At the time they announced the image they described some of the extrapolation they had to do to fill in the image [1]. IIRC I saw a talk that described some of the different methods, but I can't find it now. I recall it was about turning few frequency domain points into many spatial domain points and they used multiple different teams with different methods, which gave qualitatively similar results in the end, but my reaction at the time was that it tanked my confidence in the details of the image since I couldn't tell what was data and what was model. A first-of-its-kind-image is exactly the kind of situation where you want to extrapolate very little.<p>[1]: <a href="https://www.youtube.com/watch?v=4Ws0iPDSqI4&t=1560" rel="nofollow">https://www.youtube.com/watch?v=4Ws0iPDSqI4&t=1560</a>