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# libspng
lib**spng** (**s**imple **png**) 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
| Feature | spng | libpng | stb_image | lodepng |
|--------------------------------------|---------|--------------------|-----------|---------|
| 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 | ✅ | ✅ | ✅ | ✅ |
| 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 spng
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](docs/build.md) for details.
## Usage
```c
#include <spng.h>
/* Create a decoder 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);
/* Creating an encoder context requires a flag */
spng_ctx *enc = spng_ctx_new(SPNG_CTX_ENCODER);
/* Encode to internal buffer managed by the library */
spng_set_option(enc, SPNG_ENCODE_TO_BUFFER, 1);
/* Specify image dimensions, PNG format */
struct spng_ihdr ihdr =
{
.width = width,
.height = height,
.bit_depth = 8,
.color_type = SPNG_COLOR_TYPE_TRUECOLOR_ALPHA
};
/* Image will be encoded according to ihdr.color_type, .bit_depth */
spng_set_ihdr(enc, &ihdr);
/* SPNG_FMT_PNG is a special value that matches the format in ihdr,
SPNG_ENCODE_FINALIZE will finalize the PNG with the end-of-file marker */
spng_encode_image(enc, image, image_size, SPNG_FMT_PNG, SPNG_ENCODE_FINALIZE);
/* PNG is written to an internal buffer by default */
void *png = spng_get_png_buffer(enc, &png_size, &error);
/* User owns the buffer after a successful call */
free(png);
/* Free context memory */
spng_ctx_free(enc);
```
See [example.c](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),
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](http://www.schaik.com/pngsuite/) are decoded with all possible
output format and flag combinations and compared against libpng for [correctness](tests/README.md#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.
## Supporting spng
You can sponsor development through [OpenCollective](https://opencollective.com/libspng/), funds will be used for maintenance and further development according to the [roadmap](https://github.com/randy408/libspng/milestones).
### OpenCollective backers
#### Individuals
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#### Organizations
Support this project with your organization. Your logo will show up here with a link to your website. [[Contribute](https://opencollective.com/libspng/contribute)]
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