process_color_key_image.py

#!/usr/bin/env python3

import argparse
from scipy import misc
import numpy as np

def process_image(filepath, outfile):
    image = misc.imread(filepath)
    if image.shape[2] == 3:
        alpha = np.expand_dims(np.full(image.shape[:2], 255), axis=2)
        image = np.append(image, alpha, axis=2)

    width, height = image.shape[1], image.shape[0]
    color_key = image[0,0,:3]

    for x in range(width):
        for y in range(height):
            pixel = image[y,x,:3]
            if np.array_equal(pixel, color_key):
                image[y,x,3] = 0
    misc.imsave(outfile, image)

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("source_image")
    parser.add_argument("output_image")
    args = parser.parse_args()
    process_image(args.source_image, args.output_image)

if __name__ == "__main__":
    main()