PNG compression — Verify the result

Worked example

To verify a compressed PNG, check the dimensions, compare bytes and view it over light and dark backgrounds to confirm transparency.

The summary line after you press Compress image lists the original and the result, such as 1024 × 1024 at one size followed by 1024 × 1024 at a lower one. The saved file is named like logo-compress.png. If the status says the original was kept, the re-encode was not smaller, so the file you download is your source and there is nothing further to verify.

For transparency, view the PNG in an application that shows a checkerboard or place it on a coloured page. A logo that gained a white box has lost its alpha, which should not happen with PNG output, so the more likely cause is that you opened a flattened copy of another format. Look for pale fringes around curved letters, which show up on dark backgrounds.

Compare the exact pixels, not the impression. Zoom to 400 percent on a diagonal edge and a thin line in both files and confirm they match. Lossless means no change in colour values, so any visible difference suggests the wrong file or an earlier resize.

A common mistake is to judge by file name. If the byte size is the same as before, the compress step simply had nothing to remove, which is normal for icons and logos that came from a good exporter. Record the figures, and decide whether a resize or a WebP version is the next move.

PNG logo with alpha

PNG; transparency retained when supported

Because PNG output is lossless, any difference you can see between the two files points to a different file, not to compression.