how to save double loop output in matrix form.

i am running double loop and i want to save its output in a matrix and plot each points of the matrix on image.

[rows, colm]=size(thin_image);
bifurcation=0;
ridge=0;
for i=2:rows-1
    for j=2:colm-1
        sub_matrix=(thin_image(i-1:i+1,j-1:j+1));
        if sub_matrix(2,2)==1
            sub_matrix=sum(sub_matrix(:))-1;
            if sub_matrix==1 
               P=fprintf('it is a ridge termination');
                i
                j
               ridge=ridge+1;
            else if sub_matrix==3
                Q=fprintf('it is a bifurcation');
                i
                j
                bifurcation=bifurcation+1;
                end
            end
        end
    end
end

Answer 1

[Andrei Bobrov]

sm = conv2(thin_image,ones(3),'valid')
imat = thin_image(2:end-1,2:end-1) == 1;
ridge = sum(sm(:) == 1 & imat(:));
bifurcation = sum(sm(:) == 3 & imat(:));