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Lighting models & optimization

Lighting models & optimization. Pavel Zemčík Department of Computer Science and Engineering, Faculty of Electrical Engineering and Computer Science, Technical Univeristy of Brno, Czech Republic zemcik@dcse.fee.vutbr.cz. What are lighting models?.

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Lighting models & optimization

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  1. Lighting models& optimization Pavel Zemčík Department of Computer Science and Engineering, Faculty of Electrical Engineering and Computer Science, Technical Univeristy of Brno, Czech Republic zemcik@dcse.fee.vutbr.cz

  2. What are lighting models? • Lighting models are models of light behaviour on the objects’ surface • Global models • Local models • Behaviour at the edges

  3. Global models • Generally used in radiation methods • Physics laws (preservs model’s energy) • Simple light propagation (form factors)

  4. Local models • Approximate light propagation locally • Not necessarily physics based • Measurement based (empirical) • Often just a ‘good looking’ guess

  5. Local models geometry

  6. Phong model geometry

  7. Phong model equations • General • Details (note that Ib is constant)

  8. Phong model parameters-n • The image showsthe effect of nn= 15 7 3 1

  9. Phong model parameters-kd,kr • The image showsthe effect of kd,krkd,kr = 0.3,0.6 0.5,0.4 0.7,0.2 0.9,0

  10. Surface texture • The image wasrendered usingPhong model withsuperimposedtexture modifyingthe coefficients

  11. Normal vector texture • The image wasrendered usingPhong model withsuperimposedtexture modifyingthe normal vector

  12. Mirror model geometry

  13. Mirror model equations • General • Details (reflection direction)

  14. Mirror model example

  15. Glass model geometry

  16. Glass model energy

  17. Glass model equations • Direction • Energy distribution approximation

  18. Glass model example

  19. Other lighting models • Torrance-Sparrow (rough surfaces) • Blinn, Strauss (half-transparent objects) • Metals (fluorescent effects) • etc.

  20. Optimisation of ray tracing

  21. Optimisation of ray tracing Three general approaches • Reduction of number of evaluated pixels • Bounding volumes • Space subdivision

  22. Reduction of number of pixels Mostly using adaptive subsampling • naive would be • 40x30 • optimised 5x5 • 16x12+10x21 • 402/1200-66%

  23. Bounding volumes Bounding volume must bound all the real objects but be as small as possible • complex • done manually • speedup >10

  24. Space subdivision Scene is divided into several smaller units that are evaluated separately • simple principle • automatic butquite high cost • speedup >10

  25. CSG tree pruning

  26. CSG status tree

  27. Referenecs (in addition to the previous lecture) • Bronsvoort W F: Techniques for Reducing Boolean Evaluation Time in CSG scan-line algorithms, Computer-aided Design, vol. 18, no. 10, 1986, Great Britain, pp. 533-536 • Fujimoto A, Tanaka T, Iwata K: ARTS Accelerated Ray Tracing System, IEEE Computer Graphics & Applications, April 1986, USA, pp. 16-26 • Glassner A S: Efficient Boolean Evaluation of CSG Models for Ray Tracing, The Ray Tracing News, vol. 1, no. 1, September 1987, USA, pp. 3-7 • Strauss P S: A Realistic Model for Computer Animators, IEEE Computer Graphics & Applications, November 1990, USA, pp. 56-64

  28. The end

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