Image guides
QOI Image Format, Explained
QOI ("Quite OK Image") is a small, fast, lossless image format designed to be simple enough to implement in an afternoon. This guide explains what it is, when it makes sense, and its tradeoffs against PNG.
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What QOI is
QOI is a lossless raster format with a deliberately minimal specification: a short header followed by a small set of pixel-diff and run-length encoding operations. It supports full RGBA, including alpha.
When to use it
QOI is popular in developer and graphics-programming pipelines that specifically read or write it, where fast encode/decode speed and a simple implementation matter more than universal software support.
QOI vs PNG
Both are lossless. PNG uses deflate compression and is universally supported by browsers, operating systems, and image editors. QOI trades that universal support for a simpler format and typically faster encode/decode — file size is usually comparable, sometimes smaller for simple images and sometimes larger for complex photos.
QOI Format Explained FAQ
- Is QOI lossless?
- Yes, always. Every pixel is reproduced exactly.
- Does QOI support transparency?
- Yes, a full alpha channel, same as PNG.
- Will QOI files open in normal photo software?
- Rarely without an extension — QOI is intended for developer tooling and pipelines that read it directly.
- Is QOI always smaller than PNG?
- No. It depends on the image. QOI can be smaller for simple graphics and larger for complex photographic content.
- Where can I convert to QOI?
- Use PNG to QOI or JPG to QOI, both processed locally in your browser.
Related guides
- TGA Format ExplainedWhat TGA (Truevision TGA) is, the difference between 24-bit and 32-bit output, and why game development still uses it.
- PPM Format ExplainedWhat PPM (Portable Pixmap) is, why developer and scientific tooling still uses it, and why the files are so large.
- Best Format by Use CaseA quick reference for choosing between JPG, PNG, WebP, AVIF, TIFF, ICO, TGA, QOI, and PPM based on what you are actually trying to do.