From: eesfd@gdr.bath.ac.uk (F Dudbridge)
Newsgroups: comp.compression
Subject: Re: Fractal compression
Date: 13 Aug 92 23:29:38 GMT
Organization: School of Electrical Engineering, University of Bath, UK

I recently spent a week as a guest of Barnsley, so should like to
comment on these recent postings:

>Their performance has improved dramatically beyond what they were
>talking about in BYTE a few years ago.  Human assistance to the
>compression is no longer needed and the compression time is
>reasonable, although the more time and compute power you throw at the
>compression, the smaller the resulting file for the same level of
>quality.

At the time of the Byte article they didn't have any realistic image
compression algorithm.  The block-coding technique they have patented
is based on theory that was developed since that time.  In fact, a lot
of the work was done by Arnaud Jacquin, who has published these methods.
Rumour has it that he and Barnsley had a bust-up over intellectual property
rights: Barnsley's name is not on the papers, Jacquin's is not on the
patents, so draw your own conclusions.

>
>now that they have obtained their patents they are talking
>more about the method (since their 'competitive edge' is protected).

The fact that Jacquin published before the patent was issued may yet cause
a legal problem with the patent.  In any case they are *still not* saying
much about their methods.  Despite the fact that everyone now knows roughly
how it is done, I spent a week chatting to Barnsley and got nothing more
from him than "it's block coding and involves searching".  While such
paranoia is somewhat understandable, it's fairly unusual to find a company
where the programmers are prohibited from discussing work with the researchers,
etc... which is the case at Iterated Systems.

>Barnsley may have pissed a lot of people off because of the way he
>presents (or doesn't) his work, but that doesn't mean that his method
>is bogus.  It is quite reasonable and it works.

Is it true that he was made so unwelcome at SIGGRAPH that he left hurriedly?

>>Compression ratios (unzoomed) seem to range from 20:1 to 60:1...  The
>>quality is considerably worse than wavelets or JPEG on most of the
>>non-contrived images I have seen.
>Iterated Systems Inc. has 10 full-time mathematicians who do nothing but work
>on the fractal compression algorithms
>The observation "quality is considerably worse" is quite dated by now.

Yes the method does work.  Yes, the results are good and are comparable to
JPEG.  However, the sales pitch does need to be looked at closely.  Their
compression ratios are often given by reconstructing the fractals at a higher
resolution than the originals.  Thus the compression ratios appear higher
than they should.  Also, the decoded colour may be in 8-bits, when the
original was quantized from 24-bit data.  Ie. the quoted compression is
often reconstructed/compressed, as opposed to original/compressed.
Since fractal images have infinite resolution, it is possible to reconstruct
fractals to arbitrary resolution while avoiding pixelation, giving the 
impression of increased compression.

Interestingly, I learned from one of the mathematicians that they had
implemented their own wavelet compression algorithm, which outperformed
the fractals.  But as this defeated the point of the company, they preferred
to ignore this result.

There are 10 (very reputable) mathematicians working for Iterated Systems.
One of these is Lyman Hurd who is co-authoring one of the new books with
Barnsley.  The other co-author, Louisa Anson, is Barnsley's girlfriend.
When I met these people neither of the books were finished, so I think we'll
have to wait a while.
Having developed my own, different, algorithm for IFS compression I had
been hoping to join the research team, but it seems that their expansion
will now be in the marketing rather than research direction.

Hope this is of interest to people

-- Frank