Radiometry-Shading - 1 Image Processing : 4. 4. Radiometry...

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Unformatted text preview: 1 Image Processing : 4. 4. Radiometry and Radiometry and Shading Models Shading Models Aleix M. Martinez Radiometry By understanding how light travels from a source to a surfaces and how this creates a brightness pattern, we will be able to estimate additional data from an image. Our goal is to understand the principals and how these can be used. We will used them to build whats call shading models . Illumination ^ n ^ s a I(u,v) A 3D object illuminated with a light source. Intensity at image point (u,v) T . Reconstruction Since an image depends on its illumination, it should be possible to recover its 3D information. Images under different but known illumination. Convex Objects y 45o x y S5 S3 S2 S4 S1 45o 45o 60o Object x z Camera I 1 I 2 I 3 I 4 I 5 Hemisphere of Direction 2 Questions: how bright will a surfaces be? what is brightness? measuring light, interactions between light and surfaces. Core idea : think the light arriving at a surface around any point defines a hemisphere of directions. Simplest problems can be dealt with by reasoning about this hemisphere. Simulating the hemisphere Construct a 3D sphere to simulate a large number of illumination directions. Eliminate the shadows caused by the known illumination 3D reconstruction of the face. Generate a new view with a new illumination By analogy with angle (in radians), the solid angle subtended by a region at a point is the area projected on a unit sphere centered at that point. The solid angle subtended by a patch area dA is given by: . sin , cos 2 d d d r dA d Solid Angle Radiance The power (amount of energy per unit time) traveling at some point in a specified direction, per unit area perpendicular to the...
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Radiometry-Shading - 1 Image Processing : 4. 4. Radiometry...

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