These last weeks I was working on optimising the Interactive Global Illumination (IGI) integrator for Illumina. The implementation uses a technique known as interleaved-sampling, where the image space is divided into square regions, usually of 3×3 or 4×4 pixels, and the rays shot from the viewer through each pixel of the grid accumulate indirect illumination from a different set of virtual point lights. Although this results in a better approximation, it introduces unpleasant structured noise into the image. Enter the discontinuity buffer, and we have a technique which, in post-processing, averages the irradiance values gathered from virtual point lights to give the image a much softer and more pleasant look. While comparing the results of the IGI integrator to those of the Path Tracer, I accidentally left the discontinuity buffer post-processing on during path tracing, and the result was interesting to say the least.