Subset Warping: Rubber Sheeting with Cuts

Image warping, often referred to as "rubber sheeting," represents the deformation of a domain image space into a range image space. In this paper, a technique which extends the definition of a rubber-sheet transformation to allow a polygonal region to be warped into one or more subsets of itself, where the subsets may be multiply connected, is described. To do this, it constructs a set of "slits" in the domain image, which correspond to discontinuities and concavities in the range image, using a technique based on generalized Voronoi diagrams. The concept of medial axis is extended to describe inner and outer medial contours of a polygon. Polygonal regions are decomposed into annular subregions, and path homotopies are introduced to describe the annular subregions. These constructions motivate the definition of a ladder, which guides the construction of grid point pairs necessary to effect the warp itself.