A11107 3TD101

NBSIR 84-2924(£)

Color Calibrator for RRWDS

Radar Remote Weather Display

System

Jim L. Heldenbrand

Louis G. Porter

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Physics Division

Gaithersburg, MD 20899

September 1984

Prepared For: Federal Avaiation Administration

U.S. Department of Transportation

Washington, DC 20591

NATIONAL BUREAU OF STANDARDS

LIBRARY CJ roNBSIR 84-2924

COLOR CALIBRATOR FOR RRWDS

RADAR REMOTE WEATHER DISPLAY

SYSTEM /i?

C.

^

Jim L. Heldenbrand

Louis G. Porter

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Physics Division

Gaithersburg, MD 20899

September 1984

Prepared For: Federal Avaiation Administration

U.S. Department of Transportation

Washington, DC 20591

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TABLE OF CONTENTS

Page

1. Objectives and Technical Approach 1

2 . Color Calibrator Design 1 2.1 Components 1 2.2 Recommended Selection Criteria 2 2.3 Evaluation 4

2.3.1 Test Color Display 4

2.3.2 Test Instrumentation 4

3. Demonstration of Feasibility 5 3.1 Color Calibrator Performance 5 3.2 Recommended Photodiode/Filter Combination 5 3.3 Measured Color Calibrator Data 6

3.4 Determining Need for Fresnel Lens and Light Tubes 7

4. Results of RRWDS Performance Evaluation 8

4.1 Color Calibrator As Diagnostic Tool 8

4.2 Observed RRWD System CRT Characteristics 8

4.2.1 Background 9

4.2.2 Bright-dark Contrast 10

4.2.3 Quasi-hysteresis Effect 10

4.2.4 System Drift 11

4.2.5 Effect of Digital Level Changes 11

4.2.6 Measurement Effects Due to Power Supply Degradation .... 11

4.3 Color Splotches 12

4.4 System Limitations on Objectives 12

5. Recommendations 12

5.1 Design of the Color Calibrator as a Colorimeter 12

5.2 Use of Color Calibrator 13

5.2.1 Development of Field Calibration Procedures 13

5.2.2 Chromaticity Drift 13

5.2.3 Color Calibration Tolerance 14

5.3 Design of RRWDS 14

5.3.1 Operation of RRWDS to Maintain Calibration 14

5.3.2 Visual Detectibility 14

5.3.3 Possible Revision of Objective 15

5.3.4 Recommended Inclusion of Luminance in WIL Color

Specifications 15

5.4 Need for Field or Laboratory Analog Testing 15

6. Conclusions 16

iii
TABLE OF CONTENTS (Continued)

Page

APPENDIX A

Introduction A-l

Laboratory Evaluation Objectives A-l

Preliminary of RRWDS CRT Measurements A-l

RRWDS Color Calibration Test Mode A-2

Color Calibrator Linearity Test A-3

Observations of Systems Effects A5

Single Color Test A8

WIL Color Test A-10

Selection of Photodiode/Filter Combination A-13

Possible Troubleshooting Application A-14

Conclusions A-14

Recommendations A-14

iv
LIST OF TABLES

Table 1. Photodiode/Color Filter Combinations

Page

3

LIST OF FIGURES

Page

Figure 1.

Figures 2A-C.

Figures 2D-I.

Figures 3A-C.

Figures 3D-I.

Figures 4A-C.

Figures 4D-I.

Figures 5A-C.

Figures 5D-I.

Figure 6.

Test of color calibrator linearity by agreement with

the Inverse-square Law of Radiation

Silicone photodiodes with narrow band Wratten filters ..

Silicone photodiodes with narrow band Wratten filters . .

Silicone photodiodes with medium band Wratten filters .

.

Silicone Photodiodes with medium band Wratten filters .

.

Silicone photodiodes with wide band Wratten filters . . .

.

Silicone photodiodes with wide band Wratten filters ....

GaAsP photodiodes with dichroic filters

GaAsP photodiodes with dichroic filters

Schematic circuit diagram for engineering model color

calibrator

A-15

A-17-A-19

A-21-A-26

A-28-A-30

A-32-A-37

A-39-A-41

A-43-A-49

A-51-A-53

A-55-A-60

A-61

v
FOREWORD

This report covers the status of work by the National Bureau of Standards (NBS) on the Radar Remote Weather Display System (RRWDS) Color Calibrator. The NBS

work was supported by the Federal Aviation Administration (FAA) under Modification No. 0001 of FAA/NBS Interagency Agreement No. DTFA01-83-Y-20592

.

ACKNOWLEDGMENTS

The authors wish to acknowledge with thanks the technical advice and consultation

provided by Drs. Gerald Howett and James Worthey of NBS, the RRWDS maintenance

support provided by Mr. Nick Donato of Electrodynamics, and the active encouragement and support provided by the FAA government technical representative

Mr. Armand Maillet.

DISCLAIMER

Certain commercial equipment, instruments, or materials are identified in this

report to specify the experimental procedure. Such identification does not

imply recommendation or endorsement by the National Bureau of Standards nor

does it imply that the materials or equipment identified are necessarily the

best available for the purpose.

vi
ACRONYMS AND ABBREVIATIONS USED IN THIS REPORT

B CRT brightness control

BITE Built-in test equipment

C CRT contrast control

CCA Circuit card assemblies

CRT Cathode Ray Tube

EPROM Erasable and programmable read only memory

FAA Federal Aviation Administration

GaAsP Gallium, Arsenide, Phosphide (a type of photodiode)

NBS National Bureau of Standards

nit A unit of luminance equal to one candela per square meter

NWS National Weather Service

RAM Random addressable memory

RGB Red, Green, Blue (designating the colors of the three phosphors and the

three electron light guns used in the CRT and the filters incapsulated

in the three photodiodes used in the color calibrator

RRWDS Radar Remote Weather Display System

S/N Serial number

TBD To be determined

TDL Test digital level (refer to footnote 3, page 4 for details)

WIL Weather intensity level

vii

1. OBJECTIVES AND TECHNICAL APPROACH

The Federal Aviation Administration (FAA) uses a color Radar Remote Weather

Display System (RRWDS) to display regional weather patterns of importance to

various flight operations. The display presents six levels of weather intensity,

using combinations of three colors and two lightness levels.

To determine the accuracy of the color combinations representing the different

weather intensity levels (WIL) for an individual display, the FAA commissioned

the National Bureau of Standards (NBS) to design, fabricate, and evaluate an engineering development model of a low cost, portable color calibrator for

field use.

The objectives of this project were:

1) To design, fabricate, and evaluate an engineering development model of

a low cost (about $100 in quantity) color calibrator capable of objectively determining whether the chromaticities and luminances of six

colors, (i.e., light and dark green, light and dark yellow, and light

and dark red) are within specified limits. These six colors are used

to display areas of increasing weather intensity levels, respectively,

on the Radar Remote Weather Display System cathode ray tube display

(CRT).

2) To prepare a draft specification for use by FAA in procuring production

prototype model color calibrators for field evaluation.

The basic tasks were to: (1) select the major components and combinations

thereof (e.g., photocells, color filters, and electronic circuitry) for a simple,

reliable and inexpensive color calibrator; and (2) evaluate these combinations

under laboratory conditions in order to recommend a practical model to the FAA

for field evaluation.

The results from the design, fabrication, and evaluation of the color calibrator

model are reported in the following sections. In addition, some results relevant

to the operation and calibration of the RRWDS are also presented. Evaluation

of the color calibrator revealed some unexpected luminance and chromaticity

changes on the RRWDS as well as some other system-related problems which should

be considered in developing any set of field-calibration procedures and calibrator

procurement specifications.

2. COLOR CALIBRATOR DESIGN

2.1 COMPONENTS

The color calibrator model consists of four parts: a sensory head, quick

disconnect cable, power supply, and a digital voltmeter. The color calibrator

sensing head itself consists of three photocells, each having a red, green, or blue (RGB) encapsulated filter corresponding to the RGB phosphor colors of the

cathode ray tube (CRT) of the RRWDS. Tests were made on selected combinations

of photodiodes and light filters to select optimum combinations for the color

1
calibrator. The photodiode types included GaAsP and silicon; the filter types

included Wratten narrow-band, medium-band and wide-band; and dichroic.

Table 1 gives a detailed description of the combinations that were procured. A

schematic circuit diagram is shown in figure 6.

The amount of light impinging on each photodiode is a function of the viewing

distance, the radiance of the light source, and the transmittance of the filter.

Each filtered photodiode predominantly responds to the light energy being emitted

by its corresponding phosphor. Thus, the color calibrator measures the relative

irradiance contribution U of each phosphor to the WIL colors rather than

measuring the chromaticity of each WIL. U

2.2 RECOMMENDED SELECTION CRITERIA

Five criteria were used to evaluate the relative merits of the different types

of photodiodes or photodiode/color filter combinations used in the color

calibrator

.

The photodiode selection criteria were:

1 . Extended response out to UV to achieve a fairly strong color calibrator

response for the blue phosphor.

2. Cut-off in red region at about 750 to 800 nm to eliminate response from

infrared radiation.

The criteria for evaluating the photodiode/light filter combinations were:

3. A different numerical response by each of the three filtered photodiodes

to provide suitable discrimination among the various RGB and WIL colors.

U When the viewing distance and geometry are specified, the resulting

measurement is in terms of relative irradiance or simply radiant flux. With

appropriate calibration which involves the V( A) weighting function, the color

calibrators could be made to measure luminance. The spot photometer and

spectroradiometer both take V(A) into account, and hence, were used to

make illuminance measurements in candelas per square meter (c/m^) or nits.

Since the present color calibrator model is not so calibrated, the color

calibrator simply reflects the relative radiances of each phosphor.

U Further refinement and development of the current approach has the potential

for resulting in a true CRT colorimeter; i.e., a device whose output would be

the CIE chromaticity coordinates for a particular set of phosphors.

2
Table

1.

Photodiode/Color

Filter

Combinations

uG

•u

3* rH O *H X P-< e

tH

X ^ g

3m

4-J

G

X 3m 00 4H

tH c X M 0 G g a 6 • G o

•u 2 oXo

C/3

OCo

X)g

03 XSO

3-i ^ G

03 03 G 4J

4-J

X 03

0) 3m Pi &

eg

CM

=tt= <

r^

X

00

vOX

<3O

oo

cj

CJ

COCO I 3m CO

<D CO >% 03

03 rH

rH OO

X3G

03 X5O

3-i 3-j 03G

G

<1)

G 4-> CD 4-> g oj

3-1 3-i O &

X3C

03 XJ£o

3-*

3-i 03C

CDG 03

J-i

XJG

03 X03

tH03

G

CD CD S 4J

4-J

X 03

CD 3-i Pi &

XJc

03 XB3

tHXI

CDBG 4-* CD 4-J CD 03

Vh 3m O ^ XCGXBG

•HX

CD

G S g

4J

0) -u G G

rH

U

X ^ XcGXO

G

3-4 CD X 4-) 4J X G

CL) *h C* ^ XGGXOuX c

CD

C 4-) CD 4-J CD G

3-i 3-i O £2

XGGXXGO

3-4 X

CDG

»H 00 G G O -H

tH 4-1

4-1

G

a o O CJ &o

4-J G

3-i OXGX l

<1-1I G

3-<

X ^ • B CD X CD C O

*-H

OX

H /N

G o • s MH X

X o v-/ 3-4 r- G G G

CO o G 4-J 6

CO

C

G

4-> o o G tH rH

O 0 4-J CO X G /"~N o X B 5 • c 4-1 G V-/ V-/ G G o X ) O 4-1 X G G o O o Uh CO

00 o — c 4m

CN | tH CD

O

X /'“S 4-J 00

CO s r

G

a CD <3 \-4 v_/ O G OO G U 3-4 c O G

CM

G 3m o O

•H tH CD in CO C0

CO

C

X tH o

4-J 0 Cl

tH CO CD

r-4

•—4

CM 5 c <D G |m G 3-i X 4-J rH O G • tH G 3-i X • X 4-J G g CO u 4-J X z G 0) G o 1 X a C

X tH

X CD

X c X X a H

X

G c 0) CO

G

®

GX

G z a

GG

G

X 1 >*

H

a

X

X S X 4-1 00G o 3 X

u * 3-4 o 0) c 4-J G o 3-< 3-4 00 o 4-J G X 3-i a G u u G •H O X g 3-1 *H c a G •*-4 X 0) X O G G O tM c o G G u H C C 3-. c o 3-4 CD UH in X X G 3-4 CD X rH U-i X X CJ a) u G U rH CO X o

a) *h 3-4 *H rH «H ) X rHH

XX

O

X

X

X o 1 r4

G

rH 34 o rM AM « X o G £ CG CJ O

a» f-HXX o > a. H H z o rH CM ^ »—4

rH 1 CM| ^ I X

CD

3-i GGG

CD

3-j T-1 G

O*

<D 3
4 . Capable of detecting differential light level changes equal to or less

than one test digital level (TDL) increment or decrement of a light

gun.

5. Off-the-shelf component availability.

2.3 EVALUATION

2.3.1 Test Color Display

The color displays were generated by three RGB guns on an FAA Radar Remote

Weather Display System (RRWDS) manufactured by Electrodynamics and composed of

Weather Processor Type FA9901/6, S/N 0101, Weather Display Type FA9901/7, S/N

0071, interconnecting cabling (shortened to ten foot lengths),—' and special

EPROM circuit boards. After installation at NBS, the RRWDS system was calibrated

by a representative of Electrodynamics.

2.3.2 Test Instrumentation

The principal instruments used in taking measurements of the chromaticity and

luminance of the RRWDS and the color calibrator included:

o Chromaticity Measurements —Photo Research Model PR-703A Spot

Spectroscan Rapid Scanning Spectroradiometer , S/N 1022.

o Luminance Measurements —Pritchard Model 1980 OP PL Photometer, S/N 214

(as well as the above radiometer).

o Color Calibrator Linearity Measurement —Spindler and Hoyer Optical Bench,

o Voltage Measurements

1. Data Precision Model 2480R Digital Voltmeter, S/N 7499.

2. Tektronix Oscilloscope Model TM506, Option 2, S/N B011387.

1/ See appendix A section entitled, RRWDS Color Calibrator Test Mode, for a description of the test digital change capability for altering the DC signals

from the Weather Processor to the volatile memory in the Weather Display,

afforded by the addition of special erasable and programmable read only

memory (EPROM) boards.

bJ Replacement of the typical 100 ft coax cables interconnecting the RRWDS

processor and display units with 10 ft cables greatly improved the high

frequency video signal-to-noise ratio experienced when operating the system

in the NBS laboratory environment.

4
3. RESULTS OF COLOR CALIBRATOR EVALUATION

The results obtained to date point to the following preliminary conclusions:

3.1 DEMONSTRATION OF FEASIBILITY

The technical feasibility of the color calibrator concept (using amplified

voltage outputs from three independent RGB-filtered photodiodes) was demonstrated

for single-step test digital changes. Feasibility remains to be demonstrated

for the complex analog changes expected in the field and for meeting the hardware

cost objectives.

The color calibrator was tested for linearity of output voltage by showing

agreement with the inverse square law of radiation. The results plotted in

figure 1, page A-15, show that the output characteristic of the color calibrator

is linear over the illuminance range of interest (2 to 20 fc). (This indicates

that the observed nonlinearities in measured data from the RRWDS CRT can be

attributed to the RRWDS, and not to the color calibrator).

3.2 RECOMMENDED PHOTODIODE /FILTER COMBINATION

A critical aspect of the NBS evaluation was a determination of photodiodes/

filters for the sensing head of the color calibrator. The combinations of

photodiode/filter under consideration for the color calibrator were:

(a) silicon vs GaAsP diodes,

(b) Wratten vs dichroic filters, and

(c) if Wratten, then whether narrow-, medium-, or wide-band color filters.

The basic recommended sensitivity criterion is that at least one of the

filtered RBG photodiode channels be capable of detecting differential light

level changes equal to or less than one TDL increment or decrement in one of

the guns, for each of six WILs. For example, WIL #1 is specified as R=06

,

B=02, and G=12. Based on this criterion, a unit TDL change (increment/decrement)

in the R gun shall be detectable by at least one of the R, B or G photodiodes,

preferably the R diode. A similar change in the G gun shall also be detectable

by at least one photodiode, preferably the G diode. An exception to this

criterion will occur any time any one of the RBG guns is decremented from TDL

#02 or less as in WIL #1 and WIL #2 (B=02 in WIL #1 and #2 and R=01 in WIL

#2) —and may occur when a gun is incremented from TDL #02 (or even from TDL

#03 in some cases). Unit increments /decrements from these low digital level

settings are not detectable by the color calibrator, the spectroradioraeter , or the human visual system.

Based upon the procedures used in determining the feasibility of the color

calibrator approach, two combinations have been demonstrated to be feasible.

They are the silicon diodes with narrow-band Wratten filters, and GaAsP diodes

with dichroic filters. The use of silicon diodes with wide-band Wratten filters

has been ruled out because they fail to meet the preferred criterion stated In

5
the previous paragraph. Specifically, the red channel responded strongly to

stimulation by any one of the three RGB phosphors, and there was little or no difference between the responses of the blue and green channels for various

levels of the green phosphor stimulation.

Time and resources available did not permit testing of other possible

combinations such as silicon diodes with dichroic filters or GaAsP diodes with

narrow-band Wratten filters. Other technical issues identified in this report

appear to have first priority.

The GaAsP diodes are produced overseas and the color filters can only be

incorporated into the diode housing by the diode manufacturer. For reasons of ease and timeliness of procurement, and probably the least cost, the silicon

diode/narrow-band Wratten filter combination is recommended.

The long term stability of the Wratten and dichroic filters is unknown. The

gelatin Wratten filters, which are especially degradable by UV exposure, are sandwiched between two pieces of BG - 18 Schott glass and encapsuled in the

photocells during manufacturing. This process increases their stability.

However, the color calibrator head (quick-disconnect) should be stored in the

dark when not in use.

3.3 MEASURED COLOR CALIBRATION DATA

To validate the feasiblity of the color calibrator concept, NBS employed six

special EPROMs (provided by the manufacturer) and an extra set of RGB memory

planes in the RRWDS. The EPROMs provided the means of addressing the WIL random

access read and write memory (RAM) locations from the display numeric entry

board. Memory Plane B (three RGB circuit card assemblies (CCA)) provided a means of storing information for later comparison with incoming information

(for example the WIL color wedges from a digitizer’s built-in test equipment

BITE) or with information stored in Memory Plane A. The EPROMs were used to

make all digital level changes in the 14.7 inch diameter solid color background

whereas the Memory Planes were used to make brightness and contrast checks of

the original WIL colors. The color changes were all made on the WIL background

(i.e., 14.7 in. diameter circle). This procedure eliminated the reflections or spillover present when there were adjacent color areas.

Spectroradiometric measurements of the chromaticities of the WILs provided by

the vertical bars from the processor's BITE and the wedges from the digitizer's

BITE indicated color reflections or spillover from adjacent areas. No effort was expended to determine if the color calibrator would yield similar results.

Measurements of filtered photodiode output voltages were made for each of the

three RGB guns using the six special EPROMs. The luminance of each color phosphor

was incremented by unit test digital level (TDL) steps from 00 to 15 (16 steps)

and the color calibrator's response was plotted. Color calibrator response

changes were noted as a function of performance degradation changes in the

console's video amplifier board and high voltage block (Part No. 7030051), and

changing from power supply No. 1 to No. 2. The color calibrator responses were

plotted and the results for silicon photodiodes with narrow-band Wratten filters

6
are shown in figures 2A-C (pp. A-17 through A-19), medium-band filters in

figures 3A-C (pp. A-27 through A-30) and wide-band filters in figures 4A-C

(pp. A-38 through A-41). The results for GaAsP photodiodes with dichroic

filters are shown in figures 5A-C (pp. A-50 through A-53).

Measurements were also taken of unit digital level increments /decrements from

the TDL specified for each gun for each of the six WILs using the narrow-,

medium-, and wide-band filtered silicon diodes and the dichroic filtered GaAsP

diodes. The color calibrator responses were plotted and the results are shown

respectively in figures 2D-I (pp. A-20 through A-26), figures 3D-I (pp. A-31

through A-37), figures 4D-I (pp. A-42 through A-49) and figures 5D-I

(pp. A-54 through A-60). The results indicate that:

a. The color calibrator can detect a unit test digital level change in

chromaticity (the smallest change available from the vendor's EPROM).

b. The color calibrator (and the rapid scanning spectroradiometer) cannot

detect the absence of TDL 02 blue in WIL #1 or #2, nor TDL 01 red in

WIL #2.

Item b. appears to have no practical impact on the project, since NBS observers

also cannot visually detect any change in color under similar circumstances,

except when dark adapted in a very dark room. (NBS has previously reported on

the nonlinear (or zero) chromaticity changes experienced with the RRWDS system

at low test digital levels).

3.4 DETERMINING NEED FOR FRESNEL LENS AND LIGHT TUBES

A more stable voltage reading was obtained from the color calibrator if the

detector head was moved away from the CRT screen. However, at distances

approaching 6 feet the color calibrator no longer responded to the dark WILs

(i.e., #2, 4 and 6), unless a Fresnel lens and light tube (tunnel) were added.

A preliminary study was done to evaluate the effectiveness of various Fresnel

lenses in collecting more light and concentrating it on the photodiodes, thereby

increasing the response and stability of the color calibrator voltage. Locating

the color calibrator head in front of or behind the focal length of the Fresnel

lens improved both the magnitude of the readout voltage and measurement stability

However, the geometry has not yet been worked out for ensuring that each of the

three photodiodes in the head is equally illuminated.

Whether or not a Fresnel lens and light tube will be required accessories for

field use of the color calibrator depends on the method to be used in the field

for generating the display colors. The following table identifies both preliminary recommendations and need for further work:

7
Method of Displaying

Test Colors (assumes

dark room) Tube

Need For:

Fresnel Lens

Weather Processor BITE—bars

(near distance only)

Yes TBD

(To be determined)

Digitizer BITE—wedges (near

or mid-distances only)

Yes TBD

EPROMS—solid color

o Near distance No No

o Three feet TBD TBD

o Six feet Yes Yes

If a Fresnel lens is to be used, more work needs to be done to determine the

proper off-focus distance needed to assure uniform light over all three RGB

detectors. (Note that the data reported in appendix A was all measured without

the use of a Fresnel lens or light tube.)

4. RESULTS OF RRWDS PERFORMANCE EVALUATION

4.1 COLOR CALIBRATOR AS DIAGNOSTIC TOOL

During the course of the laboratory evaluation of the color calibrator, a number

of RRWDS equipment malfunctions were experienced. Examination of the color

calibrator data taken prior to the malfunctions generally revealed a pattern.

For example, when the tripler for Power Supply #1 failed, the data taken

preceding the failure yielded a pattern of rapidly increasing shift in the

chromaticities for each of the RGB channels. Switching from P.S. #1 to P.S. #2

resulted in a shift in the color calibrator output voltage readings approximately

equivalent to changing EPROM settings by two TDL levels, depending on the color

channel

.

Color calibrator data taken prior to failure of the high voltage (HV) junction

block revealed a somewhat different pattern. In this pattern the color calibrator output voltage reached a peak at around TDL = 1012, and then declined out to

TDL = 15. Replacement of the HV junction block yielded a steadily increasing

function up to TDL = 15 (refer to figures 2A-C, pp. A-17 through A-19). These

findings suggest that the color calibrator might be a useful diagnostic tool

(once verified in the field). It should be noted that no systematic changes were introduced into the system to verify these findings.

4.2 OBSERVED RRWD SYSTEM CRT CHARACTERISTICS

During the evaluation of the color calibrator, the RRWDS CRT console exhibited

the following characteristics which may affect the ability of the operator

8
(meteorologist) to discriminate between adjacent or nearly adjacent areas delineating differing weather intensities.

4.2.1 Background

A properly adjusted background generally minimizes, but does not eliminate

visual discrimination problems when the Brightness and Contrast (B/C) controls

are varied over their full range. A properly adjusted background is a (dim)

medium grey that is neutral in color when the B/C control positions are at

their maximum settings. As their names imply, the B/C controls permit individual

operators to make minor adjustments in both chromaticity and light-dark contrasts

to accommodate for individual preferences, particularly under different lighting

conditions. However, extreme settings of these controls should be avoided as they may produce significant changes in chromaticity of the weather intensity

levels (WILs).

Using a properly adjusted background, photometric and spectroradiometric

measurements confirmed that even small changes in the B/C controls resulted in

chromaticity and luminance changes in both single EPROM-derived colors or in

WIL colors. Chromaticity changes in the WIL colors were more complex than for

a single color. Most of these small changes in luminance and/or chromaticity

are not discriminable by the human visual system except under conditions of

direct comparison; i.e., when seen side-by-side. (Large changes in the B/C

control settings were visually discriminable.)

A slightly misadjusted background can also present significant visual

discrimination problems. Under this condition the effects of the B/C settings

appear to be magnified. For example, a "bright" grey background tends to diminish light-dark contrast at high settings of the B/C controls. A color-tinged

background distorts color contrasts significantly. Experiments with changing

the adjustment of the background and changing the settings of B/C controls for

a live weather display resulted in:

(1) WIL #5 (bright red) and WIL #6 (dark red) becoming virtually

indistinguishable

.

(2) WIL #2 (dark green) and the background becoming virtually

indistinguishable

.

(3) A requirement that the background and the B/C be kept constant in order

to properly evaluate the color calibrator.

During early phases of this project, one problem was variability in both

luminance and chromaticity data. One component of this variability was target

size. Target size was varied from an individual RGB phosphor dot, to a pixel

(RGB color triad), to a number of pixels, and to a circular area of about

2 inches in diameter. Increasing target size decreased variability in both

photometer and spectroradiometer readings by averaging out the effects of

refresh rate and the decay rates of the medium persistence phosphors.

9
4.2.2 Bright-dark Contrast

Under certain weather conditions and with a properly adjusted background, the

weather intensity represented by the brighter color of a color pair fills a larger portion of the display than the darker color. The luminance provided by

these bright colors then dominates the human visual system such that the darker

member of a color pair cannot be discriminated from the background. Two such

conditions have been observed on live weather displays:

(1) Where WIL //I (bright green) predominated, WIL #2 (dark green) became

indistinguishable from the background.

(2) Where WIL #5 (bright red) predominated, WIL #6 areas (dark red) became

indistinguishable from the background.

In both situations the more intense weather condition was located within or directly adjacent to broad areas of the less intense but more luminous weather

condition.

These situations may increase the operator workload required to detect the more

intense (darker) weather intensity. For example, increasing the settings of the

B/C controls may be used to improve the brightness contrast between the darker

WIL and the background but at a cost of undesirable chromaticity and color

contrast changes. Other Menu options, e.g., BLINK, may be used to decrease

operator workload. Blink, however, is primarily useful for attention-getting

and not continuous observation. Momentarily "masking" out the brighter WIL

areas of lesser Intensity is another option.

Excessive use of menu items (e.g., maps, range rings, azimuth lines, etc.) on

the RRWDS may add unwanted luminance, especially if the line intensity is set

to the maximum value (i.e., 07). This unwanted brightness diminishes the ability

to distinguish bright-dark contrasts. Specular reflections and veiling glare

from poorly designed room lighting also may seriously degrade a console

operator's ability to make both color and bright-dark contrast discriminations.

4.2.3 Quasi-hysteresis Effect

A hysteresis-like effect in the RRWDS was observed in measurements made with

both the color calibrator and the spectroradiometer. This effect consisted of

different functions, one for an ascending series (TDL=00 to TDL=15) and one for

a descending series (TDL=15 to TDL=00).

This effect is believed to be caused by RRWDS system drifts. The effect on developing a color calibrator procedure is that the type of color pattern to be

used, the direction of the TDL changes, and the elapsed time for warm up and

conduct of each step, may have to be specified in a way that is unrelated to

the daily operational function of the display (i.e., the test conditions will be

arbitrarily specified and not necessarily represent typical operational

conditions)

.

10
4.2.4

System Drift

System drift in the RRWDS is a complex phenomenon which alters primary colors

(single phosphors) and WIL colors differentially. If the weather background

area is filled with a single color of a high level (e.g., TDL = 15, RED), and

monitored over time, the luminance (and to some extent chromaticity ) changes.

Initially, luminance starts high, drops over the next one-half hour, and then

begins to climb back up. However, even after 8 hours, luminance usually does

not reach its initial value.

On the other hand, if the same weather background area is filled with a WIL

then something different happens. After 15 minutes, bright WILs (#1, #3, #5)

show a decrease in luminance, but dark WILs (#2, #4, #6) show an increase in

luminance. Thus, the combination of system drift and the hysteresis-like effect

means: a) the effects of a one TDL increment is not necessarily the same as a one TDL decrement, b) the effects of a one TDL change depend on the phosphor

color and its contribution to a WIL, and c) possible interactions between

color channels. The net result is that a unit TDL change in a particular gun

means something slightly different for each WIL.

Perceptually most unit TDL changes are not discriminable. However, except for

very low levels of a RGB color (e.g., as in WILs #1 and #2), unit TDL changes

are discriminable when the changed and unchanged WILs are simultaneously viewed

adjacent to one another.

4.2.5 Effect of Digital Level Changes

Although changing the TDL levels of a given color gun normally would not be

expected to cause chromaticity to change, the chromaticity does shift on the

RRWDS system at NBS . The shift is indicated by spectroradiometric data. For

example, with the guns energized to green level #15, blue level #00, and red

level #00, then as the TDL level for green is reduced, the CIE color coordinates

as measured on the spectroradiometer remain constant down to about #07. Below

TDL #07, the CIE coordinates change.

RCA, in their own lab and on the same model CRT, applied current to one gun

only (the other two guns were de-energized) and found that the CIE coordinates

did not shift as a function of decrease in current to the color gun under test.

In the RRWDS system the RGB guns are always energized. The authors conclude

that the observed chromaticity shifts are due to RRWDS system effects

(interactions between the color channels).

4.2.6 Measurement Effects Due to Power Supply Degradation

Using RRWDS display power supply No. 1, measurements of photodiode voltage vs TDL setting showed severe saturation at and above certain TDL settings, even to

the extent of complete reversal of the slope of the curve. The Contrast Con'ro

was originally set on +0.5V DC and the Brightness Control on -150V DC (there are no index marks on these controls). Switching to power supply No. 2 and

then changing the Contrast Control setting to 4- 1.5V DC eliminated the slope

reversal, greatly reduced saturation, and restored the original color (the

11
latter based on subjective judgement). Changing the Brightness Control over a range of -225V to -125V produced little noticeable effect from a single WIL so the Brightness setting was left at about its original voltage. Subsequently,

when a new voltage tripler was installed by FAA, the original Brightness and

Contrast voltage settings proved satisfactory.

4.3 COLOR SPLOTCHES

Apparent thermal warping of the shadow mask is believed to be the cause of

visible shifts in color in "splotch-like" areas covering perhaps 20 to 30 percent of the face of the CRT. It takes a fraction of an hour for such effects

to appear. The impact on the pending calibration procedure is similar to that

mentioned in section 4.2.4 above, plus the necessity to avoid the splotch areas when using the color calibrator.

Although the RRWDS CRT incorporates PERMA-CHROME , a temperature-compensated

shadow mask, the MANUAL DEGAUSS button on the CRT console and the grounded

console shielding appear to eliminate both magnetic and electrostatic warping

as the sources of the color "splotching", leaving only thermal warping as the

apparent source.

4.5 S YSTEM LIMITATIONS ON OBJECTIVES

If the operational anomalies of the RRWDS system used for NBS laboratory

measurements are typical of other sets produced of this make and model, the

overall purpose of achieving objective RRWDS color calibration in the field is

attainable only under a predetermined and restricted set of operational

conditions.

5 . RECOMMENDATIONS

At this stage of the work, several recommendations regarding the color calibrator

and RRWDS are offered for FAA consideration.

5.1 DESIGN OF THE COLOR CALIBRATOR AS A COLORIMETER

FAA may wish to consider future work to convert the color calibrator to a "true"

CRT colorimeter by the addition of a low-cost microprocessor. Preliminary

theoretical considerations and mathematical formulations have established the

feasibility of a three-photodiode colorimeter. The hardware/software implementation of the colorimeter has not been attempted. The microprocessor would permit

determination of the International Commission on Illumination (CIE) coordinates

(x,y) of any given color on the screen, for a particular set of phosphors.

These coordinates would be reproducible for use as evidence in court proceedings

whereas the current color calibrator determines whether the WIL colors produce

photodiode voltages that are within certain specified limits.

12
5.2 USE OF THE COLOR CALIBRATOR

5.2.1 Development of Field Calibration Procedures

Pursuit of the color calibrator approach requires a decision about how the

WILs on the RRWDS should be calibrated in the field; i.e., (a) EPROMs + Memory

Plane B, (b) vertical bars from the processor, or (c) wedges from the digitizer.

Supplementary or alternative techniques to the use of a light tube with Fresnel

lens as a means of reducing/eliminating color bleed-through for (b) and (c)

above would have to be explored. These might include removing the glass safety

shield during field maintenance or modifying the CRT.

Depending on FAA decisions on the recommendations in this report, additional

work may need to be done to resolve such issues as color reflections or spillover,

luminance specifications, Fresnel lens/color calibrator geometry with respect

to the CRT screen, EPROMS, etc. In addition, the impact of room lighting (as

in FAA Flight Service Stations) or darkened room conditions (as in Air Route

Traffic Control Centers) on detectability of WILS and on RRWDS calibration

procedures needs to be assessed.

Still another area which must be resolved before field calibration procedures

are implemented is a determination of the replicability of color calibrator

measurements. The following possible causes for perturbations in photodiode

voltage measurements using the color calibrator should be checked under

differing conditions:

a. Investigate whether light reflections between the surface of the CRT

and the protective glass and/or the Fresnel lens are causing the spillover of color from one color segment to another (of the multicolor

digitizer's wedge or the processor's bar type display), even when a multicolor (RGB) calibrator head is constrained by a tube to viewing

only one color segment of the display.

Alternatively, use only single-color displays for color calibration

purposes

.

b. Check for the possible presence in the NBS laboratory of electro-magnetic

interference (EMI) or conducted electrical interference that may be

causing extraneous spectral power spikes to show up in the output of

the rapid scanning spectroradiometer at low chromaticity test digital

levels (the RRWDS lab is directly above the CBT computer facility room).

5.2.2 Chromaticity Drift

Resolve issues as needed for development of an initial working draft calibration

procedure. Until the RRWDS chromaticity shifts over time are essentially

eliminated, develop:

a. A method of restricting the area of the solid color display to be checked

(e.g., visually staying away from the splotches of obviously shifting

chromaticity )

.

13
b. An arbitrary specification of the timing and sequence in which the

calibration color patterns are displayed.

5.2.3 Color Calibration Tolerance

Specification of the photodiode voltage equivalent of a plus or minus unit TDL

change is recommended as the interim maximum acceptable limit for gun drift in

the field. This recommendation is based on the fact that a unit TDL change is

visually detectable (except at TDL 01 and 02), is measurable by instrument,

and is the smallest luminance that can be produced with a vendor furnished

EPROM.

If absolute color calibrator voltage readings are to be used to set tolerance

limits for the WIL colors, some fixed distance from calibrator head to protection

screen/CRT face should be determined from field measurements.

5.3 DESIGN OF RRWDS

5.3.1 Operation of RRWDS to Maintain Calibration

If the present WIL color scheme for the RRWDS is to be retained by FAA, then in

order to deal with problems listed under section 4 it is recommended that:

a. If the FAA does not find it practical to relocate the Brightness and

especially the Contrast Control to the inside of the display unit, some other sort of restriction should be placed on the range of the Contrast

Control setting or a cautionary placard should be added to inform the

operator. For example:

"CAUTION—Changing the Contrast Control

setting (Ref +0.5VDC) can change the

colors appearing on the Weather Display," and

b. External voltmeters should be added to indicate Contrast and Brightness

voltages so that these adjustments can be included in the daily operating

procedure and the technician's color calibration procedure, or

c. External jacks should be added for convenient connection of voltmeters

to indicate Contrast and Brightness voltages to the technician during

the color calibration procedure.

5.3.2 Visual Detectability

Another problem is the discriminability of certain WILs by meteorologists

having slight color-vision anomalies. NBS recommends that the WIL colors be

reevaluated to establish WIL chromaticities and luminances that would maximize

color discrimination by persons having slight color vision defects. This reevaluation would also consider selection of luminance levels to permit all observers

to distinguish the dark WIL colors from both the background and the corresponding

bright colors. At FAA's option the basic FAA color scheme of bright and dark

14
red, yellow, and green could remain unaltered. Only minor changes in the CIE

coordinates for several of the WILs would be recommended.

5.3.3 Possible Revision of Objective

Because of chromaticity and luminance changes due to system drifting, power

supply degradation over time, and manual manipulation of external controls, the

strategy of using occasional field calibration in order to hold colors constant

appears to be only partially effective. Perhaps in future work the feasibility

of a modified strategy should be explored; namely maintaining specified degree(s)

of contrast between WILs while substantially loosening the limits on the absolute

colors. This would require a microprocessor-controlled version of the color

calibrator. Note that future modifications to the RRWDS system might make

unnecessary such a change in objective, which NBS regards as being of secondary

desirability

.

5.3.4 Recommended Inclusion of Luminances in WIL Color Specifications

The effects described in sections 4.2.1 and 4.2.2 make clear that the purpose

of achieving six highly discriminable WIL colors cannot be achieved by control

of chromaticity alone. Some minimum ratio of luminances between the light and

dark colors of each pair must be maintained to ensure adequate discriminability

.

Moreover, the need to discriminate the even-numbered (dark) WILs from blackness

(the background) necessitates setting minimum absolute luminances for those

colors. As a consequence, it is strongly recommended that the final FAA specifications for the WIL colors include luminances as well as chromaticities

.

If the color calibrator is used in the absolute mode, with a fixed measuring

distance and a single table of acceptable ranges of the diode voltage outputs,

then the luminance aspect is automatically controlled, along with the

chromaticities

.

5.4

NEED FOR FIELD OR LABORATORY ANALOG TESTING

One of the previously stated criteria for sensitivity of the filtered photodiodes

(see No. 4 in section 2.2) is intended for use with test digital level changes

in chromaticity. A feasibility demonstration of that objective is not the same

as demonstrating the suitability of the engineering model color calibrator for

such analog changes as are expected to appear in the field. Analog changes

could be due to such factors as changes in gun bias voltages, changes in grid

potentials (especially G2), video amplifier board replacement, or high voltage

block or tripler replacements in power supplies. This distinction is crucial

because a unit TDL change affects only the WIL being tested and not other WILs.

In the field, any analog change (especially in the RG guns) is expected to

affect all WILs, but not necessarily proportionally. Because of the potential

complexity of in-the-field analog changes, NBS’s demonstration of the feasibility

of the color calibrator cannot be generalized to cover analog changes In the

field without further testing.

15
6. CONCLUSIONS

In conclusion, the research reported here demonstrates the feasibility of the

color calibrator. The engineering model of the calibrator was used successfully

to measure differences between WIL levels on the RRWDS at NBS. The data suggest

that the initial objective of designing, fabricating, and evaluating a color

calibrator has been met.

Additional field testing at selected FAA facilities is recommended to verify

the feasibility of field use of the color calibrator, develop calibration

procedures, assess room illumination effects, and finalize recommendation for

chromaticity/luminance specifications on operational RRWDS Systems. This

research would result in recommendations for the tolerance limits (in terms of

chromaticity and luminance) for the colors used to indicate weather intensity,

calibration procedures for using the color calibrator with the RRWDS, and a range of lighting conditions for RRWDS operations.

16
Appendix A

COLOR CALIBRATOR TEST PROCEDURES AND RESULTS

INTRODUCTION

The project objectives, technical approach, test articles, selection criteria,

instruments used and general results are described in the main report. The

laboratory evaluation objectives and detailed experimental procedures and

results are described in this appendix.

LABORATORY EVALUATION OBJECTIVES

The three principal objectives of the laboratory evaluation were to:

1. Verify that the color calibrator responds linearly over the luminance

range of the RRWDS CRT display.

2. Determine that the color calibrator has enough sensitivity and

discrimination to detect a specified amount of relative change in the

contribution of any RGB color gun/phosphor to the specified chromaticity

of any of the six WILs.

3. Determine the best photodiode/light filter combination for detecting

relative changes in chromaticity for each of the six WILs.

PRELIMINARY RRWDS CRT MEASUREMENTS

A raster-scan (digital) CRT has certain known non-homogeneities, e.g.,

non-convergence at the perimeter, color shadow mask warping due to magnetic/

heating effects, and sloping lines with the "jaggies" to mention a few. Some of

these non-homogeneities are due to the color CRT, such as color "splotching"

which may be due to either magnetic or thermal warping. Other observed non- homogeneities may be due to systems effects which result from engineering

trade-offs to meet system objectives, such as when the CRT anode voltage is

upped to 30 KV from the manufacturer’s recommended 25 KV. Therefore, one major

concern of this project was to determine system effects on the color CRT's

luminance and chromaticity characteristics.

Photometric measurements indicated that: a) the luminance of a single phosphor

dot averaged over several scans showed both temporal and spatial (dot-dot)

variability, b) the averaged luminance of the smallest digitized area (approximately 7 to 9 pixels) showed somewhat less temporal and spatial variability, and

c) use of large viewing areas for measurement provided spatial averaging and

showed the least amount of spatial variability. On the other hand, the large areas did reveal a significant luminance variation as a function of the time

that the target had been displayed.

A-l
Time-sampled spectroradiometric measurements with calculated summary outputs

verified the luminance variability detected by the photometer. In addition the

spectroradiometric measurements indicated that there are small chromaticity

changes concurrent with the luminance changes associated with a single phosphor

color, i.e., with only a single color displayed on the CRT. Since the results

of the RCA tests show that chromaticity should not change as a function of a single phosphor's luminance change, a system effect or interaction apparently

caused these results. Changes in system components, e.g.. voltage triplers,

high voltage junction blocks, or video amplifiers also produced changes in WIL

chromaticity. Changes in the Brightness Control (B) and especially the Contrast

Control (C), produced both luminance and chromaticity changes. Although the

photometric and spectroradiometric data are not included in this report, they

were used to develop a standard set of conditions under which all color calibrator measurements were taken. These standard conditions were used to reduce

some of the nonhomogeneity and variability detected by the spectroradiometer

.

RRWDS COLOR CALIBRATOR TEST MODE

The RRWDS was converted to the color calibrator test mode by replacing the

standard 2708 EPROMs on the Display CPU/Interface circuit card assembly (i.e.,

CCA #N3NB#A1) with a set of color test EPROMs provided by the Electrodynamics

Corporation. These color test EPROMs allow entry through the console keyboard

to the WIL color and background RAMs. The programs written into the EPROMs

allow each color gun to be changed by 16 digital levels as entered from the

keyboard, i.e., from 00 to 15. In addition, a Memory Plane B was added to the

Weather Processor to provide RGB memory boards for storing the six WIL color

wedges from a Digitizer located at an FAA/NWS radar site. This permitted a choice of two modes for testing the color calibrator: a) filling the weather

display background with a single color and eliminating the alphanumerics , thus

avoiding color interference, and b) changing adjacent WIL wedges for side by

side comparisons. The latter test mode was used to determine if a unit TDL

change could be visually detected. For the bright WILs (i.e., #1, #3, #5), a unit TDL change cannot be detected visually. For the dark WIL's (i.e., #2, #4,

#6) a unit TDL change can sometimes be visually detected with the room lights

off but it appears to the observer as more of a brightness change than a chromaticity shift.

On a live weather display, the B and C Controls can be manipulated such that it

is extremely difficult to distinguish between the light and dark WILs (e.g.,

WIL #5 vs WIL #6) depending on the size of the areas involved, or between a dark WIL (e.g., WIL #2) and the CRT background color. In order to establish

standard conditions for setting these controls, a number of live weather displays were examined while adjusting the B and C controls and recording the B

and C voltages with the room lights off. The B and C controls were manipulated

so as to:

1. Minimize weather display background.

2. Maximize light-dark contrast between weather display and display

background

.

A2
3. Maximize color contrasts between WILs.

4. Maximize light-dark contrasts between WILs.

'he final Brightness and Contrast settings resulted from the subjective

-n erpretations of the investigators. Other operators using different CRTs may

arrive at different settings. Nevertheless, by keeping these settings constant

c

: roughout all data collection, a common reference point was obtained. The

. i rial values used throughout this study were B = -150 VDC and C = +0.50 VDC. The

color calibrator is sensitive to color changes resulting from B and C voltage

changes so that the same set of B and C voltage conditions should always be

used. However, it should be noted that the B and C control voltages necessary

to maintain the same color calibrator outputs may change due to switching from

Power Supply #1 to Power Supply #2 or to the normal performance degradation of

a power supply over time.

According to the manufacturer, the chromaticity of a CRT phosphor does not

change over time. However, the display may show chromaticity changes as the

CRT ages. These shifts in chromaticity are due to electrode erosion reducing

the accuracy of the beam control, thereby producing unwanted stimulation of

adjacent phosphors. Usually the red and green color guns erode first. When

the chromaticity of a WIL shifts beyond the equivalent of two TDLs , the CRT

tube (or the guns) probably should be replaced. Gun replacement requires

special facilities. Chromaticity changes in the six WILs have been noted when

other components fail, e.g., the video amplifier CCA, high voltage junction

block, or the voltage triplers for the power supplies. In several cases CRT

luminance changes noted with the color calibrator have forecast or signaled a component failure.

COLOR CALIBRATOR LINEARITY TEST

Objectives :

It is highly desirable that the output voltage of the color calibrator be a linear function of the input irradiance. One way of checking this linearity is

to confirm the inverse square law of illuminance from a point source, at least

up to the illuminance level produced by the RRWDS display at short range. Linear

response simplifies the interpretation of the color calibrator data and is

almost a requirement for practical field applications. The objectives of this

test were to:

1. Verify the linear characteristics designed into the color calibrator.

2. Remove the color calibrator as a possible cause of nonlinear

characteristics observed in measurements of the Weather Display Test

Digital Levels.

Procedure :

The inverse square law of illuminance is represented by:

E = kl/S 2 A3
where: E = illuminance falling on detector from a point source,

I = luminous intensity of the point source,

S = distance from lamp to detector (e.g., color calibrator head),

k = proportionality constant (depends on measurement units).

The inverse square law holds accurately as one backs off from a small lamp,

beyond a certain minimum distance. Hence a plot of E ±J against 1/S^ should

give a straight line.

Step #1—A Weston foot-candle meter was used to measure the illuminance provided

by the RRWDS CRT. The following conditions were established:

(a) Digital gun settings: R=15

B=13

G=15

Manufacturer ’

s

white

(b) Brightness Control: -150 VDC

(c) Contrast Control: +0.5 VDC

(d) Cosine correcting

lens of meter:

Touching

Centered

glass protective

on cursor’s home

screen. position

(e) Extraneous Light

Sources: All room lights - OFF

Console lights - Covered

Other RRWDS Indicator lights

- ON

(f) Result: The Weston foot-candle meter set at

the low light scale, yielded a reading

of 20 fc I/

\1 The color calibrator voltage should in the general case be proportional to

irradiance, but by using a lamp of fixed spectrum, illuminance can be used

instead, since they are then proportional. Alternatively, simply interpret

E and I in the inverse square law as irradiance and radiant intensity.

U The 20 fc reading does not represent the maximum illuminance that the

RRWDS is capable of providing at the protective screen; rather it represents

the illuminance resulting from the reference voltage values selected for

this project for the Brightness and Contrast Controls.

A4
Step #2—The next step was to check the linearity of the color calibrator on

the Spindler and Hoyer Optical Bench. The point source used was a 12 VDC lamp

(auto taillight). Power was supplied by a precision AC to DC converter that

supplies ripple-free 12 VDC irrespective of AC line voltage fluctuations. The

long axis of the lamp filament was placed orthogonal to the length of the light

bench. The photometer was placed on the optical bench and moved away from the

filament until 20 fc was obtained (487 mm). This distance from the filament

was the starting point for the color calibrator check.

The color calibrator was installed on the optical bench and readings taken at

various distances until a point was reached when the photometer measured 2 fc.

The red narrow band filtered photodiode (combination No. 1) was used for this

test because the 12 VDC incandescent lamp was a convenient low wattage lamp

with ample energy in the red region of the spectrum. Since there is no difference between the RGB silicon photodiodes except for the type of Wratten filter,

there was no need to check the green and blue filtered photodiodes.

Results :

As shown in figure 1, a plot of the voltage output of the calibrator against

1/S

2

yields a straight line over the illuminance range of 2 to 20 fc. Hence,

since things linearly related to the same thing are linearly related to each

other, the test established that the calibrator voltage output is linearly

related to E. In fact, the line very nearly passes through the origin (E = 0,

1/S 2 = 0). At an infinite distance S, 1/S 2 = 0 and E should be zero, assuming

that the dark current (ID) has been nulled out. Since the voltage is very

nearly zero there, this means that there is little or no output from the calibrator when no light strikes it. Thus the voltage output is actually directly

proportional to the illuminance, within a reasonable tolerance.

Conclusion :

The nonlinear results obtained from color calibrator measurements of the CRT

display are attributable to RRWDS/CRT system effects.

OBSERVATIONS OF SYSTEM EFFECTS

Five types of non-uniformities or system effects have been observed and will be

described in detail:

1. CRT display drif t/Quasi-hy steresis effect

2. Heat warping of shadow mask

3. Refresh rate

4. Color reflections

5. System interactions
1 . CRT Display Drif t/Quasi-hysteresis Effect

Certain CRT display anomalies were noted during preliminary investigation of

the RRWDS color display. These CRT display anomalies are associated with the

test methodology used to identify them and appear to be interrelated through

some overall system effect(s). These effects occur during continuous RRWDS

operation so intermittent operation of the RRWDS was not a factor in these

observations. These effects/anomalies are:

a. CRT Display Drift —At the start of an 8 hour test period, a white (TDL

of R = 15, G = 15, B = 13) was keyed into the RAM location for the (WIL)

background and the alphanumerics erased. Spectroradiometer samples were taken at appropriate intervals throughout the 8 hour test period.

The (spectroradiometer-calculated) luminance values (nits), when plotted

over time indicated that the luminance dropped considerably during the

first one-half hour, slightly fluctuated around a median value for the

next one-half hour, and then steadily increased. However, at the end

of the 8 hour test period, the luminance was still less than the

initial value.

The above procedure was replicated with each of the individual RGB

colors in turn at a TDL = 15 while the remaining two colors were at

TDL = 00. Although the luminance values were correspondingly lower,

the forms of the functional relationships between CRT luminance and

time were similar to those obtained for the white background. Further

replications using a TDL = 05 for each of the individual RGB colors

produced a different functional relationship. For these replications,

there was a slow steady increase in luminance over the first 2 hours

and then a leveling off, with minor fluctuations, out to 8 hours.

Chromaticity changes calculated by the spectroradiometer were noted in

conjunction with the luminance changes. Since the calculated CIE

(x,y) value changes were in the fourth and third decimal places, a correlational analysis relating chromaticity shifts to luminous changes

was not attempted.

b. Quasi-hysteresis Effect —Preliminary checks were made to determine if

measurements of RRWDS display characteristics using individual RGB

colors should be made in ascending (from 00 to 15) or descending

(from 15 to 00) order of TDL. Luminance measurements were made at an approximate time interval of 15 minutes .2/ For ascending TDLs it was observed that the curve of luminance (nits) against TDL was significantly displaced (to the left and above) the curve for descending

TDLs. Due to time constraints a full set of measurements was not

completed for the descending series. The ascending series approach

was adopted as a basis for evaluation of the color calibrator.

As a point of information, the investigators considered and then

rejected the possibility that the variable spectroradiometer lapsed-time

A6
measurement characteristics 2/ might have contributed to the observed

quasi-hysterisis effect, since brief checks using other instruments

not affected by time factor considerations indicated that the effect

was caused by the RRWDS.

Comment—The changes in luminance and chromaticity recorded by instrumentation

were not generally discriminable by the investigator. However, in a split-screen

display with simultaneous cross-comparisons, such changes may be discriminable

by the human visual system.

2 . Heat Warping of Shadow Mask

Apparent heat warping ft! of the thermal-compensated , color shadow mask was most

clearly noticeable under two conditions. The white color vertical bar from the

processor's BITE showed extensive warping of the mask because the bar was near

the perimeter of the 14.7 inch diameter display area and the RBG guns were set

at high heat producing levels (R = 15, B = 13, and G = 15). Another instance

of heat warping occurred when B = 15, R = 00, and G = 00 . After approximately

20 minutes a purplish area appeared in the lower left quadrant of the Weather

Display. Using 10 to 20x magnification, a red "pimple" was observed next to

the blue phosphor. This appeared to be caused by mask warpage resulting in

some of the electrons from the blue gun striking a portion of the red phosphor

dot. This heat warping may be a function of the particular CRT in the test

Weather Display.

3. Refresh Rate

Spectroradiometric measurements on a single phosphor dot were quite variable

when manually limited to short integration times but became steadier as the

integration was extended to the spectroradiometer ' s maximum integration time of

32 seconds. Spectroradiometric measurements of WILs taken over larger areas

near the center of the display area showed large chromaticity differences from

measurements taken near the perimeter of the display area. This result was expected because convergence is best controlled for the center of the display

area.

1/ Luminance measurements were taken approximately every 15 minutes to keep

the TDL-on time constant. [The spectroradiometer automatically adjusts

its sampling time as a functon of an initial luminance measurement. Hence,

at low CRT luminances, sampling time is long ( — 10 minutes) while at high

luminances it is short. Thus, measurements for the higher luminance TDLs were taken closer to the end of the 15 minute TDL-on time than was the case

for the lower luminance TDLs.]

h! Electro-magnetic and electro-static effects are eliminated by the MANUAL

DEGAUSS button as well as the magnetic shielding of the console. Electrostatic effects on RAM may change the pattern being displayed.

A7
4. Color Reflections

All calibration tests of the color calibrator were performed by filling the

14.7 inch diameter display area with a single phosphor color or a WTL color.

If instead the vertical WIL bars from the processor were to be used, the color

calibrator would require a "light tube" and a Fresnel lens (planar) to focus

equally over all three photocells in the color calibrator.

Tests to date indicate different readings obtained using the color bar technique

than from those resulting from flooding the whole screen. The chief suspected

cause is reflected light from adjacent color bars bouncing back and forth

between the CRT face and the protective glass screen. That such reflections

occur may be deduced from the fact that measured chromaticity changes for dark

WILs having adjacent bright WILs are greater than for bright WILs having adjacent dark WILs. Another problem in using the vertical bars is the small target area available for measurement.

Light reflections from adjacent WILs can be significantly reduced if test

wedges from the digitizer are used, assuming the digitizer is properly calibrated. Here, the best approach to minimizing reflections is to put the console

display in the ZOOM and Cursor ON mode and move the wedge until the appropriate

WIL covers the maximum area of the display circle.

5. System Interactions

In calibrating WILs, all six WILs should be checked even if only one gun is

suspect. For example a unit TDL decrement in the red gun is not the same for

WIL #5 (R = 15, B 3 00, G - 00) and WIL #3 (R 15, B - 00, G - 15). The

explanation for this effect is twofold. First, there appears to be a complex

system interaction whenever more than one gun is on at a time. Second, the

effect of a unit TDL increment/decrement varies as a function of the luminance

levels associated with each gun. Later in this report, plots of luminance as a function of TDL are described. Associated with these plots is a time to stabilize system drift at a given TDL of a single gun. Roughly, the higher the TDL

for a given color gun the longer it takes to stabilize the luminance reading.

SINGLE COLOR TEST

Objective :

The objective of the Single Color Test was to evaluate the ability of different

types of color calibrator heads to discriminate the various levels of an individual RGB phosphor by using one gun at a time (the other two guns are energized

but set to TDL = 00).

Procedure :

Four types of color calibrator detector heads were tested. A summary description

is given in table 1. Each head incorporated three (RGB) channels. Head

Nos. 1, 2, and 3 used silicon photodiodes, with Wratten filters of the narrow-,

medium-, and wide-band type, respectively. Head No. 4 used GaAsP photodiodes

A8
with dichroic filters. Because of the high cost and the time required for hand

manufacturing of the photodiode/filter assemblies, other possible combinations

of GaAsP photodiodes with Wratten filters and silicon photodiodes with dichroic

filters were not procured or tested. Thus, a) the measured data is for combined

characteristics of the GaAsP photodiode and dichroic filter and these are not

separable given the available data, and b) no data was obtained on whether a silicon or GaAsP photodiode is best for the color calibrator application.

The Single Color Test involved filling the display screen using a single gun at

a time; starting at TDL = 00 and proceeding to TDL = 15. All lights were OFF or covered over, including the alphanumerics , Power ON light, etc. The dark field

currents (ID) of the photocells were nulled out using the variable resistors in

the color calibrator head. The null potentiometer on the power supply was set

to give approximately equal values for the RGBs. The sensitivity potentiometer

on the power supply was set to 10.00. The color calibrator head was then placed

on a tripod at a distance of 12 inches from the glass protective screen, with

the plane of the detector head parallel to the plane of the protective screen

and centered on the Cursor HOME position. Both console and processor were continuously energized (except for equipment failure).

The Single Color Test procedure was to insert the TDLs, starting at 00, and

record voltage readings for each RGB photocell. This procedure was used for

all four color calibrator heads for all three color guns.

Results :

The results for each of the four color calibrator heads are shown in

figures 2A-C, 3A-C, 4A-C and 5A-C. Examination of these figures demonstrate the

following:

1. Each filtered photodiode was capable of detecting a unit TDL increment

of its respective RGB color. This was true for all four detector heads.

2. The narrow-band Wratten-f iltered photodiodes, and to a slightly lesser

extent the dichroic-f iltered photodiodes, responded selectively to

their respective RGB colors. The medium- and wide-band Wratten filter

photodiodes responded weakly but still dif f erentally

.

3. The R-f iltered wide-band photodiode reponded more than the G and B photodiodes to all three colors. Further, the G- and B-filtered photodiodes yielded nearly identical values for the G-phosphor color.

4. On the basis of NBS's criteria, the narrow-band and dichroic filters

provide the best fit for the color calibrator.

Examination of color calibrator data taken to explore the limits of the RRWDS

CRT display revealed some interesting effects (data not included in this report ).

One such effect appeared to result from a breakdown in the potting material

used in the high voltage power supply triplers and high voltage junction block.

The effect, detected by the color calibrator and verified with the spent r . i'l - eter, is that when a high level TDL was further increased in the system '

A9
an unexpected decrease rather than an increase in the luminance of a given RGB

phosphor. For example, prior to replacement of the triplers, the red phosphor

reached peak luminance at TDL = 11 and steadily decreased thereafter. Under

somewhat similar conditions, the luminance of the blue phosphor reached saturation at TDL = 09 and remained more or less constant up to TDL = 15. Under more

typical operating conditions the red phosphor reached a peak at R = 15, whereas

the blue phosphor reached its peak luminance at B = 13 with no further luminance

increase for B = 14 or B = 15.

WIL COLOR TEST

Objective :

The objective of the WIL Color Test was to evaluate the ability of four different

color calibrator heads to discriminate small changes in the pattern of stimulation

of the RGB phosphor when WIL colors are used.

Procedure :

The same four test articles and the same standard set of conditions and procedures were used in this test as for the Single Color Test, except for the way

the TDLs of the guns were changed. In the WIL Color Test, a WIL was entered on

the Weather Display background and allowed to stabilize for one-half hour.

Then a given RGB gun was decremented one TDL step, and the readings of the RGB

photocells recorded. The WIL was returned to its initial condition. After a 10 to 15 minute wait the same RGB gun was decremented by two steps and RGB readings

recorded. After each RGB gun had been decremented one at a time by one and two

TDL steps (except for B = 00 as in WIL's #3, #4, #5, #6) the same procedure was applied by incrementing the RGB guns one and two TDL steps. This procedure was necessitated by system drift; i.e., the color calibrator readings after returning

to the initial WILs were usually different from the original readings. Thus,

the recorded calibrator values were voltage differences which, to some extent,

obscured system drift. This same procedure was used for all four color calibrator detection heads.

The numerical portion of the figure label (i.e., 2-5) represents filter type

whereas the alphabetical portion (i.e., D-I) represents WILs #1 to #6, respectively. These figures graphically present color calibrator voltage differences.

The horizontal lines represent the original WIL TDL value for each RGB gun.

The vertical bars represent the color calibrator voltage differences as a function of one- or two-TDL step decrements/increments for each of the RGB

guns . 1! Thus, for each color calibrator detection head there are six WILs

depicted in six figures. These figures indicate the complex interaction

between the RGB channels when a single one- or two-TDL step is made in just one

of the RGB guns. No data was collected on multiple gun changes.

5 / Reading left to right the colors represented by each set of three bars

are, in order, red, green, and blue.
Results and Conclusions:

The above figures reveal several interesting characteristics and some interaction

effects:

1. The presence of (RGB) TDLs from 01 to 04 was not detectable by the

color calibrator, and TDLs from 01 to 03 were not detectable by the

spectroradiometer . Fully dark adapted human observers sometimes detected

luminance at TDL = 02 and color at TDL = 03 for each of the RGB guns. This

finding suggests that the R=01 in WIL #2 and the B=02 in WIL //I and WIL

#2 may be contributing little or nothing to the visual recognition of

these WILs.

2 . A unit TDL step decrement does not necessarily yield the same color

calibrator voltage change as a unit TDL increment. This characteristic

is a function of at least three variables:

a. The location of the original WIL RGB values on the characteristic

curve

.

b. The TDL levels for the other two guns for a given WIL.

c. The elapsed time that the WIL has been displayed.

These three phenomena appeared to be caused by a system interaction

between the electrical current levels of the three RGB guns, since all

three guns were always energized. The largest such effect involves the

G gun since it is also used to "paint” the alphanumerics.

As a consequence, if an analog change in the bias voltage of a given

RGB gun occurs, the change will likely affect all WILs (but do so differentially). This means a technician, in correcting for a change or drift, may have to evaluate his correction as it affects all six WIL's

and not just one.

The color calibrator tests were performed using special EPROMs to make

TDL step changes. In the field both analog and digital effects may occur. Hence, it is not possible to confidently generalize from digitalbased laboratory tests to unknown field conditions, although the above

generalizations should still hold true.

3. Figures 2A-I present the results of the Single and WIL Color Tests

using narrow-band Wratten-f iltered silicon photodetectors. The Single

Color Test clearly indicated that the narrow-bands responded very selectively to their appropriate RGB guns, e.g., the R filters responded

strongly to the R gun while the G and B filters responded weakly.

Comparing the results of the narrow-band Single Color Test with the

medium-band Single Color Test illustrates two points: (a) at Bright- ness (B) and Contrast (C) settings of -150 VDC and +0.50 VDC, respect ivelv,

the RGB guns were not driven to saturation, except for a slight !'.<!!•.

off of B at B = 10 ; and (b) when the RRWDS CRT display is func t i ; :

A-ll
normally, the above B and C settings are effective in preventing RGB

gun saturation.

The WIL Color Test indicated that all four color calibrator heads could

detect a unit TDL change in any RGB color gun setting for any of the

six WILs with certain exceptions. These exceptions, cited earlier,

are: (a) very low TDL settings of a RGB gun in a multi-gun WIL and

very high TDLs of a single gun in a single gun WIL (e.g., WIL #5).

As expected, the responses of the broad-band detectors, figures 4A-I, were too wide, especially the red filter. The red-filtered photocell

yielded the largest voltage of the RGB photocells for all three RGB

colors (figures 4A-C). The G- and B-filtered photocells yielded

about the same voltages with the G gun ON (figure 4C), i.e. no discrimi

nability between G and B. Thus, for the purposes of the present study,

the broad-band filters did not provide sufficient discriminability

.

The medium-band filtered silicon photodiodes and the dichroic-f iltered

GaAsP photodiodes yielded moderate discriminability but the measured

data for both are confounded with RRWDS component failures.

Figures 5A-I represent color calibrator voltages using head No. 4.

Figure 5D shows a break in the data at TDL=12 for the G gun. The

break in the data is due to the failure of the voltage tripler for

Power Supply No. 1. The automatic switch over to Power Supply No. 2 produced a significant drop in luminance. To compensate for this appar

ent drop in G luminance the Brightness control was changed to -145VDC

and Contrast to +1.50VDC. The remainder of this graph was obtained at

these new B and C settings. Later the tripler for Power Supply No. 2 and the high voltage junction block failed. Just prior to complete

failure, the color calibrator voltages for the medium-band Wrattenfiltered silicon photocells were rapidly changing as the display got

smaller and then larger.

Data for the medium-band Wratten-f iltered photodetectors were taken

shortly after replacement of the failed components, i.e., with the B

and C set at the previous Power Supply No. 2 values. From

figures 3A-C, it can be seen that under these B and C settings, the RGB

guns were driven to saturation at lower TDL's; thereby reemphasing the

need to set standard (constant) values for the B and C controls.

Following the Single Color and WIL Color Tests using the medium-band

filtered photodetectors, the entire series of test was redone. The new

settings (subjectively about the same backround of dim gray) for the B

and C controls turned out to be the same as the old, i.e., B = -150 VDC

and C = +0.50 VDC—an interesting result that should be explored in the

field. That is, the color calibrator should be investigated as a means

of detecting RRWDS degradation as part of the regular preventive

maintenance program.

Superimposed on figures 3A-B are the differences in color calibrator

voltage readings occuring when a TDL = 15 of the gun under test is:

A-12
a) first entered on the CRT display, and b) after this RGB display has

been on for 30 minutes. Ideally each TDL from 00 to 15 for each RGB

gun should be measured for drift over an 8 hour time-base. Practically,

such a procedure would be too time consuming.

SELECTION OF PHOTODIODE /FILTER COMBINATION

As shown in the aforementioned figures, the main difference observed among the

detector heads tested was in the magnitude of voltage change caused by a unit

change in TDL. The selection of the "best" combination from among the four

tested depends upon how the device will be used in the field. Two alternative

approaches will be described here: a) the colorimeter (theoretically ideal)

approach, and b) the color calibrator approach.

The colorimeter approach is based upon calculation of the CIE x and y color

coordinates, where the normalized spectral power distributions of the three

phosphors and the transmittances of the filters are known. These calculations

are complex but not formidable. In fact, the addition of a microprocessor and

associated hardware in the color calibrator would convert it to a true colorimeter which could readout the CIE color coordinates. Here the requirement for

the photodetectors (i.e., filtered photodiode) is simply that each RGB photodetector yield a unique or different value for any given color; i.e., if the

voltage outputs of two photodetectors are precisely the same value for a given

color, then discrimination is not possible. This requirement eliminates the

wide-band Wratten filters used in this study. Thus, either the medium-band

Wratten filters or the dichroic filters would be acceptable. Since the colorimeter approach requires discrete, measurable outputs from all three photodetectors, the narrow-band Wratten filters appear barely acceptable. The reason is

that the color channels other than the one matching the phosphor color being

examined have low voltage outputs that are near the noise level, so observed

differences may not be real.

The color calibrator approach is based upon the assumption that the field

technician need only determine whether the luminance produced by each RGB gun

falls within specified limits relative to reference calibrator values, to be

determined in some way. Among those tested, the "best" photodetector, in this

case, would employ silicon photodiodes with narrow-band Wratten filters.

In one method of determining reference values, for example, reference color

calibrator voltages and spectroradiometric measurements could be logged, as part of the RRWDS site-acceptance procedure. The resulting table of the relative luminances (color calibrator voltages) for each RGB gun for each of the

six WILs could then be referenced during preventative maintenance to detect

changes in relative luminance. No data is presently available on acceptable

voltage deviation limit values for each RGB gun in a given RRWDS system, or the

range of such values across all field sites. Field testing would be needed to

provide this information. It is possible that a single table of voltages vs WIL levels may suffice for all RRWDS sites. However, the information in

A-13
Constantine's paper^/ suggests that such a table may turn out to be site

specific

.

POSSIBLE TROUBLESHOOTING APPLICATION

It appears that, with sufficient field testing of RRWDS failure modes, the

color calibrator could also be used as a general trouble shooting instrument

for certain Weather Display malfunctions. For example, if one of the grid or screen voltages on N3NC1 CCA changed (particularly G2) this could be detected

using the color calibrator by looking at all six WILS. The reason is that a DC

shift in one of the RGB guns for the Weather Display background would show up

equally in all WIL bars from the processor. On the other hand a malfunctioning

resistor in an RGB ladder function of the processor's video amplifier might

eliminate the red level six in WI1 #1 but not affect any other WIL because no other WIL uses a R = 06. Although these two examples may not be precisely

correct, they should serve to illustrate the potential utility of the color

calibrator if tested further under field conditions.

CONCLUSIONS

From the data presented in this report, it is concluded that the color

calibrator

1. Is a linear (and proportional) measuring instrument.

2. Can detect a unit TDL color increment or decrement except where the

color TDL in a WIL is less than 03 (or in some cases 04), or a decrement

in very high TDLs of a single gun in a single-gun WIL (i.e., WIL #5).

3. Has potential for greater utility than originally anticipated, especially

for troubleshooting.

4. Has potential for improvement by incorporating a microprocessor and

associated hardware to convert the relative luminance color calibrator

into a true colorimeter (for a specified set of phosphors).

RECOMMENDATIONS

For an interim (at least) calibration tool and a means of developing needed

field application data and experience, NBS recommends that FAA procure sufficient

prototype color calibrators to field test the instrument and to gain experience

in developing and applying the calibrator voltage vs WIL level tables.

FAA may also wish to consider additional opportunities to more fully develop

the potential utility of the color calibrator or colorimeter.

6/ Constantine, John M. Jr, Electron Optical Techniques for an Ultra High

Resolution Color Film Recorder, Society of Photo Optical Instrumentation

Engineers, 1984.

A-14
s

s

CD E

E

c

CO

CO

1“

CO

CO

CO

CO

in

CO

00

NCO

00

o

o

o

lO

SN.

lO

o

h*» o

o

o

oa a+ ni indino aovnoA

aoivaanvo acnoo

i

A-15

Figure

1.

Test

of

color

calibrator

linearity

by

agreement

with

the

Inverse

square

Law

of

Radiation

(i.e.,

E

=

kl/s*)
Figures 2A-C. Silicon Photodiodes With Narrow-Band Wratten Filters

Single Color Tests Figure No .

Red (R) 2A

Blue (B) 2B

Green (G) 2C

Description — Color calibrator voltage readings (mVDC) for each test digital

level (TDL) setting for the R gun (figure 2A), B gun (figure 2B) , and G gun

(figure 2C) , starting from TDL = 00 to TDL = 15 (i.e., 16 steps), for each

of the three RBG photodetectors in the color calibration hed.

A-16
NARROW-BAND

WRATTEN

FILTERS

LO

CO

C\J o0)

CO

Nco

in

CO

C\J c3

60

'O

(D

J-i H

06O

i-o

CO

4-1

60 HOU<

CM

0)

l-3

60

OQ AW

A-17

TEST

DIGITAL

LEVEL
140

oa aw

A-18

TEST

DIGITAL

LEVEL
140

10

T—

CO

C\J

o

05

00

NCO

lO

CO

C\J

o

o o o

CO CM T“ OOOOOOOOOO O 05 CO^CQLOTfrCOCM 1-

O

c

3

60C

<Ua;u

60W

H

0£ CJ

l-i o

u-i

0) >

0)

to •u60

•H

u

o

oo

u

cm

<uu

3

60

Uoa aw

A-19

TEST

DIGITAL

LEVEL
Figures 2D-I. Silicon Photodiodes With Narrow-Band Wratten Filters

WIL Color Tests Figure No.

WIL #1 2D

WIL #2 2E

WIL #3 2F

WIL #4 2G

WIL #5 2H

WIL #6 21

Description — Differential voltages (mVDC) between color calibrator RBG

voltages: a) when TDLs for all RBG guns are set to manufacturer's color

specifications for the WIL number, and b) when unit incremental or decremental

TDL setting changes are made for each gun, one gun at a time. The abcissa

represents condition (a) above and the RBG vertical bars represent condition

(b). The vertical bars are read left to right in the order RBG. B is actually

used only in WILs #1 and #2. Because of the complexity of these figures the

reader may want to refer back to WIL Color Test, p. A-9.

A-20
Standard

digital

levels

(SDL):

1 1 1 1—•Ji

1 1

1 1 1 1— 1

1 o o

CM o CM 0 _JI _l + P 1 £ Q Q

C\1

II O

o

SI

_ Cl Q CD 0 o

I- SI

L_ Q. H—° c*—CD O 0)

O

x:

Q.

75 °

« ” 0

C\j 0)_D

O Q X!

II CO

CDO

II DC DC

0

CO

0O

o

£

0 o

CDc

o

a

CD -Q 0 0 *“ il

L_ 0

O £

0 T

1

”

0 O

°.q

O 1»“ o *- O o

05

xf

Q

ICM+

L- O

N-

_L _L

E C CM > ® -

1-0 11 0 ^ 11 "^0)0

0 _J

Q

OH W

i| O

5-° o

0 _J

£ -J Q

_ O CO

05 L_

,E CD >0 o

js © || 0 l_ ” >

°

oooooooooooooo ± _L

CO LO

^

CO CM '»-CMCO^tlOcOS.

oa auuv

A-21

Figure

2D.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#1

using

narrow-band

Wratten

filters
CO LO CO CM T- r- CM CO LO CO

oa aujv

T3

ti

(0soMu

COe

t>0 c

•H

CO9

CM

hJM3CMo

iHOuoM

PtAO

COa>o

CM

CO

<uoo

co Mo>

<Uo

fl

<u M

ai

4-1 MO « W U

CO <U M 4J X> rH O CJ

0)

M

M

O Ml rH CO O M U ^ w

CM

<uu3

60

•H

CM

A-22
in

ii 0

o'

o

ii CQ

in

ii cc

c

0«#-* (0

1

a

0

o

x:a

c

0)<d

i_o>

i—o

0

JQ

TJ0 Q

w O*— 0 _

<D 0

| |

0 £

o> £ O

o I 0 O •O

CQ

CC

XJ0

l_0

Ia>

k_o

JD

0

0

C

o

a

0

0

o*-< 0

.Q ©

•= "O

0 O

o =5

i- o

2 Z O sz 0 a

1o> JD

a

l~<0

I

°» (0s

- §

1

£ Q Q

O)*” w

,£ c in

>* ®

0 2 " > 0)0

© ^7

J= _i o

0)H J

f. ® o

1 0

-I £ -j

o Q 1-

1 w

1 >7)z 0 0 *- -J > Q

1-

in

_L I ± ooooooooooo N (D in Tt CO W T- t- CM CO

o o o o

Tf in CD Noa awv

A-23

Figure

2F

.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#3

using

narrow-band

Wratten

filters
Standard

digital

levels

(SDL)

00on0oo

ii m

O)o

it cc

©3

T50 0<0= • £ ° <0 — © "U

vO

— 0 0>0” O 2 a - CO .2* o 1 c O s

CD O)

of o

o°~ a

JO -O = © 0 tr o ®£® 1 0 CB O V. 1 °

O)

a

H—

k- o 1a

\-

CMI 1

-J £ Q a

09*“ 0

.E c 00 > <D o v 0 0 v- ii > °> o 0

-C _l - Q

D) HD0 0 JO > O

II o 1 | | i

T- | + 1 1 i , 

| 1 | i i o O o o o o o o o o O o O o o

N- CO in CO CM t- T— CM CO in <0

N

oa awv

-ac

<o -ao

Vi

Vi

rtC

tod

•H

cn3

<r

•JMScVo

iHooo

CO

odj;o«

d)VO

<4-1

00

(V60

fl) O>

a)oc

a>u

<u

U-l

<4-1 T3

ViO

4-1 d

Vi X>OO• O

CM

qjv3

60

tH

A-24

Wratten

filters
co m CO W r C\J CO LO CO

oa AW V

A-25

Figure

2H.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#5

using

narrow-band

Wratten

filters
>

CM ©O

— II ©o

CD O

o

II _ CO ©O

c

CO

O

D

CD

00

o

II cc

©

© ©

©

c

TJ© © .2

© 73

*- o - Si

— ^ « ©•

o

2 O

©

>

© fc. ” o

2q

Bg

Q a

1

.Q T3 = ©

© Jr O ©

of

O O)

O „

- O

a

i- »

CM n

+

O

I- 0

I- .0 +

®

a

c

5

o

c , 0 Cl © i © 0»JO JO

k_O) jQ *“ w

L.0

**—

»-“ 0

6

z

Q

H

O CM

I

- e

O TI

© -J

C C

uT ©

©

Q

CO

CMo

II >

O) ow

© _J

-Q Q

O.H W

E o

°

>* D 0

©5 » > S

-J £ -J0

CM g

1 "

1

-J © »- Q

I- >

00

| |

1 l *t 1 1 l . 1 1 1 1 1 O O O O O 0 O OOO O 0 0 0 0

N- CD 10 "<t CO CM T“ t- CM CO 10 CO Noa AUUV

A-26

Figure

21.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#6

using

narrow-band

Wratten

filters
Figures 3A-C. Silicon Photodiodes With Medium-Band Wratten Filters

Single Color Tests Figure No

Red (R) 3A U

Blue (B) 3B y

Green (G) 3C

scription — Color calibrator voltage readings (mVDC) for each test digital

el (TDL) setting for the R gun (figure 3A) , B gun (figure 3B), and g Gun

igure 3C), starting from TDL = 00 to TDL = 15 (i.e., 16 steps), for each

n of the RBG photodetectors in the color calibrator head.

"Cold start" means entering an R = 15 TDL on the display at the start of a day and then measuring the same R = 15 TDL 30 minutes later.

U The 30 means that the B = 15 TDL was left on 30 minutes after the finish

of the test and a remeasurement was then made.

A-27
260 h

MEDIUM-BAND

WRATTEN

FILTERS

u>

T“

T—

CO

CM §

t>0 4) UH&U

Ijo

<0 4J60

O)

00

I**.

CO

IO

MCO

CM cco

a>u3

60

•H

CM

M (M

r

r

r

rr

OQ AUJ

A-28

TEST

DIGITAL

LEVEL
LU

>

UJ

0

Q

I—

CO

LU

L—

oa aw

A-29

Figure

3B.

Color

calibrator

voltage

vs

test

digital

level

for

CRT's

blue

gun
280 o O O O O o o o o o o o o o

CO CM O CO CO CM o 00 CO CM

CM CM CM CM T- 1— T“ j—

OQ AW

a

9

60

cs

<v

<vp

60

U

o

p

o

M-f

Aft

CJpo

I—

I

oo

• CJCO

<1) P

9

60

•H

A-30

TEST

DIGITAL

LEVEL
h?

(A

Figures 3D-I . Silicon Photodiodes With Narrow-Band Wratten Filters

WIL Color Tests Figure

WIL #1 3D

WIL #2 3E

WIL #3 3F

WIL #4 3G

WIL #5 3H

WIL #6 31

de scription — Differential voltages (mVDC) between color calibrator RBG

/Itages: a) when TDLs for all RBG guns are set to manufacturer's color

pecif ications for the WIL number, and b) when unit incremental or decremental

DL setting changes are made for each gun, one gun at a time. The RBG abcissa

/ -presents condition (a) above and the RBG vertical bars represent condition

b) • The vertical bars are read left to right in the order RBG. B is actually

used only in WILs #1 and #2.

A-31
Standard

digital

levels

(SDL):

CM

£ h.

o

*-

+-• ° jC2

cs a

® CO

II — o

a Ji

ci ~ £ O

II GQ

CD . ° o m ©

11 DC DC J3

©

L_0»

-O T3 — ©

o ®

Jr £ 2 I O ©

O U.

. ®

01 -o

XI *- lO

Q

H -|

CM+

-1 © Q £ I 1- ~ Q 04 ?*- CO

u

>* ®m OT.

| | 1 1 1

a

1-

T“

, ^

jjSSj

, a H H

1 V 1 i

1

>

1

0

<w

1 1 O O o o o o o o o o O o o o o

K CO 10 CO CM T- CM 00 IO CO

oa auiv

A-32

Figure

3D.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#1

using

medium-band

Wratten

filters
Standard

digital

levels

(SDL):

CO

1—1—1—1—1—1—1

_l

rr

Q

1 1 1 “I 1

CM+

IT”+

CM

I 0

Iy—

1

£o

05 *“ C C

> ®

i- 0

0

Q

CO

COO

II 05 O

COo

II

<

D

cm" o

II CQ

o

II a:

o

JC

- a

-o (0 0 O

»- .C

u. a

£ c _ 0

0 0

>

0

05

0

°

.tr 0

O) D

Q -Q

O

CQ*

0

o T5

0 .2

C/5 “O

C O ° o a

© Cl

*“ TJ O i_ t; ®

CO 4-» If

0 05

O »_

u. ° f0

105

a

0

05

C

> 0

L

4 3

0 _Q

Q

CO

CMO

II O

0

fo?*-

'E-l

0 *- >

Q

CO

O

II o

o o o

CD 10

I 1 o o o

^

CO CM

o o

0M

J I L

o o o

00 10

o o

CO Is- oa AUJV

A-33

Figure

3E.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#2

using

medium-band

Wratten

filter
co m CO CM r- r- CV| CO m co OQ AWV

A-34

Figure

3F.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#3

using

medium-band

Wratten

filters
TTM

i i i i 1j i i i i i

1 i j i o o o o o o o

N (D 10 ^

(0 W r

o o

T- C\J

o

CO

o o o

CD

o

oa aluv

A-35

Figure

3G.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

if4

using

medium-band

Wratten

filters
oooooooo N (D lO ^

(0 W r

o o o o o o

CM CO to CO K

oa awv

A-36

Figure

3H.

Color

calibrator

difference

voltages

for

each

RBG

color

In

WIL

«

using

medium-band

Wratten

filters
Standard

digital

levels

(SDL):

c\j o

nO

CDO

II m

CD* o

ii cc

-Q

CD

— O

CD -C > a

CD (ft — o — f— CO

i—

r

CD

(ft C

o ®

O.'O

(ft o

21

O o

x:

cd a k_ JO T5 — <D ® Jr O ®

i—

r

5) c

<5 S

I O)

°o

CD CD

af xi

°T

O CD 0 k1 O

0-0

x>* *-

_ *-

I- o

co

a>a)

c

eo x

0

01 xT

o

z

® -I

C C

> «

k. 0)

03 iQ

0)

CVI o

II O) o

® , -J £ Q Q Oh w

•| ® o

CO s II > S

o

h- >-1 CM+

Q

ICM

I

<D ^

^ Q

Q

G)P W

l$s 03 k. II O

T-

! 1 1 L 1 1 1 1

i J 1 i 1 J 1 ooooooooooooooo S 0 If) Tf CO M r CM CO

^ If) 0 N

oa aujv

A-37

Figure

3

T

.

Color

calibrator

difference

voltages

for

each

RBG

color

In

WIL

#6

using

medium-band

Wratten

filters
Figures 4A-C. Silicon Photodiodes With Wide-Band Wratten Filters

Single Color Tests U Figure No.

Red (R) 4A

Blue (B) 4B

Green (G) 4C

Description — Color calibrator voltage readings (mVDC) for each test digital

level (TDL) setting for the R gun (figure 4A), B gun (figure 4B) , and G gun

(figure 4C), starting from TDL = 00 to TDL = 15 (i.e., 16 steps), for each

of the three RGB photodetectors in the color calibration hed.

1/ These single color tests were conducted using Power Supply #2. To obtain

the same subjective dim grey background as for Power Supply #1, the

Brightness and Contrast controls were set at B = 150 VDC and C = +1.5 VDC.

Due to the increased transmittance of the wide-band Wratten filters, there

is a corresponding increase in the scale factor.

A-38
520 U

WIDE-BAND

WRATTEN

FILTERS

i—i—i—

r

i

' r v

-

* i CO

CM

LU

>

LU

g

o

h”

CO

LU

H

I I I I I o o o o o o o O O o o o o

00 o CO CM oo O CO CM 00

CO CO CM CM CM T“ Toa aw

A-39

Figure

4A.

Color

calibrator

voltage

vs

test

digital

level

for

CRT's

red

gun
o O O o o o o O O O o o o o

CM 00 o CO CM 00 O CO CM 00

ID Tf- CO CO CM CM CM T- i—

oa alu

c

3

60

<03

H

C&O

P

o

iw

«C +J

60 •H

O

u

PQ

0)

l-i 3

60 •H

Cn

A-40

TEST

DIGITAL

LEVEL
LU

>

LU

<

H

O

Q

CO

LU

hoa aw

A-41

Figure

4C.

Color

calibrator

voltage

vs

test

digital

level

for

CRT’s

green

gun
Figures 4D-I. Silicon Photodiodes With Wide-Band Wratten Filters

WIL Color Tests Figure No

WIL #1 4D

WIL in 4E

WIL in 4F 1/

WIL #4 4G

WIL in 4H

WIL in 41

Description — Differential voltages (mVDC) between color calibrator RBG

voltages: a) when TDLs for all RBG guns are set to manufacturer's color

specifications for the WIL number, and b) when unit incremental or decremental

TDL setting changes are made for each gun, one gun at a time. The RBG abcissa

represents condition (a) above and the RBG vertical bars represent condition

(b). The vertical bars are read left to right in the order RBG. B is actually

used only in WILs #1 and #2.

U Figure 4F(a) demonstrates the effect of a 1 inch diameter, 1 inch focal

length Fresnel lens (plus light tube) on the color calibrator's response

when the photodiodes are located sufficiently behind the focal length to

equally illuminate all three photodiodes.

A-42
Standard

digital

levels

(SDL):

R=06, B=

02,

G=12

R,

B,GDigital

level

for

red,

blue

or

green

phosphor

r,

b,gcolor

calibrator

response

of

r, b

or

g-filtered

photodiode

Q

OjuO

oc

U*

A-43

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

//I

using

broad-band

Wratten
Standard

digital

levels

(SDL):

R

=

01, B

=

02,

G=06

io4mV

c

0)

oa auuv

A-44

Figure

4E.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#2

using

broad-band

Wratt

filters
i—i—i—

r

in

ii O

o

o

is CQ

in

T“

II cco

CO

©

©

>

©

©4->

‘ 5)

"O

(0 T3

C

(0

*-> co

o

jC

a

©

o£

a

c

©

©l.ot

k_o

©

_3

13

T5

©

T

3

©i-©

Iai

l.o

a

o

©

©

c

o

a©

©

0*»— ©

>

©

"cc

*-> O)

5

1 o

GO

erf

o4-» ©”_Q ©

-D © O

O

k_ O

% o

o x; O a

O O O O

N C£> lO

t

i

r

® j 3

£ O D

a>«- w

.£ c in

>> © *”

Is ® II © ^ > a» o

©

JZ- D

09 JD

CO

o

o

18 o

01

X)

o

z

>"0

»= ®

© t= >

1

o o

CO CM

O O

i- CM

O

CO

o o o o

Tf in co k

oa AWV

A-45

Figure

4F.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#3

using

broad-band

Wratten
Standard

digital

levels

(SDL):

R

=

15,

B~OQ,

G

"15

R,

B,

G

-

Digital

level

for

red,

blue

or

green

phosphor

r, b,

g

-

Color

calibrator

response

of

r, b

or

g-fiStered

photodiode

r

£ a o

co c C lO

© n

03 fe- 11 > o> o

Os n

0)©

08c©

JCo

oa a^v

A-46

Figure

4F(a).

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#3

using

broad-band

Wratten

filters

and

a

Fresnel

lens
+1

TDL

+2

TDL O

N>

©

-Q

Q

0.H »

I® 8 ^ X-X

_lQ

1-

CM1 ©

p. i o

•=®

CC k- > I 1

50

O

CD o

CO

05o

II oJo

N.

oa aw

v

A-47

Figure

4C.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#4

using

broad-band

Wratten
o

ho

CD

O

ID

O o

CO

o

CM

O O

t- CM

O

CO

O o

ID

O

CO

O

hoa awv

A-4 8

Figure

All.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

//

5

using

broad-band

Wratten

filters
"i r

Q

CD

a>>© ^o

Z 11 CO o

05 O

T3 O

TD ii

>- CD

CO . "o co 2 II CO CE

©

.2

n

TJ

©

«

>_ O

<c "5

#-» Q.©

©

<0c

o

a

© ©

© T3

*“ O

°I

2 o

•§ a

COO O

©

; o» •- o

1 c

o 8

CD a>

- k_ CC o

o

o0

105 O

n -o

ia>

co+

CM+

Q

I-<0+

_lQ

H

9

A

» <d

- ©

-Q a»

. c

i_ «

Q

t-CM

I Q

t2-1-4

£ Q Q

o*- w

c c CM > ® O

© £ » > o o

~ D

a .q >

3

a

if) o

o

ii o

II 1 4I 1 1 1 1 L i 7 ' > i i o o o

CD If) O o o

00 04

O O O

r- 04

O O O O O

oo ^ m co h0Q Awy

4)U

3

QC

A-49

Color

calibrator

difference

voltages

for

each

RBC

color

in

WIL

06

using

broad-band

Wratten
Figures 5A-C. GaAsP Photodiodes With Dichroic Filters

Single Color Tests Figure No.

Red (R) 5A

Blue (B) 5B

Green (G) 5C

Description — Color calibrator voltage readings

level (TDL) setting for the R gun (figure 5A) , B

(figure 5C) , starting from TDL = 00 to TDL = 15

(mVDC) for each test digital

gun (figure 5B) , and G Gun

(i.e., 16 steps), for each

gun of the RBG photodetectors in the color calibrator head.

A-50
140

to

co

r—

CNJ o

O)

00

N.

CD

in

CO

CMo

LU>

LU<

I-go

CO

LU

OQ AW

A-51

Figure

5A.

Color

calibrator

voltage

vs

test

digital

level

for

CRT's

red

gun
140

LU>

LU<HgQ

CO

LU

oa alu

A-52

Figure

5B.

Color

calibrator

voltage

vs

test

digital

level

for

CRT’s

blue

gun
140

in

T—

''fr

CO

CVJ

o

y—

O)

CO

K

CD

in

tjco

CVJ ooooooooooooo o

o WWrOO)O N(Olfl't(OW r

LU

>

LU

<

g

o

co

LU

oa aw

A-53

Figure

5C.

Color

calibrator

voltage

vs

test

digital

level

for

CRT's

green

gun
Figures 5D-I. GaAsP Photodiodes With Dichroic Filters

WIL Color Tests Figure No.

WIL #1 5D

WIL #2 5E

WIL #3 5F

WIL H 5G

WIL #5 5H

WIL #6 51

Description — Differential voltages (mVDC) between color calibrator RBG

voltages: a) when TDLs for all RBG guns are set to manufacturer's color

specifications for the WIL number, and b) when unit incremental or decremental

TDL setting changes are made for each gun, one gun at a time. The RBG abcissa

represents condition (a) above and the RBG vertical bars represent condition

(b). The vertical bars are read left to right in the order RBG. B is actually

used only in WILs #1 and #2.

A-54
i ~i—T"

1—

“i n—i—r—

i

Q -JA

o o o

S (D lO

o o o

CO CM 1-

<D £ _i

^s

_JQ

CO

CO >*0 0 b 0)

II > 0

| l 1 1

1 O O o O 0

CM CO lO CD

j

o

N.

oa awv

A-55

Figure

SD.

Color

calibrator

difference

voltages

for

each

RBG

color

In

WIL

#1

using

dlchroic

f

liters
CD If) CO CVJ T- CVJ CO If) CO

OQ AW

V

A-56

Figure

5E.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#2

using

dichroic

filters
i—i—i—

r

o

0

o ®

r k-

"O

®

CLW

O

10

11 0

O 0 o ©

£ *

u> °

T- ©

11 2

CC -Q

O

®

®

T

co

k_o

n

®

(oc

o

a

(0®

o t

w _

© ®

> £ © _©

"co ®

•g .t. 'o .2* =0 Q

”U I

CO 0

o

<o af

o4-* CO !•§

co o

o =5

k. o ^ o

o x: 0 a

1O)

L L

1

TMT", n "I

r

I

I

®_i £ a

.E C

> ®

J= ®

05 > o

o

0

10

V“

11 o

i

A

O

z

1

co®

a

c

cd £

O

J3

O

A

O

-O

®£ _J 4- Q O0

O

II O

a0

0

ii o

i

o

N.

O

CO

O

LO

O o

CO

o

CM

o o o o

U) CO N.

oa aiajv

A-57

Figure

5F.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

//3

using

dichroic

filters
r—r—i—n

r~i—i

i "i—i

i i i—

i

<>"N

00

o

II 0

cT

o

ii CO0

>" o

II -i ~ 'S

Q H 0 O

_co0

>

0

0

>

0

O

JZa0

o

cCa

c

0

0i_05

k.o

0

CM+

T5

0w.0

a>

u.o

00

C

o

a

0

0

o+-> 0

h ® — *0

0 O

iSO jz 0 a

105

= 0 ®

0 4-> :§ ^ Q

o i 0 0

o

0 m n

CD CC vT

J L

—I a

CM

O

b- o -lOo H

CM _ | CM +

1

I

a

i-CM4

1

a

iCM

1

to Q

o>

1 w

.E c co > ® °

a £ li >o)°

£* a

0)1- w

i§§ |ls

I

0

f o

0 »- >

I

o

CD

0)

o

II o

_L

O

K

O

CD

O

LO

O o

00

o o

CM r- O

CM

O

00

O O

lO

o

CO

o

r^

oa aw v

A-58

Figure

5G.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#4

using

dichroic

filters
oa AW7 l-3

oc »H

u.

A-59

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

//5

using

dichroic

filters
oa awv

A- 60

Figure

51.

Color

calibrator

difference

voltages

for

each

RBG

color

in

WIL

#6

using

dichroic

filters
Photodiode

m

10MQ >

AA/V-><1KQ

^4.3KQ

Figure 6. Schematic circuit diagram for engineering model color callbr.it r
NBS-114A (REV. 2-80

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBSIR 84-2924

2. Performing Organ. Report No

4. TITLE AND SUBTITLE

Color Calibrator for RRWDS Remote Radar Weather Display System

5. AUTHOR(S)

Jim L. Heldenbrand and Louis G. Porter

Publication Date

August 1984.

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

Mod. No. 1

8. Type of Report & Period Covered

NBISR 7/84-6/84

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP)

Federal Aviation Administration

800 Independence Ave., SW

Washington, DC 20591

10.

SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

A color calibrator was designed, fabricated, and evaluated with a remote radar

weather display system (RRWDS). This report describes the feasibility of an inexpensive color calibrator based on three photodiodes encapsulated with special

red, green, and blue color filters to detect light from the phosphor colors

used in the weather intensity levels. Further development of the color

calibrator is recommended to produce a "true" colorimeter, which could measure

chromaticity directly in terms of the C.I.E. coordinate system.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Calibrator; chromaticity; color calibrator colorimeter; CRT display; display

luminance; radar; RRWDS; weather radar; weather display.

13. AVAILABILITY

Uni imited Qc] For Official Distribution. Do Not Release to NTIS

H Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

80

15. Price

USCOMM-DC 6043-P80