1. A computer program product, tangibly stored on a computer-readable medium, for processing electronic images, the computer program product comprising instructions operable to cause data processing apparatus to perform operations comprising: (a) receiving an electronic image including a plurality of input pixels; (b) generating a transformed image that corresponds to a first coordinate transformation of the received image; (c) filtering the transformed image to generate a filtered image; (d) applying a second coordinate transformation to the filtered image to align the filtered image with an accumulation array that includes a plurality of accumulation elements, the aligned image specifying a respective value for each accumulation element; (e) updating each accumulation element based on the respective value in the aligned image; and (f) iterating the operations (b), (c), (d) and (e) for one or more further first coordinate transformations.