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Tag Usage

Dec 14, 2009 at 5:35 PM

I have now got BitmapTagger integrated with my test application - but I am unclear as to the correct usage of Tags

For example when looking at the ImageTagView Dialog box  under Description / Image Description,  I am looking at a photo where that Field is set to "OLYPUS DIGITAL CAMERA" .  Is that field designed for end user use ?  Or for Camera Manufacturer use ?  Is the best practice for users to overwrite this with their own description of the photo - or should I use another tag for that ??  Generally it is unclear to me which tags can and should be used by the end user to describe the photo.

Also how would you suggest that custom tags be implemented.  For example what if I wanted to add a People in the Photo Tag supporting a text with names of people in the photo. Or even better a Tag to support Photo Tagging where the tag would support a XML string defineing Names and corner co-ordinates of a shape outlineing the person in the photo, (like Facebook supports).  Does BitmapTagger support any such custom tags and if not do you think it could be extended to do so ??

One other thing - can I assume that since you ranked it first in your Options Dialog that you thing the prefered Tag System Precedence is  Exif-XMP Exif - XMP  ???

Thanks :-)



Dec 14, 2009 at 6:01 PM

When I was designing this I went back and forth on supporting custom tags. Yes, custom tags are possible; I just wasn't sure how useful these would be. The library acts as a wrapper around WIC. WIC can support almost any type of tag (custom or standard), so I made BitmapTagger handle the standard schemes so the user wouldn't need to know them. If I added support for custom tags The interpretation and query would be completely up to the user. This would mean the library would almost do nothing, it would just call down to WIC with the passed information and relay it to the user.

If you did add a custom tag with XML it would be up to you to encode and decode this tag, along with deciding where it should reside. Making the Bitmap tagger somewhat unnecessary when this is exactly what WIC does.


All fields are editable by the user. I don't want to suggest what fields only a manufacturer should write to as many manufacturers do not correctly encode their information. For instance, the value: " "OLYPUS DIGITAL CAMERA" should probably have been split into the make and model tags, but apparently Olympus decided to put it in the description, which is the "catch-all" tag.


Currently, Exif-XMP Exif - XMP, is the "prefered" order of precendence. This is because I concentrated on Exif support as it is the most commonly use tag specification. XMP also contains a scheme for Exif (Exif-XMP), so this is why I don't have many XMP only tags being supported, as all the major tags are in Exif.