On the Hierarchical Variable Block

The motion compensated coding(MCC), which exploits the temporal redundancies in the moving images, is one of the most popular techniques currently used. Recently, a variable block size(VBS) motion estimation technique has been proposed to improve the performance of the motion compensated transform coding(MCTC). This technique allows larger blocks to be used when smaller blocks provide little gain, saving the bit rates especially for areas containing more complex motion. However, there have been little eeorts in investigating an eecient VBS motion structure for reducing the motion vector coding rates further. Hence, in this paper, a new VBS motion estimation technique based on a hierarchical structure is proposed, which improves the motion vector encoding eeciency and reduce the number of motion vectors to be transmitted as well. Speciically, the gain/cost motion estimation technique with the 1 The authors are also aaliated with the selective motion prediction is utilized for the topmost level motion vector search, exploiting the redundancies among the neighboring motion vectors. Also, a restricted search with respect to the topmost level motion vector enables more exible and eecient motion vector encoding for the remaining lower level blocks. Intensive simulations on several moving image sequences show that the MCTC employing the VBS motion estimation provides a performance improvement of 0.7 1.0 dB, in terms of PSNR, compared to the xed block size motion estimation.