BMP to QOI Converter
Convert BMP to QOI in your browser. BMP files usually come from Windows Paint, legacy Windows programs, embedded displays and some scanners; QOI is the better fit for fast lossless storage in games and tools. You get a lossless RGBA QOI file. Nothing is uploaded.
- Processed locally
- No upload, no wait
- No sign-up
- No watermark
Drop images here
or choose files · paste with Ctrl/⌘ V
BMP expected · other image formats also work
How to use BMP to QOI
- 1
Add your BMP files: drop them here, choose them, or paste from the clipboard.
- 2
There is nothing to tune: the QOI is written losslessly. Resizing and rotating are under More options if you need them.
- 3
Click Convert. Each file is decoded and encoded in a background thread on this device.
- 4
Download the .qoi files one at a time or together as a ZIP.
Why use Aback Images for bmp to qoi
Where the QOI goes next
QOI opens in game engines, GIMP 3, ImageMagick, XnView MP and many small libraries.
QOI next to BMP
Both sides are lossless, so the size depends on how well the QOI encoder handles this picture compared with the BMP's usually none; RLE for some 4 and 8-bit files.
Written without a lossy pass
The QOI is written losslessly, so the pixels decoded from the BMP arrive unchanged.
Processed on your device
Your images are decoded, edited and encoded inside this browser tab by Web Workers. Nothing is uploaded to a server.
BMP vs QOI
What changes from BMP to QOI
Encoding: the BMP uses usually none; RLE for some 4 and 8-bit files; QOI uses lossless, byte-aligned run, index, difference and literal codes, and the download is a lossless RGBA QOI file.
Bit depth: 1, 4, 8, 16, 24 or 32 bits per pixel in the BMP; QOI allows 8 bits per channel, and the QOI written here has 8 bits per channel.
Colour: RGB or an indexed palette in the BMP; QOI supports RGB or RGBA, tagged sRGB or linear, written here as 8-bit sRGB.
Transparency: the BMP stores it as an optional fourth byte in 32-bit files, which many programs ignore; the QOI keeps it as a full 8-bit alpha channel.
Metadata: the BMP can carry nothing beyond the header's resolution fields (and a colour profile in rare V5 headers); QOI can carry none: a 14-byte header holds only size, channels and colour space, but nothing is copied across.
About BMP
BMP stores raw, uncompressed pixels. Files are huge but trivially simple, which is why some legacy Windows software, embedded displays and printers still ask for it.
A BMP is a 14-byte file header ('BM' and the offset to the pixels), a DIB header (40 bytes, or 108 and 124 bytes in the V4 and V5 versions that add colour masks and alpha), an optional palette, then pixel rows padded to 4 bytes and normally stored bottom-up.
BMP files usually come from Windows Paint, legacy Windows programs, embedded displays and some scanners.
About QOI
QOI is a modern lossless format that encodes 20-50 times faster than PNG with similar file sizes. It is popular in games and tools that value speed and simplicity.
A QOI file is a 14-byte header ('qoif', width, height, channels, colour space), a stream of chunks that each encode a run, an index into 64 recently seen colours, a small difference from the previous pixel or a literal value, and an 8-byte end marker.
When converting BMP to QOI makes sense
QOI is the better choice for fast lossless storage in games and tools, while BMP suits legacy software and embedded systems that require it.
QOI strengths: Extremely fast lossless encode and decode; Simple, open spec. Drawbacks to weigh: Not supported by browsers or mainstream apps.
Limitations
- BMP stores nearly every pixel literally, so almost any compressed target is several times smaller.
- A 32-bit BMP can carry an alpha byte that most programs ignore; if the image suddenly gains transparent areas after converting, that byte was set.
- Browsers and most mainstream apps cannot open QOI; it is meant for games and tools that read it directly.
- QOI files are usually close to PNG in size but much faster to encode and decode.
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Frequently asked questions
Does converting BMP to QOI lose quality?
QOI is written losslessly, so the pixels are stored exactly as decoded.
Is transparency kept in the QOI?
Yes. BMP stores it as an optional fourth byte in 32-bit files, which many programs ignore, and the QOI is written with an alpha channel, so transparent areas stay transparent.
Which apps open QOI files?
Game engines, GIMP 3, ImageMagick, XnView MP and many small libraries. It does not open in web browsers.
Are my images uploaded anywhere?
No. Processing happens inside your browser with WebAssembly and Web Workers. The site only downloads the app code and codecs; your files never leave your device. You can confirm this with the live upload counter on the tool, or in your browser's network panel.
Can I process many files at once?
Yes. Drop a whole selection or folder. Files are processed in parallel on several worker threads, each result can be downloaded on its own, and everything can be saved as one ZIP.
Is it free? Is there a file limit or watermark?
It is free with no account, no watermark and no daily limit. The only limit is your device's memory: very large images (over roughly 100 megapixels) may be refused to keep the tab from crashing.