If a photograph has unwanted little specks of color, it has "noise." You can remove noise by following these steps.
In Camera Raw under the details tab there are 3 setting - Sharpness, Luminance Smoothing and Color Noise Reduction
1 Set Sharpness at 25
2 For Luminance Smoothing zoom in as far as you can go. Start with a setting of 6 to 10.
Luminance noise appears as random speckles concentrated in darker tones. This does soften the image so limit it.
3 For Color Noise Reduction settings can be more extreme because this does not affect sharpnes as much as Luminance Smoothing. Color Noise appears as random green and magenta splotches in dark areas.
It doesn't matter whether you start with Luminance Smoothing or Color Noise reduction first. Start with the worst of the two. Take sharpening higher if necessary to get a good preview.
source: Camera Raw with Photoshop CS - Bruce Fraser p. 96 - 97
In RAW view the image at 300% with slider set all the way to the left. Move the slider to the right until the noise disappears
or in Photoshop CS2 Filter>Noise>Remove Noise
or use Noise Ninja software
source: Digital Photography (2006) - George DeWolfe p 37
Another way to do reduce noise in Photoshop is
1 Open Channels palette and inspect Red, Green, and Blue for noise. Determine which channel has noise.
2 With the noisey channel selected go to the main menu and choose Image>Mode>LAB
3 Click on channel a and select Filter>Noise>Median. Set the radius to 3. Go higher if necessary.
4 Click on channel b and select Filter>Noise>Median. Set the radius to 5. This channel usually needs a higher radius than channel a.
5 Click on channel L and use an aggressive Unsharp Mask filter setting. It should look uncomfortably crisp.
6 Select Image>Mode>RGB to complete the process.
source: Digital Photography, 2nd Edition - Eismann, Duggan + Grey p 584 - 586
Always start with the camera's internal noise filter
•Photoshop Camera Raw has a noise control. Luminance and chrominance noise are filtered separately. If the image is to be converted to grayscale, chrominance noise is less important
Source: p. 106 + 107 Mastering Black and White Digital Photography – Michael Freeman 2006Sharpening
Whenever you take a photograph or make a scan, it is good idea to sharpen it.
source: Digital Photography, 2nd Edition - Eismann, Duggan + Grey p 513 - 520
use Optipix software set at Safe Sharpen
for both sharpening can be reduced with Edit>Fade in Photoshop
source: Digital Photography (2006) - George DeWolfe p 38
I use the above settings with high resolution images. Higher amount settings seem to lead to oversharpening.
There are two books on sharpening. Both authors have well established reputations as Photoshop experts.
Image Sharpening - Bruce Fraser 2007
Photoshop Sharpening, (download Version) 2006