% read images
image_1=readNPY('image_1.npy');
image_2=readNPY('image_2.npy');
...
image_12=readNPY('image_12.npy');

% change from type uint16 to double and calculate the maximum
image1=double(image_1);
image1MAX=max(max(image1));
...
image12=double(image_12);
image12MAX=max(max(image12));

% normalizes to the maximum
reference = exp(-1)
IMAGE1=fix(image1./image1MAX/reference);
...
IMAGE12=fix(image12./image12MAX/reference);

% calculate the spot size
spot_image1 = 2*sqrt(size(nonzeros(IMAGE1),1)/pi)/1000;
...
spot_image12 = 2*sqrt(size(nonzeros(IMAGE12),1)/pi)/1000;

% plot the spot size
spot = [spot_image1 spot_image2 ... spot_image12]
xvalue = [1 2 3 4 5 6 7 8 9 10 11 12]
plot(xvalue, spot)