Slice a tall image into chunks.

slice_image.py

#!/usr/bin/env python3
"""
Slice a (possibly very tall) image into fixed-height chunks.

Creates a sibling directory called  <image stem>_slices/
and writes   slice_000.png, slice_001.png, …  inside it.
"""

import argparse
from pathlib import Path

from PIL import Image


def slice_image(path: Path, slice_height: int) -> None:
    img = Image.open(path)
    w, h = img.size

    # Where to write the chunks
    out_dir = path.with_suffix("").with_name(f"{path.stem}_slices")
    out_dir.mkdir(exist_ok=True)

    n_slices = (h + slice_height - 1) // slice_height
    for i in range(n_slices):
        top = i * slice_height
        bottom = min(top + slice_height, h)
        box = (0, top, w, bottom)
        chunk = img.crop(box)

        out_file = out_dir / f"slice_{i:03}_of_{n_slices}.png"
        chunk.save(out_file)
        print(f"wrote {out_file}  ({w}×{bottom - top}px)")

    print(f"\nDone. {n_slices} slice(s) in {out_dir}")


def main() -> None:
    parser = argparse.ArgumentParser(
        description="Slice a tall image into chunks.",
        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
    )
    parser.add_argument("image", type=Path, help="Path to the source image")
    parser.add_argument(
        "--height",
        "-H",
        type=int,
        default=1024,
        help="Height of each slice in pixels",
    )
    args = parser.parse_args()

    if not args.image.is_file():
        parser.error(f"File not found: {args.image}")

    slice_image(args.image, args.height)


if __name__ == "__main__":
    main()