Dealing with Digital Noise


If you shoot in low-lighting situations, you're bound to encounter digital noise. Is there anything worse than these large red, green, and blue dots that appear all over your photo? Okay, besides that "crazy music" those teenagers play, like Limp Bizkit or...well...Limp Bizkit, is there anything worse? This digital noise (often called "Blue channel noise," "high ISO noise," "color aliasing," or just "those annoying red, green, and blue dots") can be reduced. Here's how:

Step One

Open a photo that contains visible digital noise. Go ahead and do your color correction, and other adjustments first (like any Shadow/Highlight adjustments, Curves, etc.), because these will sometimes bring out noise in the image too. (In this case, the shot was taken at night with a point-and-shoot camera, and those red, green, and blue dots appear throughout the photo, but are especially visible in the sky. I know, it's kind of hard to see the noise in the small photo shown here, so in the next step we'll zoom in tighter so you can see the noise.)

Step Two

Go under the Filter menu, under Noise, and choose Reduce Noise. When the Reduce Noise dialog appears, click on the Plus (+) sign (that's directly below the preview window) about four or five times to zoom into the sky area. To actually see the red, green, and blue noise pixels, click-and-hold within the preview area. This shows you the original image (before the filter is applied). Release the mouse button, and you'll see how the Reduce Noise filter reduces the noise. This is a quick way to get a before and after: click to see the before, release to see the after.

Step Three

This filter seems to work best if you crank up the Strength fairly high (try 7 or 8). You want to find a sweet spot for keeping as much detail as possible, while still getting decent noise reduction, so try setting the Preserve Details slider between 40% and 50%. You want to really work the Reduce Color Noise slider (start between 60% to 70%, and then drag to the right for more reduction but without making the photo noticeably blurry). For Sharpen Details, keep that at no more than 15% to 20% (you'll probably get better results if you use the Smart Sharpen filter next, rather than applying the sharpening here). Click OK to reduce the color noise.

Tip

Some digital cameras produce what's called "Blue channel noise," because that's the channel where most of the noise winds up. To reduce that, click on the Advanced option, which lets you reduce noise in individual channels. Click on the Per Channel tab, and then from the Channel pop-up menu, choose Blue. Then, use the Strength slider to reduce noise in just the Blue channel.


Before

After (with color noise greatly reduced using the Reduce Noise filter)



    The Photoshop CS2 Book(c) for Digital Photographers
    The Photoshop CS2 Book for Digital Photographers (Voices That Matter)
    ISBN: B002DMJUBS
    EAN: N/A
    Year: 2006
    Pages: 187
    Authors: Scott Kelby

    flylib.com © 2008-2017.
    If you may any questions please contact us: flylib@qtcs.net