JPG to PNG

What you gain

Nothing in quality, the artefacts already in the JPEG stay exactly where they are. What you gain is that further edits and re-saves will not add more, since PNG is lossless. That matters if the image is going through several rounds of cropping or annotation.

Expect the file to get considerably larger, often several times over, especially for photographs.

The case where this genuinely helps

JPEG is lossy every single time it is saved. Open a photograph, crop it, save, open it again, annotate it, save again, and each round adds artefacts on top of the last, concentrated around edges and text. After four or five passes a screenshot with writing on it looks visibly chewed. Converting to PNG once, at the start, stops that chain dead: PNG is lossless, so every subsequent save is exact.

So the rule is about direction of travel. If the picture is finished and about to be published, leave it as JPEG. If it is about to go through several rounds of editing, convert now and export back to JPEG at the end, once.

When it is the wrong move

For a photograph you simply want to store or send, this makes the file three to eight times larger and improves nothing. Web pages in particular should not be served PNG photographs; it is one of the most common causes of a slow page. If the goal is a smaller file with transparency support, WebP does both jobs, and PNG to WebP is the conversion worth making after this one.

What PNG actually gives you

• Lossless storage, so re-saving costs nothing.
• An alpha channel, which lets you cut a background out later. The channel is empty on arrival from a JPEG, but it exists, which is why design software often demands PNG before you can mask anything.
• Exact colors, with no chroma subsampling. JPEG stores color at half resolution, which is why fine red text on a dark background looks smeared. That damage is already done, but it will not get worse.

Whether the image has anything worth preserving in the first place is answerable with media info, which reads the real dimensions and encoding out of the file rather than trusting the extension.

Common questions

Related tools