OpenSlide is a C library that provides a simple interface to read whole-slide images (also known as virtual slides). The current version is 3.4.1, released 2015-04-20.
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.