Subject: Re: Improvement of LZW compression.

From: [email-masked] (Luis Jose Marmisa Gazo)
Date: 13 Dec 1994 20:54:34 +0100

Corine Plazanet ([email-masked]) wrote:
: I've coded LZW compression algorithm for images, text, fax, exe. I would you to decrease the time processing. 
: Does anybody know about algorithms to improve LZW or where I can find any?
: I heard about H-coding, what about you?

: Thanks,

: 					Corinne PLAZANET
: 					IGN. 

Hi Corinne:

I am not an expert in the compression field, but I can suggest to you
two fast algorithms:

1) V.42bis from ITU. This is the standard for data compression in modems. An
8 bits microprocessor (Z80) is able to compress / uncompress a bidirectional
14.400 bps data link. I believe that V.42bis is a LZW (LZ78).

2) I had some experience with lzrw3-a from Ross Williams. This is the fastest
algorithm in the comparison table of the compression FAQ. However, it is clear
that this algoritm is not the best compressing.

'C' sources are available by ftp in:

- ftp.adelaide.edu.au:/pub/compression/lzrw3-a.c  [129.127.40.3]

lzrw3-a is not a LZW algorithm (I think), it's a LZ77. I tested this
algorithm on a 16 bits MC68000 microprocessor both for increase the data 
transfer speed (19200 bps) and for file compression. I got good
results.

I hope that this information could be useful to you.

Best regards,

        Luis Marmisa ([email-masked])

P.S.: There are some problems with your e-mail address. I can not send you 
any message.

---

From: [email-masked] (Nico de Vries [AIP-NL])
Date: Wed, 14 Dec 94 07:51:13 GMT

[email-masked] writes in article <[email-masked]>:
> 
> I've coded LZW compression algorithm for images, text, fax, exe. I
> would you to decrease the time processing.
> Does anybody know about algorithms to improve LZW or where I can find any?
> I heard about H-coding, what about you?

FTP garbo.uwasa.fi:/pc/programming/lds_11.zip contains 2 sources which
are faster than LZW at compression: Finish and LZRW. It also contains
the source AR002 which is probably faster at decompressing that your
LZW implementation, but slower at compressing. OTOH AR002 has a much
better compression ratio than LZW.

> Thanks,
> 					Corinne PLAZANET
>                                       IGN.

Take care,

     Nico de Vries.
--
[email-masked]  [AIP-NL, UltraCompressor II development]