A double motioncompensated orthogonal transform with energy concentration constraint This paper discusses a transform for successive pictures of an image sequence which strictly maintains orthogonality while permitting 2hypothesis motion compensation between pairs of pictures. We extend previous work on an orthogonal transform for image sequences which uses only 1hypothesis motion compensation between pairs of pictures. This work is motivated by the well known fact that the motioncompensated lifted Haar wavelet maintains orthogonality only approximately. In the case of zero motion fields, the motioncompensated lifted Haar wavelet is known to be orthogonal. But for complex motion fields with many multiconnected and unconnected pixels, the motioncompensated lifted Haar wavelet cannot accurately maintain its transform property and, hence, suffers a performance degradation. The presented double motioncompensated orthogonal transform strictly maintains orthogonality for any motion field. For the transform, each pixel in the highband is compensated by a linear combination of two motioncompensated pixels chosen from the corresponding lowband. That is, each pixel in the highband is associated with two motion vectors. This is in contrast to the previously presented single motioncompensated orthogonal transform where each pixel in the highband is compensated by only one motioncompensated pixel chosen from the corresponding lowband. In terms of energy concentration, the double motioncompensated orthogonal transform outperforms the single motioncompensated orthogonal transform and compares favorably with the double motioncompensated lifted Haar wavelet.

Postprocessing for decoding without update step in motioncompensated lifted wavelet video coding Motioncompensated temporal filtering is an openloop coding technique, which generally employs a motioncompensated update step. Although the update step is essential at the encoder for good ratedistortion efficiency, it might be skipped at the decoder for benefits like lower complexity and lower playout delay. Previous investigations showed that skipping the update step at the decoder results in some quality degradation at high rates. In this paper we analyze how this degradation arises and also propose a simple method to reduce this degradation. The proposed solution can also be implemented as a postprocessing procedure after conventional decoding without the update step. Experimental results show that the degradation in quality is reduced by half. For our t2D wavelet coder, this gives a gain of xe2x88xbc1.0  1.5 dB at high bitrates.