IMAGE SPACE SHADING OF 3-DIMENSIONAL OBJECTS

Two-dimensional images of 3D objects require realistic shading to create the illusion of depth. Traditional (object space) shading methods require extra data (normal vectors) to be stored with the object description. When object representations are obtained directly from measured data, these normal vectors may be expensive to compute; if the object is modified interactively, they must be recomputed frequently. To avoid these problems a simple shading method is devised which uses only information available in image space, after coordinates have been transformed, hidden surface removed, and a complete pre-image of all objects has been assembled. The method uses both the distance from the light source and the surface orientation as the basis for shading. The theory and its implementation are discussed and shaded images of a number of objects are presented.