The edges of the optical surfaces add some diffracted light to the image. Very heavily machined plates can act like irregular diffraction gratings under a point light source, especially when viewed from the side. Due to idiosyncracies of digital camera sensors, sometimes this shows up in a captured image or video, and sometimes it doesn't. To human eyes, the plates look quite different: The glints usually appear pearlescent or iridescent and the backgrounds appear. silvery.

Specular holography was born in the Artesia Lounge, a long-lost Chicago blues club that was decorated year-round in holiday tinsel. After a set one night I took off my glasses to rub my eyes and noticed that the blurred tinsel presented a different pattern of glints to each eye — one of the ingredients of autostereoscopy. I cadged a pen and started working out the geometry for shaping tinsel to so that the glints would produce a proper 3D percept. By the next day I had a solution, but a weekend spent trying to prototype in metal foils came to naught.

Yes and no. Yes, in the sense that every viewpoint sees an exactly appropriate image of a 3D scene (i.e., no discretization). And no, if you believe that holography must depend on wave interference. Generally the differences are more interesting than the similarities: Conventional holography uses wave interference to reproduce the light field of existing scene, and is most akin to photography. Specular holography uses ray optics to construct a light field for an imagined scene, and is more akin to sculpture. Conventional holograms (typically) show in garish colors. Specular holograms scintillate in pearlescent colors. Conventional holography depends on delicate wavelength-scale structures that limit piece size and require careful indoor curation. Specular holography is mediated by robust optical surfaces that can be scaled up to clad buildings: