Figure 1 - Spatially adaptive sampling can be implemented using a Gaussian pyramid, represented as a quadtree representation of the image. Progressive levels of detail are represented by nodes farther down the graph. In the above image tile, 64 pixels are represented at 4 levels of detail. The dots represent samples which require unique representation from their lower-resolution ancestors, and they correspond to nodes in the tree. The numbers correspond to a fixed sample order for the quadtree.