Hi,

the function bwconncomp returns a structure with 4 fields :

- Connectivity: connectivity of the connected components (can be defined with an input variable)

- ImageSize: size of the image

- NumObjects: number of connected objects found in the image

- PixelIdxList: a cell  array which contains the linear indices of the objects (the indices of the kth object are in PixelIdxList{k}).

If you want to acces to an object of a specific block, and find it in the whole image, you "just" have to add the x and y offset that define the position of the block in the whole image. Take care with the indices in PixelIdxList: linear indices, not row-column indices!

Thank you Mr. Raphaël Rouveure. But, is elements of cell array are also arrays contain linear indices of that connected object?

An example:

I create the image I with 2 objects

I = zeros(10,10);

 I(2:3,2:4) = 1; % first object

I(6,7:9) = 1; % second object

figure; imagesc(I); % visualization

Now we search the objects in image I:

CC = bwconncomp(I);

Disp(CC);

We see that 2 objects have been found. "CC.PixelIdxList{1}" gives the linear indices of the first object, and "CC.PixelIdxList{2}" the linear indices of the second object. 

For example, I create the variable L1 which contains the linear indices of the first object:

L1 = CC.PixelIdxList{1};

I also can transform the linear indices L1 in row-colomn indices (X1,Y1):

[X1,Y1] = ind2sub( size(I), L1 );