How Encoders Work - A Practical Guide to Video and Audio Compression - page 189

a realistic possibility. Handheld digital TV receivers are also facilitated by improved com-
pression ratios.

9.4 Preprocessing Operations

Before running the encoding process, reducing the data size is beneficial. These tasks are
called preprocessing because they are handled before the encoding stage of the compres-
sion. This accounts for the greater part of your time when compressing video. Although
this is not strictly a compression process, the preprocessing is often dealt with by the
workflow framework or application that the encoder runs in.
Sorensen Squeeze, Popwire Compression Master, and Discreet Cleaner all provide
these facilities. Most other tools do as well.
You may apply these preprocessing operations in any order you like if you use dif-
ferent tools to work on the video. For example, After Effects is useful for tracking and sta-
bilizing the video, and you can scale and crop it at the same time. Then you can import the
processed footage into Squeeze for compression. There is an opportunity to introduce
other processing outside of those two applications, too. For example, if you have some
custom-built scratch removal software, it could be used prior to loading of the images into
After Effects, and you have a chance to trim the in and out points (known as topping and
tailing) before loading the video into Squeeze.
You do need to make sure that these preprocessing steps don't introduce any
unwanted format conversion along the way, as that may degrade the quality of the output
if it introduces visible artifacts.
We will discuss all of these techniques later in Chapters 31 to 38. Here is a brief sum-
mary of some preprocessing steps that help improve the quality of the output.

Deinterlacing

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Frame rate adjustment

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Denoising (noise filtering)

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Sharpening

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Grain removal

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Color correction

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Cropping

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Scaling

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Aspect ratio correction

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Anamorphic squash

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9.5 Frame Types

Both TV and filmed content consist of a series of still images called frames. TV reorganizes
each image into a more complex structure and represents it as a series of synchronized
scan lines. TV in its purest form is manipulated electronically in the analog domain. Film
is just an image on a celluloid (or other) substrate and is manipulated using a combination