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May 2005
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2005.05.19 15:23 "Re: Looking for the definitions of (MS Specific?) tags [part 1]", by Joris Van Damme
Ulf, Kevin, all, Ulf wrote: > the requested MS-tags are not listed in awaresystems directory. I prefer to think of it as the community's directory. AWare Systems is merely the maintainer, not the owner. > I dissassembled and > iterpreted the TIFF-files myself, so I can't guerantee that the values > are all right. That's only part of the problem. But it's a part that cannot be worked around... For all we know, any unknown tag that many of us have seen hundreds of times with a particular single datatype or count, we might next encounter with another datatype, without MS or anyone else changing any single byte of code even... Reverse engineering tags is fine, if there is the need and no other option, but we should not mistake the findings of such actions to be actual facts ready for publication. The most important part of the problem, however, is the very nature of private tags. Owners, on the one hand, don't strictly need to publish specs about them, in fact sometimes I'm sure there's very good reason to keep private tags strictly in the private realm. Readers of such TIFFs, on the other hand, should not be required to know those tags. Such private tags cannot change or add to the information inside the TIFF that is crucial to exchangeable rendering. Some TIFFs might make little sense without non-disclosed information about private tags, but then these files are not intended for exchange anyway, otherwise the vender would have published that information. And even so interpreting these non-sensical files fully ignoring the private tags should still be regarded as the single only basic 'good thing' by any general reader, otherwise the spec wouldn't apply and by definition this wouldn't be a TIFF but merely something ressembling TIFF's structures. (Perfect example is many of the pre-DNG TIFF-ish raw formats.) As to the webpublishing part of things... I am almost fanatically opposed to publishing garbadge. There's no place on my site for any page that has no more content then a number and a name. Such a page is of use to nobody, and serves only in helping to pollute the web even further, making things harder on search engines and users alike, drowning actual known tags in pools of non-content, and the amount of info after adding all semi-unknown tags would be quickly invalidating JavaScript as a valid search alternative over at http://www.awaresystems.be/imaging/tiff/tifftags/search.html, which is currently my only option for reasons of technical limitation. So, personally, I am opposed to including entries in the directory for those tags that are known by number, might have a name of some origin, might be attributed to some vendor, but bear (little reverse-engineered or) no public information on their actual content. This applies to the MS tags mentioned, the PIXAR tags (unless someone over there reads this and decides to help us out), and many others... But, like I said, it's the communities directory and this last stuff about the webpublishing aspect of tags without info is merely my personal opinion and can be overriden. In conclusion, unless anyone cares to contradict, I don't think there's much of an action item for me here. Or is there? Joris Van Damme info@awaresystems.be http://www.awaresystems.be/ Download your free TIFF tag viewer for windows here: http://www.awaresystems.be/imaging/tiff/astifftagviewer.html