lecture07 - CS 551/651: Advanced Computer Graphics...

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David Luebke 1 CS 551/651: Advanced Computer Graphics Antialiasing Continued: Prefiltering and Supersampling
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David Luebke 2 Recap: Antialiasing Strategies Prefiltering: low-pass filter the signal before sampling Pros: Guaranteed to eliminate aliasing Preserves all desired frequencies Cons: Expensive Can introduce “ringing” Doesn’t fit most rendering algorithms
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David Luebke 3 Recap: Antialiasing Strategies Supersampling: sample at higher resolution, then filter down Pros: Conceptually simple Easy to retrofit existing renderers Works well most of the time Cons: High storage costs Doesn’t eliminate aliasing, just shifts Nyquist limit upwards
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David Luebke 4 Recap: Antialiasing Strategies A-Buffer: approximate prefiltering of continuous signal by sampling Pros: Integrating with scan-line renderer keeps storage costs low Can be efficiently implemented with clever bitwise operations Cons: Still basically a supersampling approach Doesn’t integrate with ray-tracing
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David Luebke 5 Stochastic Sampling Sampling theory tells us that with a regular sampling grid, frequencies higher than the Nyquist limit will alias Q: What about irregular sampling? A: High frequencies appear as noise, not aliases This turns out to bother our visual system less!
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David Luebke 6 Stochastic Sampling An intuitive argument: In stochastic sampling, every region of the image has a finite probability of being sampled Thus small features that fall between uniform sample points tend to be detected by non-uniform samples
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David Luebke 7 Stochastic Sampling Integrating with different renderers: Ray tracing: It is just as easy to fire a ray one direction as another Z-buffer: hard, but possible Notable example: REYES system ( ? ) Using image jittering is easier (more later) A-buffer: nope Totally built around square pixel filter and primitive-to- sample coherence
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lecture07 - CS 551/651: Advanced Computer Graphics...

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