libspng

libspng is a C library for reading and writing Portable Network Graphics (PNG) format files with a focus on security and ease of use.

libspng is an alternative to libpng, the projects are separate and the APIs are not compatible.

Motivation

The goal is to provide a fast PNG library with a simpler API than libpng, it outperforms the reference implementation in common use cases.

Performance

Features

Feature	spng	libpng	stb_image	lodepng
Decode from stream	✅	✅	✅	❌
Gamma correction	✅	✅	❌	❌
No known security bugs[1]	✅	✅	❌	✅
Progressive image read	✅	✅	❌	❌
Parses all standard chunks	✅	✅	❌	❌
Doesn't require zlib[2]	✅	❌	✅	✅
Encoding	Planned	✅	✅	✅
Animated PNG	Planned	✅[3]	❌	❌

^[1] The project is fuzz tested on OSS-Fuzz and vulnerabilities are fixed before they become public.

^[2] Building with miniz is supported.

^[3] With a 3rd party patch

Getting libspng

Download the latest release and include spng.c/spng.h in your project, you can also build with CMake or Meson. Refer to the documentation for details.

Usage

#include <spng.h>

/* Create a context */
spng_ctx *ctx = spng_ctx_new(0);

/* Set an input buffer */
spng_set_png_buffer(ctx, buf, buf_size);

/* Determine output image size */
spng_decoded_image_size(ctx, SPNG_FMT_RGBA8, &out_size);

/* Decode to 8-bit RGBA */
spng_decode_image(ctx, out, out_size, SPNG_FMT_RGBA8, 0);

/* Free context memory */
spng_ctx_free(ctx);

See example.c.

License

Code is licensed under the BSD 2-clause "Simplified" License.

The project contains optimizations and test images from libpng, these are licensed under the PNG Reference Library License version 2.

Security & Testing

Code is written according to the rules of the CERT C Coding Standard. All integer arithmetic is checked for overflow and all error conditions are handled gracefully.

The library is continuously fuzzed by OSS-Fuzz, code is also scanned with Clang Static Analyzer, Coverity Scan and PVS-Studio.

The test suite consists of over 1000 test cases, 175 test images are decoded with all possible output format and flag combinations and compared against libpng for correctness.

Versioning

Releases follow the semantic versioning scheme with additional guarantees:

• Releases from 0.4.0 to 0.8.x are stable
• If 1.0.0 will introduce breaking changes then 0.8.x will be maintained as a separate stable branch

Currently 1.0.0 is planned to be compatible.

Documentation

Online documentation is available at libspng.org/docs.

Known Issues

• Decoding to SPNG_FMT_G8, SPNG_FMT_GA8 and SPNG_FMT_GA16 output formats is not supported for all PNG color type and bit depth combinations, see documentation for details.
• Gamma correction is not implemented for SPNG_FMT_PNG, SPNG_FMT_G8, SPNG_FMT_GA8 and SPNG_FMT_GA16 output formats.