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Getting unwanted noise in your images is something that most digital photographers have struggled with at some time. While camera and sensor technology is improving with time, it's still something that a lot of us have problems with. While most people turn to post-production software such as Photoshop to reduce the negative effects of noise, there are also a lot of things you can do before that point to help solve the problem. They say that an ounce of prevention is worth a pound of cure, so let's look at some non-software noise reduction techniques.
What is Noise?
Most digital photographers know all too well the dread of finding noise in their images. While there are several different types of noise (technically speaking), it usually shows itself as speckles in otherwise clear areas of an image. For example, pink spots across a sky or grain across dark areas.
What Causes Noise?
There are several different potential causes of noise in your images. The most common is simply from using the higher ISO settings on a camera. As the higher ISO setting increases the light signal, so too it increases the noise signal. Another cause is heat which allows photons to escape the “photosites” on an image sensor and contaminate other photosites. In longer exposures, you also allow the sensor to collect more information which, unfortunately, includes background electrical noise and contamination.
How Can You Reduce Noise?
While many people resort to post production noise reduction software (which is great), it is also possible to take many steps to reducing noise before it becomes a problem. As most photographers know, it's good practice to attempt to get the best shot from your camera rather than relying on post production, so let's look at some things you can do.
Shoot At Lower ISO – It's a simple one, but if possible shoot at a lower ISO. This reduces the chance that the camera will amplify the existing noise in an image. Luckily cameras are getting better all the time. Recent DSLR models can go as high as ISO 6400 without noise being a major problem – only a few years ago ISO 800 would often cause some problems.
Keep Your Camera Cool – Most DSLRs come with the recommendation that they work best between 0 and 40 degrees C. You should remember that. Keeping your camera cool (or more specifically your image sensor) will help prevent photons (which become more active with higher temperatures) contaminating photosites on your sensor. Don't leave your camera where it will get hot like in your car or in a bag in the sun.
Other activities that heat up your image sensor include using burst mode or longer shutter speeds (basically anything that makes the sensor continually work). Try to avoid burst mode or longer shutter speeds as much as possible if you think noise is going to be a problem.
Shoot to the Right – You will often hear experienced photographers (especially landscape photographers) explaining the value of slightly over-exposing your images (giving you a histogram that looks like a bell on the right side of the graph). See how to read a histogram for help. This is due to the fact that correcting an underexposed image in post production (ie. making it brighter) will bring out noise in the shadows. Darkening over exposed areas is usually a better option for digital shooters in post production. If you think noise will be a problem for you, try over exposing stop or two while shooting.
Hopefully these options will deal with the worst of your noise problems that can be solved before you hit the post production process. While noise is an issue for many of us, the good news is that technology is getting better. With any luck, this article will be redundant in just a few years!