## MWG Composite Tags

This table lists special Composite tags which are used to access other tags based on the Metadata Working Group 1.01 recommendations. These tags are only accessible when the MWG module is loaded (via `-use MWG` on the command line, or `use Image::ExifTool::MWG` in the API). When reading, the value of each MWG tag is Derived From the specified tags based on the MWG guidelines. When writing, 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. For more information about the MWG recommendation, see http://www.metadataworkinggroup.org/.

A problem with the MWG specification is that although XMP:Creator and IPTC:By-line are list-type tags, the corresponding EXIF tag, EXIF:Artist, is not. So, short of changing the EXIF specification to allow EXIF:Artist to store a list of strings, the only reasonable alternative is to NOT allow MWG:Creator to be written as a list. (It is insufficient to say that EXIF:Artist may store multiple strings separated with semicolons because there is nothing in any of the MWG, EXIF, XMP or IPTC specifications that states an individual Creator string may not contain a semicolon, and for this to be feasible all of these specifications would require this restriction.) For this reason, the MWG:Creator tag is written as a single string. Multiple names may of course be written within the string (and it would be reasonable to separate them with semicolons as suggested by the MWG and EXIF specifications), but this tag is not treated as a list by ExifTool when writing.

Another potential stumbling block for MWG compatibility is the fact that ExifTool will quite happily read and write (but not create) EXIF, IPTC and XMP which has been stored in non-standard locations while the MWG recommendation states that this metadata should be ignored. This may lead to non-compliant behaviour for these types of files.

> Tag Name | Writable | Derived From | Values / 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 | (NOT a list-type tag. See "A problem with the MWG specification" above)
> 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 28, 2009

<-- ExifTool Tag Names