  Noise is always presents in digital images during image acquisition, coding,
transmission, and processing steps. Noise is very difficult to remove it from
the digital images without the prior knowledge of noise model. That is why,
review of noise models are essential in the study of image denoising
techniques. In this paper, we express a brief overview of various noise models.
These noise models can be selected by analysis of their origin. In this way, we
present a complete and quantitative analysis of noise models available in
digital images.
