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Parallelized Monte Carlo Raytracing

Parallelized Monte Carlo Raytracing. Brian Anderson. Simple Raytracing. Shoot a single ray from the eye. Determine closest intersection point. Sum the intensity of lights visible from the point. Recursively shoot single reflection and refraction rays as necessary. Assumes:

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Parallelized Monte Carlo Raytracing

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  1. ParallelizedMonte Carlo Raytracing Brian Anderson

  2. Simple Raytracing • Shoot a single ray from the eye. • Determine closest intersection point. • Sum the intensity of lights visible from the point. • Recursively shoot single reflection and refraction rays as necessary. • Assumes: • Point Lights (either visible or not) • Perfect Reflections • Camera with infinitely small aperature

  3. Monte Carlo Raytracing • Shoot (many) random rays from the aperature. • Determine intersection point. • Sum visible and partially visible light sources. • Shoot (many) random rays to the area of each light. • For fuzzy reflections: • Emit reflection rays in(many) random directions. • Weight appropriately. • = LOTS and LOTS of rays!

  4. Parallelizing Monte Carlo • Have each proccess calculate a single area of the image? • Have each process calculate it’s own image and then average all of them? • Not completely straightforward…

  5. Convergence of Monte Carlo • Quality does not only depend on number of rays. • Key: Minimize variance  Decrease noise. • Using completely random rays: • Variance converges with √N. • We can do better by selectively choosing a good distribution of rays: • Importance Sampling • Stratisfied Sampling • Variance can converge with N.

  6. Parallelizing Monte Carlo • Useful for: • Fuzzy Reflections • Easily parallelized: • Probabalistic • No coordination needed • Useful for: • Depth of Field • Soft Shadows • Parallelize by: • Partitioning strata • 1 disc with 16 strata >4 discs with 4 strata • Importance Sampling: • Stratisfication:  X

  7. Results • If parallelized naiively, serial version could converge faster, negating added processing power. • Parallelized code does not yet work. • Using methods indicated, suspect N times speedup for identical quality.

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