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Why is my centroid giving only 1 element per blob using region props?

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Elias Unk
Elias Unk on 21 Jul 2017
Commented: Image Analyst on 23 Jul 2017
they should be 2 per blob x and y elements
  2 Comments
Elias Unk
Elias Unk on 22 Jul 2017
Iregion=regionprops(bw2,'centroid');
bw2 being a binary image of objects.

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Accepted Answer

Image Analyst
Image Analyst on 22 Jul 2017
It's not clear exactly what you're calling an "element". I'll use more precise terminology. If your Iregion structure array is just one structure, then you have just one blob. The Centroid field of that structure will be a 1-by-2 array with the x and y locations of the centroid of that blob.
If you have multiple blobs, then you need to add an index after the structure variable name to get just one of the blobs, try this:
props = regionprops(bw2,'centroid');
hold on;
for k = 1 : length(props)
% Get x and y centroid of the k'th blob.
xCentroid = props(k).Centroid(1);
yCentroid = props(k).Centroid(2);
plot(xCentroid, yCentroid, 'r+', 'MarkerSize', 40, 'LineWidth', 2);
% Let user know what they are
message = sprintf('The largest blob has area %d and a centroid at (x,y) = (%f, %f)',...
props.Area, xCentroid, yCentroid)
uiwait(msgbox(message));
end
You can also get all the x and y centroids into arrays doing this:
centroids = [props.Centroid];
xCentroids = centroids(1:2:end);
yCentroids = centroids(2:2:end);
  10 Comments
Image Analyst
Image Analyst on 23 Jul 2017
It is not 56. I doubt it ever was with the image that you supplied me.

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