Same principle as Benton white-light holograms, see 2003 SPIE paper linked on the site, also "Not true holograms?" The scratches are line-scatterers, not flat

Same principle as Benton white-light holograms, see 2003 SPIE paper linked on the site, also "Not true holograms?" The scratches are line-scatterers, not flat-bottomed as Fresnel, so no focal length. Basically it's an enlarged Zoneplate rather than a fresnel lens. Arrays of curved line-scatterers can reconstruct single pixels with programmable depth. The fringes of Rainbow holograms do this, and their 3D image-reconstruction requires no interference nor monochromatic illuminators. Insight: change the spacing of the fringes of a rainbow hologram, or even randomize the spacing, and the 3D reconstruction still works fine. The 3D image doesn't depend on optical interference. A very weird effect! So, can we draw a Rainbow hologram by hand with a needle, by scratching the fringes with random spacing? Yep. We get 3D images, but they're white in color with no rainbow artifact.