diff --git a/imageset_thumbnails.py b/imageset_thumbnails.py
new file mode 100755
index 0000000..c8ce2c7
--- /dev/null
+++ b/imageset_thumbnails.py
@@ -0,0 +1,413 @@
+#!/usr/bin/env -S uv run --script
+# /// script
+# dependencies = ["Pillow"]
+# ///
+
+import argparse
+import atexit
+import logging
+import os
+import re
+import shutil
+import subprocess
+import sys
+from concurrent.futures import FIRST_COMPLETED, Future, ProcessPoolExecutor, wait
+from contextlib import ExitStack
+from dataclasses import dataclass
+from functools import partial
+from io import BytesIO
+from multiprocessing import get_context
+from pathlib import Path
+from time import perf_counter
+from typing import BinaryIO, Callable
+from zipfile import BadZipFile, ZipFile, ZipInfo, is_zipfile
+
+from PIL import Image, ImageColor, ImageOps
+
+logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s: %(message)s")
+worker_archive: ZipFile | None = None
+
+
+@dataclass
+class Source:
+    name: str
+    path: Path | None = None
+    member: ZipInfo | None = None
+    ratio: float = 1.0
+
+
+@dataclass
+class Row:
+    sources: list[Source]
+    height: int
+    widths: list[int]
+
+
+@dataclass
+class Cell:
+    source: Source
+    position: tuple[int, int]
+    size: tuple[int, int]
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser(
+        description="Create a separate justified image contact sheet for each directory or ZIP.",
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
+    )
+    parser.add_argument("inputs", nargs="+", type=Path, help="Image directories or ZIP archives; missing paths are skipped")
+    parser.add_argument("--output", type=Path, help="JPEG output for a single existing input; defaults to <input-name>_thumbs.jpg beside each input")
+    parser.add_argument("--width", type=int, default=2500, help="Sheet width in pixels")
+    parser.add_argument("--target-height", type=int, default=300, help="Preferred row height in pixels; rows may be taller or shorter")
+    parser.add_argument("--gap", type=int, default=8, help="Gap between images and at sheet edges in pixels")
+    parser.add_argument("--bg-color", default="white", help="Background color as a color name or hex value")
+    parser.add_argument("--workers", type=int, default=os.cpu_count() or 1, help="Number of resize worker processes")
+    arguments = parser.parse_args()
+    if arguments.target_height <= 0 or arguments.width <= 0 or arguments.gap < 0:
+        parser.error("width and target height must be positive; gap must be nonnegative")
+    if arguments.width <= 2 * arguments.gap:
+        parser.error("width must exceed twice the gap")
+    if arguments.workers <= 0:
+        parser.error("workers must be positive")
+    try:
+        ImageColor.getcolor(color=arguments.bg_color, mode="RGB")
+    except ValueError as error:
+        parser.error(f"Invalid background color: {error}")
+    return arguments
+
+
+def read_image(source: Source, archive: ZipFile | None) -> Image.Image:
+    with ExitStack() as stack:
+        if source.member is not None:
+            if archive is None:
+                raise ValueError("ZIP source requires an open archive")
+            stream = stack.enter_context(archive.open(name=source.member))
+            original = stack.enter_context(Image.open(fp=stream))
+        else:
+            original = stack.enter_context(Image.open(fp=source.path))
+        oriented = ImageOps.exif_transpose(image=original)
+        result = oriented.convert(mode="RGBA")
+        if oriented is not original:
+            oriented.close()
+        return result
+
+
+def read_dims_jpeg(stream: BinaryIO) -> tuple[int, int]:
+    EXIF_ORIENTATION_TAG = 274
+    ORIENTATIONS_SWAPPING_WIDTH_HEIGHT = {5, 6, 7, 8}
+    with Image.open(fp=stream) as image:
+        width, height = image.size
+        if image.getexif().get(EXIF_ORIENTATION_TAG) in ORIENTATIONS_SWAPPING_WIDTH_HEIGHT:
+            return height, width
+        return width, height
+
+
+def read_dims(image_path: Path | BinaryIO) -> tuple[int, int]:
+    EXIF_ORIENTATION_TAG = 274
+    ORIENTATIONS_SWAPPING_WIDTH_HEIGHT = {5, 6, 7, 8}
+    with ExitStack() as stack:
+        stream = stack.enter_context(image_path.open(mode="rb")) if isinstance(image_path, Path) else image_path
+        signature = stream.read(12)
+        stream.seek(0)
+        if signature.startswith(b"\xff\xd8"):
+            return read_dims_jpeg(stream=stream)
+        if signature.startswith(b"\x89PNG\r\n\x1a\n"):
+            raise ValueError("PNG images are not supported")
+        if signature[:4] == b"RIFF" and signature[8:12] == b"WEBP":
+            raise ValueError("WebP images are not supported")
+        with Image.open(fp=stream) as image:
+            if image.format == "TIFF":
+                raise ValueError("TIFF images are not supported")
+            width, height = image.size
+            if image.getexif().get(EXIF_ORIENTATION_TAG) in ORIENTATIONS_SWAPPING_WIDTH_HEIGHT:
+                return height, width
+            return width, height
+
+
+def natural_sort_key(name: str) -> tuple[str | int, ...]:
+    return tuple(int(part) if index % 2 else part.casefold() for index, part in enumerate(re.split(pattern=r"([0-9]+)", string=name)))
+
+
+def discover_sources(input_path: Path, output_path: Path, archive: ZipFile | None) -> list[Source]:
+    Image.init()
+    extensions = {extension for extension, image_format in Image.registered_extensions().items() if image_format not in {"PNG", "WEBP", "TIFF"}}
+    if archive is not None:
+        candidates = [
+            Source(name=member.filename, member=member)
+            for member in archive.infolist()
+            if not member.is_dir() and Path(member.filename).suffix.lower() in extensions
+        ]
+    else:
+        candidates = [
+            Source(name=path.relative_to(input_path).as_posix(), path=path)
+            for path in input_path.rglob("*")
+            if path.is_file() and path.suffix.lower() in extensions and path.resolve() != output_path.resolve()
+        ]
+    sources = []
+    logging.info(f"Reading metadata for {len(candidates)} images")
+    for index, source in enumerate(sorted(candidates, key=lambda source: (natural_sort_key(name=source.name), source.name)), start=1):
+        try:
+            if source.member is not None and archive is not None:
+                with archive.open(name=source.member) as stream:
+                    width, height = read_dims(image_path=stream)
+            elif source.path is not None:
+                width, height = read_dims(image_path=source.path)
+            else:
+                raise ValueError("Image source has no file or ZIP member")
+            source.ratio = width / height
+            sources.append(source)
+        except (OSError, ValueError, SyntaxError, RuntimeError, BadZipFile, Image.DecompressionBombError) as error:
+            logging.warning(f"Skipping {source.name}: {error}")
+        if index % 100 == 0 or index == len(candidates):
+            logging.info(f"Metadata {index}/{len(candidates)} ({index / len(candidates):.0%}); {len(sources)} usable images")
+    if not sources:
+        raise ValueError("No usable images found")
+    return sources
+
+
+def fitted_height(sources: list[Source], width: int, gap: int) -> float:
+    available = width - gap * (len(sources) + 1)
+    return available / sum(source.ratio for source in sources)
+
+
+def make_row(sources: list[Source], width: int, gap: int, target_height: int, justify: bool) -> Row:
+    available = width - gap * (len(sources) + 1)
+    ideal_height = fitted_height(sources=sources, width=width, gap=gap)
+    height = max(1, round(ideal_height if justify else min(target_height, ideal_height)))
+    ratio_sum = sum(source.ratio for source in sources)
+    total_width = available if justify else min(available, max(len(sources), round(ratio_sum * height)))
+    widths = []
+    cumulative = 0.0
+    previous = 0
+    for index, source in enumerate(sources):
+        cumulative += source.ratio
+        boundary = min(
+            total_width - (len(sources) - index - 1),
+            max(previous + 1, round(total_width * cumulative / ratio_sum)),
+        )
+        widths.append(boundary - previous)
+        previous = boundary
+    return Row(sources=sources, height=height, widths=widths)
+
+
+def layout_rows(sources: list[Source], width: int, gap: int, target_height: int) -> list[Row]:
+    rows = []
+    start = 0
+    while start < len(sources):
+        end = start + 1
+        while end < len(sources) and fitted_height(sources=sources[start:end], width=width, gap=gap) > target_height:
+            candidate = sources[start : end + 1]
+            if width - gap * (len(candidate) + 1) < len(candidate):
+                break
+            candidate_height = fitted_height(sources=candidate, width=width, gap=gap)
+            current_height = fitted_height(sources=sources[start:end], width=width, gap=gap)
+            if candidate_height <= target_height and abs(current_height - target_height) <= abs(candidate_height - target_height):
+                break
+            end += 1
+        group = sources[start:end]
+        justify = end < len(sources) or fitted_height(sources=group, width=width, gap=gap) <= target_height
+        rows.append(make_row(sources=group, width=width, gap=gap, target_height=target_height, justify=justify))
+        start = end
+    return rows
+
+
+def initialize_worker(archive_path: Path | None) -> None:
+    global worker_archive
+    if archive_path is not None:
+        worker_archive = ZipFile(file=archive_path)
+        atexit.register(worker_archive.close)
+
+
+def resize_with_pillow(cell: Cell) -> bytes:
+    with read_image(source=cell.source, archive=worker_archive) as image:
+        with image.resize(size=cell.size, resample=Image.Resampling.LANCZOS) as thumbnail:
+            return thumbnail.tobytes()
+
+
+def resize_with_vips(cell: Cell, vips_binary: str) -> bytes:
+    input_bytes = None
+    if cell.source.member is not None:
+        if worker_archive is None:
+            raise ValueError("ZIP source requires an open archive")
+        input_bytes = worker_archive.read(name=cell.source.member)
+        operation, input_name = "thumbnail_source", "[descriptor=0]"
+    elif cell.source.path is not None:
+        operation, input_name = "thumbnail", str(cell.source.path)
+    else:
+        raise ValueError("Image source has no file or ZIP member")
+    try:
+        result = subprocess.run(
+            args=[
+                vips_binary,
+                "--vips-concurrency=1",
+                operation,
+                input_name,
+                ".png",
+                str(cell.size[0]),
+                "--height",
+                str(cell.size[1]),
+                "--size",
+                "both",
+            ],
+            input=input_bytes,
+            check=True,
+            capture_output=True,
+        )
+    except (OSError, subprocess.CalledProcessError) as error:
+        detail = error.stderr.decode(errors="replace").strip() if isinstance(error, subprocess.CalledProcessError) and error.stderr else str(error)
+        logging.warning(f"vips failed for {cell.source.name}; using Pillow: {detail}")
+        return resize_with_pillow(cell=cell)
+    with Image.open(fp=BytesIO(result.stdout)) as image:
+        with image.convert(mode="RGBA") as thumbnail:
+            if thumbnail.size == cell.size:
+                return thumbnail.tobytes()
+            with thumbnail.resize(size=cell.size, resample=Image.Resampling.LANCZOS) as exact_thumbnail:
+                return exact_thumbnail.tobytes()
+
+
+def resize_thumbnail(cell: Cell, processor: Callable[..., bytes]) -> tuple[bytes, float]:
+    started = perf_counter()
+    logging.info(f"Resizing {cell.source.name} to {cell.size[0]}x{cell.size[1]}")
+    pixels = processor(cell=cell)
+    return pixels, perf_counter() - started
+
+
+def render_rows(
+    sheet: Image.Image,
+    rows: list[Row],
+    input_path: Path,
+    workers: int,
+    gap: int,
+    processor: Callable[..., bytes],
+) -> int:
+    cells = []
+    top = gap
+    for row in rows:
+        left = gap
+        for source, cell_width in zip(row.sources, row.widths):
+            cells.append(Cell(source=source, position=(left, top), size=(cell_width, row.height)))
+            left += cell_width + gap
+        top += row.height + gap
+    remaining = iter(cells)
+    pending: dict[Future[tuple[bytes, float]], Cell] = {}
+    processed_count = rendered_count = 0
+    archive_path = None if input_path.is_dir() else input_path
+    with ProcessPoolExecutor(
+        max_workers=workers,
+        mp_context=get_context(method="spawn"),
+        initializer=initialize_worker,
+        initargs=(archive_path,),
+    ) as pool:
+        while True:
+            while len(pending) < workers * 2:
+                cell = next(remaining, None)
+                if cell is None:
+                    break
+                future = pool.submit(resize_thumbnail, cell=cell, processor=processor)
+                pending[future] = cell
+            if not pending:
+                break
+            completed, _ = wait(fs=pending, return_when=FIRST_COMPLETED)
+            for future in completed:
+                cell = pending.pop(future)
+                processed_count += 1
+                try:
+                    pixels, duration = future.result()
+                    with Image.frombytes(mode="RGBA", size=cell.size, data=pixels) as thumbnail:
+                        sheet.paste(im=thumbnail, box=cell.position, mask=thumbnail)
+                    rendered_count += 1
+                    logging.info(f"Placed {cell.source.name} (resized in {duration:.1f}s)")
+                except (OSError, ValueError, SyntaxError, RuntimeError, BadZipFile, Image.DecompressionBombError) as error:
+                    logging.warning(f"Skipping {cell.source.name} during rendering: {error}")
+                logging.info(f"Progress {processed_count}/{len(cells)} ({processed_count / len(cells):.0%})")
+    return rendered_count
+
+
+def create_sheet(
+    input_path: Path,
+    output_path: Path,
+    width: int,
+    target_height: int,
+    gap: int,
+    bg_color: str = "white",
+    workers: int | None = None,
+    processor: Callable[..., bytes] = resize_with_pillow,
+) -> None:
+    if width <= 0 or target_height <= 0 or gap < 0 or width <= 2 * gap:
+        raise ValueError("Invalid sheet dimensions or gap")
+    if output_path.suffix.lower() not in {".jpg", ".jpeg"}:
+        raise ValueError("Output must have a .jpg or .jpeg extension")
+    if not input_path.is_dir() and not (input_path.is_file() and is_zipfile(filename=input_path)):
+        raise ValueError(f"Expected a directory or ZIP archive: {input_path}")
+    if input_path.resolve() == output_path.resolve():
+        raise ValueError("Output must differ from input")
+    if workers is not None and workers <= 0:
+        raise ValueError("Workers must be positive")
+    background = ImageColor.getcolor(color=bg_color, mode="RGB")
+    with ExitStack() as stack:
+        archive = None if input_path.is_dir() else stack.enter_context(ZipFile(file=input_path))
+        sources = discover_sources(input_path=input_path, output_path=output_path, archive=archive)
+        rows = layout_rows(sources=sources, width=width, gap=gap, target_height=target_height)
+        height = sum(row.height for row in rows) + gap * (len(rows) + 1)
+        worker_count = min(workers if workers is not None else os.cpu_count() or 1, len(sources))
+        logging.info(f"Rendering {len(sources)} images in {len(rows)} rows on a {width}x{height} sheet using {worker_count} workers")
+        sheet = stack.enter_context(Image.new(mode="RGB", size=(width, height), color=background))
+        started = perf_counter()
+        rendered_count = render_rows(
+            sheet=sheet,
+            rows=rows,
+            input_path=input_path,
+            workers=worker_count,
+            gap=gap,
+            processor=processor,
+        )
+        if not rendered_count:
+            raise ValueError("No usable images could be decoded")
+        logging.info(f"Rendering finished in {perf_counter() - started:.1f}s; saving {output_path}")
+        output_path.parent.mkdir(parents=True, exist_ok=True)
+        sheet.save(fp=output_path, quality=95)
+    logging.info(f"Wrote {output_path} ({rendered_count} images, {width}x{height})")
+
+
+def main() -> None:
+    arguments = parse_args()
+    input_paths = []
+    for path in arguments.inputs:
+        if path.exists():
+            input_paths.append(path.resolve())
+        else:
+            logging.warning(f"Skipping non-existing input: {path}")
+    if not input_paths:
+        logging.error("No existing input paths")
+        sys.exit(1)
+    if arguments.output is not None and len(input_paths) > 1:
+        logging.error("--output requires a single existing input")
+        sys.exit(2)
+    vips_binary = shutil.which(cmd="vips")
+    processor = partial(resize_with_vips, vips_binary=vips_binary) if vips_binary else resize_with_pillow
+    logging.info(f"Resize backend: {vips_binary or 'Pillow'}")
+    failed_count = 0
+    for index, input_path in enumerate(input_paths, start=1):
+        logging.info(f"Processing input {index}/{len(input_paths)}: {input_path}")
+        input_name = input_path.name if input_path.is_dir() else input_path.stem
+        output_path = arguments.output or input_path.with_name(f"{input_name}_thumbs.jpg")
+        try:
+            create_sheet(
+                input_path=input_path,
+                output_path=output_path,
+                width=arguments.width,
+                target_height=arguments.target_height,
+                gap=arguments.gap,
+                bg_color=arguments.bg_color,
+                workers=arguments.workers,
+                processor=processor,
+            )
+        except (OSError, ValueError, RuntimeError, BadZipFile) as error:
+            failed_count += 1
+            logging.error(f"Could not create contact sheet for {input_path}: {error}")
+    if failed_count:
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/imageset_thumbnails_test.py b/imageset_thumbnails_test.py
new file mode 100755
index 0000000..0509fe6
--- /dev/null
+++ b/imageset_thumbnails_test.py
@@ -0,0 +1,476 @@
+#!/usr/bin/env -S uv run --script
+# /// script
+# dependencies = ["pytest", "Pillow"]
+# ///
+
+from functools import partial
+from io import BytesIO
+from pathlib import Path
+import shutil
+import subprocess
+import sys
+from zipfile import ZIP_DEFLATED, ZipFile
+
+from PIL import Image
+import pytest
+
+import imageset_thumbnails as script
+
+
+@pytest.fixture
+def rendered_sheets(monkeypatch: pytest.MonkeyPatch) -> list[Image.Image]:
+    sheets = []
+    original_save = Image.Image.save
+
+    def capture_sheet(image: Image.Image, **keywords: object) -> None:
+        if Path(keywords["fp"]).suffix == ".jpg":
+            sheets.append(image.copy())
+        original_save(image, **keywords)
+
+    monkeypatch.setattr(Image.Image, "save", capture_sheet)
+    return sheets
+
+
+def test_directory_and_zip_natural_order(tmp_path: Path) -> None:
+    directory = tmp_path / "images"
+    directory.mkdir()
+    for name, color in [("prefix_10.bmp", "blue"), ("prefix_2.bmp", "green"), ("prefix_1.bmp", "red"), ("nested_10/prefix_1.bmp", "yellow"), ("nested_2/prefix_1.bmp", "black")]:
+        path = directory / name
+        path.parent.mkdir(parents=True, exist_ok=True)
+        with Image.new(mode="RGB", size=(20, 20), color=color) as image:
+            image.save(fp=path)
+    (directory / "broken.bmp").write_bytes(data=b"invalid")
+    (directory / "notes.txt").write_text(data="not an image")
+    archive_path = tmp_path / "images.zip"
+    with ZipFile(file=archive_path, mode="w") as archive:
+        for path in sorted(directory.rglob("*"), reverse=True):
+            if path.is_file():
+                archive.write(filename=path, arcname=path.relative_to(directory).as_posix())
+    output = tmp_path / "directory.jpg"
+    sources = script.discover_sources(input_path=directory, output_path=output, archive=None)
+    assert [source.name for source in sources] == ["nested_2/prefix_1.bmp", "nested_10/prefix_1.bmp", "prefix_1.bmp", "prefix_2.bmp", "prefix_10.bmp"]
+    script.create_sheet(input_path=directory, output_path=output, width=68, target_height=20, gap=2)
+    zip_output = tmp_path / "zip.jpg"
+    script.create_sheet(input_path=archive_path, output_path=zip_output, width=68, target_height=20, gap=2)
+    with Image.open(fp=output) as first, Image.open(fp=zip_output) as second:
+        assert first.size == second.size
+        assert first.tobytes() == second.tobytes()
+        assert first.getpixel(xy=(10, 10)) == pytest.approx((0, 0, 0), abs=5)
+        assert first.getpixel(xy=(32, 10)) == pytest.approx((255, 255, 0), abs=5)
+        assert first.getpixel(xy=(54, 10)) == pytest.approx((255, 0, 0), abs=5)
+
+
+@pytest.mark.parametrize("ratios,width,target,gap", [
+    ([1.0] * 7, 100, 30, 2),
+    ([0.5, 2.0, 1.0, 0.75, 1.5], 100, 25, 3),
+    ([100.0], 100, 30, 2),
+    ([1.0] * 5, 90, 30, 0),
+    ([0.001, 100.0, 0.001], 100, 30, 1),
+    ([0.5] * 4, 3, 20, 1),
+])
+def test_layout_geometry(ratios: list[float], width: int, target: int, gap: int) -> None:
+    sources = [script.Source(name=str(index), ratio=ratio) for index, ratio in enumerate(ratios)]
+    rows = script.layout_rows(sources=sources, width=width, target_height=target, gap=gap)
+    assert [source for row in rows for source in row.sources] == sources
+    for index, row in enumerate(rows):
+        assert row.height >= 1
+        assert all(cell_width >= 1 for cell_width in row.widths)
+        occupied = sum(row.widths) + gap * (len(row.sources) + 1)
+        assert occupied <= width
+        if index < len(rows) - 1:
+            assert occupied == width
+
+
+def test_render_gaps_equal_heights_and_last_row(tmp_path: Path, rendered_sheets: list[Image.Image]) -> None:
+    directory = tmp_path / "images"
+    directory.mkdir()
+    for index in range(4):
+        with Image.new(mode="RGB", size=(40, 40), color="red") as image:
+            image.save(fp=directory / f"image_{index}.bmp")
+    output = tmp_path / "sheet.jpg"
+    script.create_sheet(input_path=directory, output_path=output, width=100, target_height=30, gap=2)
+    with rendered_sheets[0] as sheet:
+        assert sheet.size == (100, 67)
+        for left in (2, 35, 67):
+            assert sheet.getpixel(xy=(left, 2)) == (255, 0, 0)
+            assert sheet.getpixel(xy=(left, 32)) == (255, 0, 0)
+        for position in [(0, 0), (33, 10), (65, 10), (99, 10), (10, 33), (32, 40)]:
+            assert sheet.getpixel(xy=position) == (255, 255, 255)
+        assert sheet.getpixel(xy=(2, 35)) == (255, 0, 0)
+
+
+def test_orientation_and_transparency(tmp_path: Path) -> None:
+    path = tmp_path / "oriented.jpg"
+    with Image.new(mode="RGB", size=(40, 20), color="red") as image:
+        exif = Image.Exif()
+        exif[274] = 6
+        image.save(fp=path, exif=exif)
+    with script.read_image(source=script.Source(name=path.name, path=path), archive=None) as image:
+        assert image.size == (20, 40)
+    path = tmp_path / "transparent.gif"
+    with Image.new(mode="RGBA", size=(10, 10), color=(255, 0, 0, 0)) as image:
+        image.save(fp=path)
+    with script.read_image(source=script.Source(name=path.name, path=path), archive=None) as image:
+        assert image.mode == "RGBA"
+        assert image.getpixel(xy=(0, 0)) == (255, 0, 0, 0)
+
+
+@pytest.mark.parametrize("bg_color,expected", [("white", (255, 255, 255)), ("black", (0, 0, 0)), ("#123456", (18, 52, 86))])
+@pytest.mark.parametrize("use_vips", [False, True])
+def test_sheet_background(
+    tmp_path: Path, rendered_sheets: list[Image.Image], bg_color: str,
+    expected: tuple[int, int, int], use_vips: bool,
+) -> None:
+    vips_binary = shutil.which(cmd="vips") if use_vips else None
+    if use_vips and vips_binary is None:
+        pytest.skip("vips is not installed")
+    processor = partial(script.resize_with_vips, vips_binary=vips_binary) if vips_binary else script.resize_with_pillow
+    directory = tmp_path / "images"
+    directory.mkdir()
+    with Image.new(mode="RGBA", size=(20, 20), color=(255, 0, 0, 0)) as image:
+        image.save(fp=directory / "transparent.gif")
+    with Image.new(mode="RGB", size=(20, 20), color="red") as image:
+        image.save(fp=directory / "red.bmp")
+    output = tmp_path / "sheet.jpg"
+    script.create_sheet(input_path=directory, output_path=output, width=100, target_height=20, gap=2, bg_color=bg_color, processor=processor)
+    with rendered_sheets[0] as sheet:
+        assert sheet.getpixel(xy=(0, 0)) == expected
+        assert sheet.getpixel(xy=(22, 5)) == expected
+        assert sheet.getpixel(xy=(25, 5)) == expected
+        assert sheet.getpixel(xy=(99, 5)) == expected
+        assert sheet.getpixel(xy=(3, 5)) == (255, 0, 0)
+
+
+@pytest.mark.parametrize("extension", ["jpg"])
+@pytest.mark.parametrize("orientation", [1, 6, 8])
+def test_metadata_dimensions_without_pixel_decoding(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch,
+    extension: str, orientation: int,
+) -> None:
+    directory = tmp_path / "images"
+    directory.mkdir()
+    path = directory / f"image.{extension}"
+    with Image.new(mode="RGB", size=(40, 20), color="red") as image:
+        exif = Image.Exif()
+        exif[274] = orientation
+        image.save(fp=path, exif=exif)
+    archive_path = tmp_path / "images.zip"
+    with ZipFile(file=archive_path, mode="w") as archive:
+        archive.write(filename=path, arcname=path.name)
+
+    def reject_decoding(image: Image.Image, *arguments: object, **keywords: object) -> None:
+        pytest.fail("Metadata discovery must not decode image pixels")
+
+    Image.init()
+    monkeypatch.setattr(Image.Image, "load", reject_decoding)
+    expected = (40, 20) if orientation == 1 else (20, 40)
+    assert script.read_dims(image_path=path) == expected
+    sources = script.discover_sources(input_path=directory, output_path=tmp_path / "sheet.jpg", archive=None)
+    assert sources[0].ratio == expected[0] / expected[1]
+    with ZipFile(file=archive_path) as archive:
+        with archive.open(name=path.name) as stream:
+            assert script.read_dims(image_path=stream) == expected
+        sources = script.discover_sources(input_path=archive_path, output_path=tmp_path / "sheet.jpg", archive=archive)
+        assert sources[0].ratio == expected[0] / expected[1]
+
+
+def test_rendering_skips_pixel_corruption(tmp_path: Path, caplog: pytest.LogCaptureFixture) -> None:
+    directory = tmp_path / "images"
+    directory.mkdir()
+    valid = directory / "1.bmp"
+    broken = directory / "2.jpg"
+    with Image.new(mode="RGB", size=(20, 20), color="red") as image:
+        image.save(fp=valid)
+        image.save(fp=broken)
+    broken.write_bytes(data=broken.read_bytes()[:-10])
+    assert script.read_dims(image_path=broken) == (20, 20)
+    output = tmp_path / "sheet.jpg"
+    script.create_sheet(input_path=directory, output_path=output, width=100, target_height=20, gap=0)
+    assert "Skipping 2.jpg during rendering" in caplog.text
+    with Image.open(fp=output) as sheet:
+        assert sheet.getpixel(xy=(10, 10)) == pytest.approx((255, 0, 0), abs=5)
+    valid.unlink()
+    with pytest.raises(ValueError, match="No usable images could be decoded"):
+        script.create_sheet(input_path=directory, output_path=tmp_path / "failed.jpg", width=100, target_height=20, gap=0)
+    assert not (tmp_path / "failed.jpg").exists()
+
+
+@pytest.mark.parametrize("extension,expected_format", [("jpg", "JPEG"), ("jpeg", "JPEG")])
+def test_output_format_and_exclusion(tmp_path: Path, extension: str, expected_format: str) -> None:
+    with Image.new(mode="RGB", size=(20, 20), color="blue") as image:
+        image.save(fp=tmp_path / "input.bmp")
+    output = tmp_path / f"sheet.{extension}"
+    script.create_sheet(input_path=tmp_path, output_path=output, width=100, target_height=20, gap=0)
+    sources = script.discover_sources(input_path=tmp_path, output_path=output, archive=None)
+    assert [source.name for source in sources] == ["input.bmp"]
+    with Image.open(fp=output) as sheet:
+        assert sheet.format == expected_format
+        assert sheet.size == (100, 20)
+
+
+def test_first_animation_frame(tmp_path: Path) -> None:
+    path = tmp_path / "animated.gif"
+    with Image.new(mode="RGB", size=(10, 10), color="red") as first, Image.new(mode="RGB", size=(10, 10), color="blue") as second:
+        first.save(fp=path, save_all=True, append_images=[second])
+    with script.read_image(source=script.Source(name=path.name, path=path), archive=None) as image:
+        assert image.getpixel(xy=(0, 0)) == (255, 0, 0, 255)
+
+
+@pytest.mark.parametrize("input_kind", ["directory", "zip"])
+def test_cli_process_pool_matches_single_worker(tmp_path: Path, input_kind: str) -> None:
+    directory = tmp_path / "images"
+    directory.mkdir()
+    for index in [10, 2, 1, 3, 4, 5, 6]:
+        with Image.new(mode="RGBA", size=(20 + index * 5, 40), color=(index * 20, 100, 50, 128)) as image:
+            exif = Image.Exif()
+            exif[274] = 6 if index == 2 else 1
+            image.convert(mode="RGB").save(fp=directory / f"image_{index}.jpg", exif=exif)
+    input_path = directory
+    if input_kind == "zip":
+        input_path = tmp_path / "images.zip"
+        with ZipFile(file=input_path, mode="w", compression=ZIP_DEFLATED) as archive:
+            for path in directory.iterdir():
+                archive.write(filename=path, arcname=f"nested/{path.name}")
+    outputs = []
+    for workers in [1, 2]:
+        output = tmp_path / f"workers_{workers}.jpg"
+        result = subprocess.run(
+            args=[sys.executable, str(Path(script.__file__).resolve()), str(input_path),
+                  "--output", str(output), "--workers", str(workers), "--width", "180",
+                  "--target-height", "40", "--gap", "3", "--bg-color", "#123456"],
+            check=True, capture_output=True, text=True, timeout=30,
+        )
+        assert "Progress 7/7 (100%)" in result.stderr
+        with Image.open(fp=output) as image:
+            outputs.append((image.size, image.tobytes()))
+    assert outputs[0] == outputs[1]
+
+
+@pytest.mark.parametrize("options", [
+    ["--width", "0"], ["--target-height", "0"], ["--gap", "-1"],
+    ["--width", "16", "--gap", "8"],
+    ["--bg-color", "invalid-color"],
+    ["--workers", "0"], ["--workers", "-1"],
+])
+def test_invalid_arguments(monkeypatch: pytest.MonkeyPatch, options: list[str]) -> None:
+    monkeypatch.setattr(sys, "argv", ["imageset_thumbnails.py", "images", *options])
+    with pytest.raises(SystemExit) as error:
+        script.parse_args()
+    assert error.value.code == 2
+
+
+def test_cli_names(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(sys, "argv", ["imageset_thumbnails.py", "images", "--target-height", "180", "--gap", "4", "--bg-color", "#123456", "--workers", "3"])
+    arguments = script.parse_args()
+    assert arguments.target_height == 180
+    assert arguments.gap == 4
+    assert arguments.bg_color == "#123456"
+    assert arguments.workers == 3
+    assert arguments.inputs == [Path("images")]
+
+
+@pytest.mark.parametrize("bad_input_kind,expected_status", [("missing", 0), ("invalid", 1)])
+def test_cli_multiple_inputs(tmp_path: Path, bad_input_kind: str, expected_status: int) -> None:
+    directory = tmp_path / "photos"
+    directory.mkdir()
+    with Image.new(mode="RGB", size=(20, 20), color="red") as image:
+        image.save(fp=directory / "image.bmp")
+    archive_path = tmp_path / "archive.zip"
+    with ZipFile(file=archive_path, mode="w", compression=ZIP_DEFLATED) as archive:
+        archive.write(filename=directory / "image.bmp", arcname="image.bmp")
+    bad_input = tmp_path / "bad_input"
+    if bad_input_kind == "invalid":
+        bad_input.write_text(data="not a ZIP")
+    result = subprocess.run(
+        args=[sys.executable, str(Path(script.__file__).resolve()), str(bad_input),
+              str(directory), str(archive_path), "--workers", "2"],
+        check=False, capture_output=True, text=True, timeout=30,
+    )
+    assert result.returncode == expected_status
+    if bad_input_kind == "missing":
+        assert "WARNING: Skipping non-existing input" in result.stderr
+    else:
+        assert "Could not create contact sheet for" in result.stderr
+    for output in [tmp_path / "photos_thumbs.jpg", tmp_path / "archive_thumbs.jpg"]:
+        with Image.open(fp=output) as sheet:
+            assert sheet.size == (2500, 316)
+
+
+def test_cli_all_inputs_missing(tmp_path: Path) -> None:
+    result = subprocess.run(
+        args=[sys.executable, str(Path(script.__file__).resolve()),
+              str(tmp_path / "missing.zip"), str(tmp_path / "missing_directory")],
+        check=False, capture_output=True, text=True, timeout=30,
+    )
+    assert result.returncode == 1
+    assert result.stderr.count("Skipping non-existing input") == 2
+    assert "No existing input paths" in result.stderr
+    assert list(tmp_path.iterdir()) == []
+
+
+def test_cli_output_requires_single_existing_input(tmp_path: Path) -> None:
+    first = tmp_path / "first"
+    second = tmp_path / "second"
+    first.mkdir()
+    second.mkdir()
+    output = tmp_path / "sheet.jpg"
+    result = subprocess.run(
+        args=[sys.executable, str(Path(script.__file__).resolve()), str(first),
+              str(second), "--output", str(output)],
+        check=False, capture_output=True, text=True, timeout=30,
+    )
+    assert result.returncode == 2
+    assert "--output requires a single existing input" in result.stderr
+    assert not output.exists()
+    with Image.new(mode="RGB", size=(20, 20), color="blue") as image:
+        image.save(fp=first / "image.bmp")
+    result = subprocess.run(
+        args=[sys.executable, str(Path(script.__file__).resolve()), str(first),
+              str(tmp_path / "missing"), "--output", str(output)],
+        check=True, capture_output=True, text=True, timeout=30,
+    )
+    assert "Skipping non-existing input" in result.stderr
+    assert output.exists()
+
+
+@pytest.mark.parametrize("use_vips", [False, True])
+def test_main_selects_processor_once(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, use_vips: bool,
+) -> None:
+    vips_binary = shutil.which(cmd="vips") if use_vips else None
+    if use_vips and vips_binary is None:
+        pytest.skip("vips is not installed")
+    directories = [tmp_path / "first", tmp_path / "second"]
+    for directory in directories:
+        directory.mkdir()
+        with Image.new(mode="RGB", size=(40, 20), color="red") as image:
+            image.save(fp=directory / "image_1.bmp")
+            image.save(fp=directory / "image_2.bmp")
+    lookups = []
+
+    def find_binary(cmd: str) -> str | None:
+        lookups.append(cmd)
+        return vips_binary
+
+    monkeypatch.setattr(script.shutil, "which", find_binary)
+    monkeypatch.setattr(sys, "argv", ["imageset_thumbnails.py", *map(str, directories),
+                                     "--width", "100", "--target-height", "20", "--workers", "2"])
+    script.main()
+    assert lookups == ["vips"]
+    for name in ["first", "second"]:
+        with Image.open(fp=tmp_path / f"{name}_thumbs.jpg") as sheet:
+            assert sheet.width == 100
+
+
+@pytest.mark.parametrize("input_kind", ["directory", "zip"])
+def test_vips_resizes_with_legacy_options_before_pillow_reads_pixels(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, input_kind: str,
+) -> None:
+    vips_binary = shutil.which(cmd="vips")
+    if vips_binary is None:
+        pytest.skip("vips is not installed")
+    path = tmp_path / "image.jpg"
+    with Image.new(mode="RGB", size=(400, 200), color="red") as image:
+        image.paste(im="blue", box=(200, 0, 400, 200))
+        exif = Image.Exif()
+        exif[274] = 6
+        image.save(fp=path, exif=exif)
+    cell = script.Cell(source=script.Source(name=path.name, path=path), position=(0, 0), size=(10, 20))
+    archive_path = tmp_path / "images.zip"
+    with ZipFile(file=archive_path, mode="w") as archive:
+        archive.write(filename=path, arcname=path.name)
+    original_open = Image.open
+    original_run = subprocess.run
+    reads = []
+
+    def run_legacy_vips(args: list[str], **keywords: object) -> subprocess.CompletedProcess[str]:
+        assert ".png" in args
+        if input_kind == "zip":
+            assert "thumbnail_source" in args
+            assert keywords["input"] == path.read_bytes()
+        else:
+            assert "thumbnail" in args
+            assert keywords["input"] is None
+        if "--fail-on" in args:
+            raise subprocess.CalledProcessError(returncode=1, cmd=args, stderr=b"Unknown option --fail-on")
+        return original_run(args=args, **keywords)
+
+    def read_thumbnail(fp: BytesIO) -> Image.Image:
+        assert isinstance(fp, BytesIO)
+        image = original_open(fp=fp)
+        reads.append(image.size)
+        return image
+
+    monkeypatch.setattr(script.Image, "open", read_thumbnail)
+    monkeypatch.setattr(script.subprocess, "run", run_legacy_vips)
+    with ZipFile(file=archive_path) as archive:
+        if input_kind == "zip":
+            cell.source = script.Source(name=path.name, member=archive.getinfo(name=path.name))
+            monkeypatch.setattr(script, "worker_archive", archive)
+        pixels = script.resize_with_vips(cell=cell, vips_binary=vips_binary)
+    assert reads == [cell.size]
+    with Image.frombytes(mode="RGBA", size=cell.size, data=pixels) as thumbnail:
+        assert thumbnail.getpixel(xy=(5, 2)) == pytest.approx((255, 0, 0, 255), abs=5)
+        assert thumbnail.getpixel(xy=(5, 17)) == pytest.approx((0, 0, 255, 255), abs=5)
+
+
+def test_vips_failure_falls_back_to_pillow(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture,
+) -> None:
+    path = tmp_path / "image.gif"
+    with Image.new(mode="RGBA", size=(40, 20), color=(255, 0, 0, 128)) as image:
+        image.save(fp=path)
+    cell = script.Cell(source=script.Source(name=path.name, path=path), position=(0, 0), size=(10, 5))
+    expected = script.resize_with_pillow(cell=cell)
+
+    def fail_command(args: list[str], **keywords: object) -> subprocess.CompletedProcess[str]:
+        raise subprocess.CalledProcessError(returncode=1, cmd=args, stderr=b"unsupported format")
+
+    monkeypatch.setattr(script.subprocess, "run", fail_command)
+    assert script.resize_with_vips(cell=cell, vips_binary="vips") == expected
+    assert "using Pillow: unsupported format" in caplog.text
+
+
+@pytest.mark.parametrize("input_kind", ["directory", "zip"])
+@pytest.mark.parametrize("image_format,format_name", [("PNG", "PNG"), ("WEBP", "WebP"), ("TIFF", "TIFF")])
+def test_unsupported_inputs_are_skipped(tmp_path: Path, input_kind: str, image_format: str, format_name: str) -> None:
+    directory = tmp_path / "images"
+    directory.mkdir()
+    with Image.new(mode="RGB", size=(20, 20), color="red") as image:
+        image.save(fp=directory / "supported.jpg")
+        image.save(fp=directory / f"ignored.{image_format}", format=image_format)
+        image.save(fp=directory / "disguised.jpg", format=image_format)
+    output = tmp_path / "sheet.jpg"
+    with pytest.raises(ValueError, match=f"{format_name} images are not supported"):
+        script.read_dims(image_path=directory / f"ignored.{image_format}")
+    if input_kind == "zip":
+        archive_path = tmp_path / "images.zip"
+        with ZipFile(file=archive_path, mode="w") as archive:
+            for path in directory.iterdir():
+                archive.write(filename=path, arcname=path.name)
+        with ZipFile(file=archive_path) as archive:
+            sources = script.discover_sources(input_path=archive_path, output_path=output, archive=archive)
+    else:
+        sources = script.discover_sources(input_path=directory, output_path=output, archive=None)
+    assert [source.name for source in sources] == ["supported.jpg"]
+
+
+@pytest.mark.parametrize("extension", ["png", "webp", "tif", "tiff"])
+def test_unsupported_output_is_rejected(tmp_path: Path, extension: str) -> None:
+    output = tmp_path / f"sheet.{extension}"
+    with pytest.raises(ValueError, match="Output must have a .jpg or .jpeg extension"):
+        script.create_sheet(input_path=tmp_path, output_path=output, width=100, target_height=20, gap=0)
+    assert not output.exists()
+
+
+def test_empty_and_invalid_input(tmp_path: Path) -> None:
+    output = tmp_path / "sheet.jpg"
+    with pytest.raises(ValueError, match="No usable images"):
+        script.create_sheet(input_path=tmp_path, output_path=output, width=100, target_height=20, gap=0)
+    with pytest.raises(ValueError, match="Expected a directory or ZIP"):
+        script.create_sheet(input_path=tmp_path / "missing", output_path=output, width=100, target_height=20, gap=0)
+    assert not output.exists()
+
+
+if __name__ == "__main__":
+    sys.exit(pytest.main(args=[str(Path(__file__).resolve()), *sys.argv[1:]]))