Create Small Neighborhood of image

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Yohanes Setiawan 2020-2-3

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https://ww2.mathworks.cn/matlabcentral/answers/503331-create-small-neighborhood-of-image

评论： Vinai Datta Thatiparthi 2020-2-21

I want to make small neighborhood of every pixel x. The small neighborhood has center x (pixel x be the center) in radius w.

Suppose w=5, so I have 5x5 small neighborhood with pixel x is the center of neighborhood.

How can I make it?

Thank you.

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Vinai Datta Thatiparthi 2020-2-7

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https://ww2.mathworks.cn/matlabcentral/answers/503331-create-small-neighborhood-of-image#answer_414260

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Hello Yohanes,

val = imread(' ... '); % Your input matrix/image
[xCoOrd, yCoOrd] = [ ... ] % Co-Ordinates of the center pixel
nbh = 5; % Neighborhood Size

For a square neighborhood, the variable roi will hold the intensity values of neighboring pixels.

limit = floor(nbh/2);
roi = val(xCoOrd-limit:xCoOrd+limit, yCoOrd-limit:yCoOrd+limit);

Additionally, if you want the positions of the neighbors in subscripts,

rowLen = [xCoOrd - limit: xCoOrd + limit]'; % Range of Rows
colLen = [yCoOrd - limit: yCoOrd + limit]; % Range of Columns
rowIdx = meshgrid(rowLen, 1:nbh)'; % All the X coordinates of neighbors
colIdx = meshgrid(colLen, 1:nbh); % All the Y coordinates of neighbors

Hope this helps!

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Yohanes Setiawan 2020-2-12

编辑：Yohanes Setiawan 2020-2-12

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Halo,

Thank you very much. Your answer is really help me.

For the edge cases, how if I use this:

a=xCoOrd-limit;
b=xCoOrd+limit;
c=yCoOrd-limit;
d=yCoOrd+limit;
[row col]= size(val);
if a<1
    a=1;
end
if b>row
    b=row;
end
if c<1
    c=1;
end
if d>col
    d=col;
end

Is that logical correct (especially in the neighborhood concept of image processing) for computing neighbor of a pixel? Or we need the padding as you give me the link for solution?

Vinai Datta Thatiparthi 2020-2-21

Hey Yohanes,

Yes, this approach could work as well. Simple if-else statements checking for edge cases, and then assigning the neighbors (the ones that are beyond scope) NaN values.

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