Incorrect centers with bwconncomp and regionprops

Hi, I have a matrix like the one linked.

You can see it with figure,imagesc(Matrix(:,:));

I am using this programme to find the centers of the circles of the matrix:

CC = bwconncomp(Matrix);
n=26;
m=n*n;
S = regionprops(CC,'Centroid');

and it worked. But now it finds the centers at coordinates 1000,1020 and so on... I don't know why

Answer 1

[Walter Roberson]

fig = openfig('Matrix.fig');
h = findobj(fig,'type','image');
Matrix = h.CData;

CC = bwconncomp(Matrix);
n=26;
m=n*n;
S = regionprops(CC,'Centroid');
cents = sortrows(vertcat(S.Centroid));
max(cents)

ans =

          490.682464454976          491.909090909091

So I am not observing what you are indicating.

Answer 2

[Image Analyst]

I didn't run the program, but a common cause of this is people getting (x,y) confused with matrix indexes (row, column). Note that regionprops() returns Centroid as (x,y), and plot() also uses x,y. Matrices however use (row, column), which is (y, x). Make sure you know what each argument or index really represents.

By the way, this code might be useful

xy = vertcat(S.Centroid);
xCentroids = xy(:, 1);
yCentroids = xy(:, 2);
hold on;
plot(xCentroids, yCentroids, 'r+', 'LineWidth', 2, 'MarkerSize', 30);
hold off;

and next time, don't post .fig files. Post the actual text data file or a mat file - it's so much more convenient.