  Isolated Stellar-Mass BlackHoles (ISMBHs) are potentially discernible through
microlensing observations. In this work, we study detecting and characterizing
ISMBHs with the Roman observations. We simulate a big ensemble of these events
as seen by Roman and estimate the errors in the physical parameters of the lens
objects, including their masses, distances, and proper motions through
calculating Fisher and Covariance matrices. Since the ~2.3-year time gap
between Roman's first three observing seasons and the others may lower the
efficiency of realizing microlensing events and characterizing ISMBHs, we
additionally consider a scenario where we add a small amount of additional
observations -- one hour of observations every 10 days when the Bulge is
observable during the large time gap -- which is equivalent to a total of about
one additional day of observations with the Roman telescope. These extra
observations increase Roman's efficiency for characterizing ISMBHs by ~$1-2\%$
and, more importantly, improve the robustness of the results by avoiding
possible degenerate solutions. By considering uniform, and power-law mass
functions ($dN/dM ~ M^{-\alpha}$, $\alpha=2,~1,~0.5$) for ISMBHs in the range
of $[2,~50] M_{\odot}$, we conclude that the Roman telescope will determine the
physical parameters of the lenses within $<5\%$ uncertainty, with efficiencies
of $21\%$, and $16$-$18\%$, respectively. By considering these mass functions,
we expect that the Roman telescope during its mission will detect and
characterize $3$-$4$, $15$-$17$ and $22$-$24$ ISMBHs through astrometric
microlensing, with the relative errors for all physical parameters less than
$1,~5,~10\%$, respectively. Microlensing events owing to ISMBHs with a mass
$\simeq 10$-$25 M_{\odot}$ and located close to the observer with $D_l \lesssim
0.5 D_s$ while the source is inside the Galactic disk can be characterized with
least errors.
