Apply colored overlay over a colored rgb image with some transparency in Skimage

Question

So basically I have a colored RGB image and I want to add a colored overlay over the RGB image without converting it to gray level. For example if I have a colored image(RGB). And I want to add a transparent blue color over the index like this

img[200:350, 200:350] = [0, 0, 1] # Blue block

This question is a sibling question to this one: Applying a coloured overlay to an image in either PIL or Imagemagik Difference is the color space. The above question is for gray level images rather colored (RGB).

from skimage import io, data
import numpy as np
img = data.astronaut()

Please use the above code to answer.

select the region you want to add the overlay first. Then add the color to that region — Jeru Luke, Mar 11 '17 at 10:48
@JeruLuke the problem with that is the color is not transparent. I need to see the background too. So there should be a proper alpha channel in the overlay. — Imran Salam, Mar 11 '17 at 10:52
I have the exact solution in OpenCV. Would you like to see it?? — Jeru Luke, Mar 11 '17 at 10:54

score 3 · Accepted Answer · answered Mar 11 '17 at 11:07

Here is the code in OpenCV:

import cv2

# load the image
image = cv2.imread("2.jpg")

# I resized the images because they were to big
image = cv2.resize(image, (0,0), fx=0.75, fy=0.75)

overlay = image.copy()
output = image.copy()

#select the region that has to be overlaid
cv2.rectangle(overlay, (420, 205), (595, 385),(0, 255, 255), -1)

#Adding the transparency parameter
alpha = 1

#Performing image overlay
cv2.addWeighted(overlay, alpha, output, 1 - alpha,0, output)

#Save the overlaid image
cv2.imwrite('Output'+str(alpha) +'.jpg', output)

cv2.waitKey(0)
cv2.destroyAllWindows()

Some results:

when alpha = 0.1