how to get the 1st and the 3rd boundary objects in the binary image

i segmented an image and got a binary image bw

when i do the below line, i get only 1 numberOfblobs

[labeledImage, numberOfblobs] = bwlabel(bw, 8);

but when i do

structBoundaries = bwboundaries(bw);

i get 5 boundaries, and i need only the 1st and the 3rd boundary objects in the binary image. How to get it in a new binary image with only the first and the third region?

Answer 1

[Guillaume]

Isn't it

structBoundaries([1 3])

?

By the way structBoundaries is a very misleading name, implying the variable is a structure when it is actually a cell array.

[Image Analyst]

You can use bwselect() or ismember() on the labeled image.

labeledImage = bwlabel(binaryImage);
% Extract blob #3
blob3 = ismember(labeledImage, 3); % blob3 is a binary image.