flying spot scanners, CRT's, etc.) cannot achieve resolutions much

better than several microns. Writing systems utilizing electron beams

are currently achieving better than 1-micron resolution. The electron

beam systems are typically binary and thus the transmittance function

must be quantized in some fashion into two levels, "on" or "off."

Binary holograms are attractive because binary computer-graphics

output devices are widely available and because problems with

nonlinearities in the display and recording medium are circumvented.12

When photographic emulsions are involved, granularity noise is

reduced.25

 Continuous-Tone Holograms

 When a hologram is produced optically or interferometrically, a

reference wave is superimposed with the wavefront to be recorded.

Typically, the reference wave is a tilted plane wave with constant

amplitude across the wavefront. The reference wave approaches at an

angle 9 relative to the direction of the wavefront to be recorded.

The resultant field is


 E(x,y) = f(x,y) + Aexp(j2Tray) (3.1)


where a= sin 0
 x
and the amplitude of the reference wave is 1. An interference pattern

is produced by the superposition of the waves. The fringe spacing is

dependent on the term a, known as the spatial carrier frequency, and

the details in the function f(x,y). A photographic film placed into

this field records not the field itself but rather the square

magnitude of the field. The pattern recorded on the film is then