Jean-Pierre Luminet calculated all of that back in 1979 using the IBM 7040 mainframe, an early transistor computer with punch card inputs. The machine generated isolines for his image that were "directly translatable as smooth curves using the drawing software available at the time," he told Engadget in an email.
To create the final image though, he relied on his other passion: art. Using numerical data from the computer, he drew directly on negative image paper with black India ink, placing dots more densely where the simulation showed more light. "Next, I took the negative of my negative to get the positive, the black points becoming white and the white background becoming black."
https://www.engadget.com/2017-04-19-black-hole-image-jean-pierre-luminet.html
I was surprised too, but I've also worked for companies that used hardware and software multiple generations behind...
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