Provided herein are methods, systems, devices, and computer-readable storage media for selecting a detection area for a well (e.g., as part of an assay plate) comprising a plurality of encoded microcarriers. In some aspects, selecting the detection area includes obtaining one or more images of the well; calculating a center of the well according to a two-dimensional coordinate system; assigning a position, according to the two-dimensional coordinate system, of a first encoded microcarrier from the plurality; determining whether a distance between the position of the first encoded microcarrier and the center of the well according to the two-dimensional coordinate system exceeds a threshold distance; and including in the detection area one or more microcarriers whose distance from the center of the well does not exceed the threshold distance, while excluding those whose distance from the center of the well exceeds the threshold.