Television is much more complicated than film. It involves several interlocking concepts that interact with one another. The way the picture is represented electronically and the techniques for color encoding influence how it is converted from an analog form into a digital form. This also has implications for how the compression works. The technicality of how video works is a book-length topic in itself.

The imaging mechanisms for film and TV are different. The technology requires that certain processing be done to deliver a satisfactory broadcast within the available bandwidth.

Television pictures are composed of a series of horizontal lines arranged in a sequence that scans down the entire screen from top to bottom. This is called a raster. The number of lines and how they are ordered in the scanning sequence depend on the kind of display being driven and where in the world the TV signal is being broadcast. European TV is closer to movie film projection than the American system because the display frame rates are similar, but it is still different.

If only it were possible to go back in time and reinvent some of these things. Just changing the frame rate of projected film or adjusting the way that pictures are displayed to use progressive scanning instead of interlacing on TV sets would make the world a much simpler place for video compressionists. The following factors are all relevant to understanding how TV works and by implication how compression has to work:

●  Picture sizes on different TV systems

●  Frame rates in the United States, Europe, and elsewhere

●  Aspect ratios and conversion between them

●  Analog waveforms and how to code a digital image from them

●  Coding of luma and chroma