Patent ID: 8778702

Claim:
A method comprising: imaging at least a portion of a substrate onto an array of pixels of a detector, wherein the substrate includes a plurality of regions in which microstructures are arranged according to different arrangement patterns and wherein in at least one selected region the microstructures are arranged according to a regular repetitive arrangement pattern having a repetition period, wherein an area of the substrate that is imaged onto one pixel of the detector has an extension of more than 5 times the repetition period, and wherein each selected region from the at least one selected region is imaged onto a group of selected pixels; collecting detection signals from pixels of the detector; and calculating at least one value for the group of selected pixels for each selected region using the detection signals from pixels that are members of the group of selected pixels, wherein detection signals from pixels that are not members of the group of selected pixels are not used in calculating the at least one value.