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rgb2lab = () ->
[r,g,b] = unpack arguments
r = rgb_xyz r
g = rgb_xyz g
b = rgb_xyz b
x = xyz_lab (0.4124564 * r + 0.3575761 * g + 0.1804375 * b) / X
y = xyz_lab (0.2126729 * r + 0.7151522 * g + 0.0721750 * b) / Y
z = xyz_lab (0.0193339 * r + 0.1191920 * g + 0.9503041 * b) / Z
[116 * y - 16, 500 * (x - y), 200 * (y - z)]
rgb_xyz = (r) ->
if (r /= 255) <= 0.04045 then r / 12.92 else Math.pow((r + 0.055) / 1.055, 2.4)
xyz_lab = (x) ->
if x > 0.008856 then Math.pow(x, 1 / 3) else 7.787037 * x + 4 / 29
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