An example non-transitory machine-readable storage medium encoded with instructions executable by a processor is provided. The machine-readable storage medium includes instructions to identify fiducials on a target comprising multiple sample areas, instructions to determine positions of the fiducials in relation to the multiple sample areas, and instructions to detect a different region of interest (ROI) associated with each of the multiple sample areas based upon the positions. The machine-readable storage medium further includes instructions to calculate an optical performance metric based upon the ROI associated with each sample area, and instructions to determine a text resolution based upon the optical performance metric.