Some techniques for shading machine renderings of solids

• Authors: Arthur Appel
• Venue: AFIPS '68 (Spring) Proceedings of the April 30--May 2, 1968, spring joint computer conference
• Year: 1968

Some applications of computer graphics require a vivid illusion of reality. These include the spatial organization of machine parts, conceptual architectural design, simulation of mechanisms, and industrial design. There has been moderate success in the automatic generation of wire frame, cardboard model, polyhedra, and quadric surface line drawings. The capability of the machine to generate vivid sterographic pictures has been demonstrated. There are, however considerable reasons for developing techniques by which line drawings of solids can be shaded, especially the enhancement of the sense of solidity and depth. Figures 1 and 2 illustrate the value of shading and shadow casting in spatial description. In the line drawing there is no clue as to the relative position of the flat plane and the sheet metal console. When shadows are rendered, it is clear that the plane is below and to the rear of the console, and the hollow nature of the sheet metal assembly is emphasized. Shading can specify the tone or color of a surface and the amount of light falling upon that surface from one or more light sources. Shadows when sharply defined tend to suggest another viewpoint and improves surface definition. When controlled, shading can also emphasize particular parts of the drawing. If techniques for the automatic determination of chiaroscuro with good resolution should prove to be competitive with line drawings, and this is a possibility, machine generated photographs might replace line drawings as the principal mode of graphical communication in engineering and architecture.