Aihua_DIP5_ImageRestoration图像复原解释.pptVIP

Max and min filters finding the brightest points reduces pepper noise. finding the darkest points reduces salt noise. ImageCorrupted By PepperNoise ImageCorrupted By SaltNoise Result Of Filtering Above With A 3*3 Min Filter Result OfFilteringAboveWith A 3*3Max Filter Midpoint filter The midpoint filter simply computes the midpoint between the maximum and minimum values combines order statistics and averaging works best for randomly distributed noise, like Gaussian or uniform noise. Alpha-trimmed mean filter Idea: delete the d/2 lowest and the d/2 highest gray-level values of g(s,t) in the neighborhood Sxy. Let gr(s,t ) represent the remaining mn–d pixels. A filter formed by averaging these remaining pixels is called an alpha-trimmed mean filter: where the value of d can range from 0 to mn - 1. d = 0：arithmetic mean; d = mn - 1: median filter other d: multiple types of noise, such as a combination of salt-and-pepper and Gaussian noise. ImageCorrupted By UniformNoise Image FurtherCorrupted By Salt andPepper Noise Filtered By5*5 ArithmeticMean Filter Filtered By5*5 MedianFilter Filtered By5*5 GeometricMean Filter Filtered By5*5 Alpha-TrimmedMean Filter 5.3.3 Adaptive filters Adaptive filter: whose behavior changes based on statistical characteristics of the image inside the filter region defined by the m×n rectangular window Sx,y. Adaptive, local noise reduction filter Filter is to operate on a local region Sxy。The response of the filter at any point (x, y) on which the region is centered is to be based on four quantities: (a) g(x, y): the value of the noisy image at (x, y) ; (b) ση2: the variance of the noise corrupting f(x, y) to form g(x, y) ; (c) mL: the local mean of the pixels in Sxy; (d) σL2: the local variance of the pixels in Sxy; Expected behavior: If ση2 =0, return simply the value of g(x, y). If the local variance is