film, the greatest efficiency occurs when most of the frequencies have

equal weighting and the transmission is close to 1 across the entire

hologram. This implies that the throughput of the hologram will be

largest when the image transform is nearly white.

 The following procedures determine the choice of frequency

 emphasis.

 (1) Specify the Pd and Pfa for the particular application.

 (2) Choose a high-pass emphasis which satisfies the Pd and Pfa

 requirements. Typical choices include gradient, exponential, and step

 filters.

 (3) Because the test image should be filtered in the same fashion as

 the reference image, the frequency emphasis chosen should be squared

 before inclusion in the hologram. This permits the pre-emphasis of

 the test image without a separate stage of spatial filtering. That

is, the test image is spatially filtered for pre-emphasis with the

same hologram providing the correlation.

(4) The test image is typically much larger than the reference image

and can thus contain frequencies lower than any contained in the

reference. Since those frequency components can never contribute to

correlations, all frequencies below the lowest useful frequency in the

reference should be truncated to the value of the next smaller term.

(5) The frequency emphasis (squared) greatly reduces the dynamic

range of most scenes, simplifying the coding of the CGH-matched filter

and greatly improving the efficiency. The frequency-emphasized CGH

matched filter is created, as shown in Chapter III, but utilizes a

reference image whose frequency content is modified.


F'(u,v) = IP(u,v)!2 F(u,v)


(4.2)