XMP vs. IPTC – what are the differences?

If you have searched for this article specifically, then you probably already know that the topic is about photometadata. And you are most likely asking yourself exactly that: What is the difference between XMP and IPTC?

There are many half-baked statements about this on the internet and even experienced professional photographers are regularly mistaken here. The reason for this is a categorical misunderstanding. A definition is needed to clear this up. Because if you only talk about IPTC, it is ambiguous. Various things can be meant. We will explain later what these are. First of all, suffice it to say that the title of this article should actually be: XMP vs. IPTC-IIM.

Schema and format are not the same

A digital metadata standard must take at least two aspects into account. On the one hand, the metadata fields need to be defined: What should be captured? Which and how many characters should be permitted? Etc. On the other hand, it must be specified how (in what form) and where the data should be saved (in a separate sidecar file or in a specific segement of the main file). The sum of defined metadata fields is referred to as the metadata schema, while the technical aspects of storage relate to the metadata format.

This means that only a comparison between data formats or between schemas can be meaningful, but not between format and schema.

What is the IPTC-IIM standard?

The abbreviation IIM stands for Information Interchange Model. This was the first metadata standard specifically intended for the exchange of digital images. It was developed by the International Press Telecommunications Council, or IPTC for short. The first version was published in 1991.

In 1994, Adobe made it possible to embed IPTC-IIM-compliant metadata directly into the header area of JPEG, TIFF or PSD files with Photoshop. The so-called IPTC header was born and established itself as the format for descriptive photo metadata (for technical metadata, Exif was added in 1995).

What is XMP?

XMP stands for Extensible Metadata Platform, although the term platform seems a little overstated. Just remember that with XMP, Adobe developed a technically improved metadata standard and made it available in 2001. It is based on the RDF/XML syntax and is much more flexible than IPTC-IIM.

Now comes the crucial point: XMP is designed in such a way that it can be used to map very different schemas, including the IPTC schema (divided into a main and an extended schema: IPTC Core and IPTC Extension).

The status quo of IPTC-IIM

The IPTC workgroup continues to develop the above-mentioned schemas to this day. With the Information Interchange Model, the situation is different. Further development of the format was discontinued in 1997. A minor adjustment was made in 2014, but that was it. IPTC-IIM is therefore considered as technically obsolete legacy format. Nevertheless, it is still supported by many image management programs and is still in use, especially in older archive systems. To maximize compatibility, descriptive photo metadata is therefore often created multiple times within a file: in the IIM and XMP headers and sometimes also in Exif fields.

The status quo of XMP

XMP not only offers support for numerous image and graphic formats, but also for many video and audio formats as well as for PDF documents. Since 2012, the core part of the XMP specifications constitutes the ISO 16684-1 standard. Due to the aforementioned flexibility in mapping different schemas, XMP is therefore not only used by the IPTC Council, but also by other standardization initiatives like DCMI, MWG or W3C for metadata implementation. This is why they are also referred to as XMP standards (with deliberate emphasis on the plural).

How is the IPTC metadata standard defined today?

As the name suggests, the IPTC Photo Metadata Standard was explicitly developed for digital photos and also for photo digitizations (scanned analog photos), but not for video files, vector graphics or documents. It contains all the instructions and information required to save the two IPTC schemas within a specific metadata format. Since 2004, XMP is designated for the implementation of IPTC-compliant metadata:

The IPTC standard is therefore also an XMP standard (!)

You should keep this possibly surprising realization in mind.

Deep Dive – IIM and XMP at code level

The IIM format uses numerical identifiers for the arrangement of the metadata fields, each identifier is stored as a single byte (octet). There is a prefixed area (envelope record) with 14 fields (6 of which are mandatory fields) and the main area (application record) with 57 possible fields and one mandatory field. For example, the field for the image description (caption) has the identifier 2:120, that for the intended character encoding 1:90, whereby the preceding number results from the position of the entry:

1 = Information is in the envelope record.

2 = Information is in the application record.

In fact, only the value after the colon is saved. The identifier for the image description (120) would then look like this in binary code: 01111000

A text string with a maximum size of 2000 bytes is designated for the caption field. The text is encoded as specified under 1:90 in the envelope record (usually with UTF-8 in order to be able to display special characters).

XMP data, on the other hand, consists of a single (long) text string. It is UTF-encoded and always begins with this specific sequence:

When using UTF-8, the corresponding byte pattern would look like this in hexadecimal notation:

3C 3F 78 70 61 63 6B 65
74 20 62 65 67 69 6E 3D

Software that supports XMP therefore always scans certain file segments (APP1 in case of JPEG files) for this byte pattern. With IIM, the situation is similar.

XMP uses the markup language XML. As with HTML, identifiers placed in angle brackets act as start and end tags. This may also explain why developers usualy speak of XMP tags (and not of fields).

According to the IPTC Extension schema, an entry for the city in which a photo was taken (LocationCreatedCity) would then look like this:

What advantages does XMP have over IIM?

Compatibility

Let’s not kid ourselves. IPTC-IIM is only intended for the file formats JPEG, TIFF and PSD (Photoshop); modern image formats such as WebP or HEIC do not support it. Although an IPTC-IIM header can also be “imposed” on a few less well-known file formats by using appropriate tools, IIM still is a discontinued model.

XMP, on the other hand, is supported by many proprietary Adobe formats as well as a large number of open graphic and video formats. For reasons of space, here is just a selection:

Graphic formats
JPG, TIFF, PSD, PNG, WebP, HEIC/HEIF, GIF, IND, INX, EPS, DJVU, SVG, PGF, XCF as well as DNG, CRW, NEF and other RAW formats (but in some cases only per sidecar file)

Video formats
MOV, AVI, ASF, WMV, FLV, SWF, MP4, WMA

Document formats
PDF

Extensibility

As mentioned, the X in XMP stands for extensible. The number of possible fields is not limited, but can be extended as required. XMP was developed in the knowledge that new requirements always necessitate new adaptations and extensions. And as we have shown in this article, even users who rely on tried-and-tested structures need not shy away from switching to XMP. On the contrary – as we now know, schemas such as IPTC Core (or Dublin Core to name another one) can be easily mapped using XMP.

Conclusion

IPTC-IIM is a long outdated format, a relic from another millennium, that is nevertheless still used in some archive systems. If you, as the person responsible for metadata management, have the choice, then you should of course opt for XMP.

XMP can be expanded flexibly, offers greater compatibility and is generally more widely accepted.

Metadata management with teamnext’s Media Hub

A modern digital asset management solution such as teamnext’s Media Hub naturally offers support for XMP, in fact in both directions: existing XMP metadata can be read out during import and transferred to the DAM’s database. And vice versa, metadata stored in the database can be written to the export files in XMP format.

Of course, the Media Hub also offers corresponding support for Exif metadata. And as a fallback solution, it is still possible to read IPTC-IIM headers. This ensures that no important metadata is lost during import, even with older file inventories.

Test the DAM solution from teamnext

If we have aroused your curiosity and you simply want to try out the possibilities of our professional DAM software, then you can get started right away with a free 14-day test phase for the teamnext | Media Hub. In addition, you can of course book an appointment for a free online product demo with one of our experts at any time. Simply use our contact form for this purpose.