参考：
在Python中正确地将RGB转换成YCbCr
Python中rgb与ycbcr互转

# ITU-R BT.601
# https://en.wikipedia.org/wiki/YCbCr
# RGB -> YCbCr
def rgb2ycbcr(rgb):
    m = np.array([[ 65.481, 128.553, 24.966],
                  [-37.797, -74.203, 112],
                  [ 112, -93.786, -18.214]])
    shape = rgb.shape
    if len(shape) == 3:
        rgb = rgb.reshape((shape[0] * shape[1], 3))
    ycbcr = np.dot(rgb, m.transpose() / 255.)
    ycbcr[:,0] += 16.
    ycbcr[:,1:] += 128.
    return ycbcr.reshape(shape)

# ITU-R BT.601
# https://en.wikipedia.org/wiki/YCbCr
# YUV -> RGB
def ycbcr2rgb(ycbcr):
    m = np.array([[ 65.481, 128.553, 24.966],
                  [-37.797, -74.203, 112],
                  [ 112, -93.786, -18.214]])
    shape = ycbcr.shape
    if len(shape) == 3:
        ycbcr = ycbcr.reshape((shape[0] * shape[1], 3))
    rgb = copy.deepcopy(ycbcr)
    rgb[:,0] -= 16.
    rgb[:,1:] -= 128.
    rgb = np.dot(rgb, np.linalg.inv(m.transpose()) * 255.)
    return rgb.clip(0, 255).reshape(shape)

mat = np.array(
    [[ 65.481, 128.553, 24.966 ],
     [-37.797, -74.203, 112.0  ],
     [  112.0, -93.786, -18.214]])
mat_inv = np.linalg.inv(mat)
offset = np.array([16, 128, 128])
 
def rgb2ycbcr(rgb_img):
    ycbcr_img = np.zeros(rgb_img.shape)
    for x in range(rgb_img.shape[0]):
        for y in range(rgb_img.shape[1]):
            ycbcr_img[x, y, :] = np.round(np.dot(mat, rgb_img[x, y, :] * 1.0 / 255) + offset)
    return ycbcr_img
 
def ycbcr2rgb(ycbcr_img):
    rgb_img = np.zeros(ycbcr_img.shape, dtype=np.uint8)
    for x in range(ycbcr_img.shape[0]):
        for y in range(ycbcr_img.shape[1]):
            [r, g, b] = ycbcr_img[x,y,:]
            rgb_img[x, y, :] = np.maximum(0, np.minimum(255, np.round(np.dot(mat_inv, ycbcr_img[x, y, :] - offset) * 255.0)))
    return rgb_img