The chief component in image noise and the one that’s most difficult to remove because software can’t easily distinguish between random image noise and real image detail. The result is that the more noise reduction you apply, the more you tend to lose fine image detail, resulting in images with obvious and objectionable ‘smoothing’.
One of the two types of digital image noise and caused by random variations in the colour of neighbouring pixels. Colour noise is relatively easy for software to remove without any significant impact on the image quality. Luminance (contrast) noise is the other type, and much more difficult to remove effectively.