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//Ex4_20
// Image Sharping in Frequency Domain Using the Laplacian
// Version : Scilab 5.4.1
// Operating System : Window-xp, Window-7
//Toolbox: Image Processing Design 8.3.1-1
//Toolbox: SIVP 0.5.3.1-2
//Reference book name : Digital Image Processing
//book author: Rafael C. Gonzalez and Richard E. Woods
clc;
close;
clear;
xdel(winsid())//to close all currently open figure(s).
function[H]=lowpassfilter(type1,M,N,D0,n)//lowpassfilter is used to filter an image .
u=0:(M-1);
v=0:(N-1);
idx=find(u>M/2);
u(idx)=u(idx)-M;
idy=find(v>N/2);
v(idy)=v(idy)-N;
[U,V]=meshgrid(v,u);
D=sqrt(U.^2+V.^2);
select type1
case'ideal'
H=double(D<=D0);
case'Laplacian'
H_temp=double(D<=D0);
H=(4*(%pi)^2*D^2);
H=H.*H_temp;
case'butterworth'
if argn(2)==4
n=1;
end
H = ones(M,N)./(1+(D./D0).^(2*n));
H_temp=ones(M,N)+(4*(%pi)^2*D^2);
H=H.*H_temp;
case'gaussian'
H=exp(-(D.^2)./(2*(D0^2)));
else
disp('Unknownfiltertype.')
end
endfunction
/////////////////////////////////// Main Programm ////////////////////////////////
a=imread("Ex4_20.tif");
//gray=rgb2gray(a);
gray=im2double(imresize(a,[540 540]));
figure,ShowImage(gray,'Gray Image');
title('Original Image','color','blue','fontsize',4);
[M,N]=size(gray);
h=fft2(gray);//fft2() is used to find 2-Dimensional Fast Fourier Transform of an matrix
i=log(1+abs(h));
in=fftshift(i);//fftshift() is used to rearrange the fft output, moving the zero frequency to the center of the spectrum.
inm=mat2gray(in);
filt=lowpassfilter('Laplacian',M,N,55); // User Define Function which generate Filter Mask Corresponding to Low Frequency
filt_shift=fftshift(filt);
n=filt.*h;//Multiply the Original Spectrum with the Filter Mask.
Image_filter=real(ifft(n));
Image_filter=mat2gray(Image_filter);
z=gray+Image_filter;
figure,ShowImage(mat2gray(z),'Filtered Image');
title('Filtered Image with Specific Cut-Off Frequency','color','blue','fontsize',4);
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