lecture08 - CS 551/651: Advanced Computer Graphics Advanced...

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David Luebke 1 CS 551/651: Advanced Computer Graphics Advanced Ray Tracing Radiosity
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David Luebke 2 Administrivia My penance: Ray tracing homeworks very slow to grade Many people didn’t include READMEs Many (most) people didn’t include workspace/project files or Makefiles Some people’s don’t work Nobody’s works perfectly Quiz 1: Tuesday, Feb 20
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David Luebke 3 Recap: 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 4 Recap: Stochastic Sampling Poisson distribution: Completely random Add points at random until area is full. Uniform distribution: some neighboring samples close together, some distant
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David Luebke 5 Recap: Stochastic Sampling Poisson disc distribution: Poisson distribution, with minimum-distance constraint between samples Add points at random, removing again if they are too close to any previous points Jittered distribution Start with regular grid of samples Perturb each sample slightly in a random direction More “clumpy” or granular in appearance
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David Luebke 6 Recap: Stochastic Sampling Spectral characteristics of these distributions: Poisson: completely uniform ( white noise ). High and low frequencies equally present Poisson disc: Pulse at origin (DC component of image), surrounded by empty ring (no low frequencies), surrounded by white noise Jitter: Approximates Poisson disc spectrum, but with a smaller empty disc .
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David Luebke 7 Recap: Nonuniform Supersampling To be correct, need to modify filtering step:
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David Luebke 8 Recap: Nonuniform Supersampling Approximate answer: weighted average filter Correct answer: multistage filtering Real-world answer: ignore the problem Σ Σ I ( i , j ) h ( x - i , y-j ) Σ Σ h ( x - i , y-j ) I’ ( x,y ) =
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David Luebke 9 Recap: Antialiasing and Texture Mapping Texture mapping is uniquely harder Potential for infinite frequencies Texture mapping is uniquely easier Textures can be prefiltered
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David Luebke 10 Recap: Antialiasing and Texture Mapping Issue in prefiltering texture is how much texture a pixel filter covers Simplest prefiltering scheme: MIP-mapping Idea: approximate filter size, ignore filter shape Create a pyramid of texture maps Each level doubles filter size
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lecture08 - CS 551/651: Advanced Computer Graphics Advanced...

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