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The Metadata in TIFF files » History » Version 14

Robin Mills, 13 Nov 2016 09:17

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h1. The Metadata in TIFF files
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The Tagged Image File Format is a container.  It's very flexible and can deal with multiple pages, different colour spaces, different frame configurations as well as metadata.  The specification is available from:  https://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf
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The TIFF container is so flexible it is used as the structure for most RAW formats including Adobe's DNG.  Additionally the TIFF container is used to store the metadata that lies inside the Exif blocks embedded in JPEG and PNG files.
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There is a 64bit version of Tiff called _*BigTiff*_. This is currently not supported by exiv2.
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!Tiff.png!
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The format consists of an 8 byte header which provides a 2 byte endian flag (II or MM), a 2 byte type "magic number" (42) and a 4 byte offset to an _*Image File Directory*_.
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The _*IFD*_ _(Image File Directory)_  has a two byte header which contains the length of the directory followed by 12 byte field or "tag".  The trailing 4 bytes of the the directory is the offset to the next directory _*or*_ zero to terminate the directory chain.
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A tag consists of a 12 byte record: TagID, TagType, Count and Offset which are 2,2,4 and 4 bytes respectively.  The TagID defines the purpose of the record (Width, Height, ColorSpace etc) and the TagType defines the data format.  Count and Offset are used to contain the raw data _*or*_ provide an offset in the file at which to read the raw data for this tag.
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*Example:*
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The version of exiv2(.exe) which ships with v0.25 provides options _*<code>-pS</code>*_ to reveals the structure of the TIFF and option _*<code>-pX</code>*_ is used to extract the raw XMP/xml data.
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The option _*<code>-pa</code>*_ is used to print the metadata in human readable format.<pre>$ exiv2 -pa test/data/test.tiff
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$ exiv2 -pa test/data/test.tiff 
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Exif.Image.NewSubfileType                    Long        1  Primary image
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Exif.Image.ImageWidth                        Short       1  282
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Exif.Image.ImageLength                       Short       1  212
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Exif.Image.BitsPerSample                     Short       3  8 8 8
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Exif.Image.Compression                       Short       1  LZW
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Exif.Image.PhotometricInterpretation         Short       1  RGB
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Exif.Image.ImageDescription                  Ascii      32                                 
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Exif.Image.Make                              Ascii       5  SONY
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Exif.Image.Model                             Ascii       9  DSC-S600
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Exif.Image.StripOffsets                      Long       16  4372 ...
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Exif.Image.Orientation                       Short       1  top, left
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Exif.Image.SamplesPerPixel                   Short       1  3
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Exif.Image.RowsPerStrip                      Long        1  14
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Exif.Image.StripByteCounts                   Long       16  10492 ...
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Exif.Image.XResolution                       Rational    1  96
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Exif.Image.YResolution                       Rational    1  96
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Exif.Image.PlanarConfiguration               Short       1  1
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Exif.Image.ResolutionUnit                    Short       1  inch
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Exif.Image.DateTime                          Ascii      20  2009:04:26 12:38:18
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Exif.Image.Predictor                         Short       1  No prediction scheme used
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Exif.Image.SampleFormat                      Short       3  Unsigned integer data
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Exif.Image.XMLPacket                         Byte      2505  (Binary value suppressed)
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Exif.Image.InterColorProfile                 Undefined 1352  (Binary value suppressed)
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Xmp.dc.title                                 LangAlt     1  lang="x-default" this is a test image
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$ exiv2 -pS test/data/test.tiff
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STRUCTURE OF TIFF FILE (II): test/data/test.tiff
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 address |    tag                           |      type |    count |    offset | value
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      10 | 0x00fe NewSubfileType            |      LONG |        1 |         0 | 0
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      22 | 0x0100 ImageWidth                |     SHORT |        1 |       282 | 282
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      34 | 0x0101 ImageLength               |     SHORT |        1 |       212 | 212
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      46 | 0x0102 BitsPerSample             |     SHORT |        3 |       290 | 8 8 8
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      58 | 0x0103 Compression               |     SHORT |        1 |         5 | 5
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      70 | 0x0106 PhotometricInterpretation |     SHORT |        1 |         2 | 2
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      82 | 0x010e ImageDescription          |     ASCII |       32 |       296 |                                
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      94 | 0x010f Make                      |     ASCII |        5 |       328 | SONY
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     106 | 0x0110 Model                     |     ASCII |        9 |       334 | DSC-S600
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     118 | 0x0111 StripOffsets              |      LONG |       16 |       344 | 4372 14864 25634 37110 50496 ...
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     130 | 0x0112 Orientation               |     SHORT |        1 |         1 | 1
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     142 | 0x0115 SamplesPerPixel           |     SHORT |        1 |         3 | 3
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     154 | 0x0116 RowsPerStrip              |      LONG |        1 |        14 | 14
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     166 | 0x0117 StripByteCounts           |      LONG |       16 |       408 | 10492 10770 11476 13385 13348 ...
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     178 | 0x011a XResolution               |  RATIONAL |        1 |       472 | 96/1
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     190 | 0x011b YResolution               |  RATIONAL |        1 |       480 | 96/1
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     202 | 0x011c PlanarConfiguration       |     SHORT |        1 |         1 | 1
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     214 | 0x0128 ResolutionUnit            |     SHORT |        1 |         2 | 2
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     226 | 0x0132 DateTime                  |     ASCII |       20 |       488 | 2009:04:26 12:38:18
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     238 | 0x013d Predictor                 |     SHORT |        1 |         1 | 1
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     250 | 0x0153 SampleFormat              |     SHORT |        3 |       508 | 1 1 1
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     262 | 0x02bc XMLPacket                 |      BYTE |     2505 |       514 | <?xpacket begin="..." id="W5M0Mp ...
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     274 | 0x8773 InterColorProfile         | UNDEFINED |     1352 |      3020 | ...Happl. ..scnrRGB XYZ ....... ...
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END test/data/test.tiff
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$ exiv2 -pX test/data/test.tiff  | xmllint --format -
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<?xml version="1.0"?>
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<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
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<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 4.4.0-Exiv2">
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  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
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    <rdf:Description xmlns:dc="http://purl.org/dc/elements/1.1/" rdf:about="">
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      <dc:title>
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        <rdf:Alt>
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          <rdf:li xml:lang="x-default">this is a test image</rdf:li>
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        </rdf:Alt>
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      </dc:title>
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    </rdf:Description>
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  </rdf:RDF>
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</x:xmpmeta>
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<?xpacket end="w"?>
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$ </pre>You can use the output from _*<code>-pS</code>*_ to determine the location of the XMLPacket:<pre>$ exiv2 -pS test/data/test.tiff | grep XMLPacket 
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     262 | 0x02bc XMLPacket                 |      BYTE |     2505 |       514 | <?xpacket begin="..." id="W5M0Mp ...
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$ </pre>You can see the XMLPacket of 2505 bytes stored at offset 514.   You can extract the XMP with the following command which says:  set the block size to 1 byte, skip 514 bytes and extract 2505 bytes:
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<pre>$ dd bs=1 count=2505 skip=514 if=test/data/test.tiff | xmllint --format - 
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2505+0 records in
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2505+0 records out
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2505 bytes (2.5 kB) copied, 0.0064 s, 391 kB/s
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<?xml version="1.0"?>
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<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
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<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 4.4.0-Exiv2">
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  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
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    <rdf:Description xmlns:dc="http://purl.org/dc/elements/1.1/" rdf:about="">
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      <dc:title>
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        <rdf:Alt>
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          <rdf:li xml:lang="x-default">this is a test image</rdf:li>
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        </rdf:Alt>
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      </dc:title>
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    </rdf:Description>
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  </rdf:RDF>
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</x:xmpmeta>
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<?xpacket end="w"?>
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</pre>The option _*<code>-pX</code>*_ doesn't use dd to achieve the same result and is much more convenient to use.
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To demonstrate that the metadata block in a JPEG is a TIFF file, extract and print the structure.<pre>$ exiv2 -pS test/data/Reagan.jpg 
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$ exiv2 -pS test/data/Reagan.jpg
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STRUCTURE OF JPEG FILE: test/data/Reagan.jpg
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 address | marker       |  length | data
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       0 | 0xffd8 SOI  
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       2 | 0xffe1 APP1  |    5718 | Exif..MM.*......................
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    5722 | 0xffed APP13 |    3038 | Photoshop 3.0.8BIM..........Z...
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    8762 | 0xffe1 APP1  |    5329 | http://ns.adobe.com/xap/1.0/.<?x
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   14093 | 0xffe2 APP2  |     576 | ICC_PROFILE......0ADBE....mntrRG chunk 1/1
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   14671 | 0xffee APP14 |      14 | Adobe.d@......
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   14687 | 0xffdb DQT   |     132 
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   14821 | 0xffc0 SOF0  |      17 
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   14840 | 0xffdd DRI   |       4 
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   14846 | 0xffc4 DHT   |     418 
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   15266 | 0xffda SOS  
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$ </pre>  We can extract the APP1/Exif data as follows:<pre>$ dd bs=1 skip=$((2+2+8)) count=$((5718-8)) if=test/data/Reagan.jpg of=ReaganExif.tiff
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5710+0 records in
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5710+0 records out
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5710 bytes (5.7 kB) copied, 0.026688 s, 214 kB/s
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$ exiv2 -pS ReaganExif.tif 
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STRUCTURE OF TIFF FILE (MM): ReaganExif.tif
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 address |    tag                           |      type |    count |    offset | value
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      10 | 0x0100 ImageWidth                |     SHORT |        1 |  13107200 | 200
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      22 | 0x0101 ImageLength               |     SHORT |        1 |   8519680 | 130
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      34 | 0x0102 BitsPerSample             |     SHORT |        4 |       242 | 8 8 8 8
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      46 | 0x0103 Compression               |     SHORT |        1 |     65536 | 1
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      58 | 0x0106 PhotometricInterpretation |     SHORT |        1 |    131072 | 2
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      70 | 0x010e ImageDescription          |     ASCII |      403 |       250 | 040621-N-6536T-062.USS Ronald Re ...
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      82 | 0x010f Make                      |     ASCII |       18 |       653 | NIKON CORPORATION
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      94 | 0x0110 Model                     |     ASCII |       10 |       671 | NIKON D1X
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     106 | 0x0112 Orientation               |     SHORT |        1 |     65536 | 1
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     118 | 0x0115 SamplesPerPixel           |     SHORT |        1 |    262144 | 4
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     130 | 0x011a XResolution               |  RATIONAL |        1 |       681 | 3000000/10000
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     142 | 0x011b YResolution               |  RATIONAL |        1 |       689 | 3000000/10000
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     154 | 0x011c PlanarConfiguration       |     SHORT |        1 |     65536 | 1
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     166 | 0x0128 ResolutionUnit            |     SHORT |        1 |    131072 | 2
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     178 | 0x0131 Software                  |     ASCII |       40 |       697 | Adobe Photoshop Elements 12.0 Ma ...
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     190 | 0x0132 DateTime                  |     ASCII |       20 |       737 | 2016:09:13 11:58:16
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     202 | 0x013b Artist                    |     ASCII |       34 |       757 | Photographer..s Mate 3rd Class ( ...
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     214 | 0x8769 ExifTag                   |      LONG |        1 |       792 | 792
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     226 | 0x8825 GPSTag                    |      LONG |        1 |      1400 | 1400
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    1422 | 0x0103 Compression               |     SHORT |        1 |    393216 | 6
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    1434 | 0x011a XResolution               |  RATIONAL |        1 |      1498 | 72/1
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    1446 | 0x011b YResolution               |  RATIONAL |        1 |      1506 | 72/1
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    1458 | 0x0128 ResolutionUnit            |     SHORT |        1 |    131072 | 2
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    1470 | 0x0201 JPEGInterchangeFormat     |      LONG |        1 |      1514 | 1514
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    1482 | 0x0202 JPEGInterchangeFormatLeng |      LONG |        1 |      4196 | 4196
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END ReaganExif.tif
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$ </pre>The version of the exiv2 utility that ships with v0.26 later has an option _*<code>-pR</code>*_ which _Recursively_ prints the structure of an image file.  *_Recursively*_ means  the utility prints structures embedded within other structures.  For example, the Exif metadata in a JPEG is encoded as a TIFF embedded in the APP1/Exif segment of the JPEG.<pre>$ exiv2 -pR test/data/Reagan.jpg 
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STRUCTURE OF JPEG FILE: test/data/Reagan.jpg
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 address | marker       |  length | data
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       0 | 0xffd8 SOI  
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       2 | 0xffe1 APP1  |    5718 | Exif..MM.*......................
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  STRUCTURE OF TIFF FILE (MM): MemIo
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   address |    tag                           |      type |    count |    offset | value
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        10 | 0x0100 ImageWidth                |     SHORT |        1 |  13107200 | 200
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        22 | 0x0101 ImageLength               |     SHORT |        1 |   8519680 | 130
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        34 | 0x0102 BitsPerSample             |     SHORT |        4 |       242 | 8 8 8 8
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        46 | 0x0103 Compression               |     SHORT |        1 |     65536 | 1
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        58 | 0x0106 PhotometricInterpretation |     SHORT |        1 |    131072 | 2
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        70 | 0x010e ImageDescription          |     ASCII |      403 |       250 | 040621-N-6536T-062.USS Ronald Re ...
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        82 | 0x010f Make                      |     ASCII |       18 |       653 | NIKON CORPORATION
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        94 | 0x0110 Model                     |     ASCII |       10 |       671 | NIKON D1X
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       106 | 0x0112 Orientation               |     SHORT |        1 |     65536 | 1
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       118 | 0x0115 SamplesPerPixel           |     SHORT |        1 |    262144 | 4
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       130 | 0x011a XResolution               |  RATIONAL |        1 |       681 | 681/0
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       142 | 0x011b YResolution               |  RATIONAL |        1 |       689 | 689/0
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       154 | 0x011c PlanarConfiguration       |     SHORT |        1 |     65536 | 1
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       166 | 0x0128 ResolutionUnit            |     SHORT |        1 |    131072 | 2
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       178 | 0x0131 Software                  |     ASCII |       40 |       697 | Adobe Photoshop Elements 12.0 Ma ...
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       190 | 0x0132 DateTime                  |     ASCII |       20 |       737 | 2016:09:13 11:58:16
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       202 | 0x013b Artist                    |     ASCII |       34 |       757 | Photographer..s Mate 3rd Class ( ...
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       214 | 0x8769 ExifTag                   |      LONG |        1 |       792 | 792
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    STRUCTURE OF TIFF FILE (MM): MemIo
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     address |    tag                           |      type |    count |    offset | value
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         794 | 0x829a ExposureTime              |  RATIONAL |        1 |      1254 | 1254/0
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         806 | 0x829d FNumber                   |  RATIONAL |        1 |      1262 | 1262/0
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         818 | 0x8822 ExposureProgram           |     SHORT |        1 |     65536 | 1
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         830 | 0x9000 ExifVersion               | UNDEFINED |        4 | 808596016 | 0220
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         842 | 0x9003 DateTimeOriginal          |     ASCII |       20 |      1270 | 2004:06:21 23:37:53
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         854 | 0x9004 DateTimeDigitized         |     ASCII |       20 |      1290 | 2004:06:21 23:37:53
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         866 | 0x9101 ComponentsConfiguration   | UNDEFINED |        4 |  16909056 | ...
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         878 | 0x9102 CompressedBitsPerPixel    |  RATIONAL |        1 |      1310 | 1310/0
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         890 | 0x9201 ShutterSpeedValue         | SRATIONAL |        1 |      1318 | 1318/0
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         902 | 0x9202 ApertureValue             |  RATIONAL |        1 |      1326 | 1326/0
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         914 | 0x9204 ExposureBiasValue         | SRATIONAL |        1 |      1334 | 1334/0
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         926 | 0x9205 MaxApertureValue          |  RATIONAL |        1 |      1342 | 1342/0
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         938 | 0x9207 MeteringMode              |     SHORT |        1 |    131072 | 2
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         950 | 0x9208 LightSource               |     SHORT |        1 |    655360 | 10
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         962 | 0x9209 Flash                     |     SHORT |        1 |         0 | 0
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         974 | 0x920a FocalLength               |  RATIONAL |        1 |      1350 | 1350/0
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         986 | 0x9290 SubSecTime                |     ASCII |        3 | 808845312 | 06
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         998 | 0x9291 SubSecTimeOriginal        |     ASCII |        3 | 808845312 | 06
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        1010 | 0x9292 SubSecTimeDigitized       |     ASCII |        3 | 808845312 | 06
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        1022 | 0xa000 FlashpixVersion           | UNDEFINED |        4 | 808529968 | 0100
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        1034 | 0xa001 ColorSpace                |     SHORT |        1 |4294901760 | 65535
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        1046 | 0xa002 PixelXDimension           |      LONG |        1 |       200 | 200
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        1058 | 0xa003 PixelYDimension           |      LONG |        1 |       130 | 130
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        1070 | 0xa217 SensingMethod             |     SHORT |        1 |    131072 | 2
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        1082 | 0xa300 FileSource                | UNDEFINED |        1 |  50331648 | .
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        1094 | 0xa301 SceneType                 | UNDEFINED |        1 |  16777216 | .
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        1106 | 0xa401 CustomRendered            |     SHORT |        1 |         0 | 0
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        1118 | 0xa402 ExposureMode              |     SHORT |        1 |     65536 | 1
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        1130 | 0xa403 WhiteBalance              |     SHORT |        1 |     65536 | 1
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        1142 | 0xa404 DigitalZoomRatio          |  RATIONAL |        1 |      1358 | 1358/0
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        1154 | 0xa405 FocalLengthIn35mmFilm     |     SHORT |        1 |   4128768 | 63
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        1166 | 0xa406 SceneCaptureType          |     SHORT |        1 |         0 | 0
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        1178 | 0xa407 GainControl               |     SHORT |        1 |         0 | 0
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        1190 | 0xa408 Contrast                  |     SHORT |        1 |         0 | 0
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        1202 | 0xa409 Saturation                |     SHORT |        1 |         0 | 0
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        1214 | 0xa40a Sharpness                 |     SHORT |        1 |         0 | 0
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        1226 | 0xa40c SubjectDistanceRange      |     SHORT |        1 |         0 | 0
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        1238 | 0xa420 ImageUniqueID             |     ASCII |       33 |      1366 | 127c1377b054a3f65bf2754ebb24e7f2 ...
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    END MemIo
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       226 | 0x8825 GPSTag                    |      LONG |        1 |      1400 | 1400
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      1422 | 0x0103 Compression               |     SHORT |        1 |    393216 | 6
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      1434 | 0x011a XResolution               |  RATIONAL |        1 |      1498 | 1498/0
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      1446 | 0x011b YResolution               |  RATIONAL |        1 |      1506 | 1506/0
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      1458 | 0x0128 ResolutionUnit            |     SHORT |        1 |    131072 | 2
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      1470 | 0x0201 JPEGInterchangeFormat     |      LONG |        1 |      1514 | 1514
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      1482 | 0x0202 JPEGInterchangeFormatLeng |      LONG |        1 |      4196 | 4196
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  END MemIo
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    5722 | 0xffed APP13 |    3038 | Photoshop 3.0.8BIM..........Z...
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  Record | DataSet | Name                     | Length | Data
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       1 |      90 | CharacterSet             |      3 | .%G
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       1 |      90 | CharacterSet             |      3 | .%G
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       2 |       0 | RecordVersion            |      2 | ..
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       2 |     120 | Caption                  |    402 | 040621-N-6536T-062.USS Ronald Reagan (CV...
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       2 |     122 | Writer                   |      9 | Dir. NVNS
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       2 |      40 | SpecialInstructions      |     49 | Credit as U.S. Navy photo by Elizabeth T...
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       2 |      80 | Byline                   |     32 | Photographer..s Mate 3rd Class (
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       2 |      85 | BylineTitle              |     21 | U.S Navy Photographer
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       2 |     110 | Credit                   |      8 | U.S Navy
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       2 |     115 | Source                   |     24 | Navy Visual News Service
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       2 |       5 | ObjectName               |     18 | 040621-N-6536T-062
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       2 |      55 | DateCreated              |      8 | 20040621
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       2 |      60 | TimeCreated              |     11 | 000000+0000
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       2 |      62 | DigitizationDate         |      8 | 20040621
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       2 |      63 | DigitizationTime         |     11 | 233753-0400
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       2 |      90 | City                     |     19 | Straits of Magellan
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       2 |     101 | CountryName              |     13 | South America
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       2 |      15 | Category                 |      1 | N
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       2 |      20 | SuppCategory             |     12 | 703-614-9154
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       2 |      20 | SuppCategory             |     23 | navyvisualnews@navy.mil
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       2 |      20 | SuppCategory             |     11 | UNCLASSFIED
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       2 |      10 | Urgency                  |      1 | 5
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       2 |      25 | Keywords                 |     13 | ronald reagan
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       2 |      25 | Keywords                 |      6 | reagan
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       2 |      25 | Keywords                 |      6 | cvn 76
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       2 |      25 | Keywords                 |      6 | cvn-76
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       2 |      25 | Keywords                 |     18 | straights magellan
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       2 |      25 | Keywords                 |      8 | magellan
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       2 |      25 | Keywords                 |      7 | carrier
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       2 |      25 | Keywords                 |     12 | nimitz-class
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       2 |      25 | Keywords                 |      4 | ship
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       2 |      25 | Keywords                 |      8 | underway
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    8762 | 0xffe1 APP1  |    5329 | http://ns.adobe.com/xap/1.0/.<?x
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   14093 | 0xffe2 APP2  |     576 | ICC_PROFILE......0ADBE....mntrRG chunk 1/1
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   14671 | 0xffee APP14 |      14 | Adobe.d@......
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   14687 | 0xffdb DQT   |     132 
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   14821 | 0xffc0 SOF0  |      17 
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   14840 | 0xffdd DRI   |       4 
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   14846 | 0xffc4 DHT   |     418 
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   15266 | 0xffda SOS  
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$ </pre>