THE H-229 PHOTOGRAPHIC RECTIFIER

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04747A000600080054-9
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 20
• Document Creation Date: December 28, 2016
• Document Release Date: February 8, 2002
• Sequence Number: 54
• Content Type: REPORT

Approved For Release 2002/06/17: CIA-RDP78B
,2$747AO00600080054-9
Declass Review by NIMA/DOD
THE
H-229
ANOTHER OUTSTANDING ACHIEVEMENT
PHOTOG
Featuring . ? .
EXCEPTIONAL FLEXIBILITY
HIGH RESOLUTION
AUTOMATIC OPERATION
STATINTL
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THE WHATS,
WHYS, AND
HOWS OF
PHOTO RECTIFICATION
WHAT is photo rect i f i cation?..... Rectification is a process whereby a geometrically distorted
image is transformed into a true scale photographic reproduction. In the past, limited recti-
fication was accomplished during the projection printing process. Using this technique, the
average scale can be corrected by changing the enlargement factor and the effects of lesser
degrees of camera tilt and distortion can be removed by tilting the lens or easel. This type
of rectification is usually accomplished with photos which have been taken at relatively low al-
titudes and from near-vertical positions. Photos of this type present relatively small amounts
of distortion for the rectification process to contend with.
WHAT of tomorrow's needs?...... The Space Age has brought with it a requirement for many dif-
ferent types of higher flying, longer range vehicles. The advent of this type of conveyance has
brought with it new photographic challenges which must be dealt with by the photographic scien-
tist and engineer. The problem of rendering a high-oblique, a panoramic, or an extremely
high-altitude photograph interpretable has presented stumbling blocks such as curvature of the
earth and problems caused by elements of the camera system.... lenses, mirrors, air refrac-
tion, etc. . . . all of which contribute to greater amounts of distortion in the final print. It is
with pride that
announces its new H-229 Photographic Rectifier, an out-
standing electronic achievement, which will provide a solution for these problems.
WHY is photo rectification important today?..... The answer to this question lies in the fact that
through rectification, aerial photographs can be reduced to a common scale and coordinate
system for use in mapping and. intelligence data gathering. new H-22
able toda 9, which is avail-
y, is actually a versatile image transformer and, therefore, through the use of suit-
able punched tape programs and auxiliary circuits, it can effect any transformation which can
be programmed mathematically. Such transformations might include the conversion of exist-
ing photographs to simulate photography from new camera systems, the conversion of maps
from one type of projection to another, the projection of distorted photography for flight sim-
ulators, and the transformation of drawings to different coordinate systems, as well as the re-
moval of distortion from photography.
STATINTL
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'WW
PHOTOGRAPHIC RECTIFICATION BY IMAGE SCANNING STATINTL
Rectification is a process whereby a geometrically distorted image on an
aerial photograph is transformed into a constant scale reproduction of the original
subject matter.
For aerial surveying, the ideal photograph is a true vertical view; all ob-
jects at the ground datum plane appear at the same scale. Aircraft motion causes
the majority of camera views to be slightly tilted. For many years, the photo-
grammetrist has removed the tilt effect during projection printing. The printer
lens plane and print easel are tilted to compensate for image scale variation.
This is illustrated in Figure 1 where the grid in the negative plane indicates the
effect of camera tilt on a photograph of a rectangular grid.
Today, photo reconnaissance imposes additional requirements in image rec-
tification. This arises because photographs obtained by the military are not, for
A LIGHT SOURCE
the most part, vertical, but are more likely
to be of the panoramic, high-oblique, or ex-
tremely high-altitude type. This type of
photograph requires extensive rectification
in order to transform it into a constant scale,
which is mandatory for intelligence data
gathering and the making of mosaic maps
of enemy terrain. The conventional pro-
jection rectifier has not proven satisfactory
for the large variety of image transforma-
tions often required by the military and,
considerable effort has been an-
therefore
,
RECTIFIED
PRINT plied to newer methods. The rectification
of panoramic, high-oblique, and extremely
high-altitude photography acquired with
several t
es of cameras has become a
yp
Figure 1. Optical Rectifier-Printer
vi 111NiL_ today.
has designed and constructed an engineering model of
an image scanning photographic rectifier. This design was directed toward in-
creasing the range of rectifying transformation while preserving image detail and
placement accuracy. The operation of this equipment is illustrated in Figure 2.
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YR
DIRECTION
PHOTO
MULTIPLIER
Yp
DIRECTION
Ci)
YR INDEX
MOTOR
ca<
SYNCHRONOUS
/ MOTOR
~Xp DIRECTION
Yp INDEX
MOTOR
A distorted aerial photo is scanned to convert the
image to a video signal. The image is transformed,
reproduced and printed. The relation between read-
ing and printing scan patterns determines the trans-
formation in image geometry. The grid in the neg-
ative or reading plane shown in Figure 2 illustrates
a panoramic photograph of a rectangular grid. The
engineering model has been built to prove the fea-
sibility of this method of rectification. The prin-
cipal features of this equipment are versatility and
high resolution. The machine is controlled by a
punched tape that has been programmed to command
the relative scanning pattern. The resolution of the
printed image (relative to the scale of the original
negative) is 30 photographic lines per millimeter.
Figure 2. Photo Rectification
by Scanning
Image Transformation by Scanning
Kinescope displays are often distorted for special effect by varying the rela-
tive pickup and display scanning patterns. With a fixed pattern display, the scan-
ning camera can cause the image to be rotated and stretched many ways. In adapt-
ing this technique to rectification, a fixed display pattern is also used. The scheme
used for displaying and printing the image has been selected to meet preliminary
photographic requirements.
The rectified print is exposed in a succession of narrow contiguous strips.
Each strip is of equal width and length and is composed of a raster of line scans
which are developed into a strip by optically and mechanically translating the line
scan image from the printing kinescope (refer to Figure 2). The flying spot dis-
play on a cathode ray tube is optically reduced to improve the resolution of the
image. To insure that exposure time is constant for printing film, scan velocities
are fixed throughout a rectification. The reading scan pattern is developed to per-
form a given geometric transformation. It can be seen that when a constant scale
line image is printed by a fixed velocity spot scan, the pickup sweep is not linear
for a variable scale negative image. To use linear sweeps for reading, line scans
are kept short (less than 1/8 inch on the negative) to result in negligible error from
variation in negative scale.
The relative printing and reading scan patterns for the rectification of an
oblique photograph are illustrated in Figure 3. The keystoned grid illustrates a
rectangular grid transformed by oblique photography.
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Iftemp
AYp
I I
AYR
COMPONENTS OF
READING SCAN
Figure 3. Scanning Pattern for an
Oblique Photograph
oYp = Ypn - Yp(n- 1) =
YpO, Yp1, Yp2, Yp(n-1) =
XO =
Xpl, XpZ, Xp3, Xp(n-1) =
In Figure 3, the Yr axis is se-
lected as the principal line of the nega-
tive image. The Xr axis is a perpen-
dicular coordinate through the principal
point of the photograph. A characteris-
tic of oblique and panoramic photography
is that straight lines (Yr = constant)
transform into straight lines (Yp = con-
stant). (See Appendix for more com-
plete discussion of panoramic rectifica-
tion. For information on the geometry
of rectification see Reference 1. )
To perform a rectification, the
line scan (AR) amplitude and direction
and the lens scan position (Xr and Yr)
must be controlled by the following
printing scan constants:
line scan length
position of center line of each strip scan
starting position of strip scan
evenly spaced scan positions for checking
reading strip scan position.
The reading line scan OR is produced by adding its components pYr and
OXr in the flying spot scanner deflection yoke.. For oblique and panoramic recti-
fying transformations, it can be shown that AYr is constant for any strip scan po-
sition (YpO, Ypl, etc.) and that 0 Xr = K Xp where K is a constant determined
for any strip scan position (YpO, Ypl, etc. ). The sweep amplitude A Xr varies
continuously as an analog of lens position (X).
The position of the strip scan (reading lens) can be computed by integrating
the scan rate Xr from a previously known position. (The ratio of scan velocities
Rp
is constant for any strip scan for rectification of oblique or panoramic im-
ages.) The accuracy of the computed position can be improved if it is checked at
precomputed points XrO, Xrl, etc. when the printing lens is at positions XpO, Xpl,
etc. , respectively.
The position of the negative platen (YrO, Yrl, YrZ .... ) is dependent only
upon print table position (YpO, Ypl, Yp2, etc. ). These positions can be precom-
puted to command the position of the negative for successive strip scans. The
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accurate computation and control of scans has indicated the use of a numerical con-
trol system similar to that employed for automatic contour milling.
Design
A functional diagram of the photo rectifier is shown in Figure 4. The photo
transmission system consists of reading and printing flying spot scanners and the
video link. The scanning mechanism includes the synchronized electronic sweeps
and the precision lens drive and film indexing system. The programming system
continuously computes and commands the position and velocity of scanning from
numerical data on punched tape.
Photo Transmission System
The photo transmission system is basically a closed-loop television system.
The negative is read by a flying spot scanner (using a cathode ray tube and a photo-
multiplier). A projection quality cathode ray tube is used for reading. The video
'signal (250 KC bandwidth) is displayed and the display is optically reduced on the
photographic print. Less resolution is required for printing, since the minimum
negative scale enlargement is 4X. (A 70 mm negative is enlarged to a positive
transparency on 9- 1/2 inch film. )
STATINTL
The principal consideration in the photo transmission design was good reso-
lution with a reasonable exposure range. The exposure range (or number of gray
levels) is limited by the signal-to-noise ratio of the video signal and the printing
C. R. T. The reading system employs a high quality flying spot scanner
K1725-P16) with a matching photomultiplier 1 16363-511).
STATINTL
YR INDEX
SERVO
ATTENUATOR
-LENS
SYNCHRONOUS
MOTOR
XR SERVO
AMPLIFIER
SWEEP
GENERATOR
VIDEO
AMPLIFIER
SWEEP
ATTENUATOR
Figure 4. Functional Diagram, H-229 Scanning Section
LENS xP
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STATINTL
To improve the resolution, the cathode ray tube trace was optically reduced
4X. The reduction in light gathered reduced the signal output of the photo multi-
plier. Adequate improvement in light was achieved through the use of a large aper-
ture projection lens Of/2) and by a scanning raster (as opposed to a line trace)
on the cathode ray tube. The raster scan reduced phosphor fatigue (from repeated
scans) and permitted increased beam current. Since the vertical or strip scan is
primarily made by translating the lens, the lens position and velocity were com-
pensated to correct for the raster scan.
Special attention was also given to ,filtering and the regulation of power sup-
plies.
Scanning Mechanism
The method of scanning is shown in Figure 4. Cathode ray tube displays are
optically projected for line scanning; The projection lens is translated to produce
strip scans; and film is moved to cover a sequence of adjacent contiguous strip
images.
Line scans are generated from a common sweep voltage generator. The
printing kinescope sweep is fixed in amplitude and,orientation. The linear reading
scan is varied in amplitude and rotation by driving horizontal and vertical deflec-
tion coils with the computed sweep signal components. This method of sweep ro-
tation simplifies the reading sweep amplitude computation and also causes negligi-
ble drift in the sweep center position.
Strip scans are produced by moving the projection lens carriage on a preci-
sion lead screw and ways. Precision was required for accuracy of position and
also to maintain focus. To minimize the velocity error of the scan servomechan-
ism, nuts riding on the lead screw were threaded over a 1200 arc to reduce fric-
tion.
Lead screw drives were also used to accurately position the reading table
(negative) after each strip scan.
The method of numerical control is indicated in Figure 4. Deflection signals
at the pickup cathode ray tube are attenuated by tape controlled attenuators con-
sisting of relays and precision resistors. One deflection component is also atten-
uated as an analog of lens position.
The reading platen is positioned by a servo system. This is accomplished
by comparing its numerically encoded position with program tape commands.
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To perform the image rectification, it is necessary to control the reading lens
position as a function of the printer lens position at any instant in time. Figure 5
shows how the desired reading lens position is continuously computed and regis-
tered. At the instant the printing lens reaches a starting or reference position,
the desired numerical reading lens position (for a specific scan) is read from the
tape and registered in the reference position counter.
A position pulse generator emits a pulse for a minute increment of lens dis-
placement. A count of these position pulses is a precise indication of displacement
and the pulse rate is analogous to the lens velocity.
By programming the ratio of strip scan velocity, a pulse rate can be pro-
duced analogous to the reading scan velocity. This is accomplished by multiply-
ing the pulse frequency and dividing it with a programmed counter. After the in-
itial lens position is registered by a counter, each pulse of ready velocity analog
is added in the counter. The counter continuously registers the computed numer-
ical reading scan position.
Only a minute error can result from the method of computing pulse frequency,
since only a finite number of velocity ratios can be numerically programmed. In
order to prevent the accumulation of a significant error, the registered position
in the counter is corrected from the punched tape data at frequent intervals (better
than 8 times per inch of reader lens travel).
SYNCHRONOUS
MOTOR
REFERENCE
POSITION
INDICATOR
POSITION PULSE
GENERATOR
CHECK
PULSE
DIVIDER
PRINTER
LENS
1
~I
VELOCITY
COMPUTER
XP
P
Xr GATE
CHECKING
PULSES
Xr
REFERENCE
POSITION
COUNTER
Xr
GATE
TAPE
READER
READER LENS
*REFERENCE
VELOCITY
READER LENS
REFERENCE
POSITION
Figure 5. Scan Position and Velocity Computer
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The reading lens position is controlled by the reference counter indication.
Figure 6 shows the lens servomechanism. The lens position is numerically en-
coded by integrating its pulse rate velocity analog from an initial reference posi-
tion. The position is registered by a true position counter. After comparing the
commanded and controlled positions, the numerical error is converted to a vol-
tage analog. The lens velocity is determined by the computed velocity analog (with
a velocity servo loop) and the error signal provides position control. Accelera-
tion and rate damping enable the use of a stable high servo gain with minimum
control error.
SERVO
AMPLIFIER
SERVO
MOTOR
LENS
POSITION
COUNTER
Figure 6. Lens Scan Servomechanism
The performance of the photo rectifier model has been measured by its
photographic results. The principal result was the rectification of panoramic
photographs. An aerial photograph from a panoramic camera is shown in Figure
7a. The rectified image is shown in Figure 7b. The original rectification was
reduced 4X before making the half tone print shown in Figure 7b. The overlaid
grids indicate the nature of the rectifying transformation.
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Figure 7(a). Results - Before Rectification (1:1)
Figure 7(b). Results - After Rectification
Overall system resolution was
measured by placing a Standard Air 32 m
Force Resolution Chart in the neg-
ative film platen and printing it 4X
enlarged. The result was further
enlarged 5X in a photo enlarger and
shown in Figure 8. The 16 and 32
line per millimeter targets are cir-
cled showing they were resolved.
The reading resolution was
determined by measuring the video
signal rise time when scanning a
sharp edge in the negative plane (a
Figure B. Resolution Chart
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test reticule). This measurement showed that 2000 T. V. lines per inch were well
resolved, which results in 40 photographic lines per millimeter (accepting 2 T. V.
lines per 1 photographic line). (The method of measuring reading resolution was
taken from Reference 2. )
The printing system resolution was measured by generating a dot pattern on
the printing kinescope. Better than 20 photo lines per millimeter were resolved
on the printed pattern. This corresponded to 80 lines per millimeter with respect
to the negative scale after 4X enlargement. Photographs were enlarged 4X (at the
nadir point) as well as being rectified. This substantially reduced degradation of
image detail by the limitation in printing resolution.
Exposure Range
STATINTL
The use of optical reduction reduces the effective illumination from the cath-
ode ray tubes. However, for printin , the light available was adequate to fully ex-
pose with the ASA 80 film used. 1K1405-Pll C. R. T. is used with
an f/4. 5 projection lens for printing. )
The dynamic range of exposure was better than 20:1, that is, the variation
in the density of the rectified image was less than 1-1/2 log units. The principal
exposure range limitation is the signal to noise ratio at the photomultiplier output.
Other Photographic Characteristics
Overlapping scans were used to minimize evidence of scanning lines in the
print. After 16X enlargement, evidence of scanning can be detected. Referring
to Figures 7(a) and 7(b), lines appearing in this photograph were caused by a 60
CPS interference with the magnetic deflection field.
From Figure 7(b), the effect of strip scanning is quite apparent. The strip
effect is accented in this figure by improper shading adjustment and also by an in-
adequate A. G. C. circuit. Nevertheless, lines joining the image do detract from
the appearance. This is justified for reconnaissance purposes where appearance
is secondary and the image transformation cannot otherwise be accomplished with
adequate resolution or placement accuracy. No attempts were made to soften the
strip effect by comb mattes or variable density edges.
Placement Accuracy
The placement accuracy desired for this equipment is the location of any
image element within 0. 010 inch from its ideal position, determined with respect
to the image element position on the negative and the rectifying transformation.
The engineering model fulfilled these specifications.
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The placement accuracy achieved is attributed to precision mechanisms and
numerical control. Line scans produced by a cathode ray tube were short; errors
occurring from non-linearity in sweeps (less than 1%) accounted for a minute error.
Speed of Operation
The rectification of an entire panoramic photograph such as shown in Figure
7(b) requires 40 minutes. Excepting scan retrace time, which requires almost
50% of the total time, the time required is limited by the resolution, format size
(70 mm x 7 inches), and video bandwidth (250 KC) used. A significant reduction
in scanning time will be limited by the accuracy required and the clock frequency
used in numerical contro. At present, the computing clock frequency is 1 MC/s
and the computation error is less than 0. 00025 inch.
The scanning method used here may be extended to more difficult transforma-
tions, such as earth's curvature corrections. This will require more complex
scans; non-linear scans will be required. The numerical control system employed
can be used for precise programming of non-linear motion.
The principal restraint to higher resolution in scanning rectifiers or photo
transmission systems in general is available light from small flying apertures in
reading scanners. The achievement of a resolution of 30 photographic lines per
millimeter is not represented as a limitation, but it required some reduction in
the range of exposure (to 20 or 30 to 1).
The engineering model of the rectifier described in this paper was
almost entirely, upon concepts developed by
U. S. N.
STATINTL
based,
Reference 1. Manual of Photogrammetry, Chapter VI, American Society of
Photo gramme try.
STATINTL
Reference 2. Cathode Ray Tube Recording Symposium, Jan. 13- 14, 1959,
"Methods of Determining Spot Size",
Reference 3. "Emulsion Sensitivity for the Photography of Cathode Ray
Tubes" by R. W. Tyler and F. C. Eisen, Journal of Society of Motion Picture
and Television Engineers, April, 1959. STATINTL
Reference 4. "System Design of Flying Spot Store",
Journal, March, 1959.
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Figure 9. Engineering Model of H-229 Photo Rectifier
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IqW
Programming A Panoramic Rectification
When a panoramic negative is lined up in the rectifier reading carriage, the
machine's Yr axis is the principal line of the photograph and the Xr axis intersects
the nadir point of the photograph. Then the rectifying transformation is expressed
in the equations (1) and (2). This transformation is indicated in the grid image re-
lationship shown in Figure 2.
Xr
f
Yr
f
Xp
h
1/, + hp )2
tan- 1 (hp )
(1)
(2)
where Xp and Yp are axes of the machine print plane,
f is camera focal length.
h is relative altitude (f is the scale enlargement at the nadir point
of the rectified print).
Printing scan constants are:
. Yp = Ypn - Yp(n- 1) = constant
YpO, Ypl, Yp2 = position of center of each strip scan
XpO, Xpl, XpZ = position of center of scan start and
each check point
Xpn - Xp(n- 1) = constant
To program reading scans, the variables to be precomputed are:
AYr for YpO, Ypl, Yp2, etc.
X r for YpO, Ypl, YpZ, etc.
p
Yr for YpO, Ypl, Yp2, etc.
Ip for YpO, Ypl, Yp2, etc.
2Yr
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v
The sweep amplitude A Yr can be determined by differentiating equation (2).
A Yp (3)
It can be seen that A Yr is independent of Xr and is constant for any strip
scan. The value of DYr can be computed and stored for values Yp = YpO, Ypl,
etc.
The sweep amplitude A Xr can be computed by differentiating equation (1).
f Yp A Yp (4)
Xr = -Xp (h2 + Yp2) 3~2
Amplitude Xr is jointly determined by printing lens position Xp and a function of
print table position YpO, Ypl, Yp2, etc.
The ratio scan velocities Rr results from differentiating equation (1) with
respect to time.
Tr I I + (Yh ) 2 (5)
The relative strip scan velocity is constant for any strip scan. The reading lens
velocity (fr) can be computed as a function of the print table position (Yp) and is
analogous to the print scan velocity (p).
Check positions XrO, Xrl, etc. can be precomputed for each scan (from
equation (1)) and used to correct position at time Xp = XpO, Xpl, etc.
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ENLARGED AERIAL PHOTO
(FRAGMENT)
PRINTED BY
PHOTO ENLARGER
PRINTED
AND ENLARGEDING
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STATINTL
 //
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SCAA/
L'1 0
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HOW is this new concept of rectification accomplished? .................. Basically,
scans a distorted aerial photograph, converts
the image to usable electrical signals, supplies
additional transformation data, effects the trans-
formation, and subsequently prints a rectified
reproduction of the original photo. The desired
geometrical transformation is accomplished by
controlling the relative amplitude and orienta-
tionof elemental line scans, as well as the rel-
ative velocity and placement of strip scans.
YR INDEX
MOTOR
Advanced cathode-ray scanning tubesandprojec-
tion lenses are employed to obtain high resolution. Precision lead screws are utilized for
mechanical scanning and film indexing in order to provide excellent image placement accuracy.
Reading and printing scans are synchronized by a common clock signal, and the relative scan-
ning patterns are determined by a punched tape program. The numerical control employed is
similar to that used for automatic contour milling.
Punched tape programs for different transformations can be produced quickly using any ade-
quate computer facility. Once a negative has been set up in the reading platen, the entire rec-
tification process becomes completely automatic.
The H-229 Photographic Rectifier's exceptional flexibility permits its use in many fields. How-
ever, it will probably find its most important use in the field of aerial reconnaissance.
XR MOTOR
XR
TRANSDUCER
YR INDEX
SERVO
PHOTO
MULTIPLIER
VIDEO
AMPLIFIER
Yp INDEX
MOTOR
SWEEP
ATTENUATOR
' AXR
SWEEP
ATTENUATOR
TAPE
READER
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R TRANSDUCER
INDEX =~ / LINE SCAN
INTERVAL
XR SERVO
AMPLIFIER
SWEEP
SYNCHRONOUS GENERATOR
MOTOR
p
TRANSDUCER
Xp DIRECTION
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TECHNICAL DATA
System Resolution . . . . . . . . . . . 40 lines/mm for 9-1/2 inch film
50 lines/mm for 70mm film
Film Size Handled . . . . . . . . . . . Up to 9- 1/2 inch film, any length
Magnification . . . . . . . . . . . 1:1 to' 4:1
Rectification Time (Panoramic Photograph) 25 minutes, 70mm film at 50 lines/mm
25 minutes, 9- 1/2 inch film at 40 lines/mm
15 minutes, 70mm film at 25 lines/mm
15 minutes, 9- 1/2 inch film at 20 lines/mm
Cumulative Placement Errors . . . . . . . Maximum, 0. 116%
Expected, 0.075%
Video Frequency . . . . . . . . . . . Z me
Computer Clock Frequency . . . . . . . . 5 me
Scan Spot Size at Negative . . . . . . . . 0. 0003 inch, approx. 4000 TV lines/inch or
80 lines/mm
Reader Lens Positioning Error . . . . . . . Less than 0. 001 inch
Indexing Accuracy . . . . . . . . . . . 0.001 inch
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