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Interferometers, such as the Event Horizon Telescope (EHT), do not directlyobserve the images of sources but rather measure their Fourier components atdiscrete spatial frequencies up to a maximum value set by the longest baselinein the array. Construction of images from the Fourier components or analysis ofthem with high-resolution models requires careful treatment of fine sourcestructure nominally beyond the array resolution. The primary EHT targets, SgrA* and M87, are expected to have black-hole shadows with sharp edges andstrongly filamentary emission from the surrounding plasma on scales muchsmaller than those probed by the currently largest baselines. We show that foraliasing not to affect images reconstructed with regularized maximum likelihoodmethods and model images that are directly compared to the data, the samplingof these images (i.e., their pixel spacing) needs to be significantly finerthan the scale probed by the largest baseline in the array. Using GRMHDsimulations of black-hole images, we estimate the maximum allowable pixelspacing to be approximately equal to (1/8)GM/c^2; for both of the primary EHTtargets, this corresponds to an angular pixel size of <0.5 microarcseconds.With aliasing under control, we then advocate use of the second-orderButterworth filter with a cut-off scale equal to the maximum array baseline asoptimal for visualizing the reconstructed images. In contrast to thetraditional Gaussian filters, this Butterworth filter retains most of the powerat the scales probed by the array while suppressing the fine image details forwhich no data exist.

Discretization and Filtering Effects on Black Hole Images Obtained with the Event Horizon Telescope