B-Factor by Subsets

To estimate the B-factor in maps of low to intermediate resolution, Guinier plot analysis is unsuitable because the structure factor dominates the appearance and slope of the amplitude decay at resolutions up to 10 Angstroms.

Therefore another way to estimate the B-factor is to look at how the Resolution decays over smaller and smaller subsets of the particles that form each half-map. A linear function is fit to the reciprocal square of resolutions determined by Gold-standard FSCs against the natural log of asymmetric units.

The method is described in detail in Rosenthal, Henderson 2003, and here the averaging and analysis functions subtom_maskcorrected_fsc_bfactor, subtom_parallel_sums_bfactor, and subtom_weighted_average_bfactor have been slightly modified from their non-bfactor counterparts to first generate the average of successively smaller subsets, with each subset being roughly half of the subset before it until the subset would be less than 128 particles. Then the resolution of each subset is determined and the B-factor is estimated and this estimate B-factor can then be used to sharpen the final post-processed map.