model that response to predict the transmittance of the developed

emulsion. This model should be based on actual response curve

measurements performed on the film using a calibrated sensitometer and

densitometer. This model will assist in the proper choice of average

exposure and ratio of reference to signal exposures.

 The Hurter-Driffield (H-D) curve has been used extensively to

predict photographic response. This plot of photographic density

versus log exposure demonstrates the key features of the film

saturation. A form of this curve could be described by


 { Ds when E > Es (6.4)
D = { ylog(E) log(Ebf) + Dbf Ebf < E < Es
 { Dbf E < Ebf


where s denotes saturation, bf denotes base fog, and y is the slope of

the linear portion of the curve. Modeled in this fashion, the film

exhibits a linear transmittance versus exposure only by producing a

positive print and developing to net y of -2. When this is the case,

the transmittance becomes

 { Tbf when E > Es (6.5)
Ta ={ c(E-Es) + tbf Ebf < E < Ess
 { Ts E < Ebf


where the transmittances are those of the positive print and the

exposures refer to the original negative. Thus, when the exposure is

determined by equation 6.2, this model predicts linear recording will

occur when the signal and reference amplitudes satisfy


 IRo So maxl2t > Ebf and (6.6)


 IRo + So max 2t < Es

 where So max is the maximum signal amplitude in the Fourier plane.