Compression techniques Adaptive and non-adaptive. - ppt download

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adaptive An adaptive encoder, on the other hand, carries no preconceived heuristics about the data it is to compress. Adaptive compressors, such as LZW, achieve data independence by building their dictionaries completely from scratch. They do not have a predefined list of static substrings and instead build phrases dynamically as they encode. dynamically adjusts the algorithm used based on the content of the data being compressed.
Compression techniques Adaptive and non-adaptive
non-adaptive Non-adaptive encoders contain a static dictionary of predefined substrings that are known to occur with high frequency in the data to be encoded A non-adaptive encoder designed specifically to compress English language text would contain a dictionary with predefined substrings such as and , but , of , and the , because these substrings appear very frequently in English text.
Adaptive compressors, such as LZW, achieve data independence by building their dictionaries completely from scratch. They do not have a predefined list of static substrings and instead build phrases dynamically as they encode. dynamically adjusts the algorithm used based on the content of the data being compressed..
Simple Example And Algorithm
This binary tree differs from standard binary trees by the fact that it is most easily constructed from the bottom to the top: from the leaves to the root, in other words. The procedure is as follows: first, list all the letters used, including the space character, along with the repetition with which they occur in the message..
Then follow the following steps..
The resulting code table LetterCode A0 B101 C100 D111 E1101 F1100
Huffman Tree Construction example A CE H I
Huffman Tree Construction example A C E H I 10 15
Huffman Tree Construction example C EI AH
Input ACE  Output (011)(00)(11).
Huffman Code Algorithm Overview Decoding – Read compressed file & binary tree – Use binary tree to decode file Follow path from root to leaf
Huffman Decoding C EI AH A
Huffman Decoding C EI AH ACAC
Huffman Decoding C EI AH ACEACE
Exercise For the first Example compress the following text ABCF For the first example what is the text that represent that code