# L12(shading2) - Shape from shading Surface brightness and...

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1 May 2006 SFS 1 Shape from shading Surface brightness and Surface Orientation --> Reflectance map READING: Nalwa Chapter 5 (pick up the handout from my office) May 2006 SFS 2 Shading produces a compelling perception of 3-D shape. One way the brain simplifies the task of interpreting shading is by assuming a single light source.

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2 May 2006 SFS 3 Shading as a cue to surface shape May 2006 SFS 4 Boundaries influence the interpretation of shaded surfaces
3 May 2006 SFS 5 ..and perceptual grouping of elementary features helps to segregate the Dalmatian. May 2006 SFS 6 Gradient Space • Orientation of a vector in 3-D space has two degrees of freedom. • Suppose we are interested in representing all vectors in a particular hemisphere, say z < 0 hemisphere: – We can then represent any such vector with a negative z component as (p, q). See next slide.

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4 May 2006 SFS 7 Gradient space May 2006 SFS 8 Gradient Space Let the imaged surface be Then its surface normal can be obtained as a cross product of the two surface vectors: Surface normal:
5 May 2006 SFS 9 Reflectance Map Reflectance map captures the dependence of brightness on surface orientation. At a particular point in the image, we measure the image irradiance E(x,y). This irradiance is proportional to the radiance at the corresponding point on

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L12(shading2) - Shape from shading Surface brightness and...

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