r > 1.0: r = 1.0 |
| 44 | + if g > 1.0: g = 1.0 |
| 45 | + if b > 1.0: b = 1.0 |
| 46 | + return (r, g, b) |
| 47 | + |
| 48 | + |
| 49 | +# HLS: Hue, Luminance, S??? |
| 50 | +# H: position in the spectrum |
| 51 | +# L: ??? |
| 52 | +# S: ??? |
| 53 | + |
| 54 | +def rgb_to_hls(r, g, b): |
| 55 | + maxc = max(r, g, b) |
| 56 | + minc = min(r, g, b) |
| 57 | + # XXX Can optimize (maxc+minc) and (maxc-minc) |
| 58 | + l = (minc+maxc)/2.0 |
| 59 | + if minc == maxc: return 0.0, l, 0.0 |
| 60 | + if l <= 0.5: s = (maxc-minc) / (maxc+minc) |
| 61 | + else: s = (maxc-minc) / (2.0-maxc-minc) |
| 62 | + rc = (maxc-r) / (maxc-minc) |
| 63 | + gc = (maxc-g) / (maxc-minc) |
| 64 | + bc = (maxc-b) / (maxc-minc) |
| 65 | + if r == maxc: h = bc-gc |
| 66 | + elif g == maxc: h = 2.0+rc-bc |
| 67 | + else: h = 4.0+gc-rc |
| 68 | + h = (h/6.0) % 1.0 |
| 69 | + return h, l, s |
| 70 | + |
| 71 | +def hls_to_rgb(h, l, s): |
| 72 | + if s == 0.0: return l, l, l |
| 73 | + if l <= 0.5: m2 = l * (1.0+s) |
| 74 | + else: m2 = l+s-(l*s) |
| 75 | + m1 = 2.0*l - m2 |
| 76 | + return (_v(m1, m2, h+ONE_THIRD), _v(m1, m2, h), _v(m1, m2, h-ONE_THIRD)) |
| 77 | + |
| 78 | +def _v(m1, m2, hue): |
| 79 | + hue = hue % 1.0 |
| 80 | + if hue < ONE_SIXTH: return m1 + (m2-m1)*hue*6.0 |
| 81 | + if hue < 0.5: return m2 |
| 82 | + if hue < TWO_THIRD: return m1 + (m2-m1)*(TWO_THIRD-hue)*6.0 |
| 83 | + return m1 |
| 84 | + |
| 85 | + |
| 86 | +# HSV: Hue, Saturation, Value(?) |
| 87 | +# H: position in the spectrum |
| 88 | +# S: ??? |
| 89 | +# V: ??? |
| 90 | + |
| 91 | +def rgb_to_hsv(r, g, b): |
| 92 | + maxc = max(r, g, b) |
| 93 | + minc = min(r, g, b) |
| 94 | + v = maxc |
| 95 | + if minc == maxc: return 0.0, 0.0, v |
| 96 | + s = (maxc-minc) / maxc |
| 97 | + rc = (maxc-r) / (maxc-minc) |
| 98 | + gc = (maxc-g) / (maxc-minc) |
| 99 | + bc = (maxc-b) / (maxc-minc) |
| 100 | + if r == maxc: h = bc-gc |
| 101 | + elif g == maxc: h = 2.0+rc-bc |
| 102 | + else: h = 4.0+gc-rc |
| 103 | + h = (h/6.0) % 1.0 |
| 104 | + return h, s, v |
| 105 | + |
| 106 | +def hsv_to_rgb(h, s, v): |
| 107 | + if s == 0.0: return v, v, v |
| 108 | + i = int(h*6.0) # XXX assume int() truncates! |
| 109 | + f = (h*6.0) - i |
| 110 | + p = v*(1.0 - s) |
| 111 | + q = v*(1.0 - s*f) |
| 112 | + t = v*(1.0 - s*(1.0-f)) |
| 113 | + if i%6 == 0: return v, t, p |
| 114 | + if i == 1: return q, v, p |
| 115 | + if i == 2: return p, v, t |
| 116 | + if i == 3: return p, q, v |
| 117 | + if i == 4: return t, p, v |
| 118 | + if i == 5: return v, p, q |
| 119 | + # Cannot get here |
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