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IDA-IM-139

November 24. 1959

Electronic Photo-Enhancing

of

Reconnaissance Photography

by

J. S. Goldharnmer

and

H. L. Coplen

Advanced Research Projects Division. Institute for Defense Analpses

The Pentagon

Washington 25. D. C.

Under Contract to the Advanced Research Projects Agency

Contract No. SD- 50

Copy No.

DS 594301 -

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Electronic Photo-Enhancing of Reconnaissance Photography 

BACKGROUND

Current photo-reconnaissance aircraft operate at altitudes up to 50.000 ft.

(9.5 statute miles) and utilize camera lenses of 40 to 50 inch focal lengths . This

equipment produces pictures having an over-all photographic resolution of 60 to 100

lines per mm. SAMOS photo reconnaissance satellites will operate at attitudes of

160 and 300 statute miles respectively for the Es and E2 subsystems. This is an

increase in altitude of roughly 16 to 30 times current practice. Since the ground

resolution in a photo-reconnaissance negative is proportional to focal length and

inversely proportional to altitude (or subject-to-lens distance) it is quite apparent

that the degradation in ground resolution occassioned by an increase in altitude

of 16 to 30 times cannot practically be offset by a proportional increase in focal

length. It is estimated that the practical limit in photographic lens-film system

resolution is about 150 lines per mm.

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The photo interpretation of satellite photographs will be doubly difficult

because of the current lack of any aids for the photo interpreter other than poor

quality low-power magnification. Accordingly, the detection of pertinent

intelligence data under conditions of grain aglorneration and low contrast will

be very difficult.

DISCUSSION 

Solutions to the above dilemma are discussed below specifically covering

the several facets of the problem.

First; a reduction in granularity and better contrast levels are achievable

using exposures made at the toe of the sensitornetric curve for the film emulsion

used . This technique is not currently used because of the non-linear brightness

reproduction of the original scene which confuses the interpreter and impedes his

recognition processes . An electronic scanning transducer with compensating

non-linear characteristics could be used to return a negative taken using the

above technique to its original condition.

Second; high magnification cannot be used because of the disturbing effects

of film "grain." Actually, the visual phenomena termed "grain" is actually the

distraction produced by grain aglornerations . The normal human eye can resolve

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about 100 microns (1/10 mm) at the center of the field of vision. The silver

particles in photographic emulsions are only 3 to 12 microns in length for the

highest speed films and an order of magnitude smaller for emulsions considered

r satellite photography. However. groups of particles form spurious and random

;Patterns of 100 microns or greater length and this interfere with the detection of

1.ctual patterns. The photographic process converts cantinuous tone brightness

:nage s into digital or, quantized information due to the development of images by

discrete silver and silver halide crystals. A smoothing process to convert

back to an analogue or continuous tone form is needed and could be accomplished

by an electronic scanner with an aperture sized properly to smooth the square

wave intergranular density gradations. Accordingly, a considerable magnification

will then be possible and the picture detail enhanced.

Third; the contrast of many scenes is so low as to unduly mask important

detail. The electronic scanning process can incorporate a contrast amplitude

t•nhancernent feature which, in addition. can provide variable contrast for

selection by the photo interpreter to assure optimum recognition of important

i ntelligence detail.

ON CLUSIONS AND RECOMMENDATIONS

Photo interpretation of current aircraft reconnaissance system output is

made difficult by poor image contrast and the lack of high quality magnification.

The already difficult task of photo interpretation will be made significantly more

so with the advent of large volumes of lower resolution satellite reconnaissance

photography. Accordingly. significant gains in the photo interpretation of all

reconnaissance photography are urgently needed. The above interpretation aid

and the important improvements in recognition clarity which result from its use

appear essential to the over-all satellite reconnaissance systems now in development and will materially improve data acquisition from current aircraft

reconnaissance systems.

It is therefore recommended that a system of photo enhancement suitable

for such use be supported through the experimental evaluation phase. A suggested

work statement is given below:

Develop. construct and test evaluate an experimental

electronic photo enhancement system suitable for use with

reconnaissance photography from the SAMOS project. System

omits to be developed and features to be incorporated shall

include, but not be limited to:
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IDA-IM-139

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A high resolution scanning system of sufficient

quality so as to not degrade the original photograph,

A video signal processing unit. which shall contain

the controls and circuits necessary to provide for

variable contrast, variable grey scale expansion.

linear and non-linear grey scale reproduction, and

the necessary digital and frequency selective filters

for "grain" smoothing and various other photo enhancement

techniques .

3. A high resolution display unit of 14 inches or

larger diameter for viewing the processed photograph.

Flexibility of operation controls shall be maximized to

facilitate photo interpretation and evaluation of the

features provided in the experimental model.

received October 5, 1959, from

system with the above features

about 16 months from contract

issue and for an approximate total cost of 5135,000. This fins is believed

to be responsible and competent in the intelligence data processing field.

They have investigated most of the proposed systems techniques in

previous work both under contract and with company hinds . It is known.

however. that several other firms have shown interest in electronic

image enhanc

rocs

It is e o

rom of the above mentioned firms to a common work statement similar

to the above . The most competent firm or firms to engage in the experimental

evaluation phase can then be selected on the basis of these proposals.

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