Camera College
Find out what causes image noise in your shots and how you can control it
Noise is a generic term used to describe a disturbance to an electrical signal. Often irregular and always unwanted, it is generated by all electronic devices and takes on a variety of forms – from the ‘hiss’ of audio equipment to a pixellating television display.
While discussions about sources of noise can get very deep and technical, its effects are obvious when it comes to digital photography. Broadly speaking, noise is similar to film grain in that it can obscure fine details and it gets progressively worse as the ISO is increased. But where grain can add to the mood of a picture, noise can simply leave you in an ugly mood, such is its rather artificial look. It manifests itself in a number of ways, including a curtain of dots across an image, clusters of coloured speckles, and horizontal and vertical coloured banding. Your mileage may vary over how much it bothers you: noise may be acceptable in an action-packed sports shot taken at night, for instance, but a complete turn-off when it comes to a detailed macro image.
The key factor when it comes to noise is the signal-to-noise ratio (SNR). When the ‘signal’ – the intensity of light captured by the camera’s sensor in our case – is greater than the background noise generated by the electronic circuitry, the image will show little interference. When the SNR is weaker, however, it is harder to differentiate the noise and the image information.
There are several factors that can raise the level of noise to the point where it has a detrimental effect on the