How to display the two biggest blobs in terms of area?

I have a binary image 'i' which I have attached here. From this image, I want to find the two biggest blobs in terms of area. When I tried this code, I am able to find the biggest blob which I have attached and the next biggest blob is removed.

labeledImage=bwlabel(i);
measurements=regionprops(labeledImage,'Area');
allAreas=[measurements.Area];
[biggestArea, indexOfBiggest]=sort(allAreas,'descend')
biggestBlob=ismember(labeledImage,indexOfBiggest(1));
biggestBlob=biggestBlob>0;
figure,imshow(biggestBlob,[]);

I tried to use the bwareafilt() but MATLAB R2013a does not support it. Kindly help me to display the next biggest blob.

Thanking you.

[sanyukta]

Thank you so much..It worked..

Answer 1

[David K.]

In the line

biggestBlob=ismember(labeledImage,indexOfBiggest(1));

you are finding the biggest by looking at the first index in a sorted array. So to get the second biggest you do

secondBlob=ismember(labeledImage,indexOfBiggest(2));

Then you can combine them simply by doing

twoBiggest = biggestBlob | secondBlob;

This is because both blobs are binary - 1s and 0s - so by doing an OR operation it makes every white part in both images seen in both images.

[Image Analyst]

I think

twoBiggest = ismember(labeledImage, indexOfBiggest(1:2));

would be simpler. It gets you both of the two biggest blobs all in one line of code.

Answer 2

[Image Analyst]

It'w very bad practice to call your image i (the imaginary variable). Call it binaryImage, mask, or BW instead. You might want to call imclearborder() to get rid of that outer blob, unless you want it.

mask = imclearborder(mask);

I don't believe you need to use

biggestBlob=biggestBlob>0;

because ismember() will return a logical image already.

Other than that, David's solution should work.

[sanyukta]

Thank you so much for this valuable suggestion.