THIS MONTH: UNDERSTANDING NOISE

Noise can give your pictures a sandpaper-like finish, particularly in the shadows and mid-tones

W e looked in Digital Camera 177 at the role ISO plays in photography, and the tradeoff that pushing the camera sensitivity higher means in terms of increased ‘noise’. Noise is the digital equivalent of film grain – but where grain can enhance the appearance and mood of a picture, image noise is rarely as welcome.

Noise isn’t unique to digital cameras – it’s generated by all electronic devices. The key factor is the signal-to-noise ratio (SNR). When the signal – the intensity of light captured by the sensor in this case – is greater than the background noise generated by the electronic circuitry, then the image will show little interference. When the SNR is low, it’s harder to differentiate the image information and the unwanted noise.

There are a number of factors that cause image noise to bloom. Increasing the