I have programming background with some experience with image manipulation via GIMP and Fireworks. As working with image manipulators is part of my work sometimes I decided to improve my knowledge in this area.
However, when I try looking for something like
what I am able to find are only some tutorials with how to do this logo and that image, how to apply filter and so on.
What I would need is some decent tutorial explaining the basic graphics concepts like layers, channels and so on so I can see what is happening behind the tools used in GIMP.
What should I be looking for? What are possible resources to learn these thigns?