can record only real values. Film may be used to record, at baseband,

the magnitude of a wavefront, or it may be computer-encoded and phase-

modulated (bleached) to record the phase of a wavefront. Thus,

without using a spatially modulated hologram, the magnitude or phase

may be recorded. If only the phase information of the image is needed

to represent the reference image, a baseband hologram which records

the phase portion of the image transform can be used in the optical

correlator. This on-axis phase hologram, or kinoform, is recorded as

a relief pattern in which appropriate phase delays are induced in the

illuminating wavefront. To produce a Fourier transform kinoform, the

phase is restricted to a range from pi to + pi. The arctangent of

the ratio of the imaginary and real parts yields such a result. The

film is exposed to a pattern, whose intensity is proportional to the

desired phase, and bleached to create a relief pattern.34 These

kinoforms cannot record the amplitude variation of the image transform

and thus, the filter formed is a phase-only filter.

 Several techniques have been proposed by which the phase could be

modified to introduce amplitude variation in the reconstructed

wavefront.35,36 Chu, Fienup, and Goodman18 used multiple layers of

film to represent both the phase and amplitude variation. Kodachrome

II, for color photography, contains three emulsions. The phase

variation was recorded on one emulsion and the amplitude on another.

The inventors named this technique Referenceless On-Axis Complex

Hologram (ROACH). To introduce amplitude variation to the

reconstructed wavefront, light must be removed from the wavefront,

resulting in a reduction in efficiency.