Noise is that ugly discoloration that makes your photos look “grainy” (like in the image on the left, where the noise has been exaggerated to make it more clear). It’s one of the most annoying things you’ll have to deal with in digital images.
Although you’ll never get rid of noise completely, there are a few things you can do to reduce it so it’s barely noticeable by the viewer:
#1 – Get a good exposure
The best way to avoid noise in your photos is to get the best digital exposure possible, by using the histogram. This will ensure you maximize the signal-to-noise ratio in your exposures. If you underexpose your photos and try to fix it later in post-processing, you’ll start to get a ton of noise like in the example below:
The image on the left was severely underexposed, and when I tried to fix that in post-processing, all I got was a bunch of ugly noise. On the other hand, notice how the properly exposed image on the right has virtually no visible noise.
#2 – Use lower ISOs if possible
As you increase the ISO on your camera, the noise in your images will also increase. In newer SLRs, this noise usually becomes pretty noticeable once you get past ISO 400. So, to avoid noise, use the lower ISOs available on your camera.
But, don’t be afraid to use higher ISOs when you truly need them. They come in handy when you need faster shutter speeds, like when you’re photographing birds or wildflowers. Even the extremely high ISOs (ISO 3200 or higher) have good uses: nighttime photography.
#3 – Only sharpen areas of the image that need it
Sharpening works by increasing the contrast between light and dark edges, so it’ll actually sharpen noise too and make it stand out more. That’s why it’s best to just sharpen the stuff you want sharpened, by using layer masks in post-processing.
If you sharpen an out of focus background, for example, you’ll end up increasing the strength of the noise in that background. Here’s an example:
Notice how the sharpening made the noise more visible? This is why you want to control what parts of the image are sharpened.
#4 – Turn on noise reduction for longer exposures
Once you start getting into longer exposures (anything more than one second), noise starts to become a bigger problem, so most newer SLRs have a special noise reduction option for long exposures. It’s usually buried in your camera’s menus somewhere, but it’s worth turning on for those longer exposures.
More Information on Image Noise
For a more technical explanation of image noise, check out these great resources:
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About the Author: Steve Berardi is a naturalist, photographer, computer scientist, and founder of PhotoNaturalist. You can usually find him hiking in the beautiful mountains and deserts of Southern California.