Parent Topic: ALGORITHM

GAMMA FILTER

To apply the MAP (Maximum a posteriori) approach to speckle reduction, the a priori knowledge of the probability density function of the scene is required. With the assumption of a gamma distributed scene, the Gamma MAP filter is derived with the following form:

       R   =   Im      for Ci <= Cu
       R   =   Rf      for Cu < Ci < Cmax
       R   =   Ic      for Ci >= Cmax

where:

       Rf  =   (B*Im + SQRT(D))/(2*A)
       Ci  =   S / Im
       Cu  =   SQRT(1/NumberLooks)
       Cmax =  SQRT(2)*Cu              
       Im  =   mean value of intensity within window
       S   =   standard deviation of intensity within window
       Ic  =   center pixel in filter window
       A   =   (1+Cu^2)/(Ci^2-Cu^2)
       B   =   A-NumberLooks-1
       D   =   Im*Im*B*B + 4*A*NumberLooks*Im*Ic

Parent Topic: ALGORITHM
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