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What is Compression Gain?

Posted on 2004-04-05
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Last Modified: 2010-04-03
Can someone please tell me what is meant by compression gain.
I have compressed a text string with LZW, the efficiency before compression is 99.5% and after compression 92.3% using:
(Entropy / Av Codeword Length) * 100
It takes 50 bits to encode the data before compression and 60 bits after (so its not really worth compressing with this method).

So is the compression gain simply a bit value (ie 10 bits) or is it related to the efficiency (ie 99.5 - 92.3)

Thanks In Advance

Rick
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Question by:jondow
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juliangkeller earned 50 total points
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I don't know if this helps:

http://www.dogma.net/markn/articles/lzw/lzw.htm

It does refer to bits because it is compressing data. In some cases it is possibly to acheive 30% gain (i.e 100 bits to 70 bits) but is not for all data as you seen yourself that it can raise the bits and lower the percentage.  

You can see about that here:

http://64.233.167.104/search?q=cache:fd9kx-VFXPMJ:biron.usc.edu/~sagetong/Project_3.doc+LZW+compression+gain&hl=en&ie=UTF-8

http://66.102.7.104/search?q=cache:6UG4nkjb6ZUJ:www.cms.livjm.ac.uk/pgnet2003/submissions/Paper-13.Pdf+LZW+compression+gain&hl=en&ie=UTF-8

PAGE 4 ON THE RIGHT
most people don't use LZW because of this unless it is a large file and some in Unix because PKzip is not useful.

I hope this helps.
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