Libpng

libpng is a widely used open-source library for reading and writing PNG (Portable Network Graphics) images. Implemented in the C programming language, it provides a stable, portable API for manipulating PNG data and is designed to be robust across platforms and compilers. libpng is typically used in conjunction with the zlib compression library to perform the DEFLATE compression used by PNG files.

The project originated to serve as the reference implementation for the PNG format and has been maintained by a community of contributors under the libpng project. It exposes a C API with structures and functions for creating, reading, and writing PNG images, handling various color types, bit depths, interlacing options, and error reporting. libpng relies on zlib for compression and decompression and is designed to be compatible with the PNG standard across versions.

Licensing for libpng is permissive; it is distributed under the libpng license, which is compatible with many open-source and commercial projects. Redistribution typically requires preserving notices and crediting the libpng project, but it allows broad use and modification.

Key features include support for multiple color types (grayscale, truecolor, indexed color, and their grayscale/alpha and truecolor/alpha variants), different bit depths, interlaced and non-interlaced images, filtering, gamma and color management chunks, transparency handling, and support for ancillary chunks. The library emphasizes careful memory management, robust error handling, and the ability to work with PNG streams and incremental processing.

libpng is widely integrated into image processing tools, software libraries, and applications across platforms, often used as part of broader graphics and multimedia pipelines. It remains a core component for PNG handling in many open-source and commercial projects.