PNG compression — Troubleshooting

Worked example

PNG problems are a file that barely shrinks, the original returned, an idle slider, a white box where transparency was, or another format.

If the file barely shrinks, that is expected for a PNG that already came from a good exporter, and for photographs the format simply stores every pixel. The tool performs a lossless re-encode and does not reduce colours or discard detail. A 3 MB screenshot will not fall to 300 KB this way, so resize it or convert it instead.

If you receive the original back, the status line says it was kept because the re-encode was not smaller. That is a safe outcome, not a failure. Moving the Quality slider will not change it, because the slider does not affect a PNG, so look at dimensions instead.

If a transparent logo shows a white box, the usual cause is that the file was exported as JPEG, which has no transparency and fills it with white, or that you are previewing it on a white page. Check the download name and extension: it should end in .png for a PNG source. For fuzzy edges, make sure you did not enlarge the logo before compressing.

If an AVIF or other unusual file comes out as .png, that is the fallback for sources that are not JPG, PNG or WebP. A source above 64 million pixels is refused with a message to crop or resize first. In both cases, convert or shrink the original, then compress.

PNG logo with alpha

PNG; transparency retained when supported

Only change dimensions or format when the figures need to fall; the lossless step cannot be forced smaller.