How to compress a huge amount of PNG images?

At work, on certain projects I have to manage a lot of images. Most of the time PNG files work the best for what I'm doing.

With such a huge amount of images, I've tried using PNG compression with PNG Gauntlet but sometimes the file doesn't really change and sometimes PNG Gauntlet reports it would've made the filesize bigger!

Am I just maxing out the compression or is there something more I can do?

PNG compression is a lossless compression. However, a caveat to this is that there will be times when compressing an image will not always yield the results you want (% compression ratio won't be that great). In contrast to lossful compression (like JPG compression), where you will almost always get a filesize reduction (% compression ratio might be higher), but you actually lose image quality.

Have you tried PNG Crush?

PNG compression works better for images that have large areas of flat color, like cartoons that are colored with simple color fill, as apposed to a painting which has many colors which look similar, but really aren't.

I recommend PNGOUT - it works very well. I have never had it make a file larger, and have only had it keep the same file size on rare occasions.

via Coding Horror