confusing color concepts clarified the physics teacher

8/13/2019 Confusing Color Concepts Clarified the Physics Teacher

1/4

THE PHYSICS TEACHERPublished by theAmerican Association of Physics Teachers April 1999Volume 37 / Number 4

,?ragerrsaaGD t &aE

Pr*'r1{rr.r c{rlorr .}$ Li$fr*: RED, cnEEN, SLarEsc.c.,nd,,ry coro+u, cydn, mdgcna, YellauELAE

I'R I ]IT I llG/FAI II?I IIG

NACEI{74

btaa(cvrn & xtcaxtanFlirlt.rry tal{}r{s G, *rr'i*i,,lgt?,,ir.*i$ar gyex, nuGExTe, YELLowscf,'r,.&sy corcl* Fcd, grean, blse

YELLOIfl

\\\\\1\\\1

,IItIItIII


2/4

confusing color concepts clarifiedLawrence D.Woolf,Sciences Education Foundation-General Atomics, san Diego,cA92121;Larry'woolf@gat'com

tudents studY color conceptsstarting in elementarY-schoolart classes and continuing in

advanced art, printing, computer sc1-ence, and/or physics classes. Yet, theprimary colors, comPlementarY col-ors, and the color wheel that aretaught are often different. The identi-fication and clarification of thesedifferences and some hands-onexperiments that elucidate these colorconcepts are described here' Theapproach expands on that of a previ-ous TPT article.lAdditive Colors

PrimarY colors are defined bY twocharacteristics2: (1) No combinationof two primarY colors can Produce athird primarY color; and (2)Combining the three primary colorscan produce a wider range of colorsthan using any other three colors' Theprimary additive colors of light aregenerally, and correctly, discussed inptrysics texts to be red, green, andtlue. Additive color mixing can bedescribed using "color math" asfollows:

Green + Blue = Cyan (l)Blue + Red = Magenta Q)Red + Green = Yellow (3)These relationships can be verifiedby students by examining how colors

are made on a computer screen usingan 8x magnifier.At this stage, the relationshiP ofcolor mixing to the color wheel canbe made. If it is not, then the colorwheel may be viewed as a model that

describes color for artists, butdoes not have anY relationshiPto physics. In fact, a simPlecolor wheel that models Eqs'(1) through (3) is easilY gener-ated. In the color wheel shownin Fig. 1, Yellow light isbetween red light and greenlight, because it results fromthe mixing of these colors oflight. SimilarlY, cyan isbetween green and blue, andmagenta is between blue andred.Students can also investi-gate with a magnifier howwhite is produced on a com-puter monitor: the white back-ground actuallY consists ofsmall red, green, and bluelights. Using color math, wecan write these results as:

Red+Green+Blue= White @)The concePt of comPlemen-tary colors also can be demon-

strated using the color wheel aswell as color math. Com-plementarY colors of light arethose two colors that whenadded together Produce white'Now it is quite easy to see that,for examPle, Yellow and blueare comPlementarY colors oflight:

Yellow + Blue= (Red + Green) + Blue- White (5)

magenta

yellow

BLUEFig. 1 . Color wheel lor additive color mixing' The primarycolors are red, green, and blue.

YELLOW

blueMAGENTA CYAN

Fig.2. Color wheel lor subtractive color mixing'Theprimary colors are cyan, magenta, and yellow'

YELLOW

purpleRed and cyan are arso com- ili;l; IlSil[1,1,,1il:'ffr::L:'-heer'The primarvplementarY colors, as are green

204 Tse PHvstcs TeacueR Vol. 37, April 1999 C*G*S Cotor Conce1ts Clarifi


3/4

and magenta. The color wheel pro-vides a nice way to view complemen-tary colors: they lie on opposite sidesof the color wheel.Subtractive Colors

The primary subtractive colors arecyan, magenta, and yellow. This isgenerally correctly described inphysics texts and is also well knownto printers. But if you ask an artist orlook in art books, the primary colorsof painting are red, yellow, and blue.This inconsistency is rarely addressedby either physics texts or art books,leaving the misconception that some-how primary subtractive colors inphysics or printing are different fromthose of painting.

Subtractive color mixing can alsobe described using "color math"using the following two steps. First,White-Red=Cyan

(Cyan pigment) (6)White-Green=Magenta

(Magenta pigment) (7)White-Blue=Yellow(Yellow pigment) (8)

These equations demonstrate that,for example, we see the color of an

object as cyan because it subtracts asingle primary color of light, namelyred, from the incident white light.The primary subtractive colors areso-called because they subtract one ofthe primary colors of light from theincident white light.Subtractive color mixing occurswhen two primary subtractive col-ored objects overlap (denoted belowby the symbol "/") so that both

objects subtract colors from the inci-dent white light. Therefore, this canbe written:White-Red-Green=Blue(Cyan/magenta pigments) (9)White-Green-Blue=Red(Magenta/yellowpigments) (10)White-Blue-Red=Green(Yellow/cyanpigments) (11)For example, Eq. (9) represents acyan object overlapping a magentaobject (cyan/magenta). In this case,the cyan object absorbs the red lightfrom the incident white light, whilethe magenta object absorbs the greenlight, so that the object appears blue.A color wheel that models Eqs. (9)through (l 1) is again easily generatedand is shown in Fig. 2. For example,Eq. 9 indicates that mixing cyan andmagenta pigments produces blue. Soin the color wheel, blue is betweencyan and magenta. Similarly, red isbetween magenta and yellow, andgreen is between yellow and cyan.The concept of complementarycolors can again be demonstratedusing the color wheel and color math.

PiiYSlc$Now in 2nd EditionGet hooked r lE.

A one semester textbook | -4' Pl

;iir$rd trA Problem-Solving Approach illustrated bvJesse David WallElender WallAnalog Press225 Edna StreetSan Francisco, CA 94112phone (800) 223-1974(415) 239-2338fax (415) 587-4268email: analogp @ ibm.net

Experiments for Physics Labsby Herbert H. Gottleib

lab manual for high school and preparatory physics

IED IITEEII ILUEIYAII IAGEX?[ t--ltlrVELL.,WFig.4.Confusing Color Concepts Clarified Vol. 37, April 1999 THE PHysrcs Tencsen 205


4/4

ComplementarY colors of Pigmentsare those two colors that, when over-lapped, produce black. It is apparentthat yellow and blue are complemen-tary subtractive colors, since yellowpigment absorbs blue light and bluepigment absorbs red and green light:

White - blue - (red + green)= White - (red + green + blue)= White - white = black(Yellow/blue Pigments) (12)Red and cyan are also comPle-mentary colors of Pigment' as aregreen and magenta. Again, comPle-mentary colors of Pigments lie on

opposite sides of the color wheel'Except for the switching of theprimary colors from red, green, blueto cyan, magenta, Yellow, the colorwheel for light (additive colors)shown in Fig. 1 is the same as thecolor wheel for pigments (subtractivecolors) shown in Fig. 2l (Also seecover of this issue.)Color MisconcePtions

Many factors contribute to contin-ued miiconceptions about color'3-6Art books may confuse additive pri-maries with subtractive primaries, orconfuse mixing light with mixingpigments.T But perhaps the most sig-nificant one is the incorrect colorwheel that most artists use and towhich most students are introducedin elementary school. This traditionalcolor wheel was used bY Goethe asearly as 1193.3 It is still used' appar-ently because it is sufficiently suc-cessful in describing color mixing,and because of its widespread accep-tance and Persistence in currentteaching materials. The long historyand variety of color wheels and mod-els are described in a number of pub-lications.3-6In the traditional color wheel (Fig'3), which is used for painting, the pri-mary colors are red, Yellow, and blue;these colors were chosen apparentlybecause of their vivid distinctness'8 Itshows that mixing red and Yellowproduces orange, mixing blue andyellow produces green, and mixing

red and blue Produces PurPle, asshown by this color wheel. There aremany ways to demonstrate that thiscolor wheel is incorrect. ComPle-mentary colors should lie across fromeach other on the color wheel-in thetraditional color wheel, they don't'Red, yellow, and blue are stated to bethe primary colors (of paint or pig-ment). Recall that a PrimarY colorcannot be made from mixing twoother primary colors. Yet, a red pig-ment can be made bY mixing Yellowand magenta Pigments and blue canbe produced bY mixing cYan andmagenta pigments. So red and bluecannot be PrimarY colors of PaintAnother difficulty in demonstrat-ing color mixing is the lack of com-mercially available materials withcorrect optical properties. Whilecolor paddles or films are availablefrom a number of vendors, none ofthem are of the correct color to easilydemonstrate the desired color mixing'For this reason, the author developedfilms and other color mixing materi-ais with the correct optical proper-ties.9 Comparable colored films canalso be made bY Printing large red,green, blue, cyan, magenta, and Yel-1ow rectangular colored areas (seeFig. 4) on ink-jet transparency paperuring u, ink-jet printer.l0 The use ofthese films clearly demonstrates thecolor mixing properties and comple-mentary colors previously discussed'The naming of colors also con-tributes to confusion. Cyan is oftencalled blue, because it appears to be alight or sky blue. CYan is often notused because the word is not in com-mon usage. Magenta is often calledred. Therefore, a printer may be usingthe colors of cYan, magenta, and Yel-low, but will call them blue, red, andyellowl

The sensitivitY of the human eYeto different colors also is a source ofcolor misconceptions. We do not eas-ily distinguish the color cyan fromthe color blue. Magenta and red arealso seen as similar colors.Further information about theseand related experimentsl0 and associ-ated materials9 are available from the

Sciences Education Foundation-General Atomics.llAcknowledgmentThe author would like to thankWendy Woolf for Provoking thisinvestigation and for many informa-tive discussions.References1. L. Parsons, 'As easY as R, G,Bl' Phys. Teach. 36,347 (SePt'

1 998).2. G. A. Agoston, Color Theoryand lts APPlication in Art andDesigrr (SPringer-Ver1ag, Ber-lin. 1987). PP.4445.3. F. Gerritsen, Et'oltrtion in Color(Schiffer Publishing Ltd., WestChester, PA, 1988).4. F. Gen:itsen, Color Res' APPlic'4,33 (1979).

5. F. Gerritsen, Colttur 7 j, SurvelLectures and Abstracts of thePapers Presented at the SecondCongress ttf the InternationalColour Associatiott (WileY,NewYork, 1973), PP. 494498'6. C. Parkhurst and R. L. Feller,Color Res. APPlic. 7 ' 217( 1982).7. O. G. Ocvirk, R' O. Bone, R' E'Stinson, and P. R' Wigg, ArrFundamentals Theory andPractice (Wm. C. BrownComPanY, Dubuque, Iowa,1968), P. 89.8. J. Itten, The Elements of Color,(Van Nostrand ReinholdCompanY, New York, 1970), P'29.9. www.sci-ed-ga.org/modules/materialscience/color/materials.html, item GASEF#001.

10. L. D. Woolf, "It's a ColorfulLife," available throughwww. sci-ed- ga. org/modules/m aterialscience/col or/materials.html, item GASEF#006.

11. P. Winter, Sciences EducationFoundation-General Atomics,San Diego, CA 92121; 619-45 5 -3335; FAX 619'45 5 -33'7 9 ;e-mail: Pat.Winter@gat'com;website: www.sci-ed-ga.org'

2OG .Tue Pnvstcs TrncHeR Vol. 37, APril 1999 Confusing Cotor Concepts Clarifie

confusing color concepts clarified the physics teacher

Documents