Video encoding with multi-stage projection motion estimation

Abstract

A method and apparatus for performing multi-stage motion estimation on an input video sequence to be encoded. An original image in the video sequence, such as a CCIR601 image, is preprocessed to generate first, second and third reduced resolution images which may be a QQSIF image, a QSIF image and a SIF image, respectively, which are 1/64 size, 1/16 size and 1/4 size, respectively, relative to the original CCIR601 image. A first stage motion vector search is performed on the 1/64 size QQSIF image using a (0,0) motion vector starting point and a first search range suitable for detecting global motion. A second stage motion vector search is performed on the 1/16 size QSIF image using the (0,0) starting point and a second search range smaller than the first search range and suitable for detecting local motion. A third stage motion vector search is performed on the 1/4 size SIF image using starting points based on scaled versions of the motion vectors identified in the first and second stage searches, and a search range smaller than the first and second search ranges. A fourth stage search is then performed on the original image using the motion vectors identified in the third search stage, and a motion compensation type for the original image is determined based on the results of the fourth stage search. An early field/frame decision may be made prior to the performing the fourth stage search, and may be based on a comparison of motion vectors from the first and second stage searches.