FINAL REPORT PREPARATION OF SIMULATIONS OF HIGH- ALTITUDE AERIAL PHOTOGRAPHY

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04770A000400050007-7
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 40
• Document Creation Date: December 28, 2016
• Document Release Date: July 29, 2004
• Sequence Number: 7
• Publication Date: June 15, 1970
• Content Type: REPORT

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This document contains 38 pages
Preparation of Simulations of
High-Altitude Aerial Photography
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Copy _L of 2,3 copies
Prepared by:
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SUMMARY
SUBJECT
TASK/PROBLEM
1. (Statement of Problem)
INTRODUCTION
DISCUSSION 7
8. Master Negative Stage 9
a. General 9
b. Scale 11
c. Tone Reproduction 12
d. Image Quality 15
9. Master Positive Stage 19
10. Hazed Positive Stage 20
11. Reduced Negative Stage 22
a. General 22
b. Selection of Reduced Negative Lens f/Number 23
c. Equipment 24
d. Procedure 25
e. Reduced Negative Characteristics 27.
12. Contact Positive Stage 27
13. Delivered Images 30
14. - 19.
20. - 21 .
,APPENDIX A - Threshold Modulation Theory and Application
APPENDIX B - Effect of Haze on Tone Reproduction
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Figure Title
Page
1 Flow Diagram of the Simulation Procedure 6
2 Contact Prints of Scenes 1 through 6 10
3 Characteristic Curve for Master Negative -- Scene 1 13
4 Characteristic Curve -- Scenes 2 through 6 14
5 MTF Curves for the Master Negatives 17
6 Characteristic Curve for 3404 Film in Dual-Gamma Process 26
7 Characteristic Curve for 2430 Film in the Kodak 29
Versamat Film Processor, Model 11C-M
Page
1 Measured Characteristics of the Master*Negatives 11
2 Predicted Resolution of Scenes 2 through 5 16
3 Measured Characteristics of the Hazed Positives 21
4 Conditions for Making the Reduced Negatives 25
5 Characteristics of the Reduced Negatives 28
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The contractor has prepared and delivered negatives and contact
duplicates which simulate high-altitude aerial photography of specific
ground targets at several scales and quality levels. Original photography
of six scenes was provided by the customer. Using these scenes, or the
particular area of interest within the scenes, positives were made which
represent the appearance of typical ground targets from high altitude.
These positives were then reduced onto 3101 film at the desired scale
using a controlled optical system, and subsequent dual-gamma processing.
After making contact duplicates of these reduced negatives onto
2430 film, one set of negatives and 3 sets of dupes were transmitted to the
customer. These negatives simulate scale, tone reproduction and ground
resolution typical of high-altitude photography. Some modifications in
standard simulation techniques were required to achieve the desired
quality in larger scale photography. All techniques are described in the
discussion section and appendixes.
The following characteristics were simulated:
Condition Scale
1: 6000 *
1:12000
1:30000
1: 51000
1:110000
1:188000
* The scale for condition 1 was made at approximately
1:2500 in order to achieve
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SUBJECT: Preparation of Simulations of High Altitude Aerial Photography
TASK/PROBLEM
1. Prepare simulated black-and-white aerial negatives and dupes
from original photography provided by the customer. The simulations shall
depict high-altitude photography with ground resolution
2. The customer required high-altitude aerial negatives and contact
dupes of specific military targets for detection/recognition studies.
The contractor had previously developed a technique for simulating high-
altitude photography using high-quality, low-altitude photography as an
input. This report is not intended to fully describe the theories and
procedures employed in making simulations but only those pertinent factors
relative to this specific task.
3. The flow chart for the simulation process is shown in Figure 1.
As shown, the original, or master negative,.is acquired and analyzed for
image quality and tonal content. From this original, a master positive
is made by contact printing. Tone reproduction is controlled to produce
this rendition of the original scene at a system gradient of.1.0. A
hazed positive is then made by contact printing the master positive onto a
reversal dupe film, and adding an overall flash exposure to simulate haze.
This positive simulates the appearance of the ground target from very high
altitude, and provides the input for preparation of reduced negatives.
The positive is photographed with a controlled optical system onto the
proper aerial negative film, and the optical system provides the reductions
to achieve the desired scale in the negative. Apertures used with the
-lens can be modified in size and shape to simulate the MTF of typical
high-altitude acquisition systems and to control the, limiting resolution
in the negative. However, only limiting resolution is depicted in these
simulations. The negative film is properly processed so that resultant
negatives simulate the scale, resolution, MTF and tone reproduction of high-
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Figure 1
Flow Diagram of the Simulation Procedure
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Master
Negative
Stage
Measure MTF of
System, Bmin and
Bmax of Scene
Estimate Haze
and
Flare in Photo
Master
Positive
Stage
Establish Sensi-
tometry for 1.0
System Gradient
Hazed
Positive
Stage
Reduced
Negative
Stage
Establish Sens.
and Flash Level
to Simulate Haze
Set Up Camera
Verify Operation
Determine Condi-
tions to Achieve
Image Quality
Set Up Equipment;
Prepare Apertures;
Verify Characteristics
Contact
Positive
Stage
Establish Sens.
and Exposure
Select Master Negatives-
Measure Scale
and Resolution
If
Prepare Contact
Positives; Measure
Characteristics
T
Prepare Hazed
Positive (Flash;
Measure Char.)
Make Reduced
Negatives;
Evaluate
T
Evaluate
Sensitometry
Make Contact
Positives, Slide
Mounted
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altitude photography. Standard test objects are carried through the
entire sequence to verify quality and tone reproduction. From the
reduced negatives, contact positives can be made on aerial duplicating
films.
1. Optimum simulation quality results when the characteristics
of the master negatives meet quite specific requirements. The image
quality must be such that image modulation at the desired limiting
ground resolution exceeds a minimum value defined by the parameters in
the reduction stage. In order to determine image quality in the originals,
a target which permits measurement of system MTF should be included in the
scene. In addition, the scale in the original negative should be such
that the final reduction exceeds 5X. Other targets of known brightness
should be included in the scenes and these targets should be large
enough so that image density is not influenced by micro characteristics
of the lens, film and process. These targets are used to control tone
reproduction through the simulation process.
5. Basic information and guidelines were established as follows:
a. Requirements were defined by the customer in terms of
scale and ground resolution.
b. Six original scenes were to be provided at a scale of
about 1:2000, and resolution required in the original negatives to achieve
the desired ground resolution in the simulations was defined.
c. The limitations that would be imposed if these requirements
were not met were described.
d. It was agreed that, if possible, modulation transfer
function (MTF) would be simulated.
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e. If deficiencies existed in the master negatives, the
customer and contractor would agree upon the deficiencies that would
be permitted in the final simulations prior to the start of the
simulation procedure.
f. The customer agreed to complete acquisition of photography
and delivery of the films to the contractor eight weeks prior to delivery
date for the final simulations.
6. MTF in film systems is subject to many variables, such as
adjacency effects and measurement errors, especially with dual-gamma
processing. The tone reproduction is-a function of object size, con-
trastand the densities in adjacent areas . When simulations are made
with small optical reductions, grain print-through from previous stages
increases the apparent granularity in the reduced negative. To a certain
extent these effects are ignored, and the macro-characteristic curve is
used for tone reproduction and the average of several measurements for
MTF are used. However, when reduction of the original photographs is
greater than about 20X (as is the case for the three poorest quality
simulations)the image quality is dominated by the reduced negative optical
system. Micro-image effects become insignificant. With smaller
reductions, these errors are present to some extent but are well within
normal variability associated with measurement of MTF. It was not within
the scope of this study to analyze the effect of these small errors.
7.. The original negatives received from the customer did not meet
the requirements for making optimum quality simulations. These
deficiencies were discussed with the customer. Image quality was in-
adequate for simulating 2-inch quality at 1:6000 scale. One of the
negatives had received dual gamma processing which introduces distortion
in macro-scale tone reproduction which cannot be fully compensated for
in later steps in the simulation process. Targets were not included for
measurement of MTF or densities of known ground brightnesses. Two of the
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scenes did not have sufficient image quality to simulate l kround
resolution. Agreement was reached that simulations should be prepared
with the following limitations:
a. System MTF would not be simulated.
b. Simulation of
(ground resolution at the scale
of the originals, about 1:2000, by contact printing.
c. "Haze" would be added to reduce the apparent brightness
range in all scenes to 5:1.
ground resolution would be inadequate.
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d. For scenes 2 and 6, simulations representing
ground resolution would be made at the desired scale, even though
8. Master Negative Stage
a. General
(1) Original photography was made on 3)40k film* with a
3 inch lens in a camera with intrack image motion compensation (IMC) at
an altitude of approximately 500 feet above ground level (AGL). The
customer provided these photographs to the contractor for processing and
subsequent treatment to make the prescribed simulations. Figure 2 is
a contact print of the six scenes selected for the simulation program.
The measured characteristics of the original negatives are shown in
Table 1.
* Kodak High Definition Aerial Film 340+ (Estar Thin Base)
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Figure 2
Contact Prints of Scenes 1 Through 6
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Table 1
Measured Characteristics.of the Master Negatives
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Scene.
Number
Dmax
Scene Average*
Dmin Contrast Gradient
Scale
1
1.74
0.34
20:1
1.10
1:2450
2
2.51
0.60
24:1
1.43
1:2835
3
2.50
0.56
22:1
1.43
1:2160
4
2.30
0.66
11:1
1.60
1:1910
5
2.60
0.75
19:1
1.50
1:1920
6
2.38
0.60
13:1
1.61
1:2835
(2)
Effort made at the master negative stage is to analyze the
tone reproduction and image degradation introduced by the original
negative photography, so that these effects can either be removed or com-
pensated for in subsequent stages. Included in the tone reproduction of
the original material is the combined effect of lens flare, atmospheric
haze, and the brightness distortion caused by the film characteristic curve.
It is also necessary to know the MTF of the entire master negative system
(lens, film, smear, defocus, etc.) in order to obtain the proper resolution
in the reduced negative stage.
b. Scale. The measured scale of the master negatives is also
shown in Table 1. Notice that the scenes can be classified into two groups.
Scenes 1, 2 and 6 have a scale of approximately 1:2650 and Scenes 3, 4 and
5 have a scale of approximately 1:2000. These two scale values were used
in calculating the reductions required in the reduced negative stages.
The average gradient is the slope of the line connecting
the scene Dmin and Dmax.
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c. Tone: Reproduction
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(1) Scene 1 was photographed and processed prior
to customer-contractor discussions, and images were processed in the
dual-gamma viscous process to the characteristic curve shown in Figure 3.
Since the dual-gamma process was designed to optimize tone reproduction
for high-altitude photography with haze, the characteristic curve is
inappropriate for maintaining accurate tone reproduction in low-altitude
photography without haze. The nature of the dual-gamma 3404 character-
istic curve imposes the requirement for a unique characteristic curve
in the master positive stage to achieve proper tone reproduction in the
master positives. This specialized curve cannot be achieved with normal
photographic films and processes.
(2) The remaining scenes (2, 3, 4, 5 and 6) were processed
in the Fultron processor to achieve the characteristic curve shown in
Figure 4., This process produces more linear relationship between the log
ground brightness and density in the original negative, and permits better
control of tone reproduction in the simulation process.
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(3) In order to measure the combined effect of lens
flare and atmospheric haze, it is necessary to know the brightness of at
least two objects of different reflectances in the scene. These objects
should-be uniform Lambertian reflectors, and large enough not to be influenced
by either the IMF of the system or adjacency effects in the process. Some
brightness data was obtained from the customer for vehicles in Scene 1.
However, the area measured had neither unform brightness nor the approximate
Lambertian reflectance properties required to calculate haze from brightness
measurements. Reflectance measurements were not available for Scenes 2
through 6. In the absence of direct brightness measurement, certain
assumptions must be made in subsequent steps and a less rigorous method
used in adding haze and controlling tone reproductions. However, the
method used does produce images which are typical of high-altitude photography.
(4) The effect of lens flare and haze is an equal addition
of non-image forming light to the whole photograph. This flare light
reduces the contrast of low brightness areas more than high brightness
areas, causing a distortion in tone reproduction. In high-altitude
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Figure 3
Characteristic Curve for Master Negative -- Scene 1
(exposed in IB Sensitometer)
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Sensitometer:
Source: Exposure Time: IB 1/25 sec.
----- - -- - -- ------- - ------ -------
Simulated Daylight
A
----------------- -
------ ---- ---
--4+ Hill
I ITT
11 Ir 711
--- - ---------
--- --- - ----------- - -------------
----------- -----
---- ---- ----- ----
---- -------- ---- --
Scene Dmax I'll
------ - - ------------ - ------
HHHHH 44
I Ill ITT
Average Gradient of Scene
+ 1.0
- ------ ---- ---- ---- ---
AFS Speed Point
ii HHHI
I Till
Scene Dmin
-- -------------
0
1.12 Log Exposure
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Characteristic Curve -- Scenes 2 Through 6
(exposed in TR Sensitom
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bource: Simulated Daylight
U
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1.0
1.22 (11th Step
rim ........ ft: Log Exposure
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graphy, the tone reproduction is significantly altered by haze; therefore,
the effect does not have to be removed. Only its magnitude has to be
measured so that the correct amount of additional haze can be added to
simulate high-altitude photography. See Appendix B for amore detailed
description of the effect of haze.
(5) The expected scene contrast in a low-altitude
photograph is about 100:1. The Dmin and Dmax were measured with a 0.5mm
aperture on a Kodak Model 31A densitometer for each scene and the contrast
obtained by transferring these densities through the appropriate 3404
characteristic curve. Measured values for scenes used in the simulation
vary from 11:1 to 24:1 (Table 1), indicating a significant reduction in
scene contrast from haze and lens flare. Since the amount of haze in the
original photographs could not be measured, the haze required to reduce
each scene to 5:1 contrast was added in the hazed positive stage. This
will be discussed later in paragraph 7, "Hazed Positive Stage."
(6) The scenes exhibited cos4 fall-off in exposure*
of approximately 0.12 log E at the frame edge (3-inch focal length, 70mm
film format). It was necessary to compensate for this effect also in the
hazed positive stage.
d. Image Quality
(1) Visual examination of the images showed that the lead-
ing edges of photographs were considerably better for image quality than
the trailing edges. Therefore, the usable portion of the scenes was
limited to less than one half of the total frame area. It should be noted,
however, that there was a continuous variation in image quality across the
frame, so that the quality varied within the area used.
(2) Edge gradient analysis was performed within the usable
area of Scenes 1 through 5 to obtain the MTF of the entire master negative
stage. The MTF determined in this manner includes the combined effect of
lens, image motion, and film. Crosstrack and intrack measurements were
made for each of the scenes to estimate the effect of smear. Only minor
The cos4 variation is the fall-off in illumination corresponding to the
angular distance off the optical axis for low distortion lens systems
with an internal aperture.
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differences were detected with the exception of Scene 5, which had a
somewhat better MTF in the intrack direction. The average MTF for
Scenes 3, 4 and 5, and the average MTF for Scene 2 are shown in Figure 5.
The MTF measured for Scene 1 was in error because there were. no edges
suitable for edge gradient analysis. Resolution measurements in an
adjacent frame and visual examination indicated that Scene 1 was very
similar in image quality to Scenes 3, 4, and 5. Therefore, average MTF
of these latter scenes was used as the best estimate of the MTF for Scene 1.
The MTF for Scene 2 was used as the estimate of the MTF for Scene 6, since
they were closely located in the same flight pass. Table 2 shows the
resolution predicted for 2:1 contrast targets based on the measured MTF.
(3) Resolution test results supplied by the customer for the
flight lens gave an AWAR** of 64 cycles/mm on 3404 film for an unspecified
target contrast. The observed resolution values in flight (Table 2) of
about 40 cycles/mm are conceivable for a lens of this relatively poor quality.
(4) Since the MTF curves are generally the same in the
crosstrack and intrack orientation, smear would not seem likely as the cause
for the difference between laboratory tests and flight results. The most
* These 2:1 contrast resolution values were obtained by crossing
the 3404 thresold modulation (TM) curve with the MTF curves measured
by edge gradient analysis.
Area Weighted Average Resolution (72 cycles/mm on-axis).
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Figure 5
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MTF Curves for the Master Negatives
1
Negatives 3, 4 and
----- -- - ------- -
.4
- -----------
- - ---- - ---- ---- ----
.2
Negatives 2 and 6 2:1 Contrast TM Curve for 3404
Film in Dual-Gamma Process
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likely source of degradation is random image motion caused by aircraft
vibration. Visual examination of other frames did indicate that photo-
graphs made. with longer exposure times had poorer quality than scenes
with the shorter exposures. However, there was no evidence of lack of
intrack IMC except at the longest exposure times. The images just
appeared unsharp, which is the way they would appear if random motion
degraded the photograph.
(5) MTF values for Scenes 2 and 6 are significantly
poorer than for other scenes. This would not normally be expected, as
good weather was reported at acquisition. On the other hand, this
anomaly has been noted with color acquisitions made the same day,
again with clear weather. Since the aircraft probably flew at a
lower airspeed to minimize smear, the poorer image quality might
be related to an increase of aircraft vibrations.
(6) It should be remarked that, with a good quality f/4
lens, 3404 film is capable of recording 200 cycles/mm at 2:1 contrast.
Since customer lab tests report AWAR resolutions of only 64 cycles/mm at
f/2.8, almost all of the degradation comes from poor lens quality. But as
it is probably not possible to stop the lens down to achieve better quality
because of the slow speed of 3+04 film, the best solution might be a better
quality lens with a focal length of about 6 inches to improve image quality
and reduce cos4 fall-off at the edges of the frame.
(7) The quality of Scenes 1, 3, 4, and 5 is sufficient to
make simulations at the prescribed ground resolutions I
Slight modifications in procedure are required to obtain
ground resolution. Although this program called for simulating both scale
and ground resolution, the quality of the original material is not sufficient
to obtain 2-inch ground resolution at the proper scale. By agreement with
the customer, therefore, simulations were made by contact printing
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the hazed positives onto 3404 film. These images have the appropriate
ground resolution but the scale -- and hence the film resolution --
is low by a factor of about 2.5. Also, the grain of the proceeding stages
are printed onto the 3404 image giving the image a somewhat grainier
appearance than normally would be achieved. The grainier image, however, is
not unlike an actual system image, since the images would be approximately
2.5 times smaller in scale. The quality of Scenes 2 and 6 is not sufficient
to achieve the proper ground resolution ground resolutions, 25X1
so that while simulations are made at the proper scale (except for the 2-inch
condition), the ground resolution is considerably poorer than required. Later,
actual resolutions are tablulated in the reduced negative section of the
report, paragraph 7.
9. Master Positive Stage
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a. In the master positive stage, the master negative is contact
printed to obtain a positive image with the tone reproduction corrected to
an average system gradient of -1.0. Density difference in the positive
will accurately represent scene brightness differences as they would appear
at low altitude with only a small amount of haze present. The exposure and
processing characteristics of the print film are adjusted to make the tone
reproduction as linear as possible between the densities representing scene
minimum and maximum brightness.
b. Scene 1 was processed in the dual-gamma process, which has
an extremely non-linear tone reproduction. In order to obtain a system
gamma of -1.0 over the entire density range encompassed by the scene, the
characteristic curve for the print film would have to be the reverse of
the dual-gamma curve. Since films with such a curve shape are not avail-
able, an average gradient technique was used with a print film having a
normal characteristic curve. The criterion was to have an average gradient
of -1.0 between the points representing scene Dmin and Dmax, and to
minimize deviations from a constant slope of -1.0.
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c. All master negatives were vacuum contact printed on S0-233
film*. This film is similar in image structure to 21+30**, except for a
lower gamma.
d. Exposure and processing time were varied in making contact
positives to minimize deviations in tone reproduction while maintaining an
average system gradient of -1.0.. Negatives of Scenes 2 through 6 were
processed in the Fultron processor to yield a conventionally shaped
characteristic curve for 3101+ film. A more linear tone reproduction was
obtained for these scenes.
e. Previous MTF tests have shown the vacuum contact printer with
a specular light source to have maximum response (1.0) out to 100 cycles/mm.
Therefore, effect of the printer can be neglected as a significant source
of degradation. Virtually. all degradation added in the master positive stage
comes from the MTF of S0-233 film. The degradation is very small at the
quality level of the original negative scenes. However, the measured MTF
for each scene was multiplied by the MTF of S0-233 film in the calculations
for predicting resolution at the reduced negative stage.
10. Hazed Positive Stage
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a. Tone reproduction of master positives are altered in the
hazed positive stage to simulate effect of haze in high-altitude photography.
Appendix B discusses effect of haze on tone reproduction of a scene. Since
it was not possible to add a constant haze level to each scene (because
amount of haze in each negative was unknown), the scenes were all hazed to
a 5-:1 contrast. This contrast ratio is typical for maximum and minimum scene
brightness in high-altitude aerial photographs taken under clear conditions.
* Kodak Special Low Contrast Fine Grain Aerial Duplicating Film S0-233.
This film is no longer available, but has been replaced by Kodak
Low Contrast Fine Grain Aerographic Duplicating Film (Estar Base) S0-355.
** Kodak Fine Grain Aerial Duplicating Film 2130 (Estar Base)
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b. The technique used in making the hazed positives is to add
a uniform flash exposure to a contact print of the master positive which
reduces the scene contrast to 5:1. The master positives are contact
printed on 5470* film, a direct reversal material with a gamma of -1..0.
With this product it is possible to maintain a positive image and obtain the
proper tone reproduction in one photographic step. The exposure for each
scene is adjusted to place the scene Bmin at a density of 1.20. A common
exposure can then be used in the reduced negative stage. Table 3 gives
the measured characteristics of the hazed positives.
Table 3
Measured Characteristics of the Hazed Positives
t
1
Scene Dmax Dmin Contrast
1 1.26 .46 6.3:1
2 1.14 .32 6.6:1
3 1.12 .40 5.2:1
4 1.15 .45 5.0:1
5 1.14 .46 4.8:1
6 1.14 .4o 5.5:1
. c. The cos4 fall-off in illumination caused by the taking lens
was compensated for when making the hazed positives. A photograph of a
uniform illuminator was made with a 75mm Biogon lens on 2430 film processed
to a gamma of 1.0. Since the Biogon lens has the same focal length as the
flight lens,. the cos4 fall-off will be essentially the same. The measured
variation in density of the mask was 0.12 less density at distance of about
one inch from the optical axis. Master negatives averaged 0.13 less log
exposure at one inch from axis. The mask was superimposed on the scene when
* Recordak Direct Duplicating Intermediate Film, 5470.
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contact printing to make the hazed positive. This technique eliminated
variation in average density across the field to avoid causing a
corresponding variation in the simulations. A 0.060-inch piece of glass
was used as spacer between the mask and the master positive to minimize the
transfer of the mask grain through the system.
d. The MTF for the 5470 film is essentially 1.0 over the
frequency range covered by the master negatives, so this stage does not
significantly degrade image quality of the system.
11. Reduced Negative Stage
r
a. General
(1) The stages through the hazed positive are designed
to alter a low-altitude photograph so that it represents the scene as it
would appear at high altitude. In the reduced negative stage, the hazed
positive is optically reduced with a lens with controlled MTF onto the film
used in the system being simulated. This reduced negative has essentially
the same optical characteristics as a small film chip taken out of a
photograph made with that system. The image will depict the film character-
istics, processing, ground and film resolution, tone reproduction, and
granularity typical of the system.
(2) It was not possible to simulate the actual system MTF
curves except at the three lowest quality levels. Since MTF of the
original negatives was a major contributor to the degradation in these
simulations, it was not useful to attempt simulating system MTF even at
the poorest quality levels. Firstly, edge gradient analysis is very sus-
ceptible to error, and generally gives only a first cut at the actual MTF
in the original negatives. This MTF must be known accurately to simulate
a total system MTF. Secondly, the different MTF's for each master
negative would require a different MTF in the reduced negative stage,
requiring a modification of the pupil function of the reducing lens for
each scene. Manipulating numbers with such uncertainty, especially
considering the variation in quality across the frame, would be a waste-
ful effort.
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1
f
(3) The lens used for making the reduced negative is a
90nm f/2.0 Leitz Summicron. The through focus MTF for apertures from
f/4 to f/16 has been calculated by a computer program based on the lens
design data in 546mm light. Subsequent measurements made with an electronic
MTF measuring device, and lab tests with resolution and sine wave test
targets, have verified the calculated MTF curves.
(4) The limiting tri-bar resolution in the reduced negative
stage was predicted using MTF/TM techniques. The threshold modulation concept
(TM) is discussed in Appendix A. The simulation output MTF used for predict-
ing resolution is the combined MTF's of each stage multiplied by the target
modulation. The intersection of the combined MTF curve for the system and the TM
curve of the reduced negative film should occur at the frequency of limiting
resolution. This limiting resolution should be equal to the limiting resolu-
tion of the simulated system, within the error associated with resolving
power measurement. Since the MTF's of the master negative, master
positive and hazed positive stages are already determined, the MTF of the
reduced negative stage must be varied to control the reduced negative
resolution.
b. Selection of Reduced Negative Lens f/Number
(1) To determine the output MTF curve for a specific
simulation it is necessary to know the MTF and scale of the master negative,
master positive, and hazed positive stages, and the MTF of the reduced
negative lens. Mathematically, we can describe the process for calculating
the output MTF curve as :
(MTF u) (MTF MP U) (MTF HP U) OMS (u ) = NN U) (MTFRPdu) [C-1
C+1
where: OMS = Output modulation of the simulation system
u = Spatial frequency in the reduced negative
R Reduction in the reduced negative stage
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t
f
MTFu
MTFMpu
MTFHP U
MTFRN U
C
C-1
= MTF of the master negative stage
= MTF of the master positive
= MTF of the hazed positive
= MTF of the reduced negative lens
= target contrast
= target modulation
(3) To predict limiting tri-bar resolution for a given
reduced negative, lens f/number and reduction, the appropriate reduced
negative MTF curve was multiplied by the MTF of the master negative-positive
stages at several frequencies close to the limiting resolution of the system
to be simulated. Crossing this curve with the appropriate TM curve gave an
estimated limiting resolution.
c. Equipment
(1) Three set ups were used to make the reduced negatives.
Table 4 lists the data on each condition used to make simulations. For
Condition 1, 7, and 13 vacuum contact prints were
made with a specular light source. Conditions 2, 3, 8, 14 and 15 employed
the Sununicron lens and a collimator. Scale of the hazed positive was
adjusted by an optical system that presented an aerial image at the focal
point of the collimator. Focal length of the collimator was adjusted by
changing the working distance.
(2) Resolution measurement data is to be supplied with
all simulations sent to the customer. Such data, based on preliminary
results, compares very well with the predicted values shown in Table 4.
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Table 4
Conditions for Making the Reduced Negatives
1
v
i
Desired Predicted Predicted
Film Film 2:1 Contrast
Scene Required Resolution Resolution Lens f/No.
Condition Number Reduction (cycles/mm) (cycles/mm) Resolution Used
*1 1 2.27X 118 42 - Contact
2 1 4.55X 118 111+ 180 5.6
3 1 11.36X 170 165 215 4
4 1 20.45X 134 132 139 9
5 1 41.67X 155 160 170 6.9
6 1 71.21X 155 163 170 6.9
*7 3,4,5 3.OX 118 42 - Contact
8 3,4,5 6.ox 118 118 167 6.3
9 3,4,5 15.OX 170 162 197 5.6
10 3,4,5 27.OX 134 134 139 9.0
11 3,4,5 55.OX 155 161 170 6.9
12 3,4,5 94.Ox 155 165 170 6.9
*13 2,6 2.27X 118 23** - Contact
14 2,6 4.55X 118 86** 18o 5.6
15 2,6 11.36X 170 145** 215 4
16 2,6 20.45X 134 129 139 9
17 2,6 41.67X 155 159 170 6.9
18 2,6 71.21X 155 162 170 6.9
d. Procedure
(1) All final photography was made on 3404 film processed
in the dual-gamma process. The exposure criterion used was to place the
scene Bmin at the AFS speed point (0.30 above fog). Figure 6 shows the
characteristic curve for the film/process combination.
* Simulations were not made to required scale, so ground resolution
could be maintained as specified.
* Image quality does not meet specifications.
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Figure 6
Characteristic Curve for 3404 Film in Dual-Gamma Process
(exposed in IB Sensitometer)
I
t
{?
., i. { ,1
{
Exposure Time: 1/25 sec.
j t t7 f.1# 1r7 r #.~1 f ( ~4k{ 41
k t tt! !ir; !,f
Sensitometer: IB ! !
L
!
t
f I
li
f = lii.
f }
i 4-f
RAI 0 -4 A-
i
z l
lF
-_ II
2.0
- ft
t ..
1.0
l
AFS Speed Point
0
Log Exposure
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I
r
(2) For each scale-f/number combination, the following
procedure was used to establish that the simulations would have the
required characteristics.
(a) First, resolving power tests were made with a
2;1 contrast test target to verify that the system was achieving the
appropriate resolution.
(b) Second, an exposure series was made with a 1.20
density patch to determine the exposure required to place the scene Bmin
at the film speed point.
(c) After it was verified that the system was achiev-
ing the proper resolution and the exposure was correct for the scenes,
simulations were made.
(d) Ten reduced negatives were made for each scene.
(e) Resolution targets and density patches representing
the scene Bmin were also made at each condition to demonstrate that the system
was operating as required when the final images were made.
e. Reduced Negative Characteristics. Table 5 summarizes
pertinent characteristics of the reduced negatives. High-quality targets
are used to checkout the lens in the reduction system. Resolution measured
in this manner is usually better than predicted resolution for simulations.
This is because the hazed positives are actually degraded images. To
achieve the proper ground resolution in the reduced negative it is
necessary to have a lens MTF better than the actual system. The predicted
resolution shown in the table in the best estimate of the actual 2:1 contrast
resolution in the reduced negative.
12. Contact Positive Stage
a. Reduced negatives were contact printed using a vacuum print
frame with a specular light source onto 2430 film processed to a gamma of
1.4. The characteristic curve for the film-process combination with the
nominal density range covered by the scenes is shown in Figure 7.
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Table 5
Characteristics of the Reduced Negatives
25X1
Scene
Condition Number Scale
1
I
1 1 1:2,450
2 1 1:119100
3 1 1:27,800
4 1 1:50,000
5 1 1:102,000
6 1 1:174,000
7 3,4,5 1:2,000
8 3,4,5 1:12,000
9 3,4,5 1:30,000
10 3,4,5 1:59,000
11 3,4,5 1:110,000
12 3,4,5 1:188,000
13 2,6 1:2,840
14 2,6 1:13,000
15 2,6 1:32,200
16 2,6 1:58,000
17 2,6 1:118,000
18 2,6 1:202,000
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Figure 7
Characteristic Curve for 2+30 Film in the Kodak Versamat
Film Processor, Model 11C-M
3.0
Sensitometer: EG&G
Exposure Time: 1/100 Sec.
Source: Simulated Daylight +)
m
-------------
--- --- - - ------ ---
---- ------- -- - ----- ----- - ----------
- ----- - -- --- - ----- --- -- ------- ----------
----- ---- --------
2.0
-------- -- -- -- --- ---- --------
+ -44
---- - ------ ------
----------- --
--- - - ---- -----------
-------- - -------
--- - ------- --
------- -----
1.0
------ --------
T-F +P
--- -- ----------
------- - ------ --- ----------
--- ---- ---- ------ ----
------ ---------- -----------------
--------------
----------------------------------
5-44
Range for Scenes
0
1.30 (11th Step)
Log Exposure
1111 W-:
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r
1
1
b. Scenes were sandwiched between glass, and mounted in
2" x 2" slide mounts for ease of handling and viewing. Each scene was
labeled with a number from 1 through 54 selected by drawing a number
out of a hat. The code for identifying the simulation images was
transmitted to the customer along with the images.
13. Delivered Images. Delivered images included three sets of
contact positives mounted in 2" x 2" slide mounts and one set of unmounted
reduced negatives. The remaining images, including master positives,
hazed positives, reduced negatives and contact positives, are on file
at the contractor's facility.
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14. Objectives defined by the-customer have been met with respect
to simulations -- the contractor produced simulations for each of six
scenes at six different quality levels.
15. Master negatives did not have sufficient image quality to make
r
I
simulations demonstrating both scale and. resolution at the
1 -1
ground resolution condition. By agreement with the customer the approximate
ground resolution was obtained by contact printing the hazed positive and
thus not obtaining the desired scale. Quality of the master negatives
for Scenes 2 and 6 was inadequate for simulating ground resolution at the
evels.
16. The lens used in acquiring the flight negatives was the principal
contributor to the poor image quality at the master negative stage.
17. Only limiting 2:1 contrast ground resolution is depicted by these
simulations. No attempt was made to simulate system MTF, since it could
only be simulated for the two poorest quality systems.
18. Inclusion of both reflectance and edge targets in the same
acquisition frame simplifies the preparation of simulations. Characteristics
for these target types are given in the recommendations, paragraph 18.
19. Master negatives acquired at low altitude normally have a high
scene contrast range, and should therefore be processed to use as much
as possible of the straight-line portion of the characteristic curve.
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1
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1
20. Consider using a higher quality lens for making master
negatives.. It would also be preferable to use a longer focal length lens
to reduce the cos4 fall off in the image plane. (However, consultation with
the contractor is suggested to determine compatibility of the required
simulation characteristics and equipment limitations before any future
original negatives are made.)
21. In future efforts, attempt to photograph the following targets
in the same frame as (or the closest possible frame to) the objects of
interest in the simulation:
a. Reflectance Targets, These targets should be large enough
so they are not influenced by the micro characteristics of the lens, and
include ground measured brightnesses, made at the time of photography.
b. Edge Targets. A 2:1 to 5:1 contrast edge target should
be included in the scene with an average reflectance of approximately
12 percent. The size of such targets should be at least 100 microns on the
master negative film.
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V. k
APPENDIX A
Threshold Modulation Theory and Application
1
I
1
1. In the simulation process, the TM (threshold modulation) concept
is used to establish the conditions required to produce proper resolution
in the images.
2. TM theory and measurement is described more extensively in
a recent article in Applied Optics.* Basically, however, a film TM
curve describes the amount of modulation in an aerial image required
to produce a resolvable tri-bar image in the film. The film TM curve
is a specific characteristic for a film process combination. Such a
curve is somewhat unique in that it is determined by the use of both MTF
and tri-bar resolution. The product of lens MTF and tri-bar target
contrast is a measure of the modulation in the aerial image presented to
the film. The TM curve is a plot of the minimum modulation required in
the aerial image to produce a resolvable image in the film at a given
frequency in cycles/mm. The curve is derived in exactly this manner in
the laboratory by photographing targets of known contrast with lenses of
known MTF. Images are read by a group of readers to determine limiting
resolution. A series of data points are determined relating resolution
and aerial image modulation and a curve is fit to these points. The form
of a typical curve is shown in Figure A-1.
3. The curve can be used to predict the limiting resolution that will
be obtained with other lenses and targets for which MTF and contrast are
known. Limitations in the use of such curves, and some measure of con-
fidence intervals, are described in the Applied Optics article mentioned
earlier.
T.J. Lauroesch, G.G. Fulmer, J.R. Edinger, G.T. Keene, and T.F. Kerwick,
"Threshold Modulation Curves for Photographic Films," Applied Optics,
Vol. 9, No.4, pp. 875-887, April 1970.
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1
4. In the simulation process, the ultimate resolution in final
simulations can be predicted by cascading the MTF of the various stages
and combining. these data with the TM curve for 3404 film. The MTF
of the original negatives are determined by edge gradient analysis
or from knowledge of the original acquisition system. MTF of the contact
printing stages was determined in previous laboratory studies. The final
step is to modify the optical system used in reductions to produce the
proper total system MTF in presenting images to the 3404 film in the
reduced negative stage (text, paragraph 8).
5. Previous studies, carrying specific test objects through the
entire system, have shown that predictions are valid within the confidence
limits placed on TM curves and MTF measurements. This technique permits
the establishment of requirements for the original photography.
6. The optimum situation is to deal with only coarse frequencies in the
original in the final reduction stage. However, to achieve fine ground
resolution in a final reduction, it is necessary to deal with fairly high
frequencies in the original. If MTF is sufficiently degraded in the original, it
becomes impossible to achieve the proper ground resolution in the simulation.
7. Ideally, an original should be such that a reduction of at least
lOX is required, and the modulation in the hazed positive stage (text,
paragraph 7) at the desired limiting ground resolution must exceed a
minimum value described by the curves in Figure A-2. If these conditions
do not exist, a valid simulation cannot be made, proper ground resolution
cannot be achieved and system MTF cannot be simulated. In any case, the
characteristics desired in the simulation impose definite requirements on
the original photography. The original photography thus should be geared
for the intended job.
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Figure A-2
Modulation Required in the Hazed Positive to Obtain Limiting 2:1 Contrast
Resolution on 3404 Film in the Dual-Gamma Process
1.0
ffiFT
.8
HHHHHHHH-
.4
------------
.2
Ila ---------- Note for Use of Graph
Divide the reduced negative frequency by the reduction in the
reduced negative stage to obtain the frequency in the hazed
positive for which the corresponding modulation is required.
:$ -- Hiiiiiii
0
60 80 100 120 140 160 180 200
Reduced Negative Frequency (cycles/mm)
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APPENDIX B
Effect of Haze on Tone Reproduction
1. At high altitudes, haze luminance has a significant effect on
photography. Solar illumination incident on the atmosphere is scattered,
and a portion of this radiation is seen by the camera, adding a uniform
haze luminance to the luminance of ground objects. The haze luminance is
not constant, but varies as a function of such factors as solar altitude,
weather, and camera look angle. In addition, the atmospheric layer does
not have 100 percent transmittance. Therefore, the atmosphere affects
the apparent brightness of ground objects viewed from high altitudes
according to the following approximate expression:
Be = (Bo) (T) + BH
where: B is the apparent brightness above the atmosphere in
e foot-lamberts
Bo is the ground object luminance in foot-lamberts
T is the transmittance of the atmosphere
1
BH is the haze luminance in foot-lamberts
Since BH is constant for a given photograph, haze luminance reduces the
brightness range and scene contrast. It is important that simulations
include the effects of haze, because scene contrast has a significant
effect on image quality.
2. A study of scene luminance characteristics has shown that the
average haze luminance at a solar altitude of 40 degrees is about 400
foot-lamberts. If a 5:1 contrast target having ground brightnesses of
200 and 1000 foot-lamberts is photographed in the presence of this amount
of haze, the apparent contrast is reduced to less than 3:1 (600 and 1400
foot-lamberts). Experience has shown that 5:1 contrast targets are re-
quired to provide a 2:1 contrast input to high-altitude photographic
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systems, Similarly, it has been observed that the average apparent
brightness range in scenes as viewed in clear weather from high altitude
is about 5:1.
3. In making simulations, the optimum situation is to have known
brightnesses photographed in the master negative. Using photographic
photometry, the amount of haze and flare in the original negative can
be determined.
4. In the simulation process additional haze can be added to simulate
any haze level. To prepare typical simulations, a total of 400 foot-
lamberts of haze would be added. In the absence of calibrated brightnesses,
the best compromise is to reduce the brightness range in the hazed positive
to 5:1. This is a reasonable approximation if the scenes contain a typical
range of ground objects from dark foliage and shadows to bright, man-made
objects.
5. All scenes used in this project were considered typical. The
brightness range in each hazed positive was reduced to 5:1 by applying a
uniform flash exposure. Densities in the positives were balanced so
that a common exposure could be used in making the reduced negatives.
Exposure in the reduced negative stage was controlled to place the minimum
brightness at the speed point of 3404 film. This produced simulations
which are typical of properly exposed high altitude photographs.
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