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<h1 class='up'>ExifTool FAQ</h1>
<font size='+1'><b>Index</b></font>
<table><tr><td><ol>
<li><a href="#Q1">Discussion forum</a>
<li><a href="#Q2">Determining tag names</a>
<li><a href="#Q3">Problems with duplicate tags</a>
<li><a href="#Q4">Aperture and shutter speed</a>
<li><a href="#Q5">Date and time formats</a>
<li><a href="#Q6">"Can't convert TAG" errors</a>
<li><a href="#Q7">Deleting all EXIF from a TIFF</a>
</ol></td><td valign='top'><ol start=8>
<li><a href="#Q8">Writing the Make or Model tag</a>
<li><a href="#Q9">Tag locations when copying</a>
<li><a href="#Q10">Coded character sets</a>
<li><a href="#Q11">User-defined tags</a>
<li><a href="#Q12">Database import</a>
<li><a href="#Q13">Output file size</a>
</ol></td></tr></table>
<hr>
<a name="Q1"></a>
<p>1. <b>"Is there a forum for discussing ExifTool issues?"</b></p>
<blockquote>
ExifTool issues can be discussed on the CPAN forum at
<a href="http://www.cpanforum.com/dist/Image-ExifTool">http://www.cpanforum.com/dist/Image-ExifTool</a>
</blockquote>
<a name="Q2"></a>
<p>2. <b>"How do I determine the tag name for some information?"</b></p>
<blockquote>
When you run exiftool, by default it prints descriptions, not tag names, for
the information it extracts. To print the tag names instead, use the
<code>‑s</code> option. Also, see the <a href="TagNames/index.html">tag names
documentation</a> for a complete list of available tag names.</blockquote>
<blockquote>Tag names may be optionally prefixed by a family 0 or 1 group name
to specify a particular information type or location. Use the
<code>‑g0</code> and <code>‑g1</code> (or
<code>‑G0</code> and <code>‑G1</code>) options when extracting
information to see the corresponding group names.
</blockquote>
<a name="Q3"></a>
<p>3a. <b>"ExifTool reports the wrong value for a tag"</b>,
<br>3b. <b>"ExifTool doesn't write a tag properly"</b>, or
<br>3c. <b>"Other software can't read information written by ExifTool"</b></p>
<blockquote>
Make sure you are looking at the right information. Information may be
duplicated in different locations within an image. When in doubt, use
"<code>exiftool -a -G1 FILENAME</code>" to show all information and the
locations in the file. In this command, <code>‑a</code> allows
duplicate tags to be displayed, <code>‑G1</code> shows the family 1
group name (ie. the location) of each tag, and "<code>FILENAME</code>" is the
name of your image file. Also, it may be helpful to add <code>‑s</code>
to show the actual tag names instead of the descriptions.</blockquote>
<blockquote>If you are having problems with other software reading information
written by ExifTool, if possible try first writing the information from the
other software, then use ExifTool to determine where the information was
written. Once you know where it should go, you can use ExifTool to write to this
location.</blockquote>
<blockquote>You can read or write information in a specific location by
prefixing the tag name on the command line with the desired group name. ie)
"<code>‑ExifIFD:DateTimeOriginal</code>"
</blockquote>
<a name="Q4"></a>
<p>4. <b>"ExifTool reports more than one shutter speed or aperture value, and
they are slightly different"</b></p>
<blockquote>
There are a number of different ways that aperture and shutter speed information
get saved in an image. The standard EXIF values (EXIF:FNumber and
EXIF:ExposureTime) should correspond to the values displayed by your camera, but
these values may have been rounded off. The APEX values (EXIF:ApertureValue and
EXIF:ShutterSpeedValue) may be different due to their own round-off errors. If
available, the MakerNotes values are the typically the most accurate because
they haven't been rounded off at all, but you may see odd values like 1/102
instead of 1/100, etc.
</blockquote>
<a name="Q5"></a>
<p>5. <b>"How do I format date and time information for writing?"</b></p>
<blockquote>All information (including date/time information) is written in the
same format as it is read out. ExifTool converts all date and time information
to standard EXIF format, so this is also the way it is specified when writing.
The standard EXIF date/time format is "<code>YYYY:MM:DD hh:mm:ss</code>",
and a timezone may be specified by adding
"<code>+hh:mm</code>", "<code>‑hh:mm</code>" or "<code>Z</code>".
If the meta information format requires a timezone and one is not specified,
"<code>+00:00</code>" (or "<code>Z</code>") is assumed. For example:
<pre>exiftool "-dateTimeOriginal=2005:10:23 20:06:34-05:00" a.jpg
</pre>
</blockquote>
<a name="Q6"></a>
<p>6. <b>"I get the following error when writing a tag:
'<code>Can't convert TAG (not in PrintConv)</code>'"</b></p>
<blockquote>
ExifTool applies a print conversion (PrintConv) to the printed values of all
tags. These print conversions are documented for all tags in the <b>Values</b>
column of the <a href="TagNames/index.html">Tag Name documentation</a>. For
example, the GPSAltitudeRef tag defines the following conversions:
<pre>0 = Above Sea Level
1 = Below Sea Level
</pre>
For this tag, a value of '0' is printed as 'Above Sea Level', and '1' is printed
as 'Below Sea Level'. Reading and writing with ExifTool is symmetrical, so a
value that is printed as 'Above Sea Level' must also be written in that form.
(ie. The inverse print conversion is applied when writing values.) For example,
to write GPSAltitudeRef you can type:
<pre>exiftool "-gpsaltituderef=Above Sea Level" image.jpg
</pre>
or any unambiguous short form may be used and ExifTool will know what you mean, ie)
<pre>exiftool -gpsaltituderef=above image.jpg
</pre>
Alternatively, the print conversion can be disabled with the <code>‑n</code>
option. In this case the printed value of GPSAltitudeRef will be '0' or '1', and
the value is written in the same way. So the following command has exactly the
same effect as the commands above:
<pre>exiftool -gpsaltituderef=0 -n image.jpg
</pre>
Integer values may also be specified in hexadecimal (with a leading '0x'). For
example, the following commands are all valid and accomplish the same thing:
<pre>exiftool -flash=1 -n image.jpg
exiftool -flash=0x1 -n image.jpg
exiftool -flash=fired image.jpg
</pre>
Programmers: If you are calling Image::ExifTool functions from your own script,
the two techniques look like this:
<pre>$exifTool->SetNewValue(GPSAltitudeRef => 'Above Sea Level');
$exifTool->SetNewValue(GPSAltitudeRef => 0, Type => 'ValueConv');
</pre>
</blockquote>
<a name="Q7"></a>
<p>7. <b>"I can't delete all EXIF information from a TIFF file using
'<code>exiftool -exif:all= img.tif</code>'"</b></p>
<blockquote>
This is because of the way a TIFF file is structured. With a JPEG image, this
command will remove IFD0 (the main Image File Directory) as well as any
subdirectories, thus removing all EXIF information. But with the TIFF format,
the main image itself is stored in IFD0, so deleting this directory would
destroy the image. Instead, ExifTool just deletes the ExifIFD subdirectory, so
any information stored in other directories is preserved.</blockquote>
<blockquote>Use "<code>exiftool -a -G1 -s img.tif</code>" to
see where the information is stored. Any information remaining in other IFD's
must be deleted separately from a TIFF file if desired.
</blockquote>
<a name="Q8"></a>
<p>8a. <b>"All maker note information is lost if I change the Make or Model tag"</b> or
<br>8b. <b>"I can't copy maker note information to an image"</b></p>
<blockquote>
The Make and Model tags are used by some image utilities (including ExifTool) to
determine the format of the maker note information. Deleting or changing either
of these tags may prevent these utilities from recognizing or properly
interpreting the maker notes. Also beware that the maker notes information may
be damaged if an image is edited when the maker notes are not properly
recognized. So it is a good idea not to edit the Make and Model tags in the
first place.</blockquote>
<blockquote>If you really want to delete the Make and Model information, you
might as well delete the maker notes too. You can do this with the following
command:
<pre>exiftool -make= -model= -makernotes:all= image.jpg
</pre>
For the same reason, maker notes can not be copied to an image with an
incompatible Make or Model. To do this, the Make and Model tags must also be
copied. ie)
<pre>exiftool -tagsfromfile src.jpg -makernotes -make -model dst.jpg
</pre>
</blockquote>
<a name="Q9"></a>
<p>9a. <b>"The information is different when I copy all tags to a new file"</b>, or
<br>9b. <b>"The tag locations change when I use <code>‑tagsfromfile</code>
to copy information"</b></p>
<blockquote>
This feature is explained in the
<a href="exiftool_pod.html#item__2dtagsfromfile_srcfile_or_fmt">exiftool
application documentation</a>, but the question is common enough that it is
discussed here in more detail.</blockquote>
<blockquote>By default, ExifTool will store information in preferred locations
when either writing new information or copying information between files. This
freedom allows ExifTool to write or copy information to files of different
formats without requiring the user to know details about where the information
is stored.</blockquote>
<blockquote>The preferred locations for information written to JPEG images are
1) EXIF, 2) IPTC, 3) XMP and 4) MakerNotes. As an example, information
extracted from the maker notes will be preferentially written (on a tag-by-tag
basis) in EXIF format when copying information between two JPEG images. But if
a specific tag doesn't exist in EXIF, then the tag is written to the first valid
group in the order specified above. The advantage of "translating" the
information to EXIF is that it then becomes readable by applications which only
support standard EXIF. The disadvantage is that you don't get an exact copy of
the original information structure.</blockquote>
<blockquote>But ExifTool gives you the ability to customize this behaviour to
write the information to wherever you want. This is done by specifying a group
name for the tag(s) to be copied. This applies even if the group name is
"<code>all</code>", in which case the original group is preserved. So to copy
all information and preserve the original structure, use this syntax:
<pre>exiftool -tagsfromfile src.jpg -all:all dst.jpg
</pre>
By specifying a group name with "<code>‑all:all</code>", the location of the
information is preserved. (Specifically, since no destination tag was
specified the source group "<code>all</code>" was assumed, thus preserving
the original group.)</blockquote>
<blockquote>Here are some examples to show you the type of control you have over
where the information is written. All commands in each example are equivalent:
<pre><span class='blk'># copy all tags to preferred groups (no destination group)</span>
exiftool -tagsfromfile src.jpg dst.jpg
exiftool -tagsfromfile src.jpg -all dst.jpg
exiftool -tagsfromfile src.jpg "-all>all" dst.jpg
exiftool -tagsfromfile src.jpg "-all:all>all" dst.jpg
<span class='blk'># copy all tags, preserving original group (destination group 'all')</span>
exiftool -tagsfromfile src.jpg -all:all dst.jpg
exiftool -tagsfromfile src.jpg "-all>all:all" dst.jpg
exiftool -tagsfromfile src.jpg "-all:all>all:all" dst.jpg
<span class='blk'># copy all tags to EXIF group only (destination group 'exif')</span>
exiftool -tagsfromfile src.jpg "-all>exif:all" dst.jpg
exiftool -tagsfromfile src.jpg "-all:all>exif:all" dst.jpg
<span class='blk'># copy XMP tags to XMP group (destination group 'xmp' or 'all')</span>
exiftool -tagsfromfile src.jpg "-xmp:all" dst.jpg
exiftool -tagsfromfile src.jpg "-xmp:all>xmp:all" dst.jpg
exiftool -tagsfromfile src.jpg "-xmp:all>all:all" dst.jpg
<span class='blk'># copy XMP tags to preferred groups (no destination group)</span>
exiftool -tagsfromfile src.jpg "-xmp:all>all" dst.jpg
<span class='blk'># copy XMP tags to EXIF only (destination group 'exif')</span>
exiftool -tagsfromfile src.jpg "-xmp:all>exif:all" dst.jpg
</pre>
The same rules illustrated above also apply when copying individual tags.</blockquote>
<blockquote>Note: If no destination group is specified, a new tag is created if
necessary only in the preferred group, but if the same tag already exists in
another group, then this information is also updated. (Otherwise inconsistent
values for the same information would exist in different locations. Of course,
you can always generate inconsistencies like this if you really want to by
specifically writing contradictory information to different groups.)
</blockquote>
<a name="Q10"></a>
<p>10. <b>"How does ExifTool handle coded character sets?"</b></p>
<blockquote>
Certain meta information formats allow coded character sets other than plain
ASCII. Unless otherwise specified, 8-bit encodings are passed straight through
ExifTool without translation, and multi-byte encodings are translated to UTF-8
by default, or Windows Latin1 with the <code>‑L</code> option (or by
setting the "<code>Charset</code>" option to "<code>Latin</code>" via the API).
When writing, the inverse translation is performed. (Alternatively, special
characters may be translated to HTML character entities by using the
<code>‑E</code> option, but this only applies when reading.) More
specific details are given below about how character coding is handled for EXIF,
IPTC, XMP and ID3 information:</blockquote>
<blockquote><b>EXIF</b>: Most textual EXIF information is stored in ASCII
format, however some EXIF tags (UserComment, GPSProcessingMethod and
GPSAreaInformation) may be also be encoded in Unicode or JIS. When reading
information, Unicode text is translated to UTF-8, or Windows Latin1
with the <code>‑L</code> option. Other encodings are not translated.
When writing, text is stored as ASCII unless the string contains special
characters, in which case it is translated from UTF-8 or Latin1 (depending on
the <code>‑L</code> option) and stored as Unicode. The EXIF "XP" tags
(XPTitle, XPComment, etc) are always stored as Unicode, and are read and written
as either UTF-8, or Windows Latin1 with the <code>‑L</code>
option.</blockquote>
<blockquote><b>IPTC</b>: The value of the IPTC:CodedCharacterSet tag determines
how the internal IPTC string values are interpreted. If CodedCharacterSet
exists and has a value of "<code>UTF8</code>" (or
"<code>ESC % G</code>") then string values are assumed to be stored as
UTF-8, otherwise Latin1 (cp1252) coding is assumed. When reading, these strings
are translated to UTF-8 by default, or Latin1 with the <code>‑L</code>
option. When writing, the inverse translation is performed. No translation is
done if the internal (IPTC) and external (ExifTool) character sets are the same.
Note that ISO 2022 character set shifting is not supported. Instead, a warning
is issued and the string is not translated if an ISO 2022 shift code is found.
See the <a href="http://www.iptc.org/IIM/">IPTC specification</a> for more
information about IPTC character coding.</blockquote>
<blockquote><b>XMP</b>: Exiftool reads XMP encoded as UTF-8, UTF-16 or UTF-32,
and converts them all to UTF-8 internally. Also, all XML character entity
references and numeric character references are converted. When writing,
ExifTool always encodes XMP as UTF-8, converting the following 5 characters to
XML character references: <code>& < > ' "</code>. By default
no further translation is performed, however the <code>‑L</code> option
may be used used to translate text to Windows Latin1 when reading or from
Windows Latin1 when writing.</blockquote>
<blockquote><b>ID3</b>: The ID3v1 specification officially supports only ISO
8859-1 encoding although some applications may incorrectly use other character
sets. ExifTool assumes proper ISO 8859-1 encoding and translates to UTF-8 by
default, or disables translation with the <code>‑L</code> option (since
ISO 8859-1 is a subset of Windows Latin1). ID3v2 text is may be stored with a
number of different encodings, and ExifTool translates them all to UTF-8 by
default or Windows Latin1 with the <code>‑L</code> option. ExifTool does
not currently write ID3 information.</blockquote>
<a name="Q11"></a>
<p>11. <b>"My user-defined tags don't work"</b></p>
<blockquote>
For examples of how to add user-defined tags, see the
<a href="config.html">ExifTool_config</a> file in the ExifTool distribution. To
activate this file, rename it to "<code>.ExifTool_config</code>" and copy it to
your <b>HOME</b> directory. With this installed, you should be able to write and
read the example tags (such as "<code>NewXMPxxxTag1</code>"). Try this first
before you attempt to define your own tags.</blockquote>
<blockquote>If this doesn't work, the most common problem is that the
"<code>.ExifTool_config</code>" configuration file isn't getting loaded
properly, and there are two things you
can try: 1) Set either the <b>HOME</b> or the <b>EXIFTOOL_HOME</b> environment
variable to the name of the directory where you put your
"<code>.ExifTool_config</code>" file, or 2) put the config file in the same
directory as the exiftool script. (Also, be sure the config filename starts
with a dot! In the Windows GUI you may be not be able to generate a file name
that starts with a '<code>.</code>', but it can be done from the command line
using the '<code>rename</code>' command.)</blockquote>
<blockquote>If necessary, you can verify that ExifTool is loading your config
file by adding the following line to your file:
<pre>print "LOADED!\n";
</pre>
If you see a "<code>LOADED!</code>" message when you run exiftool, but your new
tags still don't work, make sure you are using the proper tag name and that the
file you are writing can support these names. Try copying the
"<code>t/images/Writer.jpg</code>" file from the distribution and running
exiftool with the following command:
<pre>exiftool -v3 -NewXMPxxxTag1=test Writer.jpg
</pre>
If ExifTool recognizes the new tag, the first line of output from this command
should be
<pre>"Writing XMP-xxx:NewXMPxxxTag1"
</pre>
Then you can read back the new tag with "<code>exiftool -s Writer.jpg</code>".
</blockquote>
<a name="Q12"></a>
<p>12. <b>"How do I import information into a database from exiftool?"</b></p>
<blockquote>
It is usually easiest to import information which is formatted as a
tab-delimited list of values. The following exiftool options may be useful
for this purpose:
<pre>-t - use a tab instead of spaces to separate output values
-S - very short format (with -t, prints only tag values)
-q - quiet (supresses any other messages)
-f - force '-' to be printed for non-existent values
-r - recursively process files in subdirectories
</pre>
And here is an example of an actual command using these options:
<pre>exiftool -t -S -q -f -r -filename -aperture -ISO t/images > out.txt
</pre>
This command recursively processes all images in the "<code>t/images</code>"
directory, extracting FileName, Aperture and ISO tags, and writing the
output to a file called "<code>out.txt</code>". After the command has
executed, the output file will contain information in the following format:
<pre>Canon.jpg 14.0 100
Casio.jpg 2.0 -
Nikon.nef 3.5 200
OlympusE1.jpg 4.5 400
</pre>
It should be possible to import a file like this directly into most database
applications. On the command line, any list of tag names may be used, and
any number of file or directory names may be specified. (Hint: If your
command line starts to get too long, you may want to look into using the
<code>‑@</code> option and/or the <a href="index.html#shortcut">ShortCut</a>
feature).
</blockquote>
<a name="Q13"></a>
<p>13. <b>"Why is my file smaller after I use ExifTool to write information?"</b></p>
<blockquote>
There are various specific reasons why this can happen, but the general answer
is: When ExifTool writes an image, the meta information may be restructured in
such a way that it takes less space than in the original file.</blockquote>
<blockquote>For instance, the EXIF/TIFF standard allows for blocks of
unreferenced data to exist in an image. Some digital cameras write JPEG or
TIFF-based RAW files which contain large blocks of unused data, usually filled
with binary zeros. The reason for this could be to simplify camera algorithms
by allowing variable-sized information to be written at fixed offsets in the
output image. When ExifTool rewrites an image it does not copy these unused
blocks. This can result in a significant reduction in file size for some
images.
</blockquote>
<blockquote>Also, the size of an XMP record may easily shrink or grow when it is
rewritten, even if no meta information is changed. This is partly due to the
fact that the XMP specification recommends a few KB of padding at the end of the
record (ExifTool adds 2424 bytes by default), and partly due to the flexibility
of the XMP format which allows the information to be written in various styles,
some of which are more compact than others.
</blockquote>
<hr>
<i>Last revised Apr. 30, 2007</i>
<p class='lf'><a href="index.html"><-- Back to ExifTool home page</a></p>
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