image noise
Because image acquisition, processing, transmission and other processes will inevitably be polluted by noise, which hinders people's understanding and analysis of images. Common image noises include Gaussian noise, salt and pepper noise, etc.
1.1 Salt and Pepper Noise
Salt and pepper noise, also known as impulse noise, is a kind of noise that is often seen in images. It is a random white point or black point, which may be black pixels in bright areas or white pixels in dark areas ( or both). The salt and pepper noise may be caused by sudden and strong interference of the video signal, analog-to-digital converter or bit transmission error, etc. For example, a failed sensor results in a minimum pixel value, and a saturated sensor results in a maximum pixel value.
1.2 Gaussian noise
Gaussian noise refers to a type of noise whose noise density function obeys a Gaussian distribution. This noise (also known as normal noise) model is often used in practice due to the mathematical tractability of Gaussian noise in the spatial and frequency domains. The probability density function of a Gaussian random variable z is given by:
