Python实现RGB转Lab颜色空间，PS：和PhotoShop转换结果一下

由于工作要求，需要把rgb颜色转成Lab颜色空间。网上一搜一大把的代码，但是和PS一对比，基本上都不对。

下面这张图是OpenCV官方文档的计算方法。

 用Python实现代码如下：

from math import pow

param_13 = 1.0 / 3.0
param_16116 = 16.0 / 116.0

Xn = 0.950456
Yn = 1.0
Zn = 1.088754


def RGB2XYZ(r, g, b):
    x = 0.412453 * r + 0.357580 * g + 0.180423 * b
    y = 0.212671 * r + 0.715160 * g + 0.072169 * b
    z = 0.019334 * r + 0.119193 * g + 0.950227 * b
    return x, y, z


def XYZ2Lab(x, y, z):
    x /=  255 * Xn
    y /= 255 * Yn
    z /= 255 * Zn
    if y > 0.008856:
        fy = pow(y, param_13)
        l = 116.0 * fy - 16.0
    else:
        fy = 7.787 * y + param_16116
        l = 903.3 * fy

    if l < 0:
        l = 0.0

    if x>0.008856:
        fx = pow(x,param_13)
    else:
        fx = 7.787 * x + param_16116

    if z>0.008856:
        fz = pow(z,param_13)
    else:
        fz = 7.787 * z + param_16116

    a = 500.0*(fx-fy)
    b = 200.0*(fy-fz)

    return [round(l,2), round(a,2), round(b,2)]


def RGB2Lab(r, g, b):
    x, y, z = RGB2XYZ(r, g, b)
    return XYZ2Lab(x, y, z)


if __name__ == '__main__':
    rgb = [134, 156, 106]
    print("Lab: " + str(rgb))
    lab = RGB2Lab(rgb[0], rgb[1], rgb[2])
    print("Lab: " + str(lab))

下面测试一下运行结果：

rgb: [255, 0, 0]
Lab: [53.24, 80.09, 67.2]

rgb: [134, 156, 106]
Lab: [80.7, -10.37, 14.71]

rgb: [110, 99, 165]
Lab: [70.6, 11.6, -20.76]

 从对比可以看出当rbg为(255,0,0)时和PS的着色器对比基本差不多，但是后面两个就差得多了。

于是乎经过一番操作，终于实现了和PS结果一样的算法，代码如下：

def rgb2lab(rgb):
    r = rgb[0] / 255.0  # rgb range: 0 ~ 1
    g = rgb[1] / 255.0
    b = rgb[2] / 255.0

    # gamma 2.2
    if r > 0.04045:
        r = pow((r + 0.055) / 1.055, 2.4)
    else:
        r = r / 12.92

    if g > 0.04045:
        g = pow((g + 0.055) / 1.055, 2.4)
    else:
        g = g / 12.92

    if b > 0.04045:
        b = pow((b + 0.055) / 1.055, 2.4)
    else:
        b = b / 12.92

    # sRGB
    X = r * 0.436052025 + g * 0.385081593 + b * 0.143087414
    Y = r * 0.222491598 + g * 0.716886060 + b * 0.060621486
    Z = r * 0.013929122 + g * 0.097097002 + b * 0.714185470

    # XYZ range: 0~100
    X = X * 100.000
    Y = Y * 100.000
    Z = Z * 100.000

    # Reference White Point

    ref_X = 96.4221
    ref_Y = 100.000
    ref_Z = 82.5211

    X = X / ref_X
    Y = Y / ref_Y
    Z = Z / ref_Z

    # Lab
    if X > 0.008856:
        X = pow(X, 1 / 3.000)
    else:
        X = (7.787 * X) + (16 / 116.000)

    if Y > 0.008856:
        Y = pow(Y, 1 / 3.000)
    else:
        Y = (7.787 * Y) + (16 / 116.000)

    if Z > 0.008856:
        Z = pow(Z, 1 / 3.000)
    else:
        Z = (7.787 * Z) + (16 / 116.000)

    Lab_L = round((116.000 * Y) - 16.000, 2)
    Lab_a = round(500.000 * (X - Y), 2)
    Lab_b = round(200.000 * (Y - Z), 2)

    return Lab_L, Lab_a, Lab_b

对比一下结果：

rgb: [255, 0, 0]
Lab: (54.29, 80.81, 69.89)

rgb: [134, 156, 106]
Lab: (61.66, -14.83, 23.57)

rgb: [110, 99, 165]
Lab: (45.21, 16.45, -34.45)

 

从结果可以看出和PS的结果基本一致。