Lab.py

import numpy as np

def func(t):
    if (t > 0.008856):
        return np.power(t, 1/3.0);
    else:
        return 7.787 * t + 16 / 116.0;

def RGBtoLab(rgb):
    #Conversion Matrix
    matrix = [[0.412453, 0.357580, 0.180423],
              [0.212671, 0.715160, 0.072169],
              [0.019334, 0.119193, 0.950227]]

    # RGB values lie between 0 to 1.0
    rgb = [num/255 for num in rgb] # RGB

    cie = np.dot(matrix, rgb);

    cie[0] = cie[0] /0.950456;
    cie[2] = cie[2] /1.088754;

    # Calculate the L
    L = 116 * np.power(cie[1], 1/3.0) - 16.0 if cie[1] > 0.008856 else 903.3 * cie[1];

    # Calculate the a
    a = 500*(func(cie[0]) - func(cie[1]));

    # Calculate the b
    b = 200*(func(cie[1]) - func(cie[2]));

    #  Values lie between -128 < b <= 127, -128 < a <= 127, 0 <= L <= 100
    Lab = [b , a, L]
    return Lab