FoNnazroNpGroncro RoNcHr ,r.@, Studio Art CentersInternational Palazzodei Cartelloni

D. HOCKNEY,J.TSPIKE, S. GRUNDY, R. LAPUCCI, F.CAMEROTA, C.M. FALCO, C. PERNECHELE

PaintedOptics Symposium Re-examiningtbe Hockney-Falcotbesis 7 yearson

Florence, September7 -9, 2008

Via San Felice a Ema 20 501.25Firenze, Italia http://ronchi.isti.cnr.it Firenze 2009 Ibn al-Haytham'sContributions to Optics,Art, and Visual Literacy

CHARLESI\4, FALCO, AIMEE L, \(EINTZ ALLEN C')

Introduction

In his book, Seuet Knowledge:rediscouering tbe lost tecbniquesof tbe old Masters(2001,2006), the artistDavid Hockney reported visual discoveries within someof the bestknown European paintings that affectlong-held understandings of the developmentof westemart overthe courseof the past600 years. Subse- quently,a collaborationcombining the visualskills of oneof the world'sgreatest artists(Childers, 1996; Langmuir & Lyrrton,2000) with the analyticalskills of an opticalphysicist (Charles M. Falco),resulted in Hockneyand Falcodeveloping the foundationsof a new methodologyfor extracdnginformation from complex, optics-basedimages (Hockney & Falco,2000,2004, 2005a, 2005b, 2005c). As will be discussedin this paper,this methodologyalso contributes to our burgeoning understandingof visualliteracy. Visualliteracy is not limited to the naffativeand symbolicqualities of pic- turesand images (Duncum,2001; Hockney, 1998), but it is alsorooted in the sci entificand culturalstudy of opticsand the visualsystem (Edgerton & Steinberg, 1987;Greenstein, 1997; Grootenboer, 2007). As we will discuss,the genesisof this conceptcan be tracedto the work of the 11'hcentury Arab polymath,Ibn al- Haltham (LatinizedAlhazen or Alhacen),rvhose scientific exploration of vision significantlyimpacted the studyand practice ofvisual art, as well asour cognitive capacityto interpretit.

Historic Theoriesof Vsion

During the first two centuriesofthe IslamicGolden Age (8th-1Jthcenturies), translationof ancientwritings on the scienceof opticsoffered contemporary in- tellectualswith variousphilosophical theories of vision.Euclid, Ptolemy, Galen

(n) CollegeofOptical Sciences.University ofArizona, Tucson8J721 USA T

116 C.M. Falco,A.L. \N/etutzAllan and Aristotle, whose Greek texts were hanslated into Arabic dudng this period, provided disparateviervs on the way the organ of the eyereacts with light to aid in vision. Greek theorieswere largely appropdated by Islamic scholarsuntil the first quarter of the 11ihcentury, when a new method of inquiry rvasintroduced by Ibn 'scientific al-Haytham. Vith the method' he introduced to the rvodd, al-Haythanl used experimental evidence to develop a remarkably accurate theory of vision. His design and interpretation of elegantexperiments became the root sourcefor 'Westernunderstandings ofoptics up to the 17thcentury (Lindberg, 1967). Born in Basra in 965, Ibn al-Haytham primarily worked in Cairo's al-Azhar Mosque - an epicenter for academic inquiry - where he wrote prolifically on subjects as diverse as poetry and politics. He is primarily known however, for his writings on geometrical optics, astronomy, and mathematics.His landmark sevenvolume treatiseon the human visualsystem,Kitab al-Manazir lBook ol Oy> ticsJ,published sometime between 1028 [418 A.H.] and 1018 [429 A.H.], u.as incorporated throughout the core ofpost medieval\Western culture. This seminal work initiated an unbroken chain of continuous developmentof the modern un- derstanding of both optics (i.e. science),as rvell as understandingsrelated to two dimensional pictorial representationsof three dimensionalspace (i.e. art).

FrG.1 lbn al Hattham's descriptionof the human visualsystem. From a copy othis Kitab al-Manaztu108i [175 A.H.] in the SiileyminiyeLibrary, Istinbul. Ib n al-Haltham's Cofttibutions. Ill

Frc. 2 The anatomyof the eyeaccording to Ibn al-H^yrh^m, horn Ki/abal,ManziL MuseumVictoria.

Prior to thework oflbn al-Ha1tham,theories ofvision could be broadly clas- sifiedinto oneofthree categories:extramission, intromission, or a combinationof the two. Extfamissiontheories require that somesort of illuminatingparticles be emittedby the eye.Euclid and Ptolemyare well-known scholars associated with this category(Linberg, 1981). Although there are obvious flaws with extramrssron theories,they do get the geomeryright, with a one-to-onecorrespondence be- tweenpoints on the objectand points on the eye.Intromission theories, with Ar, istotleas a prominentproponent, postulated that objectscontinuously sloughed off microscopicallythin replicasof themselvesthat then travelledto the eyeof the observerIntromission theories avoid some obvious problems of extramission theories,such as near and far objectssimultaneously being visible the momentthe eyeis opened.A third alternative,supported by Platoand Galen(and Aristode, to a lesserdegree), combines the trvotheories, proposing that light emittedby the eyeengages in someway with the interveningair and aforementionedreplicas, or species(Lindberg, 1,967 , 1981,). Like othersbefore him, Ibn al-Haltham also recognizedthat therewere problemswith all existingtheories of vision,but he viasuniquely successful in findinga solutionthat hadeluded the bestminds of antiquity.He proposeda type 118 C.M.Falco, A.L. \VeintzAllcn of intromission theory ofvision, and validatedhis cor.rclusionsby empirical under standing deduced from scientific experimentation, This methodology expanded his understanding beyond the theoretical,which resulted in the incorporation of psychology to explain vision, in combination with the behavior of light and the physiology of tl.reeye.

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Ibr.r al Haytham also linked sight and vision with the properties of light throughout his studies.His experimentssubsequently verified scienti6cprinciples conmonly associatedwith what is known todayas optical'ray tacing'. Theseex' periments included using flat and curved mirrors to control and manipulate light, but primarily involved obseruing the effect of light pouring through aperturesof varioussizes into dalkenedspaces (i.e. camera obscura) (Smith,2001a, 2001b). Perhapsmost inrportantly, they provided him a theoreticalbasis for the existence of rays; a theoretical construct that he used as a meansfor describing and inter preting the visualsystem.These lays are subsequentlyrepresented by geometrical lines associatedon a point by point basisu'ith an object in space. Al Haytham did get one important aspectof vision l'rong: the fact that an image projected by a lens is upside down and flipped right-toJeft apparently rvas more than he could acceptin a theory olvision, eventhough it is containedrvithin his optical fornalism. Leonardo da Vinci also failed to accept this when he ap proached the problem much later (Kemp, 1977).Ultimately, it rvould take another live hundred yearsbefore Kepler would follow Ibn al Haytham's formalism to its inevitable and logical conclusionin developing the theory of the retir.ralimage. Smith (2005) poir.rtsout that such contasting theo es of vision in the pre ceding centuriesbefore Kepler had profound epistemologicalimplications on me- dieval culture. The Platonist perspectivistssupporting extromission,for exampie, suggestthat the eye has powers which extend outward as a meansfor engagrng reality rvhich, in a general sense,can be understood as a "r'isual finger reaching out to palpate things" (Smith, 2005, p. 223). Intromissiolr theories howeveq are uniquely Aristotlian. They ascribe to the idea that, "Knowledge is inductive... lbn al Haytham's Contribrtions. .. I19

Sensationand its representationsare therefore not to be deprecatedas the bearefs of falsehood(Platonism) but ratherto be prizedas the bearersof tuth" (Smith, 2001,p. cx). Perhapspredictably, as cultural understandings of visionard cognitionex pandedto includethese disparate theories, so too did evolvingcultural consid- erationsfof conceptsseemingly unrelated to the scienceof optics,the impactof whichwas not relegatedto the sciencecommunity alone but spreadout to include the humanitiesat large.

3. Interdisciplinary disseminationand appropriation of Kiffib al-Mdndzir

Thereis little debatethat Ibn al-Haltham'sseminal work, Kitab al-Manazir, translatedinto Latin asDe Aspectibus In theearly to mid-1.1th century, is largelyre, sponsiblefor the widespreadappropriation of its contentsby \WesternEuropean intellectuals(Lindberg, 1967). Smith recognizesthat variationsexist among the Latin versionas compared with theArabic original, not simplyin its organizarion- al sructurebut in theinterpretation of specificterms (2001). From thebeginning, however,knowledge of the coreprinciples and experimentsdetai.led throughout the manuscriptby its originalauthor were not limited to lWesternreaders alone, or to scientificaudiences specifically. De Aspectibusis first referencedin Bartolomeo Anglicus'De proprietatibus rcrun,lOn thePrcpertyof Thingsl c1220-1T0(Smith.2001), a monumentaland earlyencyclopedia covering a widevariety of subjects.The text refersto the study ofoptics andIbn al'Haythamspecifically several times. It wasrequired reading at the Universityof P arisin 1296,avatlable in the universitylibrary of the Sorbonne by 1306,and usedwidely as referencematerial at Oxford, Cambridge,Canter- bury andMerton Collegeby the mid-fourteenthcentury (Holbrook, 1998). Specificproposals contained withn De Aspectibzzshowever, are most sig nificantly referred to in the well known optics manuscriprs, Perspectiuaby Roget Bacot (c7268),Perspectfuaby EruzmusWneIo (c127 8), andPe$pectiua comnxunis by John Pecham(c1280) (Lhdberg, 1967).Although today we thhk of these scholarsas optical scientists,they approachedtheir work astheologians which, in turn, influencedtheir interpretationof medievaloptical theories. Bacon, for example,was a Franciscanfriaq who ftansmittedhis scientificmanuscripts to the Papalcourt in semecy(Smith, 2005). Pecham and rVitelo werepriests as well, who relied on Ibn al-Haythamin constructingtheir own evolvingoptical theo- ries,but who alsotook libertieswith their interpretationsand infusedthem with spiritualundertones. The work ofthesescholars, collectively and respectively, had enormousilfluence on the progr€ssionof opticalunderstandings throughout the centu ries that immediately [olJowed. The natureof light, vision and cognirionare so directlylinked with onto, logicalaspects of the humanexperience that they alsoappeal to considerations beyondthe scientific.As the encyclopedicand monastic traditions of scholarship 120 C.M. Fabct,A.L. \YleintzAllen propelled intellectual cudosity, and as images increasingly became the popular visual culture of the day,it should not be surprising that the scienceof oplics en tered other areas.It is remarkable,though, just horv widely it pelmeated \Western Europeanconsciousness and the bloader culture.

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\X/oodcutcover image of a 16rh cenrury transl,rl rr ut P,tltdtua Catttnunt,by lohn l'ech,rnr.tdir-J br Lu," Cruri.o. clr n.

Popular literary examples published during this period illustrate just how widespread the interest and understanding of optics had become. Ibn al-Hay- tham, for example, is referred to severaltimes in the epic poem Roman de la Rose lRomance of the Rose] by Guillaume de Lorris and Jean de Meun, one of the most widely read works in the French languagefor 300 yearsafter its publication in c1275 (flardi,2007 ). In the text the authors descdbethe properties ofmirrors, with the text exhibiting a surprisingly non trivial understanding of optics. One short passagefrom thesefour pagesmakes its debt to Ibn al Haytham (Alhacen; Alhazen) quite clear: Ibn al-Haytbam'sContributians. . . 121

There lin Alhacen's Obsen ationsl he u'ill be able to discover the causes and the suengths ofthe mir-rorsthat have such marvelousporvers that all things that are very small then letters, very narro.,vu'riting, and tiny grains of sand - are seenas so great and large and are put so close to the observers {or ev eryone can distinguish among them that one can read them and count then from so far off that anyonervho seenthe phenomenon and wanted to tell about it could be believed by a man rvl,o had not seenit or did not know its causes. This would not be a caseof belief, since he rvould have the knowledge of the phenomenon/Tlardi. /007. p. a4 .

A century later Geoffrey Chaucer refers to Ibn al Haytham rn Canterbury ?Z/es,written over the period 1187 1400,and the first major piece oflirerarure in the vernacular English language.Chaucer, too, was influenced by his understand- ing of the content of Ibn al Haytham'sworks on vision and optics, asis ciear from the following passage: They spokeof Alhazenand Vitello and Aristotle,rvho wrote of curious mirrorsand of perspecriveglasses, as they know rvho have heard their books. (NeCastro,2007,p. l) As medieval optical theories increasingly informed scientific inquiry and, furthermore, epistemologicalframeworks of society and culture, interest in the visual system- particularly how it might be applied to artificial repfesenrations of spaceand spatial perception (i.e. painting and drawing) were consideredfor usein the visual arts. Interestingly,although Ibn al'Haytham's developmentswere disseminatedthrough the works of Bacon, Pecham and \X/itelo,what transpired was not so much a period of scientific discovery in optics, but rather a prolific period of advancementof uisual liteMCJ),with the scienceof optics providing the syntllx upon which new spatial understandingswere constructed.As Greenstein (1997,p. 682) states: Becausevision is a cognitiveprocess involving inner senseand intellect, opticslinks sightwith semantics,semiotics, and theoriesof the soul.It makes useof suchfundamental Aristotelian concepts as form, substance,accident, quaiity,individual, universal, species, and whatness.

Art and optics

What influence perspectivist theories of vision had on the visual arts lead, ing up to and throughout the Renaissance,however, has yet to reach a consen- sus among scholars.1X/riting on the influence of optical scientistson visual artists Klein (1961,p.212) states,"'We may observethe widespreadconviction that there was a close connection between their disciplines,reaily an identity". He further states, "If one can believe Rafaello Maffei, the ancient scienceof Alhazen and Vitellio now included artistic applications and was almosr identified with the fine arts" (Klein, 1961,p. 212). Kemp (2005) remains cautiousof considerationsthat 122 C.M.Falca, A.L. WdntzAllen superimpose perspectivist theories of vision directiy upon the development of linear perspective or visual transitions in the visual arts. A nore favorabre arcr syr- ergistic point of view, however, can be found the introduction of Snith's (2001) English translation ol De Aspectibus, 's/here he st.rtes: The representation of visual space in Renaissanceart wds the expres- sion of a u'orltl r'ieu, inrplicir in the Perspectivistanall,sis of sight, a world vie*. 'georretrization' based upon the of visual space. If, l-rou'ever-,Alhacen and his 'see' Pelspectivistfollou'ers taught Renaissanceartists to the \,,,orldin such spa tial terms, those aflists in turl taught early modem thinkers to seetl,e rvorld in tl-rosesame terns and thus to conccivc oli it lrs a Euclidean coltinuum.

l.rc.5 Illustrarionof Albcrtispicturc plane, intemrpting the visrral ravs or rDepersPecarvrst pyrarxd, 'Luclidean \Written evidcnce of this contiltuunr' is interpretable in the rvrit ings of such well knou'n Renaissanccmasters as Alberti, Ghiberti and da Vinci, and equally important visual evidence is evident in the actual inages created throughout the peliod. Alberti's most notable rvork, On Painting, c1415,for ex- ample, errtploysa model for vision taken directly fi-om Ibn al-I{aythan.r.Green stein (1997, p. 682) valid21s5a paraijelism between Ibn al Haytham and Alberti's respectivemodels of vision by stating, "Alberti's viewer first seesunder aspects lalpecimuslathen recognizesby intuition llntuentes.. . dignoscirzza.rl ; and finally discernswith greaterdiscrimination [arpiciefttes dittinct:ius... discernitnus]" .These stagesof visual successionimply that Alberti understood spatial perception ds a Ibn al-Haytham's Contributions. . . t23 layeredand complexcognitive process; one that mustaccount for the perceptual tendenciesthe viewerapplies as a meansfor interpretingany given scene. There is supportfor the ideaas well that the 'Euclideancontinuum' informed Alberti's understandingof the visualpyramid (Lindberg, 1981). Kemp (1990,p. 345)however, is conservativein his estimateo{the influence opticshad on transitionsin visualart practiceevident in paintingstating, "Medi evaloptical science created far moreproblems than it solvedfor Renaissanceart' ists".For example,that Alberti is explicitabout having composed, On Paintingfor artistsand demonstrates indifference to debatesabout which directionvisual rays might reachthe eyeof the viewer,i.e. intromission vs. extromission, is interpreted by Kemp (1997)as a breakin Alberti with scientifictradition. Kempt conclu- sions,however, do not wholly considerthe practicalimplications which occur whenthe visualsystem is orientedand applied to visualart practice,and pre'date the discoveriesof the Hockney-Falcothesis by a decade. Alberti wasaware of the debateborn out of the perspectivistoptical tradi tion about visualrays; aware enough to put forth that such considerationsare 'useless' for artisticpurposes (Kemp, 1997). Subsequendy, Alberti focuseshis at- tention insteadon conceptsrelative to spatialdisposition and composition,and how thesetwo principlesare translated and reoriented as objects on a two dimen- sionalpicture plane.In short,Alberti wasthe first to interrupt (in writing) the visualpyramid by placingthe canvasperpendicular to the visualrays, specifically at the vertex of the pyramid.\X/hether Brunelleschi's panel expedmentsat the Piazzadel Duomoor the Piazzadella Signoria, in Florence,were actually the first experimentalillustration of this effect,will not be discussedhere. Howeveq the latter certainlyinformed the former (Arnheim,1978; Kemp 1990).The neces- sarylevel of understandingfor providingaudiences with instructionof thesead- vancedvisual considerations subsequently required a new form of eruditionand language,namely pe$pective. LorenzoGhiberti's efforts to makea contributionto the discussionaoDear a decadeor soafter Oa Paintingwasfirst publishedand immediately translaied into Italian.Ghiberti attempted a theoreticalunderstanding of the arts,relying heavily on the opticaltheories of Pecham,\X/itelo and others,which in turn reliedon Ibn al'Haytham.Ghiberti certainlyhad accessto a 14,bcentury Italian translation of Ibn al-Haytham,given that entireportions of it areincorporated in Book3 of his Commentari(Fragenberg, 1986; Greenstein, 1997, etc.). The bookwas incomplete at the timeof Ghiberti'sdeath but is describedby Lindberg(1981, p. 152)as:

The most transparent caseof the influence ofmedieval visual theory c'rra quattrccentro afiist... he lGhiberti] presentsa complete survey of the mathe- matical tradition in optics consistingmainly of excerpts and paraphrasesdrawn from the perspectivists.

Subsequently, by the time da Vinci v'ould consider the wotks of these same opticalscientists, he too would be forcedto reconcilefor himselfthe relationship betweenvision. perception. and pictoriaJ representation. 124 C.M. Falco,A.L. \VeintzAllen

Kemp's (1977, p. 147) researchon da Vinci makes it clear that the arrisr es- tablished an "Increasingly sharp separationbet\veen perspective as the scienceof vision and percpectiveas a geomerical meansfor constructing a rational pictufe 'perspective space",which da Vinci refers to respectivelyas made by nature' and 'perspective 'prospettiua 'plospettittt made b y art', ot naturale' and accidentdle'.It is also clear that Alberti and Ghiberti's shortcomingsin affirming or denying the function ofthe visual pyramid are too laconic in the mind of da Vinci, who subse- quently embarks on an intense period of experimentation, applying a methodol ogy and conducting experiments remarkably similar to those of Ibn al-Haytham (Smith,2001). Given the progressionof eventsoutlined throughout the preceding sections it seemsunusual that an artist like Alberti was so familiar with the perspectivisr tradition, and yet so little is known about how he arrived at the principles oflinear perspective.Nevertheless, a clear languageofvisual literacy has been established, beginning most significantly with the work of Ibn al Haytham and culn.rinatir.rg with Alberti's visual pyramid for artistic production during the Renaissance.

5. Conclusion

Consideration of the lineage of medieval optical theories leading up to and throughout the Renaissanceis necessaryfor understanding the methodology Hockney and Falco developed,centuries later, for analyzingwell known Europe an paintings, as well as the larger impact of the perspectivisttradition as it relates to realist image production. This methodology is one based on a framework of visual understanding, i.e. visual literacy; one that datesback to the perspecrivist tradition and explicitly recognizesthe optical principles evident within artificial and natural representationsof space. Smith eloquently and accuratelyiliusrates the complex relationship that ex- ists between visual literacy and reading by interpreting Ibn al Haytham:

In likeningspatial perception to reading,Alhacen underscores that the easewith whichu'e read 'space', like the easewith whicl we readwords, masks the arduousnessof acquiringthat readingskill in the6rst place. Reading space, in short,is far moreintellectual than it is tactile(Smith, 2005, p. 2005).

That the mind of a painter is as intrinsically involved in the oeative process, asis his hand in creatingpaintings, makes original works of art highly complex sub jects to analyze.Hockney and Falco however,demonstrated that optical evidence existswithin the visual compositionsof certainpahtings. This evidenceis therefore subjectto visual (qualitative)as well asoptical (quantitative)interpretation. 'optical Such evidence' might consist of visual elementsobserved within a painting that do not reflect the perspectivistworld-view of the age in which the image was created. Unlike an image projected onto film or canvas,for example, Ibn al-Hdythan's Contributio]1s.. . r25

the hunan eye constantly adjusts its aim and focus as tlte mind constructs the scenc it is vierving. As a coDsequence,humans do not simultaoeouslysee part of a scene in focus and part of it out of focus. Although modeln humiurs have obscrved the effect of scenesdepictcd out of focus countlesstinres in the form of photographs,in novics, and on televisior.r,it is not an effect that is part of natural human vision. IIence, a simple example of the indirect use of optics is if an artist has pair.rtedd distant portion of zrscene as if it were out of focus, replicating the depth-of-field ofan imageprojected by a lens.'fhis is preciselythe effect Hocknel, and Falco identified from their observatiols of Lorenzo L otto's Poltrdit of d Mdr ried Cc.tuple,c152,1-5 (Hockney & Falco,2005).

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t Ic, b Llusbattl antl Vzfe, Lorenzo Lotto, c.1521.1.96cm x 116cm.flockney and Falco observethat the octag_onalpattem in the centerof the rableclothappears to go our offocus - one pieceoT the oqtical cvidenc.efiat Lotto usedoprics ;hen conj osing tnls portlon ol the pamtmg-

While optically assisted techniques for artistic production are known to have become common by the 19th century, including tracing projected images (Pas chall, 2001), earlier use of optics has been difficult to identify and analyze hin, dered, we believe, by the lack of sufficiently close inreracrion between art histori- ans with artists and scientists. Sullivan's (2004;2005;2006) tesearch of arr pracice as a verifiable form of research affirms this belief, and suggests that Hockney 126 C.M. Falco, A.L. \Veintz Allen and Falco's approach for observationand deduction, essentiallyborn out of their practice of art and optics respectively,might account for why their theones were rejected, at least initially, by some art historians (2005). Additionally, lack of detailed understanding of optics and the history of optics continues to affect interpretation of historic realist images.For example, despite documentary evidenceshowing that concavelenses and mirrors of high enough quality were availablein the first quarter of the 15thcentury (Ilardi, 2007), such evidencehas done little to achievewide acceptanceby historians that a con- cave mirror can, in fact, project useful imagesfor artists (Campbell, Syson,Falo- mir. & Fletcher.2008).

IIG, / RogerBacon! diagramsrelating to the scientificsrudy ofoptics, from Pe$pectiod, BririshLib:ary, n.. Ro),rl/ L Vill, i. i4\.

Despitethese challenges, recent study of Hockneyand Falco'scollaborative processhighlights the specificmanner in whichtheir respective practice ofart and opticsenabled them to identifyoptical evidence within a numberof Renaissance paintings,and ultimately demonstrate that artistsas eady asJan van Eyck (c1425) Ihn al Haytham's ContributioLts.. . 121 used optical projections as aids for producing portions of their paintings (Allen, 2007). Hockney and Falco'smethodology of visuallyinterpreting optics,basedim agesstipulates that visually evident compositional details qualify certain paintings 'photorepresentations' as composedboth by the hand and mind of the artists,but resulting from optical geometry aswell. Hockney and Falco's methodology and findings have implications for the histories of scienceand art, as u'ell as scienceand art education. This unique ap- proach for analyzingworks of art is within the long, interdisciplinary,progression towards a new visual language;one historically informed by the scienceof medi eval optics, but put into action by visual artists during the Renaissance.

Acknowledgements

We gratefully acknowledge David Hockney for his invaluable insights on painting through his investigation of over 1000 yearsof European arr. These in, sightsprovided the foundation for ongoing work subsequentlybeing pursuedwith Dar'ld Graves,resulting in locating documentsreiated to the eady useof optics by artists, the origin of which we have raced to the writings of Ibn al Haytham.

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