libgd

libgd is a graphics library for the dynamic creation of images. It provides a C API for drawing and manipulating images in memory and is used by many applications to generate images on the server side without invoking external tools. The library supports several common raster formats, including JPEG, PNG, GIF, BMP, WebP, and WBMP, and can convert between formats during processing.

Key features include support for truecolor images, alpha transparency, drawing primitives (lines, rectangles, polygons), text rendering with font support via FreeType, color allocation, and image transformations such as resizing, cropping, and applying simple filters. libgd is designed to be lightweight and embeddable, offering a straightforward API that can be linked into C or used by language bindings. Widely used in dynamic web environments, it serves as the underlying image engine for many web applications.

Bindings exist for several programming languages; most notably, PHP integrates libgd through the GD extension, which provides functions like imagecreatetruecolor and imagejpeg. Other languages offer bindings or wrappers maintained by the community.

libgd originated in the 1990s as part of the GD project and has since been maintained by an open-source community. It is released under a permissive license (the libgd license), allowing broad reuse with relatively few restrictions.