1. A method of processing an input image, comprising: computing spatially-shifted forward transforms of the input image to generate respective sets of forward transform coefficients; applying nonlinear transforms to the forward transform coefficients of each set; computing inverse transforms of the sets of nonlinearly transformed forward transform coefficients to generate respective intermediate images; computing respective measures of local spatial intensity variability for pixels of each of the intermediate images; and computing an output image with pixel values computed based at least in part on the computed measures of local spatial intensity variability.