Sketching shadows and highlights to position lights

In inverse shading, a user provides information about the desired shading as she/he would like it to appear in the final image. The computer then interprets this information to identify the best values for the various shading parameters that would lead to the desired visual effect. The authors introduce an approach based on sketching in order to position light sources. Point light sources are positioned by sketches of shadows or highlights. Extended light sources are positioned by sketches of umbra or penumbra. The resulting system allows one to quickly position light sources and to refine their positions interactively and more intuitively