Image processing - web resources

I'm coming to realise that image processing to get all available information out of astro images is a bigger part of this game than I thought. I found an interesting article online regarding the 'unsharp mask' that I thought I would share with you at http://www.ifa.hawaii.edu/%7Ewang/gallery/random_notes/USM.pdf If anyone else has found useful resources like this, I for one would much appreciate the references.

Clear skies to all.

Tim