1. A computer graphics system for generating a pixel value for a pixel in an image, the pixel value being representative of a point in a scene as recorded on an image plane of a simulated camera, the computer graphics system comprising: A. a photon map generator configured to generate a plurality of photon maps, each photon map being associated with a respective point in time during a time interval; B. a sample point generator configured to generate a set of sample points in accordance with a selected low-discrepancy sequence, each sample point representing a respective point in time during said time interval; and C. a function evaluator configured to generate at least one value representing an evaluation of a selected function using selected ones of said photon maps associated with respective ones of the points in time associated with the sample points generated by said sample point generator, the value generated by the function evaluator corresponding to the pixel value.