Notes
Slide Show
Outline
1
Announcements
    • Today:  evals
    • Monday:  project presentations (8 min talks)
2
Photometric Stereo
  • Readings
    • R. Woodham, Photometric Method for Determining Surface Orientation from Multiple Images. Optical Engineering 19(1)139-144 (1980). (PDF)
3
Diffuse reflection
4
Shape from shading
  • Suppose
5
Photometric stereo
6
Solving the equations
7
More than three lights
  • Get better results by using more lights
8
Computing light source directions
  • Trick:  place a chrome sphere in the scene







    • the location of the highlight tells you where the light source is
9
Recall the rule for specular reflection
10
Depth from normals
  • Get a similar equation for V2
    • Each normal gives us two linear constraints on z
    • compute z values by solving a matrix equation (project 3)
11
Project 3
12
Limitations
  • Big problems
    • doesn’t work for shiny things, semi-translucent things
    • shadows, inter-reflections
  • Smaller problems
    • camera and lights have to be distant
    • calibration requirements
      • measure light source directions, intensities
      • camera response function
  • Newer work addresses some of these issues
  • Some pointers for further reading:
    • Zickler, Belhumeur, and Kriegman, "Helmholtz Stereopsis: Exploiting Reciprocity for Surface Reconstruction." IJCV, Vol. 49 No. 2/3, pp 215-227.
    • Hertzmann & Seitz, “Example-Based Photometric Stereo: Shape Reconstruction with General, Varying BRDFs.” IEEE Trans. PAMI 2005