MATLAB: How to analyze one image 100 times using for loop

image processingMATLAB

Hello,
I have an image. I want to divide the image into 100 frames and analyze each frame separately. Please find my code below:
img = imread('1F1.jpg');
k = 1;
    for j = 1: 100
            dblSubtractedImage = img(j) - img(k);
            s = dblSubtractedImage*5;
            L = mat2gray(s);
            imshow(L);
            im = imclearborder(255-imclearborder(255-s));
            hc = sum(im,2);
            mask = hc >= 14500;
            fr = find(mask, 1, 'first');
            lr = find(mask, 1, 'last');
            cr = im(fr:lr, :);
            D = std2(cr);
            meanIntensityValue = mean2(cr);
            % imshow(cr)
            K = mat2gray(cr);
            min_image = min(K(:));
            max_image = max(K(:));
            % figure
            imshow(K)
            [rows, columns, numberOfColorBands] = size(K);
            if numberOfColorBands > 1
                grayImage = K(:, :, 2);
            end
            binaryImage = grayImage~= 40;
            area2 = sum( binaryImage,'all');
    end
    
AverageArea = (sum(area2))/100;
AverageStandardDeviation = (sum(D))/100;
AverageIntensityValue = (sum(meanIntensityValue))/100;
The first frame is used as a reference. The first frame is subtracted from all the other frames subsequently. The resulting images are then masked using a threshold which is shown above. Few other parameters such as the mean, standard deviation and the area of each of the resulting image are found. At the end of the for loop, the average value of the parameters above are found. However, I am getting the error message below. Any help would be appreciated. Thank you.
>> f
Index exceeds the number of array elements (0).
Error in mat2gray (line 38)
if limits(2)==limits(1) % Constant Image
Error in f (line 17)
K = mat2gray(cr);

Best Answer

Hi,
I understand that you wish to analyze each frame separately. However, there’s some problem in the code you have written.
In line 4, you subtract the 2 images and store the output in sblSubtractedImage. Now, when you display sblSubtractedImage, you get 0 as output. Hence, the variables you use thereafter are also 0 and variable cr stores a 0 ×1 empty uint8 column vector. And therefore, you get error while using mat2gray.
What is happening in your case is, you have saved the file normally (using Windows option to save file) and you are reading subtracting first 2 pixels which are both white. However, if you use imwrite (MATLAB function) to save the image you will get the desired portion and this should solve your error.
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