1. A method for histogram calculation using a graphics processing unit (GPU), comprising: storing image data in a two-dimensional (2D) texture domain; subdividing said domain into independent regions or tiles; calculating in parallel, entirely within said GPU, a plurality of tile histograms, one for each tile; summing up in parallel, entirely within said GPU, said tile histograms so as to derive a final image histogram; and , wherein said step of calculating a plurality of tile histograms comprises: counting intensity in a texel determined by texel texture coordinates, the number of histogram bins, and the size of said image data.