1. Multi-resolution Real-time Stereo on Commodity Graphics Hardware 第 12 組 組員：吳冠璋 家庭自動化實驗室 Author: Ruigang Yang and Marc Pollefeys Publication: IEEE Computer Society Conference on Computer Vision and Pattern Recognition, 2003

2. Introduction Real-time stereo vision  2 parallel camera Optimized algorithm with hardware acceleration  Correlation-based stereo algorithms  Assembly-level optimization  MMX  Multi-processor PC  Graphic Processing Unit

3. Method SSD  (I’ x,y – I x,y ) 2  I’ x,y and I x,y denote pixels in two images For parallel camera, no more image processing is need.

4. SSD on GPU  The same as standard SSD, but window size is limited  n = support size (2 a * 2 b )  a, b = any GPU supported size  x, y = center coordinate of texture  p, q = pixel on texture

5. SSD on GPU For SSD  Large windows the curves mostly only have a single strong minimum  Small windows the minima are typically well localized Combine the global characteristics of the large windows with the well-localized minima of the small windows  Sum up multi-level mipmap SSD

6. Computer Graphic Basic Mipmap Multi-texture Pixel Shader

7. Mipmap (1/2) A set of texture that  Pre-generated  Multiple resolution  Linear interpolated Mipmap generation  i = Mipmap level  u, v = Texture coordinate  p, q = support size (2 n * 2 n )

8. Mipmap (2/2) Paper said that mipmap generation is fast on GPU, with some ext. supported With mipmap Without mipmap gluBuild2DMipmaps(…) /* Get generated map size at level n */ glGetTexLevelParameteriv(…) malloc(…) /* Copy texture from graphic memory to system memory */ glGetTexImage(…) /* Select a texture stage */ glActiveTextureARB(…) glEnable(GL_TEXTURE_2D) glBindTexture(…) /* Copy texture from system memory to graphic memory */ glTexImage2D(…)

9. Multi-texture Apply two or more distinct textures to a single fragment

10. Pixel Shader Replace standard multi-texture processing order  Programmable  ARB_multitexture  GL Shading Language  OpenGL 2.0 Vertex Shader Pixel Shader Object spaceWindow spaceFramebuffer IN OUT Textures

11. Multi-mipmap SSD Compute SSD and sum them up on GPU  GPU SSD, pixel-by-pixel  Special scoring and the selection method [1]  SSD score is computed on CPU, pixel-by-pixel (My impl.)

12. My Result (100 steps) CPU: T2500 (1 core) GPU: Intel 940gm graphic  4 sec : 0.25 fps CPU: Althon X2 4200+ GPU: GeForce 6150  1 sec : 1 fps

13. Result in Paper 4 MML 0 MML + texture shift

14. Reference [1] R. Yang, G. Welch, and G. Bisop. Real-Time Consensus-Based Scene Reconstruction Using Commodity Graphics Hardware. In Proceedings of Pacific Graphics 2002, pages 225– 234, Beijing, China, October 2002.

15. End of Slides Thank you