Lecture - Optical Flow

# Lecture - Optical Flow - ComputerVision Optical Flow Some...

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Computer Vision  Optical Flow Some slides from K. H. Shafique [http://www.cs.ucf.edu/courses/cap6411/cap5415/] and T. Darrell

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Bahadir K. Gunturk EE 7730 - Image Analysis II 2 Correspondence Which pixel went where? Time: t Time: t + dt
Bahadir K. Gunturk EE 7730 - Image Analysis II 3 Motion Field vs. Optical Flow Scene flow: 3D velocities of scene points. Motion field: 2D projection of scene flow. Optical flow: Approximation of motion field derived from apparent motion of brightness patterns in image.

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Bahadir K. Gunturk EE 7730 - Image Analysis II 4 Motion Field vs. Optical Flow Consider perfectly uniform sphere rotating in front of camera. Motion field follows surface points. Optical flow is zero since motion is not visible. Now consider stationary sphere with moving light source. Motion field is zero. But optical flow results from changing shading. But, in general, optical flow is a reliable indicator of motion field.
Bahadir K. Gunturk EE 7730 - Image Analysis II 5 Applications Object tracking Video compression Structure from motion Segmentation Correct for camera jitter (stabilization) Combining overlapping images (panoramic image construction)

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Bahadir K. Gunturk EE 7730 - Image Analysis II 6 Optical Flow Problem How to estimate pixel motion from one image to another? H I
Bahadir K. Gunturk EE 7730 - Image Analysis II 7 Computing Optical Flow Assumption 1: Brightness is constant. Assumption 2: Motion is small. ( , ) ( , ) H x y I x u y v = + + (from Taylor series expansion)

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Bahadir K. Gunturk EE 7730 - Image Analysis II 8 Computing Optical Flow Combine t I 0 t x y I I u I v = + + In the limit as u and v goes to zero, the equation becomes exact (optical flow equation)
Bahadir K. Gunturk EE 7730 - Image Analysis II 9 Computing Optical Flow At each pixel, we have one equation, two unknowns.

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## This note was uploaded on 11/28/2011 for the course EE 4780 taught by Professor Staff during the Spring '08 term at LSU.

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Lecture - Optical Flow - ComputerVision Optical Flow Some...

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