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5-1-1981 The alH ftone effect in photographic enlargements Rick Crowsey

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Recommended Citation Crowsey, Rick, "The alH ftone effect in color photographic enlargements" (1981). Thesis. Rochester Institute of Technology. Accessed from

This Thesis is brought to you for free and open access by the Thesis/Dissertation Collections at RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. THE EFFECT IN COLOR PHOTOGRAPHIC ENLARGEMENTS

by

Rick Crowsey

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 of the Rochester Institute of Technology

Hay, 1981

Rick Crowsey Signature of the Author . Photo~iiphic Science and Irtstrumentation

C. N. Nelson Certified by -.····.········.······ . Thesis Adviser

Accepted by . Supervisor, Undergraduate Research THE HALFTONE EFFECT IN

COLOR PHOTOGRAPHIC ENLARGEMENTS

by

Rick Crowsey

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

Effect" In continuous-tone photography, a 'Halftone

sometimes occurs that alters the tone reproduction in a distinctive way. Highlight contrast is decreased and middletone densities are lowered. Published data show that

this effect occurs in -and- photography when the grain pattern of the is reproduced very sharply in the print . High-magnification enlargements are especially

susceptible. Does a corresponding effect occur in color photography? A search of the literature reveals no answer.

The research here described is to determine, by direct measurements of densities in sharp and blurred enlargements, the magnitude of the halftone effect in particular color enlargements from color negatives. The validity of the procedure and the adequacy for the was tested by using black-and-white enlargements that demonstrate the halftone effect. The magnitude of the halftone effect was measured for color prints produced at a magnification of

25X. Grainless prints for comparison were obtained by rotating the print material during the . The experimental results showed that the expected changes in density and contrast do not occur in the color materials

studied . ACKNOWLEDGMENTS

My thanks to all those who without their help this research would not have been possible, especially to C. N. Nelson, my

adviser always a gentleman and an encouraging scientist; to

Pat and Ray at Color Methods, who graciously allowed me to have free run of their company and smilingly endured; and to

the CIA for their financial support.

11 TABLE OF CONTENTS

List of Tables iv

List of Figures v

Introduction 1

Theory of the Halftone Effect 3

Experiments 13

Results and Conclusion 17

Notes 19

Bibliography 22

Appendices 24

m LIST OF TABLES

Table 1. Densities of the Wedge in a Process Control Sensitometer, Model 101 27

Table 2 . Exposure Information 29

IV LIST OF FIGURES

FIGURE 1 The Density Difference in Black-and-White 4 Enlargements Due to the Halftone Effect

FIGURE 2 A tone reproduction diagram showing the 7 large difference in curve shape and density which exists, theoretically, between two prints from the same negative, one print having the grain pattern of the negative sharply reproduced in the print as a two- tone image of black-and-white spots and the other print having the grain pattern sufficiently blurred so that a continuous- tone image is obtained.

FIGURE 3 An idealized example of the halftone effect. 10

FIGURE 4 The mean reflectance, Rm, of the resolved 12 pattern is usually greater than the reflec tance, Ru, which results from the mean exposure, Eu, of the unresolved pattern.

FIGURE 5 A of the target used in the 26

experimentation .

FIGURE 6 Sensitometer illumination measurement and 28

setup .

FIGURE 7 Top view of portrait setup. 31

FIGURE 8 Density - Log H showing halftone effect in 35 black-and-white, the change in contrast is 21 percent and the density drop is significant.

FIGURE 9 Density - Log H showing lack of halftone 36 effect in color materials used. , , , and neutral density plots did not show a halftone effect. The change in contrast and middletone density was statistically

ins ignificant .

v INTRODUCTION

For most photographic prints, the principles governing

continuous-tone printing apply- The print densities can be

predicted by means of tone reproduction analysis based on

normal sensitometric procedures. When the grain pattern

of the negative is produced sharply onto the paper, it will

begin to behave like a halftone-dot pattern. This is known

as the halftone effect. The halftone effect can be briefly

defined as follows: !'For a given printing exposure, the

average density produced in a continuous-tone print is

usually lower when the granular structure of the negative material is reproduced sharply in the print image than it is when the granular structur-e is not resolved or when it does 2 exist." not The present study was made to determine the magnitude of the halftone effect in color photographic

enlargements .

The halftone effect has been previously investigated in 3 black-and-white materials by Altman and Peden, and Clark 4 and Nelson. Clark and Nelson found that the halftone effect lowered the highlight contrast of grainy enlargements by 25 percent at a print density of 0.20. A change in middletone density because of the halftone effect was found to be significant, but the magnitude of this drop was

small. An extensive search of the literature reveals no estimate of the halftone effect with regard to color photographic enlargements.

This study entails research geared to determine the magnitude of the halftone effect in color photographic

enlargements . The same procedures used for color materials are also used for black-and-white photographic

enlargements . The purpose of the work in black-and-white is to achieve and insure an experimental line of action able to detect any halftone effect that may occur in color

photographic enlargements .

In black-and-white printing, a loss of contrast is sometimes attributed to stray when large (10X or more) prints are made. Stray light may be the culprit occasion ally; but if the enlargement is such that the grain is imaged sharply in the print, the halftone effect can be the cause for the apparent degradation. This study was initiated to determine if this same problem is encountered in color photographic enlargements. THEORY OF THE HALFTONE EFFECT

The halftone effect has been defined earlier. This

effect is most often encountered in enlarging because of the

increased size of the grain images, and its effect on the

tone reproduction of black-and-white enlargements has been

described by Clark and Nelson . When the grain pattern of

the negative is reproduced with unusual clarity in the print, as would be the case in some enlargements, the pattern will behave like a halftone-dot pattern to a degree which is dependent on the sharpness of the grain image produced on the print. Figure 1 shows the experimental halftone effect using black-and-white photographic

enlargements .

Tone reproduction curves may be used in continuous-tone systems to accurately predict the resulting density or tone reproduction in a finished print. A tone reproduction curve is a description of the macroreproduction characteristics of the photograph. The required densities are usually measured on the photograph with instrument having diameters greater than 0.5 mm and the are measured on corresponding large areas in the scene. The tone repro duction curve is an important factor in the analysis of fine Rotated

Fig. 1. The density difference in enlargements due to

the halftone effect. detail reproduction also. For example, if the gradient of a

certain portion of the curve is nearly zero, the fine detail

reproduced at densities lying on that portion of the curve

is likely to be invisible or of poor quality. Increasing or

decreasing the overall gradient of the tone-reproduction

curve normally produced a corresponding increase or decrease

in small area density differences in the fine detail of the 7 8 photograph. The halftone theory described by Ives is

based on the rule that the reflectance R of the print is

related to the transmittance T of the negative consistent

with the following formula:

R = 1 - Tn

where Tn - percent area occupied by the dots.

Therefore, if 40 percent of an area of a negative is clear,

then 60 percent of the corresponding area of the print will be black. The above formula fails to take into account that

"black" the dots of the halftone print do not have zero 9 reflectance. It has been suggested that this formula be

corrected. The corrected formula, presented in log form, is

shown below:

Dp = L0G| 1-Tn (1-r)

Where Dp is the reflection density of the print and r is the

"black" reflectance of the dots of the print. The print densities predicted by the halftone theory are

independent of changes in the gradient characteristics of

"black" the photographic paper if the densities to which the

"white" dots and the areas are printed remain constant. For

continuous-tone printing, the densities of the print are dependent on the gradient characteristics of the print material . The only way to achieve results that are

equal, in a comparison of continuous and halftone systems,

is to use print systems for which the reflectance vs exposure function is linear. Actual photographic papers are, however, extremely nonlinear. Figure 2 is a tone- reproduction diagram showing the large theoretical difference in curve shape and density between two prints made from the same negative. One print has the grain pattern of the negative sharply reproduced in the print as a two-tone image of black-and-white spots. The other print has the grain pattern sufficiently blurred so that a continuous-tone image is obtained. The tone-reproduction

12 curves in Figure 2 were derived from the negative density vs log exposure curve in the lower right quadrant and the two transfer functions shown in the lower left quadrant. The transfer function for the continuous-tone

exposure curve for printing is the density vs log the photographic paper that was used to make the print. The transfer function of the sharp-grain print was calculated by Oneg

0.5 1.0 Oprint

Fig. 2. A tone-reproduction diagram showing the large difference in curve shape and density which exists, theoritically, between two prints from the same negative, one print having the grain pattern of the

negative sharply reproduced in the print as a two-tone image of black

and white spots and the other print having the grain pattern sufficiently blurred so that a continuous-tone image is obtained. assuming the use of the same negative material and applying

the theory of halftone printing described by Ives, 14 15 n f> Murray, Yule, and Clapper and Yule. The

halftone effect occurs as a result of the different ways in

which the density is distributed in a halftone negative and

a continuous-tone negative. Suppose that two negatives are

available, each with a minimum density of zero and a maximum

of 2.0. of One the negatives is completely uniform, the

other has fine structure such that at any point it either

transmits 100 percent or 1 percent of the light incident on

it. Suppose also that a suitable broad area on each

negative transmits 50 percent of the light incident on it.

These two areas would be identical visually and each would

give a density reading of 0.30 on a standard densitometer.

In the continuous-tone negative the absorption would take

place equally throughout the region. The fine structure

negative would pass about 50 percent of the light in a large

area.

Suppose now that a positive print is made from each of

these negatives onto a material with an idealized straight-

line characteristic curve which yields a density equal to the log exposure. If the exposure is so adjusted that the maximum density of 2.0 in the negative gives a density which is just perceptible in the positive, then the print from the density region of 0.30 in the continuous-tone negative would have a density of 1.70. For the negative with the fine

structure, half of the area on the positive would yield a

density of zero, and the remainder a density of 2.00. These

would combine to give a total transmittance of about 50

or percent, a density of 0.3 . This example is shown

graphically in Figure 3.

In figure 4 a different way of considering the halftone

effect is shown. Consider again the case of a grainy pattern

which is opaque over 50 percent of its area. This corres

ponds to a negative whose density above base is 0.30. If

this pattern is sharply imaged onto a photographic paper,

the characteristic curve of the paper would idealy be that

of the straight line in Figure 4. When the print is made,

the exposure E-. received by an element of area of the

positive stock under a grain is fairly low. Likewise, the

exposure E2 received under a clear area is high. On

processing, these areas produce the reflectance R-, and

R9 respectively, according to the characteristic curve.

The measured reflectance of a finite area of the sample will

be the average Rm of R, and R^ .

If, on the other hand, the same exposure is given under

conditons such that the granular structure is not resolved,

the curved line in figure 4 best repesents the

characteristic curve of the paper. Now instead of producing

Rm from the average exposure, the result will be Ru. As we 10

HALFTONE CONTINUOUS TONE

D = 2.0 NEGATIVES T=0.01

V

Logh a, ^a. .30

IDEALIZED PAPER D-LOG H

1.0

Dpos

2.0

D= 2.0 POSITIVES

-D = 0

D = 0.30

Fig. 3. An idealized example of the halftone effect. 11

can see, the difference in curve shape between the sharp and unsharp case in figure 4 has the most dramatic effect in the middle portion of the curve, and very little effect at the high and low ends. In terms of density, the density in the nongranular case will be higher than it is when the granular pattern is resolved. It is apparent from Figure 4 that the difference between Rm and Ru depends on the difference

1 ft between the two levels of exposure E-, and E2 In other words, the greater the difference between the minimum and maximum exposures in the grainy image, the lower will be the overall level of density of the developed print. This means that improving the imagery of the individual grains contributes to the halftone effect as well as to the improved transfer of information from the negative. 12

R1

\ \ POSITIVE PAPER CHARACTERISTIC

REFLECTANCE(%)

V-ajJ ^k \ V R vs E for the Blurred Case

= Rmean (R1 + R2)/2 a- _4r

X RvsE for the Sharp Case

Ru

R2 ^^"**>*,.^^

El Eu = (E1 + E2V2

Fig. 4. The mean reflectance, Rm, of the resolved pattern

is usually greater than the reflectance, Ru, which results from the mean exposure, Eu, of the unresolved pattern. 13

EXPERIMENTS

The hypothesis that was tested is, "Does the halftone

effect occur in color enlargements as in black-and-white

enlargements?" . The progress of the experimental work can

be partitioned into four, somewhat consecutive, tasks:

(1) obtain suitable black-and-white and color negatives,

"blurring" (2) construction of a easel, (3) producing

suitable black-and-white and color prints from the negatives

and, (4) analysis. The method that was adopted to determine

the magnitude of the halftone effect on print density in projection printing was to make two enlargements from the

same negative, one with the grain pattern of the negative

sharply focused and one with the grain pattern blurred by a rotating easel at the paper plane of the projection printer.

The densities of the two prints were then measured with a reflection densitometer which read an area large enough to include many grains. Using these densities to construct tone reproduction curves for each print, the halftone effect would then become immediately obvious by comparing the two tone reproduction curves.

KODhAK TRI-X Pan Film and KODACOLOR 400 Film were chosen to be used because of the grain structure in each. It was 14

hoped that by working with films that had a coarse grain

the structure, halftone effect would be easier to see if it

is present.

The target chosen was a combination of gray and color

scales and a suitable model. Since, in black-and-white, the

halftone effect is most apparent in enlargements, simulaton

of actual use of film would reveal information pertinent to

consumers of the film as well as being scientifically perti

nent. The target consisted of the following items: (1)

card, (2) grey scales and, (3) color patches. A fourth year-

professional photography student at Rochester Institute of

Technology was hired to photograph a model and the target as

a portrait. The films were kept at 30F except for warm-

up and exposure until 24 hours before processing. The

appendix contains detailed information on sensitometric

exposures, processing, the target, and the recording of the

scene .

Initially a vibration sander, masonite, and hardware were obtained in the hopes of constructing an easel which would blur any one point on the easel into a circle of about

1-3 mm in diameter. This device was discarded as a blurring easel when, upon activation, it persisted in vibrating across the workbench toward the floor. A phonographic turntable

was then obtained and proved to be delightful to work with and capable of blurring the grainular pattern of the negative suitably- 15

A Chromega D Dichroic II enlarger with a 25 mm f/1.9

Kodak II lens was used to produce the black-and-white

and color prints at a magnification of 25X. This is

"normal" approximately three times the magnification used in

printing, and will display the halftone effect if any is

present. Enough of the two papers, Kodak Polycontrast rapid

II RC type F paper, and Kodak Ektacolor 74 RC paper, type F,

was obtained to complete the project using the same

emulsion, so that no variability would be introduced via

different paper emulsions. The black-and-white prints were

processed with a Kodak Ektamatic processor using Kodak

Ektamatic A10 activator and Kodak Ektamatic S30 stabilizer

chemistry. The color prints were processed using a Colenta

processor and Kodak Ektamatic II chemistry. Control strips

were run before and after processing to insure that the

processed prints were in control. Data was collected from

the processed prints using a MacBeth TR-524 densitometer.

All the prints were replicated six times. Six runs of

"good" each print required the production of 128 prints. To have replicated more than six times would have meant that I would still be in the dark making prints, and to have done fewer than six would have yielded a poor estimate of v

and a . The sample standard deviation, sample mean, and 95 percent conficence limits around the mean were calculated and plotted in the form of a tone reproduction curve. The formula used and sample calculation can be found 16 in the appendix. A significant middletone density

(middletone density range is D = 0.40 to D = 1.5) difference was indicated by at least three of the four density levels in the middletone density range being statistically different (i.e., the confidence limits on the sharp and unsharp prints could not overlap) . The merit function for a

"contrast" difference in between the sharp and unsharp images was chosen as follows: If the contrast between the sharp and unsharp tone reproduction curves differed by more than 20 percent, they were considered statistically

"contrast" different. A 20 percent difference in was the minimum experimental difference which was statistically significant. The contrast was calculated as the slope of the straight line between the valves corresponding to relative log exposure equal to 0.70 and 1.60. 17

RESULTS AND CONCLUSIONS

Using the materials and experimental methods outlined,

it was determined that the halftone effect is not noticeably

present in color photographic enlargements. Appendix C

shows the results, in summary, in the form of comparison

tone reproduction curves. The black-and-white setup dis

played the halftone effect, confirmed the integrity of the

experimental setup, and agreed well with previous work. The

color photographic enlargements failed to manifest a

signficant difference in contrast or middletone density- A

slight drop of the curve for the sharp color images in the

middletone density was noticed, but by the criteria chosen,

difference" a verdict of "no was handed down.

Two possible reasons can be given for the failure of

the halftone effect to appear in color photographic

enlargements. First, in the color negative film, the

"image" is composed of three layers of clouds rather

than grains. The black-and-white negative is

"clear" composed of discrete silver grains suspended in a

gelatin. The discrete nature of the black-and-white

emulsion lends itself readily to becoming a psuedo-halftone dot pattern upon sufficient magnification, producing 18

"black" "white" discrete grains in a surround. The color

emulsion, on the other hand, appears as a conglomeration of

three color dye clouds somewhat overlapping. Even under

high "discrete" "clear" magnifications, no grains in a

surround are apparent. For the halftone effect to occur,

"dots" "clear" there must be discrete in a surround.

Second, the greater the difference between the minimum and

maximum exposures in the grainy image, the lower will be the 21 overall level of density of the developed print. With

the color emulsion, the differences between the minimum and

maximum exposures in the grainy image are smaller than the

differences when using the black-and-white emulsion.

The halftone effect in color photographic enlargements

is small enough to be neglected and is statistically not

significant. The halftone effect was demonstrated using black-and-white photographic enlargements to insure the validity of the experimental setup, and the results obtained 22 agreed well with previous work. The major causes for the nonappearance of the halftone effect are thought to be the nondiscrete nature of the color emulsion and the smaller

clouds" differences in exposure between the "dye and the

"clear" surround. 19

NOTES 20

NOTES

1. L. D. Clark and C. N. Nelson, Photographic Science and Engineering, Volume 6, Number 2, p. 84, 1962.

2. J. H. Altman and R. M. Peden, Photographic Science and Engineering", Volume 6, Number 3, p. 130, 1962.

3. Ibid.

4. Clark.

5. Clark.

6. Clark.

7. The Theory of the Photographic Process, Fourth Edition, ed. T. H. James, p. 536-561, 197 7 .

8. H. E. Ives, Journal of the Optical Society of America, 13:537 (1926)

9. Clark.

10. Ives.

11. Clark.

12. L. A. Jones, The Photographic Journal, 89B:126 (1949)

13 . Ives .

14. A. Journal of the Franklin Institute, Murray,(19363- 221:721

15. J. A. C. Yule, Journal of the Franklin Institute, 236:473 (1943).

16. E. R. Clapper and J.A.C. Yule, Journal of the Optical Society of America, 43:600 (1953).

17. Principles of Color Photography, R. M. Evans, W. T. Hanson, Jr., and W. Lyle Brewer, Wiley St Sons, 1953, p. 224-225. 21

18. Altman.

19. Clark.

20- An "Statistics, Introduction", A. D. Rickmers and H. A. Todd, McGraw-Hill, NY, p. 96-98, (1967).

21. Altman

22 . Altman. BIBLIOGRAPHY 23

BIBLIOGRAPHY

J. H. Altman, and Peden, R. M. Photographic Science and Vo 6 May- Engineering , lume , Number 37 June 1962, p. 130-134?

Clapper, F. R. and Yule, J. A. C., Journal of the Optical Society of America, Volume 43, p. 600 (1933)

L. D. and C. N. Clark, Nelson, , Photographic Science and Volume Number 2 Engineering, 6, , March-April 1962, p. 84-91.

R. M. W. T. and Evans, , Hanson, , Jr., Brewes, L. W., Principals of Color Photography, John Wiley and Sons, New York, 1953,

H. R. Journal of the Optical of Ives, , Society America Volume 13, p. 537, 1926.

James, T. H. (ed.),The Theory of the Photographic Process,

Fourth Macmillian Co. Inc . New Edition, Publishing , , York, 1977, p. 536-562, Chapter 17 "Tone and Color Reproduction" I. Tone Reproduction - C. N. Nelson

Jones L. A., The Photographic Journal, Section B, Volume 89B, 1949, p. 126.

Murray, A., Journal of the Franklin Institute, Volume 221 p. 721 (1936).

D. and H. W. An Rickmars, A. Todd, , Statistics, Introduction, McGraw-Hill Book Company, New York, 1967 p. 96-98.

Yule, J. A. L., Journal of the Franklin Institute, Volume 236, p. 473 (1943). 24

APPENDICES 25

APPENDIX A 26

APPENDIX A

+ 3

I

in the Fig. 5. A photograph of the target used

experimentation.

with a model for the The above is the target used upper right quadrent is an 18 photographic print. The lower half is a large gray scale, percent gray card. The the left quadrant is a small and the uppermost half of top a of the left quadrant is scale. The lower half top gray qualitative color scale. 27

TABLE 1

Densities of the Wedge in the KODAK Process Control Sensitometer, Model 101

Step Density

1 3.13 2 2.98 3 2.83 4 2.64 5 2.54 6 2.40 7 2.26 8 2.11 9 1.95 10 1.80 11 1.66 12 1.52 13 1.37 14 1.21 15 - 1.05 16 0.91 17 0.76 18 0.61 19 0.44 20 0.29 21 0.12

Black-and-white and color films and papers were

"customer" processed at color methods as normal film. Kodak control strips were run with all processing. The lab has a good history of quality control. All processes which were

control" used had been "in for 30 business days prior to my use and for at least 10 days after my use.

The equipment used was as follows: Kreonite color processor, Kodak Ektamatic processor, and the Colenta tube processor. All processors were being run by manufacturers suggested procedures. 28

Sensitometric exposures were recorded on each of the films using a KODAK Process Control Sensitometer, Model 101, Serial No. 101-881, RIT No. 58732, lamphouse setting -.5, lamp Serial No. 207, calibration current 0.780 A. Below is: (1) A diagram of the setup used to determine the flux incident at the film plane, (2) a list of the filters used, (3) and a table of the densities of the sensitometer step wedge, KODAK Serial No. 101-882, RIT No. 58732.

DETECTOR z 101 SENSITOMETER ?

FILTER HOLDER

*. n 2 5116 Inches

Fig. 6. Sensitometer illumentation measurement setup.

Configuration Flux

103 No filter 1.70 x 80B + 80D 341.00 lux 80B + 80D + 1.50ND 14.12 lux 7.53 lux 2 . 40ND 29

TABLE 2

Camera Exposure Informat ion

Stops from B&W Color Shutter "Normal" f/Stop Speed (seconds) Speed (seconds)

11-16 +5.0 1.00 2 .00

11 +4.5 .50 1 .00

11-16 +4.0 .50 1 .00

11 +3.5 .25 .50

11-16 +3.0 .25 .50

11 +2.5 .125 .25

11-16 +2.0 .125 .25

11 +1.5 .067 .125

11-16 +1.0 .067 .125

11 +0.5 .033 .067 "normal" 11-16 .033 .067

11 -0.5 .0167 .033

11-16 -1.0 .0167 .033

11 -1.5 .008 .0167

11-16 -2.0 .008 .0167

11 -2.5 .004 .008

11-16 -3.0 .004 .008

11 -3.5 .002 .004

11-16 -4.0 .002 .004

11 -4.5 .001 .002

11-16 -5.0 .001 .002

"Normal" exposure was determined by the as

- he would in any portrait job. f/11 f/ll-16 gave enough so that all the scene would be in focus.

Only the shutter (focal plane) speed was changed to change exposure so that no variability would be introduced because

of different sizes. 30

APPENDIX B 31

APPENDIX B

The following items can be found in Appendix B:

(1) camera/scene exposure information and, (2) statistics used in analysis.

Camera equipment used to photograph scene:

Nikon FE 135 mm Nikon f/2.8 background 2 scoop 1 plat light 1 light with an umbrella 1 hairlight

BACKGROUND

HAIRLITE

PERSON

TARGET

PLAT

LIGHT WITH UMBRELLA SCOOPS

? CAMERA

Fig. 7. Top view of the portrait setup. 32

The sample mean (x) and the sample standard deviation

"canned" (s) were calculated using programs available to

TI-58/59 owners . The formula used for each program is as

follows :

Sample Mean _ x = E x.

N

Sample Standard Deviation

I x - 0 s = N

N - 1

Where N is the number of samples taken and x . is the

data point.

The confidence limits around the mean point, plotted in

the comparison tone-reproduction curves, were calculated with the following formula:

x " < V < x + V 2 J* V f (/)

v A-2 of Where t , was found in Table , Critical Values

Students Distribution, in Statistics, An Introduction by

Rickmers and Todd. v is (N-l) and a was chosen as 0.05 to allow 95 percent confidence in our limits. 33

Sample Calculation

Sample Density

1 1.56 2 1.54 3 1.52 4 1.53 5 1.56 6 1.54

T. x,

1 - x = N = 6 N

1.54

2 -i 1/2 E x (2 = X..) S = 0.16 N

N

t5, 0.025 = 3.1634

x - t5, 0.025 < y < x + t5, 0.025 V1 V1

1.52 < y < 1.56 34

APPENDIX C 35

1.9 BLACK AND WHITE

1.6

DENSITY vs LOG H

1.3 m

)

1.0

0.70

SHARP

0.40

0.10 .^^.^AfftAiaflBaji^G^^^Qr

1 t

0.10 1.6

Relative Log H

I I 1 1 I I I 95 percent confidence lines data points

Fig. 8. Density-Log H showing the halftone effect in black and white, the change in contrast is 21 percent and the density drop is significant. 36

COLOR

2.2

DENSITY vs LOG H

1.0

0.40

0.10 Il. 0.40 0.70 1.0 1.3 Relative Log H

data points 1 1 1 1 1 1 1 1 95 percent confidence lines

Fig. 9. Density-Log H showing the lack of the halftone effect in the color material used. Red, green, blue and neutral density plots did not show a halftone effect. The change in contrast and middletone density was statistically insignificant.