3.1: Variable-Length Encoding
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In Chapter 2 Morse code was discussed as an example of a source code in which more frequently occurring letters of the English alphabet were represented by shorter codewords, and less frequently occurring letters by longer codewords. On average, messages sent using these codewords are shorter than they would be if all codewords had the same length. Variable-length encoding can be done either in the source encoder or the compressor. A general procedure for variable-length encoding will be given in Chapter 5, so a discussion of this technique is put off until that chapter.