how to trace ordered external counter of an object
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Silvia Caruso
on 30 May 2015
Commented: Image Analyst
on 30 May 2015
Hello,I need to order point on boundary.I have a logical image so I use bwtraceboundary, but the results is a Bb matrix empty.Can someone help me to understand the reason?I wrote this code:
[filename,pathname]=uigetfile('*.jpg');
im=imread([pathname filename]);
figure,imshow(im,[])
T=graythresh(im);
It=im2bw(im,T);
figure, imshow(It,[])
Bb=bwtraceboundary(It,[12 33],'E',8,Inf,'clockwise')
where r=12 e c=33 is the first pixel of the boundary that I want to order. I attach also the image. Thank you
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Accepted Answer
Walter Roberson
on 30 May 2015
It = ~im2bw(im,T);
Remember, black is "no object" for the purpose of boundary tracing.
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More Answers (1)
Image Analyst
on 30 May 2015
To get ordered points, use the much simpler bwboundaries(). You only would need to use bwtraceboundaries() if you, for some reason, wanted to start at one special, known pixel location. I have never ever needed to do that in all my image processing with MATLAB, or even before (that I can remember). The starting point just doesn't make any difference to me. It can start wherever it wants to as far as I'm concerned. That relieves me of having to find a starting point, which is not easy, or at the very least, a step that does not need to be done with bwboundaries(). Are you sure you need to start at one specific point? If so, why?
5 Comments
Image Analyst
on 30 May 2015
OK, good luck. What a funny coincidence -- that is the same paper Walter mentioned in the link I gave you in my last comment. I have not done that before so I don't have any code for it.
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