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Stereo March 8, 2007 Suggested Reading: Horn Chapter 13
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Stereo Vision Stereo vision: ability to infer information on the 3-D structure and distance of a scene from two (or more images) taken from different view points. Two main problems: 1.Find Correspondences 2.Reconstruction (geometry)
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Simple Stereo System Coordinates origin at the midpoint of the two camera centers.
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Simple Stereo System
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Disparity
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Stereo Imaging
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Range vs. Disparity
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Stereo Calibaration
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More Practical Stereo Model
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Epipolar Geometry p OLOL OROR Epipoles Epipolar line O R =O L +T P r = R(P l -T) P r : P in the right camera’s frame P l : P in the left camera’s frame
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Essential Matrix An important problem: Determine the epipolar geometry. That is, the correspondence between a point on one camera and its epipolar line on the other camera. The rigid transformation not important p OLOL OROR Epipoles Epipolar line T
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Essential Matrix S has rank two. Dividing by Z r, Z l, Essential matrix E is the mapping between points and epipolar lines!
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Fundamental Matrix Essential matrix uses camera frames. We need matrix that works directly with pixel frames. F: rank 2 and has eight degree of freedom.
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Eight Point Algorithm To determine F, we need eight corresponding pairs. Each pair of corresponding points give a linear equation (with variable the entries of F).
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Eight Point Algorithm Let A be the resulting linear system. Find F as the unit vector that minimizes | A F |. 1.SVD of A = USV. F will be the last row of V (if the diagonal entries of S is in descending order). 2.Recall that F has rank two. SVD of F = USV. Let F = US’V where S’ is obtained from S by replacing the smallest singular value of F with 0.
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Locating Epipole p OLOL OROR Epipoles Epipolar line T Where is the epipole? Epipole is the null vector of F F has rank two. This means that it has one dimensional null space.
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