Can someone explain to me what advantages the TIFF format has over PNG, and why that is not used instead? This would reduce file size without the need for an intermediary compression step, and as far as I'm aware maintain image fidelity as well as TIFFs, and much better than JPEG.
- Ray 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'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 >> [email protected] >> >> >> -----Original Message----- >> From: Matt Morgan [mailto:[email protected]] >> Sent: Tuesday, November 29, 2005 10:39 AM >> To: [email protected] >> 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 >> >> >> >> >> --- >> You are currently subscribed to mcn_mcn-l as: [email protected] >> To unsubscribe send a blank email to >> [email protected] >> > > --- > You are currently subscribed to mcn_mcn-l as: [email protected] > To unsubscribe send a blank email to > [email protected] >
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