finding interior or exterior points

Hi, I have a matrix as follows: I =

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

L=bwlabel(I)

L =

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

Here label 1 makes a continuous curve line. I need to know where point (5,4) belongs to, upper portion or lower portion. Thanks

Answer 1

[Andrei Bobrov]

Have matrix

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

We need to know where point (5,4) belongs to, upper portion or lower portion.

Variant of solution.

idx = {5,4};
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
if L(idx{:}) == L(1,1), disp('pixel in upper portions' );
elseif L(idx{:}) == L(end,1), disp('pixel in lower portions' );
else disp('pixel on boundaries of portions' );
end

_*best way, as in http://www.mathworks.com/matlabcentral/answers/10501-finding-region*_

L = bwlabel(~BW2,4);
if L(idx{:}) == max(L(1,:)), disp('pixel in upper portions' );
elseif L(idx{:}) == max(L(end,:)), disp('pixel in lower portions' );
else disp('pixel on boundaries of portions' );
end

[Mohammad Golam Kibria]

Ok, thanks

Answer 2

[Walter Roberson]

The upper and lower portions are the same, as your curve of label 1 does not partition the space: you can go around by way of (3,1) to pass between "upper" and "lower" without encountering any "1".