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March 2007
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2007.03.20 13:42 "Re: TIF IFD pointer", by Joris Van Damme
Sascha, Sascha Sebastian Willmes wrote: > I am quite unfamiliar with TIFF readout routines. > Can anybody tell me how to use the 4-byte pointer to the IFDs? > > Why does it contain 4 bytes? It's not completely clear to me what you are refering to. Are you talking about the first IFD offset, in the header? If so, you don't need to do anything with it, normal open routines access it immediatelly. Are you talking about the pointers to the next IFD, that follow all IFDs? If so, again, you don't need to access them directly, you use TIFFReadDirectory instead to advance to that next IFD. Or are you refering to the SubIFDs or EXIF IFD or private IFD tags? In that case, the answer is a bit more involving. It contains 4 bytes because it's a 32 bit value. One good reason to try and not fiddle with it directly, is that it is this aspect of ClassicTIFF that changes in the BigTIFF design, where it becomes a 64 bit value. Not fiddling with it directly, is recommended as that'll guarantee your code will work beautifully and identically before and after that upgrade that we are currently implementing. If this doesn't answer your question, please elaborate. Best regards, 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