Most of what you said is correct but there is a final step you are missing, the image is not entirely constructed from raw data. The interferometry data is sparse and the 'gaps' are filled with mathematical solutions from theoretical models, and using statistical models trained on simulation data.

Paper: https://arxiv.org/pdf/2408.10322

We recently developed PRIMO (Principal-component Interferometric Modeling; Medeiros et al. 2023a) for in- terferometric image reconstruction and used it to obtain a high-fidelity image of the M87 black hole from the 2017 EHT data (Medeiros et al. 2023b). In this approach, we decompose the image into a set of eigenimages, which the algorithm “learned” using a very large suite of black- hole images obtained from general relativistic magneto- hydrodynamic (GRMHD) simulations