Matt Morgan wrote:
Richard Urban wrote:
Matt,
Generally compression isn't recommended for a few reasons. While Zip and
LZW are fairly reliable compression algorithms, they add another layer of
complexity to the file.
Understood--thanks to you and to Tim Au Yeung.
It's possible that the compression could make
unpacking them more difficult down the line. I've heard it suggested that
this is particularly true if there is some bit level corruption of the file,
which could cause the compression to fail. (comments from people who get
under the hood with files would be appreciated...sometimes I feel like these
are digital urban legends).
I misunderstood what you were saying here. Although maybe then zipping
will expose the bit-level corruption of the file, which would be nice
:-). But probably that's just a fantasy.
I'd be interested in seeing any hard data on
this.
If there is such a problem, it would be in the different
implementations, not in the algorithm, which is mathematically perfect.
Perhaps nobody has gotten the hard data you're asking for, but if not,
it's probably only because other industries do not doubt the
reversibility of compression in the way we do. I mean, zillions of
files are compressed and uncompressed every day, and for years, almost
every PC hard drive was dblspaced or drvspaced.
I understand that you're talking about problems not necessarily visible
to the eye, or that we just wouldn't worry about in a spreadsheet or
memo, but in demonstrated practice, common forms of reversible
compression are safe for files. Can I go on that? How much more
convinced can we get?
The other concern is over the patents held on both compression algorithms.
There was a time where the patent holders were attempting to claim control
over the patents, suggesting that you'd need a license to unpack your files
(or least the people making the software you use would). These mostly seem
to have gone away, but the patents are still out there. Generally this is
why we've steered away from proprietary formats towards open standards.
I'm all for open standards, especially for museums and libraries--and
ZIP is at least as open (now) as most RAW formats. In any case, there
are other compression algorithms that are well-tested and more open
than ZIP has been in the past. So it just seems like this is a minor
issue compared to the complexity problem.
Thanks,
Matt
Richard Urban
Graduate School of Library and Information Science
University of Illinois at Urbana-Champaign
rjur...@uiuc.edu
-----Original Message-----
From: Matt Morgan [mailto:m...@concretecomputing.com]
Sent: Tuesday, November 29, 2005 10:39 AM
To: mcn-l@mcn.edu
Subject: Re: [MCN SIG: Digital Media] Uniiversal Photographic Digital
Imaging Guidelines
Newman, Alan wrote:
Curious coincidence. I just distributed this link today to my staff and I
was preparing a post to MCN-L. We've adopted most of these guidelines in my
division at the National Gallery.
I'm curious to know which recommendations you haven't adopted ... let us
know!
I read through the UPDIG recommendations and found it really interesting and
helpful. I thought their recommendation for RAW format was relatively
unconvincing, though. Almost like they were saying "we want to recommend RAW
format, but we realize you're going to convert them anyway, at least until
the DNG format is widely-supported." Their best arguments for RAW applied to
oddball cameras--which to me is an argument not to buy an oddball camera. Is
anyone behaving differently, and storing files in RAW (but not also storing
in TIFF)? I think, although I'm not sure, that the UPDIG Working Group has
more faith in RAW than the museum and library worlds do.
The other question I've been asking myself a lot lately, but haven't seen
addressed much, is why not store files with some form of reversible
compression like zip (or gzip or bzip2)? UPDIG doesn't address this
(although it allows that compression is valuable and acceptable for
delivery). ZIP (and bzip2 and gzip) is perfectly reversible, and it's tried
and true. Why store 100Mb TIFF files when we could be storing 10Mb tiff.zip
files? Has anyone out there opted to use reversible compression in digital
repositories? If not, why not?
I realize that JPEG2000 would also solve the compression problem, but ZIP
ought to have less of an acceptance problem than JPEG2000 (as ZIP is already
so established).
Thanks,
Matt
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