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Finding number of connected components of a single value of pixel

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I have an image in the form of a matrix:
A zoomed-in portion of the upper right part is:
I would like to remove the disconnected black region, i.e. set that particular region's pixel values equal to that of the white region around it. I tried finidng the number of connected components using
CC = bwconncomp(filled_win);
but I am getting only 1 connected component.
CC.Connectivity = 8, CC.ImageSize = [416, 349]
CC.NumObjects = 1, CC.PixelIdxList = 1 X 1 cell
I have attached the relevant .mat file for reference. Can someone please help me with this?
  1 Comment
Ankit Sahay
Ankit Sahay on 18 Aug 2020
The filled_win.mat matrix is not binarized. It can be binarized using
filled_win = imbinarize(filled_win);
Even after doing this,
CC = bwconncomp(filled_win);
doesn't work. Maybe my concept of connected components is wrong, or maybe I am not using the command in the right way. Please help.

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Accepted Answer

jonas on 18 Aug 2020
Edited: jonas on 19 Aug 2020
If you want to find the two black (false) components, then you need to pass the complement and use 4-connectivity (no diagonal connections).
filled_win = imbinarize(filled_win);
CC = bwconncomp(~filled_win,4);
filled_win(CC.PixelIdxList{2}) = true;
What you found before was the single white component that is the white backgrund and the "boundary", returned as one object (as they are actually connected diagonally).

More Answers (1)

Image Analyst
Image Analyst on 23 Aug 2020
There are multiple ways to do it. You could just use bwareafilt() to extract the largest blob:
filled_win = bwareafilt(filled_win, 1, 4); % Take largest 4-connected blob.
If the interior blob was the largest blob (not your case) then that could take the interior blob. A different way is to assume that the interior blob has no pixels to the left of the containing blob. Then just take the left most blob, which will have a label of 1
labeledImage = bwlabel(filled_win, 4);
filled_win = ismember(labeledImage, 1); % Take outer blob.
  1 Comment
Image Analyst
Image Analyst on 23 Aug 2020
Don't forget to invert your mask! In MATLAB all the functions operate on the white blobs, not the black blobs.

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