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phoboslab / qoi

The “Quite OK Image Format” for fast, lossless image compression
MIT License
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QOI Logo

QOI - The “Quite OK Image Format” for fast, lossless image compression

Single-file MIT licensed library for C/C++

See qoi.h for the documentation and format specification.

More info at https://qoiformat.org

Why?

QOI offers sweet-spot of compression ratio and throughput for lossless image encoding. QOI's compression is roughly comparable to PNG (usually worse than libPNG, but better than stb_image_write.h), while throughput is a lot higher.

Benchmark results on a few thousand images can be found here: https://qoiformat.org/benchmark/

The QOI format is also extremely simple, which helps a lot when porting to other languages.

Example Usage

MIME Type, File Extension

The recommended MIME type for QOI images is image/qoi. While QOI is not yet officially registered with IANA, I believe QOI has found enough adoption to prevent any future image format from choosing the same name, thus making a MIME type collision highly unlikely (see #167).

The recommended file extension for QOI images is .qoi

Limitations

The QOI file format allows for huge images with up to 18 exa-pixels. A streaming en-/decoder can handle these with minimal RAM requirements, assuming there is enough storage space.

This particular implementation of QOI however is limited to images with a maximum size of 400 million pixels. It will safely refuse to en-/decode anything larger than that. This is not a streaming en-/decoder. It loads the whole image file into RAM before doing any work and is not extensively optimized for performance (but it's still very fast).

If this is a limitation for your use case, please look into any of the other implementations listed below.

Improvements, New Versions and Contributing

The QOI format has been finalized. It was a conscious decision to not have a version number in the file header. If you have a working QOI implementation today, you can rest assured that it will be compatible with all QOI files tomorrow.

There are a lot of interesting ideas for a successor of QOI, but none of these will be implemented here. That doesn't mean you shouldn't experiment with QOI, but please be aware that pull requests that change the format will not be accepted.

Likewise, pull requests for performance improvements will probably not be accepted either, as this "reference implementation" tries to be as easy to read as possible.

Tools

Implementations & Bindings of QOI

QOI Support in Other Software

Packages

Packages for other systems tracked at Repology.