Halftone Dot Method for Image Evaluation of High-Resolution Films Applied to Vesicular Film

Rochester Institute of Technology

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4-1-1980

Halftone Dot Method for Image Evaluation of

High-Resolution Films Applied to Vesicular Film

Mark Gulden

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Recommended Citation

HALFTONE DOT METHOD FOR IMAGE

EVALUATION OF HIGH-RESOLUTION

FILMS APPLIED TO VESICULAR FILM

by

Mark P. Gulden

A thesis submitted in partial fulfillment

of the requirements for the degree of

Bachelor of Science in the School of

Photographic Arts and Sciences in the

College of Graphic Arts and Photography

of the Rochester Institute of Technology

Apri I ' 1980

Mark P. Gulden

Signature of the Author ...

.

Photographic Science

and Instrumentation

Name Illegible

Certified by ... .

Thesis Adviser

J.

F. Carson

HALFTONE DOT METHOD FOR IMAGE

EVALUATION OF HIGH-RESOLUTION

FILMS APPLIED TO VESICULAR FILM

by

Mark P. Gulden

Submitted to the

Photographic Science and Instrumentation Division

in partial fulfillment of the requirements

for the Bachelor of Science degree

at the Rochester Institute of

Technology

ABSTRACT

A feasible technique for

deriving

the spread function and

modulation transfer function of a vesicular film has been determined.

This technique is based on a method described

by

R. Byer which does

not require the use of a _{microdensitometer,} but _only that of a "macro"

densitometer. The method utilizes the fact that a halftone dot will change in size as a function of exposure. The spread function of the

vesicular film was approximated with a mathematical model. The results,

although favorable in many ways, are not conclusive. Some of the

advantages and disadvantages associated with this technique as applied

ACKNOWLEDGEMENTS

I would like to thank _my adviser, R.

Byer,

for all of his guidance

and encouragement. A special thanks goes to _{my wife,}

Barbara,

for her

assistance in the lab and with the art work.

And,

I am grateful to S.

Harding

for her typing. I would also like to thank Xidex Corporation

TABLE OF CONTENTS

INTRODUCT ION 1

OBJECTIVE 12

EXPERIMENTAL 13

RESULTS 21

ANALYS IS 37

CONCLUS ION

43

INTRODUCTION

Vesicular photography is a _relatively new photographic process

in terms of _commercially successful

imaging

systems. The Kalvar

Corporation,

first in the production of vesicular film for commer

cial _use, began its operation in the late 1 950'

s.

Today

there are

only two major producers of vesicular films- Xidex Corporation and

3M Corporation.

Vesicular _photography has _many uses in _{micrographics,} but the

majority of the film used _today is for

duplicating

COM

(Computer

Output Microfilm).^ _{Another important}

use is in the area of micro

film information storage and retrieval systems. L2

Vesicular films are low _speed, ultra-violet _sensitive, and

heat developed. The film consists of a polyester film

base,

_usually

Mylar,

coated with a thin plastic polymer _containing the radiation

sensitive diazonium salt. Upon exposure to UV _radiation, nitrogen

gas is released from the diazonium molecule. The nitrogen gas is

entrapped in the plastic polymer for a short period.3 This is in

effect the "latent image". The film must be developed

by heating

within this short period before the nitrogen gas diffuses out of

the film. The diffusion rate _may range from one-half second to

ten minutes before a noticeable change is observed in the charac

teristic curve. Development temperatures can _vary from 230F to

350F and dwell times vary from 0.1 to 1.4 seconds. Caution

must be taken in _adjusting the development temperatures as found

toe

density,

as well as _giving the film a brown color in the viewer

due to light scatter from small size vesicules. Overdevelopment

will produce image decomposition in the higher densities and a loss

in resolution. The

heating

process causes the nitrogen gas to

expand and form microscopic vesicules. These vesicules have an index

of refraction different from that of the _surrounding medium _causing

the light to scatter. The light scattering vesicules can _vary in

9 9

size from _0.5 to 2.0 micrometers in diameter. ' '

The film can

be fixed

by

an overall exposure to UV radiation without development.

The nitrogen gas is then allowed to diffuse out of the film.

Because vesicular films scatter light rather than absorb light

to form its

image,

diffuse

density

is _relatively low.

Measuring

density

in the _way in which the film is used, i.e. projection den

sity, will produce densities between 2.0 and 3-0. The projection

density

obtained is a factor of lens aperture of the projection

system.

Vesicular photography,

being

a _relatively new photographic

system, and the fact that limited literature is available on the

image characteristics demonstrates the need for research in this

area. Rabedeau stated that the

macro-and microimage character

istics of Kalvar film differ considerably from those of silver

7

halide photographic materials. Because of the _scattering effect,

the vesicular material mi crodensi_tometry is more difficult to per

form. The scattered light is reflected off the metal surfaces with

flare _causing erroneous results.

It was also found that the

density

of a given sample varies

as a function of the size of the area of the sample illuminated. At

high

densities, doubling

the narrow presilt widths reduces the den

sity

by

0.25. It was concluded that this effect was due to scat

tering within the layer.

Noting

this _relationship of

density

as a

function of illumination in adjacent _areas, Rabedeau postulated

that

density

of adjacent areas would affect measurements of a given

area _uniformly illuminated well beyond the image area. He called

this

"viewing

adjacency"

effect. There is an additional problem

with microdensi_tometry of high resolution vesicular

films,

that is

the resolution limits of the optical system. The optics used in

conven-o

tional microdensi_tometry are limited to about 200 to 250 cycles/mm.

9 10 There are better techniques with higher resolution _{capabilities,} '

but these systems are designed to handle silver halide products.

Also these newer systems are expensive and not _readily available.

Therefore,

the use of a more conventional microdensitometer for

deriving

the spread functions of high resolution images will result

in erroneous output data above 250 cycles/mm. A system is needed

which will eliminate the uncertainties and provide _reliable, con

sistent output. The output should also be free of _any transfer

characteristics of the measuring instrument.

There has been a great deal of discussion thus far _concerning

the microcharacteri sties of vesicular film and the

diffuculty

in

determining

these characteristics. The question _may be raised as

and modulation transfer characteristics of the film in order to

describe the microcharacteri stics. An industrial _customer, al

though he _may not realize

it,

is

dealing

with the film's spread

function everyday. The spread

function,

as the customer views

it,

is composed of two elements. The first is the _scattering and

reflecting of the light that takes place within the film due to the

fundamental characteristics of the film. The customer has no

control over this element. The second element concerns the

spreading of the light as a function of _exposure, or _simply

stated, exposure latitute. Image size will _vary with exposure

(e.g.

increasing

exposure will cause an increase in the image

size).

(See

_photographs)

Exposure Xidex SX High Contrast Film

IX

2X

3X

4X

F234E

0

HHS

\

.DM0803 .PUI

SY2

R

XOEMPLT

_ _

HCI

ft

VCD

Y

JCS

psam _ . -= ~ '~

tCtlVIO

|T

JCt

Print 1

-Photographs of a microfiche exposed at 4 exposure levels onto

Xidex SX high contrast film.

(Magnification

approx.

400X)

If this _relationship of the scattering of light versus exposure

is

known,

it would be possible to determine the exact image dimen

sions for a particular exposure.

Therefore,

exposure limits can

in which the vesicular films are most used are information storage

and _retrieval, and COM

(Computer

Output Microfilm). Both of these sys

tems require tight limits on image

dimensions,

hence an understanding of

the spread function would be an asset.

The _{understanding} of the film's spread function is important

in yet another way. Film speed can change for various reasons

(e.g.

_aging, variations in the _{manufacturing} of the

film,

stor

age etc.). With knowledge of the spread

function,

speed changes

can be calculated

by

a simple measurement of the image dimensions.

Clearly

then, there is a need to find a feasible technique

for

determining

the spread function of the vesicular film.

A method is described

by

R. J. Byer in which the spread

function of high resolution films can be determined without

using mi crodensi_tometry. The problems in _using the microden

sitometer are therefore removed. This method has been used with

silver halide films and found to be successful. There is reason

to believe that this technique could be applied to vesicular

f i lms.

12

Byer's method is based on a technique devised

by

Goldberg.

The idea is that the image size will increase as a function of

increasing

exposure. If the image spread can be measured at

various exposure

levels,

then essentially the spread function has

been determined.

All photographic materials are turbid to a greater or lesser

degree. Radiation _striking the sensitized layer will be scattered

of radiation is also caused

by

emulsion-base and base-air reflec

tions. The _turbidity of the emulsion and inter-layer reflections

of radiation within the film are the two parameters that describe

the spread function.

In Byer's _system, the _spreading of light is measured _using

a "hard-dot" halftone tint. The tint is contact printed onto a

film in a vacuum frame. As the exposure

increases,

the _spreading

of the dot image also increases to produce a

"soft",

_unsharp dot.

The _unsharp dot image must be made sharp. This is accom

plished

by

contact printing the test

film,

"soft" dot

image,

onto

a high contrast film using a constant exposure. This exposure is

determined such that a high contrast film image of the vesicular

film image of the measuring tint will produce a dot radius equal

to that of the measuring tint. Said differently, the image of

the _measuring tint on the vesicular film has one exposure level

in which the measuring tint dot is exactly reproduced. When the

vesicular image at this exposure level is contact printed onto

the high contrast

film,

the exposure given to the high contrast

film is adjusted so that this dot is again _exactly reproduced.

This will ensure that all dots are made "hard" in the same way.

Because the high contrast film exposure remains _constant, the

dot radii of the test film as a function of exposure can be com

pared. The assumption here is that the exposure given to the high

contrast film is adjusted to lie on the straight-line portion of

the characteristic curve. Because the straight-line portion of

is _needed, the effect of the high contrast film is nulled out.

Densities of the halftone image on the high contrast film

are measured with a densitometer _using an aperture of two mi 1 1 i

meters or larger.

Knowing

the

density

at each exposure

level,

dot radii can be computed with the

following

relation:

R =

transmittance of high contrast film X

unit area tint

if

2, where

1,-rDensity ,.

transmittance =10 'or percent area of clear dot

unit area of tint = _{the area of a 100}

percent dot

(for

a 150 lines/inch _screen, the unit area is 28,674yu.m

)

Once the radii of the dots have been determined at various

exposure

levels,

a dot spread curve can be generated. Silver

halide films have a linear increase in image spread

(increase

in

1>

dot radii) with the logarithm of the exposure. This would in

dicate an exponential decrease of the scatter of light around the

image site. With this dot radii versus exposure _technique, it

is possible to measure a change in dot radii of about 0.6/ym.

Figure 1 shows an example of a dot spread curve for a high resolu

tion silver halide film.

Using

this dot spread _curve, it is possible to determine the

edge spread function. Because the dots receive the same exposure

on the high contrast

film,

all the dots must have the same

density

emulsion is determined

by

_comparing I , the initial

intensity

needed to produce R , the dot size equal to the measuring tint and

k,

the relative

intensity

(constant

time) needed to produce a

dot _radius, R. . At a distance

(R--R

)

from the edge of the

l 1 o

original

dot,

the relative

intensity

of the light is the antilog

(k-L).

For _example, if

I,

was ten times I and the increase in dot radius

I o

from R to R was

5jmm,

then at a distance of 5 /^m from the original

edge the

intensity

would be one-tenth I .

Relative

Log

Intensity

(Constant Time)

Figure 1 Example of a dot spread curve for a high resolution silver

hal ide film

The convolution theorem requires the

intensity,

I at

RQ,

the original edge to be one-half the incident

intensity,

L^-I =1 II

O -oo

To generate a curve of relative

intensity

versus distance from

an edge, which is the spread function curve, is a simple matter.

The relative

Log

exposure is converted to relative

intensity,

remembering that I =l_oo/2, and !t is then Plotted against the

[image:13.520.39.476.57.473.2]

Rq

is much larger than

d,

the increase in dot _radius, the

intensity

distribution at the dot's edge can be approximated

by

the

edge spread function. Because the edge spread function is sym

metrical, only half of the function need be examined.

1Q-d/r

'd^'-oo

2

=

ec'9e sPread function

The line spread function is the differential of the edge spread

function with respect to d.

2-3 in_d/r ,

j r

j ₁₀ = _line

spread function

It follows

directly

that the integral of the line spread function

must equal the edge spread function.

'd

f>

V'-co

~

\

-'^S/r ds

(See

Appendix I for

derivations)

where

d = _{distance from the}

original edge

s = _{distance from the}

infinitely

narrow slit

r =

change in distance

(radius)

for a 10X change in exposure

I = _incident

intensity

14 ₁₅

According

to H. Frieser and

Byer,

the spread function of

a silver halide film is composed of two major components. One

part

being

the _slightly diffused light scattered

by

the grains

and the other part due to the _scattering

by

the base. Frieser's

approximation for the spread function which was modified

by

Byer

10

V'-ocT

P10"d/r1 ₊ (l-p)l0"d/r2

2

where

^

and r are the "one-tenth widths"

of the

intensity

distributions of the two types of _scattering and _p indicates

the relative contribution of r- type scatter of light scattered. Frieser used

k,

and

Byer,

in his modified _equation, set k=2r. Frieser made his images from a line and measured changes in line

width, where in Byer's _technique, the change in dot radius is measured. It must now _{be emphasized, that this is} the _theory and equation that describe silver halide films. Frieser has listed several other equations that could approximate the spread

func-, . ,.. 14

tion for various films.

Modulation transfer function curves can be derived

by

_taking

the Fourier transform of the spread function. The modulation trans

fer function for Frieser's approximation to the spread function is _given as fol lows:

M. _P

(1-p)

Mo

1 +

(.002iT

1+

(

.0021T r?0 12. 3)2

where M. is the modulation of the input

frequency,

M is the

modulation of the output

frequency,

r. and r are the "one-tenth

widths", p is the relative contribution of r type scattering, and

~v is the

frequency

in cycles/mm.

Byer's procedure for

deriving

spread functions and conse

quently modulation transfer curves for film is an _easy, inexpen

11

would allow the vesicular film users to determine transfer char

12

OBJECTIVE

The objective of this _study is to test the hypothesis that R.J,

Byer's halftone dot method is a feasible technique which could be

13

EXPERIMENTAL

The basic design of the experiment is described in the intro

duction. The technique which Byer used will be modified and tested

for UV sensitive vesicular films.

The first _step to be taken was to make some sensitometric

tests on the vesicular film. There are three important characteristics

that must be determined for the vesicular film in order to _apply the

halftone dot technique effectively;

(l)The

maximum and minimum diffuse

densities must be known.

(2)The

effects of _varying

lag

time

(time

be

tween

initializing

exposure and

developing

the

film)

must be deter

mined.

Investigating

the effects of

lag

time is essentially measuring

for _{any reciprocity} law failure which is caused

by

loss of

density

due

to diffusion of nitrogen gas from the emulsion.

(3)The

spectral sensi

tivity of the film must be known. The vesicular

film,

as mentioned

earlier, forms an image

by

_scattering light rather than _absorbing

light.

Therefore,

its diffuse

density

is _very low. The Dmax and Dmin

densities are 0.45 and _0.15 respectively. The effect of

lag

time was

determined

by

making a series of constant time exposures

(45

seconds).

The

intensity

was modulated with a continuous tone

density

wedge so

that the specular

density

could be measured on the Quantascan and com

pared

(Figure

2). This demonstrates that a

lag

time of about two min

utes or less will not have a noticeable effect on _reducing the densities,

At about six minutes there is a change in the Dmax

densities,

but the

curve shape remains the same. The spectral _sensitivity of the film was

provided

by

the manufacturer. The _sensitivity range for Xidex SX high

14

10 sec.

60 sec.

300 sec.

00 sec.

0 1.0 2.0

Log

Relative Exposure

Figure 2

Lag

time between

initializing

exposure and _processing the

Quantascan traces of vesicular film were made with a

f/4.5

aperture _setting

with maximum _sensitivity at 405nm.

The Atlantic Printer was used to make all exposures on the vesi

cular film. The Atlantic Printer is a UV contact printer. Its

source is a mercury vapor

lamp,

and it employs a vacuum frame easel.

The vacuum frame is _necessary with the halftone dot technique, because

intimate contact is needed between the film layers.

The processor used for

developing

the film was the Kalvar 160

Processor. This processor operates

by

_pulling the film over a hot

platen. The film dwell time is _{approximately} two seconds. The

platen temperature is 25020" F.

It was observed that the

density

over a sheet of film was not

uniform. Film exposed and processed

by

Xidex Corporation demonstrated

the same non-uniformities. Therefore it was concluded that this was

an inherent problem with Xidex film. The Eastman Kodak vesicular film

[image:19.520.115.321.31.245.2]

15

The second _step deals with

finding

a high contrast film that will

fit the

following

requirements:

(l)The

high contrast film must produce

a

density

range of _{approximately} 2.00 over a

log

exposure range of

approximately 0.35 and remain on the straight-line portion of the DLogE

curve.

(2)The

film must produce this high contrast index using a cont

inuous tone rather than a litho

(infectious)

developer. The infectious

developer is not used because it will cause nonl inearities in the

Log

Exposure-Density

response. Three films were tested- Dupont

CRF,

Dupont

C0S-4,

Dupont BLC film. The Dupont CRF film had a contrast index of

approximately 8 when developed in Eastman Kodak D

19 developer for six

minutes at 68F. The contrast index was obtained

by locating

the point

on the characteristic curve .10 above base plus fog. Then a straight

line 2.0

Log

Exposure units in length is drawn from the point .10

above base plus

fog

to the point where it intersects the Curve. The

slope of this line is the contrast index. In this _way the CRF film

fulfills both requi rements.The C0S-4 and BLC did not meet the requirements.

The dot size and distance separating the dots determines the sensi

tivity and reliability of the measurements. Small dots with small dis

tances between them means very small changes in dot size can be detect

ed. Larger

dots,

spaced further apart gives more reliability. A

95%,

150

lines/inch,

photographic silver screen was felt to be a good

compromise of _sensitivity and reliability. The reason a

35%,

150

lines/

inch tint was _chosen, rather than one where the dots Were smaller and

closer together was because the spread function of the film _may have

been to wide. This would have meant that the dots would have _overlapp

16

work with _any commercial film.

The modulator used throughout the experiment was a Carbon-M _type,

square-root of two-stepped wedge. Because the carbon particles in the

stepped wedge are at a distance many times their diameter _away from

the vesicular emulsion, the stepped wedge will have little affect on

the _spreading of light in the vesicular film.

The vesicular film and measuring tint are placed emulsion to emul

sion. The carbon-M wedge is then placed over the _measuring tint and

film and put inside the vacuum frame. It is also _necessary to have a

Dmin and Dmax area on the film. It was found that a two minute, fif

teen second exposure time was required to obtain a range of exposure

levels,

which would include an exposure that is ten times the exposure

needed to reproduce the _measuring tint dot exactly.

Two problems occurred, one of which was overcome and the other was

determined to be negligible. The first problem was one that is common

in vacuum frame

printing-Newton's rings. The vesicular emulsion is

very thin and has very little texture. The step wedge is made

by

lami

nating two pieces of plastic over the carbon particles. The result of

having

many smooth surfaces together in a vacuum is an excessive

amount on Newton's ring patterns. This problem was overcome

by

_using

"Anti-Newton's Ring" powder. A fine mist of particles

("Ant

i-Newton's

Ring"

powder) of _{approximately} 10yum in diamter was sprayed onto the

measure tint and step wedge. A very small amount of the powder was

used, in that the average distance between particles was _many times

the diamter of the dots on the measuring tint.

remove the

dust,

e.g. blow it off with a high pressure stream of _air,

brush it off with an anti-static

brush,

an anti-static _{film cleaning}

solution was also _tried; but _nothing seemed to work. The Anti-New

ton's

Ring

powder was not the cause of the

dust,

because _printing with

or without the powder had no effect. It was felt that the dust spots

on the film would effect the

density

_{measurements,}

however,

under

close examination the total area of dust spots were a small percentage

of the dot area. The conclusion was made that the dust spot(s) would

have a negligible effect on the measurements.

A tungsten "point" light source was used for _making the exposure

onto the Dupont CRF film. The vesicular film image of the _measuring

tint was placed emulsion to emulsion with the CRF film in a vacuum

frame. The correct exposure was determined as described in the intro

duction. Should this exposure be

improperly

calculated, the results

would remain the same except for an addition of a constant term.

This is true as

long

as the exposure has not moved off the

straight-1 ine portion.

An aid used to determine the proper exposure for the CRF

film,

(i.e.

when the dot size of the _{measuring tint,} vesicular film and,

CRF film are equivalent) is a microscope with a filar eyepiece. The

filar eyepiece is a microscope eyepiece with a ruled liner and a mov

ing

crosshair.

Densities of the CRF film are determined _using a MacBeth 504

transmission densitometer with a 2mm stage aperture. The densitom

eter was zeroed on the _Dmin, which is produced

by

the Dmax area on

18

The _{non-uniformity} of the vesicular

image,

as discussed _earlier,

were imaged onto the CRF film. This caused large variations in the

density

measurements. The large _variance, made it necessary to make

replicates and take _many

density

measurements off of each replicate.

The

density

measurements were taken over a 0.8 X

4.5cm.

rectangle.

Each measurement was independent of the other. The

density

measure

ments for each exposure level on each replicate were summed and the

mean was calculated. These densities were then used to calculate the

dot radius. This calculation is given in the introduction. One modi

fication had to be made to this equation. Because the Dmax is not

opaque, as the equation _assumes, the amount of light transmitted

through the

background,

Dmax _area, had to be subtracted from the total

light transmitted

by

the sample. A dot spread curve is plotted for

each replicate and a smooth curve is fitted to the data.

The constants

(p,

r.., r_) for the spread function approximation

were derived using the sum of the least square error method.

Twenty

sets of points were taken from the spread function curve of each _rep

licate. A computer was used to compare all combinations of ten poss

ible values for each of the three constants. The values for the

con-* _{The equation for}

determining

_{the radius becomes:}

R=

A

transmittance of the high contrast film

-transmittance

of the background area

(Dmax

_area) X unit area tint

For _example, with a

95%,

150 line/inch _measuring tint the unit area is

27674/^m2. If the

density

of the film is 0.85

(i.e.

transmittance =

0.14)

and the background Dmax area is opaque

(i.e.

transmittance is

0.0)

the dot radius is 35.91/<m. If the background Dmax area has a

density

of 2.00

(i.e.

transmittance =

19

stants were changed and the program was computed again until the best

least square fit was achieved.

It was found that Frieser's Spread Function approximation was a

poor model for this film. Other spread function models were attempted

and the Gaussian curve was found to be the best fit.

The equation

finally

used to approximate the spread function was

a sum of two Gaussians.

(p)e-fl(d/r,)2+

d -oo

The transform fo this equation normalized to one at a

frequency

of

zero is as fol lows:

(p)(

)e-r(.ooirio))2+

(]_p)(

M. ' l

I

M0

=

p(r1) +

(1-p)r2

(See

reference 16 for derivation)

where again r and r are the "one-tenth widths"

of the two major

types of scatter measured in /j.m, p is the contribution of r. type

scattering, d is the distance from the edge, and %> is the

frequency

in cycles/mm.

Five sets of experiments were _{made, according} to the techniques

which were just described.

1

)

ThIs first experiment was to test the system for a film with a

known MTF. Kodak Recordak

AHU 5460

(silver

halide) film tested.

20

minute fifteen second exposure was used to expose the vesicular film.

A one minute exposure was used to expose the CRF film. The "Anti-New

ton's Ring" powder was used in both exposures.

3)Five replicates _using Xidex SX high contrast film were made. The same

exposures were used as in Experiment 2. In this experiment no

"Anti-Newton's Ring"

powder was used. This experiment would demonstrate the

effect, if any, that the Newton's Rings might have on the results.

4)Five replicates _using Xidex SX high contrast film were made. In this

experiment the exposure given to the vesicular film was varied

by

_chang

ing

the time of the exposure rather than the intensity. The exposure

to the CRF film was the same as in Experiment 2. The "Ant i-Newton' s

Ring"

powder was used in both exposures.

5)Five replicates _using the Eastman Kodak Recordak Thermal Print film

1953 were made. Other than the film change it was the same as in Ex

RESULTS

The basic steps which were followed to obtain the modulation trans

fer

Curve,

after the exposures were _made, were the following:

1)

Ten independent

density

readings at each exposure level of each re plicate were taken

(The

densitometer was zeroed on the Dmin area produced

by

the Dmax area of the vesicular film.).

2)

The mean

density

at each exposure of each replicate was determined.

3) The dot radius was calculated

(The

background Dmax area was included

in this calculation.).

4)

The data from each replicate was plotted on the dot spread curve.

A smooth curve to best approximate the data was drawn.

5)

Spread function curves, were generated from the dot spread curves.

6)

Twenty

points from the spread function curve were used to derive the constants

(

_{p, r^,} r

)

for the spread function model which approx

imated the actual curve.

7) The constants derived in _step 6 were used for the Fourier Trans form of the spread function approximation to determine the modul

ation transfer function.

The figures on the

following

pages are the results of the five

experiments that were made. For each

figure,

the three curves represent

ed the mean and two standard deviations. The table is a tabulation of

the constants

(p,

r , r

)

which were derived for each replicate.

The standard deviations were found

by

plotting the values for all

replicates, then the mean and standard for the values _along the "y" axis

were calculated for a particular point _along the "x" axis.

An approximation of the spread function curve had to be found in

order to generate a modulation transfer curve. The curve that represents

the average spread function and two standard deviations to this curve

approx-22

imation curves, then _taking the mean and standard deviation.

The average of _p, r , r , derived from the approximating equation

closely approximated the mean curve which was generated

by

_taking

the average of individual points on each replicate's calculatd

spread function.

The modulation transfer curve was generated _using the constants

(

p, r- , r

)

which were used to approximate the spread function.

Figures

(21,22)

are the average spread function and modulation

transfer curve for experiments

2,3,4,

in which the Xidex SX film was

23

DISTANCE FROM EDGE (m4ii)

Figure 3. Spread function curves of Recordnk AHU 5^60 measured

with halftone dot technique and calculated from

r =f4.5. r?=5.0, and p=.30 _using Byer's modified equation.

100

E 10

'

Manufac turer's data

10 100 1*00

SPATIAL FREQUENCY (CYCLES/mm)

Figure *4.

Modulation transfer curves for Recordak AHU 5^60 _comparing the edge gradient

[image:28.520.106.352.61.330.2] [image:28.520.58.403.67.632.2]

24

EXPERIMENT 2

Ten replicates _using Xidex SX high contrast film were made. A two

minute fifteen second exposure was used to expose the vesicular film.

A one minute exposure was used to expose the CRF film. The

"Anti-Newton's Ring"

powder was used in both exposures.

1 .20

RELATIVE LOG EXPOSURE

Figure 5. Dot spread curve

-The avreage and two standard deviations

[image:29.520.38.454.262.659.2]

25

16

DISTANCE FROM EDGE yim)

Figure 6. Spread function curves for Xidex film _taking the average of 10 replicates andI two standard deviations measured

from the dot spread curves. (Exp. 2)

DISTANCE FROM EDGE (/4m)

[image:30.520.81.327.61.329.2] [image:30.520.78.324.377.642.2]

Table 1

Experiment 2

Repl icates

1 .90 15.0 18.0

2 .90 12.0 2.0

3

.50 15.0

6.0

4 .90 15.0 3-0

5 90 16.0 12.0

6 70 18.0 14.0

7 .85 14.0 13.0

8 .95 12.0 8.0

9 .80 16.0 18.0

10 70 12.0 11.5

average .81 14.8 10.6

26

100

E io

<

1 ""

I 1 1 1 1_JJr r*

~^ ""A

i i II11'!

\

\

\

1 1

-\

\

*

-1

\

I

: '

\

. 1

\

1

\

1

\

1

t

1

J J 1 1 1 1 1 i 1 1 1 1 . , 1 1 1

10 100 1*00

Figure

SPATIAL FREQUENCY (CYCLES/mm)

Modulation transfer curves for Xidex film taking the average of 10 replicates and two standard deviations using the constants in Table 1 and the

[image:31.520.117.340.69.274.2] [image:31.520.57.409.325.646.2]

27

EXPERIMENT 3

Five replicates _using Xidex SX high contrast film were made. The

same exposures were used as in Experiment 2. In this experiment no

"Anti-Newton's Ring" powder was used. This experiment would demon

strate the _{effect, if any, that the Newton's Rings}

might have on the

results.

RELATIVE LOG EXPOSURE

Figure 9- Dot spread curve

-The average and two standard deviations

[image:32.520.37.455.239.647.2]

28 50 40 30 20 10

L>

1

1

\\

\

M i M

\ \ 1

1 1 i

-i i

I,, i

i i

i _i

1

V

_t

1

\

v

-\VL

.,1,1,1 i

1

12 16

DISTANCE FROM EDGE ^um)

Figure 10. Spread function curves for Xidex film _taking the average of 5 replicates andi two standard deviation measured

from the dot spread curves. (Exp. 3)

50 40 30 ^ 20 10 \A'

1 1 "1 -T"

1

\

\ ' ' ' i

\

\

L \

\\

^

-\\ \

M

\

V

\

\

\

- M \

-1

\

_\ 1

\

\

\

\

\

1

\

\

\

\

\

v

\

\ x

\

_^

x

\

^

^

\

\

_

\

\

N \

\

x

\\n

\ \

N A

v

^-, \

r

\

, \ i

1

12 16

DISTANCE FROM EDGE (wn)

Figure u. Spread function curves for Xidex film taking the average of 5 replicates and two standard deviations using the

[image:33.520.79.335.62.329.2] [image:33.520.77.323.382.648.2]

Table 2

Experiment ₃

Repl icates

1 .60

4.5

9.0

2 .90 9.0

7.5

3 90

7.5

9.0

4 90

6.0

15.0

5 .70

4.5

12.0

average .80

6.3

10.5

29

100

10

1 1 1 ' ' ' ' ' *

'-g=-j~A i i i i i i i | 1 ,

- 1 ^*^:^. 1

. \ " NX\ -" \

\

\ \

\

\ \

\

\

\

\ ^ \ \ \ V \

\

\ \

\

^ : \ \ \ \ 1

\

x

-iiii.I , ,

1

i i i i i i 1 , ,

10 100 400

SPATIAL FREQUENCY _(CYCLES/mm)

Figure 12. Modulation transfer curves for Xidex film _taking the average of 5 replicates

andi two standard deviations using the constants in Table 2 and the

[image:34.520.52.401.371.640.2]

30

EXPERIMENT 4

Five replicates using Xidex SX high contrast film were made. In this

experiment the exposure given to the vesicular film was varied

by

changing the time of the exposure rather than the intensity. The

exposure to the CRF film was the same as in Experiment 2. The

"Anti-Newton's Ring"

powder was used in both exposures.

40 36 -~ 32 E o < 28 on o 24 20

1

'

1

'

1

'

1

'

1

/ / / / / / / /

/

y

/

/ /

/

'

-' _X '

'

^

s

^ ^r^

S

*^

_ **"

a0^t^ """* "\,--^ *** y ^***^ y^ -- -" y y ^* y ^x S-^^ ^ _ * ^ / s S

1

,

1

I

1

,

1

I

1

.30 .60 ,90 1.20

RELATIVE LOG EXPOSURE

Figure 13. Dot spread curve

-The average and

i

two standard deviations [image:35.520.42.453.275.623.2]

31 50 40 30 20 -10

\

'

1

'

1

'

1

1 1

[\

-*A\

V

*V

A\

\\\

-\v

*V v\\ -

'\

\v \\\ \V \\\ \_v \\-x \\

N_\\ "> N_^

\ w "^ ^_{^^^_}

^^"

,,1,1,1 1

1

16

DISTANCE FROM EDGE (|im)

Figure 14. Spread function curves for Xidex film _taking the average of 3 replicates andt two standard deviations measured

from the dot spread curves. (Exp. 4)

50

40

30

20

-10

S 1 1 1 1 1 i

\\ 1 1 1 '

V

V

1

-i

-l\\

\V

\\v "

>L

v

\

\ v

\\

\\\

\ \x

\\>

_\ Vs

V-^r

**.

^-, 1 ,

1

*"

, 1 ,

1

12 16

DISTANCE FROM EDGE ^im)

Figure 15- Spread function curves for Xidex film taking the average of 3 replicates and two standard deviations using the

[image:36.520.81.330.63.334.2] [image:36.520.80.328.384.647.2]

Table 3

Experiment 4

Repl icates

1 .80 5.0 22.0

2 .75 4.0 17.0

3 50 3.0

10.5

average .68

4.0

16.5

32

100

10

10 100 400

Figure 16.

SPATIAL FREQUENCY (CYCLES/mm)

[image:37.520.59.406.369.641.2]

33

EXPERIMENT 5

Five replicates _using the Eastman Kodak Recordak Thermal Print film

1953

were made. Other than the film change it was the same as in Experiment 2. 40 36 -32 E y < 28 or: o

24

20

-I

'

I

'

I

'

I

'

I

^* y ---^y *"^ ~ ~ ~~~ ' / *>** _S '" y y __-~^ y ' _^ /

^

/ "

/ y* _y""""

/ _/ ^ '

/

' / _/ / /

/

/ /

/

/ / /

/

/

/

/

I

I

I

1

I

1

I

I

I

.30 .60 .90 1.20

RELATIVE LOG EXPOSURE

The average and two standard deviations

Figure

17-Dot spread curve

[image:38.520.41.457.270.642.2]

34

12 16

DISTANCE FROM EDGE (ujn)

Figure IS. Spread function curves for Recordak Thermal Print film

1953 taking the average of 5 replicates andi two standard deviations measured from the dot spread

curves. (Exp. 5)

12 16

DISTANCE FROM EDGE (^m)

Figure 19. Spread function curves for Recordak Thermal Print film

1953 taking the average of 5 replicates and two standard

deviations using the Gaussian approximation to the

[image:39.520.81.328.61.332.2] [image:39.520.78.324.353.637.2]

Table

4

Experiment 5

Repl icates

1 .70 10.5

4.5

2 .90

8.0

10.0

3

.90 9.0

1.5

4 .90 11.0 6.0

5 90 12.0 2.0

average .06 10.1

4.3

35

100

~1 > 1 t I I I ^u~

10

10

SPATIAL FREQUENCY (CYCLES/mm)

100 400

[image:40.520.122.349.66.204.2] [image:40.520.54.404.372.641.2]

36

[image:41.520.105.351.60.328.2]

DISTANCE FROM EDGE ( m)

Figure 21. Spread function curves for the Xidex film - ₍₁₎

using

the "Antinewton'

s rings"

powder, (2) without _using the

"Antinewton's rings"

powder, (3) with the "Antinewton'

s

rings"

powder, without the carbon wedge.

100

3

Z 10

Figure 22.

SPATIAL FREQUENCY (CYCLES/mm)

Modulation transfer curves for the Xidex film (l) using the "Antinewton1

rings"

powder, (2) without using the "Ant inewton's

rings"

powder, (3) with the "Antinewton'

s

rings"

[image:41.520.61.413.306.638.2]

37

ANALYSIS

Experiment 1 was designed to compare the results of this technique

with the results published

by

the manufacturer. The Eastman Kodak AHU

5460 high resolution film tested with this technique is within 20% of

the modulation transfer response of the manufacturer's data.

However,

these results were obtained with _only one trial. One reason the spread

function is _{wider, may} be because of the "Anti-Newton ' s Ring" powder.

The Frieser approximation to the spread function was used as a model for

the spread function curve

(Figure

4). Figure 4 shows the modulation

transfer curve generated

by

the manufacturer and

by

the dot radius versus

exposure technique.

The image produced

by

the vesicular

film,

discussed _earlier, was

not uniform. This _uniformity problem was noticeableas can be seen from

the results of experiment 2. The results show the variance in the dot

spread and spread function curves was large.

(Figure

5 and 6). To

obtain the average dot spread _curve, ten replicates were needed and at

each exposure level on each replicate ten

density

measurements were taken.

In other _words, 100 samples at each exposure level were used to determine

the average dot spread durve. This dot spread curve was then used to

generate the spread function curve which had to be curve-fit to the

model. This was _very tedious and time consuming work, although it is

necessary to make _many measurements, this _may be the _only technique avail

able for

determining

the spread function of vesicular film. As discussed

by

Rabedeau mi crodensi_tometry of vesicular film is _very difficult if not

38

Figure 6 shows the measured spread function as the average and

two standard deviations of the ten replicates. Figure 8 shows the mod

ulation transfer curves _{corresponding} to the calculated spread curves.

(

Figure ₇ shows the average of the calculated spread function curve

)

This modulation transfer curve could not be compared to the man

ufacturer's date because the manufacturers do not publish modulation

transfer curves. Table 1 is a tabulation of the constants obtained from

the sum of the least squared fit program used to fit the spread function

curves. The variance in this technqiue as applied to vesicular film is

quite large. It is believed that the majority of this variance is due

to the _{non-uniformity} of the vesicular film. The "Ant i-Newton 's Ring"

powder was an attempt to eliminate the noise created

by

Newton's rings

which formed in the vacuum frame. The problem that the "Ant i-Newton' s

Ring"

powder could cause is discussed in the

following

paragraphs.

Any

variance caused

by

the dust spots formed

during

the contact _printing

could be eliminated _using a"clean air station"

when the exposures were

made.

(The

author did not have one available to use.)

There might be some question raised concerning the contact _printing

of a vesicular film onto another film. There may be some doubt as to

whether or not the vesicular image can be reproduced exactly, because of

its mechanism of image formation. The two sets of photographs below

represent the vesicular image

(left)

and the CRF image (right). Each

set represents a different exposure level on the vesicular film. At

each exposure level the size on both films correspond _very closely.

(The

CRF film is not a copy of the exact four

dots,

but of dots in the same

39

vesicular film are not _completely formed do the contact copies not re

produce the image exactly.

(Photos

not shown) At the low exposure levels

the dots are not at Dmax. The dots at higher exposure levels are at Dmax.

When the vesicular film is printed onto the

CRF,

the low exposure dots

will no longer be clear and for this reason the smaller dots cannotibe

used.

Exposure.

8X

Xidex SX Film CRF Fi 1m

Print 2. Photographs of the vesicular film at two exposure levels

imaged onto the CRF film.

(Magnification

approx.

400X)

The approximation to the spread function was Gaussian in nature.

This differs from Friesers equation for silver halide film. This fact

is not surprising when the type of _scattering in the two films are com

pared. The silver halide films scatter light due to the grain size and

inter-layer reflections. The vesicular film has essentially no grain

structure. The radiation sensitive salts are of a molecular level.

Therefore,

the spreading of radiation can only be caused

by

inter-layer

reflections. The radiation would either be absorbed or passed

directly

40

layer or passed out of the film. The radiation could again be ab

sorbed

by

the sensitized salts or reflected back to the base. The majority

of the radiation would be absorbed in the first few reflections. The dis

tribution of radiation

(i.e.

the spread

function)

appears to be

(but

cannot

be mathematically proven

by

the _author) a normal distribution

(i.e.

_Gaussian)

Experiment 2 and 3 were designed to determine the effects of _using

the "Anti-Newton' s Ring" powder and a stepped wedge.

Comparing

the results

of experiment 2

(Figure 5-8)

and the results of experiment 3

(Figure 9-12)

and those of experiment 4

(Figure

13-16),

it is observed that the spread

functions without _using the "Ant i-Newton's Ring" powder and the spread

function where the stepped wedge was not used are much narrower than the

spread function where the "Anti-Newton' s Ring" powder was used.

In experiment 4 the "Ant i-Newton' s Ring" powder was _used, but the exposure was varied

by

_using a constant

intensity

and _moving an opaque

object over the film while exposing. In the region where the exposure is

critical

(5

to 30 seconds) it was difficult to _correctly time the exposure.

Because of this

difficulty,

two replicates of the five which were made,

could not be used.

Therefore,

the spread function curves

(Figure

_10,11)

were determined using only three replicates. In addition reciprocity law

failure was observed at the longer exposures. The results of experiment 4

are not complete therefore, conclusions from this experiment could not be

drawn.

Examining

the measured spread functions with and without using the

"Ant i-Newton's

Ring"

powder, it is difficult to determine the exact cause

for the difference. It would appear that the "Ant i-Newton' s Ring" powder

41

explanations which could explain the differences in the results. The

first explanation deals with the space created between the _measuring

tint and the film. The space created is _{approximately} tenam. Although

this is a small

distance,

it will allow the light which is

defract-ed at the _measuring tint to form a larger image of the dot. The dot

sizes on the vesicular film and CRF film were compared. At a parti

cular exposure level the dot size of the vesicular film and CRF film

were equal on the average. At one exposure level the dot diameters

were not _exactly the same. The densities of the carbon wedge were

uniform across each step.

Therefore,

the variation had to be due to

either the difference in the distances between the tint and film

caused

by

the powder or due to the scatter of light

by

the powder.

In _comparing the dot size with the microscope, it was difficult to

determine if the exact dot was reproduced.

Therefore,

there was some

factor causing the measured spread function to be wider when the

"Anti-Newton's Ring"

powder was used. The second explanation concerns the

intensity

distribution of the light caused

by

the Newton's ring.

The Newton's _ring patterns are cosine in nature. The cosine

intensity

patterns, after going through the characteristic curve will not pro

duce a cosine

density

distribution. Newton's rings will cause

non-linearity

in the system. The noise _may not be averaged out

by

_taking

many repl icates.

In experiment

5,

the Recordak Thermal Print film 1953 was ex

amined. Again the "Ant i-Newton' s Ring" powder was used so it is diffi

cult to determine if the spread function which is measured is indeed

42

of _{the Recordak Thermal}

film has a narrower spread function than that

of the Xidex film

(Figure 6-18).

_{The Recordak Thermal}

Print film

should have a spread

function

_{narrower than the Xidex film in}

that the

resolution of the Recordak is twice the resolution of the Xidex

film.*

Although

the technique is not perfected it produced results which

would indicate it is _feasible.

In _summary, there are problems with the contact _printing that must

be overcome. The results indicate

feasibility,

but modifications are

required for the technique to be reliable.

Feasibility

has been _shown, but methods of _overcoming the

problems in contact _printing techniques should be investigated.

Investigation of different "Ant i-Newton' s ring"

powder

(i.e.

dif

ferent size particles) could be made. This would demonstrate the

effect of separation between layers has on the spread function.

The effect of the modulator should be examined. The dimensions

and _geometry of the UV _exposing source could be varied to see what

effect it might have on the spread function. These are some of

the more urgent problems that must be investigated in order to

perfect the halftone dot technique as applied to vesicular film.

Manufacture's data: Recordak Thermal Print

1953,

_resolving

43

CONCLUSION

A technique for

deriving

the spread function and modulation

transfer function of the vesicular film has been determined which

does not require the use of a microdensitometer.

Therefore,

the

problems associated with microdensi_tometry of vesicular films

are eliminated. This technique utlizes the fact that a dot image

will increase in size as the exposure increases and that this change

in dot size can be measured _{using many} small dots and a "macro"

densitometer. Modifications in the contact _printing technique must

APPENDIX I

44

Derivation

of the edge spread function,

Figure A1 Dot Spread Curve

r =

radius of the image which is equivalent to the measuring tint dot size

r1 =

radius of the dot at an exposure level of 1 0X E

1 o

E = _{exposure level which will reproduce the}

measuring tint dot

E- = _{exposure which is 10X E}

(time

_{of exposure is}

constant,

intensity

is increased

by

_10X)

The edge spread function can be derived from the dot spread

function. The initial exposure, E is the exposure needed to _exactly

reproduce the measuring tint dot.

Assuming

the exposure is varied

by

adjusting

intensity

and

keeping

exposure time constant the

intensity

will describe the exposure. The

intensity

I will produce a dot radius,

r with a particular

density

distribution in the _vicinity around the

edge. An intensity, I.

(

corresponding to EL which is 10X I will

produce a dot radius r. with the same

density

distribution at the edge

as that of r . This means that at a distance of

(r,

-r

)

from an _edge,

o ' o

the intensity will be one-tenth the

intensity

at the edge.

The edge spread function is shown in figure A-2. The _spreading of

[image:49.520.43.445.132.393.2]

45

in figure A-2, the spreading on either side can be considered. The

spreading of light on one side is symmetrical with the other.

In figure A-1

(the

dot spread curve) it was shown that at the

distance

(r1

-r

)

from an _edge, the

intensity

is 1/10 of I . This

represents the area under the opaque side of the edge where d goes

from zero to positive infinity.

Figure A2 Edge Spread Function

Using

these

ideas,

the edge spread function can be determined

from f igure A-1 .

d = _distance from _{the edge}

(edge

_{corresponds to} r

)

r = _distance

(r.

-r

)

Log

(

I ,/I

)

= _the logarithm of the

intensity

at some distance d

from an edge with respect to ' j/'

_<j0 >

the incident

intensity

(l_o0=2lQ)

I can now be considered to be 1/10 of I

Using

the equation of the

line and applying it to the straight line portion of figure

A-1,

the

edge spread function can be derived:

d =

rLog(2(ld/l_03

))

Log

(2(ld/l_00)) = _d/r

I ./I

= ₁₀ d -bo

d/r

where d is negative

and in general

l,/l ^

= ₁₀

d

46

Derivation

of the line spread function:

Lsp =d(e(x))

dx

where e(x) is the edge spread function.

10x/r

e(x) =

, where x is negative

d f

(x)

f

(x)

i / \ * i / \

using

^

p '

=

p

ln(p)

f'

(x)

d(e(x)

)

_

2.3

inx/r

cc j

=

^ 10 = LSF, where x is negative

dx 2r 3

and in general

LSF =

\^-

10_ld/rl

,

letting

x

= _d

2r

I ,/l is obtained from the spread function as follows

I 2r

3 s/r

10 ds , where d is negative

'!

s/r

ln(lO)

,

e ds

10d/r

and in general

d'

-, 2

Derivation of the Fourier transform of the Frieser approximation:

io-ld/rl

Frieser equation = _I ,/l

= =

-47

Using

the property of sum of two functions Fourier transforms to

the sum of the Fourier transform of each function.

g(x) +

f(x)

transforms to

G(f)

+

F(f)

setting

h(x)

=

x/r

x>0

h(x)

=0 x<0

H(f, =^e^3W/re^ixfdx

-U2)

f"e"((2-3/r)

+

2*if>xdx

2

Jo

'

v

1 -((2.3/r)-2n1xl

((2.3/r)

+ 2

if)

1

(2.3/r)

+ 2?fif

2.3/r

(2.3/r)2

+ (2frf)2 (2.3)2 + (2rrf)2

2-rfif

since e

I

' is an even function the

imaginary

part does not exist.

2.3/r

H(f) =

-(2.3)2

+

(2rrf)2

normalizing the function so that H(f) = _{1 when f} = ₀

1

H(f)

= .

1 +

(2flfr/2.3)

If r is in^m and f is in _cycles/mm, f must be multiplied

by

.001

It follows that:

M.

Mo

1 +

48

e

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e

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