同學那里copy來的代碼，僅供使用時參考

理想低通濾波器

M=256;
N=256;
d0=50;
m=fix(M/2);
n=fix(N/2);
%h=zeros(256,256);
for i=1:M
    for j=1:N
        d=sqrt((i-m)^2+(j-n)^2);
        if(d<=d0)
            h(i,j)=1;
        else
            h(i,j)=0;
        end
    end
end
mesh(h)

巴特沃斯低通濾波器

clc;
clear;
M=256;
N=256;
d0=50;
n=2;
m=fix(M/2);
n=fix(N/2);
%h=zeros(256,256);
for i=1:M
    for j=1:N
        d=sqrt((i-m)^2+(j-n)^2);
        h(i,j)=1/(1+0.414*(d/d0)^(2*2));
    end
end
mesh(h)
axis off

高斯低通濾波器

clc;clear;
M=256;
N=256;
d0=50;
m=fix(M/2);
n=fix(N/2);
%h=zeros(256,256);
for i=1:M
    for j=1:N
        d=sqrt((i-m)^2+(j-n)^2);
        h(i,j)=exp(-(d^2)/(2*(d0^2)));
    end
end
mesh(h)
axis off