The first time I saw a “noise reduction feature” on a camera it confused the heck out of me. I get reducing background noise while shooting a video, but what does noise reduction mean when all I am doing is taking a picture? Noise is tiny spots of discoloration made by the sensor of a digital camera. The best way to explain this is to remember that grainy look of old films. That is very similar to the noise digital cameras produce. So why might so situation create a lot of noise and others so little that you would never even notice?
Remember back in the days before digital cameras and we had to choose the “speed” of the film. The less light you have in the environment, the higher speed of film will be required. Digital cameras also have different speeds; again you use higher speeds for lower light pictures. Unfortunately, these higher speeds also lead to more noise. Many digital cameras have sensors that adjust the speed setting based on the ambient light and you may or may not be able to change these settings manually. Additionally, lower speeds can lead to blurry of your images.
Another major cause of increase noise in photographs is the size of the image sensor. This is a particular problem for very small cameras that have high quality pictures. The sensor size is also small and yet a high quality photo must be produced. This increases the likelihood for errors, or misinterpretation of data.
There are three main ways to reduce noise in photographs. The simplest method is to reduce the size of your pictures. While the noise is still there it is not nearly as visible.
The second method is post-production. Most photo editing software is able to effectively remove the noise from photographs. Sometimes this results in a blurred look in the photograph, while high quality software is able to create a crisply clear finished photo. The final option is an in-camera noise reduction mode. The drawback to this method is if the camera misinterprets important signals for noise your pictures will be negatively altered. Once the picture is taken you cannot add the noise back in, while if your photo editing software makes a mistake you can just start over.
So we now know what noise is and how to remove it, the question remains, should we remove the noise on every photograph? In short, no, there are times when noise reduction is either not needed or will actually diminish the quality of your photograph. For example, in well-lit situations cameras take very quick exposures and the noise level is very low; so, noise reduction should not be necessary. If you are taking a photograph where the tiniest detail is critical a camera’s inboard software may confuse some of those details with noise. In these cases you can try photo editing software but you may still get a better result by leaving the photo untouched.
Some photographers actually use noise in very long exposure time photography to get a specific look for their photographs. As with all photography experimentation and practice will give you the best sense of what noise is and when to use software to fix it.