Home How-To Image Processing Keep The Noise Down In Your Digital Images
Wednesday, September 3, 2008

Keep The Noise Down In Your Digital Images

It’s the grain of the digital age. Learn how to tame it.

This Article Features Photo Zoom

Working With Noise In The Computer
No matter what you do, you may end up with noise in your pictures. But you can reduce noise in the computer and increase its appearance as well; so we need to address that issue.

1. Sharpening. When you use Unsharp Mask and find noise to be an issue, set the Threshold to a number between 6 and 12. Smart Sharpen in Photoshop is problematic because it doesn't have a Threshold setting, so it's not the tool to use when you have noise issues.

Another technique is to selectively sharpen your photograph. Copy your photo to a new layer, sharpen that layer and remove the parts that are causing noise problems. (See the article "Selective Sharpening" at www.pcphotomag.com for more details.) Photoshop Lightroom also includes a masking slider for its sharpening tool that can reduce the sharpening of noise (hold down the Option/Alt key to see where it affects the photo; white is the sharpened area).

2. Color and exposure adjustments. Over-enhancing the color of skies can increase the effect of digital artifacts, which makes the sky have more noise. You need to be careful when using the Hue/Saturation adjustment, because this often can increase noise quickly if it's set too high.

Noise-Reduction Tools
Once you have noise in a photograph, you can reduce it with special programs. Adobe products have some noise-reduction tools built in. You can find them in Photoshop under Filter > Noise > Reduce Noise; in Lightroom, go to the Develop module under Detail. Many other programs also include noise-reduction tools. These generally work fine for minor amounts of noise, but if you have very strong noise, you'll probably prefer the results of specialty software designed to deal with it.

Here's a good exposure that doesn't suffer from noise because there was ample light, and a low ISO was used.

By using noise-reduction software, I've been able to make a photo with a higher ISO setting look like it was shot with a considerably lower setting. I've also been able to use cameras with smaller sensors and have the results equal the results from cameras with larger sensors.

I haven't used all the noise-reduction programs on the market, but I've found that Nik Software Dfine 2 works very well. Version 2 is a complete redesign, and it's extremely easy to use. I've been impressed with how well it removes noise from a picture without hurting the sharpness details of the photo. Noise is essentially small details, so if you reduce it, you often reduce other small—but important—details for sharpness. In addition, Dfine has advanced features that allow you to selectively control noise in certain areas. For example, you can tell it to reduce the noise in a blue sky without affecting detail in other parts of the photograph.

Selectively Reducing Noise
You may find that noise appears only in certain areas of an image. This is common with a well-exposed picture that has dark areas that need to be brightened. When the dark areas are brightened, noise shows up.

The solution is to selectively control the noise. Copy your image to a new layer, apply noise reduction to the whole thing and then remove everything from that layer except the problem area with the noise. You can do that by erasing the parts of the picture that don't have a noise problem or by using a layer mask.

Final Thoughts
Follow the tips in this article, and you'll begin to control noise in your photographs. As you work with noise, you also may find that some images look better if you actually add a little noise. This is a whole different story, but it can be a fun way to work with photos, especially if there's a lot of noise in the images to begin with.

Clean up noisy images with Nik Software's Dfine 2.0, a Photoshop plug-in that lets you selectively eliminate noise. Using U Point technology Control Points, you can constrain adjustments to just where they're needed. List Price: $99. Contact: Nik Software, www.niksoftware.com.

Check out Rob Sheppard's new photo blog, www.photodigitary.com.


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