python OpenCV - add alpha channel to RGB image

Question

What is the best way to convert RGB image to RGBA in python using opencv?

Let\'s say I have one array with shape

(185, 198, 3) - it is RGB
         


        

Answer 1

Since OpenCV images are just Numpy arrays, you can do this in one-line, nice and fast with Numpy. So here is the setup code:

import numpy as np

# We'll synthesise a random image and a separate alpha channel full of 128 - semitransparent
im    = np.random.randint(0,256,(480,640,3), dtype=np.uint8)
alpha = np.full((480,640), 128, dtype=np.uint8)

And here is the solution which is simply to stack the alpha channel onto the image in the "depth" axis, hence dstack():

result = np.dstack((im, alpha))