One of the largest problems many folks have with digital photography is the amount of noise that ends up in the final image. Noise basically presents itself as graininess or speckles, usually most recognizable across larger areas of uniform colour such as sky. While sometimes it is a desirable effect such as in some of the photos below, often you will want to minimise it. The bad news is that there is no perfect solution to noise problems, but the good news is that there are things you can do to reduce, and in many cases, eliminate noise in your photographs.
What Causes Noise?
Truly knowing how to reduce or eliminate noise is better served by knowing what causes it. In photography there are several causes of noise.
The first scenario is that image sensor heat can increase enough to stimulate electrons (“Thermal Noise”). These superfluous electrons then get mixed in with the “true” photoelectrons that are the real target of our image sensor. The analog signal (which is converted to pixels by the sensor) is therefore contaminated before it even gets to that point.
In some situations the above scenario can cause each of the photosites on an image sensor to generate superfluous signals which can then contaminate the neighboring photosites. On smaller image sensors which cram more photosites into a smaller area, this effect can be magnified.
Another common cause of noise is shooting at higher ISO settings. As these settings basically magnify the light signal, they also magnify other unwanted signals such as background interference (eg. heat sources). When you are photographing an area of low light, the background signals can be strong enough to compete with the signals from the limited light of the area you are shooting.
What Can a Photographer Do About Noise?
As with anything, photography presents us with a series of compromises when it comes to solving the problem of noise. Here are some of the more obvious things you can do to reduce noise in your images.
Shoot At a Low ISO – It's a simple one, but if the situation will allow it, then turn down the ISO. Reducing the sensitivity of the sensor reduces the chance that it will pick up unwanted interference.
Reduce Shutter Speed – This simply reduces the chance that unwanted signals will get mixed in with the ones you really want to capture. Again, it's really only a solution if the shooting conditions allow for you to reduce shutter speed.
Utilise the In-Camera Noise Reduction Feature – Most DSLRs come with an in-camera noise reduction feature. In many cases this does a fine job of reducing noise during image processing. The downsides to this are that the processing time of the image is often increased (sometimes by many seconds) and there can also be loss of finer detail in the shot.
Don't be Afraid to Use Post Processing – There are several pieces of dedicated software available to digital photographers with the sole purpose of reducing noise in your images. Many people recommend noise reduction software as an integral part of any photographer's arsenal. You can also utilise noise reduction techniques in other software such as Photoshop, GIMP or Lightroom. Some tutorials you might be interested in include:
- Turn Down the Noise in Photoshop
- Noise Removal with Selective Gaussian Blur in GIMP
- Noise Reduction in Lightroom 3 Video Tuorial
Keep Your Camera Cool – This one is often overlooked, but many people report that simply keeping your camera cool (or at least out of hot storage areas) immediately before a shoot can have a significant impact on improving noise in photos. The idea here is to minimise electrons that are stimulated by heat on your sensor therefor reducing contamination in the signal.
Noise is simply one of those challenges that photography throws at us from time to time that make it challenging to get that perfect shot. With a little forethought it's easy enough to account for it and continue the chase!