MATLAB: How to find neighbour pixels of a central pixel in a binary image

chain codeneighbour pixel

I am working on a binary image so how to find its neighbours. I have successfully found neighbour pixels in gray scale image but after its conversion from gray to binary its not giving me the pixels of binary image, its still showing me the pixels of gray scale image. Can anyone provide help on this?

Thanks in advance.

Best Answer

What do you need to do with the neighbours? Do you specifically need to know their indices? If so then in what order?

If you are doing a calculation such as region finding then you would normally use regionprops() or one of the image morphological operators.

If you are doing a calculation such as mean you would normally use conv2()

If you are doing a calculation such as local min or local max then one of the morphological operators can handle that.

If you are doing more complex arithmetic calculations on a block centered around the pixel then nlfilt()

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MATLAB: Random close numbers within an array

I would choose a random integer from 1 to 10000. We can use that as a linear index into the elements of your array, as if the array were unrolled into a vector. Since there are 100*100=10000 elements in total, this works.

Next, whatever the element is, which elements are adjacent to it? Thus up, down, right, left? For a 100x100 array, how would we find them? The trick is to understand how MATLAB stores elements in an array, and how that unrolled index works.

I'll do this for a fully general sized array, to make it more clear how things work. So assume an array of size nr by nc, thus nr rows and nc columns.

nr = 100;
nc = 100;
offset = [1 -1 nr -nr]; % down, up, right, left
% choose a random element in the matrix
randelem = randi(nr*nc,1); 
% what are the neighbors of this element?
neighbor = randelem + offset;
% which of those neighors fall off the edge of the world?
[r,c] = ind2sub([nr,nc],neighbor);
neighbor((r < 1) | (c < 1) | (r > nr) | (c > nc)) = [];
% a random choice among one of those that remain
neighbor = neighbor(randi(numel(neighbor),1));
% convert back to row and column indices:
[r,c] = ind2sub([nr,nc],[randelem,neighbor]);
r
r =
    55    56
    
c
c =
    81    81

MATLAB: How to perform grayscale reconstruction by erosion

There is an imreconstruct that does reconstruction. You give it a smaller "marker" image and your larger binary image and it returns an image with only the blobs that have marker(s) in them. See my attached demos.

Best Answer

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MATLAB: Random close numbers within an array

MATLAB: How to perform grayscale reconstruction by erosion

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