Comments on: Connected component labeling - Part 5

By: Steve

Steve — Sun, 15 Nov 2009 14:38:59 +0000

Alvin—I already wrote a lot about these algorithms in this series. Be sure to check out all the related posts. There’s also quite a lot of information about connected components labeling available in other online sources.

By: Alvin

Alvin — Sun, 15 Nov 2009 09:35:20 +0000

Hi steve,
I go thru’ the bwlabel and bwlabeln, but i don’t understand how to write the algorithm with referring its theory. Mind to put on a simple example for my reference?
Million thanks to you, Steve.

Rgds,
Alvin

By: Steve

Steve — Fri, 22 Aug 2008 13:25:03 +0000

DP—There are one or two Image Processing Toolbox product demos that might be helpful.

By: DP

DP — Fri, 22 Aug 2008 13:18:01 +0000

Hi Steve:
i am happy to saw that your update on “Image visualization using transparency” to label the two connected objects as a single object.
However, i am having a problem with seperating two overlap object to seperate. in binary image i am trying to seperate two/three overlap rectangular object to seperate them and calculate the centroids of each seperated object. could you please show me one example?

Thank you.
Sincerely,
DP

By: Steve

Steve — Fri, 22 Aug 2008 13:12:29 +0000

Nawal—You can the convex hull of each connected component via regionprops. Then you need a routine to determine if two polygons overlap. You don’t a routine that works for general polygons, because the convex hull polygons will be, well, convex. :-) You might try searching the MATLAB Central File Exchange in addition to Google.

By: Nawal

Nawal — Thu, 21 Aug 2008 23:52:53 +0000

Thank you Steve.

Sorry, in my case there is an overlap between bounding box of connected component not in connected component it self. I read today in some research paper the follwing idea we can use convex hull of connected component. where if there are an overlaping between two convex hull there are an overlap between bounding box of component.

By: Steve

Steve — Thu, 21 Aug 2008 17:22:26 +0000

Nawal—You can’t have two connected components that are overlapping. “Overlapping” indicates that you really only have one connected component.

By: Nawal

Nawal — Thu, 21 Aug 2008 15:05:55 +0000

hi steve.
How we can detect an overlaping between connected cmponent.
can you help me.

Thanks in advance
Nawal

By: Steve

Steve — Tue, 15 Jul 2008 16:54:04 +0000

Karthik—You didn’t check your A matrix. This line:

A(1:5+1:end) = 1;

doesn’t do what you thought it would.

See this comment from Tim Davis about efficiently putting 1s on the diagonal of a sparse matrix.

By: Karthik

Karthik — Tue, 15 Jul 2008 16:23:54 +0000

Hi Steve, i have a problem in using dmperm function, as my adjacency pairs are not incremental. ie. example in below case i dont have label 4, as it forms a individual un-connected cluster.

pairs = [ 2 3; 3 2; 1 2; 2 1; 5 6; 6 5];

here i have 5 nodes in total (ie. 1,2,3,5,6)

A = sparse(pairs(:,1), pairs(:,2), 1);
A(1:5+1:end) = 1;

[p, q, r, s] = dmperm(A);

this does not give correct result. how to solve this problem?