1. A method of processing an input image with a processor, comprising: applying a forward transform operation to a first shifted version of the input image to generate a first set of forward transform coefficients with the processor; applying the forward transform operation to a second shifted version of the input image that differs from the first shifted version to generate a second set of forward transform coefficients with the processor; applying first and second nonlinear transforms to the first and the second sets of forward transform coefficients, respectively, to generate first and second sets of nonlinearly transformed forward transform coefficients with the processor; computing first and second inverse transforms of the first and the second sets of nonlinearly transformed forward transform coefficients, respectively, to generate first and second intermediate images with the processor; computing first and second measures of local spatial intensity variability for first and second pixels, respectively, of the first and the second intermediate images, respectively, with the processor; and producing an output image from the first and the second intermediate images, wherein the output image includes an output pixel value that is computed from first and second pixel values corresponding to the first and the second pixels, respectively, and at least one of the first and the second measures of local spatial intensity variability with the processor.