US Patent 7277590 Image processing method and apparatus

An image processing method for conducting anisotropic diffusion filtering on a pixel value Ii,j in a two-dimensional image, comprises: finding conduction coefficients Cn, Cs, Cw, Ce, Cnw, Csw, Cne and Cse in eight surrounding directions for each pixel based on a pixel value gradient ∇I to produce a two-dimensional distribution image of the conduction coefficients; and finding pixel value first partial differentials ∇nI, ∇sI, ∇wI, ∇eI, ∇nwI, ∇swI, ∇neI and ∇seI in the eight surrounding directions for each pixel to calculate a pixel value in an output image according to: