Function for overlaying transparent (PNG) images in python

cv2_transparent_overlay.py

import cv2
import numpy as np

def overlay_transparent(background_img, img_to_overlay_t, x, y, overlay_size=None):
    """
    @brief      Overlays a transparant PNG onto another image using CV2
    
    @param      background_img    The background image
    @param      img_to_overlay_t  The transparent image to overlay (has alpha channel)
    @param      x                 x location to place the top-left corner of our overlay
    @param      y                 y location to place the top-left corner of our overlay
    @param      overlay_size      The size to scale our overlay to (tuple), no scaling if None
    
    @return     Background image with overlay on top
    """
    
    bg_img = background_img.copy()
    
    if overlay_size is not None:
        img_to_overlay_t = cv2.resize(img_to_overlay_t.copy(), overlay_size)

    # Extract the alpha mask of the RGBA image, convert to RGB 
    b,g,r,a = cv2.split(img_to_overlay_t)
    overlay_color = cv2.merge((b,g,r))
    print(overlay_color.shape)
    
    # Optional, apply some simple filtering to the mask to remove edge noise
    #mask = cv2.medianBlur(a,5)

    h, w, _ = overlay_color.shape

    x, y = int(x-(float(w)/2.0)), int((y-float(h)/2.0))
    roi = bg_img[y:y+h, x:x+w]

    print(h,w)
    print('x y: ', x,y)
    print(roi.shape, mask.shape)

    # Black-out the area behind the logo in our original ROI
    img1_bg = cv2.bitwise_and(roi,roi,mask = cv2.bitwise_not(mask))
    
    # Mask out the logo from the logo image.
    img2_fg = cv2.bitwise_and(overlay_color,overlay_color,mask = mask)

    # Update the original image with our new ROI
    bg_img[y:y+h, x:x+w] = cv2.add(img1_bg, img2_fg)
    return bg_img
  
  if __name__ == '__main__':
    
    # Load overlay with transparency
    img_transparent = cv2.imread('overlay.png',-1)
    
    # Load Background
    background_img = cv2.imread('background_image.jpg')
    
    # Perform overlay
    image_with_overlay = overlay_transparent(background_img, img_transparent, 50, 50)