If the modeling is only an approximation to the process 
and other than the correct threshold modulation curves are used, 
then the analysis cannot be rigorously defined as a system MTF 
and caution is emphasized in quoting results. 
As shown in the Skylab program, the use of these pseudo- 
"MIFs" is still quite useful; and helpful image quality data is 
derived from the analysis. Welch, too, has demonstrated that useful 
image quality data can be derived from approximation "MTF" techniques. 
It is suggested that the distinction between a true MIF and approximate 
"MTF" be made clear, and caution be exercised in producing image 
quality data from these processes. Caution can be translated here 
to include generation of a large data base so that noise can be 
recognized and averaged out. 
5.10 Sweden 
5.10.1 Film MIF 
Johansson and Biedermann used a Multiple-Sine-Slit Micro- 
densitometer (MSSM) in obtaining measures of MIF for film. The 
method avoids any degrading lens optics and provides high signal- 
to-noise ratio by matching a narrow band test signal and a narrow 
band filter in the scanning instrument, 
The test signal is a set of sinusoidal irradiance distri- 
butions generated by lazer two-beam interference. The scanning 
function is the sinusoidal irradiance distribution of unlocalized 
interference fringes. Shifting of the phase in one beam relative 
to the other moves the pattern across the sample. The light trans- 
mitted is collected by an integrating sphere and fed to a detector, 
which varies periodically. 
Since the MTF of a recording material is defined as the 
ratio of modulation in effective exposure to modulation in incident 
exposure, the distributions measured in transmittance or density 
are traced back to exposure over the macroscopic characteristics 
curve, Necessary corrections for instrumentation are made. 
Favorable comparisons between the MSSM and the microdensi- 
tomer methods are shown for several films.