format conversion

PNG to JPEG

This is the trade this tool was built to show. The JPEG is almost always smaller, and the question is whether what it costs is something your image was using.

What actually changes

  • Transparency is flattened onto a colour

    JPEG has no alpha channel. Whatever was see-through in the PNG is painted onto the colour set under “Behind transparency”, which starts white — so a logo meant to sit on a dark page comes back with a white box behind it.

    Source The converter’s Output panel — src/copy/en/convert.ts

  • The tool will argue with its own measurement

    When JPEG comes out smallest but your image uses transparency, the results table names JPEG as the smallest row and recommends a different one — and says why. The measurement is not hidden, it is explained.

    Source The results table’s recommendation rule — src/copy/en/convert.ts

  • A paletted PNG is rewritten in full colour first

    PNGs with 256 colours or fewer store an index into a palette. The conversion decodes to full colour before anything is encoded, so a small paletted PNG can produce a JPEG larger than itself.

    Source The note under the results table — src/copy/en/convert.ts

  • It is lossy, and the loss is not visible in the byte count

    The JPEG is smaller because pixels were changed. The converter shows both files at their own pixels either side of a seam you can drag, at full size and never scaled, so the change is something you look at rather than something you are told about.

    Source The comparison seam — src/components/convert/SeamView.tsx

  • Camera and colour data is dropped unless you ask for it

    EXIF, ICC profiles and comments are off by default. The orientation tag is dropped either way, because the picture has already been turned the right way up and keeping the tag would turn it again.

    Source The converter’s Output panel — src/copy/en/convert.ts

The short answer

Take the JPEG for photographs with no transparency. For a logo, a screenshot or anything with flat colour and hard edges, compare the WebP on the same page first.

Convert it here

The converter takes your file, writes it as PNG, JPEG and WebP at the same pixel size, and shows you what each one weighs — measured on your file rather than on an average. It runs on the page using WebAssembly; the image never leaves your device.

Open the image converter

The other conversions

Every pair this tool can actually do. There are nine because it reads four formats and writes three, and a format cannot be converted to itself.

This page carries 5 facts and a source for each one. It is one of nine, generated from the same list the converter reads — so a page cannot exist here for a format the file picker would refuse.