Lempel Ziv Welch Compression technique

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LZW Compression

In this technique trick is that string-to-codeword mapping is created dynamically by the encoder also recreated dynamically by the decoder need not pass the code table between the two is a lossless compression algorithm degree of compression hard to predict depends on data, but gets better as codeword table contains more strings.

step 1.Initialize table with single character strings

step 2.STRING = first input character

step 3.WHILE not end of input stream

1. CHARACTER  = next input character
2. IF STRING + CHARACTER is in the string table
   1. STRING = STRING + CHARACTER
3. ELSE
   1. Output the code for STRING
   2. Add STRING + CHARACTER to the string table
   3. STRING = CHARACTER

step 4.END WHILE

step 5.Output code for string

LZW De-Compression

step 1.Initialize table with single character strings

step 2.OLD = first input code

step 3.output translation of OLD

step 4.WHILE not end of input stream

1. NEW = next input code
2. IF NEW is not in the string table

S = translation of OLD

S = S + C

step 5.ELSE

S=translation of NEW

1. EndIF
2. output S
3. C = first character of S
4. OLD + C to the string table
5. OLD = NEW

step 6.END WHILE

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