The PNG format is very useful as an image format for the web, because it is the only widely supported image format that supports partly transparent images.
Unfortunately, most image editing software, among which Photoshop, is not very good at compressing PNG files. This results in more than necessary large file sizes, which swallow bandwidth and take longer time for the user’s browser to download.
TinyPNG is a web app which handles that problem. TinPNG compresses PNG files by reducing the ammount og color and by converting the heavy 24 bit PNG files to the lighter 8 bit ones. Thus, TinyPNG is able to reduce the file size with up to 70% and the result is really hard to distinguish from the original.
The tool is really handy to web designers, because the PNG files it produces will use considerably less bandwith and makes the website load faster.