Abstract: Image synthesis of realistic 3-dimensional models is one of the most widely researched fields these days. Display of natural scenes such as mountains, trees, the earth, and the sea, have been attempted. This paper discusses shading models for volumetric objects in natural scenes.

A precise shading model is required to display realistic images. This paper describes rendering methods for physically-based images taking into account light scattering due to particles in the atmosphere and water, which include sky color, sky light, clouds, fog effects, smoke, snow, the earth viewed from space, water color, and optical effects within water such as caustics and shafts of light. For these effects, a single scattering and multiple scattering models are discussed.