MATLAB: How can i draw circles on every black pixel area and keep the maximum circle that fit the black areas to find the fiber pore size

Question

Here is my image

I do not know how to select those black areas and draw circles on every black areas to find the mean pore size. Need help.

Answer 1

Invert the image, Then ask regionprops for the area or equivalent circular diameter, and centroid

binaryImage = grayImage < 128;
labeledImage = bwlabel(binaryImage);
measurements = regionprops(labeledImage, 'Area', 'EquivDiameter', 'Centroid');
allAreas = [measurements.Area]
allDiams = [measurements.EquivDiameter]
allCentroids = [measurements.Centroid]
xCentroids = allCentroids(1:2:end);
yCentroids = allCentroids(2:2:end);
% Plot red circles over centroids
plot(xCentroids, yCentroids, 'ro', 'MarkerSize', 10, 'LineWidth', 2);
% Get mean ECD (pore size)
meanDiameter = mean(allDiams);