1. A method of determining the tendency of a receptor to bind to a ligand comprising: (a) exposing a labelled receptor to a substrate, said substrate comprising a plurality of ligands at known locations; (b) at a plurality of pixels within each of the known locations, determining an intensity value for the amount of signal generated from within each pixel; and (c) for each known location, identifying a subset of pixels that fall within a statistical norm of intensity values for all pixels within the known location; and (d) determining relative binding of the receptor to the ligands from the subset of pixels wherein steps (b)-(d) are performed by a digital computer.