Merge alpha channel from an image to another image (OpenCV is required)

marge_alpha.py

import argparse
import cv2

def main():
    args = parse_args()
    alpha, img = read_images(args)
    new_img = marge_alpha(args, alpha, img)
    write_image(args, new_img)

def parse_args():
    parser = argparse.ArgumentParser(description='Merge alpha channel from an image to another image')
    parser.add_argument('aipha_image_path', help='Path to image to extract the alpha channel')
    parser.add_argument('color_image_path', help='Path to image to extract the color channels (r, g, b)')
    parser.add_argument('-o', '--output', help='Path to write the result image. If it is omitted, the result will overwrite the image in color_image_path')
    parser.add_argument('-g', '--gray', action='store_true', help='Force gray-scale to be used as alpha')
    return parser.parse_args()

def read_images(args):
    alpha = cv2.imread(args.aipha_image_path, cv2.IMREAD_UNCHANGED)
    img = cv2.imread(args.color_image_path)
    return alpha, img

def marge_alpha(args, alpha, img):
    b, g, r = cv2.split(img)

    if alpha.shape[2] < 4 or args.gray:
        # Use gray-scale as alpha
        gray = cv2.cvtColor(alpha, cv2.COLOR_BGR2GRAY)
        new_img = cv2.merge((b, g, r, gray))
    else:
        _, _, _, a = cv2.split(alpha)
        new_img = cv2.merge((b, g, r, a))

    return new_img

def write_image(args, img):
    if args.output is not None:
        cv2.imwrite(args.output, img)
    else:
        # Overwrite color image file
        cv2.imwrite(args.color_image_path, img)

if __name__ == "__main__":
    main()