[pimlottc]

Haven't tried this, but another related tool that works great for re-compressing existing files is AdvanceCOMP [0]. It can lossless optimize zip, png and mng files in-place, which is particularly handy for zip files.

I used this on a project to drastic reduce the size of generated Powerpoint decks, in order to stay below the email attachment limits for our distro list recipients. Very handy!

0: http://www.advancemame.it/comp-readme

[anderskaseorg]

That kind of tool is useful too, but for different purposes. Precomp lets you recover the original compressed data stream byte-for-byte, not just a differently compressed version of the same uncompressed data.