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To: losinger@earthlink.net
Subject: Re: [Tiff] Read EXIF Tag
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Chris,

Based on my experience, the TIFFTAG_EXIFIFD just provides the address of where the exif  IFD is located in the file.
It doesn't actually provide the entire exif blob.  It would have been 
better if it was more like the icc Profile tag which does return the 
entire blob.


long  value32;

if (TIFFGetField(m_TIFFHandle, TIFFTAG_EXIFIFD, &value32) == 1)
{
        // open the file in binary mode 
        // read the tiff header to determine byte order 
        // seek to "value32"
        // read and parse IFD at "value32";
}

Lou Sakey
DFIS WW S+SE LOWELL DEVELOPMENT CTR 
Lou.Sakey@kodak.com
KNET 27-67676
978-323-7676




Chris Losinger <losinger@earthlink.net>
Sent by: tiff-bounces@lists.maptools.org
10/19/2005 09:47 PM

 
        To:     tiff@lists.maptools.org
        cc: 
        Subject:        [Tiff] Read EXIF Tag



                 i just dropped-in LibTiff v3.7.4, and i'm having trouble 
reading tag 
0x8769 (TIFFTAG_EXIFIFD).

    long *offset = 0;
    UINT16 count = 0;
    BOOL bFound = TIFFGetField(tif, 0x8769, &count, &offset);

                 ... yields bFound = 0

                 in 3.7.0, i had a _TIFFMergeFieldInfo extender setup that 
would grab 
that tag and a couple of others. now, i see that LibTiff has support 
for reading that tag natively, so i've disabled my extender, and am 
trying to read that tag the same way i'd read any other tag. but, it 
doesn't seem to grab it from my test TIFFs. (v3.7.0 with the extender 
does)

                 is there anything i need to do before trying to read that 
tag ?

                 note that i'm not trying to parse the EXIF IFD with 
LibTiff (yet), 
i'm just trying to get the raw tag data.

                 -c
----
Chris Losinger
losinger@earthlink.net
smallest@smalleranimals.com          http://www.smalleranimals.com

_______________________________________________
Tiff mailing list: Tiff@lists.maptools.org
http://lists.maptools.org/mailman/listinfo/tiff
http://www.remotesensing.org/libtiff/



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<br><font size=2 face="sans-serif">Chris,</font>
<br>
<br><font size=2 face="sans-serif">Based on my experience, the </font><font size=2 face="Courier New">TIFFTAG_EXIFIFD</font><font size=2 face="sans-serif"> just provides the address of where the exif &nbsp;IFD is located in the file.</font>
<br><font size=2 face="sans-serif">It doesn't actually provide the entire exif blob. &nbsp;It would have been better if it was more like the icc Profile tag which does return the entire blob.</font>
<br>
<br>
<br><font size=2 face="Courier New">long </font><font size=2 face="sans-serif">&nbsp;</font><font size=2 face="Courier New">value32</font><font size=2 face="sans-serif">;</font>
<br>
<br><font size=2 face="Courier New">if (TIFFGetField(m_TIFFHandle, TIFFTAG_EXIFIFD, &amp;value32) == 1)</font>
<br><font size=2 face="sans-serif">{</font>
<br><font size=2 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; </font><font size=2 color=#008000 face="Courier New">// open the file in binary mode</font><font size=2 face="sans-serif"> &nbsp; &nbsp; &nbsp; &nbsp;</font>
<br><font size=2 color=#008000 face="Courier New">&nbsp; &nbsp; &nbsp; &nbsp; // read the tiff header to determine byte order </font>
<br><font size=2 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; // seek to </font><font size=2 face="Courier New">&quot;value32&quot;</font>
<br><font size=2 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; // read and parse IFD at </font><font size=2 face="Courier New">&quot;value32&quot;</font><font size=2 face="sans-serif">;</font>
<br><font size=2 face="sans-serif">}<br>
<br>
Lou Sakey<br>
DFIS WW S+SE LOWELL DEVELOPMENT CTR <br>
Lou.Sakey@kodak.com<br>
KNET 27-67676<br>
978-323-7676</font>
<br>
<br>
<br>
<table width=100%>
<tr valign=top>
<td>
<td><font size=1 face="sans-serif"><b>Chris Losinger &lt;losinger@earthlink.net&gt;</b></font>
<br><font size=1 face="sans-serif">Sent by: tiff-bounces@lists.maptools.org</font>
<p><font size=1 face="sans-serif">10/19/2005 09:47 PM</font>
<br>
<td><font size=1 face="Arial">&nbsp; &nbsp; &nbsp; &nbsp; </font>
<br><font size=1 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; To: &nbsp; &nbsp; &nbsp; &nbsp;tiff@lists.maptools.org</font>
<br><font size=1 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; cc: &nbsp; &nbsp; &nbsp; &nbsp;</font>
<br><font size=1 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; Subject: &nbsp; &nbsp; &nbsp; &nbsp;[Tiff] Read EXIF Tag</font></table>
<br>
<br>
<br><font size=2 face="Courier New"><br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; i just dropped-in LibTiff v3.7.4, and i'm having trouble reading tag <br>
0x8769 (TIFFTAG_EXIFIFD).<br>
<br>
 &nbsp; &nbsp;long *offset = 0;<br>
 &nbsp; &nbsp;UINT16 count = 0;<br>
 &nbsp; &nbsp;BOOL bFound = TIFFGetField(tif, 0x8769, &amp;count, &amp;offset);<br>
<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ... yields bFound = 0<br>
<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; in 3.7.0, i had a _TIFFMergeFieldInfo extender setup that would grab <br>
that tag and a couple of others. now, i see that LibTiff has support <br>
for reading that tag natively, so i've disabled my extender, and am <br>
trying to read that tag the same way i'd read any other tag. but, it <br>
doesn't seem to grab it from my test TIFFs. (v3.7.0 with the extender does)<br>
<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; is there anything i need to do before trying to read that tag ?<br>
<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; note that i'm not trying to parse the EXIF IFD with LibTiff (yet), <br>
i'm just trying to get the raw tag data.<br>
<br>
 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; -c<br>
----<br>
Chris Losinger<br>
losinger@earthlink.net<br>
smallest@smalleranimals.com &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;http://www.smalleranimals.com<br>
<br>
_______________________________________________<br>
Tiff mailing list: Tiff@lists.maptools.org<br>
http://lists.maptools.org/mailman/listinfo/tiff<br>
http://www.remotesensing.org/libtiff/<br>
</font>
<br>
<br>
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