Removing Digital Noise in Photoshop

If you take pictures in low-light conditions, by all means you'll to encounter digital noise. There's nothing worse than these large red, green, and blue dots that appear all over your photo The digital noise (often called "Blue channel noise", "high ISO noise" or "color aliasing") can be removed. Here's how:

First:
Open a image with visible digital noise

Second:Under the Image menu->Mode->Lab Color. Switching to Lab Color is a non-destructive mode change, and won't damage your RGB picture — you can switch back and forth between RGB and Lab Color any time. You won't see any visible difference in your photo on the screen, but if you look up in the title bar for your document, you'll see "Lab", to let you know you're in Lab Color mode.



Third:
When  in RGB mode, your picture is made up of three channels: Red,  Green, and Blue. When they are combined, they create a full-color photo. When you convert to Lab Color, Photoshop composes your photo in a different way — though it looks the same, it's now made up of a Lightness channel (the luminosity of the photo, where the detail is held) and two color channels, called "a" and "b." Go to the Channels palette and you'll see these channels. Click on  "a" channel .

Fourth:
Now that you're affecting only the "a" channel (which consists of color data), go under the Filter menu, under Blur, and choose Gaussian Blur. When the Gaussian Blur dialog appears (shown at left), increase the Radius (amount of blur) until you see the dots pretty much disappear, and then click OK.

Fifth:
Now, in the Channels palette, click on the "b" channel. Press Control-F to apply the Gaussian Blur filter to this "b" channel with the exact same setting we used on the "a" channel. Because you're using the re-apply shortcut, you won't see the Gaussian Blur dialog box—it will just automatically apply the filter for you.

Sixth:
Go back under the Image menu, under Mode, and choose RGB to return to RGB mode. You'll notice that the spots are much less pronounced because they no longer appear in red, green, and blue. You blurred the color channels, and by doing so, you eliminated those colors that are distracting to the eye. The effect appears much more muted, and in some cases (depending on the photo) will nearly disappear.