When you need this conversion
The usual trigger is an upload that fails without explaining why. Screenshots on Windows and macOS save as PNG by default, as do many scanner apps and design tools, so people arrive at a form holding a PNG without ever having chosen one.
The second trigger is file size. A form asking for 50KB will not accept a PNG photograph, because PNG stores images losslessly and simply cannot compress that far. Converting to JPG solves both problems in a single step.
What changes in the file
PNG keeps every pixel exactly as it was and supports transparency. JPG discards fine detail the eye is least sensitive to and has no transparency at all. Converting therefore does two things: the file gets much smaller, and any transparent area becomes solid white.
For a photograph that trade is worth making. For a logo meant to sit on a coloured background, it is not, and you should keep the PNG for that use.
After converting
- Check the file size. If the form has a KB limit, compress the JPG afterwards rather than converting again.
- Check the dimensions. Conversion does not change pixel dimensions. Resize separately if the form specifies them.
- Keep the original PNG. Once transparency is flattened it cannot be restored, so hold on to the source file.
- Open the result before uploading. Confirm nothing that was transparent now looks wrong against white.
Frequently asked questions
Why do forms reject PNG files?
Portals standardise on JPG so every stored image behaves the same way, and because PNG photographs are far larger than the size limits those portals set. Rather than police two formats, most simply accept one.
What happens to a transparent background?
JPG has no concept of transparency, so anything transparent becomes white. For a logo or a cut out that is usually fine on a white page, but the transparency cannot be recovered later.
Will converting reduce my file size?
Almost always, and often dramatically. A photograph saved as PNG can be several times larger than the same photograph as JPG, because PNG stores every pixel exactly rather than discarding detail you cannot see.
Does the conversion lose quality?
JPG is lossy, so some detail is discarded. This tool saves at a high quality setting, so the difference is not visible at normal viewing size for photographs. Screenshots of text suffer more, since JPG blurs sharp edges.
Is a screenshot better left as PNG?
For your own use, yes, because PNG keeps text crisp. Convert only when a form or a recipient requires JPG.
Can I convert back to PNG afterwards?
You can, but nothing is restored. The detail JPG discarded is gone, and converting back simply stores the reduced image in a larger file.