finding region

Question

Mohammad Golam Kibria 2011-6-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/10501-finding-region

Hi I have a matrix as follows:

I=

   1     0     0     0     0     0     0     0     0     
   0     1     1     0     0     0     0     0     0     
   0     0     0     1     1     1     1     1     1     
   0     0     0     0     0     0     0     0     0     
   0     0     0     0     0     0     0     0     0

Here 1 has divided the matrix in two parts I need to have the indices of these two separate parts. say idx1 will be upper zeros and idx2 contains lower zero indices.Can any one help.

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Answer 1

Andrei Bobrov 2011-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/10501-finding-region#answer_14451

so in http://www.mathworks.com/matlabcentral/answers/10396-finding-interior-or-exterior-points

BW2 = bwmorph(I,'diag');
L = bwlabel(~BW2);
Id1 = bwdist(I,'chessboard') == 1;
for i1 = 1:max(L(:))
    L(bwdist(L == i1,'chessboard')==1 & Id1) = i1;
end
idx1 = find(max(L(1,:))==L);
idx2 = find(max(L(end,:))==L);

EDIT as at Sean

L = bwlabel(~I,4);
idx1 = find(max(L(1,:))==L);
idx2 = find(max(L(end,:))==L);

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Mohammad Golam Kibria 2011-6-30

Thanks

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Answer 2

Sean de Wolski 2011-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/10501-finding-region#answer_14454

CC = bwconncomp(~I,4);

CC.PixelIdxList will contain the linear indices. To get the sub indices either use regionprops with the 'pixellist' option or ind2sub

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Andrei Bobrov 2011-6-29

+1

Hi Sean! I stupid, forgotten about the variable 4-connectivity. Thanks

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Answer 3

Paulo Silva 2011-6-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/10501-finding-region#answer_14463

Just for fun

I=[1     1     0     0     0     0     0     0     0     0     
     0     0     1     1     0     0     0     0     0     0     
     0     0     0     0     1     1     1     1     1     1     
     0     0     0     0     0     0     0     0     0     0     
     0     0     0     0     0     0     0     0     0     0];
up=[];down=[];
for c=1:size(I,2)
    d=0;u=1;
    for r=1:size(I,1)
        if(d==1)
            down=[down sub2ind(size(I),r,c)];
        end
        if(I(r,c)==1)
            d=1;u=0;
        end
        if u==1
            up=[up sub2ind(size(I),r,c)];
        end
    end
end
disp('index of zeros bellow the 1')
down
disp('index of zeros above the 1')
up
%for big arrays it's better to pre-allocate the up and down vectors, much faster