1. A method for processing a base image having a resolution of X times Y pixels, the method comprising: re-sampling the base image to a resolution of 2M times 2N pixels, wherein X is equal to at least 2M and Y is equal to at least 2N; producing a first sub-image by decimation of the re-sampled base image to a resolution of M times N pixels; and producing a second sub-image by shifting the phase of the re-sampled base image and then decimation of the phase shifted image to a resolution of M times N pixels.