Re: [digitalradio] Compressing Data

2009-08-01 Thread Rein Couperus 
PSKmail uses normal zip compression and B64 encoding.
On small files with english text the compression reached by using varicode 
alone is better.
That is why I abandoned compression for email text. Also, when you want 
to use simple compression schemes your result has to be 1-bit clean, 
which requires ARQ in all cases.

73,

Rein PA0R

 -Ursprüngliche Nachricht-
 Von: Stelios Bounanos digra...@enotty.net
 Gesendet: 23.07.09 16:23:18
 An: digitalradio@yahoogroups.com
 Betreff: Re: [digitalradio] Compressing Data


  On Thu, 23 Jul 2009 09:45:54 +0200, Simon (HB9DRV) 
  simon.br...@kns.ch said:
 
  Thinking to myself - when we use a mode such as Olivia / MT63 with extensive
  error correction, why don't we compress the text?
 
  Given that fldigi has the wrap feature then surely compression could be /
  should be considered for some modes?
 
 I've been planning to do some testing with fldigi's file wrapping using lzma
 compression.  Because the modems used for this are not 8bit-clean, flwrap uses
 base64 encoding for binary files, which adds a sizeable overhead to any
 compressed transfer.  Nevertheless, I expect that in most cases compression 
 will
 result in a speed-up.  And because the file sizes involved are usually tiny,
 even lzma compression only takes a few milliseconds, so you can always 
 compress
 and simply throw away the result if it turns out to be larger than the 
 original.
 
 
 -- 
 
 73,
 Stelios, M0GLD.
 
 
 
 
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Re: [digitalradio] Compressing Data

2009-08-01 Thread Stelios Bounanos 
 On Sat, 01 Aug 2009 14:52:10 +0200, Rein Couperus r...@couperus.com 
 said:

 PSKmail uses normal zip compression and B64 encoding.
 On small files with english text the compression reached by using varicode 
 alone is better.
 That is why I abandoned compression for email text. Also, when you want 
 to use simple compression schemes your result has to be 1-bit clean, 
 which requires ARQ in all cases.

I expect lzma to do better than zip.  As you say, for some modes it will
be more efficient to send plain text rather than compress and base64
encode it.  Flwrap will have no way of knowing how the data will be
transmitted, but it will have options to disable the compression or use
it only for binaries.


-- 

73,
Stelios, M0GLD.

Re: [digitalradio] Compressing Data

2009-07-23 Thread Rick W 
Is it possible to compress a file and lose even one bit during the 
transfer and still have something usable on the receiving end when you 
uncompress? Normally, you must use ARQ to insure perfect copy. Even MT63 
or Olivia can take a hit every so often.

73,

Rick, KV9U


Simon (HB9DRV) wrote:


 Thinking to myself - when we use a mode such as Olivia / MT63 with 
 extensive error correction, why don't we compress the text?
  
 Given that fldigi has the wrap feature then surely compression could 
 be / should be considered for some modes?
  
 I think I'll add something in my own code that shows the saving were 
 the standard ZIP compression algorithm to be applied my gut feeling is 
 a saving of 80%, I'll report back later today.

Re: [digitalradio] Compressing Data

2009-07-23 Thread Simon (HB9DRV) 
Depends on the compression, but with ZIP - no, one lost bit and you're - 
lost!

Simon Brown, HB9DRV
www.ham-radio-deluxe.com

- Original Message - 
From: Rick W mrf...@frontiernet.net


 Is it possible to compress a file and lose even one bit during the
 transfer and still have something usable on the receiving end when you
 uncompress? Normally, you must use ARQ to insure perfect copy. Even MT63
 or Olivia can take a hit every so often.