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.