University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell Photon Mapping and Irradiance Caching

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell Bidirectional Paths Light path Eye path Shadow ray

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell Bidirectional Paths flux (photons) radiance shadow ray

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell Weighting the paths Pixel estimate is weighted sum of path radiances where Choice of weights is critical for low variance see Veach for details

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell Advantages and disadvantages Bidirectional path tracing Good for small sources of strong indirect illumination (caustics) Path tracing Good for outdoor scenes with only a small part of the model visible Both have trouble sampling mirror images of caustics Both need lots of samples to avoid objectionable high frequency noise

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell Photon mapping Cache light paths for efficiency? Decouple geometry and illumination Don’t use illumination maps where number of samples needed is dependent on primitive size and scene complexity Get rid of high-frequency noise efficiently Density estimation However, density estimation produces biased (but consistent) samples

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell Two pass approach Pass one: photon tracing Build the photon map data structure Pass two: rendering Trace eye paths using photon map to produce radiance estimates efficiently

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2007 Don Fussell