Image Processing Reference
Figure 32-1 Presenter
against static background.
Minimizing the movement of the presenter and using a totally static, but still visually
interesting, background gives the encoder a very good chance of maintaining a low bit
rate. In Figure 32-1 the presenter is set against a static, draped curtain.
If you have facilities to chroma-key the background behind the presenter, then you
could set up a workflow that introduces moving or static backgrounds as required by the
output platform. This could be added to the workflow control in your content-management
system so that broadcast output takes advantage of the higher bit rates. Low-bandwidth
versions of the video can have still backgrounds so that they compress more efficiently.
Any rapid movement in the picture over a large area will introduce a peak into the bit-rate
coding requirements. A stationary scene with a truck driving across it will introduce some
movement that the compression system must deal with, but motion compensation should
cope with that. A slow pan will introduce movement as well, but the compression algo-
rithms have motion detection and compensation built in so as to take advantage of pixels
that may have moved from another position in the frame.
Choosing the Codec Before Shooting
Another important thing to decide before proceeding is which codec you will eventually
use for coding the video. This might determine some of the preprocessing steps and how
you set them up.