Equalize_and_Histeq.m

function im2 = equalize(im)
    %Input: im (uint8 grayscale image)
    %    or:im (uint8 colored image)
    %Output: im2 (uint8 output image after histogram equalization)
    %Get the size of the input image
    [rows, cols] = size(im);
    
    %Compute the histogram of the input image (256 possible intensity values for uint8)
    histogram = zeros(1, 256);
    for i = 1:rows
        for j = 1:cols
            intensity = im(i, j);    %Get the pixel intensity value
            histogram(intensity + 1) = histogram(intensity + 1) + 1;  
        end
    end
    %Compute the cumulative distribution function (CDF)
    cdf = zeros(1, 256);
    cdf(1) = histogram(1);  %First value of CDF is the first histogram value
    for k = 2:256
        cdf(k) = cdf(k - 1) + histogram(k);
    end
    %Normalize the CDF (Scale it to the range [0, 255])
    cdf_min = min(cdf(cdf > 0));  %The first non-zero CDF value
    cdf_max = cdf(end);  %The last value in the CDF (total number of pixels)
    
    %Create a mapping of each intensity value to the new equalized intensity
    equalized_map = zeros(1, 256);
    for k = 1:256
        equalized_map(k) = round((cdf(k) - cdf_min) / (cdf_max - cdf_min) * 255);
    end
    
    %Apply the mapping to get the new image
    im2 = zeros(rows, cols, 'uint8');
    for i = 1:rows
        for j = 1:cols
            im2(i, j) = equalized_map(im(i, j) + 1);  
        end
    end
end

%Plot the histeqed images
%im1_histeq = histeq(im1);
%im3_histeq = histeq(im2);


%Load the original image, show the original image, perform equalize
%function, & show the equalized & histeq image                   
 
im_raw = imread('image_colored.tif');
% Can also be replaced with grayscale image
% convert RGBA image (4 channels) to RGB (3 channels)
if ndims(im_raw) == 3 && size(im_raw, 3) == 4
    im = im_raw(:, :, 1:3);  
else
    im = im_raw;
end

subplot(1, 3, 1); 
imshow(im); 
title('Original'); 
ylabel('image');

im2 = equalize(im); 
subplot(1, 3, 2); 
imshow(im2); 
title('Equalized');

im1_histeq = histeq(im);
subplot(1, 3, 3);
imshow(im1_histeq);
title('histeq');

% plot the histograms in another figure
figure; 
subplot(1, 3, 1);
imhist(im);
title('Original Histogram');

subplot(1, 3, 2);
imhist(im2);
title('equalized Histogram');

subplot(1, 3, 3);
imhist(im1_histeq);
title('histeq Histogram');