Image Processing Reference
In-Depth Information
Figure 2-2 Run-length encoding.
Temporal Compression
Video presentation is concerned with time and the presentation of the images at regular
intervals. The time axis gives us extra opportunities to save space by looking for redun-
dancy across multiple images.
This kind of compression is always lossy. It is founded on the concept of looking for
differences between successive images and describing those differences, without having to
repeat the description of any part of the image that is unchanged.
Spatial compression is used to define a starting point or key frame. After that, only
the differences are described. Reasonably good quality is achieved at a data rate of one
tenth of the original data size of the original uncompressed format.
Research efforts are underway to investigate ever more complex ways to encode the
video without requiring the decoder to work much harder. The innovation in encoders
leads to significantly improved compression factors during the player deployment life-
time without needing to replace the player.
A shortcut to temporal compression is to lose some frames, however it is not recom-
mended. In any case, it is not a suitable option for TV transmission that must maintain the
frame rate.
Why Do I Need Video Compression?
Service providers and content owners are constantly looking for new avenues of profit
from the material they own the rights to. For this reason, technology that provides a means
to facilitate the delivery of that content to new markets is very attractive to them. Content
owners require an efficient way to deliver content to their centralized repositories. Cheap
and effective ways to provide that content to end users are needed, too. Video compres-
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