RGB to CIELab color space conversion

rgb2lab.py

# RGB to Lab conversion

# Step 1: RGB to XYZ
#         http://www.easyrgb.com/index.php?X=MATH&H=02#text2
# Step 2: XYZ to Lab
#         http://www.easyrgb.com/index.php?X=MATH&H=07#text7


def rgb2lab(inputColor):

    num = 0
    RGB = [0, 0, 0]

    for value in inputColor:
        value = float(value) / 255

        if value > 0.04045:
            value = ((value + 0.055) / 1.055) ** 2.4
        else:
            value = value / 12.92

        RGB[num] = value * 100
        num = num + 1

    XYZ = [0, 0, 0, ]

    X = RGB[0] * 0.4124 + RGB[1] * 0.3576 + RGB[2] * 0.1805
    Y = RGB[0] * 0.2126 + RGB[1] * 0.7152 + RGB[2] * 0.0722
    Z = RGB[0] * 0.0193 + RGB[1] * 0.1192 + RGB[2] * 0.9505
    XYZ[0] = round(X, 4)
    XYZ[1] = round(Y, 4)
    XYZ[2] = round(Z, 4)

    # Observer= 2°, Illuminant= D65
    XYZ[0] = float(XYZ[0]) / 95.047         # ref_X =  95.047
    XYZ[1] = float(XYZ[1]) / 100.0          # ref_Y = 100.000
    XYZ[2] = float(XYZ[2]) / 108.883        # ref_Z = 108.883

    num = 0
    for value in XYZ:

        if value > 0.008856:
            value = value ** (0.3333333333333333)
        else:
            value = (7.787 * value) + (16 / 116)

        XYZ[num] = value
        num = num + 1

    Lab = [0, 0, 0]

    L = (116 * XYZ[1]) - 16
    a = 500 * (XYZ[0] - XYZ[1])
    b = 200 * (XYZ[1] - XYZ[2])

    Lab[0] = round(L, 4)
    Lab[1] = round(a, 4)
    Lab[2] = round(b, 4)

    return Lab

This is really useful, thanks!