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November 2003
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2003.11.17 16:07 "TIFF, v3.6.0. Fetching "custom" tags", by Frank Warmerdam
Andrey Kiselev wrote: > On Sun, Nov 16, 2003 at 07:45:43PM -0500, Chris Losinger wrote: > > > "Custom tags can be set and fetched normally using TIFFSetField() and > > TIFFGetField(), and appear pretty much like normal tags to application > > code. " > > I assume I can get rid of the tags/xtiff stuff and LibTiff will > > happily read and store any tags that it finds, even non-core tags, like > > 34665. > > But, it doesn't seem to be working. When reading the TIFF dir, i > > get warnings about "unknown field with tag 34665 (0x8769) encountered", and > > when i call TIFFGetField, nothing is returned. It looks like v3.6.0. is > > behaving pretty much exactly like 3.5.7: complain about strange tags, then > > ignore them. But that's not what the documentation says is supposed to > > happen. > > > You should register all extended tags before you can work with them. See > a sample code attached. Andrey, The intent is that new tags encountered should auto-register themselves. I checked with photometric.tif, and sure enough TIFFGetField() didn't work. I looked into the code, and it seems that in tif_dirinfo.c 1.21 the line dp->tdir_tag = IGNORE was added in causing the newly defined tag to be ignored. This is something that I had removed in rev 1.17. Why was it re-introduced. Even in 1.17 I wasn't clear on why the code had ever been there, so perhaps there is a reason you added it? With that line removed, the fetching of the new tag works fine. In fact it is even reported by tiffinfo (named "Tag 34665"): warmerda@gdal2200[17]% tiffinfo photoshop.tif TIFFReadDirectory: Warning, photoshop.tif: wrong data type 1 for "XMLPacket"; ta g ignored. TIFFReadDirectory: Warning, photoshop.tif: unknown field with tag 34665 (0x8769) encountered. TIFF Directory at offset 0x8 Subfile Type: (0 = 0x0) Image Width: 600 Image Length: 450 Resolution: 300, 300 pixels/inch Bits/Sample: 8 Compression Scheme: LZW Photometric Interpretation: RGB color Date & Time: "2003:07:24 11:31:44" Image Description: " " Make: "NIKON" Model: "E990" Samples/Pixel: 3 Rows/Strip: 4 Planar Configuration: single image plane Photoshop Data: <present>, 6162 bytes RichTIFFIPTC Data: <present>, 6 bytes Software: Adobe Photoshop 7.0 Tag 34665: 695892 Predictor: horizontal differencing 2 (0x2) I haven't committed the change to tif_dirinfo.c yet, pending feedback on why the IGNORE setting was there. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent