Simple but reasonably flexible

slitscan.py

#!/usr/bin/env python

"""Simple slitscan generator

$ slitscan.py source slice destination

Where:
- source is a video or a directory of images;
- slice is either "c" for column or "r" for row
  and an integer, e.g., r1 or c42; and
- destination is an image file.

For example:
$ slitscan.py example.mp4 r100 example.png
Or perhaps:
$ slitscan.py directoy_of_frames c0 example.tiff

To do:
- error usefully when slice is larger than source
- warn when a frame is wrong-size?
- warn if dtype seems larger than dest can handle?
- safer slice parsing; test negative indexes (ranges?!)
- combine the separate code paths, within reason

By Charlie Loyd. Last update 2024-08-30.
Distributed under the Blue Oak Model License 1.0.0:
https://blueoakcouncil.org/license/1.0.0

"""

from imageio import v3 as iio
from tqdm import tqdm
from sys import argv
from pathlib import Path
import numpy as np


def make_dst(height, width, depth, length, dtype, axis):
    if axis == "r":
        return np.zeros((length, width, depth), dtype=dtype)
    else:
        return np.zeros((height, length, depth), dtype=dtype)


src_path = Path(argv[1])
if not src_path.exists():
    raise FileNotFoundError(f"{src_path} does not exist")

axis, posn = argv[2][0], int(argv[2][1:])
if axis not in ("c", "r"):
    raise ValueError(f"Use c for column or r for row, e.g., r1 or c42")

dst_path = Path(argv[3])
if dst_path.exists():
    raise FileExistsError(f"{dst_path} already exists")

dst = True  # you don’t have to declare variables in python, they said

if src_path.is_dir():
    files = sorted(list(src_path.glob("*")))
    t = iio.imread(files[0])
    dst = make_dst(
        height=t.shape[0],
        width=t.shape[1],
        depth=t.shape[2],
        length=len(files),
        dtype=t.dtype,
        axis=axis,
    )
    for i, f in tqdm(enumerate(files), total=len(files)):
        frame = iio.imread(f)
        if axis == "r":
            dst[i] = frame[posn]
        else:
            dst[:, i] = frame[:, posn]
else:
    props = iio.improps(src_path)
    if props.shape[0] == 0:
        raise RuntimeError(
            "The video i/o library can’t tell the video’s length.\n"
            "Try using ffmpeg to drop its frames to images, something like:\n"
            f'$ mkdir frames; ffmpeg -i \"{src_path}\" -f image2 "frames/f%04d.png"\n'
            "and run this script again with the frames folder as the input."
        )
    dst = make_dst(
        height=props.shape[1],
        width=props.shape[2],
        depth=props.shape[3],
        length=props.shape[0],
        dtype=props.dtype,
        axis=axis,
    )
    for i, frame in tqdm(enumerate(iio.imiter(src_path)), total=props.shape[0]):
        if axis == "r":
            dst[i] = frame[posn]
        else:
            dst[:, i] = frame[:, posn]


iio.imwrite(dst_path, dst)