PNGmicro is a free tool which rewrites PNG files to reduce their size, normally without losing any image quality (although you can turn on lossy compression for even greater savings).

The program looks great. There's a sleek, black interface, panels slide out smoothly while flat buttons carry out its main actions.

Getting started is as simple as hitting the add button and choosing your source images (or just dragging and dropping them onto the program).

Tapping the Options icon shows various compression settings. You can set a compression level, enable/ disable interlacing, remove any embedded colour profile, even enable and adjust lossy compression for maximum size reductions.

There's also good control over the name and location of the destination files, with options to rename them, save them to a new folder, overwrite the originals, and more.

The results you'll see will depend very much on your source images, but they can be impressive. We took 100 small PNGs grabbed from websites, so you'd expect them to be very efficient already, but enabling lossy compression saved from 33% (miminum level) to more then 50% (maximum).