% script3.m: Sharp Filter
% Jan Rothen
% 9th of June 2004
% start with: matlab -nojvm -nodesktop

function script3 = script3(filename)
    img = imread(filename); % Load the image file 
    
    img = rgb2gray(img); % Convert to gray scale   
    img = im2double(img); % Convert data into double values

    subplot(2, 1, 1)
    imshow(img); % Display original grayscaled image
    title('Original');
    
    filterLow  = [ 1,  4,  6,  4, 1; % Low pass filter
                   4, 16, 24, 16, 4;
                   6, 24, 36, 24, 6;
                   4, 16, 24, 16, 4;
                   1,  4,  6,  4, 1];
    filterLow = 1/256 * filterLow;
                           
    filterHigh = [ -1, -1, -1; % High pass filter
                   -1,  8, -1;
                   -1, -1, -1];
                                                      
    kL = zeros(size(img)); % Increase filter size
    kL(1:5, 1:5) = filterLow;
    
    kH = zeros(size(img)); % Increase filter size
    kH(1:3, 1:3) = filterHigh;
    
    filterLow = fft2(kL); % Fourier Transfom  
    filterHigh = fft2(kH); % Fourier Transfom  
    filterCombined = filterLow + filterHigh; % Combine both transformed filters
        
    img = fft2(img); % Fourier Transfom  
    img = img .* filterCombined; % Convolution
    img = abs(ifft2(img)); 

    imwrite(img, 'script3_processed.png', 'png'); % Write result to file
     
    subplot(2, 1, 2)
    imshow(img); % Display processed Image
    title('Sharp filtered');