Convert images between JPG, PNG, WebP and AVIF

A PNG screenshot of a document can be 10× the size of the same image as JPEG, and portals that cap size reject it purely on format choice.

Going the other way, logos, signatures on transparent paper and charts need PNG because JPEG cannot represent transparency honestly.

For the web, WebP and AVIF cut bytes by 25–60% against JPEG at the same visual quality — the single easiest Core Web Vitals win on a site you control.

Format rejection is the least informative failure a portal can hand you: the upload simply does not appear, or returns a generic error, because the file header says WebP or HEIC while the requirement says JPEG. Converting is a thirty-second fix that removes a whole class of dead ends.

The reverse case matters for the web. Serving WebP or AVIF instead of JPEG typically saves a quarter to half the bytes for the same visual quality, which is free page-speed improvement for anyone with a website or blog.

Conversion is one of the few operations where doing it in the browser is not merely a privacy nicety — passing a photograph through an unknown converter often adds a watermark or silently shrinks it, and neither happens here.

This tool exists for images handled in a hurry: no queue, no account, no upload, and a result you can verify on the spot. The explanation below is the same one we would give a colleague who asked how it works.

Choose the format from what the image is, not from what is fashionable. A photograph is a smooth continuum of tone, which JPEG handles beautifully and PNG handles expensively. A screenshot, a logo, a signature on white paper or anything with a small palette is the opposite: PNG compresses it losslessly to a fraction of what JPEG costs, and keeps the hard edges hard. WebP and AVIF are excellent for the web and are still frequently refused by government and bank upload widgets.

Photographs from phones carry more metadata than most people realise — capture timestamp, camera model, the orientation tag that decides whether the picture displays upright, and often GPS coordinates precise to a few metres. Because every operation on this site writes a fresh file, that metadata does not survive by default. For a photograph of a marksheet or a bank statement, that is a privacy gain; for an archival photograph, note the date before you process it.

Accepted inputs are JPEG, PNG, WebP, AVIF, HEIC, GIF and BMP images up to 50 MB each. SVG, HTML and other script-bearing formats are refused outright rather than sanitised, because a file that can execute code has no business being re-encoded — and an upload field that accepts one is a security hole rather than a feature. Several files can be queued where the workbench supports it. Batch, page and memory limits apply; check every output.

Decoding goes through the browser's own codecs (or libwebp/libavif via WASM where the platform lacks support). Encoding to JPEG flattens alpha onto white, because JPEG has no alpha channel and silently corrupting transparency to black is a classic conversion bug. PNG output is passed through OxiPNG for lossless recompression at level 2, which typically shaves 10–20% with no pixel changes whatsoever. Each format has its own decoder and encoder path. JPEG, PNG, WebP and AVIF are handled by WebAssembly codecs compiled from the reference libraries, so the same quality decisions apply as in a desktop tool. Transparency is preserved for PNG and WebP, and composited onto white for JPEG, which has no alpha channel — the opposite behaviour to naïve converters that leave transparent regions black. Repeated conversion between lossy formats is discouraged in the interface, because each pass costs a little quality. Conversion decodes to pixels and re-encodes in the target format, which is why a format change is a real operation and not a renamed extension — portals that read the file header will agree with the tool about what the file actually contains. Transparency is composited onto white for JPEG, since JPEG has no alpha channel, and preserved for PNG and WebP.