TONAL SCALE SIMULATION STUDY - 2.3 GAMMA GEMS BY(Sanitized)

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A000700010012-1
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 23
• Document Creation Date: December 28, 2016
• Document Release Date: March 29, 2002
• Sequence Number: 12
• Content Type: STUDY

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Tonal Scale Simulation Study -
STATINTL
Declass Review by NIMA/DOD
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General
In an effort to improve both the resolution and contrast
of GEMS, it has been suggested that a positive master transparency
be employed in the simulation process with a cascaded processing
gamma greater than unity. The resolution and contrast of such
masters would be improved over that which is obtainable by print-
ing a master to a cascaded gamma of unity from an original negative
with a gamma of 2.3. However, high gamma masters would require
that a new technique be developed in order to predictably control
the convolution of modulation transfer functions, MTF, in a non-
linear sensitometric system.
The desired sensitometric curve is another parameter of
the simulation process that cannot be ignored when discussing the
contrast of GEMS. A brief sensitometric study was performed which
demonstrated that the contrast of mission material is simulated
best when both the original negative and master transparency
receive unity gamma one step processing. Further investigation
is required in order to determine the resolution that would result
for the optimum conditions of contrast.
MTF Simulation Technique
The formal procedure established for controlling the
shape and radius of a spread function has been to generate a
positive GEMS master transparency with a cascaded processing gamma
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of unity. The spread function of the GEMS instrument mask can be
convolved with the spread function of the GEMS master without
introducing nonlinearities; since, over the straight line portion
of the sensitometric data, the transmittance of the master is
linearly proportional to ground exposure. If a positive master
transparency, possessing a cascaded gamma other than unity, is
employed, the nonlinearities associated with the sensitometric
data must be accounted for in the prediction of the negative GEMS
spread function. The procedure required to control the convolution
of spread functions in a nonlinear system may be complex.
Sensitometric Study
Before investigating whether it would be possible to
predictably control a nonlinear convolution of spread functions,
a brief study was performed to determine the sensitometric behavior
-of the negative GEMS' scene density range. On the basis of main-
taining a negative GEMS cascaded gamma of 2.3, a number of tone
reproduction cycles were established for the hypothetical original
negative gammas of 2.3, 1.0, and 1.4. The GEMS master sensitometric
input values were positioned on the master's tone reproduction
cycle to yield the maximum scene density range. The maximum density
of the GEMS master was positioned on the tone reproduction cycle
of the negative GEMS to print out as a typical base plus fog value.
In the different Case studies, the gamma sequence folios*-
ing the Case identification title indicates the one step processing
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gammas for the original negative, the GEMS master, and the negative.
GEMS, respectively. (The sensitometric curves presented in this
report are those published in the Eastman Kodak "Manual of Physical
Properties.")
(1) Case I with gammas 2.3, 1.0, and 1.0.
Reference - Figures 1 through 4.
For the first tone reproduction cycle, it was
assumed that an original negative with a gamma of
2.3 was employed to generate a master with a cas-
caded gamma of 2.3 The unity gamma processing was
repeated again for the negative GEMS' cycle. By
referencing the cascaded curve in Figure 4, it
becomes apparent that the maximum GEMS' density
achievable is 1.3 and the minimum exposure range is
compressed, extremely.
On a theoretical basis, the calculated cascaded
gamma for the sensitometric curve involved is 2.3.
However, due to the regions of the sensitometric
curves employed, the resulting cascaded gamma is
only 1.8.
(2) Case II with gammas 1.0, 1.0, and 2.3.
Reference - Figures 5 through 8.
The Case II sensitometric considerations yields
the highest negative GEMS density range and still
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maintains the approximate sensitometric curve shape
required. The 1.95,density range of Figure 8 can
be increased to a density range of 2.10 by adjust-
ing the maximum density value of.the master to
print at a base plus fog value of .14 instead of
.10 on the negative GEMS film.
(3) Case III withlgammas 1.4, 1.35, and 1.4.
Reference Figures 9 through 12.
The third Case study. demonstrates that the
exposure range in the toe and shoulder areas of the
cascaded sensitometric curve become compressed when
the one step processing gamma of each photographic
step is made greater than unity. Note that the
maximum density of the negative GEMS is less than
that obtainable in Case II.
(4) Case IV with gammas 2.3, 2.3, and 2.3.
Reference Figures 13 through 16.
Case IV represents the combination of one step
processing gammas that yields a negative GEMS density
range equivalent to that of mission material. Scenes
processed in this nature would be composed of basi-
cally black. and white imagery with very little gray
scale information.
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Conclusion
It appears possible to improve the previously achieved
negative GEMS' density range from approximately 1.0 density units
to 2.0 density units by the gamma sequence described in Case II.
To actually simulate the appropriate mission material sensitometric
curve by a simple modification of the simulation technique is
virtually impossible. The sensitometric study indicates that the
films employed in the master and negative GEMS printing cycles
must be capable of preserving the original negative sensitometric
relationship. Commercial film exists to reasonably accomplish
the task; however, both the resolution and granularity requirements
Although the processing cycle sequence described in Case
II will improve the appearance of GEMS, the deficiencies of this
sensitometric sequence are the following:
(a) it is possible for the density range of mission
material to exceed the density range of the negative
GEMS.
(b) for the Case study cascaded curve shown in Figure
8, the low exposure region of negative GEMS is com-
pressed to a greater degree than actually exists
in mission material. The same condition will exist-
for the high exposure region of GEMS as they approach
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(c) in a simulated exposure series, part of the sequence'
of GEMS will appear to have their maximum density
values approach the maximum densities of normal
exposed mission material before truly representing
an over-exposure situation.
(d) when a GEMS actually represents an over-exposure
of mission material, the base plus fog level of the
negative GEMS will be much higher than that of the
mission material.
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 (7)
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ON ors. 3404
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