rgb, ycbcr, opencv, numpy, skimage

rgb2ycbcr.py

import numpy as np
import cv2
import skimage.color
import torch


rgb2ycbcr = np.array([[65.481,   128.553,    24.966],
                           [-37.797,   -74.203,     112.0],
                           [112.0,   -93.786,   -18.214]]).T
# from scipy import linalg
# rgb_from_ycbcr = linalg.inv(ycbcr_from_rgb)
ycbcr2rgb = np.array([[4.56621005e-03,  1.18087999e-09,  6.25892897e-03],
                           [4.56621005e-03, -1.53632369e-03, -3.18811095e-03],
                           [4.56621005e-03,  7.91071623e-03,  1.19774970e-08]])

img = (np.ones((2,2,3)) * 255).astype(np.uint8)
img[..., 0] *= 1
img[..., 1] *= 2
img[..., 2] *= 3

# img = cv2.imread('../images/butterfly.png')

mul = np.matmul(img / 255.0, rgb2ycbcr)
mul[..., 0] += 16
mul[..., 1] += 128
mul[..., 2] += 128
print('matmul', mul)
print('ski', skimage.color.rgb2ycbcr(img))
print('opencv', cv2.cvtColor(img, cv2.COLOR_RGB2YCrCb))

output

matmul [[[234.30005882 127.41256078 128.51064314]
  [234.30005882 127.41256078 128.51064314]]
 [[234.30005882 127.41256078 128.51064314]
  [234.30005882 127.41256078 128.51064314]]]

ski [[[234.30005882 127.41256078 128.51064314]
  [234.30005882 127.41256078 128.51064314]]
 [[234.30005882 127.41256078 128.51064314]
  [234.30005882 127.41256078 128.51064314]]]

opencv [[[254 129 127]
  [254 129 127]]
 [[254 129 127]
  [254 129 127]]]