find a rectangle in an image in matlab in matlab

main.m
% read image 
img = imread('input_image.jpg');

% convert to grayscale
gray_img = rgb2gray(img);
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main.m
% apply edge detection using Canny algorithm
edge_img = edge(gray_img, 'Canny', [0.1, 0.2]);
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main.m
% find all the boundary pixels in the edge image
[B,L] = bwboundaries(edge_img, 'noholes');

% get the number of boundaries found
num_boundaries = size(B,1);
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main.m
% set minimum and maximum threshold for rectangle area
min_area = 100;
max_area = 10000;

% set minimum and maximum threshold for rectangularity
min_rectangularity = 0.80;
max_rectangularity = 1.20;

% loop through each boundary
for i=1:num_boundaries
    % convert the boundary pixels into a polyshape object
    poly = polyshape(B{i}(:,2), B{i}(:,1));
    
    % compute the area of the polyshape
    area = poly.area;
    
    % compute the perimeter of the polyshape
    perimeter = poly.perimeter;
    
    % compute the rectangularity of the polyshape
    rectangularity = area / (perimeter^2);
    
    % check if the polyshape is a rectangle based on its area and rectangularity
    if (area > min_area) && (area < max_area) && ...
       (rectangularity > min_rectangularity) && (rectangularity < max_rectangularity)
        % plot the rectangle
        plot(poly,'Color','red');
    end
end
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