Reducing noise
The Detail tab of the Camera Raw dialog box has controls to reduce image noise, the extraneous visible artifacts that degrade image quality. Image noise is made up of luminance (grayscale) noise, which makes an image look grainy, and chroma (color) noise, which is usually visible as colored artifacts in the image. Photographing with a higher ISO or less-sophisticated digital camera can result in images with objectionable noise.
Luminance Smoothing reduces grayscale noise, while Color Noise Reduction reduces chroma noise. Moving a slider to zero turns off its noise reduction.
When making Luminance Smoothing or Color Noise Reduction adjustments, first zoom in on the preview image for a better view.
Moving the Luminance Smoothing slider to the right reduces grayscale noise, and moving the Color Noise Reduction slider to the right reduces chroma noise.