The higher the ISO value, the greater the camera’s light sensitivity and the better its ability to shoot in low-light conditions. However, higher values also introduce electrical noise into the resulting image, which may make give them a grainy appearance
a quote from my Olympus C-4000 manual.
What it means is that digital cameras are very prone to a characteristic grainy noise when you are using long exposure in low light. I have lots of examples and felt I should be possible to "fix" the graininess. I've tried the UNsharpen mask and despeckle filters in most editors I've come across and was generally unimpressed.
So I posted the example images below at Sharing Photos Worldwide's Forum and got some good recommendations including trying the noiseworks program. Noiseware the developers of Noiseworks is definitely a site worth a visit (I've only downloaded the free "community version", because it is much smaller and therefore will avoid the bandwidth police, but there are pro versions available which include an add on to photoshop, batch processing of groups of images, saving the EXIF info and other goodies). There are lots of controls in the free version but I just used the default settings to got the result show3 below.
I particularly like the click and hold option in noiseworks which lets you toggle back and forth between the pre and post filtered versions. I reckon noiseworks is a nice tool, worth keeping.
Compare this with the unimpressive results I got with the DESPECKLE FILTER in Adobe Photo Elements
My camera by the way does have a noise reduction setting, which seems to work well in all but the darkest photos, but I had turned it off so I could use the bracketing feature. I realize this is a very dark photo, but it is that mood that I was trying to capture.
The Moral don't be afraid to ask others, and on-line forums are great places to find others in the same situation as you.