the metrics alone one immediately notices that the electron densities do not suffer from such a drastic falloff in resolution at very low signal. In effect, the support constraint during phasing restores the smoothness of the speckles even when the total number of photons per 3D speckle (Shannon voxel) is low, partially negating the effect of insufficient total signal. For the highest photon dilution ($p=1/1024$), the average signal level used to determine the orientations is just 33.9 photons/frame.

[l r c c c c]{} Fraction & ph/fr & Frames & CC$_{1/2}$ & PRTF & FSC\
\
$1$ & & & 9.02 & 10.19 & 8.75\
$1/2$ & & & 9.16 & 9.16 & 8.75\
$1/4$ & & & 9.33 & 9.16 & 8.75\
$1/8$ & & & 9.50 & 9.33 & 8.75\
$1/16$ & & & 9.69 & 9.33 & 8.75\
$1/32$ & & & 9.69 & 9.33 & 8.75\
$1/64$ & & & 11.2 & 9.50 & 8.75\
$1/128$ & & & 11.2 & 9.50 & 8.75\
$1/256$ & & & 11.4 & 10.9 & 8.75\
$1/512$ & & & 11.7 & 10.9 & 8.75\
$1/1024$ & & & 20.1 & 11.2 & 8.75\

\[table:dilution\]

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    ![(a) Histogram of 