2000.10.26 13:46 "Write tags", by Markus Neifer
Thread
2000.10.27 08:24 "Re: Write tags", by Klaus Bartz
Hello Markus,
it's really difficult to modify an existing IFD.
The story with the SubIFD ( tag 330, defined in TTN1 ) is a little bit other thing. There is an excelent software on the market which copies ( for it ) unknown tags with it's contents to a new file. Pointers also. But the contents of the area to which the offset points not ( theSubIFD is not copied and the resolution reduced child also not ). Only a problem for programms which uses tag 330; but for those the file is corrupted.
It's not a back reference, else a forward reference. No problem if it is in a dead IFD. But if you copy such a tag ( a tag with a offset ) be aware there is a chain ( an offset to an "object" which contains offsets to offsets... ).
References to the old IFD I have seen in a private Tag related too a well known product - it's simple a page offset table for faster access.
You see, there are some reasons why libtiff doesn't do that things...
Klaus
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