Problems with kmeans clustering

31 Mar 2017
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Updated 3 Apr 2017
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OI have used the following code to segment the attached image. But each iteration on the same image shows different result. How can i solve this by using rng('default'); ?

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Adam
Adam on 31 Mar 2017
You should just need to explicitly set the seed (either to 'default' I guess or to any seed of your choice) before each call to kmeans if you want the same result each time.
sam CP
sam CP on 31 Mar 2017
Edited: sam CP on 31 Mar 2017
%k-means clustering algorithm
imData = reshape(Y,[],1);
imData = double(imData);
[IDX nn] = kmeans(imData,'default');
imIDX = reshape(IDX,size(Y));
figure, imshow(imIDX,[]),title('Image after applying k-means Clustering Algorithm');
Where can i apply the rng('default'); ?

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 Accepted Answer

the cyclist
the cyclist on 31 Mar 2017
Edited: the cyclist on 31 Mar 2017

2 votes

Looking at your code, you should be able to put the line
rng('default')
literally anywhere before the call to kmeans, because you do not call any other random number functions. But the safest bet might be to call it in the line just before the call to kmeans, in case you do something differently later.
But, also, I don't think you put 'default' in the actual kmeans call. So it should be like this ...
%k-means clustering algorithm
imData = reshape(Y,[],1);
imData = double(imData);
rng('default')
[IDX nn] = kmeans(imData);
imIDX = reshape(IDX,size(Y));
figure, imshow(imIDX,[]),title('Image after applying k-means Clustering Algorithm');

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sam CP
sam CP on 31 Mar 2017
Edited: sam CP on 31 Mar 2017
Error using kmeans (line 155) At least two input arguments required.
Error in Untitled2 (line 49) [IDX nn] = kmeans(imData);
Is there again need to specify the cluster number after applying rng('default') this line into my code.
Adam
Adam on 31 Mar 2017
Edited: Adam on 31 Mar 2017
Your original (from your comment above)
[IDX nn] = kmeans(imData,'default');
is not valid syntax for calling kmeans as far as I can see. There is no function signature where 'default' makes sense as a 2nd argument.
The code you attached calls it totally differently so just use that exactly as you did before.
sam CP
sam CP on 31 Mar 2017
Error using kmeans (line 265) K must be a positive integer value.
Error in Untitled2 (line 49) [IDX nn] = kmeans(imData,'default');
Adam
Adam on 31 Mar 2017
I;m really not understanding how your code relates in any way to the code you are saying creates an error. At a glance your code here looks fine, just add
rng('default')
on the line above
[cluster_idx, cluster_center] = kmeans(ab,nColors,'distance','sqEuclidean', ...
'Replicates',2);
I don't know where:
[IDX nn] = kmeans(imData, 'default');
is coming from at all.
sam CP
sam CP on 31 Mar 2017
The result will not be changed in each iteration on the same image. Thank you. The code works.
sam CP
sam CP on 31 Mar 2017
What changes i have to make in the code when i want to make 4 clusters?
Adam
Adam on 31 Mar 2017
Change nColours to 4.
Image Analyst
Image Analyst on 31 Mar 2017
Yeah, but let's put "works" in quotation marks because kmeans() is not a good method for finding brain tumors. Imagine what your algorithm would find for class 4 if there were no tumor present, or a very small one. Yeah, see what I mean?
sam CP
sam CP on 3 Apr 2017
I have already found that the kmeans clustering method can't be detect the tumor when it is very small.

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sam CP
sam CP
on 31 Mar 2017

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sam CP
sam CP
on 3 Apr 2017

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