Crop PNG

Many tools accidentally render transparent PNGs onto an uninitialized HTML5 black canvas buffer. PDFixel explicitly retains the full 32-bit RGBA alpha channel so transparent icon backgrounds stay 100% clear.

No. PNG is a lossless format, so the pixels inside your crop box come out byte-for-byte identical to the source. There is no quality setting to get wrong either — the browser canvas encoder ignores the quality parameter entirely for PNG, so the only thing cropping changes is which pixels survive. This is the opposite of JPEG, where every save re-encodes and discards a little more detail.

Because many PNGs on the web are 8-bit indexed images that store a palette of at most 256 colours, and re-encoding one through a canvas produces full 32-bit RGBA instead. Four bytes per pixel across a smaller area can still outweigh one byte per pixel across a larger one. It is not a bug and the image is not damaged — run the result through PNG Compressor if the size matters, which will re-quantise it back to a palette where the image allows.

Yes, and PNG is the only one of the three common web formats where this works properly. The circular crop writes alpha 0 into the corner pixels, so an avatar sits cleanly on any background colour. Cropping the same shape as a JPEG cannot work, because JPEG has no alpha channel at all and the corners have to be filled with an opaque colour.