lec8 - Last lecture in a nutshell Photometric Stereo BRDF...

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1 CS252A, Fall 2010 Computer Vision I Photometric Stereo Computer Vision I CSE252A Lecture 8 CS252A, Fall 2010 Computer Vision I Last lecture in a nutshell • BRDF • Light Sources – Point source – Point at infinity – Line & area sources – Spherical harmonics • Shadows • Inter-reflections –CSE 252A Phong Lobe –CSE 252A • For uniform BRDF, capture 2-D slice corresponding to variations in normals Point sources Distant point sources (point source at infinity) Line source Area source Spherical Harmonics (diffuse, distant lighting) Light field (function on 4-D space) CSE 252A, Fall 2009 –CSE 252A m =-1 m =-2 m =0 m =1 m =2 l =0 l =1 l =2 . . . (Borrowed from: Ramamoorthi, Hanrahan, SIGGRAPH’01) Green: Positive Blue: Negative Order
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2 A point that can’t see the source is in shadow For point sources, the geometry is simple Cast Shadow Attached Shadow –CSE 252A Local shading model Surface has incident radiance due only to sources visible at each point Advantages: – often easy to manipulate, expressions easy – supports quite simple theories of how shape information can be extracted from shading Used in vision & real time graphics Global shading model surface radiosity is due to radiance reflected from other surfaces as well as from surfaces Advantages: – usually very accurate Disadvantage: – extremely difficult to infer anything from shading values Rarely used in vision, often in photorealistic graphics –CSE 252A Figure from “Mutual Illumination,” by D.A. Forsyth and A.P. Zisserman, Proc. CVPR, 1989, copyright 1989 IEEE At the top, geometry of a gutter with triangular cross-section; below, predicted radiosity solutions, scaled to lie on top of each other, for different albedos of the geometry. When albedo is close to zero, shading follows a local model; when it is close to one, there are substantial re±exes. CS252A, Fall 2010
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lec8 - Last lecture in a nutshell Photometric Stereo BRDF...

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