Noise Reduction

©Doug Weldon Photography - www.dougweldon.com 

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Almost all digital images have some noise in them, just as most film images demonstrate some grain. Noise shows up most dramatically in dark areas and areas that have uniform colors. Noise usually is more evident at higher ISO's. Regardless of why it is present, we want to know how to remove it. 
 

It is very difficult to demonstrate both noise and a noise reduced image on a web page, because the images are small, making it difficult to see the problem and the solution. A good monitor is required to adequately see the images in this tutorial. 


For purposes of illustration, we will temporarily abandon the image we have been working on in favor of one that has much more noise, and we will exaggerate the problem and the solution. Look at the following image. It was shot at a very high ISO to accommodate a hand held shot at night. I got the shot, but suffered a great deal of noise.

 

noise1

 

This is a very noisy image. It is hard to see, because the image size has been reduced for display on this page. If we take a crop of a small area of the image and blow it up, we will be able to see the noise more easily. Of course, a drastic crop introduces more problems, but we will ignore them for the moment. 

 

Noise2

 

Notice the graininess of the buildings and the sky. As indicated earlier, the image was shot at a very high ISO to accommodate a hand held shot at night. The noise that you see here is fairly typical of high ISO captures. 
 

If we reduce the noise in the image, it looks like what you see below. Keep in mind that this is an exaggerated example for purposes of illustration on a web page. I have gone after the noise a bit more aggressively than I normally would, again introducing other problems that we will ignore for the moment. 

 

Noise3

 

The resultant image is certainly "cleaner" looking. The noise has been pretty much eliminated, but now the image looks soft. (In this exaggerated, cropped example, it is softer than would normally be the case.) That will be taken care of with some careful sharpening. It is important to reduce noise before sharpening, because sharpening worsens noise and makes it more obvious. 


On the PC, I use a plugin for Photoshop called Neat Image (http://www.neatimage.com), to reduce noise. It does a better job than Photoshop's noise reduction tool, and offers more control. On the Mac, I use Nik Software's Dfine (http://www.niksoftware.com) . Other excellent noise reduction plugins are available as well .


Neat image is accessed from the Filter Menu in Photoshop. It is automatically installed in the Photoshop menus when you install the program. You can see two other plugins from Nik Software installed here as well. 

 

neatimage

 

Because all plugins will work a bit differently, full tutorials on Neat Image and Dfine are not supplied here. Go to the Neat Image, or Nik Software web sites for excellent introductions to their products. 
 

You will notice that this time, using Neat Image, we are not using a layer. We are working directly on the image's pixels. We can use a layer to reduce noise, but it is a bit more complicated to do so. Dfine automatically uses layer-based noise reduction. We will reserve layer-based noise reduction and sharpening for the advanced sections of the tutorials. 

 


 

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