if PNG is a losless format, then what's the compression slider for?

just curious, but why even have a slider for a format that does not lose any data when it’s compressed? why would you not want to always compress 100%?

discussion here is welcome!

Compression does not always mean loss of data. For example, some graphics formats use RLE (run length encoding), which is lossless, but it’s also not highly efficient. The formats used for archiving data, such as zip, also compress, but in no way is data loss acceptable for them! High-compression image formats like JPEG, and most video codec algorithms, actually convert the source data to various schemes that reduce the amount of data that needs to be recorded, based on the way the human eye perceives color imagery. In the process they lose much of the original data, hence the “lossy” label for those processes.

I don’t know PNG in detail but I imagine the slider is there to control how much time the compression takes – higher-quality compression usually takes longer, so time per frame is increased.

ahhhh, ok i see. a trade-off between amount of compression and the amount of time it takes to compress it, which is probably not worth caring about for still images, but for animations i can see how that could save some time. thanks guys!