'Noise' is those red, green and blue colored speckles in areas where they should not be. They become particularly visible in photographs taken in low light or at high ISO. You can eliminate them in either of two ways in Photoshop.

I currently use several Canon digital cameras including a pocket sized Powershot and the new (and marvelous) Rebel XT. I am particularly pleased with the lack of significant noise in low light, and in dark areas of the images, and at high ISOs in Canon cameras. Nikon digital cameras have a problem with noise in all situations and it is very bad in low light and at ISOs of 400 and up.

IMPORTANT NOTE: In your camera settings and in Photoshop be sure to change from the default sRGB to Adobe RGB. sRGB is a very truncated color space devised by Microsoft because of the limitations in its operating system and to cut down on transmission time on the Web. Among the problems is that sRGB significantly reduces the color space in the blues, and blues are the most difficult thing to get correct in prints. Go to Photoshop: Color Settings (not Preferences): Custom: Adobe RGB (1998).

In Photoshop there are two ways to blend the RGB speckles together into the color they should have been. Both ways work by separating the color information from the grayscale information (called luminosity) and blurring the color information. The color information can be blurred without effecting the sharpness and detail of the image which is contained in the luminosity like a grayscale photograph.

The two ways to separate the color information from the luminosity information are with the Lab color mode, which lets you see why it is happening, and working with an easy Gaussian Blur formula in RGB. Both ways are described and illustrated below.

USING GAUSSIAN BLUR AND THEN FADE TO ELIMINATE THE EXTRANEOUS COLORS IN NOISE
1) Open your photo in Photoshop.
2) Apply as much Gaussian Blur as is needed to blur out speckles-
don’t worry about image detail, that will all come back.
3) Under Edit: Fade: Gaussian Blur: choose Color. At Opacity 100% all the detail
comes back but the speckles of red, green and blue are now consolidated
into the color the area should have been.

USING LAB COLOR TO ELIMINATE THE EXTRANEOUS COLORS IN NOISE

Note: Changing back and forth between Lab color and the usual RGB color mode does not change the information in the file, but only displays it in a different way. Changing the color mode to any of the other options such as CMYK or Index, does permanently change the color information in the file.

1) Open your photo in Photoshop.
2) Under Preferences: Display & Cursors: select 'Show Channels in Color'.
3) Under Image: Mode: change to Lab Color.
4) Open the Channels window.
The image looks the same on the screen but under Channels instead of RGB
channels you now have a channel for Lightness (luminosity),
which contains all grayscale information about the details of the photo,
and under that channels marked ‘a’ & ‘b’ which contain the color information.
4) Select Channel 'a' and apply Gaussian Blur until the color speckles are blended.
5) Select Channel 'b' and apply Gaussian Blur until the color speckles are blended.
6) Change the Mode back to RGB.
You will see that the color speckles are now blended into the color
they should have been if the color hadn't been broken up into noise.

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