Caption/Item Description [EXIF/IPTC module]

I want to prevent TIFF Image Description being added to Gallery's Description when the photo (in Aperture) doesn't have a Caption as described below.

The Minolta G1 RAW file creates a field identified as "IFD0—Image Description" and is associated with TIFF is some cases.

Many photo programs (in my case Aperture) allows you to caption photos; the field is variously called IPTC Caption/Abstract/Description. The Caption field, if it not blank, gets mapped during import to Gallery's "Item Description" which is desirable since it can be shown with the photo. I think this is set up in the EXIF/IPTC options:
When photos are added to Gallery check for EXIF Image Description and apply to:
√ Item Description.

However if the Caption field is blank for my Minolta images, the TIFF Image Description is mapped to "Item Description" which is NOT desirable—I want nothing to show if I don't have a Caption. (The TIFF Image Description is always "Minolta DSC" and looks odd as a caption to say the least.) (Photos taken with my Canon don't have a TIFF Image Description field and therefore nothing is shown if the photo hasn't been captioned.)

Presumably somewhere in the theme or elsewhere, this behavior can be changed. How is this done? Thanks

I had previously posted some of this in the X_treme theme section, but it's not an issue with that theme, but it seems to be an EXIF/IPTC module issue .