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UBC Theses and Dissertations
Shading and inverse shading from direct illumination Poulin, Pierre
Abstract
An understanding of light and its interaction with matter is essential to produce images. As the modeling of light sources, light transport and light reflection improves, it becomes possible to render images with increasing realism. The central motivation behind this thesis is to improve realism in computer graphics images by more accurate local shading models and to assist the user to obtain the desired lighting effects with these more complex models. The first part of the thesis addresses the problem of rendering surfaces illuminated by extended (linear and area) light sources. To compute the light reflected by a surface element in a given direction, one needs to determine the unoccluded regions (shadowing) of each light source and then to compute the light reflection (shading) from each of these regions. Traditionally, point light sources are distributed on the lights to approximate both the shadowing and the shading. Instead, an efficient analytical solution is developed for the shading. Shadowing from extended light sources is a fairly expensive process. To give some insights on the complexity of computing shadows, some properties of shadows and algorithms are presented. To reduce the cost of computing shadows from linear light sources, two acceleration schemes, extended from ray tracing, are introduced and evaluated. The second part of this thesis addresses the problem of achieving a desired shading effect by building up systems of constraints. This approach is called inverse shading. It allows a user to obtain a desired lighting effect by interacting directly with the scene model. An interactive modeling system has been built to study the introduction of rendering issues into the modeling process itself. Two rendering aspects are considered: shading and shadows. By specifying a highlight position and size, the unique direction of a directional light source as well as the surface glossiness are determined. Interactively moving this highlight on the surface redefines the light direction while changing its size redefines the surface glossiness. By manipulating shadow volumes (the volume within which a particular light cannot be completely seen), the light source definition and position can be modified. By assigning colours to various points in a 3D scene, information about the colour of a surface as well as other surface characteristics can be deduced. This relatively new concept of defining the causes by manipulating the effects is expected to have a major impact on the design of future computer graphics modeling systems. It begins a new family of tools for the design of more intuitive user interfaces.
Item Metadata
Title |
Shading and inverse shading from direct illumination
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1993
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Description |
An understanding of light and its interaction with matter is essential to produce images.
As the modeling of light sources, light transport and light reflection improves, it becomes
possible to render images with increasing realism. The central motivation behind this
thesis is to improve realism in computer graphics images by more accurate local shading
models and to assist the user to obtain the desired lighting effects with these more
complex models.
The first part of the thesis addresses the problem of rendering surfaces illuminated
by extended (linear and area) light sources. To compute the light reflected by a surface
element in a given direction, one needs to determine the unoccluded regions (shadowing)
of each light source and then to compute the light reflection (shading) from each of these
regions. Traditionally, point light sources are distributed on the lights to approximate
both the shadowing and the shading. Instead, an efficient analytical solution is developed
for the shading. Shadowing from extended light sources is a fairly expensive process. To
give some insights on the complexity of computing shadows, some properties of shadows
and algorithms are presented. To reduce the cost of computing shadows from linear
light sources, two acceleration schemes, extended from ray tracing, are introduced and
evaluated.
The second part of this thesis addresses the problem of achieving a desired shading
effect by building up systems of constraints. This approach is called inverse shading. It
allows a user to obtain a desired lighting effect by interacting directly with the scene
model. An interactive modeling system has been built to study the introduction of rendering issues into the modeling process itself. Two rendering aspects are considered:
shading and shadows. By specifying a highlight position and size, the unique direction of
a directional light source as well as the surface glossiness are determined. Interactively
moving this highlight on the surface redefines the light direction while changing its size
redefines the surface glossiness. By manipulating shadow volumes (the volume within
which a particular light cannot be completely seen), the light source definition and position can be modified. By assigning colours to various points in a 3D scene, information
about the colour of a surface as well as other surface characteristics can be deduced. This
relatively new concept of defining the causes by manipulating the effects is expected to
have a major impact on the design of future computer graphics modeling systems. It
begins a new family of tools for the design of more intuitive user interfaces.
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Extent |
3305182 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-06-04
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0051267
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1995-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.