imagemotion-2

# imagemotion-2 - Image Motion The Information from Image...

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Image Motion

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The Information from Image Motion 3D motion between observer and scene + structure of the scene Wallach O’Connell (1953): Kinetic depth effect http://www.biols.susx.ac.uk/home/George_Mather/Motion/KDE .HTML Motion parallax : two static points close by in the image with different image motion; the larger translational motion corresponds to the point closer by (smaller depth) Recognition Johansson (1975): Light bulbs on joints http://www.biols.susx.ac.uk/home/George_Mather/Motion/index .html
Examples of Motion Fields I (a) Motion field of a pilot looking straight ahead while approaching a fixed point on a landing strip. (b) Pilot is looking to the right in level flight. (a) (b)

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Examples of Motion Fields II (a) (b) (c) (d) (a) Translation perpendicular to a surface. (b) Rotation about axis perpendicular to image plane. (c) Translation parallel to a surface at a constant distance. (d) Translation parallel to an obstacle in front of a more distant background.
Optical flow

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Assuming that illumination does not change: Image changes are due to the RELATIVE MOTION between the scene and the camera. There are 3 possibilities: Camera still, moving scene Moving camera, still scene Moving camera, moving scene
Motion Analysis Problems Correspondence Problem Track corresponding elements across frames Reconstruction Problem Given a number of corresponding elements, and camera parameters, what can we say about the 3D motion and structure of the observed scene? Segmentation Problem What are the regions of the image plane which correspond to different moving objects?

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Motion Field (MF) The MF assigns a velocity vector to each pixel in the image. These velocities are INDUCED by the RELATIVE MOTION btw the camera and the 3D scene The MF can be thought as the projection of the 3D velocities on the image plane.
Motion Field and Optical Flow Field Motion field: projection of 3D motion vectors on image plane Optical flow field: apparent motion of brightness patterns We equate motion field with optical flow field 0 0 0 0 1 0 0 0 0 ˆ by to related image in induces , velocity has point Object z r r r r r r v r v v v = = = f dt d dt d P i i i i

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2 Cases Where this Assumption Clearly is not Valid (a) (b) (a) A smooth sphere is rotating under constant illumination. Thus the optical flow field is zero, but the motion field is not. (b) A fixed sphere is illuminated by a moving source—the shading of the image changes. Thus the motion field is zero, but the optical flow field is not.
What is Meant by Apparent Motion of Brightness Pattern? The apparent motion of brightness patterns is an awkward concept. It is not easy to decide which point P' on a contour C' of constant brightness in the second image corresponds to a particular point P on the corresponding contour C in the first image.

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The aperture problem
Aperture Problem (a) Line feature observed through a small aperture at time t .

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## This note was uploaded on 01/12/2012 for the course CMSC 733 taught by Professor Staff during the Spring '08 term at Maryland.

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imagemotion-2 - Image Motion The Information from Image...

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