How to Convert BMP to AVIF in Your Browser

How BMP becomes AVIF

1. The browser reads the BMP's DIB header to determine bit depth and row order, then reads the pixel array directly — BMP data is typically stored uncompressed, with a full color value written out for every single pixel.
2. Those raw pixels are placed onto an in-memory canvas exactly as read; because there's no compression to reverse, nothing about the source image is altered or lost at this stage.
3. The canvas is handed to the browser's native AVIF encoder, which applies AV1 intra-frame coding at your chosen quality — often the first real compression this pixel data has ever undergone.
4. The output is verified as a genuine image/avif file before the download starts.

What changes when you convert

Because BMP files are typically stored with zero compression, converting one to AVIF is likely the single largest size reduction of any conversion path in this tool — going from an uncompressed bitmap straight to one of the most efficient image codecs available can shrink a file dramatically, often by well over 90%, with no perceptible loss of detail at reasonable quality settings.

Transparency rarely factors into this conversion: most BMP files are 24-bit with no alpha channel at all. On the rare 32-bit BMP that does carry a real alpha channel, whether it survives depends on the browser's own AVIF encoder correctly reading and re-encoding it — this converter does not add transparency that wasn't already in the source.

AVIF output here comes from your browser's built-in encoder rather than a bundled WASM library, unlike most other targets in this tool — so encoding quality and availability can vary by browser, with Chromium-based browsers giving the most consistent results.

When AVIF is the right choice — and when it isn't

If a BMP just needs to exist somewhere for web delivery — a screenshot, a scanned graphic, an old asset — converting to AVIF is close to a pure win: the uncompressed source has essentially nothing to lose by moving to an efficient modern codec.

It's the wrong move if the BMP needs to stay a BMP for compatibility with legacy Windows software that expects that exact format, or if you need a simple, universally-readable raster format rather than a codec-based one. And if the image needs to remain lossless for archival purposes, TIFF preserves that uncompressed fidelity in a more space-efficient container than BMP without introducing AVIF's lossy compression.

Limitations and privacy

Since most source BMPs carry no alpha channel, there is usually no transparency to preserve either way. On the rare BMP that does have real alpha data, AVIF's alpha support depends on the browser's own encoder and isn't a hard guarantee.

Conversion runs entirely in your browser; the BMP file is never uploaded to a server. Files up to 25MB and 8192px per dimension are supported.