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Simulated Bas-Relief Through Bump Mapping

IP.com Disclosure Number: IPCOM000102294D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 132K

Publishing Venue

IBM

Related People

Todd, SJ: AUTHOR [+2]

Abstract

This article describes an extension to bump/texture mapping in computer graphics which provides a useful and computationally efficient range of functions in picture production. A three-dimensional scene is viewed and transformed into a two-dimensional picture, in which the surface normals are retained. That picture is then used a surface texture. Instead of just being a coloured surface, like a poster, the normal information is used to interact with the lighting of the new scene and recreate an illusion of depth. Textures with small depths, such as bricks and tiles, or the more elaborate, such as flutings on columns, radiator panels, or pictorial bas-reliefs, can be modelled more economically than if detail was modelled explicitly. Basic Technique

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Simulated Bas-Relief Through Bump Mapping

       This article describes an extension to bump/texture
mapping in computer graphics which provides a useful and
computationally efficient range of functions in picture production.
A three-dimensional scene is viewed and transformed into a
two-dimensional picture, in which the surface normals are retained.
That picture is then used a surface texture.  Instead of just being a
coloured surface, like a poster, the normal information is used to
interact with the lighting of the new scene and recreate an illusion
of depth.  Textures with small depths, such as bricks and tiles, or
the more elaborate, such as flutings on columns, radiator panels, or
pictorial bas-reliefs, can be modelled more economically than if
detail was modelled explicitly.
Basic Technique

      The technique is described in terms of existing WINSOM (IBM
Winchester Solid Modeller System) and IAX tools, although it is
generally applicable to computer graphics systems.  The generation of
a bas-relief etching of one model (RELIEF) into another model (BASE)
uses the following steps.  First, generate a depth image RELIEFD from
RELIEF model.  A depth image is an image where the value in each
pixel records the distance from the eye of the surface visible
through that pixel.  (This may be done using SLED, and processing the
SLED image to extract only the depth information.)  Any colour
definitions held in the RELIEF model are ignored, and do not affect
RELIEFD image.  An example SLED input to produce RELIEFD is:
RELIEF = ... definition of relief model ...
DRAW(RELIEF);

      The second step is to map the depth image onto the BASE model
by a WINSOM run, using the WINSOM TEXTURE(IMAGE) image mapping
method.  The image is applied with bump mapping, which modifies the
surface normal used in the lighting calculation to simulate a raised
surface.  The image is not used to texture or colour the BASE model.
An example WINSOM input is:
BASE = ... definition of base model ...
BDEF(99) TEXTURE(IMAGE) NAME(RELIEFD)
 BAND(1) COLOUR(WHITE) BUMPHEIGHT(0.1);
DRAW BASE COLOUR(99);
Addition of Colour

      Colour may be added by producing two images from RELIEF:  the
depth image RELIEFD as before, plus a colour image.  The processing
of the pair of images may carry the colour information in one of two
ways, as a red/green/blue(rgb) value, or as a bundle identifier.
Carrying the rgb value is easier; carrying the bundle identifier is
more flexible.  To produce a colour image RELIEFC containing rgb
values requires a conventional WINSOM run against RELIEF MODEL.  This
run includes the bundle definitions for the bundles that colour
RELIEF.  RELIEFC should be produced with full ambient and no other
lights. RELIEFC thus captures colour information, but not information
relating to surface shape; this information is captured in RELIEFD.
An exemplary WINSOM output to produce RELIEFC is:
RELIEF = ... definition of relief model ...
SUR...