Matlab: How to get the surface (m2) of an area from which i have 1 coordinate

Question

I have a binary image in matlab and i have a centroid of an area (see the * in the picture) which was previously calculated. Now based on this centroid x and y, i would like to get to get the surface (m2) of the circle the centroid is in. But i don't know how to select an area which is very similar to the rest of the circles and i only know the centroid of the one i want. Any suggestions ? Thx in advance .

Answer 1

This is very easy with morphological reconstruction. While I don't know how you can access the matlab implementation, you should use a black image as a single white pixel at your centroid position as the marker image, and your shown binary image as the mask image, and the resolut of a morphological reconstruction by dilation will be an image just showing the selected circle in white. Count white pixels and you are done.