GetValue syntax

[Archive]

[Originally posted by scarvalhojr on 2007-05-31 13:48:06-07]

Hi,

This might be a stupid question, but... I'm writing a script to fix a few metadata fields from my camera files at once, but I'm struggling to find the correct syntax for getting specific fields with GetValue.

Code:

# this works (and returns the value on "Composite:ISO" if Exif:ISO is empty)
$exif_iso = $exifTool->GetValue("ISO");

# but these don't
$exif_iso = $exifTool->GetValue("Exif:ISO");
$exif_iso = $exifTool->GetValue("Composite:ISO");

I've tried a few variations but I can't seem to find how to do it...

[Archive]

[Originally posted by exiftool on 2007-05-31 18:23:58-07]

Admittedly this is a bit confusing, but GetValue() takes a
tag key, which resembles a tag name, but has a copy number
appended if there is more than one tag with the same name.
The tag keys are the keys of the $info array returned by
ImageInfo() or GetInfo().

If you want to specify a particular group, either specify
it in the call to ImageInfo() or GetInfo(), or check the
group of all returned keys using GetGroup(), and select
the desired group:tag that way.  ie)

Code:

my $info = $exifTool->ImageInfo($file, 'ISO');
my $tag;  # note: this is a tag key
foreach $tag (keys %$info) {
    next unless $exifTool->GetGroup($tag) eq 'EXIF';
    print "EXIF:ISO is $$info{$tag}\n";
}

or like this:

Code:

$exifTool->ExtractInfo($file);
my $info = $exifTool->GetInfo('EXIF:ISO');
my ($tag) = keys %$info;
print "EXIF:ISO is $$info{$tag}\n" if $tag;

Disclaimer: This code is off the top of my head -- I didn't test it out
to check for typos.

I hope this helps.

- Phil

[Archive]

[Originally posted by scarvalhojr on 2007-06-01 16:23:42-07]

Thanks for clarifying this, Phil! This is what I'm doing now:

Code:

my @tags = qw(exif:iso composite:iso makernotes:canonexposuremode...);
$exifTool->ExtractInfo($file);
$info = $exifTool->GetInfo(\@tags);
$exif_iso = $$info{$tags[0]};
$comp_iso = $$info{$tags[1]};
$canonmode = $$info{$tags[2]};

...which seems to work fine. I use this inside a loop to process several files. Is that ok?

[Archive]

[Originally posted by exiftool on 2007-06-01 16:55:54-07]

What you have done is a bit dangerous because there isn't necessarily a
1:1 correspondence between the tags you request and the tag keys which
are returned.  However, this is only a problem if there are multiple entries
of a specified tag.  Since you are very specific about the tags you request
(ie. you specify a group), this is unlikely, yet it is possible to have two
EXIF:ISO tags in the same file.  So to be safe, you should set the Duplicates
option to 0 so only one value is returned for each requested tag.

With Duplicates set to 0, I think what you have done should be fine.

- Phil