gamma_map.m

SAR图像三种滤波方法： 1、gamma_MAP滤波； 2、均方差滤波： 3、Lee滤波

function ret_im = Gamma_MAP( im, w_size, out_size, NL, bound, flag)
%GAMMA_MAP Gamma-MAP filter for SAR speckle reduction
%   im：SAR影像
%   w_size：窗口大小，奇数 3 5 7 9等
%   out_size：输出图像的大小，可以是'same'或者'full'
%   NL：number of Looks，等效视数
%   bound：边缘扩展模式，分为'symmetric'，'replicate','circular'。
%   flag：计算时是否包含中心像素，0为不包含，1为包含。
%
%   ret_im：滤波结果影像
%
% barbara_gammaMAP = Gamma_MAP( barbara_noisy, 5, 'same', 3, 'symmetric', 0);


im = double(im);

[im_Mean, im_Var] = im_mean_var(im, w_size, out_size, bound, flag);

im_Std = sqrt(im_Var);

Cu = sqrt(1/NL);
Cmax = sqrt(2)*Cu;

Ci = im_Std ./ im_Mean;

A = (1+Cu^2) ./ (Ci .^2 - Cu^2);
B = A - NL - 1;
D = im_Mean.^2 .* B.^2 + 4.*A.*NL.*im_Mean.*im;

Rf = (B.*im_Mean + sqrt(D)) ./ (2.*A);

tmp1 = (Ci<=Cu);
tmp1 = tmp1 .* im_Mean;

tmp2 = (Ci>Cu & Ci<Cmax);
tmp2 = tmp2 .* Rf;

tmp3 = (Ci >= Cmax);
tmp3 = tmp3 .* im;

ret_im = tmp1+tmp2+tmp3;