Reducing Digital Noise

Digital noise is the polka-dot effect in images with long exposures or images shot at high ISO settings in low-light situations. The effect is most noticeable in images shot in low-light situations. Many consider digital noise to be a synonym for film grain. Although the causes are the same, the effects are quite different. Some film photographers purposely shoot images with enhanced grain for artistic effect.
However, digital noise detracts from the image because of the sporadic bright pixels within solid colors, and lacks the aesthetic qualities of enlarged film grain.

You can reduce digital noise by taking your photographs at ISO settings between 100 and 400. The 400 ISO setting provides more exposure latitude, but even 400 ISO exhibits a little noticeable digital noise. If your subject is not moving and you can’t use a flash, using a tripod can allow you to shoot successfully with low ISO settings. Many DSLR models come with a noise-reduction feature. If you turn on the noise reduction feature, it is automatically activated when you shoot long exposures. The camera color corrects at the pixel level, processing the image as it’s shot. The main negative aspect to digital noise reduction on the camera is the significant lag time required for the image to process between shots. One way to avoid this lag time between shots is to keep the noise-reduction feature on your camera off and use the Aperture Noise Reduction adjustment controls after you’ve imported your images.