how to detect black colors

How can I detect a lot of black colors and mark bounding boxes from overall gray image?

[Rik]

What di you try? Have a read here and here. It will greatly improve your chances of getting an answer.

In this case, it looks like a simple threshold will do (maybe follwed by regionprops).

Answer 1

[yanqi liu]

yes，sir，may be the view：https://ww2.mathworks.cn/matlabcentral/answers/1656655-how-can-i-detect-black-color-and-mark-bounding-box-from-overall-gray-image

or use the follow code

img = imread('https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/905790/Screenshot_20220224-200026_Samsung%20Notes.jpg');
mask = imdilate(~im2bw(img, 100/255), strel('square', 39));
props = regionprops(mask, 'BoundingBox');
figure; imshow(img, []); 
hold on;
for i = 1 : length(props)
rectangle('position', props(i).BoundingBox, 'EdgeColor', 'g', 'LineWidth', 2)
end