napari-virtual-reader

Experimental software - Alpha status. APIs and behavior may change without notice. Validate results independently before relying on them for analysis.

Open image files as lazy, reference-backed OME-Zarr in napari. No pixel conversion, copied image data, or intermediate archive is required.

The plugin uses refkv directly. It does not depend on czitools, pylibCZIrw, or the napari-czitools plugin.

Install

Python 3.12 or newer is required. Install into the environment running napari:

python -m pip install napari-virtual-reader

A working Qt backend is required. For a fresh environment:

python -m pip install "napari[pyqt6]" napari-virtual-reader
napari

Restart napari after installation. The package registers an npe2 reader and widget through its napari.manifest entry point; no manual registration is required. Check Plugins > Plugin Manager for napari-virtual-reader.

Open an image

In napari, choose Plugins > napari-virtual-reader > Open Data as virtual OME-ZARR, select the input, and click Open. Preparation runs in a background worker; napari provides its normal layer, contrast, time, and Z controls.

You can also use File > Open or drop a file on the napari canvas and choose the napari-virtual-reader reader. Drop a file on the plugin dock to select it without opening it yet.

import napari

viewer = napari.Viewer()
viewer.open("image.czi", plugin="napari-virtual-reader")
napari.run()

Raw images are virtualized in memory through refkv.zarrify.zarrify. Existing .vzip archives are opened directly. Original image files must remain available and unchanged for as long as their layers are used. Nothing is written beside the source by default.

Save a VZIP Archive

In Plugins > napari-virtual-reader > Open Data as virtual OME-ZARR, select an image and enable Save VZIP archive before clicking Open. Choose the destination in the save dialog; the suggested filename is a sibling .vzip. Saving runs in the background, and the resulting image still opens lazily with the metadata panel. The status shows the saved filename, with its full path available on hover.

Saving stores references to the original image, not converted pixel data. The archive covers the complete source, including all scenes and pyramid levels. Existing destinations require explicit replacement confirmation; failed writes leave the old archive intact. Cancelling the save dialog cancels the open action. The save option is disabled for inputs that are already VZIP archives. File/Open and canvas drops remain in-memory operations without automatic saving.

Metadata Inspector

The Virtual Zarr metadata dock opens on the right when using the refkv reader through File/Open or drag-and-drop, without opening the plugin widget first. It also appears with Plugins > napari-virtual-reader > Open Data as virtual OME-ZARR. Both workflows share one inspector that follows the selected image layer.

• Zarr structure shows expandable groups and arrays, including original shapes, dtypes, attributes, chunk grids and codec configuration.
• Metadata shows the selected layer's OME metadata, source and channel information, plus original scene transforms for stacked CZI images.
• A filter finds matching properties; selecting a row shows its complete, selectable value below the tree.

The inspector uses a metadata-only snapshot collected in the background. It does not scan pixel data or reconstruct the source hierarchy from displayed layer shapes. Selecting an unrelated layer clears the inspector.

Scope

• CZI, TIFF/OME-TIFF, and other refkv-supported files that expose OME image series. Reader registration includes common microscopy and volumetric image extensions; actual support is determined by refkv's parser and the file's metadata/codecs.
• One layer per channel. Compatible CZI scenes are stacked lazily along a leading S axis, in numeric series order. This also applies to CZI-derived VZIP archives. Other formats retain separate series layers.
• CZI stacking requires matching axes, shapes, dtypes, physical scales and pyramid levels. Incompatible scenes remain separate without cropping or resampling. Scene-dependent stage origins are replaced by local coordinates on the stacked layer; original origins and metadata remain available in the layer's metadata["scenes"] list.
• Stored multiscale pyramids, OME axis ordering, physical scale/origin, channel names, colors, and display windows.
• Regular and rectilinear chunk grids, without scanning complete lazy arrays for contrast limits. Files without display windows use dtype bounds (0-1 for floating point); adjust contrast in napari as needed.
• OME-Zarr 0.4 and 0.5 image metadata, including nested image hierarchies.

This is deliberately not a replacement for every refkv dataset interface: non-image tables, audio, arbitrary tensors, remote inputs, and stores without OME image metadata are outside this first version. There are no custom dimension sliders or CZI-specific options.

Development

git clone https://github.com/sebi06/napari-virtual-reader.git
cd napari-virtual-reader
python -m pip install -e ".[testing]"
python -m pytest
python -m ruff check .

Install a Qt backend as above if the development environment does not already provide one. Development installs register the same napari plugin as PyPI installs.

Releases

GitHub Actions tests pull requests and pushes to main. Publishing runs only after the test matrix passes on a release tag in the form vX.Y.Z.

Set project.version in pyproject.toml to the intended release version before tagging; tags do not change the package version. PyPI requires a new version for every upload. Manual workflow runs test and build without publishing.

See the changelog for the change history and the release notes for release-specific features, validation, and limitations. Published tags and release details are available on GitHub Releases.