find endpoint coordinates(x,y) of connected components using pixelidxlist

raw_image:

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CC = bwconncomp(zz_out);
numPixels = cellfun(@numel,CC.PixelIdxList);

figure, imshow(zz_out);

[smallest,idx] = min(numPixels);
zz_out(CC.PixelIdxList{idx}) = 0;

• I have an image which has some concurrent connected components, say as: line segments.Now i want to extract all the endpoint's coordinates(x,y) of those lines using pixelidlist.*

Answer 1

[Walter Roberson]

bwmorph() and ask for 'endpoints'

[Image Analyst]

bwmorph(skelImage, 'endpoints') will give an endpoints image but it's just an image of dots and the dots are not associated with any blob in particular. If you want to know what endpoints are associated with each blob, you can skeletonize and then label and call regionprops() asking for PixelList (NOTE, NOT 'PixelIdxList'). From there, there are couple of approaches. For example you could call endpoints and use find() and ismember() to find out what endpoints are associated with each blob. Or you can see which PixelList coordinates are rightmost and leftmost, or closest to some corner of the image to identify which pixels in PixelList are the endpoints (you wouldn't need bwmorph('endpoints') in that approach but that doesn't mean it's necessarily the fastest.

[sufian ahmed]

can u provide me the demo code please, Thanks :)

[Walter Roberson]

[L, Num] = bwlabel(zz_out);
for K = 1 : Num
  [epr{K}, epc{K}] = find( bwmorph(L == K, 'endpoints') );
end

Now epr{K} is the list of row indices of all of the endpoints of component #K, and epc{K} is the corresponding list of column indices. Any component that is not an isolated pixel should have at least two endpoints, and could have more if there are branches in it. (Note, though: I do not know how endpoint detection works if there are loops in the component.)