finding neighbours around central rows and columns

Hi,

I was wondering if some can help me regarding the row-column looping.

I have my row, col positions as [row,col]. e.g. array 300X2

I am trying to find their 8 neighbour values as:

 neighbors_id= [matrix_cell_id(row, col),...
        matrix_cell_id(row-1, col-1),...
        matrix_cell_id(row-1, col),...
        matrix_cell_id(row-1, col+1),...
        matrix_cell_id(row, col-1),...
        matrix_cell_id(row, col+1),...
        matrix_cell_id(row+1, col-1),...
        matrix_cell_id(row+1, col),...
        matrix_cell_id(row+1, col+1)];

however when I run this code I get multiple values (matrix 300*2700) instead of 300row x 9 columns (corresponding to those neighbors) array.

Any clue is more than welcome,

Thanks a lot,

[Walter Roberson]

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

[Sajid Rahim]

clear all;

[filename pathname]=uigetfile('*.jpg;*.png;*.tif;*.tiff;*.gif;*.bmp;');

inputimage=imread([pathname filename]);

I=inputimage;

% I = imread('5.png') ;

I = rgb2gray(I) ;

[y,x] = find(I) ;

figure imshow(I)

hold on

plot(x,y,'.b') % x

% y

% z=(y+x)/2

% plot(z,'.r')

a=x(1)

b=y(1)

plot(x(1),y(1),'*y')

plot(x(end),y(end),'*y')

% neighbors(1) = (a,b-1);

neighbors(1) = I(a,b-1);

plot(a,b-1,'*r')

neighbors(2) = I(a,b+1); plot(a,b+1,'*r')

neighbors(3) = I(a,b+2);

plot(a,b+2,'*r') neighbors(4) = I(a+1,b);

plot(a+1,b,'*r')

neighbors(5) = I(a+1,b+1);

plot(a+1,b+1,'*r')

neighbors(6) = I(a+2,b+2);

plot(a+2,b+2,'*r')

neighbors(7) = I(a+2,b);

plot(a+2,b,'*r')

neighbors(8) = I(a+2,b+1);

plot(a+2,b+1,'*r')

neighbors(9) = I(a+2,b+2);

plot(a+2,b+2,'*r')

Answer 1

[Jan]

Try it with one element at first:

ThePoint = matrix_cell_id(row, col);
size(ThePoint)

What do you observe? This replies a matrix, which is bigger than you expect.

Use sub2ind to get the single elements.

index = sub2ind(size(matrix_cell_id), row, col);

Now the surrounding elemnts can be determined by simple additions to the linear index also.

[sensation]

Thanks for your answer Jan.

I tried this on my data but sub2ind rewrites ids, so I can not extract I think the right ids and areas in the second step. I have 670*9 matrix now but it does not take into account anymore my original rows and columns.

[Walter Roberson]

[r_of_index, c_of_index] = ind2sub(size(matrix_cell_id), index);