finding endpoints of a label

Hi, I have the following matrix. I =

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

[B,L,N,A]=bwboundaries(I,'noholes');

L =

     0     0     0     0
     0     1     1     1
     0     0     0     0
     0     0     0     0
     0     0     2     0
     0     0     2     0
     0     0     2     0

idx=find(L==1) endpoints of label 1 are (2,2) and (2,4)

I need to find that endpoints similarly in case of label 2. Thanks endpoints of label 1 are (2,2) and (2,4)

Answer 1

[Oleg Komarov]

Based on the idea of http://www.mathworks.com/matlabcentral/answers/10293-finding-neighbor-of-a-position

I = [0 0 0 0
    0 1 1 1
    0 0 0 0
    1 0 0 0
    1 0 0 1
    1 0 0 1
    1 1 1 1];

[L,num] = bwlabel(I,4);
sz = size(I);
InEn = zeros(num,2);

for n = 1:num
    % Find initial point of connected component
    InEn(n,1) = find(L == n,1,'first');
    l = InEn(n,1);
    co = 1;

      while true
          % row and col subs
          [r c] = ind2sub(sz,l(co)); % c = ceil(l/4); r = mod(l,4)+ c*sz(1)
          % Calculate 4-connected subs
          neigh(1:4,1:2) = [r+[0;-1;+1;0] c+[-1;0;0;1]];
          % Convert to positions
          idx = (neigh(:,2)-1)*sz(1) + neigh(:,1);
          % Keep positions in the range of L
          idx = idx(ismember(idx,1:prod(sz)),:);
          % Move onto next 4-connected component
          co = co+1;
          idx = idx(~ismember(idx, l) & L(idx)  == n);
          % If empty then we reached the end
          if idx
              l(co) = idx;
          else
              break
          end
      end
      % Assign end
      InEn(n,2) = l(end);
  end

[Mohammad Golam Kibria]

This works good for this matrix.But if my matrix becomes as follows:

I = [0 0 0 0

0 1 1 1

0 0 0 0

1 1 1 1

1 1 0 1

1 1 1 0

1 1 1 0];

then it shows the following error?

??? In an assignment A(I) = B, the number of elements in B and

I must be the same.

[Oleg Komarov]

In this case the question is which ones are the endpoints?

Answer 2

[Walter Roberson]

B = bwboundaries(I,'noholes');
xy_1_first = B{1}(1,:);
xy_1_last = B{1}(end,:);
xy_2_first = B{2}(1,:);
xy_2_last = B{2}(end,:);

[Mohammad Golam Kibria]

But in case :

I =

0 0 0 0

0 1 1 1

0 0 0 0

1 0 0 0

1 0 0 1

1 0 0 1

1 1 1 1

L =

0 0 0 0

0 2 2 2

0 0 0 0

1 0 0 0

1 0 0 1

1 0 0 1

1 1 1 1

It is not showing proper output,xy_1_first should be (4,1)

and xy_1_last should be (5,4) or vice versa.

Answer 3

[Andrei Bobrov]

L = bwlabel(I)
I2 = bwmorph(I,'endpoints')
epout = arrayfun(@(i1)find(I2 & L == i1)',1:max(L(:)),'un',0)

example:

I =
     0     1     0     1     1     1
     1     1     0     0     0     1
     1     0     0     0     0     0
     1     0     1     1     1     0
     0     0     1     0     0     0
     0     0     1     0     1     1
     0     0     1     0     0     0
     0     0     0     0     0     0
     1     1     0     0     1     0
     0     1     1     0     1     0
     0     0     1     0     1     0
     0     0     1     0     1     0
     0     1     1     0     1     0
     0     1     0     0     0     0
     0     1     0     1     0     0
     0     1     1     1     0     0
     0     0     0     0     0     0

>> L = bwlabel(I)
I2 = bwmorph(I,'endpoints');
epout = arrayfun(@(i1)find(I2 & L == i1)',1:max(L(:)),'un',0);
L =
     0     1     0     4     4     4
     1     1     0     0     0     4
     1     0     0     0     0     0
     1     0     3     3     3     0
     0     0     3     0     0     0
     0     0     3     0     5     5
     0     0     3     0     0     0
     0     0     0     0     0     0
     2     2     0     0     6     0
     0     2     2     0     6     0
     0     0     2     0     6     0
     0     0     2     0     6     0
     0     2     2     0     6     0
     0     2     0     0     0     0
     0     2     0     2     0     0
     0     2     2     2     0     0
     0     0     0     0     0     0
>> epout{5}
ans =
    74    91
>>

[Mohammad Golam Kibria]

can I extend this for any size of I is much larger than this

, for example if I want to find the end point of label 5.

[Andrei Bobrov]

I think you can

[Mohammad Golam Kibria]

But where to change