If we saw a sample of the photos, it would be easy to determine if they could be fixed. Its hard to understand what the exact problem is from a text description, but the general answer is: Yes, anything can be done with The GIMP / PS.

GREYCstoration [ensicaen.fr]. Ugly name, but does the same job, and is open source. Haven't tried it, but there appear to be several plugins for various open source digicam programs and image editors (bottom of their downloads [ensicaen.fr] page).

Then you add that as a layer in photoshop, subtract it from the real image, and the non-random noise disappears.

I doubt that that will work. Once in the computer, the pixel values are not proportional to the absolute brightness, see gamma correction [wikipedia.org] on wikipedia. You would need to do the substraction on linearly encoded data (12 or more bits rather than 8). Maybe photoshop can indeed do this, provided you find the right settings, but GIMP as far as I know doesn't.

One of the best ways is to use a translucent lens cap and a fairly bright light that provides a fairly uniform illumination.

We used to just point the telescope up during the day and take a picture of a nice blue sky -- it worked very well. (Of course, this was 15 years ago, and maybe things have changed somewhat and there are better ways to do it now.)

Because this is Ask Slashdot, where users try not to do any real thinking, instead seeing if people have done it for them.

I think that this section has had 1 good question in the last month.

Still do skyflats :-) but it does depends on what passband you care about for imaging - twilight sky flats work pretty well in B. These are sort of bothersome on larger telescopes because you don't want to saturate but you do want good statistics but you don't want to cut into observing time, and you have to slew between each one to reject any bright early rising stars. A lot of big telescopes use quartz lamps to illuminate a screen and image that. Dome flats are pretty common these days, especially in spectroscopy, but for photometry its nice to still get a set of sky flats. I take a bunch of flats for each instrument setup and median them before flat fielding. There are more sophisticated methods around the corner that will vastly improve calibration for projects like Pan-STARRS and later LSST - http://arxiv.org/abs/astro-ph/0609260 [arxiv.org] (Disclosure: I work with some of the people on said paper but not on this project)

Dark frames aren't actually as useful anymore for instruments on larger telescopes that use LN2 or a cryotiger for cooling.

Ok here is a list to quell your doubts:

Photoshop has:

Adjustment layers which allow you to change filters after the fact
Filter layers which allow you to switch a stack of filter on and off and season to taste after tha fact (in CS3)
      These two features allow you to view image processing more like a spreadsheet in the same way that Excel is better than a calculator

Can do filters on the GPU in hardware (in CS3)
Save for web
Absolute color systems (Lab color)
Capability too do color proofing for printing presses (needs absolute color conversions)

Import and manipulation of smart object layers and changing them after the feact
Layer styles which allow you to change the llayerr after the fact. With copy and paste which are really useful to make lots imagges in the same style
16 and 32 bit and HDR color
Better macro recording (Gimp is probably easier too program though)
The history brush
The patch tool
MUCH better image size interpolations (if you resize an image iit look better in PS
A text tool that dooes preview on the image and not in some box outside of it
Much better text layers
A UI that was not written by the spawn of Satan

Basically, Photoshop is like a spreadsheet and GIMP is like a calculator. PS allows you to do do much better look and feel stuff

An no, the price comparison argument does not really hold. Gimp's competitor is Photoshop Elements which has all the features except the press stuff.

Many cameras do this automatically as you say, like my FZ30, for instance. It's called a dark frame, and it simply closes the shutter and takes a dark image right after the actual shot, using the same shutter speed, then subtracts it from the original using some algorithm. This will take out hot spots that are mostly consistent over a short period of time, but won't touch any other noise.

Replying to TFA:

surprised (disappointed, since I expect digital perfection) at the variance in adjacent pixels.

Digital perfection does not exist! You (the submitter) are taking images of the real world, where light moves around somewhat randomly in energy packets called photons, not in perfect rays. Noise can not be eliminated, ever. There's also some noise from the electronic components of the camera itself, which you also have to live with, unless you get a better quality camera. Or use some careful noise reduction. You do have the option of creating digital perfection, though. 3ds Max is popular, I gather. :)

If color variance is the problem, however, that's due to the CCD design. The CCD in nearly every camera is a single chip for all three colors (4 in some rare cases), but a single photosite ("pixel") can only detect one color. This means the sites need to be mosaiced in a regular pattern, usually RGBG, which is then decoded into a raster image like JPEG. For your 7.1 Mpix camera, than means about 3.5 Mpix resolution for green golors, and 1.8 Mpix for red and blue each. This can cause colored blotches in supposedly even areas, but this kind of noise is fortunately really easy to remove with any decent noise-removal plugin. Perhaps it's possible to avoid this noise in the conversion from the raw data, though?

Most importantly, inspecting the noise of a camera by oogling at 200% isn't very useful, look at larger areas instead. Most noise disappears when put into its normal scale for viewing.

To answer the last question in TFS, yes, if there are bad pixels, it's not hard to find them and create a mask or an action (in PS) that eliminates them. You can also take a noise print for your camera at different ISOs/shutter speeds (at least in Neat Image), and store them for later use in other photos, so you don't need to analyze the noise over and over again. Again, if you want less noise to begin with, make sure you're using the lowest ISO setting that gives you a usable shutter speed, or get a camera with larger sensor area, that can capture more photons in the same amount of time. Also remember that some noise is good noise. A noiseless picture tends to look a bit unnatural, so don't try to remove all of it.