Neighbor and center points of matrix

Hi, I have matirx of 256 \times 256. I want to find and save indices of nine neighbors of each center point in 1D matrix or in 256\times 256 matrix.

[Jan]

What does "each center point" mean? Can you give a small example of the wanted output?

[Ghulam Murtaza]

I means that I have M=256x256 matrix and after padding it it becomes 258x258. Now select on center and its neighbors after that move to next center not sharing neighbor with previous center and so on.

Answer 1

[Steve Eddins]

See my 25-Feb-2008 blog post called "Neighbor indexing" for a general technique.

You'll need to pay careful attention to what happens with matrix elements that are on the edges of the matrix, as these elements don't have nine neighbors. I often zero-pad to simplify the code.

Also, in that blog post, you'll see this line of code:

neighbors = bsxfun(@plus, idx, neighbor_offsets)

In today's MATLAB, you can write that more simply as:

neighbors = idx + neighbor_offsets