This paper discusses a transform for successive pictures of an image sequence which strictly maintains orthogonality
while permitting 2-hypothesis motion compensation between pairs of pictures. We extend previous work
on an orthogonal transform for image sequences which uses only 1-hypothesis motion compensation between pairs
of pictures. This work is motivated by the well known fact that the motion-compensated lifted Haar wavelet
maintains orthogonality only approximately. In the case of zero motion fields, the motion-compensated lifted
Haar wavelet is known to be orthogonal. But for complex motion fields with many multi-connected and unconnected
pixels, the motion-compensated lifted Haar wavelet cannot accurately maintain its transform property
and, hence, suffers a performance degradation. The presented double motion-compensated orthogonal transform
strictly maintains orthogonality for any motion field. For the transform, each pixel in the high-band is compensated
by a linear combination of two motion-compensated pixels chosen from the corresponding low-band.
That is, each pixel in the high-band is associated with two motion vectors. This is in contrast to the previously
presented single motion-compensated orthogonal transform where each pixel in the high-band is compensated by
only one motion-compensated pixel chosen from the corresponding low-band. In terms of energy concentration,
the double motion-compensated orthogonal transform outperforms the single motion-compensated orthogonal
transform and compares favorably with the double motion-compensated lifted Haar wavelet.
Motion-compensated temporal filtering is an open-loop coding technique, which generally employs a motion-compensated
update step. Although the update step is essential at the encoder for good rate-distortion 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 post-processing procedure after conventional
decoding without the update step. Experimental results show that the degradation in quality is reduced by half.
For our t+2D wavelet coder, this gives a gain of approximately 1.0 - 1.5 dB at high bit-rates.
This paper investigates video coding with wavelet transforms applied in the temporal direction of a video sequence. The wavelets are implemented with the lifting scheme in order to permit motion compensation between successive pictures. We improve motion compensation in the lifting steps and utilize complementary motion-compensated signals. Similar to superimposed predictive coding with complementary signals, this approach improves compression efficiency. We investigate experimentally and theoretically complementary motion-compensated signals for lifted wavelet transforms. Experimental results with the complementary motion-compensated Haar wavelet and frame-adaptive motion compensation show improvements in coding efficiency of up to 3 dB. The theoretical results demonstrate that the lifted Haar wavelet scheme with complementary motion-compensated signals is able to approach the bound for bit-rate savings of 2 bits per sample and motion-accuracy step when compared to optimum intra-frame coding of the input pictures.
Multi-hypothesis prediction extends motion compensation with one prediction signal to the linear superposition of several motion-compensated prediction signals. These motion- compensated prediction signals are referenced by motion vectors and picture reference parameters. This paper proposes a state-of-the-art video codec based on the ITU-T Recommendation H.263 that incorporates multi-hypothesis motion-compensated prediction. In contrast to B-Frames, reference pictures are always previously decoded pictures. It is demonstrated that two hypotheses are efficient for practical video compression algorithms. In addition, it is shown that multi-hypothesis motion-compensated prediction and variable block size prediction can be combined to improve the overall coding gain. The encoder utilizes rate- constrained coder control including rate-constrained multi- hypothesis motion estimation. The advanced 4-hypothesis codec improves coding efficiency up to 1.8 dB when compared to the advanced prediction codec with ten reference frames for the set of investigated test sequences.
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