How to find boundaries of a blob such that they bound the image and not include it

Hi,

I have an image with adjacent blobs. I want the boundaries of these blobs such that the boundaries are outside the blob and contain the blob completely inside it. How can I do so?

bwboundaries gives the boundaries such that the it is on the edge of the blob and hence do not contain the blob completely inside it.

Answer 1

[Walter Roberson]

Extract the blobs separately. For example,

labeled = bwlabel(YourImage);
for idx = 1 : numblob
   thisbwimage = labeled == idx;
   ...
end

For each one, imdilate() with ones(3,3) and subtract the original from that, and then ask for the boundaries of that: the boundary should enclose the blob.

Note: this procedure will fail if the blob touches the outside edge, unless you pad the original with a sliver of black all the way around to prevent blobs from touching the edge.