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METHODS OF SIMULATING SHADOWS FROM CHROMATIC TRANSLUCENT OBJECTS

IP.com Disclosure Number: IPCOM000008466D
Publication Date: 2002-Jun-17
Document File: 25 page(s) / 2M

Publishing Venue

The IP.com Prior Art Database

Abstract

The present invention relates generally to computer graphics, and more particularly to a method for simulating the translucent shadow phenomena in a computer image generation system.

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METHODS OF SIMULATING SHADOWS FROM CHROMATIC TRANSLUCENT OBJECTS

DESCRIPTION

Field of the Invention

The present invention relates generally to computer graphics, and more particularly to a method for simulating the translucent shadow phenomena in a computer image generation system.

Background of the Invention

Shadow generation in computer graphics systems attempts to increase realism of three dimensional shaded objects by simulating shadows to vary as a function the lighting environment and to emphasize the changing direction of the light source.  Most shadow generation algorithms currently used operate under the constraint of a point light source which means that shadows will have hard edges, with a sharp transition from a dark shadow area to a bright non-shadow area.  As a result, they tend to produce hard edge, point light source shadows without consideration to shadow grade offs.

Moreover, the case where shadows are cast from transparent or translucent objects is further complicated by the partial emission of light through the object.  When a light source is shining on an opaque object, all the light is blocked by this object.  The opaque object is considered to be casting an opaque shadow.  Light shining on a translucent object, however, penetrates the object and causes the translucent object to cast a translucent shadow onto the object that is in both the light’s and translucent object’s path.  Some examples of translucent objects include glass and plastic.  As the light passes through these objects some of its energy may be absorbed.  Usually this absorption occurs at preferred wavelengths causing light to change color on exiting object.  That is, light penetrating the translucent object will have its spectrum modified by object’s physical properties.

Accordingly, one of the major goals in automatic image generation is to create physically realistic lighting which considers both gradual shadowing effects and modulates translucency of shadows cast from various objects having different surface properties.  In Figure 1, a surface called a shadow casting surface 102 blocks the light beam 106 to a surface called a shadow catching surface 104 and produces a shadow 108 on the shadow catching surface 104.  One known approach of producing shadows relies on a z-buffer at the light source to produce shadows.  The z-buffer or depth buffer used in this application is referred to as a shadow buffer.

The shadow buffer sees the scene from the light’s point of view.  Request can be made while rendering the eye point z-buffer to determine what the light source sees at this point in the scene.  Normally, this is done by comparing distances to the closed surface or point that the light sees.  If the distance is greater than some tolerance, it assumes the light is not seeing the same point in scene space and the point being rendered is assumed to be in shadow.  The strategy used in this approach relies on giving each unique object a different object identifier (OID).  An o...