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February 2004

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This list is run by Frank Warmerdam
Archive maintained by AWare Systems

2004.02.20 15:41 "bug in libTiff", by Nick Basargekar

There appears to be a bug in libTIFF 3.6.1(for win32) which prevents the
writing out of changed TIFF fields.  

*
 * Flush buffered data to the file.
 *
 * Frank Warmerdam'2000: I modified this to return 1 if TIFF_BEENWRITING
 * is not set, so that TIFFFlush() will proceed to write out the directory.
 * The documentation says returning 1 is an error indicator, but not having
 * been writing isn't exactly a an error.  Hopefully this doesn't cause
 * problems for other people. 
 */

int
TIFFFlushData(TIFF* tif)
{
        if ((tif->tif_flags & TIFF_BEENWRITING) == 0)
               return (0);
        if (tif->tif_flags & TIFF_POSTENCODE) {
               tif->tif_flags &= ~TIFF_POSTENCODE;
               if (!(*tif->tif_postencode)(tif))
                       return (0);
        }
        return (TIFFFlushData1(tif));
}
 

Frank's comment's don't make any sense because returning 0 is an error
indicator according to the docs. 

So I changed it to 

        if ((tif->tif_flags & TIFF_BEENWRITING) == 0)
                return (TIFFFlushData1(tif));

and then reading/writing of fields started working. 
 

Basically, I'm trying to write out a byte array to a private field for use
within this organization. 

The contrib\tags example in libTiff doesn't appear to be compatible with
3.6.1, so I  followed the instructions at
http://www.libtiff.org/internals.html#AddingTags
<http://www.libtiff.org/internals.html#AddingTags>  and along with the
change mentioned above, reading/writing of the private field works ok with
libTiff.  

However Windows Preview can't view the file after the tag is added.
Photoshop 7.0 gives a nasty warning dialog about the file possibly being
corrupt, but the file seems to open fine.  

I found that even changing a "normal" field like "TIFFTAG_ARTIST" caused the
same problems.  I'm just wondering if anyone has encountered a similar issue
or has any info on the subject.  Any feedback at all is greatly appreciated.

Nick Basargekar
Software Engineer, Core Technology Group
PEI/Atari, Inc. 
http://www.atari.com <http://www.atari.com>