2004.06.29 07:29 "Re: [Tiff] Saving Exif with TiffLib", by Joris
My task is to save Exif-data into tiff-images. According to Exif specification I should put Exif-specific data into subIFDs, that are not linked into common directories chain. And, as far as I understand, there is no regular mechanism to create such IFDs, because SUBIFD tag, specified by TiffLib has its own hardcoded value, while Exif-tags with offsets to corresponding Exif-SubIFDs should have other values, that are defined by Exif-standart. Should I modify TIffLib (add Exif-tags and made some extension of SubIFD-mechanism) to solve my problems, or there is any other way?
I don't think this is going to be very helpfull, and for that I appologise, but I just got to say it anyway.
Why is it that the EXIF gets promoted to an IFD? In my humble opinion, any additional data, like EXIF data, should be a single tag, like all of us mortals add proprietary data to an IFD. That defines its relationship to the image, ie the tag is part of the image's IFD. It is by promoting itself to a complete and independent IFD, that the problem of relationship to the image arises. Furthermore, it is this promotion that is the cause of your problem here, *and* is breaking a number of readers that can't make sense of an IFD without ImageWidth and ImageLength tags (nor should they), *and* is breaking the TIFF specification in a number of ways, in my humble opinion.
So this comment might not be helpfull, but may nevertheless be worth considering. Perhaps some people that are more knowledgable than I will respond to this and perhaps they have a clue what is the sensible thing to do in this situation.
Joris Van Damme
Download your free TIFF tag viewer for windows here: http://www.awaresystems.be/imaging/tiff/astifftagviewer.html