motion estimation and compensation for very low bitrate video coding
motion estimation and compensation for very low bitrate video coding
motion estimation and compensation for very low bitrate video coding
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Chapter 2<br />
Motion in the Framework<br />
of Video Coding<br />
The extraction of <strong>motion</strong> in<strong>for</strong>mation from a sequence of time-varying<br />
images has numerous applications in the eld of image processing: medical<br />
image analysis, mobile robot navigation, automatic tracking of moving<br />
objects, interpretation of atmosphere observation (remote sensing),<br />
image interpolation <strong>and</strong> restoration,... as well as digital <strong>video</strong> compression.<br />
As seen in the introduction to (VLBR) <strong>video</strong> <strong>coding</strong> (cf. Chapter<br />
1), <strong>motion</strong> <strong>estimation</strong> & <strong>compensation</strong> plays a key role in <strong>video</strong><br />
compression as it results in the most per<strong>for</strong>ming compression gains.<br />
This chapter does not claim to propose a complete overview of all existing<br />
<strong>motion</strong> <strong>estimation</strong> techniques in the <strong>video</strong> <strong>coding</strong> context. This<br />
task has already been successfully achieved with numerous results <strong>and</strong><br />
comments in specialized books like [127] or articles like [108, 31], in<br />
which extensive references are given. Yet, it seems important to review<br />
the most classical techniques in order to present the state of the art <strong>and</strong><br />
to highlight the contribution put <strong>for</strong>ward by the present work.<br />
Another aim is to emphasize the distinction between the <strong>estimation</strong> <strong>and</strong><br />
the <strong>compensation</strong> stages of a codec. Figure 2.1 brie y reminds one<br />
that <strong>estimation</strong> is per<strong>for</strong>med at the encoder side in order to extract the<br />
<strong>motion</strong> parameters of the <strong>video</strong> sequence, while the decoder uses the<br />
estimated <strong>motion</strong> in<strong>for</strong>mation during the <strong>compensation</strong> phase. A parallel<br />
can be established between the general principles of <strong>video</strong> compression<br />
(cf. Section 1.2) <strong>and</strong> <strong>motion</strong> <strong>estimation</strong> & <strong>compensation</strong> processes,<br />
which are based on three main steps: