BTW, I should add that as far as linear interpolators go this is all really old hat ... stuff like this is a little more fresh :
http://www-ist.massey.ac.nz/elai/Pub...eilei_2008.pdf
This method is pretty cute and easy to implement (basically doing a little unsharp before interpolation) :
http://www.ing.unibs.it/~marco.dalai/pub/DLM_VLBV05.pdf