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Create a pyramid of texture maps. Each level doubles filter size. David Luebke 1/19/99 ... Every ray hit deposits some of its energy into surface's illumination map ... – PowerPoint PPT presentation
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Title: David Luebke1/19/99
1
CS 551/651 Antialiasing Wrap-up
- David Luebke
- cs551dl_at_cs.virginia.edu
- http//www.cs.virginia.edu/cs551dl
2
Administrivia
- Hand in Assignment 1
- Hand out Assignment 2
- Sampling strategies in RSRT
- Due Tuesday March 9
- Read Sections 10.1, 10.4
3
Recap Antialiasing Strategies
- Prefiltering
- Supersampling
- A-Buffer
- Adaptive supersampling
- Stochastic supersampling
4
Recap Nonuniform Supersampling
- To be correct, need to modify filtering step
5
Recap Nonuniform Supersampling
- Approximate answer weighted average filter
- Correct answer multistage filtering
- Real-world answer ignore the problem
? ? I(i, j) h(x-i, y-j)
I(x,y)
? ? h(x-i, y-j)
6
Recap Antialiasing and Texture Mapping
- Texture mapping is uniquely harder
- Potential for infinite frequencies
- Texture mapping is uniquely easier
- Textures can be prefiltered
7
Recap Antialiasing and Texture Mapping
- Issue in prefiltering texture is how much texture
a pixel filter covers - Simplest prefiltering scheme MIP-mapping
- Assumption approximate filter size, ignore
filter shape - Create a pyramid of texture maps
- Each level doubles filter size
8
Recap Mip-Mapping
- Tri-linear mip-mapping
- Pixel size ? depth d
- Linearly interpolate colors within 2 levels
closest to d - Linearly interpolate color between levels
according to d
9
Antialiasing Mip Mapping
- Q Whats wrong with the mip-map approach to
prefiltering texture? - A Assumes pixel maps to square in texture space
- More sophisticated inverse pixel filters (see
FvD p 828) - Summed area tables
- Elliptical weighted average filtering
10
Backwards Ray Tracing
- Traditional ray tracing traces rays from the eye,
through the pixel, off of objects, to the light
source - Backwards ray tracing traces rays from the light
source, into the scene, into the eye - Why might this be better?
11
Backwards Ray Tracing
- Backwards ray tracing can capture
- Indirect illumination
- Color bleeding
- Caustics
- Whats a caustic?
- Give some examples
- Where do caustics get the name?
12
Backwards Ray Tracing
- Usually implies two passes
- Rays are cast from light into scene
- Rays are cast from the eye into scene, picking up
illumination showered on the scene from the first
pass
13
Backwards Ray Tracing
- Q How might these two passes meet in the
middle?
14
Backwards Ray Tracing
- Arvo illumination maps tile surfaces with
regular grids, like texture maps - Shoot rays outward from lights
- Every ray hit deposits some of its energy into
surfaces illumination map - Ignore first generation hits that directly
illuminate surface (Why?) - Eye rays look up indirect illumination using
bilinear interpolation
15
Backwards Ray Tracing
- Watt Watt, Plate 34
- Illustrates Arvos method of backwards ray
tracing using illumination maps - Illustrates a scene with caustics
- Related idea photon maps
16
Distributed Ray Tracing
- Distributed ray tracing is an elegant technique
that tackles many problems at once - Stochastic ray tracing distribute rays
stochastically across pixel - Distributed ray tracing distribute rays
stochastically across everything
17
Distributed Ray Tracing
- Distribute rays stochastically across
- Pixel for antialiasing
- Light source for soft shadows
- Reflection function for soft (glossy) reflections
- Time for motion blur
- Lens for depth of field
- Cook 16 rays suffice for all of these
18
Distributed Ray Tracing
- Distributed ray tracing is basically a Monte
Carlo estimation technique - Practical details
- Use lookup tables (LUTs) for distributing rays
across functions - See WW Figure 10.14 p 263
19
Advanced Ray Tracing Wrapup
- Backwards ray tracing accounts for indirect
illumination by considering more general paths
from light to eye - Distributed ray tracing uses a Monte Carlo
sampling approach to solve many ray-tracing
aliasing problems
20
Next Up Radiosity
- Ray tracing
- Models specular reflection easily
- Diffuse lighting is more difficult
- Radiosity methods explicitly model light as an
energy-transfer problem - Models diffuse interreflection easily
- Shiny, specular surfaces more difficult
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