Grouping boundary points of several ROIs

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Sunetra Banerjee
Sunetra Banerjee 2021-6-23
评论： DGM 2021-6-23
Hi,
I have 6 region of interests (ROI) and their boundary points and centroids. I got this boundary points randomly through MATLAB programming. Do you have an idea how to group them according to corresponding ROIs in MATLAB? I need individual ROI's boundary points for further calculations.
I have applied Kmeans and it didn't work.
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Sunetra Banerjee
Sunetra Banerjee 2021-6-23
Thank you so much. I got
idx =
6×1 cell array
{170×1 double}
{210×1 double}
{190×1 double}
{243×1 double}
{182×1 double}
{162×1 double}
So, That means the first ROI has 170 boundry points, 2nd has 210 boundary points and so on. Right?
DGM
DGM 2021-6-23
Yes, but like I said, bear in mind which one is "first", "second", etc. The label array L contains a map of each object it found in the image, each labeled with their ordinal value. In this case, the objects are numbered [5 6 4 3 2 1] from top to bottom.

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DGM
DGM 2021-6-23
编辑：DGM 2021-6-23
This may be extraneous, but if you don't need the boundary coordinates for anything other than finding the extrema, consider this instead:
inpict = imread('lumber.png')>128;
% you'll need the centroid anyway
S = regionprops(inpict,'centroid','extrema');
imshow(inpict); hold on
for n = 1:numel(S)
% calculate the right and left extrema of this object
rextrema = mean(S(n).Extrema(3:4,:),1);
lextrema = mean(S(n).Extrema(7:8,:),1);
% for sake of demonstration, show where the extrema are
plot(rextrema(1),rextrema(2),'*')
plot(lextrema(1),lextrema(2),'*')
end
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Image Analyst
Image Analyst 2021-6-23
For next time, look up bwboundaries() - better than boundary(). Also look up bwferet() if you want extrema locations and distances.
DGM
DGM 2021-6-23
That's a good point. I was assuming the goal was to find the horizontal extrema instead of the maximal diameter.

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