From: Jean-Christophe Kermagoret []
Just an idea,
You could for example call imagemagick converter through a RunExec command. You should have all the image magick parameters. 
Yes, that sorta thing might be a reasonable approach... if there were not already a direct solution built into Cocoon! :-)
It's for this very reason that ImageReader exists... so that things like ResourceReader and DatabaseReader do  not have to know about images.
Separation of concerns... "do one thing and do it well"... "once and only once"... yada yada yada... :-)