1. A method for post-processing a computer-generated image of a three-dimensional object for display as a series of pixels, having a focus depth specified for each image frame, wherein: image pixels are filtered using contributions from other pixels of the image about the image pixel and with filter coefficients determined in part by the focus depth; the image pixels are grouped into a plurality of blocks of adjoining image pixels with a single respective depth value specified for each block; and all pixels of a block are filtered with the same filter coefficients, said filter coefficients being additionally determined by the block depth value.