Image Processing Reference
In-Depth Information
3
What Are We Trying to Compress?
3.1
Where Do You Want to Go Today?
That was a very good advertising line dreamed up by Microsoft. It is full of adventure and
potential excitement and is based on you, the consumer, making a choice. So now we have
to make a choice about what kind of moving-image content we are going to compress. Will
it be film, video, or computer-generated digital imagery? They are all different. Let's find
out why in the next few chapters.
3.2
What Is a Moving Image?
Think about moving pictures. How are they captured? They are two-dimensional record-
ings of an array of pixels at an instant in time. Film and TV cameras both capture motion,
but the resulting images have very little in common when they are examined from a tech-
nical standpoint.
3.3
What Sort of Compression Do You Need?
There are two basic kinds of compression. The first is utterly lossless, while the other sac-
rifices some fidelity in order to improve the compression ratio. Lossless compression is a
format-conversion process that compresses the physical manifestation of the video. Lossy
compression actually compresses the informational content of the video. This is a subtle
and very important distinction. Lossy compression ranges from high quality with unde-
tectable artifacts down to massively degraded viewing experiences. The developers of
video-compression technology continually strive to improve the ratio of quality to bit rate
or compression.
3.4
What Sort of User Are You?
Video compression is of interest to a variety of users. Professionals see it as a full-time
occupation and may have significant funding to support building large and complex
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