Fig 4.

Reduction in mean residual error by refinement of positions with Sobel filtering, plotted against the mean residual of alignment solution, for tilt series from plastic sections (open circles) and frozen-hydrated samples (closed circles). The one poor result for a plastic section was observed recently and prompted a modification of Beadtrack so that it falls back to centering with the centroid when Sobel centering gives a worse mean residual.