(Color online) Plots (a), (b), and (c) represent the RMS_Diff values corresponding to each pattern obtained for artificial eyes A1, A2, and A3, respectively. Larger values of this metric indicate greater differences between the pattern and the reference. The thicker horizontal line represents the threshold corresponding to each eye for this metric. Values of RMS_Diff below this threshold indicate that the differences are due to variability in the measurement and not to differences between patterns. Plots (d), (e), and (f) show the dendrogram obtained from the hierarchical cluster analysis for eyes A1, A2, and A3, respectively. “Dist.” stands for “distance.” The less distance between patterns, the greater the similarity.