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# lecture18 - Motion Estimation Why estimate motion Lots of...

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1 Motion Estimation Why estimate motion? Lots of uses Motion Detection Track object behavior Correct for camera jitter (stabilization) Align images (mosaics) 3D shape reconstruction Video Compression

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2 Optical flow Measurement of motion at every pixel Optical flow An image from Hamburg Taxi Sequence
3 Video Mosaics Video Mosaics

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4 Video Mosaics Video Compression
5 Geo Registration Video Segmentation

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6 Structure From Motion Optical flow Measurement of motion at every pixel
7 Problem definition: optical flow How to estimate pixel motion from image H to image I? Solve pixel correspondence problem given a pixel in H, look for nearby pixels of the same color in I Key assumptions color constancy: a point in H looks the same in I For grayscale images, this is brightness constancy small motion : points do not move very far This is called the optical flow problem Optical flow constraints (grayscale images) Let’s look at these constraints more closely brightness constancy: Q: what’s the equation? small motion: (u and v are less than 1 pixel) suppose we take the Taylor series expansion of I:

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8 Optical flow equation Combining these two equations In the limit as u and v go to zero, this becomes exact Optical flow equation Q: how many unknowns and equations per pixel?
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lecture18 - Motion Estimation Why estimate motion Lots of...

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