(Robert Maas, http://tinyurl.com/uh3t)
wrote in :

With enough information it would be possible to distinguish
foreground stars and background galaxies by their colors,
magnitude, redshift, proper motion, etc.

Yes, that is my idea as information going into this process. I've
been under the impression that Sloan and or Hipparchus contains a
listing of all point sources visible in medium-sized telescopes,
with enough data about each to make such a classification.

Then semi-accurate info about the sky coordinates and scale and
orientation of some old image, plus modern image-processing
software to match features between the image and a sky map, ought
to produce a near-exact mapping between image pixel coordinates and
sky coordinates, whereby the pixel coordinates of each cataloged
object can be calculated. Then an algorithm can verify that the
point source is visible in the image, and remove by averaging it
down to the local context so that it shows as a gray smudge instead
of a bright spot. It might even be possible to gray-out the
diffraction spikes around the spot.

Whether or not this has actually been done to
make a pretty picture -- rather than just to categorize the objects
for scientific study -- I don't know,

I posted to find out if anybody knew if this had actually been
done, at least for some of the common images such as M31 that are
so very commonly posted for public view. (I also posted it as a
challenge to anyone with access to all the data (and understanding
how to use it), and access to suitable image-processing software
(ditto), in case they might say "AFAIK it was never been done
before, but after you posted I did it!!".)

From: Bluuuue Rajah Bluuuuue@Rajah.
It's a good question, because you forgot the part where it would
be useful for producing a high contrast image, uncontaminated by
"light pollution" from foreground stars.

Yeah, that was most of my idea: When we look at an image such as
M31, we see lots of bright spots of light. We can't tell from
looking at the image which are foreground stars having nothing to
do with M31 and which are bright stars or globular clusters within
M31. This makes it very difficult to fully understand what we are
viewing. If we see something that looks out of place, we have no
way to know whether it's a feature of M31 that we need to
understand, or just a foreground star that we ought to not be
seeing in the image except for our location within our own galaxy
with hoardes of stars interfering with our view of M31.

The answer to his question is "probably not," since techniques
probably don't exist for masking out more than one star.

Perhaps you misunderstood my idea. I'm talking about
post-processing of the already-collected (archival) digital image
to remove artifacts including foreground stars, not physically
placing a occluding disk in the focal plane when making a new
image. Surely if you know the locations of ten foreground stars
within the archival image, and you can process the image to
"eliminate" one of the stars, you can repeat the process for each
of the other stars just the same.

The average person would use Photoshop for that, but did you stop to
think that there will then be a big black disk on the picture of the
galaxy? That would be only slightly less annoying than the star that
was originally blocking your view. :P

If the OP is serious, he should make a catalog of all the stars
blocking the images of all the easy to find galaxies, to see if
there's a situation where the contrast of one nearby galaxy could
be boosted by eliminating just a single star.

That's not my purpose. I expect removing the foreground stars from
an image won't significantly reduce the peak pixel intensity, thus
won't permit ramping up the contrast much more than it was set
already to achieve maximum span from black to white. Maybe some
single foreground star is brighter than the peak central brightness
of the core of M31, maybe not.

Also, I don't know how to get access to the key data I would need
to determine how many known foreground stars are visible in some
region around M31.

This should be possible by adapting the existing techniques. If
so, this idea is definitely worth a proposal for preliminary study,
and the OP could suddenly find himself a PI and an employed
scientist, rather than just a speculative amateur, sitting at his
PC and inventing wild ideas.

I really don't think this idea would warrant a professional
research project. But it might be useful for some company that
manufactures telescopes and sells a package of image processing
software and GoTo control for the telescope. It could brag that the
GoTo database includes all of the catalogs that exist to date, and
that it can automatically find all known objects within any region
of interest, and can edit images according to several algorithms
using that data, such as masking out foreground stars to gray (to
make them go away) or purple (to make them stand out like "sore
thumbs"). The advertisement could then show comparative images of
M31 with and without masking out of foreground stars. It could brag
"this is how M31 normally looks when viewed from Earth, and this is
how M31 *really* looks without our own galaxy blocking the view".

There is a programming language associated with Photoshop, but if you
want to do it yourself, you'd have to write a program to edit the image
file. It should be simple enough to just set the various pixels within
a specific range to black, but different photos would have different
exposures and contrasts, and I have no idea how you'd handle that.

Another possible type of person who might be interested in my idea
are the people who submit their best images to the Gallery section
of Sky and Telescope. I'd like to see somebody post an image of M31
with foreground stars removed. If S&T can post images of landscapes
at night with polar star trails in background, and images of an
eclipse viewed through pretty clouds, and images of sun dogs, I
think there's also room to post a galaxy image with foreground
stars removed. Once such an image gets constructed and published,
then maybe one of the advertisers would adopt the same idea in
their ads.

OT: Another neat thing I'd like to see is a stereoscopic view of
common asterisms such as the coathanger which have been proven as
chance line-ups of unrelated stars of varying distances. Or maybe a
3-stereoscopic view, with a central image just the way the asterism
looks from Earth, and views to each side showing how the asterism
would look as viewed a few lightyears to each side, so you can
choose either two adjacent images to get a stereoscopic view from
that side of the Earth line of sight. Or maybe a hologram that
shows true (scaled) distances which can be viewed from any
direction with any orientation.

The difference between a professional and an amateur is not just
having a good idea. It's having a good idea that can be made
into a real research project that get published. This could
probably be done, but it would take work. Maybe there's a needy
PhD student out there looking for a dissertation project.

Ignoring the fact that I don't think my idea would have any
significant true scientific value, only advertising value or
show-off value or public-education value (helping the public to
understand what a galaxy really looks like, without the distraction
of the foreground stars giving a wrong impression of the galaxy),
there's the fact that I don't have the English writing skill to
write a research or R&D proposal even for the kinds of projects
that I truly feel would be worth pursuing for scientific or
technological or society-improvement value. For example, see my Web
page listing several projects in Web software that I'd like to find
somebody else to work with me to brainstorm the design and help
with testing even if I do all the actual work.
http://shell.rawbw.com/~rem/WAP/projectIdeas.html
I have no idea how to find anyone interested in working with me on
any of those projects, and I have no idea how to write up any of
them as a formal proposal that anyone would pay serious attention
to.

I have a friend with a company that does precisely this, but he charges
real money. I'm not sure that he's ever written a proposal for a
government grant, either, so he pobably wouldn't be able to do what you
need. See if your phone book has listings for either "business plans"
or "business consultants."

And even if I did take a chance at writing a formal proposal, I
have no idea how to find anybody else to proofread it to show me
all the stupid mistakes I made so that I can make the proposal
halfway decent before I submit it to some funding agency.

From what I hear, it takes a few tries, but they will give you copies of
other people's grants that were approved.