In a firm like ours, where the problem in making videogames for the
mobile enviroment is always the lack of resources to run all the funny
detail we imagine, having the maximum compression level for our graphics is a must. That allows us not only more graphics, but also more behaviours, or more levels or bigger levels in our games.
That's why we pay attention to the compression tools we get across which promises a good performance. To this point we had managed to achieve a fluid working process with complete compatibility with our development app, Unkasoft Platform, and low weight using a three-tools processing.
The base work was done with Photoshop, giving good working speed and versatility at high image weights, but sometimes lacking the necessary compatibility with Unkasoft Platform. After that, and to ensure the compatibility we opened the files and exported them from the free-code application Gimp. The weight goes down, but is still too high.
Last, we have tried several tools specific for the compression of png images, the format used on the mobile enviroment, an come to the, to this point, best tool, which is Pngout.
We started by using the command-line version, assuming a loss of time, but when we noticed the windows version was available and could do batch processing with a even better compression rate than the prior, we immediately acquired it.
Recently we detected some tools the user said to beat pngout capabilities, specifically Xat image optimizer (http://www.xat.com), pngquant (http://libpng.nigilist.ru/pub/png/apps/pngquant.html), and superpng (http://www.fnordware.com/superpng).

The first one is an application which, at first seems very useful. It automates the process of reducing the colour palette using its own algorithm, which gives fairly good results; but, as for Unkasoft, it is not very useful, as we select the colour palette very carefully, even selecting the colours one by one to optimize the product. And, as a compressing tool it is really acceptable, but cant beat the windows version of pngout, and that's why it is not very useful to us.

The next one, pngquant, neither can beat pngout as a compressor, but has a capability that can be extremely useful; It can create a png file with only 8 bit colour information (indexed colour palette) and include another 8 bit channel for the transparency information, thus allowing us to have a 16 bit file with true transparency, instead of the 32 bits Photoshop needs. The images to the left are, the left one a 32 bit photoshop image, and the second a 16 bit pngquant version of it, but to be able to see them correctly you will need a prepared navigator, like mozilla. It seems pngout will support this kind of file, but for the moment being it does not seem to.

And last is superpng, a plug-in for Photoshop which enhances the possible png variants it can export or read, which especially to the Photoshop 7 version is very limited. At the same time, it optimizes the size of the pngs, and that's where it is more useful, as its reduction of weight does not overlap but adds to the reduction achieved by pngout, giving a final file even smaller.

Resuming, this three applications, and specially pngquant and superpng are to be taken in account when it comes optimizing our possibilities without losing image quality.