finding region

Hi I have a matrix as follows:

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

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.

Answer 1

[Andrei Bobrov]

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);

[Mohammad Golam Kibria]

Thanks

Answer 2

[Sean de Wolski]

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

[Andrei Bobrov]

+1

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

Answer 3

[Paulo Silva]

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

[Mohammad Golam Kibria]

Thanks. Its also ok.How to pre-allocate the up and down vectors?