Quad Tree Image Decomposition
Decomposing an image into regions of homogeneous colors can be useful in applications such as image compression or image segmentation. The boundaries between quads are shown on the left. On the right, each quad is pictured by its average color; less extreme compression schemes would result in less lossy representations.
For a definition of quad tree and other uses, see http://en.wikipedia.org/wiki/Quad_tree.