Share 'image sampling'

hi,   I am trying to sample and image and compare the result for a certain value (color) or a colour close withing a certain proximity to that. where that condition is met, I would like to do something. trouble is that I am obvioulsy gettig 3 (RGB) values per point. I have tried creating a unique "checksum" out of that (ie. x/y+1/z+1) so I have one number per pixel to compare to. (the +1) is in c…