Splitting and merging image color channels

On several occasions, we might be interested in working separately with the red, green, and blue channels. For example, we might want to build a histogram for each channel of an image.

The cv2.split() method is used to split an image into three different intensity arrays for each color channel, whereas cv2.merge() is used to merge different arrays into a single multichannel array, that is, a color image. Let's take a look at an example:

import cv2
img = cv2.imread('4.2.03.tiff',1)
b,g,r = cv2.split (img)
cv2.imshow('Blue Channel',b)
cv2.imshow('Green Channel',g)
cv2.imshow('Red Channel',r)
img=cv2.merge((b,g,r))
cv2.imshow('Merged Output',img)
cv2.waitKey(0)
cv2.destroyAllWindows()

The preceding program first splits the image into three channels (blue, green, and red) and then displays each one of them. The separate channels will only hold the intensity values of that color, and they will be essentially displayed as grayscale intensity images. Then...