How to use looping method to crop image dynamically (auto-cropping)?

Hello. How to crop image using dynamic cropping method in matlab? Is there any example implementation codes?

Lets say, my original image have two different sizes which are 482 x 841 pixels and 608 x 865 pixels, so can I use loop step at first to extend the pixels which those that not enough pixels if I want to crop into 512 x 512 pixels? If the image size is enough to crop into 512 x512 pixels so no need to extend the pixels. I recently use this code:-

%To read input image
I=imread('1_776.jpg');
imfinfo('1_776.jpg')

First image, image size 482 x 841 px

Second image, image size 608 x 865 px

%To resize image
out = padarray(I, [10 10], 0, 'both');
imshow(out);
imwrite(out,'resize1.jpg');

but this is manual. Now I want it to automatically crop only specific area.

[Rik]

So you want to crop images if they exceed 512 pixels in either height or width, and want to pad them with black if they are smaller than 512x512?

Answer 1

[Tejas]

Hello Dayangku,

I am assuming you want to automate the process of resizing images to 512 x 512 pixels by adding padding if any dimension is smaller than 512 pixels and cropping if any dimension exceeds 512 pixels.

To achieve this, follow the steps below:

• List the names of the images to be resized in a cell array.
• Loop through each image in the cell array.
• Check if the image’s rows or columns require padding.
• Add padding to the rows or columns if necessary.
• Crop the image to the desired size using the ‘imcrop’ function.
• Save the cropped image using the ‘imwrite’ function.

The code snippet below demonstrates how this can be done:

% Add the names of images to be resized
listOfImages = {'I1.jpeg', 'I2.jpeg'}; 
desiredCropSize = [512, 512];

for itr = 1:length(listOfImages)
    % Read image based on current index
    I = imread(listOfImages{itr});
    [rows, cols, ~] = size(I);
    
    % Check if row/column require padding
    if rows < desiredCropSize(1) || cols < desiredCropSize(2)
        % Calculate padding sizes
        padRows = max(0, desiredCropSize(1) - rows);
        padCols = max(0, desiredCropSize(2) - cols);
        
        % Evenly add padding to the image. Image is padded twice 
        % to deal with odd number of padRows/padCols
        I = padarray(I, [ceil(padRows/2), ceil(padCols/2)], 'both');
        I = padarray(I, [floor(padRows/2), floor(padCols/2)], 'both');
    end
    
    % Crop the image to the desired size
    croppedImage = imcrop(I, [1, 1, desiredCropSize(2)-1, desiredCropSize(1)-1]);
    
    % Display the cropped image
    imshow(croppedImage);
    
    % Save the cropped images
    outputFileName = sprintf('Image_%d_resized.jpg', itr);
    imwrite(croppedImage, outputFileName);
    imfinfo(outputFileName)
end

For a better understanding of the functions ‘imcrop’ and ‘for’, refer to the following links:

• imcrop : https://www.mathworks.com/help/images/ref/imcrop.html
• for: https://www.mathworks.com/help/matlab/ref/for.html