1. A computer program product, tangibly embodied in a machine-readable storage device, comprising instructions operable to cause data processing apparatus to: define a parametric surface interpolating an input raster image, the parametric surface being defined by a parametric equation in two parameters, parameter value pairs defining points on a surface parameter space; receive image edge locations in the surface parameter space; and use the image edge locations to reparameterize the parametric surface near the edge locations, the reparameterization including applying a mapping function to points on the surface parameter space such that one or more points within an edge transition region adjacent to the edge locations of the reparameterized parametric surface are mapped to one or more corresponding points outside the edge transition region in the surface parameter space.