Motion estimation using limited-time early exit with prequalification

Abstract

Motion estimation using limited-time early exit with prequalification matrices and a predicted search center reduces computational time for a video compression encoder. The partial absolute error obtained for a given location within a search area is compared periodically with a prior absolute error obtained for a prior position within the search area to determine whether the partial absolute error is greater than such prior absolute error. If the partial absolute error is greater, then the processing for that position may be terminated and the search moved to the next location within the search area. Using the triangle inequality a series of prequalification matrices are generated for the reference image and for the current image being searched. Comparing the prequalification matrices using early exit further reduces the computational time. Also by using a motion vector for a neighboring block of pixels to determine a predicted center point within the search area, one of the first few locations within the search area generally produces the best difference, so that all subsequent locations result in early exit, reducing computational time even further. Finally to assure that the motion vectors for a frame are determined within realtime constraints, the amount of time required to process a block as measured in terms of a number of AbsSum8 operations is used to terminate the processing of a block if the processing has not yet produced a final absolute error minimum. For those blocks which complete early, the saved 'time' is averaged over the remaining blocks.