motion estimation and compensation for very low bitrate video coding

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