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2007.03.16 17:53 "Re: How to identify maker notes IFD", by Phil Harvey
Hi Anurag, On 16-Mar-07, at 1:01 PM, tiff-request@lists.maptools.org wrote: > I am parsing Exif IFD and want to provide proper handling for maker > notes, but i am not able to identify either it's ordinary maker notes > or maker notes IFD. > > Example for makenotes tags, it's written as > > 92 7c 00 07 00 00 0e ca 00 00 13 64 > > So how can anyone sure that it's makernotes IFD? Even i know that it's > maker note ifd, but not able to difrenciate with normal case. > > Is there any tags through which we can identify? > How would I identify these two different cases? This is not part of the TIFF specification. The maker is free to write whatever he wants in these notes. If you really need to parse makernote IFD's you will earn yourself a big headache, take my word for it. To to this you will need to generate some smart algorithms which scan for things that look like IFD's and validate the entries as much as possible to test for proper IFD structure. As well, you need an algorithm to determine what type of offsets are being used (absolute as TIFF, relative to maker notes position, or relative to IFD entry), and you must take into account that absolute offsets can be shifted if the makernotes are moved by some other dumb utility. But even if you do this correctly, you will find the need to have special logic for individual camera models since each has its own quirks. The struggle begins. - Phil