reconstructed electron densities for three different selection fractions. The voxels with low densities are present because the support is slightly larger than the particle. At higher photon counts, one can see a separation between the higher densities in the core of the virus compared to the capsid shell. This distinction disappears at the very low signal levels corresponding to $p=1/1024$. (b) Slices through representative electron densities with the same selection fractions. One can see the gradual disappearance of the double-shell structure with reducing fraction.[]{data-label="fig:dens_hist"}](dens_hist.pdf "fig:"){width="3in"}
                                                                                                                                                                                                                                                                                                                                            (a)
   ![(a) Histogram of reconstructed electron densities for three different selection fractions. The voxels with low densities are present because the support is slightly larger than the particle. At higher photon counts, one can see a separation between the higher densities in the core of the virus compared to the capsid shell. This distinction disappears at the very low signal levels corresponding to $p=1/1024$. (b) Slices through representative electron densities with the same selection fractions. One can see the gradual disappearance of the double-shell structure with reducing fraction.[]{data-label="fig:dens_hist"}](dens_slices.pdf "fig:"){width="3in"}
                                                                                                                                                                                                                                                                                                                                            (b)
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We also studied the effect of reducing data on the histogram of electron density values retrieved in real space. Figure \[fig:dens\_hist\] shows the histogram 