I Since this is a library supposed to be used with other applications there M is not very much in ways of a flashy demonstration available. Still there is  O a simple demo application gddemo, which reads demoin.png and produces from this  demoout.png and demooutp.png.   M Of actual use to tweak PNG images is the webpng program. To get a description I of the available options run webpng without parameters. The example uses  . webpng to report on the input file for gddemo.  ? These tests can be invoked using the provided freeware_demo.com      