Image Converter

The conversion is easy; the cost is what nobody tells you

Changing an image's format takes a second. What is worth knowing is what you give up, and it differs for every pairing — so this page says it before you download the file rather than after you have overwritten your only copy.

What it reads, and what it writes

This reads JPEG, PNG, WebP, AVIF and GIF — five formats a browser can already open. It writes only three: JPEG, PNG and WebP. An AVIF or a GIF goes in; a JPEG, PNG or WebP comes out. A GIF converts from its first frame only — the result is one still picture, and the animation is not kept, which the page says as soon as you choose one.

What each conversion costs

• PNG to JPEG — much smaller for photographs. Transparency becomes white and cannot be brought back. Poor for screenshots, logos and anything with text or flat color, where JPEG smears the edges.
• JPEG to PNG — almost always much larger, and it recovers nothing. PNG stores the JPEG's artefacts as faithfully as its detail. People do this hoping to improve a photo; it cannot.
• Anything to WebP — usually the right answer. Roughly a quarter to a third smaller than JPEG at the same apparent quality, and transparency survives.
• WebP to JPEG — for the places that still refuse WebP. Larger, and transparency is lost.
• A format to itself — a re-encode, not a copy. A lossy format loses a little more every time it is encoded, so do it only if you mean to change the quality.

Lossy and lossless, briefly

JPEG and WebP are lossy: they throw detail away to get smaller, and the choice is permanent. PNG is lossless: it never discards anything, which is why it is right for logos and screenshots and wrong for photographs.

The consequence that catches people out: moving from lossy to lossless preserves what you have, it does not restore what was lost. A JPEG converted to PNG is a perfect copy of an imperfect picture.

When the format is not the problem

This one changes only the format. If the file is too big to send, the Image Compressor is the tool. If you need particular dimensions, that is the Image Resizer. Keeping them separate means each asks one question rather than three.

Nothing is uploaded

Your browser does all of it: decode, redraw, encode. Nothing is sent anywhere, and the test suite for this page records every network request made while a file is processed and fails if one of them could carry it.