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4 Getting the Right Exposure > Dealing with Noise

Dealing with Noise

Image noise is that random grainy look 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 Sony cameras, which generally have good ISO noise characteristics, noise may become visible at ISO 800, and is usually fairly noticeable at ISO 1600 and above. 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 non-signal information randomly, creating noise. The Sony Alpha SLT-A77 automatically applies noise reduction that is strong enough to be visible as a reduction of sharpness in the image for any exposures taken when the ISO is set at ISO 1600 or higher. Figure 4.20 shows two pictures shot during different at-bats at the same baseball game. Both were exposed at ISO 1600, but with noise reduction applied in the version at top, and with no noise reduction at bottom. (I’ve exaggerated the differences between the two so the grainy/less grainy images are more evident on the printed page. The halftone screen applied to printed photos tends to mask these differences.)


  

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