Interesting... this implies 64 bits per pixel. What format would that be, 16 bits per color RGBA?
edit: reading the link in the GP closer, they seem to refer to the full imagine, but it looks like they extracted the drawing underneath the painting. So I'd guess something must be from outside the visible spectrum.
[1] https://www.youtube.com/watch?v=z_hm5oX7ZlE [2] https://www.hasselblad.com/h-system/h6d-400c-multi-shot/