PNGmini is a simple free tool which rewrites PNG files to reduce their size, without losing any image quality.

The program looks great. There's a sleek, black interface; red status bar and highlighting; menus slide out smoothly, while flat buttons carry out its main actions.

The problem here, though, is there really aren't that many actions. There's no "Add" button to import files, so you must drag and drop them onto PNGmini. There are no options or settings to consider. All you get is an Optimize button which rewrites each file, trying to save space, before displaying the results.

This simplicity is certainly appealing, but it does have one important consequence. You don't get to choose an output folder, or decide how the rewritten PNG files will be named: PNGmini will by default overwrite the original files.

To be clear: PNGmini will overwrite your original files. This shouldn't be a major issue - the worst that's likely to happen is they won't be reduced in size - but just in case of problems, you should always work with copies.

What results can you expect? We ran PNGmini through our two standard PNG compression tests.

First, we passed it 100 web graphics taken from real websites, and it reduced their size by 20.04%. That's disappointing, as tools like File Optimizer achieve around 40% here.

Our second test uses 25 HD photos, 200MB of data. This is much tougher, but PNGmini still cut them down by 4.22%, comparable with the market leaders.

Version 2.0 brings:
 - a new "backup" setting tells the program to create .BAK copies of any source files. The original copies will still be overwritten, but at least the BAK files will be there if you need them.
 - an "optimisation level" setting affects compression and performance (low = minimal compression but works quickly, high = maximum compression but is extremely slow).

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PNGmini delivered below-average compression rates on our test PNG web graphics. The program was much better at optimising our HD photos, though, so if you're working with larger files then it might be worth a try. Just keep in mind that it will overwrite your source files. Enable the option to create backups, or just make sure you're always working with copies of your original images.