Images
What is a QOI file?
QOI (Quite OK Image) is a lossless image format built for speed rather than wide compatibility. It compresses and decompresses images dramatically faster than typical image formats while keeping every pixel exact, and it supports transparency. The catch is that almost nothing outside of games and image tools can open it directly.
- Extension
- .qoi
- Type
- Images
- Typically
- Fast lossless game/tool format
- Transparency
- Supported
Why QOI exists
QOI appeared in 2021 as a simple alternative to older lossless formats, designed by a game developer who wanted encoding and decoding fast enough to happen in real time. The format's whole pitch is that a full image can be packed or unpacked in the time it takes to read this sentence, without the overhead heavier formats carry.
Under the hood, QOI works through a short set of straightforward rules: it looks at each pixel, checks if it matches a recently seen color or a small predictable shift from the pixel before it, and only stores new information when it has to. There's no complex math involved, which is exactly why it runs so fast and why the format itself is small enough to implement in a few hundred lines of code.
Most people run into QOI as an export or working format inside a game engine, a pixel art tool, or an image processing pipeline, not as something they receive from a friend or download from a website. When that file needs to go anywhere else, like a browser, a phone gallery, or a document, it has to be converted first, since general photo viewers and editors typically don't recognize it.
The trade-offs
Strengths
- Encodes and decodes much faster than most other lossless formats
- No quality loss, every pixel stays exact
- Supports transparency
- Simple format that's easy for developers to build tools around
Watch-outs
- Not supported by web browsers, phone galleries, or most photo viewers
- Barely any mainstream apps can open it without a plugin
- File sizes can end up larger than a well-compressed PNG of the same image
- Needs converting before you can share or view it normally
A note on privacy
QOI files themselves don't carry the kind of metadata standard photo formats do, but the images stored in them can still be sensitive, screenshots, game assets, or design work you don't want passing through someone else's server. Running the conversion on your own computer means the image never leaves your machine on its way to becoming a PNG or JPG.
Questions
How do I open a QOI file?
Most everyday image viewers and photo apps can't open QOI directly. You'll generally need to convert it to PNG or JPG first, or use a tool built for developers and pixel artists that specifically supports the format.
Is QOI better than PNG?
QOI encodes and decodes much faster, which matters for games and real-time tools. PNG usually compresses images a bit smaller and is supported almost everywhere, so for sharing or storing photos, PNG is the more practical choice.
Why does my game or app save files as QOI?
Some game engines and image tools use QOI internally because loading images quickly matters more than squeezing out the smallest possible file size. It's a working format, not one meant for sharing.
Can I convert QOI without uploading it?
Yes. A desktop app like Morphjet converts QOI files on your own computer, so the image never has to travel over the internet to become a PNG or JPG.
Morphjet opens and converts QOI, one of 2,748 conversions it runs on your own computer. Available now.
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