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# 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](https://github.com/glennrp/libpng/blob/libpng16/png.h),
it outperforms the reference implementation in common use cases.
## Performance
## Features
| Decode from stream | ✅ | ✅ | ✅ | ❌ |
| Gamma correction | ✅ | ✅ | ❌ | ❌ |
| No known security bugs<sup>[1]</sup> | ✅ | ✅ | ❌ | ✅ |
| Progressive image read | ✅ | ✅ | ❌ | ❌ |
| Parses all standard chunks | ✅ | ✅ | ❌ | ❌ |
| Doesn't require zlib<sup>[2]</sup> | ✅ | ❌ | ✅ | ✅ |
| Encoding | Planned | ✅ | ✅ | ✅ |
| Animated PNG | Planned | ✅<sup>[3]</sup> | ❌ | ❌ |
<sup>[1]</sup> The project is fuzz tested on [OSS-Fuzz](https://github.com/google/oss-fuzz) and vulnerabilities are fixed before they become public.
<sup>[2]</sup> Building with miniz is [supported](docs/build.md#miniz).
<sup>[3]</sup> With a 3rd party patch
## Getting libspng
Download the [latest release](https://libspng.org/download) and include `spng.c/spng.h` in your project,
you can also build with CMake or Meson. Refer to the [documentation](https://libspng.org/docs) for details.
## Usage
```c
/* 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](https://github.com/randy408/libspng/blob/v0.6.0/examples/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](http://www.libpng.org/pub/png/src/libpng-LICENSE.txt).
## Security & Testing
Code is written according to the rules of the
[CERT C Coding Standard](https://wiki.sei.cmu.edu/confluence/display/c/SEI+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](https://github.com/google/oss-fuzz),
releases are scanned with Clang Static Analyzer, PVS-Studio, and Coverity Scan.
The test suite consists of over 700 test cases,
175 [test images](http://www.schaik.com/pngsuite/) are decoded with all possible
output format and flag combinations and compared against libpng for correctness.
## Versioning
Releases follow the [semantic versioning](https://semver.org/) 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](https://github.com/randy408/libspng/issues/3).
## Documentation
Online documentation is available at [libspng.org/docs](https://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.
* `spng_crc_set_action()` is partially implemented, `SPNG_CRC_DISCARD` has no effect.