RE: Lossless Compression Help!

["BUTLER, Tony, FM" <tony.butler@xxxxxxx>]

Title: Message

At a very simplistic level, compression algorithms often use:

Oh look - there are 10 spaces (for example) now.  I will replace them with

one space and a count of the number of spaces.

Getting more complex, the algorithms find recurring sequences of bytes - eg the word 'googleplex' appears 20 times in your file.  This is replaced with a (much smaller) token and somewhere in the file a copy of token=googleplex, so at decompression time, the token can be replaced with the original word.

Beyond that, I dunno - some algorithmic equivalent of David Blaine works it's magic and reduces the whole file to a single word :D

 

 

Tony

-----Original Message-----
From: Kenneth Watt [mailto:kennwatt@xxxxxxx]
Sent: 28 May 2002 13:02
To: ukha_d@xxxxxxxSubject: RE: [ukha_d] Lossless Compression Help!

Kinda, I honestly can't remember how it's done I read an article on the subject donks ago, IIRC, it takes out "blank" bits of info and replaces them with said blanks at the de-compression stage it's all very clever stuff I don't need to know about really but I think that's why you can get a text file that can be 70 odd % compressed and yet most images struggle to get beyond 10%.

 

Or I could be misguided ;-)

 

K.

 

-----Original Message-----
From: Ben McCormack [mailto:ben.mccormack@xxxxxxx]
Sent: 28 May 2002 12:55
To: ukha_d@xxxxxxxSubject: RE: [ukha_d] Lossless Compression Help!

 

but unzipping a zip file will replace that junk

-----Original Message-----
From: Kenneth Watt [mailto:kennwatt@xxxxxxx]
Sent: 28 May 2002 12:52
To: ukha_d@xxxxxxxSubject: RE: [ukha_d] Lossless Compression Help!

 

Just remember the next time you zip a file, your doing the impossible!

 

Not at all, a .ZIP file in most instances removes the junk from the file which is not really needed, look at the compression ratios for various files and you will see what I mean, some are more efficient than others at being zipped. Like a text file can be compressed far better than a JPEG or a BMP file.

 

K.

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