Cross-comparisons of reconstructed images with varying isotropic input FWHMs using symmetrically normalized root-mean-square error (SNRMSE). The SNRMSE grid shows a greater correspondence of images with input FWHMs near the true mean FWHM of 55 μas, marked by the dashed black lines. The reconstructed images with varying input size (5–90 μas) are all compared to each other, where image 1 and image 2 are the two images to be compared ( and respectively in Eq. (19)). The diagonal is each image compared to itself. The SNRMSE grid gives a range of plausible input FWHMs for ℛ_Σ that result in high fidelity images even when the true source size is unknown.