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Take control of digital noise with Photoshop's Reduce Noise filter

Added on Sunday 22nd of June 2008 07:20 am EST
 
Application:
Adobe Photoshop CS/CS2/CS3
Operating Systems:
Microsoft Windows, Macintosh


Even with carefully set image exposure, digital noise can appear and degrade the best of images. By using Photoshop’s Reduce Noise filter, you can remove even the worst noise from your images easily.

To demonstrate how to use the Reduce Noise filter effectively, we’ll:
 

  • Explain what causes digital noise and how to identify it in your images.
  • Review the Reduce Noise filter functions to understand how the different settings can affect your images.
  • Apply the Reduce Noise filter to a sample image to demonstrate noise removal.

Digital noise isn’t always bad. Sometimes you’ll welcome a little noise in your digital images for a nostalgic film grain appeal, or maybe for the illusion of a sharper image. But most often, noise distracts from an image’s aesthetic beauty and degrades its quality. And even if you take great care to get the exposure right, sometimes you can’t avoid introducing noise in your digital images. But you can take control with the Reduce Noise filter and eliminate the noise, as shown in Figure A. Let’s explore how.


A

Where does digital noise come from?
Digital image noise isn’t hard to recognize; it appears as a coarse graininess, most easily seen in the image’s shadow areas, as shown in Figure B. There are two types of digital noise: luminance and chrominance.
  • Luminance is similar to film grain, and often appears when a Photographer uses a high ISO setting or when he captures an underexposed image.
  • Chrominance is color noise and appears when red, green, and blue pixel information differs from reference color data. This occurs during digital image capture or during RAW image processing when converting to RGB.
In either situation, digital noise is distracting when you don’t want the effect. Let’s open a sample image and explore how to remove the luminance noise.


B

Open and inspect an image
Let’s open a sample image shot using an ISO of 800. If you want to follow along using our example, download the file noise.zip from the URL given at the beginning of this article, and extract the file noise.psd.

To inspect the image noise:
  1. Launch Photoshop and open the file noise.psd, shown in Figure C.
  2. Press [command]0 ([Ctrl]0 in Windows) to preview the image at 100% magnification, as shown in Figure D.
  3. Inspect the noise in your image. Note in which areas the noise is most noticeable and in which areas it’s least noticeable. This will help you to determine later the amount of noise reduction to use.
  4. Open the Channels palette and inspect each channel separately.
  5. Determine if any channel appears to have a greater amount of noise than the other two.
For our example, the Blue channel, as shown in Figure E, appears to have more noise than the other two channels. This will be useful information to know if we decide to use the advanced options of the Reduce Noise filter later.


C


D


E

Review the Reduce Noise filter
The Reduce Noise filter contains several option slider controls. Let’s first copy our image layer to preserve the original, and then review what the controls do.

To review the Reduce Noise filter:
  1. Select the RGB layer in the Channels palette.
  2. Switch to the Layers palette, select the Background layer, and drag it to the Create a New Layer button to duplicate the layer and preserve the original image.
  3. Select Filter > Noise > Reduce Noise to open the Reduce Noise dialog box shown in Figure F.


F
The filter has four settings that control different aspects of how the filter reduces noise from an image. They are as follows:
  • Strength. The Strength setting controls the amount of luminance noise reduction applied to all image channels.
  • Preserve Details....