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December 2005

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2005.12.03 07:15 "Attempting to parse EXIF data (in a JPEG) with libtiff", by Joshua Muskovitz

2005.12.03 13:59 "Re: Attempting to parse EXIF data (in a JPEG) with libtiff", by Andrey Kiselev

2005.12.03 17:04 "Re: Attempting to parse EXIF data (in a JPEG) with libtiff", by Bob Friesenhahn

2005.12.03 07:15 "Attempting to parse EXIF data (in a JPEG) with libtiff", by Joshua Muskovitz

Hi all,

I'm trying to implement an JPEG/EXIF parser using libtiff.  Separately, I am 
able to extract the EXIF block from the source jpeg image, and I can see 
that it has the proper "II" preamble for TIFF.  I can also see the textual 
EXIF data within the block.

When I try to parse the data with libtiff, I fail in this logic in 
TIFFReadDirectory, called from TIFFClientOpen:

    if (!TIFFFieldSet(tif, FIELD_IMAGEDIMENSIONS)) {
        MissingRequired(tif, "ImageLength");
        goto bad;
    }

which fails, and then I'm dumped out of the file and unable to parse it. 
Now valid EXIF blocks supposedly have no image data in the 0th IFD, and I 
suspect this is the reason it chokes.

As a reality check, I *am* able to parse actual TIFF image files using my 
libtiff wrappers, so I have confidence that that isn't the problem.

Am I nuts to be attempting this in the first place?  Is there something 
obvious I'm missing here?

Joshua Muskovitz
Lead Software Engineer
Preclick Corporation
josh@preclick.com
www.preclick.com