With varying degrees, all digital cameras produce electronic noise, extraneous pixels sprinkled throughout an image. Higher ISO, underexposure, long exposure, and oversharpening can increase this effect. Lightroom's Noise Reduction feature can easily reduce the effect of electronic noise, while maintaining image detail.
Lightroom's Noise Reduction controls are found under the Detail pane. Figure 4-48
Noise isn't necessarily bad. It can give an image dimension and authenticity.
Examine Image First
Noise isn't always apparent when you examine an image at low magnification. Use Lightroom's magnifying tools to enlarge your image after applying tone and color controls (but before applying additional sharpening), and the noise will become apparent. Figure 4-49
Pay particular attention to areas of continuous tone and shadow areas. Note the makeup of the noise. Does it look like a colored patchwork quilt? Or is the noise speckled and monochromatic?
Some images actually contain a combination of chromatic (color) and luminance (monochromatic) noise. Getting a handle on the type of noise will help determine which Lightroom control —Luminance or Color, or both—will be more effective.
Noise Reduction Procedure