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Painting Environment Maps Through Reverse Ray Tracing

IP.com Disclosure Number: IPCOM000121773D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 116K

Publishing Venue

IBM

Related People

Woodwark, JR: AUTHOR

Abstract

A graphical method is disclosed that enables users to place lights on an object in a scene specifying highlights, but avoiding the need for positioning source-lights directly in graphical space. Combined are the benefits of both rendered and artist-generated highlights on an object.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Painting Environment Maps Through Reverse Ray Tracing

      A graphical method is disclosed that enables users to
place lights on an object in a scene specifying highlights, but
avoiding the need for positioning source-lights directly in graphical
space.  Combined are the benefits of both rendered and
artist-generated highlights on an object.

      Environment maps are part of a standard technique to produce
pictures of shiny objects, for instance, musical instruments from a
brass band, that appear to be reflecting light from a complex
surrounding scene, without the trouble of actually modelling that
scene in three dimensions.  It is achieved by having an appropriate
image recorded on a surface, such as a box or sphere, which encloses
the scene.  Assuming that rendering is done by ray-casting, reflected
rays that would otherwise 'go off to infinity' are taken to hit the
map, and the appropriate color is fed into whatever lighting models
are being used.  Distorted pieces of the map thus appear as
highlights on objects in the scene.  The technique is unrealistic, to
the extent that parallax effects are ignored but, for a distant scene
observed only through reflections in curved surfaces, this is not a
significant drawback to an economical process.  Environment maps may
be constructed in a number of ways: for instance by being painted
directly, obtained from photographs or rendered pictures, or derived
from a simple model (e.g., of the brightness of the sky at different
angles).  It is possible to combine environment mapping with a
background image, but the techniques do not have to be linked; the
rays directly from the viewer need not be compared with the map, or
can be taken to strike a different image.  Similarly, the 'shading',
or Lambert's law lighting calculation, is usually performed with a
simple lighting model (e.g., parallel illumination) that is
independent of the map.

      The disclosure is an extension of the SLED utility concept
contained in the Winchester Solid Modeller (WINSOM) System.  It
creates environment maps from highlights painted on to objects in the
scene.  Thus, a designer who has made a surface model would be able
immediately to use standard sorts of paint brush function to color-in
a view of that object.  In the simplest implementation, one
appropriate for the car styling, assume that the color of the surface
has been specified, also an appropriate direction of Lambertian
illumination.  From this information the color that the surface would
be, were it matt, can be obtained.  Any extra intensity or coloration
is then assumed to have come from the environment, and a reflected
ray is traced back to the map and colors it.

      The designer gets the shape of highlights that accords with his
own idea of how things should be rendered, but with the advantage of
a consistent model which will produce new and changed highlights if
the object is modified, extended, or moved.  While an en...