GIMP :: Seeking Better Green Screen Method

Gimp 2.6.6 on Ubuntu Linux 8.04.Scanning using VueScan Professional 8.5.20 with an "Epson Perfection 4490 Photo" scanner. Color profile has been built for the scanner using available photo color target from a well-known German source (can't remember name).Almost all my scanning is of postage stamps and related items -- scanning the actual physical objects, not photos of the objects.

Problem:

The stamps are currently scanned on a black background (for lack of other color possibilities; the final goal is on a black background). After scanning, the background is selected and turned to 100% black to have greatest contrast for the object. When a stamp has a postmark that crosses the edge of the stamp paper, the color of the postmark (usually dark or black) is very close to the color of the scanning background and thus when the background is selected, the selection "leaks" and "follows" the postmark onto the stamp. We have to manually exclude those "leaks" from the desired selection area.

Goal:

To be able to select the background (for change to 100% black) without any "leakage" of the selection onto the stamp objects AND without ANY non-black color artifacts remaining after changing the selection to 100% black.

Attempted Solutions:

We have tried scanning on many different non-black background colors and surfaces, but there are always some extreme-edge color artifacts remaining ... leaving a sort of "halo" effect around the stamp object.Some of this could be attributable to the particular model of scanner, though every scanner I have ever owned had a similar problem to a greater or lesser degree. The width of the "halo" usually depends upon which side of the object it is on vs the direction of travel of the scanner device.

In television broadcasting it is extremely common for somebody to stand in front of a "green screen" and for the green to be electronically replaced with some image or video, etc. (For example, the weather person standing in front of a weather map.) It is rare to see a green "halo" if everything has been done correctly and if the person is wearing the correct type of clothing fabric.

Is there some Gimp method or plug-in or other tool that will better handle this type of use?Recently poster Ron Guilmette discussed his use of "Darla-PurpleFringe.scm" plug-in to remove an artifact caused by a digital camera and subsequent processing.

Is there something like that which can be used to remove a color "halo" that results from using a "green screen" approach to scanning? (I would likely have to select different colors of "green screen" so that such colors are not included in the design of the postage stamp.