8-neighbors of a pixel
The points ND(P) and N4(P) are together known as 8-neighbors of the point P, denoted by N8(P).
Some of the points in the N4, ND and N8 may fall outside image when P lies on the border of image. See the following table :
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4-neighbors of a pixel p are its vertical and horizontal neighbors denoted by N4(p)
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8-neighbors of a pixel p are its vertical horizontal and 4 diagonal neighbors denoted by N8(p)
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Summary is as follows :
ND
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N4
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ND
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N4
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P
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N4
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ND
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N4
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ND
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N4 – 4-neighbors
ND – diagonal neighbors
N8 – 8-neighbors (N4 U ND)