a=imread('F:\學習\數字圖象\作業(yè)\第一次上機\小丑.jpg');             %讀取
b=double(a);                                      %數據類型轉換便于傅立葉變換   
F=fftshift(fft2(b));                              %傅立葉變換
A=sqrt(real(F).^2+imag(F).^2);                    %求頻譜    
A=(A-min(min(A)))/(max(max(A))-min(min(A)))*255;  %頻譜歸一化
%頻譜處理（去噪）------------------------------------------------
for i=83:89
for j=74:80
F(j,i)  =0;
end
end
 for i=100:113
for j=35:45
F(j,i)  =0;
end
 end
 for i=17:30
for j=84:97
F(j,i)  =0;
end
 end
 for i=40:47
for j=49:56
F(j,i)  =0;
end
 end
%--------------------------------------------------------------
F=F*(1/(1+(72/sqrt(i^2+j^2))^100));
A=sqrt(real(F).^2+imag(F).^2);
A=(A-min(min(A)))/(max(max(A))-min(min(A)))*255; %頻譜處理

f=ifft2(ifftshift(F));                           %反變換
c=uint8(f);                                      %數據類型還原
figure;                                          %打開新窗口
imshow(c);                                       %去噪之后的圖