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Transparent overlays with Python OpenCV

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  • Last Updated : 29 Mar, 2022
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In this article, we are going to see how to Transparent overlays with Python OpenCV.

For this program to work, first we’ll need two inputs: Background Image, Overlay Image. We’ll then create a NumPy array with the same dimension as the background image, with all values as 0. Then we’ll create a mask using this array and the overlay.

Now the main part of our program the overlay will be done by using the cv2.addWeighted() method. 

cv2.addWeighted() :This method basically calculates the average weighted sum of the two input arrays to return an output array.

Image can be downloaded from here: Geekslogo, Background

Below is the Implementation: 


import cv2
import numpy as np
# Loading our images
# Background/Input image
background = cv2.imread('Assets/img1.jpg'
# Overlay image
overlay_image = cv2.imread('Assets/overlay3.png'
# Resize the overlay image to match the bg image dimensions
overlay_image = cv2.resize(overlay_image, (1000, 1000))
h, w = overlay_image.shape[:2]
# Create a new np array
shapes = np.zeros_like(background, np.uint8)
# Put the overlay at the bottom-right corner
shapes[background.shape[0]-h:, background.shape[1]-w:] = overlay_image
# Change this into bool to use it as mask
mask = shapes.astype(bool)
# We'll create a loop to change the alpha
# value i.e transparency of the overlay
for alpha in np.arange(0, 1.1, 0.1)[::-1]:
    # Create a copy of the image to work with
    bg_img = background.copy()
    # Create the overlay
    bg_img[mask] = cv2.addWeighted(bg_img, 1 - alpha, shapes,
                                   alpha, 0)[mask]
    # print the alpha value on the image
    cv2.putText(bg_img, f'Alpha: {round(alpha,1)}', (50, 200),
                cv2.FONT_HERSHEY_PLAIN, 8, (200, 200, 200), 7)
    # resize the image before displaying
    bg_img = cv2.resize(bg_img, (630, 630))
    cv2.imshow('Final Overlay', bg_img)


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