  Radiative transfer coupled with highly realistic simulations of the solar
atmosphere is routinely used to infer the physical properties underlying solar
observations. Due to its computational efficiency, the method of
short-characteristics is often employed, despite it introducing numerical
diffusion as an interpolation artifact. In this paper, we quantify the effect
of the numerical diffusion on the spatial resolution of synthesize emergent
intensity images, and derive a closed form analytical model of the diffusion
error as a function of viewing angle when using linear interpolation. We
demonstrate that the image degradation adversely affects the comparison between
simulated data and observations, for observations away from disk-center, unless
the simulations are computed at much higher intrinsic resolution than the
observations. We also show that the diffusion error is readily avoided by
interpolating the simulation solution on a viewing-angle aligned grid prior to
computing the radiative transfer. Doing this will be critical for comparisons
with observations using the upcoming large aperture telescopes --- the Daniel
K. Inouye Solar Telescope and the European Solar Telescope.
