Announcements

		Today:  evals
		Monday:  project presentations (8 min talks)

Photometric Stereo

	Readings
		R. Woodham, Photometric Method for Determining Surface Orientation from Multiple Images. Optical Engineering 19(1)139-144 (1980). (PDF)

Diffuse reflection

Shape from shading

	Suppose

Photometric stereo

Solving the equations

More than three lights

	Get better results by using more lights

Computing light source directions

	Trick:  place a chrome sphere in the scene
		the location of the highlight tells you where the light source is

Recall the rule for specular reflection

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)

Project 3

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