I) Image noise is random variation of brightness or color information in images, and is usually an aspect of electronic noise. It can be produced by the image sensor and circuitry of a scanner or digital camera.Image noise can also originate in film grain and in the unavoidable shot noise of an ideal photon detector.

ii) The best way to reduce noise in an image will always be to just avoid it in the first place. Methods like adding artificial light, increasing shutter speed, or widening apertures to let more light through your lens are effective ways to brighten your exposure instead of increasing ISO.