OpenSlide 4.0.1 adds support for ARGOS AVS, Huron TIFF, and some Zeiss CZI files, improves support for Aperio, DICOM, Hamamatsu, and MIRAX files, fixes two security issues, and adds other improvements.
Binary build 4.0.1.1 updates to OpenSlide 4.0.1.
Binary build 4.0.0.14 fixes an arbitrary memory write with a crafted Ventana BIF file (CVE-2026-48977) and updates various dependencies.
OpenSlide Python 1.4.6 and
OpenSlide Java 0.13.3 add a constant for the
openslide.barcode property.
Binary build 4.0.0.13 adds a build fix and updates glib.
Binary build 4.0.0.12 fixes a regression in build 4.0.0.10 that returned uninitialized data in the bottom tile row of non-JPEG, non-JP2K TIFF levels, and updates various dependencies.
Binary build 4.0.0.11 updates several dependencies.
Binary build 4.0.0.10 drops Python 3.8 support in the Python binary packages, enables SIMD JPEG decoding on macOS x86_64, and updates many dependencies.
OpenSlide Python 1.4.3 adds support for free-threaded Python and drops support for Python 3.9.
OpenSlide Java 0.13.1 fixes backward compatibility of JARs built with Java newer than 22.
Older news is available here.
OpenSlide is a C library that provides a simple interface to read whole-slide images (also known as virtual slides). The current version is 4.0.1, released 2026-06-07.
Python and Java bindings are also available. The Python binding includes a Deep Zoom generator and a simple web-based viewer. The Java binding includes a simple image viewer.
OpenSlide and its official language bindings are released under the terms of the GNU Lesser General Public License, version 2.1.
The library can read virtual slides in the following formats:
It provides a simple C interface for programmers to use to decode images of these kinds.
OpenSlide’s support for these formats is not endorsed by their respective vendors and may be incomplete. Problems should be reported to the OpenSlide mailing list or issue tracker.
OpenSlide is a product of the research group of M. Satyanarayanan (Satya) in the Carnegie Mellon University School of Computer Science.
See how some projects use OpenSlide.
There is a web-based demo of OpenSlide rendering various slide formats.
First, try the search box at the top of the page. It covers the OpenSlide website, mailing list, issue tracker, and wiki.
Questions should be sent to the users mailing list. If you think you have found a bug, please report it in the appropriate issue tracker.
There are two mailing lists for OpenSlide:
Some developer documentation is available:
Development of OpenSlide happens on GitHub:
Some freely-distributable test data is available.
The design and implementation of the library are described in a published technical note:
OpenSlide: A Vendor-Neutral Software Foundation for Digital Pathology Adam Goode, Benjamin Gilbert, Jan Harkes, Drazen Jukic, M. Satyanarayanan Journal of Pathology Informatics 2013, 4:27 HTML
There is also an older technical report:
A Vendor-Neutral Library and Viewer for Whole-Slide Images Adam Goode, M. Satyanarayanan Technical Report CMU-CS-08-136, June 2008 Computer Science Department, Carnegie Mellon University Abstract PDF
Whole-slide images, also known as virtual slides, are large, high resolution images used in digital pathology. Reading these images using standard image tools or libraries is a challenge because these tools are typically designed for images that can comfortably be uncompressed into RAM or a swap file. Whole-slide images routinely exceed RAM sizes, often occupying tens of gigabytes when uncompressed. Additionally, whole-slide images are typically multi-resolution, and only a small amount of image data might be needed at a particular resolution.
There is no universal data format for whole-slide images, so each vendor implements its own formats, libraries, and viewers. Vendors typically do not document their formats. Even when there is documentation, important details are omitted. Because a vendor’s library or viewer is the only way to view a particular whole-slide image, doctors and researchers can be unnecessarily tied to a particular vendor. Finally, few (if any) vendors provide libraries and viewers for non-Windows platforms. Some have gone with a server approach, pushing tiles through a web server, or using Java applets, but these approaches have shortcomings in high-latency or non-networked environments.
OpenSlide has been supported by the National Institutes of Health and the Clinical and Translational Science Institute at the University of Pittsburgh.
Development of DICOM and ICC functionality was supported by NCI Imaging Data Commons and has been funded in whole or in part with Federal funds from the National Cancer Institute, National Institutes of Health, under Task Order No. HHSN26110071 under Contract No. HHSN261201500003l.