cbcr_plot.py

#!/usr/bin/env python

# simple visualization of the Cb/Cr plane of an image

from skimage import io
import numpy as np
from sys import argv

src = io.imread(argv[1])
print src.shape

R, G, B = src[:,:,0], src[:,:,1], src[:,:,2]

Y = (0.299 * R) + (0.587 * G) + (0.114 * B)
Cb = (-0.169 * R) - (0.331 * G) + (0.499 * B) + 128
Cr = (0.499 * R) - (0.418 * G) - (0.0813 * B) + 128

# traditional vectorscope orientation:
Cr = 256 - Cr

dst = np.zeros((256, 256), dtype=np.uint16)

for x in range(src.shape[0]):
  for y in range(src.shape[1]):
    dst[int(Cr[x, y]), int(Cb[x, y])] += 1

io.imsave(argv[2], dst)