ycocg-vectorscope.py

#!/usr/bin/env python

# simple visualization of the Co/Cg plane of an image
# https://en.wikipedia.org/wiki/YCoCg

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

src = io.imread(argv[1])

if src.dtype == np.uint16:
  src = (src / 2**8).astype(np.uint8)

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

Y = 0.25 * R + 0.5 * G + 0.25 * B 
Cg = -0.25 * R + 0.5 * G - 0.25 * B + 0.5
Co = 0.5 * R - 0.5 * B + 0.5

Co = Co + 127
Cg = Cg + 127

Co = 255 - Co

dst = np.zeros((256, 256, 3), dtype=src.dtype)

for x in range(src.shape[0]):
  for y in range(src.shape[1]):
    dst[int(Cg[x, y]), int(Co[x, y])] = np.array([R[x, y], G[x, y], B[x, y]])

io.imsave(argv[2], dst)