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Canon® EOS Rebel XSi/450D Guide to Digital SLR Photography by David D. Busch

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Dealing with Noise

Image noise is that random grainy effect that some like to use as a visual effect, but which, most of the time, is objectionable because it robs your image of detail even as it adds that “interesting” texture. Noise is caused by two different phenomena: high ISO settings and long exposures.

High ISO noise commonly appears when you raise your camera’s sensitivity setting above ISO 400. With Canon cameras, which are renowned for their good ISO noise characteristics, noise may become visible at ISO 800, and is usually fairly noticeable at ISO 1,600. This kind of noise appears as a result of the amplification needed to increase the sensitivity of the sensor. While higher ISOs do pull details out of dark areas, they also amplify ...

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