newton interpolation image matrix

I worked on the Newton Interpolation. The Function is: yi = NtnInter(x,y,xi) My question is: How do I enter the x, y, xi values from my Image Matrix ?

   % function newton interpolation code

function y = newtonInterpolation(X,Y,x) % interpolate values y at points x using data vectors X and Y n = length(X); % build coefficient table D = diag(Y); for m = 1:n for i = 1:n-m j = i+m; D(i,j) = (D(i+1,j)-D(i,j-1))/(X(j)-X(i)); end end % return final value y = Y(1)*ones(size(x)); for k = 2:n s = D(1,k); for i = 1:k-1 s = s.*(x-X(i)*ones(size(x))); end y = y+s; end end