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Updated 16/11/2012Home » Video Glossary » Motion estimation

Motion estimation

Motion estimation is the process of determining motion vectors that describe the transformation from one image to another; usually from adjacent frames in a video sequence.

It is an ill-posed problem as the motion is in three dimensions but the images are a projection of the 3D scene onto a 2D plane. The motion vectors may relate to the whole image (global motion estimation) or specific parts, such as rectangular blocks, arbitrary shaped patches or even per pixel. The motion vectors may be represented by a translational model or many other models that can approximate the motion of a real video camera, such as rotation and translation in all three dimensions and zoom.

Applying the motion vectors to an image to synthesize the transformation to the next image is called motion compensation. The combination of motion estimation and motion compensation is a key part of video compression as used by MPEG-1, MPEG-2 and MPEG-4 as well as many other video codecs.