Whatever happened to compressed read/write filesystems

Yes, there is, Pismo File Mount Audit Package http://www.pismotechnic.com/pfm/ap/

you can mount zip iso, etc as folders, and and it has an optional ecrypted container folder

freeware, no nags

Better-compressed images (i.e. with a smaller file size) should generally take less time to load than the same image with a larger size.

If you want to minimise the filesize when saving a PNG file, the sacrifice comes in the time it takes to compress the file.

The PNG compresses image data with DEFLATE (the same algorithm used in zlib and PKZIP). One way DEFLATE saves space is to encode recurring byte sequences by just providing a runlength, and an distance back to where it previously appeared in the stream. (e.g. A B C D E F A B C A B C D could be encoded as A B C D E F [3,-6] [4,-9]. (It could also encode it as A B C D E F [3,-6] [3,-3] D.)

The compressor has to use an algorithm to look for matching sequences before it can encode them. Algorithms vary, but many of them can be made to work harder or go faster using certain parameters. When an algorithm works harder, it might find more or longer matches, which usually result in better compression, but it will take longer to do it.

By contrast, the decompression algorithm is very simple and doesn't have to do much work - it just decodes the stream in a fairly linear fashion, and it doesn't have to search for matches because they are provided by the compressor - it just looks up the length/distance codes provided to it.

Generally, the fewer bits it reads in, the faster the PNG decompression is likely to be.