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What is qoi?

phoboslab/qoi — explained in plain English

Analysis updated 2026-06-24

★ 7,480CAudience · developerComplexity · 2/5LicenseSetup · easy

In one sentence

QOI is a fast, lossless image format implemented as a single C/C++ header file, compression similar to PNG but substantially faster to encode and decode, with no extra build steps to add it.

Mindmap

mindmap
  root((QOI format))
    What it does
      Lossless compression
      Encode images
      Decode images
    Compared to PNG
      Similar file size
      Much faster encode
      Much faster decode
    Implementation
      Single header file
      C and C++ only
      No build steps
    Ecosystem
      GIMP plugin
      Godot plugin
      Unity and Unreal
      macOS and Windows
    Limits
      400M pixel max
      No streaming decode
      No format extensions
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Code map

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filefunction / class

What do people build with it?

USE CASE 1

Replace PNG for image saving and loading in a game engine where read/write speed matters more than absolute file size.

USE CASE 2

Drop the single .h file into any C or C++ project to add fast lossless image export without extra dependencies or build steps.

USE CASE 3

Use a QOI plugin for GIMP, Paint.NET, or Godot to edit and save .qoi images directly in your existing creative or game workflow.

USE CASE 4

Benchmark your image pipeline by swapping PNG for QOI to see how much throughput you gain when processing large numbers of images.

What is it built with?

CC++

How does it compare?

phoboslab/qoijart/blinkmerbanan/rtl_433
Stars7,4807,4977,448
LanguageCCC
Setup difficultyeasymoderatemoderate
Complexity2/54/53/5
Audiencedeveloperdeveloperops devops

Figures from each repo's GitHub metadata at analysis time.

How do you get it running?

Difficulty · easy Time to first run · 5min
MIT license, use freely for any purpose including commercial projects, just keep the copyright notice.

So what is it?

QOI, short for "Quite OK Image Format," is a lossless image format designed to be fast at both encoding and decoding. The entire implementation is a single C/C++ header file under the MIT license, so adding it to a project means dropping in one file with no extra build steps. The format sits in a practical middle ground between raw speed and compression size. Its compression output is roughly comparable to PNG, though typically not as tight as the most optimized PNG libraries. Where QOI stands out is throughput: encoding and decoding are substantially faster than PNG, which matters when reading or writing many images quickly. Because the format specification itself is extremely simple, it has been ported to dozens of programming languages, including Python, Rust, Go, Java, Zig, Swift, Elixir, OCaml, and many others. The format is finalized and intentionally has no version number in file headers. A working QOI implementation today will be compatible with all QOI files in the future. The project does not plan to extend the format or accept pull requests that change it. This reference implementation loads an entire image into memory before processing, and is capped at 400 million pixels. It is not a streaming decoder. For images beyond that size, the README points to third-party implementations. The recommended file extension is .qoi and the recommended MIME type is image/qoi. The ecosystem around QOI has grown considerably. There are plugins for Windows Explorer, macOS Finder, GNOME, GIMP, Paint.NET, Godot, Unity, and Unreal Engine 5. Tools exist for viewing QOI images in terminals, desktop applications, and web browsers, and Microsoft PowerToys added QOI preview and thumbnail support for Windows Explorer. Format-level benchmarks comparing QOI, PNG, and other options are published at qoiformat.org.

Copy-paste prompts

Prompt 1
I want to use the QOI format in my C game engine to save screenshots faster than PNG. Show me the minimal C code to encode a raw RGBA pixel buffer into a .qoi file using the single-header library.
Prompt 2
Using the QOI reference implementation in C, write code that loads a .qoi image file into memory and returns its width, height, and a pointer to the raw pixel data.
Prompt 3
Explain the QOI file format encoding scheme from the spec, what are the different run-length and pixel-difference opcodes it uses to compress image data?
Prompt 4
I need to load QOI images in Python. Show me how to install and use a Python QOI library to open a .qoi file and convert it to a Pillow Image object.
Prompt 5
Compare QOI and PNG for my use case: I need to save thousands of lossless screenshots per hour in a C++ application. What are the tradeoffs in file size, encode speed, and decode speed?

Frequently asked questions

What is qoi?

QOI is a fast, lossless image format implemented as a single C/C++ header file, compression similar to PNG but substantially faster to encode and decode, with no extra build steps to add it.

What language is qoi written in?

Mainly C. The stack also includes C, C++.

What license does qoi use?

MIT license, use freely for any purpose including commercial projects, just keep the copyright notice.

How hard is qoi to set up?

Setup difficulty is rated easy, with roughly 5min to a first successful run.

Who is qoi for?

Mainly developer.

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