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August 2005
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2005.08.19 08:06 "Re: TIFF Thumbnail", by Katrina Maramba
Joris wrote: > > The definitive document on thumbnails in TIFF, and related, is the > specification supplement that describes the SubIFD tag, which can be > found here: > > http://partners.adobe.com/public/developer/en/tiff/TIFFPM6.pdf > > In short, it says that the SubIFD tag can contain the offset of a > thumbnail image IFD. That solves a lot of trouble. > > [..] > > > How can the reader determine if a particular image has a thumbnail > > or not? > > I recommend your code to do this, in this particular order: > - Check existence of SubIFD tag. If it's there, make additional sanity > checks. If all works out, you've got the thumbnail in a child IFD. > [...] Assuming that I have determined that this image has a thumbnail indeed, can I go and look for the thumbnail's IFD and and parse it like the main image's directory (which is (for example) call TIFFReadDirectory)? And if so, can I also go and look for the thumbnail's strip (using strip offsets and strip byte count) and process the thumbnail using TIFFReadRGBAStrip (which would generate RGB data)? If not, what would be the correct API to call to process the thumbnail? Thank you, Katrina