Contents
What is motion vector image?
motion vector: a two-dimensional vector used for inter prediction that provides an offset from the coordinates in the decoded picture to the coordinates in a reference picture.
How do you find the motion vector?
A “motion vector” is calculated by finding a correspondence between rectangles at time t, and rectangles at time t − 1, where t is the frame index in a video signal. Motion vectors were originally invented for video coding.
What is the purpose of motion vectors?
Motion vectors are typically used to compress video by storing the changes to an image from one frame to the next. We use these vectors creatively to detect and track motion and to find an alternative to traditional video decoding using phase shifting.
What is a closed vector diagram?
A closed vector diagram is a set of vectors drawn on the Cartesian using the tail-to-head method and that has a resultant with a magnitude of zero. This means that if the first vector starts at the origin the last vector drawn must end at the origin.
How is image motion a function of 3D motion?
Image motion is a function of both the 3D motion (V) and the depth of the 3D point (Z)! Quotient rule: D(f/g) = (g f’ – g’f)/g^2 Slide adapted from K. Grauman.! 9 Motion field and parallax • Pure translation: Vis constant everywhere Z f V V x vx z x Z f V V y vy z y ( ), 1 v v 0V z p Z v 0=(f V x,f V y) Slide adapted from K. Grauman.! 10
How are motion vectors related to the vis constant?
• Pure translation: Vis constant everywhere • V zis nonzero: – Every motion vector points toward (or away from) v 0, the vanishing point of the translation direction • V zis zero: – Motion is parallel to the image plane, all the motion vectors are parallel • The length of the motion vectors is inversely proportional to the depth Z
What is the definition of optical flow vector?
• Optical Flow Field = Projection of the motion field onto the 2d image! 3D motion vector 2D optical flow vector u =(u,v)
How to calculate the velocity of a motion field?
Motion field and parallax • P(t) is a moving 3D point • Velocity of scene point: V= dP/dt • p(t) = (x(t),y(t)) is the projection of Pin the image • Apparent velocity v in the image: given by components