J

Investigation by:

Mo Gilbert

Report written by:

M. Gilbert

RESEARCH DEPART1ffiNT

COLOUR. ACUITY

(SECOND INTERIM REPORT)

Report No. r1'o035 Serial Noo 1952118

/-'-r9~( -I"" A\.'/,(~~· r

-" (Wo Proctor Wilson)

REPORTlfO. T.035

COLOUR ACUITY

(SECOND INTERIM REPORT)

Section Ti tle ~

SUMlvlARY - - - - - - - - - - - - - - - - 1

INTRODUCTION - - - - - - - - - - - - - 1

1 APPARATUS - - - - - - - - - - .~ - - - - 2

2 CALIBRATION - - - - - - - - - - - - - - 4

3 PROCEDURE - - - - - - - - - - - - - - - 5

4 RESULTS - - - - - - - - - - - - - - - - 6

CONCLUSIONS - - - - - - - - - - - - - - 8

REFERENCES - - - - - - - - - - - - - - 10

Tl'.BLBS 1 to 3.

FIGS. 1 to 3(b).

-- --- 000-- --

Research Department

SUMMARY

REPORT N9 .?-'.~Q35

(Serial No. 1952/18)

COLOUR ACUITY

(SECOND· INTERIM REPORT)

CONFIDENTIAL

September, 1952~

Fig. Nos. 1 to 3(b).

Acuity to fine detail has been measured with various colour combinations of detail and background. The results indicate that

. acui ty with blue detail or with a blue background is not the same as wi 1;h othe:r colours. })To differenoe was found between red, green and white eit~er fo~ detail or baokground coiour •. The results are compared with those obtained by Jesty t who made a similar type; of measurement over a more limited range, and with those obtained by Bedford, whose e~f~riments were more appropriate to the application of "mixed highs" ~ )

INTRODUCTION

This report deals "vi th a continuation of the experiments' commenced and discussed in an Interim Report on Colour Acuity, B.B.C. Research Department Report No. T.030. In those experiments visual acuitY'was meaoured for coloured letters viewed on black backgrounds and black letters viewed on coloured backgrounds. The results indicated that.visual acuity was similar at comparable lovels of brightness, for combinations of white, red or green with blaok, but in the case of blue with black, howevor, the measuro of visuf'.l aoui ty was e,lways lower than for the other three cases. These results indicated that it would be of value to centinue the investigation and measuro acuity to combinations of ono colour with another colour, such as rod with blue, and green vdth red, e tc.

Jos~§)measUrod acuity to tricoloursro~, groen and blue, each viewod 'Vd th black, using' the brightnass levol for each . colour that it would have as part of a·trioolour mixture synthesizing a white of 10 ft .• lamberts brightness. Hisvaluos. woro:

whiteg rod: groen: blue:

10 ft. lamberts 4.65ft • lamberts.' 4.65; ft. lamberts -0.7 ft • lamberts

and he used an'adapting field of brightn~ss one-thi~d that of tho test object peak brightness. He meast~ed' acuity by me~~s of geometrical test objects which subtonded knovm angles at the observer's eye. His investigation, therefore, was simil0.r in typo to the present investigations, in that 'perception of coloured fine detail was measured. The major part of his work was concerned with black and'white contrast and brightness, howevor, rather than the dotailod investigation of oelour.

Bedfo~a)measured a different type of acuity~ He plaoed two celours, or ono colour and ble,ck, sido by side, so that three- .. quarters of the length of tho'border botween the two was a sharp edge,. but ono",:,Q:un:rter of it was blurred. The subje'cts in tho ,oxpori-,' ment he.d to state the dist.ance e.t which the, di£forencebetween the blurred cdge and thesharpedgo could no longer be distinguished. Acui ty was then definod in terms of the' angle su btendod at "liho eye by the width of, the "blur"~ , This e.cUity is diroctly applicable to. 'the problomof "mixod highs" in colour tolevision, with' which Bod-ford Vi/'as concerned :tn his 'measuroments.

The fundamental data. that arc requirod when considering the pos.sibili ties of "mixed highs" are relatod to the percoption of colour in the fine detail, rather than the perception ef finedotail which is colourod. 1:~en colour cc.n no longer be perceived in a small object or ontho border between two objocts , it can be replaced' vdth a neutral hUQ, of equivalont brightness. When coloured fine detail can no longer be porcoi ved as a small object ,then it necd, not be transmitted at all~

The preliminary investigation inte acuity to coloured fine detail indicated, however, that colour does'influenoe ncuity in some circumstances, and it wns fait desirable to' isolnte md mensure this r.sPOct in order to determine what rell'.tionshipnnd influenco

. it might have 'ontho other aspect, that of po roe pt ion of colour in fine detail. The measurement of acuity to coloured detail in itself will not hr.ve. n direct bearing on the possible s0-ying 9f bl'.ndwidth by such methods as "mixed highs"; Howevor, tho results win bo applic~ble to systems in which frequoncy division multiplex is used for the transmission of the colour sig~als.For such systems the tote.l bandwidth may bo reduced by subdividing the b.l'.ndwidth roquired for the individual colour signals in accordance with measured

acuities o The results may also be 'of v8.1ue in the design of scones for transmission. In particulnr, thoy may influence the oolour of onptions and backcloths in colour televisio:n.

10 APPARATUS

Tho apparatus is a Slightly modified version (Fig. 1) of that

; .. "

3

used for the earlier experiments. A white screen contnined an apertureS"x 6" uniformly illuminated from the rear by tungsten lamps inside a box with an opal perspex face. TIle screen itself was fro~t-illuminated by the light from a projeotor, a lantern slide wi t~n blaok mask enabling an image to be thrown on to' the screen so that an area approximately 26", x 26/1 Vlttg, uniformly illumin-nted, but the centre aperture did not receive any light from this sdurce. A second projector was arranged to throw a beam of light iqto the centro,ofthe aperture to illuminate froll,l tAe front the letters of. any tos't chart inserted there.. Care was' taken to avoid any light from this'source being directly reflected back to the subject from the opal f?-oo ,Of the box behind the screon.

The test charts used for those measurements were composed of' rows of whito Snellen type letters painted on to a transparent back-ground. This type of chart was considered. representative of the type of task normally demanded of a viewer. Tho letters were of such a size that 'when Viewed by a subject at 10 ft. the angles sub-tended by the fine detail in each line wero 2.0, 1.5, 1.0. 0.75, 0.5 and 0.33 minutes 'of arc respectively. Six different charts wore used during the observations, to minimise the chances of sub-jects memorising tho letters .. With the exc,eption of the two largest lines on the charts, each line was composed of eight letters which were used in different combinations :for the corresponding lines of each chart, to ensur~ equality of stand~rd.

Tho amount of illumination falling bnto the letters from the . second projector was adjusted by means ofa Variac transformer regul(l~ting: the projector lamp voltage. Coloured filters placed in front of the projector lens controlled the apparent colour of the ' letters. Dufay-Chromex tricolours red, green and blue were used. In the case of white lettors,a diaphragin vias used to reduce' the' amount of light from the lemp'at lower values of illumination, in order to maintain a fairly const'e..nt colour temperature of approximately 29000 K. ,The illumination" from this source, that fell on to the trans-parent portions of the" chart, was mostly transmitted' by it and partly reflected by it at such an ~ngle that it was not visible to the subject.

The amount of illumination transmitted by the clear portion of, the chart from the light box behind it was controlled by means of the number of,sheots of diffusing materip.1 placod in front of the lamps in the box ~ and' to a small extent by' menns of a Variac con.trolling lamp voltage. The colour tomperatUre was again.kept fairly constant. Tricolour red, groen and blue filters, of identical characteristics' to those used for the 'ietter . colours, could also be inserted behind, tho tes·c chart. The '. surround illumination was provided by the first projoctor, and adjusted bf moans of' a Variac regulating the projector

-4-

lamp vol tago and: also by means, of neutral filters, so that - a reasonably constant: coloUr tempera,tura of :the order of 2900

0 K ~~s maintained.

. . . . . Th~s I,t the oolour and brightn~~s -of the le tiers land . background of

tll.o, .test ohart were both variable ind~pendently of ouch other and the brightne,~s of the surround could also be varied independently of the chart. - " ,

The fiel,d of view oonsisted of the test chart ,8" ,x 611 , and a white, surround, 26" X 26"; the bt1ckground of the chart was iilUmin-' ated from tho ren.r, the white, lettors of the che,rt woro illuminated independently of the backgroUnd by a projeotor plaoed to one sido of the subject. Tho surround was illuminl',tod by another' pro jootor ple-ood behind and to ono side of the subjoct.' The angles;subtendod p,t the subject1s eyes, 10ft. from thochart 1 wero: ' '

Chart: ~o 30 ' "t 1 ~ x aro (-!'PPJ;'onma e y

'Surround: 120 x 12°'" 11

2 • CALIBRA!!Q!!.

The, variation, of illumination, with ohfJ..ngo of lamp volt ago ,filtc:rs and quantity of diffusing material,' wnf'; mee,.sured,e.,s. before , with an S.E.:f:. photomoter. The trr:.nsm1ssion ourves of ,the trioolour f~lters wore measure~ ,on a,' Unicam spootrol)J.otorp.oter, ('l~nd the resulting tr2..ns-missien of' light from, tho tungsten s,ources cr:.lqulatod. From the values obtained ,it yms possible tf) adjust the variables and, to obtain 1.0, 3.0 and 10.0 ft. lambert levels of illumination- tJ;lrough the tri-colour filters and for "'\:Vhi tell light. An additional chock on the accuracy ,of thelevols wns· avnitable on this modifiod apparatus, by making th~ ,backgroUJ:ld and the lotters·' tho samo colour and adjusting tho illu.mination of one of ,them until the letters mergodwi th thoback-grQund.,~ The voltn.ge nt which this occurrodvms ohaokod wi tll the voltage required for the two' br;i.ghtnossosto bo oqual acoorcling to the S.E.I. cnlibrations. A good measure of p~greoment was found'to exist between the two mO(l,suromonts.

Str(l,y light was pro'sent on the chart be,ckground duo to both the surround illumination nnd to ~ha lotter illurnin(l,tion. The formorwas caused by flara in·the Ions of the projector 1runpo Under the 00ndi tions of those ox~rimonts, it was found to vary in magnitude from O.15~ to 1.5~ of the bMk::ground illumination. Tha strny light from the source of lotter illuminl".tion Wfl.S due to genoral scnttor from the surface of the op(l,l, the, surfl'..ce of the ch(l,rt, and tho letters thomsolves, nnd was found to va:ryfronO.30%to 3.0% of the background illumination. The t?tal (l,mount of scattered light. therefore, novor exceedod 5~ in the very worst cnse nnd was usufl.lly much loss than this value.

5 -:-.

Soattered light on the letters ?nd surroUnd was too small to be measured.

3. PROCEDURE

Eleven of the fifteen subjeots used in the earlier experiments were· availe.ble for' this, oontinuation of the invf3stigation, the details of which are given in Te.ble 1. One subject was oolour deficient protano;Pi~, the .rest,had . normal colour vision. Three subjeots had, spectacies to oorrect refractive error~ in thoir vision.·

A . subject, was seated 10 ft. from the soreen. ,This· was further than would beexpeoted ,in normal viewipg conditions with a 10" television tube, as' represented by. tho 811 x 611 ;'transpare'ncy. OWing to difficulties in maldng sufficiently small whi.t.o letters on the transparenoy, howevor, it'was not prD.ctioable to soat the subjeotat a oloser distanoe. All oombinations of the colours on the baokground and on tho letters were used, e.g. red on blue, blue on blue, blue on red, red on red, eto~ In addition, threo levels of illumination, 1.0, 3.0 r.nd 10.0 ft. lamberts, were used on both, the letters. rmd their b?-okgrounds, in all possible combinations ,for o8,ch of the oolour combine.tions. investigated.

The dete.iled prooedure for assessing. the visual perfor;nanoe of eaoh individual subject'under the various conditions to be investigated was similar,to the earlier method: '. '. . .

A chart, baoked by a filter of the oolour required for investigation as a baokground, was plaoed .in tho soroep. apert1.lre and illuminated to '

, 1.0 ft. leinbert, the surround ~oreen also being of that o,rder o,f bright-noss. A filter of the coloUr required for investigation as a letter colour :was placod ov~r the' e.ppropri'C1te projector lens and the letters illuminatod.to 1:0 ft. Inmbert. The subjeot wc-s seated in a ohair so that. when he leant comfortablYr'.gninst the chf'.ir back, his eyes were

/ 10 ft. from the. cha;rt. .. After nllowing n few minutos to ['.dnpt to that level of ~llumination, the subject road ~s fa~as he oould and the experimenter noted the ncuity to 1/4 chart lino.

The test was' then repeated 'IIn til 3.0 ft. l

.;.. 6

moasure acuity on the oocasions when the background'aud tho lotter illuminations and oolours were the same.

A final set of observations was made with coloured lotters, at 1.0 ft. lambert, 3.0 ft. lamborts and 10 ft. lamberts illumination, viowed on 0. black background and \Vi th a black surround. Thoso might

,bo expected to yield rather different rosu1ts from the earlier experi-ments quoted in T.030, in which the surround was made equal to the letter illumination, so that tho adaptaticin levels in tho two oases are difforent. '

A maY~mum of six oombinations roquiringdifferont charts wore used on anyone oooasion, so 'as to avoid 'usingtho' same chart for two '

different runs on the; same day, thus eliminating as far' as possi ble tli~ effect of memorising. ,\ "

4. RESULTS '

Tho rosu1ts of tho acuity moasuromentsof the eloven subjocts wore nvoragodand Table 2 givos the deta.:i.ls of lwerage acuity for tho various colour combinations. From theso data 1't can be soon that when the bnckgroundcolour is bluo ~ acuity is in:fl:uoncod by changes ot illumin-ation in a rathor different marinor from that in" tho oas'o of othor oolour backgrounds. This differonce, howevor, if! small. The i'nfluenco of illumination on aoui ty whon bluo 10 ttors nroprosonted on any c,olour background is markedly difforent from thoinfluonoo of illumi'niltion on' acuity when any othor colour letters are viewed. Tho difference betweon 'rod, vII'hito andgroen appears to bo nogligi bIo, both for backgroUnds and

letter ,colours, ' The' Mui ties' for those :oolours, thorotoro., havo beon averaged, so that acuity: to rod ,~eon or whi to lotto'rs on red, groen or' whi to baolq;rounds oan bo compared with Mui ty to blue letters on" rod, greon' or Vihi to backgrounds. The case of red, iJ-een or' whi to letiars ,on" bluebackgTounds has alsoboen averaged a~d all tho rosultsaro sho~vn in Tnblo 3.. Results froIl} the ol'u'lier exporimonts using oolour/black '-combinations havo boon inc;Luded for oomparison. Fig. 2 iilustrato's the curvos for all exoept bluo baokgrounds, which hnve boen omi tt,ed as boing differont, 'although not signifioantly so ,from tho rod,' groen or white hackgrounds~ Br'iefly, bltl0 baokgrounds aroslightly botter than tho other colours when tho brightnosses of both lottors p..nd backgrounds are low. The three diniensions of background brightnoss" lettor briglitno~s., and acuity t 'iliustrated 1.n tho' curVOG of Fig. 2, havo boon u~ed to' spocify tho axes of a solid figUro, ~igs. 3(a) and (b), so that tho variation of acuity to blue Md to othor colourod lettors with both the parametors of background e.nd lottor bri,ghtness OM be seen on the surfaces roprosonting the threshold of vision in the two cases. For oxample, to find the aoUity to red 10tters o£ 3 ft. lamborts brightnossona.white bacl~~ound of 1 ft. lrumbert brightness, Fig. 3(b) is required. The value of 1 ft. lambert is found on tho horizontal (background brightnoss)

, '

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axis •. ' ~;loving in the 'plane throUgh this point, ropresont:lng"a plane perpendicular to the pnper, the value of 3 f to lamb0rts (10tter brightness} is found. . A vertical is raised from this peint to the acuity surface. The hoight of this verticnl on the I ft. lambert b8.ckgrOlmd brightness rle.ne is found to be approximately 0~84' arc, anddtbat CM bo it-ken I:'.S a mensuro of acm tyunder tho specified con ~'e~ons.

In general, the curves illustrate that up to I ft. lambert bnckground br.ightness, acuity is lower for blue lottors 1;han for the other colours. At 3 ft. lamberts bnckground brightn~ss this differ-onco becomes negligible nnd at 10 ft. Inmberts acuity tonds to be rather. better with blue letters thnnwith the other colours. Acuity to blue dotr:,il, therefore t depends to every ll'l.rge extent On the baclQSround brightness, and, incidentally, on the level of adl'l.pt-ntion of the subjects' eyesg the surround brightness influencing ['.dnptation was at about the snme level [1.S the background brightness. As the letter brightness tends to low vhlues, the letter colollr will obviously becomo less important and at zoro brightnoss I'l.ll colours must convorge to a common point. This can be seen to happen in the curves illustrating blue and othor colours, on illuminated back-grotmds. With a letter brightness of 10 ft.lnmbertsand a back-ground brightness of 1ft. lambert, the difference in acuity when vio1Fring blue letters and when viewing other coloured letters is 0.47' arc. This difference is allproxiriately 501; of the absolute values of acuity to the letters, in minutes of arc, and is equivalent to a difference of nenrly two Snollen lines. .t'i.pplying the "tiff t.est to this particulnr point, the probability of this difforence occurring by chance is less than o.i%. .

Vv11en the background is' dark, the difference between blue 2nd other coloured letters increl'l.ses ~s the letter brightness docreases, becoming very marked at 1 ft. lambert letter brightness. It is in these conditions thnt some rod receptors might be expected to be operating. This is the type of rocoptor in the eye which operates in twilight cOI').di tions, rmd acuity is poor when vision depends on it. Tho 'rods aro nolO 'sensi ti ve to blUe ligl1tthan the ordinnry daylight receptors normally functioning at higher levels of illumination, and normp,lly used for the perception ,of fine detc..il. . It .may, therefore, be the explanation for the difforence in acuity botween blue and other colour detail at low letter brightnesses viewed on dark backgrounds.

* The "t" test is. a standard statistioal method of determining the significDnco of' the differonce between two vRlues which' (",re tho me2.ns of two distributions, in this case the mO£1.ns of the two s cts of observations of elevon subjects.

-8 CONCLUSIONS

The results briefly discussed above have shovm that between 1 ft. lambert andlO ft. lamberts, all combinations of red, green and white, for detc.il and background are ~qua1.ly visible. ll.CuHy in all cases is substantially the same. In the case lof blue detail or blue b2.ck--ground, however, a difference arises~

When both the detail brightness and the background brightness are low, of the order of 1 ft. lambert, aouity to red, green or white detail is improved if the background colour is blue, rather than any other colour, including white. If the background brightness is. high, however, of the order of 10 ft. lamberts, whilst detail brightn~ss remains lovv, acuity \T.Lth a blue baokground is loss than in the other cases. Tho only difference in acuity vdth blue backgreunds ooours in those two s])ecial instanoes, and ncuity is improved in the former and worsenod in the latter rolativo·toother colour bacl~ounds.

In thocase of blue detail, m'lch greater differences rtrise when backgreund illumination is low and detail brightness is high. Acuity to blue detnil is thon very 10'llY. At intermediate vdues of brtokground brightness, however, tho differonce'becomes very small,and if anything, blue dotail is slightly oasior to seo than any other ooloured detail. It is necess1'1.ry to considqr the 'ordor of brightnesses at which oolours might be o~pected to appear on tho face of atelovision tube. White must bo tho brightost colour it is possiblo to Mhicvo, boce-use, whatever the mothod of synthesizing it on tho screen, it is m~o up of the addi tion of the red, green and blue oomponents. The r elntive proportions of these ~e very roughly 0.413 0.568 0.03, so that for reproduction of the· primnry colours alono, giving tho gro'atest satur-ation possible by the system, red cr,n never bo more than 0.41 times r,s bright ~s white, greon 0.56 times, and blue 0.03 times. If peak white on n scroonwero 15 ft. lamberts, therefore, the brightest fully saturated colours possible would be .

. '. I 1 ' Rod~ 6 ft. lamberts, Greeng ~ft. lamberts, Blue 2ft. la.mbort

. In actual fact, hO'l;vover, the primary colours thomsolves ocour vory raroly, if at ali, in a scene. They are usur,lly dosatur['..ted ,T.Lth white to dit'eator or lesseroxtent, c.nd can thus achiove substantially highor brightnessos. In tho case of .bluo, however, it is obvious that . by the time the brightness has boon incroasodto ['..s much RS 3 ft. 'lemberts by dostituretion with white, .it would be a very paleand.dosaturatod blue inde9d. .I.t wouldap:)elU' rORsonablo to tako a valueo! I ·ft. "lambert as rel)rosontativo of the brightness of Fm avere..ge blue ~ in ordor to consider its visibility from the l)rOsont eXl)orimentaldatA;. In this caso thore is little or no difference "betwoon blue and other colour detail. Acuity will be low, not bec['..use of anyspecifio difference in blue as a colour, but because of the inhorently low brightnesses associated with blue. vVhilst the maximum brightness for blue vdll be

e,

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1 ft. lambert the maximum brightness for other colours or white o~ be up to 10 ft~lamberts. They vdll also occur at btightnesses below the maximum, of course, but acuity normally increases with bright-ness and it is,desirable to consider the case of m~imum acuity rather than the mean case. The eye is attracted to the brightest object in the field of view, and it is desirable that the brightest object should appear to be well defined. Acui ty to a blue detail of 1 ft. le.mbert brightness, assuming a normal background of 3 ft. lamberts, is approximately 0.84' arc. Acuity to red, green or white detail of 10 ft. lamberts brightness, assuming the snme background, is approximately 0.82' arc. The ratio of relative visibility of blue detail to other coloured detail, thereforo, is approximately 0.98g1, which is n.ot significant.

Jesty obtained greater Md si&"!lificant differences in acuity to blue or to other COlours, but he investigated a lowor detail bright-ness (0 .. 7 ft. lambert) on a black background. By extrapolat';.on of the present relevant curve, Fig. 2, bottom curve, the m&gnitude of the differenoe in e.cuity to blue and to other colours is found to be similar to Jesty's findings. Bedford found greater differences in acuity to . the blur between blue and black c.md the blur between other colours 2.nd black.. He also found that Mui ty to the blur betwoel. different colour combinations varied vdth all the colours, including blue, and these differences arc presumably due to the different parameter that he was measuring, with "mixed highs" in mind. The present'results indicate. that the possible saving in bandwidth in ? throo-chnn:t1.el syst~m, of colour transmission, duo to differences in aouity to fine detail in colour, is negligible. The main valuo of these results would apPOar to be- directed more towards influenoing the design of a soeno to be trnnsmitted in colour effeotively. The results alse indicate that differences in aouity to colour in fine detail arc greater than differences in acuity to fine detail in colour.

];IG/DC

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REFERENCES

'(1) Bedfo-rd,A.V., . 1li~ed Highs in Colour TeleVision. Froc. LR.E., VI 38, p. 1003, 1950.

(2) Jesty, L.C., and Phe1p, N.R., The Evaluation of Picture Quality with special reference to TV Systems. . Parts I and II, Marconi ReVieW', v. XIV, Nos. 102 and 103, . 1951. .

- I

Subject

B

C

D

E

R

I

J

re

L

Q

Report No. 'r.035

TABLE 1

DETAILS OF VISION OF ELEVENSTJBJ:illCTS lflAlITNG OBSERVATIONS FOR COLOUR l .. CUITY

Standard Snellen Acuity l'Iea.sllreci at 20 ft.

Daylight Illunination )0 ft. lamberts

6/6 = loO' arc

(1/4)·6/3 = 0.60' " 6/4 = 0067 ' If

(1/2) 6/4 = 0.83' 11

6/4 .: 0.67' 11

6/4 = 0.67' 11

·6/4 = 0.67' 11

(3/4) 6/4_ = 0.75' "

(1/2) 6/4 = 0.83' 11

(1/4) 6/4 = 0.92 1 fI

Type of Vision

Ast:j.gmat ( corrected)

Emmetrope

!I

" n

11

"

n

Astigrnat (corrected)

Myope «

Emmetrope

Number of :Mistakes made on Ishihara Test

2

0

1

0

3

1

22 (protanope)

5

0

2.

0

Report No. T.035

TABLU

MEAN VALUES OF ACUITY OF ELEVEl'i SUBJECTS VIF~\iING COLOURED LETirERS

ON COLOURED BACKGROUNDS

(Viewing Distanoe 10 ft.)

Background Brightness&- 1 3

Letter Brightness8-

Baotsground Letter

Colour Colour

(White

\Filii te Green ted (Blue

(White (Red

Red (Green ( (:~lue

(Vfui te , (Red

Green (Green

~Blue I

(White (Red

Blue (Green

~]lUC

~)

1 3 10

0.84 0.78 1.09 0.81 0.80 1.19 0.86 0.78

1.26 1.33 1.29

1.26 0.90 0.80 - 0.82 0.80

0.95 0.81 0.78

0.94 1.02 1.04

1.15 0.84 0.18 1.00 0.83 0.76

0.86 0.81

1.11 1.27 1.44

0.89 0.82 0.79 0.86 0.83 0.81 0.81 0.810.81

1.28 1.09

---1 3 10

1.01 - 0.81 0.95 0.98 0.85 0.92 1.02 0.82

0.83 0.85 0 .82

1.12 1.03 0.81 1.08 - 0.81 1.11 0.90 0.80

0.82 0.82 0.80

1.01 1.11 0.78 0.98 Q.95 0.80 0.91 - 0.86 0.87 0.86 0.89

0.94 0.82 0 • .79 1,,00 0.830.81 0.90 0.83 0.80

1.04 - 0.94

10 ft. lamberts (r------:. 1 i 10 ft. lamberts

0 .. 77 0.80 -0.79 0.78 0~89 0.80 0.83 0.89

0.78 0.78 0.78

0.85 0.90 0.86 0.83 1.05 -0.84 0.92 0.85

0.77 0.76 0.77

0.82 1.01 0.81 0.82 0089 0083 0.83 1.02 -0.81 0.83 0.82

1.01 0.89 0.80 0.99 0.88 0,81 '0.97 0.83 0.78

1.05 1.08 -All figures are minutes of arc subtense at the subject's eye. Acui ty, therefore', improves as the minutes ef arc subtenso

decreases for just discernible detail.

Report No. T.032

TABLE 3

AVERAGED Vii-LUES OF RED, GREEn MID WRITE LETTERS ON RED, G~.,;Jl})lJ! WHITE .6lrD BLUE BLCICGROUN"DS!

1J.iTD 1,V.illRAGED V ALlJES OF BLUE LETTERS Ol-T _RJ]D, GREmTlllfD 'WHITE Bl~CICGROmIDS

Bacl~ound Brightness~-

Letter Brightness~-

Letter Colour Background

Blue Red, Red, green, white Red, Red, green, white Blue

Surround Brightnessg-

Background Brightncssg-

Lotter Brightness3-,

Blue Lettersg ~11 Other Lotters:

Background Brightnessg

Black Letters g

green, green,

Colour

white \lhite

1 ,........---# .---" 1 3 10

1.10 1.21 1.26 1.11 0.84 0.79 0.87 0.82 0.80

3 ('----:-)

1 3 10

0.84 0.84 0.84 1 .. 02 1 .. 00 0.82 0.95 0.83 0.8:>

10 (--~

1 3 10

0.79 0.79 0.79 0.82 0.90 0.86 1.00 0.87 0.80

From Interim Roport

Equals letter brightness Later Measurements

Equ~ls background brightness

0 0 o ft. lambert 0 0 Oft. lambert 1 3 ·10 ft. lamberts 1 3 10 ft. lamberts

.1.38 1.10 0.95 1.28 1.03 0.94 0.94 0.84 0.74 0.88 0.85 0.82

1 3 10 ft. lamberts

1.13 0·97 0.82

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ADAPTATION LEVEL AND

BACKGROUND BRIGHTNESS (ft. lamberts)

MEA~J RESULTS '")F BLUE LETTERS ON RED OH GREEN OR WHITE BACKGROUNDS, SHOWN AS A SOLID FIGURE.

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FIG 3(b) RESULTS OF RED OR GREEN OR WH ITE LE TTERS

OR WHITE BACKGROUNDS, SHOWN AS A SOLID

ADAPTATION LEVEL AND

BACKGROUNDS BRIGHTNESS (ft. lambert')

ON RED OR GREEN FIGURE