function ret_v = vignet(r, x)
    %x(1) = focal length
    %x(2) - x(6) parameters for geometric polynomial
    ar = 1./((1+(r./x(1)).^2).^2);
    gr = 1-x(2)*r-x(3)*(r.^2)-x(4)*(r.^3)-x(5)*(r.^4)-x(6)*(r.^5);
    ret_v = ar.*gr;
end