Pepper=black, salt=white; image bipolar noise (bipolar), mathematically defined as p(y)={alpha,y=x when; beta,y=a when; gama,y=b when.} , where x is the original image pixel, the pretzel noise is noted as z, y is the contaminated noise, here alpha + beta + gama = 1, the image contaminated by pretzel noise is statistically described, the pixel that appears to be pretzel noise, the pixel of the image with the noise will only appear in two values: a or b. From the Digital Image Processing, Wang Qiao, Science Publishing House.