Finding number of connected components of a single value of pixel

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Ankit Sahay
Ankit Sahay . 2020년 8월 18일
댓글: Image Analyst . 2020년 8월 23일
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?
  댓글 수: 1
Ankit Sahay
Ankit Sahay 2020년 8월 18일
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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채택된 답변

jonas 2020년 8월 18일
편집: jonas 님. 2020년 8월 19일
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).
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추가 답변 (1개)

Image Analyst
Image Analyst 2020년 8월 23일
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.
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Image Analyst
Image Analyst 2020년 8월 23일
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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