Labels (Colour labels) and Rating (Star rating) are parts of the XMP / IPTC standard (as far as I can see). I think XnView should follow to the specifications / standard developed by Adobe / IPTC.
I use iView Media Pro to catalogue my photos. iView Media Pro is now owned by Microsoft and will be a part of Microsoft Expression Studio. See:
http://www.microsoft.com/products/expre ... fault.mspx
Ratings or Star Ratings in MediaPro are mapped to Adobe’s XMP standard for ratings. Labels or Colour Labels are written to the IPTC standard’s Urgency annotation field.
To clarify the use of (Star) Ratings and (Colour) Labels, I quote from iView Media Pro’s User Manual page 63-65:
Reviewing and marking media
Once you have imported a collection of media into a catalog, you will likely want to review and classify the media. For example, after importing images from a shoot, photographers typically edit images, marking their favorites and unusable ones. To assist in this process, MediaPro provides two methods of classifying and ranking media: star ratings and color labels. Using keyboard commands, labels and ratings can be easily assigned in any view, the light table and during slide shows.
Rating media
Star ratings provide a ranking system for items in your catalogs. You can now rank your media from one to five stars, or no stars. […]
Ratings as annotations
Ratings in MediaPro are mapped to Adobe’s XMP standard for ratings. When annotations for images in a catalog are synchronized (written) to the original files, all ratings will be written into the files. If you open the image in Adobe Bridge, the star ratings will be displayed. Likewise, if you have assigned a rating to a file in Bridge, the rating will be displayed when you import that file into a MediaPro catalog.
Color labels
Labels provide a visual identification and classification system for items in your catalogs. A color label can be used to: mark favourite items; mark items to delete, archive or convert; or to track items that are in different stages of a workflow (See example A). After you label your items, you can quickly sort the catalog using the Label section of the Catalog Field index in the Organize Panel. A label can also be used as a temporary method of marking items that will be later assigned a particular annotation. After assigning the annotation, the labels can be cleared from the images. To accommodate your desired method of marking items, the colors and names of labels can be customized in MediaPro as a global application preference. Because this customization is global, shared catalogs will inherit the label names and colors of the user that is opening the catalog and not the preferences of the person who created the catalog. […]
Labels as annotations
Labels in MediaPro are mapped to the IPTC standard’s Urgency annotation field. When annotations for images in a catalog are synchronized (written) to the original files, all images tagged with a label will have the corresponding label number (1-9) written into the Urgency field. For Photoshop CS users, these are the same values used in the Urgency field of the File › File Info › Origin panel. Even if you have customized the colors and names of labels, the values 1-9 are written into the Urgency field in order to comply with the IPTC annotation standards. If the Urgency field is important to your workflow, you might customize the label names to match the standard (see example C, pg 64).
Quote end.
Regards,
Jøran Toresen