motion estimation and compensation for very low bitrate video coding

16 Chapter 1. Digital Video Coding at Very-Low BitRate
closer look at some of the underlying concepts of video compression.
The scheme of gure 1.1 introduces the classical chain of tools used to
compress moving pictures.
Input image(s)
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Source Coding Channel Coding
Tranform, analysis,...
Quantization
Transcription
Entropy Coding
Figure 1.1: Operators classically involved in a compression process of
(moving) images
Hereafter is a brief description of the aim of every step. The way the
process is reversed at the decompression stage is also tackled. More
detailed overview of compression techniques may be found in [86, 59,
113].
Compression
{ First, the image characteristics are analyzed: the analysis
may consist in frequential waveforms analysis, likewavelet [66],
matching pursuits [90], or more simply block transform (e.g.
the Discrete Cosine Transform, DCT [2], like in JPEG [135]),
or in spatial contours and texture analysis. It may also consist
in an estimation of the motion eld between two successive
frames. This analysis step aims at detecting the redundant
parts of the images and proposing another way of transmitting
the same information.
{ The resulting parameters are then usually quantized in order
to suppress all irrelevancies of the signal. Quantization can
be scalar or vector [41, 89].