Example of the assignment scheme of labels adopted in the training set of the 3D U-Net within SubDLe. Here red particles trace the substructures to be identified, and blue particles are part of a background. In the upper panel, at most one particle is present in each grid pixel, thus the substructures (associated with the label “1” in the right-hand grid, whereas the background is labeled as “0”) are simply those containing one red particle. In the lower panel, more than one particle is allowed in each grid pixel, so the assignment of labels is performed with a majority vote.