[a1369209993]

> they seem to be almost lossless

The should be just plain (completely) lossless unless your image encoder is doing something evil behind your back.

[gwbas1c]

I thought there are "lossy" encoders that do things like dither and reduce the colorspace?

[gpvos]

There are, but those are not the ones one thinks of by default when talking about PNG. If they do, they should clearly tell you they are doing something nonstandard.