Author Topic: A few questions about Tags  (Read 2135 times)

Tarn

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A few questions about Tags
« on: March 28, 2013, 04:40:51 AM »
Hi Phil,

    Using the same file, I added information to a number of tags via PhotoShop CS2, and saved it as 5253a.psd. Next I issued the following commands:
-a -u -g1 5253a.psd >> 5253.txt
echo. >> 5253.txt
echo. >> 5253.txt
-a -u -g1 5253.psd >> 5253.txt
    This gave me a file that listed all of the Tags in 5253a.psd, two blank lines, and all the tags in 5253.psd.

    The first question is: "Artist" shows up in 5253a.psd, under the IDFO heading; but not in 5253.psd. Yet when I search for -IDFO:Artist, it does not show in either file; while a search for -Artist does. Is the Artist tag not in the IDFO group?

    Another question, and I guess I'm just not understanding the, I'll call it "existence" of Tags, a search for the Artist tag, without the -f option, Artist does not print out unless it has been assigned a value. I understand that part. In a search with the -f option, the tag name is displayed, followed by a dash. I understand that, too. What I don't understand is: Does the Artist tag actually exist in the file, but simply has no data in it? Or is it created when I issue a command like -Artist=me?
    Along with that, a search for -Artist and -TwoDogsAndABeer, without the -f option reveals nothing for either tag. Obviously, as Artist has nothing in it and TwoDogsAndABeer doesn't even exist. Yet, with the -f option, they both are displayed and have a dash folling them. At this point, I can write information to -Artist, but not -TwoDogsAndABeer. Why is that? Or maybe I should ask why does it seem that I can "create", so to speak, the Artist tag (which does not show up with the -a -u -g1 search) but I cannot create the TwoDogs tag?

Thanks in advance.

Phil Harvey

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Re: A few questions about Tags
« Reply #1 on: March 28, 2013, 07:17:11 AM »
   The first question is: "Artist" shows up in 5253a.psd, under the IDFO heading; but not in 5253.psd. Yet when I search for -IDFO:Artist, it does not show in either file; while a search for -Artist does. Is the Artist tag not in the IDFO group?

It should be in IFD0, but I have seen it written incorrectly into the ExifIFD by some software.

Quote
    Another question, and I guess I'm just not understanding the, I'll call it "existence" of Tags, a search for the Artist tag, without the -f option, Artist does not print out unless it has been assigned a value. I understand that part. In a search with the -f option, the tag name is displayed, followed by a dash. I understand that, too. What I don't understand is: Does the Artist tag actually exist in the file, but simply has no data in it? Or is it created when I issue a command like -Artist=me?

If the Artist tag exists but is empty, it will show up as an empty string (with or without -f).  If it shows up as a "-" with -f then it doesn't exist (or contains the string "-", which is unlikely).

Quote
I can write information to -Artist, but not -TwoDogsAndABeer. Why is that?

You can only write tags that are known to ExifTool.  See the EXIF tag name documentation for a list of EXIF tags.  The reason is that ExifTool must know the Tag ID, format and location to write a tag before it can be created.

- Phil
...where DIR is the name of a directory/folder containing the images.  On Mac/Linux, use single quotes (') instead of double quotes (") around arguments containing a dollar sign ($).

Tarn

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Re: A few questions about Tags
« Reply #2 on: March 29, 2013, 01:30:52 AM »
Hi Phil,

Quote
You can only write tags that are known to ExifTool.  See the EXIF tag name documentation for a list of EXIF tags.  The reason is that ExifTool must know the Tag ID, format and location to write a tag before it can be created.

    The light just came on! Okay! I got it.

Thanks