Finding black region of an image

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Seyed Mousavikia 2022-9-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1810870-finding-black-region-of-an-image

14.PNG

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Hi I have an image like what I have attached (14.png) and I want to detect the black and white rectangles.

I have written a code to detect white rectangle like following:

img1 = imread('14.png');
img1r = imresize(img1,[240,320]);
subplot(1,2,1)
imshow(img1r)
title('Original&Resized Image')
img1rgray=im2gray(img1r);
white1 = img1rgray > 240; % Detect white parts of an image
maskwhite1 = bwareaopen(white1, 100); % Get rid of small blobs 100 pixels or smaller.
maskwhite1center = regionprops(maskwhite1, 'Centroid'); % Find centroids of what's left
subplot(1,2,2)
imshow(maskwhite1)
title('White Region and Its Center')
hold on
plot(maskwhite1center.Centroid(1),maskwhite1center.Centroid(2), 'r+', 'MarkerSize', 30, 'LineWidth', 2);
maskwhite1area = regionprops(maskwhite1, 'area');
fprintf('Area of White Part is: %d',maskwhite1area.Area);

It outputs area and center of the white region as I want it. How can I do it for black rectangle? Utilizing the same algorithms as above doesn't give good answer for black region... Any suggestions?