MWG Composite Tags

The Metadata Working Group (MWG) recommendations provide a set of rules to allow certain overlapping EXIF, IPTC and XMP tags to be reconciled when reading, and synchronized when writing. The ExifTool MWG module is designed to aid in the implementation of these recommendations. (See http://www.metadataworkinggroup.org/ for the complete MWG technical specifications.)

The table below lists special Composite tags which are used to access other tags based on the MWG 1.01 recommendations. These tags are only accessible when the MWG module is loaded. The MWG module is loaded automatically by the exiftool application if MWG is specified as a group for any tag on the command line, or manually with the -use MWG option. Via the API, the MWG module is loaded with "use Image::ExifTool::MWG".

When reading, the value of each MWG tag is Derived From the specified tags based on the MWG guidelines. When writing, the appropriate associated tags are written. The value of the IPTCDigest tag is updated automatically when the IPTC is changed if either the IPTCDigest tag didn't exist beforehand or its value agreed with the original IPTC digest (indicating that the XMP is synchronized with the IPTC). IPTC information is written only if the original file contained IPTC.

Loading the MWG module activates "strict MWG conformance mode", which has the effect of causing EXIF, IPTC and XMP in non-standard locations to be ignored when reading, as per the MWG recommendations. Instead, a "Warning" tag is generated when non-standard metadata is encountered. This feature may be disabled by setting $Image::ExifTool::MWG::strict = 0 in the ExifTool config file (or from your Perl script when using the API). Note that the behaviour when writing is not changed: ExifTool always creates new records only in the standard location, but writes new tags to any EXIF/IPTC/XMP records that exist.

A complication of the specification is that although the MWG:Creator property may consist of multiple values, the associated EXIF tag (EXIF:Artist) is only a simple string. To resolve this discrepancy the MWG recommends a technique which allows a list of values to be stored in a string by using a semicolon-space separator (with quotes around values if necessary). When the MWG module is loaded, ExifTool automatically implements this policy and changes EXIF:Artist to a list-type tag.

Tag Name WritableDerived FromValues / Notes
City Y IPTC:City
XMP-photoshop:City
CurrentIPTCDigest
IPTCDigest
 
Copyright Y EXIF:Copyright
IPTC:CopyrightNotice
XMP-dc:Rights
CurrentIPTCDigest
IPTCDigest
 
Country Y IPTC:Country-PrimaryLocationName
XMP-photoshop:Country
CurrentIPTCDigest
IPTCDigest
 
CreateDate Y EXIF:CreateDate
EXIF:SubSecTimeDigitized
IPTC:DigitalCreationDate
IPTC:DigitalCreationTime
XMP-xmp:CreateDate
CurrentIPTCDigest
IPTCDigest
("creation date of the digital representation" - MWG)
Creator Y+ EXIF:Artist
IPTC:By-line
XMP-dc:Creator
CurrentIPTCDigest
IPTCDigest
 
DateTimeOriginal Y EXIF:DateTimeOriginal
EXIF:SubSecTimeOriginal
IPTC:DateCreated
IPTC:TimeCreated
XMP-photoshop:DateCreated
CurrentIPTCDigest
IPTCDigest
("creation date of the intellectual content being shown" - MWG)
Description Y EXIF:ImageDescription
IPTC:Caption-Abstract
XMP-dc:Description
CurrentIPTCDigest
IPTCDigest
 
Keywords Y+ IPTC:Keywords
XMP-dc:Subject
CurrentIPTCDigest
IPTCDigest
 
Location Y IPTC:Sub-location
XMP-iptcCore:Location
CurrentIPTCDigest
IPTCDigest
 
ModifyDate Y EXIF:ModifyDate
EXIF:SubSecTime
XMP-xmp:ModifyDate
CurrentIPTCDigest
IPTCDigest
("modification date of the digital image file" - MWG)
Orientation Y EXIF:Orientation 1 = Horizontal (normal)
2 = Mirror horizontal
3 = Rotate 180
4 = Mirror vertical
5 = Mirror horizontal and rotate 270 CW
6 = Rotate 90 CW
7 = Mirror horizontal and rotate 90 CW
8 = Rotate 270 CW
Rating Y XMP-xmp:Rating  
State Y IPTC:Province-State
XMP-photoshop:State
CurrentIPTCDigest
IPTCDigest
 

(This document generated automatically by Image::ExifTool::BuildTagLookup)
Last revised Oct 4, 2010

<-- ExifTool Tag Names