Image Coding
Fundamental Concepts of Coding
A code is a mapping of words from a source alphabet into the words of a code alphabet;
A word is a finite sequence of symbols from an alphabet.
A code is called distinct if each code word is distinguishable from the other code words.
A distinct code is uniquely decodable if every code word is identifiable when immersed in a sequence of code words.
A desirable property of a uniquely decodable code is that it should be decodable on a word-to-word basis. This is ensured if no code word may be a prefix to another; the code is then instantaneously decodable.
A code is said to be optimal if it is instantaneously decodable and has the minimum average length for a given source PDF.