(a) Eigenimages of Hsp26 are shown in the left panel. Eigenimage 1 represents the total sum of the dataset. Eigenimage 2 shows the continuous outer circle which indicates the characteristic size difference range within the dataset. The right panel shows the entire dataset separated into four classes via MSA by only using these first four eigenimages. The big class is highlighted with a white circle around its perimeter, the small class is highlighted with a dashed white circle, and the remaining two classes represent a mixture of large and small Hsp26 images. (b) Eigenimages of BSMV. The size difference is shown in images 11 and 12 (adapted from [18
]). (c) A representative micrograph showing the heterogeneity of the SPP1 bacteriophage procapsids where different sizes are clearly seen [19
]. (d) The classes of the procapsid images are labelled according to their size, big (B, in blue) and small (S, in yellow).