In figure 10 an interference pattern is recorded, and an enlarged view of this pattern is shown in figure 11a. (To produce an erect image, the hologram pattern from figure 10 has been rotated 180deg.) This pattern has an obvious similarity to the curved scratches of "abrasion holograms." Because Rainbow holograms reconstruct images via line-scatterer optics, the optical interference produced between neighboring fringes can be neglected. If we delete some fringes to increase the fringe-spacing in figure 11a to resemble figure 11b, the hologram will still reconstruct the same image point. If some distortion is tolerable, the fringe pattern can even be changed to resemble figure 11c. This concept explains why "abrasion holograms" have so many of the features of Rainbow holograms.
Rather than seeing these abrasion holograms as being crude stepchildren of rainbow holography, we could reverse our perspective... Rainbow holography is a unique method for harnessing coherent optics to conveniently produce all the line-scatterers required by any arbitrary "abrasion hologram."
If a Rainbow hologram is wavelength-independent, then it follows that the spacing of the fringes in its zone plate are size-independent. If we could blow up a rainbow hologram to an enormous size, so its fringe spacing was on the order of millimeters (or centimeters. or even meters!) the hologram would continue to function. We could even replace the hologram with an array of hand-drawn scratches forming the conic-section shape of the fringes on the hologram. As long as the angles of those scratches on the film plane were the same as the angles of the fringes in the original hologram, the rainbow hologram would still be a rainbow hologram. It would still reconstruct the same image. The rainbow-colored artifact would vanish, and the allowed vertical viewing angle would increase, but the shape of the virtual image would remain the same.
Doesn't this mean that we can readily produce Rainbow holograms the size of roadside billboards using crude mechanical methods? I don't know. I haven't tried it. (I don't see why it wouldn't work!) Also note that the line scatterers only require a surface that produces specular reflection in the dimension along the scratch; they don't have the far stricter surface (or emulsion) requirements needed to produce optical interference fringes. They can be scribed onto crude surfaces, and in theory they can be made extremely large. Or we could even abandon scratches entirely, and create Rainbow Holograms where the individual "fringes" take the form of curved, polished metal wires or rods.