Appearance Synthesis

Computer graphics has developed practical methods for the description of scenes and their interactions with light. Appearance synthesis is concerned with algorithmic, automated methods for the production of real-world items which look as close as possible to the specified models.

Fig. 1: When illuminated from the back, this reflectance field display renders the picture of a scene as if it was actually illuminated by the light behind the display. As time passes, shadows and highlights in the scene move according to the sun moving over the sky.

Fig. 2: The reflectance field, here disassembled into parts, does not require electronic components.

One possible solution for appearance synthesis is the concept of a passive reflectance field display: optical constructions which embody a coded reflectance field so that the illumination falling on the display creates an image there, as if another scene was rendered in this illumination [Fuchs et al., SIGGRAPH 2008]. Simple variations of this technique consist of inexpensive components (see fig. 1) and may be assembled with off-the-shelf office equipment. More complex constructions comprise hundreds of optical lenses in precise alignment. In either case, the appearance can be modified by exchanging a pattern printed on a transparency sheet inside the display without modifying the design of the optical components around it. Thus, the appearance of a real-world item may be programmed.

Fig. 3: 3D prints created with the methods by Hašan et al.: stackings of different plastic materials creates the appearance of complex materials that expose light transport under the surface.

Reflectance fields decouple the looks of a physical artifact from its actual geometry. While this enables self-rendering pictures, this separation of shape and appearance is not always desirable. The method by Hašan et al. [SIGGRAPH 2010] therefore proposes a solution, which stacks different types of plastics with a 3D printing process so that they approximate the appearance of other materials. The techniques focuses on materials such as marble, which transport light below the surface.