Resize an animated GIF to 512 x 512 by scaling and padding.

resize_gif_to_512x512.py

"""
Resize an animated GIF to 512 x 512 by scaling the photo to fit
then padding the remaining space with the color of the topleft pixel.

Note: May not work well with GIFs with transparency.

To turn GIFs into animated stickers for Signal, resize them with this script before
converting them to APNG with the gif2apng CLI (http://gif2apng.sourceforge.net/).
"""

from PIL import Image, ImageOps, ImageSequence


def resize(from_path: str, to_path: str) -> None:
    with Image.open(from_path) as gif:
        frames = []
        size = gif.size
        ratio = 512 / max(size)
        for frame in ImageSequence.Iterator(gif):
            c = frame.getpixel((0, 0))  # Topleft pixel as padding color
            frame = frame.resize((round(size[0] * ratio), round(size[1] * ratio)))
            dw = 512 - frame.size[0]
            dh = 512 - frame.size[1]
            padding = (dw // 2, dh // 2, dw - dw // 2, dh - dh // 2)
            im = ImageOps.expand(frame, padding, fill=c)
            im.info = frame.info
            frames.append(im)
    frames[0].save(to_path, save_all=True, append_images=frames[1:], disposal=2)