That is one of the mysteries of the image creation modalities. It was not light, as it attenuated very quickly. It also did not penetrate the linen. Its effect is there down to the ability of our instruments to detect it, though. The intensity of the image is proportional to the distance of the body to the surface of the linen fibers. . . And there is no image affect under the bloodstained areas. So, blood stain first, image effect next.
There are no image affects inside the fibers are inside fiber bundle of threads, however, in some most intense areas, a shadow image does appear on the obverse side of the Shroud where the body touched the cloth, but only on the exterior surface. Between the touching area and the obverse, where both areas show discoloration, in between fibers and threads do not. It is as if the causal affect discolored the entry surface, passed through with zero visible or detectable effect, and exited but then discolored the surface on exit. This implies an electrical charge.
However, as you mentioned, the other oddity is the pure detailed focus. This works only in the vertical direction with minimal angular deviation from the starting point, implying a maser or laser like collimating beam. What’s more, this has a positive and negative directional component in the Y axis, equally collimated and acting similar affect and effect.
This implies the potential for a localized Birkeland current and plasma phenomena and the intense magnetic fields.
In one of those TV shows where they recreated the 3D image/sculpture of the head there was a woman - a nuclear physicist iirc. She talked about something called a singularity iirc. I don’t recall exactly, but in my mind I thought of the original creation (”let there be light” - which now I think refers to “energy”) and Jesus’ RE-creation. Both using the same mechanism.