Thresholding multi-channel images like CMYK using OpenCV

# Thresholding C and K values
binaryImage = cv.inRange(
    inputImageCMYK,
    (128,   0,   0,   0),
    (255, 255, 255, 196))

Remarks:

You can then display the thresholded images:

plt.imshow(binaryImage, cmap='gray')