SPECIALREPORT PAR 25-6-2 

PERFORMANCE COMPARISON TEST PLAN 

FOR MANN-DATA MIC RODENSITOMETER VERSUS 

KODAK MODEL 5 MICRODENSITCHETER 

20 October 1965 

Prepared by: 

S. Perry 

RELEASE 

1 

NROAPPROYE 

22june2015 

DOCUff.ET 

CONTAgS 15'PAGES BB-45-700-126- 

Approved by: 

4/ 

. L. Greet' -• 

. . 

Contract EB-11:92 
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A test plan is offered for comparing the optical systems 

r ept the Kodak and Mahn-Data microdensitometers. This plan is intended 

as a-guide-far the preparation of a comprehensive test method. After 

negotiation between participants and preliminary testing, a final pro- • , 

cedur4 car' be written. 

The general guide lines are given in the text for tests 

measuring the follawing.characteristics. 

a.. Resolving power: 

be Modulation Transfe]f 

Spread Rion, 

Power Spect 

Stray Light 

A preliminary test procedure is given in Appendix 1 for 

a starting point in writing the final detailed test procedure. 
-p106,-Apiprt151.11 

22 June 2015'.L.'J;I 

A. Introduction 

1. Two types of microdensitoieterS are currently in use in determining the image quality. of missions by means of edge' tracing. It 

seems essential to eg;are, in Aome objective manner, the performanCe 

of the Mann-Data instrument with that of the"1odak Model 5. Testing of 

photographic microdensitometera is discuSSed:Oy Altm-an,(1) 1einsihger,.(2) 

Charman,(3) and Snider,(4); (See indicated references at the end of this 

write-up.) : No attempt-Will bemade.lhere therefore, to desCitbe exhaustive 

testing for all chEiraaoristics pertineht to this instrumePOs usage'in 

photographic research. For example* the ability to read the.absolutedenaity of microareasto some degree of precision is- the fundamental 4P-. 

pliCation Of a ticrodeneitometer, and yet this characteristic'is of little 

interest;in:this testing_since the current methods of edge tracing' utilize 

4-0 

relative density rather than absolute density.. The ability to hold talibration for several hours.and the:. ability to follow rapid changes inedensity 

become more important than attaining a high abtOlute'acCuracy. 

2.' A microdensitometer is composed of mechanical, electrical and 

optical systems. While a testing of the performance of all subassemblies 

is desirable, this test plan will-concentrate on measurement of"the optical 

system on the assumption that: 

ca. The mechanical and electrical systems are working reliably. 

:b.' These systems are"Of secondary interest 

-c* Soi fOrMe of. mechanical or-electricalMalfUnctiono#14. 

be noticed in the suggested optical testa* 
3. The optical testing will include discussions of and, where 

available; priacedures for measuring the resolution modulation' transfer 

function, spread funN 

microdensitometer. 

B. Test Plan Discussion 

1., ResolVing Power 

a. Of historic interest, if perhaps of no longer fundamentalimportance in edge trading, is the resolution cf the optital t-ysteM. 

0 

- However the ability to quickly and reliably brink the inicrodensitdmeter 

to focus is necessary. A test object for. measurement of resolution could 

be any high qUality, photographic long bar target. Also, some form of 

special.diffractiongrating could be made in which a limited number of 

lines are ruled in bands, with the bands arranged in a freqUency series.- 

A•test object similar to, the' latter form- is the Graysons Rulings, 

(Beck, London--no longer available),which has been used by microscopists 

for resolution testing.(1) • Lacking a test object, resolutiOn can be 

inferredbT the MTF/edge trace measurements given in the section on 

Modulation Transfer Function. 

v./ 

b. In comparing the resolution orthe Mann instrument with 

A 

that of, the Kodak Model 5, it is recommended that one or more special 

photographic test objects be scanned on the two microdensitometers. The 

specific test` abject. paaern is not critical, provided it besome form 

having long parallel bars arranged in a frequency series, A maximum frequency equal to or Rreater than 5O4ViineSiMillimeter is desirable. Spans 
22, j4c1610715 

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made in the two instruments with equivalent slits Can be compared on 

the basis of the percentage of modUlatipn retained at the high,frequencies. 

morecomplicated analysis could bebesed on measurements of the prOfile 

wave shape) of.,the two sets of traces. This approach would be 

recommended only if satisfactory answers cannot be arrived at withi:simpler 

methods in the areas of interest. 

2. Modulation Transfer Function 

a. The modulation transfer function of the mictodensitometer' 

can be estimated, 'but not measured directly, by tracing a sharp photographic edge.P),.(3)' Thp characteristics of the edge, such as sharpness, 

variability along the length of the edge,/grain,, and density-range,influences, 

the, results of the measurement. An obvious'problem here, as in all suggested 

Microdensitometer tests,,is that of obtaining a- gdod test object. 

b. The procedure for_MTF testing at this facility is 

(1) An X-ray exposed edge on Kodak - High Resolution 

!'late or High Resolution FiIM (available from N.B:S. by special arrangement) 

is. used as a test object., The maximum density should be less than 2.9; the 

edge should be several inches long, and only the best portions should be used... - , 

(2) Make recordings of the edge, using the particular main 

slit cOnfigUratiOn of interest (e.g :,1 microh by 80 microns). The 

shOuld be as sialifas poisible and edge/Main slit alignmentahould be care7 

flay adjusted. Carry all digital data to..at:Ie;St three_ipifica7 

(3) ,Data sampling ShoAld be qp.t Spacings such as 040 

to 0.25 micron to high frequency information* 
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(4) rake any analog recording at almoStHtaXimum. 

scale expansion. 

.(5) )Trace across several placesalpng. the edge. fiurn 

the PhotographiC edge 180!. and trace siMilarlYlin the oppPsite direction. 

(6) Take at least 100 data points per trace sn- that areas 

adjaPent to the edge are represented. 

(7) The digital data is transformed into instrument MTF by 

means of FOurier'methods in the comotter.(2),(L) The resultant data'reore... 

sents the best estimate of the frequency response of the microdensitometer.- 

c. The etrorSAnherent_in this method have not been measured. 

The straightforkard technique for-measuring the MTF of a ticrodensitometer, 

by tracing calibrated sinusoidal test,objects is suggested by -Snider,(4) 

, t 

but he does not indicate whether such test objects are available. 

3. Spread Function: A valuable: measurementneedipg-development.is.' 

that of direct measurement of the spread function of the microdensitometer. 

A test object for this characteristic would probably consist of an, extremely 

narrow clear line on a dark surround. *Such .a test object is.not known to 

exist. Spread function can be derived from edge trace measurements, but 

• 

will include the errors associated with edgetracing. 

h. Power Spec a 

a. A microdensitometer perfornance test which appears to have 

promise is in an early ,stage of development. This test involves the 'determinatibn of the pdwer spectrtm (spectral density function). Standhrdized 
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test methods. have not been established at this :tline , but:a typical 

periment will he described below. The methOds'for interpreting the fresults. 

A p 

of the measureme.qt:;Llso , .are not > ell established., The principle is', that if 

. . 

a scan is made of a white noise test object, the power. spectr* produced is 

• , . • . 

that of the slit/optici ,function of theMicrodensitometer.:(5) If‘the.test 

object is not whfbe noise, the scan will produce a spectrum which has 

•. 

Components of both thp test object and the-microdrsitometer.- 

Z1) A'test objecticurrently in use is a flashed' and 

processed strip'of Type 344 film having a. series:of densities. 

(2) The film strip is scanned using :the normal slit 

• 

*gaometry- (e. .: 1 by 80 microns)!. 

3) - Density samples are collected at Small increments Of 

• 

distance (approXmiately 0.4 microns), and the data values are recorded to 

three'significant digits each. 

(4). Maximum sensitivity or "density" expan 

Three thousand or more data points should be taken. 

, 

on is_employed. 

(5) The density-data. are converted to transmission values 

and are reduced in.the computer through autocorrplation techniques to power'. 

spectral detsity.(64(7)(8) The resultant plot of per vt. frequency., 

in a comparative measurement, show'the relative sensitivities (nresfolution") 

of the instrventS to the baild of frequencies. 

b. Spurious noise coming from thecinstrUment shoUld be noticeible. 

provided the test objeCt grain_dpnSity distribution is reasonablyuniform.,. 

C. The reliability, errors, methods, and' interpretatibia of 

results of power.spectrum measurements o# microdensitometers are currently 

under'study. "Good comparison data is expected from this approach haweteri. 

despite current lack of experience with the method. 
Stray Light 

a. An image degrading effect present-in, all optical instruments 

is, stray light or veiling glare. It is noticeable in Mitrodensitogietert as 

ah error in the ;Density recorded for fine black line4 on a large, lowdensitY. 

'.(clear) surround. Stray light is also a detrimental factor in edge tracing. 

Control is achieved through gooddesign fe.g.; baffling, blackening, and' 

glass surfate coating) and good maintenance (i.e.:. clean optics). When 

using'inser.bments where hooding of the optical parts is not extensive, it 

.may be necessary, to operate in subdued light. 

' b. A qualitative teat for stray light in a microdenffitmeter 

is the following: . 

(1) 

4

A special test with a series of parallel black 

lines on a clear surround is required. The line width should vary in . a 

series,from approximaZely 100 microns to less than,5 microns. The test 

00o, 

object exposure (via- X-rayss constant and brush, developing irs employed 

so that the denaities-of all the lines are equal. 

(2) -The test object0 is scanned with a narrow slit (e.g.: 

1 x 80 microns). The pre-slit should be only slightly larger than the 

main slit, following regular practice. It is also infOrmative to make 

• 

runs with larger pre-sliis. 

(3) In interpreting the results of the scans, the amount -

of stray light and its influence on fine detail can be inferred from any 

progressive tall off,in recorded deniity as the sample line width is decreased, 
R.B.Blabkmanoand J.W.Iukey, The Measurement of Power Spectra, 

Dover., 1959, 

E:Rttrzen, "An Approach to Empirical Time Series Analysis," 

J. Research Natlt Bur. Standards, Rad. Sol., 68D, 937-951, 

September, 1964. 

8, R.C.Jennison, Fourier Transforms and`Convolutions for the Experimentalist,: 

PergaMon Press, 1961. 

Reference's: 

1. - J.H.Altman.& K.F.Siultz,- "Microden§itometer for Photographic 

Research,',Z, Rev. Sci. Insti.',.27, 1033-1036, December, 1956. 

I,J,KIeinsinger, A.J.Derr,-i,naTT.,4GiUffre, "Optical Analysis' 

of a Microdensitometer4ystem," Appl. Opt., 3, 116771170,, 

• OCtober,-196W: ' 

3. W.N.Charman, "Practical Tests Of a Microdentometer 

ApPl. MarCh, 1965. 

, 

4". G.H.Snider, NidradenSitometeapability and Interpretation Study, 

Final Reports I and Cornell Aeronautical Laboratory, Inc., 

December, 1964. 

• 

H.J.Zweig, "Autocorrelation and Granularity, III.. Spatial 

Frequendy:Response of the Scanning System and Grariularity 

Correlation Effects Beyond the Aperture," J. Opt, Soc. Am., 49., 

2)8-244„ March, 1959. 
. JO' 

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,Appendix l.a. Proposed Micr hstometer Test ProCe8ure,, 

1. . General' 

'a. Record name andSerilal number of instrument. 

b. Describe in de. tqii4,04,041 pOnents used An teat, including 

(a) Chart rate: 

'10 

per 

k v focal length nd nTe5ical apertures of all objectives,- 

-magdifi4ion.of eyeWejeCe8.-if used, and magnification of 7 

illumination and pickup syste . 

• c. ° Reaord'tYpe of..lightsOurce .and operating •conditiOns..- 

. • 

d. Record type' of .photomultiplier. 

2. Resolving. Power, 

• . 

-'a. .Purpose: to indicate the resolving power of the microdenSitometer 

in the scanning mode and in the -viewing mode. 

• 

b. Procedure: 

(1)-Test Object: Photographic, U.S.A.F. 1962 machine readable, 

frequency range 200 to 1000 lines permilliMeter, clear 

bars on a blaciç. surround, high contrast. 

(2) Microdensitometer operating conditions:' 

(a) Slit:. 0.5 microns- by 80 midrons. 

4 (b) Stage rate: 0.025 millimeters per 'Minute. 

(c) Photometer amplifier controls: jnormal density settings. 

(3) Analog data recorV: 
4 

20' -Oct' 65 

.(b) Zero:. Drain onlow part.of charti 

(c) Sensitivity: expand recording to place -Dmax 

on high pert *chart. 

Digital data: not applicable. 

Number of repetitions: None.' One reading only. 

c. Report: Report maximum frequency recorded on chart. 

0. Special comments: 

(1) Note whether best visual focal setting.yields beet, 

recorded resoling power. 

2) Note resolving power of viewing system. 

3. Modulation Transfer Function 

a. . Purpose: to estimate the modulation transfer fp:notion (optical 

frequency response) and spread function of the microdensito 

-b. • PrOcedure:- 

(1) Test Object: sharp edge exposed by i-rays - On icodik.High; 

Resolution Plate. Density ,range (60)'of 0.50 t 0.10. 

(2) Microdensitometer Operttt;ing, conditions: 

• (a) 1.0 microns by 80 MiCrons. 

(b) Stage rate: 0.0166 mm/min. 

'(c) Photometer amplifier controls: normal density:setting. 

(3) Analog data recording (hplpfui for verl.fication, bUt not 

essential): 

(4) 

(5) 

Chart rate: 8 inchesimtnute. 

Zero: Dmin recording on low part.of,qart. 

Sensitivity;, Dmax reading near highest...part oTHchart 
IA0:401.4. 0 FCTI REcgoE''. 

• , 

Digital data collection: 

(a) Sample rate: 80 samples (3 digits each) per minute. 

(b) Scale expansion: adjust controls such that both 

• 

clear and dark sides of the edge record with 3 digits 

and there is tle( largest spread between minimum and 

maximum 'values fox increased precisichl 

(5) NuMber or repetitions: at least six runs over the sane 

edge are necessary to permit averaging.. 

domputation and. Rport: 

(1) Convert digital data to transmission data in computer. 

(2) Determine response by Fourier methods at frequency 

increients of 10 to 20 lines per 'millimeter. to 400 lines 

(3) Plot response' versus frequency. 

Special Comments,: 

This method yields the estimate of the prrF for the micro-

, 

dens itometer including the slit width function. 

The spread function Can usually be obtained as pnrtc of the 

------ computer data k reduction. 

Scanning- from clear to b„lack and black to clear should 

expose any non-Uniform behavior !e.g.: fatigue) in the 

photometer circuits. 

(0 The stage rate and punch rate suggested may not be available 

On all instruments. Other combinations are equally ,seitable 

' provided the data point sampling rate is less than 0.300 micron: 

between 'data points. The" stage rate ebbed be'slow enough tbat 

the responee time of the recording equipment. does not effect 

the measurement. 
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22 June,20,15 , • 

Spread Function. 

Purpose: To directly measure the overall optical performance 

of the microdensitometer by a method-simpler than edge 

derivation. 

Procedure: Currently there is not adequate information for a 

preliminary test plan. However, once a suitable test object 

• is available, a procedure can be devised. 

c. Special comments: While tpread function is derivable frma, 

- , 

edge tracing in the preceding MTF.test a special spread 

function test should include less error. 

. Power Spectrum 

a. Purpose: to determine the approximate power spectral density 

function of the instrument. Note'that this method includes 

any noise present in the test object. 

• b. Procedure: 

(1) Test Object: a uniformly flashed and processed strip of 

Kodak 3404 film, density Q.50.± 0.10. 

_(2)L MiCrodensitomeer parating Conditions: — _ 

- (a), Slit: I micron by -80 microns. 

(b) Stage rates 0.0166 millimeters per Minute. 

.(C) Photometer amplifier controls: normal dentity setting. 

(3) Analog data recording (not essential): 

(a) Chart rates 2 inelles per minute.,- 
Zero control setting: adjuSt control so that the 

lowest recording is near zero on'thechart. 

Sensitivity control setting: expand the.densiy . 

recording to maximum. 

-(4) Digital data .recording: 

(a) Punch rate: 80 samples (3 digits) per minute. a 

(b) Scale expansion: use fullest practical (preserve 

e. 3-digit readings) scale expansion to aid retention 

of significant digits in subsequent computer-

' data reduction, 

(5) Number of data points: collect at least 3Q00 data points 

.yer'run. Several runs would be desirable to help estimate 

the precisicynpfthis method. 

. Computation and Report: 

(1) Convert the 'digital data to density (or transmission) in 

the computer.' 

(2) Determine the autacorrelation function. 

(3) Take the Fourier transform of the -autocorrelatien_funotion; 

(4) Plot the power spectrum versus frequenCi.. 

d. Special Comments: As in the measurement of modulation transfer 

functiont the stage rate and punch rate, may be different than 

that proposed above, provided that' data samplipg is-taken 'at 

rates slaw enough to minimize problems associated with the time . 

constants of the recording equipment wtd.Ustill maintaining 

close data point spacing,on the simple. 

49 
20 :opt-1965 

Stray Light Measurement:. 

Purpose: to determine the control of stray light (veiling 

4 

glare) withIA-the_picrodensitameter. 

b. Procedure: -7— 

Test. Object:,a series of black lines of equal density 

on a clear surround having line widths, varying from . 

5 to 100 microns. 

(2) Microdensitometer Operating Condition 

(a) Slit: 1 micron by 80 microns. 

(b) Prerslit:' 5 microns by 85 microns. 

(c) Stage rate: 0.050 millimeters per minute. 

(d) Photometer controls: normal for density operation. 

(3) Analog,Data Recording: 

(a) Chart rate: h inches per minute. 

(b) Zero: normal for density calibration. 

(c) Sensitivity: normal for density calibration. 

(4) Digital Data Collection: • not applicable. 

Number of'.repetitio4: None. One reading is adequate. 

• P 

c. Report: The density.of the lines recorded on the analog chart 

is plotted against the width of the lines. The fall-off of 

density in the narrow lines-i8 a measure of the uncontrollqd 

stray light within the instrument., 

d. Special Commehtsr This test is relative in nature being dependeat 

on the unifoimitY of the test object density', Also, the results 

are a funCtionokfthe contrast of the 44rk bir and itlE(04*004 

0 

ti 

(1) 

(5 ) 

•