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draw oriented rectangle around a blob

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function y=cadre(x)
info = regionprops(x,'Boundingbox') ;
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) ;
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');
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
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);
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)

Image Analyst
Image Analyst on 26 Mar 2022

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.




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