sldread

Read SlideBook .sld microscopy containers in Python via Bio-Formats, with the vendor SlideBook reader jar added to the JVM classpath.

A .sld file is a proprietary container holding multiple images (captures / scenes). sldread reads a chosen scene eagerly into a NumPy array (C, Z, Y, X) together with basic metadata (scene/channel names, physical pixel sizes), and can hand a scene to napari.

Runtime dependencies are minimal: numpy + scyjava only. scyjava pulls in JPype, provisions a JVM (via cjdk) on first use, and fetches Bio-Formats from Maven. napari is an optional extra.

Why does this repo exist? (and when it should disappear)

This is not meant to be yet another microscopy reader. It exists only to work around a single, specific bug in the upstream SlideBook Bio-Formats reader:

• The native reader (loci.formats.in.SlideBook6Reader) keeps a single, process-global file session. It is not re-entrant and not safe across the open/close/reopen and threading patterns that modern lazy I/O stacks rely on.
• Because of this, bioio / bioio-bioformats cannot read SlideBook pixels reliably: their lazy/dask path opens short-lived helper readers and suspends/reopens the file, which trips the global session (AssertionError: File already open. / File not open.). It is fundamentally a threading / multiple-open problem, not something a wrapper can configure away.
• The only reliable pattern is one uninterrupted setId() → openBytes() → close() session per process. sldread does exactly that, eagerly, in an isolated subprocess — nothing more.

So sldread is deliberately tiny and single-purpose. If the upstream issue is fixed — i.e. a future SlideBook reader build gives each reader an independent native session so that reopen-after-close and concurrent/threaded readers work — then this package becomes pointless and bioio should be used directly instead. At that point this repository will be archived and forgotten. Please prefer the upstream tools the moment they work. (The bug has been reported to the vendor, 3i.)

Read this first. SlideBook's native reader has a hard constraint that shapes the whole design — see Limitations. In short: a .sld file can only be read reliably in one uninterrupted reader session per process, so lazy/dask access does not work. sldread reads eagerly and isolates each read in its own subprocess.

Install

pip install sldread
# with napari support:
pip install "sldread[napari]"

Or with uv for development:

uv sync

Requires Python ≥ 3.10 (the floor set by scyjava).

The SlideBook reader jar (proprietary — not bundled)

The SlideBook6Reader.jar is proprietary and is NOT redistributed with this package. You must obtain it yourself, subject to the vendor's (3i / SlideBook) terms. sldread locates it, in order, from:

1. the jar_path= argument (or --jar on the CLI),
2. the SLIDEBOOK_READER_JAR environment variable,
3. ./jars/SlideBook6Reader.jar (relative to the working directory).

A convenience downloader is provided (standard-library only, no extra deps), which fetches the pinned build from the SlideBook ImageJ update site:

sld-read download-jar            # -> ./jars/SlideBook6Reader.jar
sld-read download-jar /some/dir  # custom destination

Downloading the jar is your responsibility and governed by the vendor's licensing terms; this convenience command does not grant any rights to it.

The verified build is SlideBook6Reader.jar-20250730183505 from https://sites.imagej.net/SlideBook/jars/bio-formats/.

Usage

Library

from sldread import list_sld_scenes, read_sld_scene, sld_scene_to_napari

list_sld_scenes("file.sld")                  # -> ['undiff_WT_...', ...]

data, meta = read_sld_scene("file.sld", scene=0)
# data: numpy array, axis order (C, Z, Y, X)
# meta: scene_name, n_scenes, all_scene_names, channel_names,
#       physical_pixel_sizes {z, y, x in µm}, scale_zyx, shape, dtype,
#       dims_order, n_timepoints, timepoint

# napari (each channel becomes a layer, with physical scale on Z, Y, X):
import napari
img, kwargs, _ = sld_scene_to_napari("file.sld", scene=0)[0]
napari.view_image(img, **kwargs)

Public API:

read_sld_scene(path, scene=0, *, t=0, jar_path=None) -> (ndarray (C,Z,Y,X), dict)
list_sld_scenes(path, *, jar_path=None) -> list[str]
sld_scene_to_napari(path, scene=0, *, t=0, jar_path=None) -> napari LayerData list
napari_get_reader(path) -> reader callable or None

If sldread[napari] is installed, the .sld reader is also registered as a napari plugin (via a napari manifest), so files open through napari's File → Open.

A ready-to-run demo lives in examples/view_scene_napari.py:

uv run --extra napari python examples/view_scene_napari.py path/to/file.sld 5

Command line

sld-read list "file.sld"           # list scenes
sld-read read "file.sld" 0         # read scene 0, print a summary
sld-read read "file.sld" 0 --view  # open scene 0 in napari (needs the napari extra)
sld-read download-jar              # fetch the reader jar into ./jars

The jar is found via --jar, SLIDEBOOK_READER_JAR, or ./jars/.

Limitations (and what NOT to implement)

These come from the SlideBook native Bio-Formats reader (loci.formats.in.SlideBook6Reader), not from this code:

• One open per process. The reader keeps a single, process-global native file session. Opening the same file a second time in one process is unreliable (intermittent AssertionError: File already open.), and closing one of two readers that have the file open deterministically breaks the other (AssertionError: File not open.). The only reliable pattern is a single, uninterrupted setId() -> openBytes()... -> close() session — which is why each read here runs in a fresh subprocess. (Reported upstream to the vendor, 3i.)
• Eager only. Reads load a whole scene into memory (≈ C·Z·Y·X·bytes; e.g. ~99 MB for a 3×12×1200×1200 uint16 scene). Fine for typical scenes; not suitable for very large time-lapses in one shot.
• Single timepoint by default. read_sld_scene reads t=0; pass t= for another timepoint. All Z and channels of that timepoint are read.
• No RGB/interleaved planes. Expects one sample per plane (true for the SlideBook files seen here) and raises NotImplementedError otherwise, rather than returning wrong data.

Do not spend time on the following — they are blocked by the reader limitation above, not by missing effort:

• Lazy / dask-backed loading of SlideBook pixels. Any access pattern that opens the file more than once per process, or keeps a reader open and reopens it later, fails non-deterministically.
• A long-lived shared reader reused across many calls in one process.
• Using bioio / bffile for pixel data. Their lazy pixel path opens/closes helper readers and hits the one-open-per-process limit.

If a future SlideBook build gives each reader an independent native session, these constraints can be revisited — until then, eager + process-isolated is the correct design.

Development

uv sync
uv run pytest                 # API tests run anywhere; the read test is gated
uv build                      # build sdist + wheel into dist/

The end-to-end read test is skipped unless both SLIDEBOOK_READER_JAR and SLDREAD_TEST_SLD (a sample .sld file) are set, so CI and other contributors can run the suite without proprietary data.

Publishing

uv build
uv publish                    # uploads dist/* to PyPI

uv publish accepts a token via --token / UV_PUBLISH_TOKEN, or use PyPI trusted publishing from CI (no long-lived token needed).

License

MIT (this package). The SlideBook reader jar is not covered by this license and is not distributed here.