ELECTROPHOTOGRAPHIC PROCESSING TECHNIQUES FIRST INTERIM TECHNICAL REPORT

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04770A000600010015-0
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 39
• Document Creation Date: December 28, 2016
• Document Release Date: July 30, 2004
• Sequence Number: 15
• Publication Date: December 16, 1965
• Content Type: REPORT

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TASK ORDER NO. 03 (100, 762) 65-R
ELECTROPHOTOGRAPHIC
PROCESSING TECHNIQUES
FIRST INTERIM TECHNICAL REPORT
Prepared for
NGA Review Complete
Issued: December 16, 1965
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 STAT
SPAT
STAT
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I
TASK ORDER NO. 03 2)65-R
ELECTROPHOTOGRAPHIC
PROCESSING TECHNIQUES
FIRST INTERIM TECHNICAL REPORT
Prepared for
THE U.S. GOVERNMENT
Issued: December 16, 1965
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This is the first of a series of interim technical reports
on a study of electrophotographic processing techniques.
This twelve-month study comprises the investigation and
development of photographic and electronic techniques for
processing photographic images. This report covers the
work performed by the F_ I
during the period from June 22 to October 22, 1965.
The principal authors of this report are :
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Section Page
I INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . 1
II TECHNICAL DISCUSSION OF IMAGE PROCESSING
TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . .
A. Processed Imagery Systems . . . . . . . . . . . . . . 3
B. Image Processing Techniques . . . . . . . . . . . . . . 5
III ELECTRICAL-CHEMICAL PROCESSING TECHNIQUES . . 9
A. General . . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Equipment Procurement and Calibration
(Task 1) . . . . . . . . . . . . . . . . . . . . . . . 9
2. Film Evaluation and Selection (Task 2) . . . . . . . 9
3. Breadboard Modulated-Light Contact Printer
Development (Task 3) . . . . . . . . . . . . . . . 9
4. Transparency Investigation (Task 4) . . . . . . . . 10
5. Processing Experiments (Task 5) . . . . . . . . . 10
6. Techniques Study and Evaluation (Task 6) . . . . . 10
B. Technical Approach . . . . . . . . . . . . . . . . . . . 10
1. Statement of the Problem . . . . . . . . . . . . . . 10
2. Program Plan . . . . . . . . . . . . . . . . . . . 11
C. Materials and Equipment . . . . . . . . . . . . . . . 14
D. Evaluation of Material . . . . . . . . . . . . . . . . . 17
1. Photographic Film . . . . . . . . . . . . . . . . . 17
2. Film Processing Chemicals . . . . . . . . . . . . 17
E. Modulated-Light Contact Printer . . . . . . . . . . . . 17
1. General . . . . . . . . . . . . . . . . . . . . . . 17
2. Design and Mode of Operation . . . . . . . . . . . 17
3. Relationship of Contact Printer to Other Efforts . . 22
IV ELECTRONIC PROCESSING TECHNIQUES . . . . . . . . 23
A. Program Plan . . . . . . . . . . . . . . . . . . . . . . 23
1. Feasibility Investigation (Task I) . . . . . . . . . . 23
2. Preliminary Breadboard System Construction
(Task II) . . . . . . . . . . . . . . . . . . . . . . . 23
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 Section
IV
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TABLE OF CONTENTS (Continued)
Pag
ELECTRONIC PROCESSING TECHNIQUES (Continued)
3. Final Breadboard System Construction (Task III) . . 23
4. Processing Experiments (Task IV) . . . . . . . . . 24
5. Techniques Study and Evaluation (Task V) . . . . . 24
6. Rear Projection Viewer Study (Task VI) . . . . . . 24
B. Breadboard Electronic Image Processing System
1. General Description . . . . . . . . . . . . .
2. Operation . . . . . . . . . . . . . . . . . . .
24
24
25
C. Experiments . . . . . . . . . . . . . . . . . . . . . . 27
1. System Stability . . . . . . . . . . . . . . . . . . 27
2. Signal-to-Noise Ratio . . . . . . . . . . . . . . . 28
3. Resolution . . . . . . . . . . . . . . . . . . . . . 28
4. Exposure . . . . . . . . . . . . . . . . . . . . . . 29
D. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . 33
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Figure Page
1 General Representation of Processed Imagery Systems . . . . 4
2 Image Processing Steps . . . . . . . . . . . . . . . . . . . . . 6
3 Modulation Transfer Function as it applies to Low-
Frequency Suppression . . . . . . . . . . . . . . . . . . . . . 7
4 Experiments Measurements Plan . . . . . . . . . . . . . . . . 12
5 Acutance Experiment Plan .. . . . . . . . . . . . . . . . . . . 13
6 Controlled Film-Processing Room . . . . . . . . . . . . . . . 15
7 Measurements Room . . . . . . . . . . . . . . . . . . . . . . . 16
8 Modulated-Light Contact Printer . . . . . . . . . . . . . . . . 18
9 Modulated-Light Contact Printer, Mechanical and
Optical Layout . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10 Modulated-Light Contact Printer, Block Diagram . . . . . . . 20
12 Breadboard Electronic Image-Processing System,
Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . 25
13 Breadboard Electronic Image-Processing System . . . . . . . 26
14 Exposure of Four Fields (4/60 second) Modulating
Light Source Only . . . . . . . . . . . . . . . . . . . . . . . . . 29
15 Exposure of Eight Fields (8/60 second) Modulating
Light Source Only . . . . . . . . . . . . . . . . . . . . . . . . 30
16 Exposure of 16 Fields (16/60 second) Modulating
Light Source Only . . . . . . . . . . . . . . . . . . . . . . . . 30
17 Exposure of 32 Fields (32/60 second) Modulating
Light Source Only . . . . . . . . . . . . . . . . . . . . . . 31
18 Exposure of 32 Fields (32/60 second) Sensing Light Source . . 31
19 Exposure of 64 Fields (64/60 seconds) Sensing Light Source . . 32
20 One-Second Exposure With Mechanical Shutter Using Both
Light Sources and a Positive Light Mask . . . . . . . . . . . . 32
21 One-Second Exposure With Mechanical Shutter Using Both
Light Sources and Negative Light Mask . . . . . . . . . . . . 33
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The current investigation of Electrophotographic Processing Techniques (EPT)
is one of three related Programs to Improve Photographic Image Perceptibility
in which the uis
engaged.
STAT
(1) A Prototype Modulated-Light Film Viewing Tables development program,
which covers the development and delivery of two viewing tables. With
this equipment, photographic transparencies will be illuminated by a fast-
moving spot of light whose intensity will be automatically varied to effect
large-area contrast compression. The design of these tables is based
upon a breadboard modulated-light film viewer which was built under a
previous contract. The feasibility of various modulated-light source
and pickup techniques was demonstrated in this prior program.
(2) A Spatial Frequency Analyzer study which covers the breadboard develop-
ment and feasibility demonstration of a photographic image spatial fre-
quency analyzer. The high-resolution electronic image processing equip-
ment being developed for the EPT investigation will be modified for use
with an electronic frequency spectrum analyzer to provide records of the
spatial frequency contents of photographic images. Feasibility demon-
strations, technique evaluations, and equipment development recommend-
ations are included in the program tasks.
The EPT program covers the investigation, development, and evaluation of electri-
cal-chemical and electronic techniques for processing photographic images to im-
prove their perceptibility to human observers. The key to electrical-chemical
processing will be the control of acutance and granularity in processed transpar-
encies by (1) adjustment of density thresholds, (2) expansion and contraction of
density variations, and (3) variation of the illuminating spot from a modulated-light
(cathode-ray tube) printing source. The key to electronic processing, analogous
to electrical-chemical processing, will be separate and simultaneous operation on
the high- and low-frequency information in photographic images and the employ-
ment of a high-resolution kinescope as a modulated-light printing source.
Prior to the start of this EPT investigation, preliminary study and experimentation
under= sponsorship had resulted in the demonstrated feasibility of certain
electrical-chemical image processing or correcting (deblurring) techniques. Im-
proved Ranger, Nimbus, TIROS, and lunar telescopic photographs had been obtained
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by careful and selective modification of image densities and by pro rammed opera-
tion of a commercial modulated-light (cathode-ray tube) printing source.
Additional study had shown that the development of electronic techniques could lead
to a significant reduction in the number of image processing steps required in
electrical-chemical processing and therefore correspondingly reduce the time for
final improved image perception. Electronic equipment construct? d by I nd
other activities had successfully utilized flying-spot scanners and ; specially de-
signed circuits (e.g. , filters, thresholders, limiters, and amplifi,-rs) to enhance
the properties of photographic images. Immediate and variable ed re enhancement
is an example of what has been achieved with electronic image processing.
An important element common to both the proposed electrical -cher.Acal and elec-
tronic image processing systems was a modulated-light printing scurce. Although
the performance specifications (and therefore the actual componen ;s) of the source
would differ from system to system, each set of techniques would include the final
exposure of a transparency by modulated-light from a cathode-ray tube. The feasi-
bility of various modulated-light techniques, including isotropic beim scan, remote
photomultiplier pickup, and negative feedback operation, had been lemonstrated for
the previously cited Government-sponsored study of modulated-light film viewing
systems.
The objective of the EPT program is to further the development of both electrical-
chemical and electronic techniques for processing photographic im ages to improve
their perceptibility to human observers. These techniques are exlected to be com-
patible with the additional goal of eventually developing high-speed high-capacity
processing equipment. Although the program is principally experimental in nature.,
an orderly schedule of study, testing, and analysis is being pursue I to achieve the
stated objective.
The program plan is divided into and discussed under two sub-heacings:
Electrical-Chemical Processing Techniques, emphasizing chemical manipulations
of image densities, and Electronic Processing Techniques, stressing electronic
operations on photographic images. These two areas are interrei.ted
and a constant interchange of analytical and experimental results i:j maintained
between the two approaches. By way of emphasizing this point, Section II of this
report discusses electrophotographic image processing techniques in the context
of a common, simplified theory of image processing. Sections III 3.nd IV discuss
Electrical-Chemical and Electronic Processing Techniques, respectively.
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TECHNICAL DISCUSSION OF IMAGE PROCESSING TECHNIQUES
The purpose of this section is to discuss electrophotographic image processing
techniques in the context of a simplified theory of image processing. A conceptual
model of processed imagery systems serves as a base for the discussion.
A general representation of processed imagery systems is given by Figure 1.
The model incorporates six basic transducers: a sensor, a processor, a human,
a translator, a processor controller, and a sensor controller. The purpose of the
sensor is to detect (observe) and record the object to be imaged. The output of
the sensor is the original image, e. g. , a photographic transparency. The sensor
may be a photographic or electronic camera.
The purpose of the processor is to convert the original image (transparency) into
a processed image for display to a human interpreter. The processor is generally
a multi-process device employing combinations of chemical, electronic, and optical
techniques. Typical processors are contact printers, electronic viewers, and rear-
view projectors.
The human who constitutes the final element in the image system, converts the
processed image into a perceived image. The inputs to the human are the original
image, the processed image, and psychophysiological factors that include the en-
vironmental conditions affecting the photo-interpreter.
A preliminary function of the human is the generation of image criteria, i. e. ,
criteria leading to improved processor and sensor operation and/or design. For
example, a photo-interpreter may view an initially processed image and decide
that edge-sharpness will improve his ability to perceive some detail in the trans-
parency. This information would then be fed back to the processor to produce a
more desirable display.
Since the image criteria generated by the human are often not expressed in con-
ventional technological terms, a translator is included in the model to convert
these criteria into image data that, in turn, serve as inputs to the processor and
sensor controllers, respectively. The function of each controller is to supply
control, as required, for the respective transducer.
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OBJECT
(SCENE)
ORIGINAL IMAGE
(TRANSPARENCY)
SENSOR
CONTROLS
I L
PROCESSOR
CONTROL
FUNCTIONS
SENSOR PROCESSOR
CONTROLLER CONTROLLER
LPI-
IMAGE
CRITERIA
Figure 1. General Representation of Processed Imagery Systems
OTHER INPUT DATA
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B. IMAGE PROCESSING TECHNIQUES
The information content in any given photograph cannot be increased by
any operation in which only the information in that photograph is available.
However, this information can be processed in viewing or in reproduction to
make it more accessible to the interpreter, so that he can work more
accurately and more rapidly. For example, the contrast steps in detail may
be too small for perception by the eye, but may have sufficient signal-to-noise
content so that a stretch in constrast permits perception.
Certain basic principles underlie systems of useful processing, including the
electrical-chemical system and the electronic system which are being
developed in this program. These principles can be incorporated into an
analytic model which is being developed, and which should provide guidance
for the direction of the experimental programs.
The model is at present in a preliminary state. It will become more complete
and refined as the work progresses. It is clear, however, even at this early
stage, that a system for improving the visibility of detail, as shown in
Figure 2, includes the following operations:
(1) An image signal is generated that yields a point-by-point measure of
the density content of the original image.
(2) Background brightness information, i. e. , low (spatial) frequency
contrast, is suppressed in this signal.
(3) A brightness threshold is applied to the modified signal. (This bright-
ness threshold may be the toe in the D-LogE curve of the reproducing
film. )
(4) The new signal is amplified.
(5) A bias level is applied.
(6) The resulting signal is amplified and reproduced or displayed (as a
processed image).
In electrical-chemical processing systems, many of the above functions are not
performed in real time; delays may be excessive. Electronic processing techni-
ques, however, may ultimately lead to the expected improved image output, in
what may approach real time. A brief description of the electronic techniques for
providing the above functions is given in the paragraphs that follow.
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A. PRIMARY IMAGE SIGNAL B. LOW-FREQUENCY SUPPRESSION
Figure 2. Image Processing Steps
Assume that the image to be processed is given by a photographic transparency.
A common technique for generating the image signal involves photo ;ell detection
of light transmitted by the transparency. The light source may be i cathode-ray
tube. The photocell output is a voltage analog of the brightness dis :ribution in
the original image.
Suppression of background brightness information or low (spatial) :requency con-
trast is achieved by unsharp negative masking (also called automat.c dodging)
techniques. A combination of modulation transfer curves can be used to illustrate
how negative masking operates to reduce low-frequency contrast. Figure 3 shows
the modulation transfer curve* of the original transparency and the modulation
* Contrast as a function of image size or spatial frequency.
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Figure 3. Modulation Transfer Function as it Applies
to Low-Frequency Suppression
transfer curve of the masking image, which is subtracted (fed-back negatively)
in the reproduction (or display) process. The masking signal may, for example,
be implemented by a defocussed cathode-ray tube beam. Unsharp negative
masking signals have less contrast and lower cut-off frequencies than do their
original image signals.
By cascading the masking modulation transfer function with that of the original
image, low-frequency contrast is reduced without affecting the high frequencies.
Thus, low-frequency suppression yields a flatter response with a relative
increase of high-frequency information. Obviously great operating flexibility
can be achieved with a feedback response whose amplitude and cutoff frequency
can be varied. These properties can, for example, be exhibited by a
cathode-ray tube beam with variable spot size. Figure 3 actually illustrates a
case in which the modulation transfer function has been modified across a
substantial part of the spatial frequency spectrum.
Following the suppression of low-frequency contrast, a brightness threshold
may be applied to the signal. As can be seen in Figure 2, detail information
which had been "riding" above various background brightness levels (View A)
now "sits" on top of a nearly constant brightness level (View B). Thresholding
(View B) then acts to pass only this detail information through the rest of the
system. It should be apparent (from View A) that thresholding cannot precede
suppression of the low frequencies.
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In a proper system design, the brightness threshold, preamplifier, and bias level
cooperate to make full use of the dynamic range of the final amplifier. The trans-
fer characteristic of the final amplifier, which influences the design and operation
of the other processing system elements, provides the output sign:Ll or processed
image. When the final amplifier is photographic copy film, the transfer character-
istic of the final amplifier is the film's D-LogE curve.
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ELECTRICAL-CHEMICAL PROCESSING TECHNIQUES
The Electrical-Chemical Processing Techniques portion of this program is
directed toward the further development of essentially photographic techniques for
processing photographic images that will lead to improved perceptibility by human
observers. Some of these techniques were applied in a limited way to specific
images; the current efforts are concerned with a more general approach to
processing photographic images.
The Electrical-Chemical Processing Techniques portion of the EPT program
comprises the following tasks, some of which have been performed during this
reporting period:
1. Equipment Procurement and Calibration (Task 1 )
Special test equipment required to perform the electrical-chemical
processing experiments has been specified and ordered. Following delivery and
installation, these items were calibrated to ensure consistency of experimental
results and to relate properly the findings to other efforts.
2. Film Evaluation and Selection (Task 2)
Materials required to perform the electrical-chemical processing
experiments have been specified and ordered. Photographic films of many types
have been evaluated for their properties, in order to select films which are
compatible with the system requirements.
3. Breadboard Modulated-Light Contact Printer Development ( Task 3)
A high performance modulated-light contact printer has been designed for
use in the electrical-chemical processing experiments. The design objective for
the (light) spot size at the front surface of the transparency is one millimeter.
Based upon this design, printer components (cathode-ray tube, lenses, etc. )
were specified and breadboard construction was accomplished. Checkout and
calibration of the experimental printer will be completed in the electrical-
chemical processing laboratory.
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4. Transparency Investigation (Task 4)
Government-supplied transparencies (scenes) will be analyzed in terms of
density distribution, image shape and structure, resolution, and detiil spacing.
This data will then aid in the design and operation of the processing ,ontrols. In
addition, the fabrication of experimental samples and the utilization of controlled
test samples (GEMS, Edge-GEMS, etc.) will be investigated for application to
the current efforts.
5. Processing Experiments (Task 5)
Upon completion of system checkout and calibration, film eval nation and
selection, and the preliminary transparency investigation, processing experi-
ments will begin. The general effectiveness and utility of the propored photo-
graphic techniques will be determined. Modifications of the test prccedures and/
or equipment will be based upon the results of initial tests with simple transpar-
encies. Further study and evaluation of these and other electrical-chemical
processing techniques will be reflected in continuing experiments.
6. Techniques Study and Evaluation (Task 6)
The state-of-the-art of electrical-chemical processing technicues will be
reviewed in light of the current program objectives. The breadboar I equipment
and proposed modifications thereto will be analyzed to predict expec ;ed perform-
ance and future capabilities. The results of processing experiments, as evaluated
STAT by and Government personnel, will be reviewed for agreement with theoretical
predictions. Finally, recommendations for future efforts in this are,i will be made.
In this branch of the program, the objectives of enhancing image percep-
tibility by increasing contrast where it is required and improving acuteness are
to be implemented by manipulation of the density relationships in the copy
transparency. Part of the density manipulation will be accomplishec by copying
with the modulated-light contact printer, with which negative maskin; at spatial
frequencies to about one cycle per millimeter will be achieved. Further operations
involve the resetting of increments in the density scale in copying ani processing
procedures which do not rely on the use of modulated light.
The transformation of the density scale will critically depend on the ?roperties of
the materials which are to be used. Calibration is therefore requirE d for the film
materials, with respect to the spectral content of the light sources used in
measuring and replication equipment, chemicals, processing time, and processing
temperature.
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2. Program Plan
The program plan therefore includes a preliminary phase dealing with the
systematic calibration of equipment and materials, so that reproducibility and
repeatability of density ratios and density ranges may be achieved. When this
phase is completed, the processing of transparencies will be undertaken. The
program plan is detailed below.
The calibration plan is diagrammed in Figure 4. The step standards
will be measured for density and transmittance characteristics and will be copied
onto various types of film. Each of the copies will then, in turn, be measured
for density and transmittance characteristics. Since the light source in each
piece of replication equipment varies in spectral response, each copy film will be
measured along with each step standard against each piece of replication
equipment.
Each copy film and each step standard will be calibrated in terms of illumination
intensity and time in exposure. Chemical processing will be investigated in terms
of various chemicals, processing times, and processing temperatures, exercising
one variable at a time.
Processing Program Plan
The processing program plan is diagrammed in Figure 5. The input
transparency will be measured for film-response characteristics by means of a
microdensitometer. Then on the isodensitracer, density distribution will be
mapped. This film will next be placed on a transparency viewer, and transmit-
tance measurements will be obtained by means of a microscope photometer. The
characteristics of the input image will thus have been determined.
Prior to the replication cycle, standard density/resolution targets will be
reproduced on various types of film and modified as required. Both the standards
and the modified copies of the standards will be measured for density and
transmittance characteristics in the same manner that the input transparencies are
measured.
Following analysis of both the input film and the modified copies of the standards,
the replication program will be undertaken. This part of the program is intended
to provide a range of transparencies at different density ratios at several density
levels as a function of image characteristics. The output of the replication cycle
will be measured for density and transmittance characteristics. The results of
these measurements will be compared with the results of the initial measurements
to ascertain what physical improvement has been achieved. Further the output
transparencies will be compared by skilled interpreters with the input
transparencies for their operational value.
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STANDARDS:
DENSITY STEP TABLETS
SAYCE
RESOLUTION
REGISTRATION
MODIFIED STANDARDS
FILM COPY
FILM TYPE!
S0243, S02472 S04427
S05427, 3404
KODALITH ORTIIO TYPE 3
MEASURE DENSITY AND
TRANSMITTANCE WITH
STANDARDS
EQUIPMENT:
CRT PRINTER
OPTICAL PRINPER
MICROCOPIER
ENLARGER
CHEMICALS:
D-II, D-I9, D 76
DK-50, MICRI DEL
RODINAL, ACL TOL
INSTRUMEI` TS:
SENS I TOMETI R
MICRODENSIT)METER
ISO DENSITRi,CER
MICRO PHOTCMETER
TRAVELLING MICROSCOPE
OUTPUT
COLLECTION OF FILM TYPES AND CHARACTERISTICS
WITH DENSITY RANGES AND RATIOS FOR PRINTING
AND TRANSMITTANCE VALUES FOR VIEWER
Figure 4. Experiments Measurements Plan
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COPY FILM -COMPATIBLE
WITH INPUT TRANSPARENCIES
MEASUREMENTS
STANDARDS DENSITY AND TRANSMITTANCE
ESTABLISH CRITERIA FUR
REPLICATION CYCLE
STANDARDS I DENSITY AND TRANSMITTANCE
ANALYZE CHANGES
IN ACUTANCE
MODIFIED SPECIMENS OF INPUT
TRANSPARENCIES WITH RELATED
DENSITY TRANSMITTANCE DATA
Figure 5. Acutance Experiment Plan
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C. MATERIALS AND EQUIPMENT
The working area of about 760 square feet is divided into two rooms, each
with provisions for light tightness and ventilation. It is a complete ;:elf-contained
photo techniques laboratory.
In one room, shown in Figure 6, the controlled film processing experiments are
performed using nitrogen-burst agitation and time-temperature cont ?ols. A
micron retention water filtration system is used to preclude the deposit of
contaminants on the photographic films.
The second room, shown in Figure 7, is used for photo-replication _.nd physical
measurements. The photo-replication equipment consists of an= breadboard
intensity modulated cathode-ray tube printer, I optic it printer,
STAT Imicroprinter, and a modifiedII enlarger. Measurement
STAT instruments include a Imicrodensitometer, which can be used with a
Tech/Ops isodensitracer; traveling microscope; and a Gamma scien;ific photo-
STAT metric microscope, to be used with a transparency viewer . By the
reporting date it is expected that all equipment processed will be in ise with the
exception of the modulated-light contact printer. The design and development
effort on this piece of equipment is described in Paragraph E of this section.
Individual equipments have been calibrated and the capability for rer eatability has
been established. A measurements program is beginning to build ur in that pro-
cedures and modes of operation are being developed with non-imaging type stand-
ards. Step tablets are being converted to relative standards for use in the
measurements program. Consequently, the photo-techniques laboratory has
reached the stage of making meaningful measurements and determining how to
effectively use the precise measuring equipments to verify the procedures laid out
in the plan. The capability for applying precisely all the equipment,,- and
instruments to the measurements and acutance experiments progran, is in the
order of 85 percent complete.
STAT
ST"T
STT
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Figure G. Controlled Film-Processing Room
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 STAT
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1. Photographic Film
Thirty-two types of film were reviewed by studying manufacturer-furnished
film-characteristics curves. These curves were examined in terms of density
range/ratio response to the specific light sources used in the replication equip-
ment. Six film types have been selected with which to begin preliminary
measurements.
2. Film Processing Chemicals
The selection of chemicals was based on grain-size development capability
and density ratio control contribution. After analysis, eight types of chemicals
were selected for experimentation.
The design and construction of the modulated-light contact printer is nearly
complete. A special feature of this equipment is the provision, through electronic
means, of a negative light mask with which the contact print will be made. The
equivalent density of the negative mask, the resolution of the mask, and the ex-
posure time are all variable.
It is expected this equipment will be operational by November, following electri-
cal checkout.
2. Design and Mode of Operation
A photograph of the modulated-light contact printer is shown in Figure 8,
a schematic diagram of the mechanical and optical layout is shown in Figure 9,
and a block diagram of the electrical components is shown in Figure 10.
The equipment is mounted on a massive drill-press base and column, which stands
approximately seven feet high. The raster of light from a flying-spot scanner tube*
passes through an enlarging lens** to the negative to be copied, which is held in
contact with the positive copy film by a film press, as shown in Figure 11.
* Developmental Kinescope Model No. C74325, which is a 5ZP16 tube with
Pi l phophor.
** Focal length 8 inches; f/2. 8, with iris.
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lu
PHOTO MULTIPLIER'
zzL
LENS
IRIS
LENS
SEMI-
TRANSPARENT
MIRROR
Figure 9. Modulated-Light Contact Printer,
Mechanical and Optical Layout
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'RIANGULAR
WAVE
I IENERATOR
1 IORIZONTAL
VARIABLE-
FREQUENCY
OSCILLATOR G
- __r_-
PHOTO
Ii MULTIPLIER
AND
1PRE-AMPLIF ER'
NEGATIVE FILM ---~-"
1I~ - -
JEFI-ECTION F
I FOCJS
I t- ~
OR VERB I VOL?AGE
REGULATOR
VII ;.0
AMF'L IER
GAIN AND
El :CK
LE 'EL
CONTROLS
ULT ?R
POV ER
SUP '~Y
20 :V
AMPLIFIER
AND iI- ---= L
'RIGHTNESS
CONTROL
BLANKING I
"r it ur.- i U. Modulated- li.ight Contact Printer Block Diagram
'l.'he illumination passes through the negative to the copy film in intensities that
vary with the densities in the negative. A Fresnel field lens conde ises the ilium-?
e ation passed through the copy film. This condensed illumination is then trans-
Iitted to the photocathode of a photomultiplier tube for feedback pi !kup. The
zal.ectrical signal so produced is fed back to the grid of the flying spat tube so as
to modulate the exposure of the cony film.
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Thus, in the areas where the density of the negative film is light, the illumination
intensity of the flying spot is reduced or in areas where the densities are heavy,
the illumination is increased. In this manner the exposure contrast in the copy
film is reduced. This contrast compression is not effective in detail smaller
than the diameter of the flying spot at the film; the contrast in fine detail is there-
by enhanced relative to contrast in broad areas. The minimum size of the flying
spot will be one millimeter; the size can be increased by optical or electron opti-
cal defocussing.
Before the copy film is actually exposed, a "set-up" operation is required. In
this case there is no copy film in the film holder. Instead, a copy-film chip is
placed in front of the photomultiplier which serves to produce the same optical
attenuation that would occur under exposure conditions. The electrical signal
so produced is fed to the grid of the flying-spot scanner thereby modulating the
light passing through the film holder. A half-silvered mirror between the con-
densing lens and the photomultiplier reflects part of the transmitted light so that
it may be imaged onto a ground-glass screen at eye-level for viewing. This screen
is provided with two small photocells, so that the transmitted contrast range may
be measured.
The raster scans in an isotropic pattern; each element is scanned in two orthogonal
directions during each frame of exposure. The crystal-controlled scanning fre-
quencies are 1023 and 1024 cycles per second, so that a frame of exposure is ac-
complished in one second. This scan pattern produces a line density equivalent
to that of a 1450-line picture using unidirectional scan. With a one-millimeter spot
at the negative, there is more than a six-fold overlap of lines, and no scanning
structure should be visible in the copy.
The exposure raster, with a one-second cycle, is inconvenient for viewing and
set-up. Provision has therefore been made for a faster coverage of the field
during the set-up period, at a rate of up to at least 30 frames per second, with
correspondingly fewer lines.
The exposure can be controlled in several ways. Duration of exposure can be pre-
selected to be one, two, three, or four frames (always in an integral number of
seconds). Intensity of exposure can be controlled by the bias of the grid of the
electron gun in the flying-spot tube, and by the iris of the enlarging lens.
The equivalent density of the negative mask (the modulation of the flying spot)
is controlled by the gain in the feedback loop. The attainable equivalent density
will be evaluated during the checkout of this equipment.
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Relationship of Contact Printer to Other Efforts
'T'his equipment is functionally similar to equipment which is "eing developed
for Electronic Film Processing, but has a more limited range of cr oability.
The contact printer will provide a negative mask with a resolution ;f up to one
cycle per millimeter. One stage of processing is obtained; further orocessing to
enhance image perceptibility will be accomplished by electrical-ch( mical photo-
graphic techniques.
1 '..'le resolution capability of the breadboard Electronic Film Processor in forming
a mask is substantially higher, 10 cycles per millimeter-, and with he high-
resolution Ferranti kinescopes should reach 60 cycles per millimeter. Within
this resolution range, either negative or positive masking may be ajplied, or the
mask may be negative in one part c: f the resolution rang+- and positive in another,
or the mask may be otherwise shal,ed. The processing to achieve improved image
perceptibility in the copy film is to be achieved primarily by manipulation of the
shape and equivalent density of the mask.
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1?LECTRONIC PROCESSING TECHNIQUES
The objective of the Electronic Processing Techniques portion of this program is
the development of electronic image-processing techniques that will lead to
photographic records with improved image perceptibility. The current effort is
concerned with utilizing the flexibility of electronic circuits and components in
combination with high-resolution photographic copying methods to achieve in one
step the results obtained previously in many steps. The investigations in this
area will, for the most part, be performed on a breadboard high-resolution elec-
tronic image-processing system.
A. PROGRAM PLAN
The Electronic Processing Techniques portion of the EPT program com-
prises the following tasks:
1. Feasibility Investigation (Task I )
A preliminary electronic image-processing system analysis will be per-
formed to identify critical aspects of the proposed two-kinescope system. Bread-
board equipment will then be designed, constructed, and assembled to test hypoth-
eses and demonstrate operating principles. Experiments with this equipment will
lead to the design of a preliminary breadboard system.
2. Preliminary Breadboard System Construction (Task II)
The characteristics of various electronic components and circuits will be
investigated and reviewed in terms of system requirements and overall program
objectives. A preliminary breadboard electronic image-processing system, in-
corporating standard kinescopes, conventional beam scan, and broadband negative
and positive "feedback" , * will be designed, constructed, and assembled to provide
valuable data on system stability, signal-to-noise ratio, and light characteristics.
Experiments with this preliminary system will lead to the design of a final bread-
board system.
3. Final Breadboard System Construction (Task III)
The results of Tasks I and II will be applied to the design, construction, and
assembly of a final breadboard electronic image-processing system incorporating
a high-resolution modulating kinescope, isotropic beam scan, and variable-band
* As is discussed later, this will not be a true feedback system, because it
operates open-loop.
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{ (iltered) negative and positive feedback combinations. Experimet is with this
high-resolution processing system will establish )perattng charact ~ristics anti
control parameters for the processing experirnen-.s.
Prot essing experiments, be~zlnnin ; i~ rth s tnniple tq_ st transpai encies, will
34 performed with both the preliminary anc: final~~readt,oard systems. The gen-
oral effectiveness and utility of the proposed electronic- techniques will be deter-
mined. As with the electrical-chi, rnical processing experiments, ;modifications
oL the test procedures and/or equi:.pntent will be based non results of initial tests.
Yurther study and evaluation of electronic processing techniques w LI be reflected
hi continuing experiments with the breadboard sv, tem.
>chniqucs Study and Evalu~ntion (T,:~sk V 1
Thu state=--of-the-art of electronic processing tecminiques will be reviewed
in light of the current program oh,Tectives. The breadboard systen~ and modifi-
ations thereto will be analyzed to predict performance and growth capabilities.
The results of i)rocessing experiments, to be expressec.i in terms c i' actual and
subjective evaluations of the processed images b5 =_tnd Govern nent personnel,
,will be reviewed for agreement with theoretical expectations. A mathematical
,-(.yodel of the electronic processing sv stem, similar if nit identical to the electri-
cal-chemical system model, will be developed. i-'inall,y , recomm? ndations for
uture efforts in this area will be proposed.
Rear-Projection Viewer. Study (Task VI)
in addition to the above efforts, an analytical inv+nstigation of the feasibility
,11 applying modulated-light techniques to roar-projecti,_~rt viewing gill be made.
Also,, recommendations for future o,iforts in this area -~- ill be proposed.
The present test setup whici, constitutes the feasmility demo istration unit
h a two-kinescope sv stem. as shown in l u,ure i:-'. T i,.- sensing k nescope is an
=5ZP--16 and the modulating kinescope is the same !ape of tube except for the
phosphor, which is the yellow component of silicate P-c . The deflecting equip-
ment is the same as used on an F-I1fecording lProject and consists of two yokes
Lenticular Film Color Project
STAT
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operated in parallel with a single deflecting driver, which also produces 27 kilo-
volts at I milliampere of current in a flyback circuit for the ultor supply. Indi-
vidual focus supplies are obtained from a regulated RF supply. These are
adjustable above and below 6 kilovolts which is the center voltage. A single lens
is used in conjunction with a light splitter. The lens is a Wollensack f/1. 9
Oscillo-Raptar in an Alphax shutter. The condensing optical system on the
sensing side of the transparency consists of two 4-inch diameter Fresnel lenses
(equivalent to convex-side to convex-side) spaced 1/2-inch apart. The photo-
multiplier is an=8575 with a 12-stage multiplier operated at 1000 to 1500
volts. Video amplifiers have a bandwidth of 20 megacycles per second. The
power supplies are Lambdas, a Sorensen Nobatron, and a Northeast Scientific.
Two views of the test setup are shown in Figure 13.
2. Operation
The sensing kinescope scans the original photographic negative with a fine
spot of violet light at a low intensity. This light passes through the copyfilm
and is picked up by the photomultiplier and an electrical signal is generated.
VIDEO
AMPLIFIER
MINUS YELLOW FILTER
PHOTO MULTIPLIER ^8575)
Figure 12. Breadboard Electronic Image-Processing System,
Schematic Diagram
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l' r 1:1. BYeauijoar(I . t(J Lr 'ia i.iYlrt,-- '-Pt', ~tessin Sys er11
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This signal is amplified, processed, and applied to the modulating kinescope.
The fine spot of yellow-green light generated by the modulating kinescope exposes
the copy film through the original negative. The minus yellow filter prevents
the yellow-green light from reaching the photomultiplier and affecting the signal.
Exposure of the copy film emulsion depends on the product of the transmittance
of the negative and the sum of the sensing and modulating illumination. The ex-
posure, in this process, is performed from point to point sequentially as the
negative is scanned by the light.
Compensation for the propagation delay between the two scanning beams is made
by an optical register of the rasters so that the light from the modulating kine-
scope passes through the same portion of the negative as the corresponding light
from the sensing kinescope.
The fundamental problems were carefully investigated with the results
described below.
1. System Stability
Achieving system stability with a 20-megacycle video bandwidth using feed-
back with the loop closed is difficult when the phase shift in the system is over
180 degrees. In the test setup described previously, the phase shift from de to
20 megacycles is 720 degrees, or two complete loops; it is linear with frequency.
Based on past experience, it was decided to achieve the effect of feedback by
color separating the sensing and modulated light sources by means of colored
optical filters.
By employing a combination of STAT
Idichroic filters between the multiplier phototube and the transparency,
practically none of the modulated yellow light gets through to the multiplier
phototube, but the sensing light source is attenuated only a small amount. The
two wavelengths of light eventually reaching the transparency are 4100 Angstroms
for the sensing light and 5300 Angstroms for the yellow-green modulated light.
With this system, the video gain has been increased to the point where the
modulation is mostly noise without system oscillation. This condition cor-
responds to a current gain of several million.
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Signal-to-Noise Ratio
Achieving a high system signal-to-noise ratio requires reduction of the
noise generated by the input element, which, in this case is the multiplier
phototube and circuit. Besides the usual thermal noise it was founc that much
noise is generated by leaky components. The following precautions were, there-
fore taken: r'1) A multiplier phototube was chosen with a high curre it gain and
STAT low dark current I1 8575). (2) All insulation connected with the ube, the
socket, and the voltage divider is teflon. (:s) All filter capacitors u;e Mylar in-
sulation or the equivalent. (4) The multiplier phototube uses no plu;, instead
the pins come directly out of the glass envelope. A special teflon s )cket comes
with the tube. (5) The voltage divider was made with encapsulated r ietalized
resistors for low thermal noise. These were mounted on teflon dis s arranged
coaxiaily in a shielded cylinder. (() The input amplifier stage is at 06CW4
nuvistor used as a cathode follower driving a 75-ohm line to the phc sphor-
correcting amplifier and mounted In the photomuitiplier unit close t), the anode
to rminai.
All these precautions resulted in a much improved signal-to-noise a atio. Based
on the system operating with 50 microamperes ultor current for the sensing
kinescope, the lens set at f%2. 8, and the video gain adjusted for a h.ghlight
brightness equivalent to 50 microampere ultor current in the modul sting kine-
scope, signal-to-noise ratios were obtained, as follows:
Film No. S05427 was the most opaque to 410t:--Angstrom ight
;:.nd gave a signal-to-noise ratio of fifteen decibels, base( on the
i atio of peak signal to rms noise.
films S0243 or S03404 were the least opaque and gave s: 4nal-to-
s_oise ratios of 25 decibe-s.
All other films tested, SO 235, S0 266, SP474, 502427, royal blue X-ray, and
gravure copy, fell between these values.
Achieving over 25 cycles per millimeter resolution over an area of 2 by
2 inches requires equipment not yet received. The present raster ( ptically re-
duced 5 to I produces 508 television lines per inch on the transpare icy, which
corresponds to 254 cycles per inch or 10 cycles per millimeter. T e two kine-
scope rasters are mechanically brought into register by means of p -ecision
mounts. Registration is essentially perfect over most of the central area of
the picture, being only slightly misregistered around the edges. In proved
registration requires a more rigid mount for all optical component,- and yokes
that are more identical. This is being planned for the high resoluti )n setup.
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4. Exposure
Test exposures were made using the kinescope light sources both separately
and in combination. For the same ultor current in each of the two kinescopes, the
same exposure times gave an 8-to-1 ratio of actual exposure on No. SO 243 film.
The modulated light source gave the higher exposure so that the sensing light will
dilute the modulated light only 12 percent for SO 243 film. During the next report-
ing period data will be taken with other film.
All of the photographs shown in Figures 14 through 21 were made from contact-
printed negatives that were one inch in diameter with the prints enlarged three
diameters. Figures 14 through 19 show the effect on the film when exposure
times for the individual light sources are varied.
1`igure 14. Exposure of Four Fields (4/60 Second)
Modulating Light Source Only
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:sre i5. i aposur( c c.i? it i, ietci , (8/t Second)
kf)du att uuy ,LLhL -mirca-, i )n1V
I- ,gure L6. _:x~o u ui It) 1Eid5 16/ ij ecorid)
Only
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Figure 17. Exposure of 32 Fields (32/60 Second)
Modulating Light Source Only
Figure 18. Exposure of 32 Fields (32/60 Second)
Sensing Light Source
:31
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,cre P), r:xposu T,e of 64 Fields (64/6! Seconds)
`i'ensnh I.i