Combine two images vertically as save as a png file (python)

combine_images.py

'''Combine two images vertically

- arg1 file will be on top while arg2 will be at the bottom
- arg1's width will be the reference to resize arg2 if arg2 has different width
- output file will be saved in the directory of arg1 as "merged.png"

2025-01-15 jkang first created
'''

import os
import sys
from PIL import Image

NEW_FILE = 'merged'

def check_files(filename):
    if not os.path.exists(filename):
        raise Exception(f'{filename} does not exists')


def main(img1_file, img2_file, fileid):

    check_files(img1_file)
    check_files(img2_file)
    print(f'file1: {img1_file}')
    print(f'file2: {img2_file}')

    if not fileid:
        fileid = NEW_FILE

    img1 = Image.open(img1_file)
    img2 = Image.open(img2_file)

    ref_width = img1.width
    if img1.width != img2.width:
        target_height = int(img2.height * (ref_width/img2.width))
        print(f'target size: w={ref_width} x h={target_height}')
        img2 = img2.resize((ref_width, target_height), Image.Resampling.LANCZOS)

    img_merge = Image.new(img1.mode, (img1.width, (img1.height+img2.height)))
    img_merge.paste(img1, (0, 0))
    img_merge.paste(img2, (0, img1.height))

    filepath = os.path.abspath(img1_file)
    filepath = os.path.dirname(filepath)
    newfile = os.path.join(filepath, fileid+'.png')
    try:
        img_merge.save(newfile)
        print(f'{newfile} is created')
    except Exception as e:
        print('ERROR OCCURRED:')
        print(e)


if __name__ == '__main__':
    img1_file = sys.argv[1]
    img2_file = sys.argv[2]
    fileid = sys.argv[3]

    main(img1_file, img2_file, fileid)