draw oriented rectangle around a blob

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function y=cadre(x)
info = regionprops(x,'Boundingbox') ;
imshow(x)
hold on
for k = 1 : length(info)
BB = info(k).BoundingBox;
rectangle('Position', [BB(1),BB(2),BB(3),BB(4)],'EdgeColor','g','LineWidth',1) ;
end
I am using this code with a segmented image in input, and I have this result :
input output
I would like the rectangles to be the smallest and with the same orientation as the objects, to get the angles for exemple.
How can I modify my code ?

Accepted Answer

Scott MacKenzie
Scott MacKenzie on 27 Mar 2022
Edited: Scott MacKenzie on 27 Mar 2022
Something like this seems to work:
img = imread('testimage.jpg');
bw = imbinarize(im2gray(img),'adaptive','Sensitivity',0.45);
info = regionprops(bw, 'all');
imshow(img);
hold on;
minSize = 50; % ignore small/noise regions (adjust as necessary)
angles = [];
for k = 1:length(info)
% get region properties
w = info(k).MajorAxisLength;
h = info(k).MinorAxisLength;
x = info(k).Centroid(1) - w/2;
y = info(k).Centroid(2) - h/2;
theta = info(k).Orientation;
if h < minSize % skip the small/noise regions
continue;
end
angles = [angles theta];
ps = polyshape([x, x, x+w, x+w], [y, y+h, y+h, y]);
ps2 = rotate(ps, -theta, [x+w/2 y+h/2]);
plot(ps2, 'EdgeColor','r', 'FaceColor','none', 'LineWidth',2);
end
angles
angles = 1×2
67.7787 -44.8710
  1 Comment
Image Analyst
Image Analyst on 27 Mar 2022
OK but note that the boxes don't completely contain the blobs.

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More Answers (2)

Walter Roberson
Walter Roberson on 26 Mar 2022
Edited: Walter Roberson on 26 Mar 2022
Note that if you are looking for the angles then regionprops() 'Orientation' will give you the angle of the major axes.

Image Analyst
Image Analyst on 26 Mar 2022

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