Fusing images with Pillow

Every once in a while I think it's nice to print out some photos, but often the paper sizes available to me are a bit to large and not appropriate for what I want to use the printouts for. A workaround I usually employ is fusing the images together pairwise, printing the fused images on the paper size I have available and then cut the printed images in half. Doing this manually is really frustrating so I managed to create a little script that does this for me, given a directory with images with the same aspect ratios.

from PIL import Image
import sys
import os

def fuse_images(image1, image2):
    if max(image1.size) > max(image2.size):
        larger = image1
        smaller = image2
    else:
        larger = image2
        smaller = image1
    larger.thumbnail((max(smaller.size), max(smaller.size)), Image.ANTIALIAS)
    if larger.size[0] > larger.size[1]:
        larger = larger.rotate(90, expand=True)
    if smaller.size[0] > smaller.size[1]:
        smaller = smaller.rotate(90, expand=True)
    fused = Image.new('RGB', (smaller.size[0] + larger.size[0], larger.size[1]))
    fused.paste(smaller, (0,0))
    fused.paste(larger, (smaller.size[0], 0))
    return fused

def main(directory):
    images = [Image.open(os.path.join(directory, f)) for f in os.listdir(directory)]
    images.sort(key=lambda im: im.size[0] * im.size[1])
    if len(images) % 2 != 0:
        print('Warning - uneven number of images means that the following image will be ignored: {}'.format(images[-1].filename))
    for image1, image2 in zip(images[::2], images[1::2]):
        fused = fuse_images(image1, image2)
        filename = 'fused_{}_{}.jpg'.format(os.path.basename(image1.filename), os.path.basename(image2.filename))
        path = os.path.join(directory, filename)
        fused.save(path)

if __name__ == '__main__':
    directory = '.' if len(sys.argv) < 2 else sys.argv[1]
    if not os.path.exists(directory):
        print('{} is not a valid directory. Provide the location of the images or let the script default to the current working directory.'.format(directory))
        sys.exit(1)
    main(directory)

It is fairly easy to add logic to filter for the aspect ratio. A predicate to distinguish between 4:3 and 3:2 could look like this:

three_two = lambda x: abs(3/2 - max(x.size)/min(x.size)) < abs(4/3 - max(x.size)/min(x.size))

Thought I'd leave this up here if it's of use to anyone and (mainly) for when I inevitably want to repeat the process having forgotten how I did it the last time.

Written on July 12, 2019