CODEWITHSUNDEEP
ccompressionzip7ziplzw
user2902744
user2902744

Reputation: 3

Compressing ZIP file using a LZW compresion creates a too large size compressed file

I tried to compress zip file using a LZW compression method(code provided in following link),

http://rosettacode.org/wiki/LZW_compression#C

It creates encoded file length as too long than original file size, what is the reason for that? please anybody help me to understand the what is happening in real time.

Upvotes: 0

Views: 838

Answers (1)

Eric Postpischil
Eric Postpischil

Reputation: 222302

It is impossible for a lossless compression to compress every file to a shorter file.

This is because there are 256N files that are N bytes long, but there are (256N-1)/255 files that are shorter than N bytes. So not every file can be mapped to shorter files.

More than that, if any file becomes shorter, then some shorter file had to give up its spot to make that possible. So some files must become larger.

Lossless compression works by recognizing common patterns in typical files created by humans and converting long high-probability sequences of bytes to shorter sequences. The price for this is that some sequences become longer. The goal of the design is to make typical files compress, but atypical files must get longer.

If a compression does its job, redundant information is removed from a file, and the output is similar to random data. Then the output cannot be compressed further.

Upvotes: 1

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