Variable-Length Binary Encodings

Table I gives three different encodings for representing the letters of the alphabet and the space symbol in binary form. These encodings have several special properties which are of some interest. First, each is a variable-length encoding; that is, the code for each letter is a sequence of binary digits, but the codes assigned to different letters are not all required to consist of the same number of binary digits. The first two of these encodings have the prefix property; that is, no one of the codes is a prefix of any other code of the same encoding. This property makes it easy to decipher a message, since it is only necessary to look at enough binary digits of the message until it agrees with one of the codes if it is desired to find the first letter of the deciphered message. The first of these encodings, called the Huffman encoding, is constructed by the method given by Huffman, 1 and has the property of being a minimum-redundancy encoding; that is, among all variablelength binary encodings having the prefix property, this is an encoding 933