A method and a corresponding metrology device and computer program for determining properties of a target on a substrate are disclosed. The method includes determining a plurality of intensity asymmetry measurements from pairs of complementary pixels including a first image pick in a first image of a target and a second image pixel in a second image of a target. The first image is obtained from the first radiation scattered by the target, the second image is obtained from the second radiation scattered by the target, and the first radiation and the second radiation contain complementary non-zero order diffractions. . Thereafter, the characteristic of the target is determined from the plurality of intensity asymmetry measurements.