Image Processing Reference
sequence. You will no doubt have a limited bit rate budget and the complexity of the con-
tent may require more data than you can afford to send. So you will have to trade off some
complexity to reduce the bandwidth requirements. Degrading the picture quality is one
option, or you can reduce the frame rate. The opportunities to improve your encoded
video quality begin when you plan what to shoot.
In Chapters 32 to 38, you will have a chance to practice using the encoding system we just
built. We will discuss all those complex little details such as scaling and cropping, frame
rate reduction, and the effects of video noise on the encoding process. Don't worry that
there are a lot of factors to consider. If we are systematic in the way we experiment with
them, we will not get into too much trouble.
Planning Future Trips
Chapter 39 draws some conclusions and looks at where you might go next. It also looks at
what the future of video compression systems might be as the world adopts and adapts to
a wholly digital video scenario. The appendices follow the final chapter, and they contain
some useful reference material. The scope of the topic allows for only a limited amount of
this kind of reference material, but it should be sufficient to enable you to search for more
information on the World Wide Web. Of particular note is the problem solver in Appendix
A. It is designed to help you diagnose quality issues with your encoded video.
Likewise, due to space constraints, we do not delve into the more esoteric aspects of
audio and video. Many interesting technologies for surround sound and video production
can only be mentioned here, so that we can remain focused on the compression process.
You should spend some time looking for manufacturers' Web sites and downloading tech-
nical documents from them. There is no substitute for the time you spend researching and
learning more about this technology on your own.
Film size is always specified in metric values measured in millimeters (mm). Sometimes
scanning is described as dots per inch or lines per inch. TV screen sizes are always
described in inches measured diagonally. Most of the time, this won't matter to us, since we
are describing digital imagery measured in pixels. The imaging area of film is measured in
mm, and therefore a film-scanning resolution in dots per mm seems a sensible compromise.
TV pictures generally scan with interlaced lines, and computers use a progressive
scanning layout. The difference between them is the delivery order of the lines in the pic-
ture. Frame rates are also different.
The convention for describing a scanning format is to indicate the number of physi-
cal lines, the scanning model, and the field rate. For interlaced displays, the field rate is