bwboundaries mistaking holes for children

I have the following binary image that I trying to use bwboundaries.

Simple image from a threshold operation

obstacles = ~bwareaopen(majorityFilter,10000);
imshow(obstacles)

Total of 10 obstacles correct? When I apply bwboundaries, I'm getting 13 obstacles.

[currPoly,L]=bwboundaries(logical(~obstacles),8,'holes');

currPoly =

13×1 cell array

{ 553×2 double}

{ 565×2 double}

{ 574×2 double}

{ 747×2 double}

{ 855×2 double}

{ 880×2 double}

{1242×2 double}

{ 484×2 double}

{ 609×2 double}

{ 700×2 double}

{ 257×2 double}

{ 21×2 double}

{ 13×2 double}

Any idea why this is happening?

Answer 1

[Walter Roberson]

You specifically ask for the boundaries for 'holes', so the boundaries you get back include the boundaries for holes.

Your black and white image, top, is after area openning, and you are not doing any hole-filling after that area open.

Your top right and bottom right blobs both have essentially pinholes. Those pinholes account for two of the three extra boundaries.

Your bottom right blob has the larger quadralateral hole; that provides the 13th boundary.

Answer 2

[Image Analyst]

Try filling holes

obstacles = imfill(~obstacles, 'holes');
[currPoly, L]=bwboundaries(obstacles);