XMP is a flexible tool used to write nearly any kind of metadata to a file. This can include informational metadata, such as IPTC metadata, as well as image adjustment instructions. In fact, anyone can define an XMP namespace, and write data safely to file types that support XMP.
XMP (eXtensible Metadata Platform) is not actually a schema, but rather a method to write metadata. XMP is a variant of XML that Adobe developed for the storage of image metadata. It offers an efficient way to wrap up a tag so you can know what that tag means. In Figure 1 below, the web address, www.peterkrogh.com is wrapped in some text that means, "here is the start of the web address" and "here is the end of the web address". This is, in turn, wrapped up in some text that means, "here are some metadata fields that Adobe has created to tag your pictures with usage rights".
This "wrapper" structure makes XMP data very easy to pass around and interpret correctly.
Figure 1shows the XMP data from a sidecar file that describes the copyright information that you can see in Figure 2. The wrappers are highlighted in red. The blue text indicates that the image will be marked as copyrighted, the green is the web statement, and the purple is the usage rights statement.
|Figure 2shows how the XMP data in Figure 1 looks when the file is opened in Photoshop, and File Info is opened.|
The XMP data can live in one (or more) of several places:
- XMP data can be embedded metadata in the file itself for file types that support XMP storage, such as TIFF, JPEG, PSD, and DNG.
- The XMP information can also live in a text sidecar file that resides in the same folder as the image file as shown in Figure 3. If you use Adobe Camera Raw to work on proprietary raw files, you’ve probably seen XMP sidecar files appear in your folders.
- Some programs put all the XMP data for an entire folder in one sidecar file in that folder.
- XMP data can also live in the database of a catalog program.
|Figure 3Adobe Bridge puts a text file in the folder with raw images to hold the metadata. This is called an XMP file, even though it’s just text.|
XMP was created to allow anyone to come up with metadata schemas, and to do so in a standardized way. Several companies have done so, and you can see their work if you know where to look. Here are some examples:
Adobe Camera Raw
When you adjust an image with Adobe Camera Raw or Lightroom, your parametric image editing instructions are saved as XMP data. Every slider, checkbox, or other adjustment is noted in the XMP space for that image (a sidecar file for proprietary raw, in the file for JPEG, TIFF, PSD, and DNG). If you open an XMP sidecar file, you’ll also see some other stuff in there that does not come from ACR. Adobe annotations, like labels and rating stars, are saved to the XMP space, as is all the IPTC file info and the EXIF data.
Media Pro (formerly iView MediaPro and Microsoft Expression Media)
Media Pro uses an XMP schema for the metadata it creates. This enables the image itself to be a carrier of the data. Catalog sets, people, and events are part of the schema and can be written to the file or sidecar file. Because an XMP schema has been used since the program was in its earliest form as iView MediaPro, there are two different ways that catalog data can be written to XMP — the iView syntax and the Expression syntax, as shown in Figure 4.
|Figure 4 When Microsoft bought iView MediaPro, they added a duplicate set of XMP tags with their own wrapper. Expression Media can read iView MediaPro XMP, but iView doesn’t know what to do with the Expression syntax. The new version, Phase One Media Pro, can read both sets.|
The PLUS licensing data can be written to the file using XMP metadata. This is an example of how the XMP standard is used in ways that were not even envisioned when the standard was created. In order to make it work, the PLUS Coalition is creating an XMP-compliant syntax for the information. Once that is done, PLUS will create a set of panels to let Photoshop and Bridge users see the PLUS data more easily.
Read more about Licensing Information in this section.