Painting Gradients: Free-form Surface Design Using Shading Patterns

An interactive system for designing curved surfaces is proposed which is based on direct manipulation of a single-view shaded image of this surface. Apart from functions like carving in the surface or adding to it, and local smoothing, sharpening or shifting of selected surface regions, the system supports painting local gradient distributions. An iterative algorithm enforces conservativity of the gradient map at all times, so that the shaded image corresponds everywhere to a possible 3-dimensional surface. This surface can be output either as a gradient map, to be used e.g. in bump mapping, or as an adaptively tiled triangular mesh.