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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'then
+        H=double(D<=D0);
+        
+    case'Laplacian'then
+        H_temp=double(D<=D0);
+        H=(4*(%pi)^2*D^2);
+        H=H.*H_temp;
+        
+    case'butterworth'then
+        if argn(2)==4 then
+            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'then
+        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);
+
+
+
+
+
+
+
+