how to find the neighbors of a pixel in a binary image

I have a binary image i want to determine the 8 neighbors of this pixels.

[Andrew Chen]

What do you want exactly? Do you want the coordinates of the white pixels around the pixel in question? Do you want a sum of the white pixels around the pixel in question, i.e. if it has 3 white neighboring pixels out of 8 do you want the output to just be 3?

[kmla]

I want to know if my pixel is totally around by white pixels or black pixels

[Andrew Chen]

When you say totally around, do you mean if all 8 surrounding pixels are white or not? What do you want the program to tell you if there are only 5 pixels that are white out of the 8?

[kmla]

yes the all 8 surrounding pixels are white

Answer 1

[Walter Roberson]

conv2(BinaryImage, [1 1 1; 1 0 1; 1 1 1])

The result of this will be 8 for locations that a completely surrounded by white pixels, and will be 0 for pixels that are completely surrounded by black pixels, and will be in-between for pixels that are partly surrounded.

[Walter Roberson]

is_surrounded_by_white = conv2(BinaryImage, [1 1 1; 1 0 1; 1 1 1]) == 8;

Note: this assumes that the corner and edge pixels are not to be considered as being surrounded by white, that only pixels "in the middle" are to be found.

[Walter Roberson]

https://www.mathworks.com/matlabcentral/answers/265690-how-to-find-neighbour-pixels-of-a-central-pixel-in-a-binary-image#comment_427252

[kmla]

I have this part of image

i want to determine if the pixels in the red circle is in the black region or white region

[Walter Roberson]

Index the is_surrounded_by_white result at the row and column indexes to determine if the pixel is completely surrounded or not.

However, consider that if you were to move the left circle a bit further right, it could end up being on the boundary between white and black.

    WWWBBBBB
    WWWBBBBB
    WWOBBBBB
    WWWBBBBB

The circle is intended to be shown positioned on top of a 'W'. It would be "in" the white area as far as 5 of its 8 neighbours are concerned, and I think if asked very few people would say that it is part of the black area.

What result would you like to have output in such a case, where something is not completely surrounded by white or black?

    WWWWWW
    WWWBWW
    WWOWWW
    WWWWWW
    WWWWWW

Is the O (with 'W' there underneath) in the white region or is the presence of that single black pixel enough to say that the O is outside of the white region?