Question

I have a grayscale image, which I convert to black and white image, and do some processing on it. After the processing, I have a black and white image which has groups of white pixels in a black image. So I want to place circles around the areas which are white in resultant image, but in original image.
I have thought of many approaches but am still unable to start with any approach.
Please help.

Answer 1

You can use regionprops to get some statistics about connected white regions in a binary image, and estimate a region radius from that.

im = imread('moon.jpg');
bw = im2bw(im);

stats = regionprops(bw);

imshow(im);
hold on;

t = 0:.01:2*pi;
for i = 1:numel(stats)
    bb = stats(i).BoundingBox;
    radius = mean([bb(3),bb(4)])/2;

    plot(bb(1)+radius+radius*sin(t), bb(2)+radius+radius*cos(t));
end

Gives: