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2006.09.22 13:52 "Handling of EXIF IFD in Libtiff", by Anurag Singh
2006.09.22 15:20 "Re: Handling of EXIF IFD in Libtiff", by Joris Van Damme
2006.09.23 07:39 "Re: Handling of EXIF IFD in Libtiff", by Anurag Singh
2006.09.23 13:39 "Re: Handling of EXIF IFD in Libtiff", by Joris Van Damme
2006.09.25 14:22 "Re: Handling of EXIF IFD in Libtiff", by Phil Harvey
2006.09.25 16:15 "Re: Handling of EXIF IFD in Libtiff", by Joris Van Damme
2006.09.25 16:58 "Re: Handling of EXIF IFD in Libtiff", by Phil Harvey
2006.09.25 17:27 "Re: Handling of EXIF IFD in Libtiff", by Joris Van Damme
2006.09.26 05:46 "Re: Handling of EXIF IFD in Libtiff", by Anurag Singh

2006.09.25 16:15 "Re: Handling of EXIF IFD in Libtiff", by Joris Van Damme

Phil,

Phil Harvey wrote:
> > i mean to say is there any other EXIF tag which have offset and on
> > that offset may be some data, just like image data.
>
> I don't know if this is what you mean, but the ExifIFD contains the
> InteropIFD and the maker notes, both of which may contain pointers to
> information that must be handled properly when rewriting the image.

..which
a) goes against the TIFF spec that says tag data must be self-contained
and cannot include pointers to anywhere outside of that tag data.
b) is not a problem if you don't copy tags you don't fully know, like I
recommended Anurag in the first place though he didn't seem to think
that recomendation was worth considering.

It's b) in particular that indicates to me Anurag doesn't quite get the
concept of private tag, and is thus wondering if these EXIF tags contain
some information required in a rendering interpretation of the image.
Hence also the quoted 'just like image data'.

But I see your interpretation of his question may be more likely
correct. I'd just thought I add this note to it, taking the opportunity
to once again highlight the trouble caused makernote-style
out-of-tag-data pointers on the one hand, and blind copying of unknown
tags on the other hand. Seems to me we should always stress that,
otherwise we risk that our explanation of the bad things is incorrectly
interpreted as an indication that such is a perfectly valid thing to do.


Best regards,

Joris Van Damme
info@awaresystems.be
http://www.awaresystems.be/
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