Metrology system and method for determining a characteristic of one or more structures on a substrate

An apparatus for determining a characteristic of interest relating to at least one structure on a substrate, the apparatus comprising:

• an illumination branch comprising a radiation source and configured to direct illumination radiation at the substrate;
• a detection branch comprising a detector and configured to detect scattered radiation from the at least one structure on the substrate;
• and
• a processor configured to:
• computationally determine phase and amplitude information from an electric field of the scattered radiation in a measurement acquisition, and
• computationally re-image the measurement acquisition of the at least one structure subsequent to a measurement to obtain at least one computationally re-imaged image,
• wherein computationally re-imaging the measurement acquisition comprises digitally altering an apodization of the illumination radiation for the measurement acquisition, and
• wherein digitally altering the apodization is based on the at least one structure.