[kuya_noel]

here's a cool median filtering algorithm (extensible to bilateral filtering/surface blur) which exhibits O(log r) performance: http://www.shellandslate.com/download/fastmedian_5506.pdf http://www.shellandslate.com/download/medianslides.pdf

also related are adobe's local laplacian filters: http://people.csail.mit.edu/hasinoff/pubs/ParisEtAl11-lapfil...

at recent SIGGRAPHs, they showed off the halide DSL which can optimize filtering/schedule of image processing kernels for CPUs/GPUs.

also pretty cool related algorithms are domain transform edge aware filters: http://www.inf.ufrgs.br/~eslgastal/DomainTransform/ if you use open cv, they're in 3.0 called DTFilter