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May 2004
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2004.05.10 20:28 "Re: Tiff questions", by Frank Warmerdam
Chris Cox wrote: > The full details are in the Photoshop SDK - but you should be able to > work it out from tiff info (look at the sub IFDs). > > Chris Jim, I see now. There are two approaches to embedding overviews in a TIFF file. One is to have additional "pages" that are marked as overviews and sort of implicitly associated with the full resolution image. The other approach is to keep the overviews in a "subIFD". A directory (or chain of directories) not in the main chain list but referred to from the base image from which the overviews are derived. The SubIFD approach is "purer" in that the overviews are unambigously associated with image. However, the geospatial applications I work with have used the other approach. I would add that tiffinfo does not traverse into subifds to report on them though you can force it to read the directories at a particular offset if you want to read them. The contrib/addtiffo stuff is all based on the additional pages approach. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent