Trying to use libpng

I am currently (i.e. during the night, my only free time) trying to use the libpng in order to open PNG files and process them later. I haven’t read the entire manual yet but, following their example.c, I succeeded in opening a file, check if it’s really a PNG, read all the data and display some basic information about it (width, height, bit depth, …). Next step: process the data (I will probably only be able to do it during the next week-end).