Vectorization, check if points coordinate is exist in an image or no

Can anyone help me to vectorize this for loop. It is basically ckecking if the x and y coordinate of is one in N matrix or not. Thank you

for i = 1:length(coordinates)
    DD = coordinates(i,:);
    DDD = N(DD(1),DD(2));
    if DDD ==1
        %%%if the dicom point is inside the mask
        signVector(i) = -1;
    else
        %%%if the dicom point is outside the mask
        signVector(i) = +1;
    end
end

Answer 1

[Teja Muppirala]

signVector = ones(size(coordinates,1),1);
inds = sub2ind(size(N),coordinates(:,1),coordinates(:,2)); % Convert to linear indices
signVector( N(inds)==1 ) = -1;

[Mahsa]

Thank you. I was not aware of sub2ind function.

Answer 2

[Andrei Bobrov]

ii = coordinates;
d3 = N(ii(:,1),ii(:,2));
signVector = -ones(numel(d3),1);
signVector(d3 ~= 1) = 1;

[Mahsa]

Thank you. but it did not work d3 should be a vector not a matrix

[Image Analyst]

Give us code, or a .mat file, to generate coordinates so we can see what you're seeing.

Answer 3

[Image Analyst]

Be careful. If coordinates is an array of (x,y) and N is an array, then you'll need to check N(y, x), not N(x,y) as you have perhaps done. Remember (row, column) is (y, x) NOT (x,y).

[Mahsa]

It is true. Thanks