I = imread('rice.png');

BW = imbinarize(I);

[B,L] = bwboundaries(BW,'noholes');
imshow(label2rgb(L, @jet, [.5 .5 .5]))
hold on
for k = 1:length(B)
   boundary = B{k};
   plot(boundary(:,2), boundary(:,1), 'w', 'LineWidth', 2)
end

BW = imread('blobs.png');

[B,L,N,A] = bwboundaries(BW);

imshow(BW); hold on;
colors=['b' 'g' 'r' 'c' 'm' 'y'];
for k=1:length(B),
  boundary = B{k};
  cidx = mod(k,length(colors))+1;
  plot(boundary(:,2), boundary(:,1),...
       colors(cidx),'LineWidth',2);

  %randomize text position for better visibility
  rndRow = ceil(length(boundary)/(mod(rand*k,7)+1));
  col = boundary(rndRow,2); row = boundary(rndRow,1);
  h = text(col+1, row-1, num2str(L(row,col)));
  set(h,'Color',colors(cidx),'FontSize',14,'FontWeight','bold');
end

figure
spy(A);

BW = imread('blobs.png');

[B,L,N] = bwboundaries(BW);

imshow(BW); hold on;
for k=1:length(B),
   boundary = B{k};
   if(k > N)
     plot(boundary(:,2), boundary(:,1), 'g','LineWidth',2);
   else
     plot(boundary(:,2), boundary(:,1), 'r','LineWidth',2);
   end
end

BW = imread('blobs.png');

[B,L,N,A] = bwboundaries(BW); 
figure; imshow(BW); hold on; 
% Loop through object boundaries  
for k = 1:N 
    % Boundary k is the parent of a hole if the k-th column 
    % of the adjacency matrix A contains a non-zero element 
    if (nnz(A(:,k)) > 0) 
        boundary = B{k}; 
        plot(boundary(:,2),... 
            boundary(:,1),'r','LineWidth',2); 
        % Loop through the children of boundary k 
        for l = find(A(:,k))' 
            boundary = B{l}; 
            plot(boundary(:,2),... 
                boundary(:,1),'g','LineWidth',2); 
        end 
    end 
end