Image Processing Reference
In-Depth Information
Spatial Preprocessing
This stage of the preprocessing workflow is all about the content of the frame. Here we set
the overall dimensions of the frames and move the content around in them so that it com-
presses effectively.
We want to clean up any noise around the edges and frame the interesting part of the
video so that we don't compress any more area than we have to. Scaling and cropping to
clean up the edges is very worthwhile.
There are some quality gains to be had if you can avoid stretching or shrinking the
image. Pixels can be interpolated or averaged when this scaling happens, and that leads
to loss of detail. A crop is always preferable to a scaling operation.
The same aliasing effects that we discussed in the audio sampling (see Chapter 7) can
exhibit themselves in video if you are shooting strongly patterned material. Scaling the
image when someone in the shot is wearing a checked shirt can lead to some very nasty-
looking artifacts.
Stabilizing Film and Telecine Content
If you are coding some old film footage that has been transferred via a telecine machine,
then it is worthwhile to make sure the film is clean before the telecine process takes place.
If you forget to do that, then later you might be able to apply some noise-reduction filters
to remove dust and scratches from the digitized film.
Unless your telecine system is of especially high quality and the footage was shot on
a stabilized camera platform with a good-quality camera, the subject matter will move
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