how to store histograms

i want to store histograms of various images separately and use them afterwards for histogram matching.

how can i store the histograms and create a proper database ?

please help

Answer 1

[Anudeep Kumar]

Hey @sakshi Garg,

To store histograms of various images, you can use 'imhist' to calculate the histogram of image data and then MATLAB struct and hold and save it in a .mat file.

You can refer to the below sample code with appropriate changes to the 'imageFolder' and 'imageFiles'

% Set the folder containing your images
imageFolder = 'Enter_your_Image_path';
imageFiles = dir(fullfile(imageFolder, '*.jpg')); % Change extension if needed

% Choose histogram type: 'grayscale' or 'rgb'
histType = 'grayscale'; 

% Create a structure to store histograms
histDB = struct();

for i = 1:length(imageFiles)
    % Read image
    imgPath = fullfile(imageFolder, imageFiles(i).name);
    img = imread(imgPath);
    
    % Compute histogram
    if strcmp(histType, 'grayscale')
        grayImg = rgb2gray(img);
        histVals = imhist(grayImg);
    elseif strcmp(histType, 'rgb')
        histVals = [];
        for c = 1:3
            histVals = [histVals; imhist(img(:,:,c))];
        end
    end
    
    % Normalize histogram
    histVals = histVals / sum(histVals);
    
    % Store in structure
    histDB(i).filename = imageFiles(i).name;
    histDB(i).histogram = histVals;
end

% Save to .mat file
save('image_histograms.mat', 'histDB');
disp('Histograms saved to image_histograms.mat');

Later you can load the .mat file and compare the histogram based on any distance meteric you want.

I have attached the documentation of 'imhist' for your reference:

https://www.mathworks.com/help/releases/R2024b/images/ref/imhist.html

Also here is the documentation on 'struct' and 'matfile' in MATLAB and how to use them:

https://www.mathworks.com/help/releases/R2024b/matlab/ref/struct.html

https://www.mathworks.com/help/releases/R2024b/matlab/ref/matlab.io.matfile.html