Using Gimp 2.6.6 on Ubuntu 8.04 (Hardy) Linux.  (Working great, NO
crashes as some people complain of.)

The answer to this question is not as straight-forward as it sounds.

Problem:

- Scanning (xsane from within gimp) images of canceled postage stamps.
(Also tried with Photoshop/Windows using various scanner drivers.)
Usually there are 10-30 stamps in each scan (for productivity) which are
then cut apart into individual images.  We scan up to hundreds per week,
thus this is an ongoing issue.

- The stamps' designs are of varying colors, though their paper is
usually white-ish and the designs of the stamps usually does _not_ reach
the edge of the paper.

- However, the _postmarks_ (usually black) DO reach the edge of the
stamps' paper.

- The desired end result is the stamp on a black background, like this:

http://jsa.viewimage.net/jsa/web/Lists/Finland/SpecStamps/Regular/sc0197_used-fvf-superb-pm_142761_r_m.jpg

- We usually scan against a black background and this works well unless
the postmark reaches the edge of the stamp paper as in the above image.
Even though we are scanning against a "black" background, it is never
100% black and we consider it _critical_ to make it 100% black. Thus we
select the "black" background/surrounding area and fill it with black.
However, in the process of selecting the background/surrounding area, it
is almost impossible for the selection to avoid eating into (and
following) the postmark into the design.  We thus have to manually,
tediously exclude the postmark from the selection before filling with black.

Experiments so far:

We have tried using TV's equivalent of a "blue screen" by which the
stamps are against a colored background that is intended to be replaced
with a different color.

We have tried using backgrounds of various colors (physically putting
colored paper on the scanner back), but invariably, we run into the
problem of a "shadow" of whatever the background color is along the
stamps' perforations on one or more sides.  The result is different from
one model of scanner to another, but they all seem to have a "direction
of light travel" and thus at least one side has a shadow of whatever
color.  This seems to be the nature of flatbed scanners.

Removing that color shadow is even more problematic than deselecting the
postmark problem areas.

Using a digital camera has not produced the desired results, both from a
productivity standpoint and a quality standpoint.  Clarity and focus of
image quality is absolutely critical.  "Good enough" is not good enough.
There are lighting problems, distortion (curvature, plane, depth of
field) problems, etc, etc., etc. to say nothing of the need to keep the
object flat and digital cameras don't like shooting through glass (we
have purchased heavy optical glass, but end up seeing the second side of
the glass).  And that is all before the issue of background color which
still remains!

So....

I am hoping for suggestions as to a) how to avoid the color shadow of
using a colored background and b) if it cannot be avoided, how to fix it
in gimp without a lot of messing around and/or other color distortion
problems.

Thanks.

Jay

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