convert band pass to band reject

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mecheal
mecheal 2013-7-16
i've this code for band pass filter ,any one can convert it to band reject filter ??
% Bandpass Butterworth Filter
clearall;
closeall;
clc
micro = imread('grass2.jpg');
micro = double(micro);
[nx ny] = size(micro);
nx
ny
u = micro;
micro = uint8(u);
imwrite(micro,'grass5.jpg');
fftu = fft2(u,2*nx-1,2*ny-1);
fftu = fftshift(fftu);
subplot(2,2,1)
imshow(micro,[]);
subplot(2,2,2)
fftshow(fftu,'log')
% Initialize filter.
filter1 = ones(2*nx-1,2*ny-1);
filter2 = ones(2*nx-1,2*ny-1);
filter3 = ones(2*nx-1,2*ny-1);
n = 4;
fori = 1:2*nx-1
forj =1:2*ny-1
dist = ((i-(nx+1))^2 + (j-(ny+1))^2)^.5;
% Use Butterworth filter.
filter1(i,j)= 1/(1 + (dist/120)^(2*n));
filter2(i,j) = 1/(1 + (dist/30)^(2*n));
filter3(i,j)= 1.0 - filter2(i,j);
filter3(i,j) = filter1(i,j).*filter3(i,j);
end
end
% Update image with passed frequencies.
fil_micro = fftu + filter3.*fftu;
subplot(2,2,3)
fftshow(filter3,'log')
fil_micro = ifftshift(fil_micro);
fil_micro = ifft2(fil_micro,2*nx-1,2*ny-1);
fil_micro = real(fil_micro(1:nx,1:ny));
fil_micro = uint8(fil_micro);
subplot(2,2,4)
imshow(fil_micro,[])

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Image Analyst
Image Analyst 2013-7-16
Just invert the filter. Make filter3 = 1-filter3. Try that.
  1 个评论
mecheal
mecheal 2013-7-16
do u trace my code ? is it correct ? how can i identify the frequencies that included in the rejected band ??

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