FoNnazroNp Groncro RoNcHr

,r.@,Studio Art Centers International

Palazzo dei Cartelloni

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

Painted Optics SymposiumRe-examining tbe Hockney-Falco tbesis 7 years on

Florence, September 7 -9, 2008

Via San Felice a Ema 20501.25 Firenze, Italia

http://ronchi.isti.cnr.itFirenze 2009

Ibn al-Haytham's Contributions to Optics, Art,and Visual Literacy

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

Introduction

In his book, Seuet Knowledge: rediscouering tbe lost tecbniques of tbe oldMasters (2001,2006), the artist David Hockney reported visual discoveries withinsome of the best known European paintings that affect long-held understandingsof the development of westem art over the course of the past 600 years. Subse-quently, a collaboration combining the visual skills of one of the world's greatestartists (Childers, 1996; Langmuir & Lyrrton, 2000) with the analytical skills of anoptical physicist (Charles M. Falco), resulted in Hockney and Falco developingthe foundations of a new methodology for extracdng information from complex,optics-based images (Hockney & Falco,2000, 2004, 2005a, 2005b, 2005c). As willbe discussed in this paper, this methodology also contributes to our burgeoningunderstanding of visual literacy.

Visual literacy is not limited to the naffative and symbolic qualities of pic-tures and images (Duncum,2001; Hockney, 1998), but it is also rooted in the scientific and cultural study of optics and the visual system (Edgerton & Steinberg,1987; Greenstein, 1997; Grootenboer, 2007). As we will discuss, the genesis ofthis concept can be traced to the work of the 11'h century Arab polymath, Ibn al-Haltham (Latinized Alhazen or Alhacen), rvhose scientific exploration of visionsignificantly impacted the study and practice ofvisual art, as well as our cognitivecapacity to interpret it.

Historic Theories of Vsion

During the first two centuries ofthe Islamic Golden Age (8th-1Jth centuries),translation of ancient writings on the science of optics offered contemporary in-tellectuals with various philosophical theories of vision. Euclid, Ptolemy, Galen

(n) College ofOptical Sciences. University ofArizona, Tucson 8J721 USA

1 1 6 C.M. Falco, A.L. \N/etutz Allan

and Aristotle, whose Greek texts were hanslated into Arabic dudng this period,provided disparate viervs on the way the organ of the eye reacts with light to aid invision. Greek theories were largely appropdated by Islamic scholars until the firstquarter of the 11ih century, when a new method of inquiry rvas introduced by Ibnal-Haytham. Vith the 'scientific method' he introduced to the rvodd, al-Haythanlused experimental evidence to develop a remarkably accurate theory of vision.His design and interpretation of elegant experiments became the root source for'Western understandings ofoptics up to the 17th century (Lindberg, 1967).

Born in Basra in 965, Ibn al-Haytham primarily worked in Cairo's al-AzharMosque - an epicenter for academic inquiry - where he wrote prolifically onsubjects as diverse as poetry and politics. He is primarily known however, forhis writings on geometrical optics, astronomy, and mathematics. His landmarkseven volume treatise on the human visualsystem, Kitab al-Manazir lBook ol Oy>ticsJ, published sometime between 1028 [418 A.H.] and 1018 [429 A.H.], u.asincorporated throughout the core ofpost medieval \Western culture. This seminalwork initiated an unbroken chain of continuous development of the modern un-derstanding of both optics (i.e. science), as rvell as understandings related to twodimensional pictorial representations of three dimensional space (i.e. art).

FrG. 1

lbn al Hattham's description of the human visual system. From a copyothis Kitab al-Manaztu 108i [175 A.H.] in the Siileyminiye Library, Istinbul.

T

Ib n al-Haltham's Cofttibutions. I l l

Frc. 2

The anatomy of the eye according to Ibn al-H ̂ yrh^m, horn Ki/ab al,ManziLMuseum Victoria.

Prior to the work oflbn al-Ha1tham, theories ofvision could be broadly clas-sified into one ofthree categories: extramission, intromission, or a combination ofthe two. Extfamission theories require that some sort of illuminating particles beemitted by the eye. Euclid and Ptolemy are well-known scholars associated withthis category (Linberg, 1981). Although there are obvious flaws with extramrssrontheories, they do get the geomery right, with a one-to-one correspondence be-tween points on the object and points on the eye. Intromission theories, with Ar,istotle as a prominent proponent, postulated that objects continuously sloughedoff microscopically thin replicas of themselves that then travelled to the eye ofthe observer Intromission theories avoid some obvious problems of extramissiontheories, such as near and far objects simultaneously being visible the moment theeye is opened. A third alternative, supported by Plato and Galen (and Aristode,to a lesser degree), combines the trvo theories, proposing that light emitted by theeye engages in some way with the intervening air and aforementioned replicas, orspecies (Lindberg, 1,967 , 1981,).

Like others before him, Ibn al-Haltham also recognized that there wereproblems with all existing theories of vision, but he vias uniquely successful infinding a solution that had eluded the best minds of antiquity. He proposed a type

1 1 8 C.M. Falco, A.L. \Veintz Allcn

of intromission theory ofvision, and validated his cor.rclusions by empirical understanding deduced from scientific experimentation, This methodology expandedhis understanding beyond the theoretical, which resulted in the incorporation ofpsychology to explain vision, in combination with the behavior of light and thephysiology of tl.re eye.

t IG. '

l . r n u n f r , k . l l , l . l l ; . i \ , 1 . t 4 l 2 . , l 4 t 4 , d , 1 d l ' h o s i n s a p p r o x i m . r . c h z ' " - o t r r .i l . c . 5 o . 7 . n r L , j n r i n c r . B i r r u , i r . i \ , r ' ; r s o l L r c r s p c L r i \ L ; n N . d i n e n . i . ' r r J l L r J c , : ,specLFc inforri,,ti,'n .in be eLi.jtcd aboui the mannel in rvhich imagcs are produced.

Ibr.r al Haytham also linked sight and vision with the properties of lightthroughout his studies. His experiments subsequently verified scienti6c principlesconmonly associated with what is known today as optical'ray tacing'. These ex'periments included using flat and curved mirrors to control and manipulate light,but primarily involved obseruing the effect of light pouring through apertures ofvarious sizes into dalkened spaces (i.e. camera obscura) (Smith,2001a, 2001b).Perhaps most inrportantly, they provided him a theoretical basis for the existenceof rays; a theoretical construct that he used as a means for describing and interpreting the visualsystem. These lays are subsequently represented by geometricallines associated on a point by point basis u'ith an object in space.

Al Haytham did get one important aspect of vision l'rong: the fact that animage projected by a lens is upside down and flipped right-toJeft apparently rvasmore than he could accept in a theory olvision, even though it is contained rvithinhis optical fornalism. Leonardo da Vinci also failed to accept this when he approached the problem much later (Kemp, 1977). Ultimately, it rvould take anotherlive hundred years before Kepler would follow Ibn al Haytham's formalism to itsinevitable and logical conclusion in developing the theory of the retir.ral image.

Smith (2005) poir.rts out that such contasting theo es of vision in the preceding centuries before Kepler had profound epistemological implications on me-dieval culture. The Platonist perspectivists supporting extromission, for exampie,suggest that the eye has powers which extend outward as a means for engagrngreality rvhich, in a general sense, can be understood as a "r'isual finger reachingout to palpate things" (Smith, 2005, p. 223) . Intromissiolr theories howeveq areuniquely Aristotlian. They ascribe to the idea that, "Knowledge is inductive...

lbn al Haytham's Contribrtions. .. I19

Sensation and its representations are therefore not to be deprecated as the bearefsof falsehood (Platonism) but rather to be prized as the bearers of tuth" (Smith,2001, p. cx).

Perhaps predictably, as cultural understandings of vision ard cognition expanded to include these disparate theories, so too did evolving cultural consid-erations fof concepts seemingly unrelated to the science of optics, the impact ofwhich was not relegated to the science community alone but spread out to includethe humanities at large.

3. Interdisciplinary dissemination and appropriation of Kiffib al-Mdndzir

There is little debate that Ibn al-Haltham's seminal work, Kitab al-Manazir,translated into Latin as De Aspectibus In the early to mid- 1.1th century, is largely re,sponsible for the widespread appropriation of its contents by \Western Europeanintellectuals (Lindberg, 1967). Smith recognizes that variations exist among theLatin version as compared with the Arabic original, not simply in its organizarion-al sructure but in the interpretation of specific terms (2001). From the beginning,however, knowledge of the core principles and experiments detai.led throughoutthe manuscript by its original author were not limited to lWestern readers alone,or to scientific audiences specifically.

De Aspectibus is first referenced in Bartolomeo Anglicus' De proprietatibusrcrun,lOn thePrcperty of Thingsl c1220-1T0 (Smith.2001), a monumental andearly encyclopedia covering a wide variety of subjects. The text refers to the studyofoptics and Ibn al'Haytham specifically several times. It was required reading atthe University of P aris in 1296, avatlable in the university library of the Sorbonneby 1306, and used widely as reference material at Oxford, Cambridge, Canter-bury and Merton College by the mid-fourteenth century (Holbrook, 1998).

Specific proposals contained withn De Aspectibzzs however, are most significantly referred to in the well known optics manuscriprs , Perspectiua by RogetBacot (c7268), Perspectfuaby EruzmusWneIo (c127 8), and Pe$pectiua comnxunisby John Pecham (c1280) (Lhdberg, 1967). Although today we thhk of thesescholars as optical scientists, they approached their work as theologians which,in turn, influenced their interpretation of medieval optical theories. Bacon, forexample, was a Franciscan friaq who ftansmitted his scientific manuscripts to thePapal court in semecy (Smith, 2005). Pecham and rVitelo were priests as well,who relied on Ibn al-Haytham in constructing their own evolving optical theo-ries, but who also took liberties with their interpretations and infused them withspiritual undertones. The work ofthese scholars, collectively and respectively, hadenormous ilfluence on the progr€ssion of optical understandings throughout thecent u ries that immediately [olJowed.

The nature of light, vision and cognirion are so directly linked with onto,logical aspects of the human experience that they also appeal to considerationsbeyond the scientific. As the encyclopedic and monastic traditions of scholarship

120 C.M. Fabct, A.L. \Yleintz Allen

propelled intellectual cudosity, and as images increasingly became the popularvisual culture of the day, it should not be surprising that the science of oplics entered other areas. It is remarkable, though, just horv widely it pelmeated \Western

European consciousness and the bloader culture.

:io. /.lrcblcpifcopi {snnrrricnl5'j0criircctiuq commun16.

f t c . 4

\X/oodcut cover image of a 16rh cenrury t ransl , r l r r ut P, t l tdtua Catt tnunt ,byl o h n l ' e c h , r n r . t d i r - J b r L u , " C r u r i . o . c l r n .

Popular literary examples published during this period illustrate just howwidespread the interest and understanding of optics had become. Ibn al-Hay-tham, for example, is referred to several times in the epic poem Roman de la Rose

lRomance of the Rose] by Guillaume de Lorris and Jean de Meun, one of themost widely read works in the French language for 300 years after its publicationin c1275 (flardi,2007 ). In the text the authors descdbe the properties ofmirrors,with the text exhibiting a surprisingly non trivial understanding of optics. Oneshort passage from these four pages makes its debt to Ibn al Haytham (Alhacen;

Alhazen) quite clear:

Ibn al-Haytbam's Contributians. . . 121

There lin Alhacen's Obsen ationsl he u'ill be able to discover the causesand the suengths ofthe mir-rors that have such marvelous porvers that all thingsthat are very small then letters, very narro.,v u'riting, and tiny grains of sand- are seen as so great and large and are put so close to the observers {or everyone can distinguish among them that one can read them and count thenfrom so far off that anyone rvho seen the phenomenon and wanted to tell aboutit could be believed by a man rvl,o had not seen it or did not know its causes.This would not be a case of belief, since he rvould have the knowledge of thephenomenon /T la rd i . / 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 inthe vernacular English language. Chaucer, too, was influenced by his understand-ing of the content of Ibn al Haytham's works on vision and optics, as is ciear fromthe following passage:

They spoke of Alhazen and Vitello and Aristotle, rvho wrote of curiousmirrors and of perspecrive glasses, as they know rvho have heard their books.

(NeCastro,2007, p. l)

As medieval optical theories increasingly informed scientific inquiry and,furthermore, epistemological frameworks of society and culture, interest in thevisual system - particularly how it might be applied to artificial repfesenrationsof space and spatial perception (i.e. painting and drawing) were considered foruse in the visual arts. Interestingly, although Ibn al'Haytham's developments weredisseminated through the works of Bacon, Pecham and \X/itelo, what transpiredwas not so much a period of scientific discovery in optics, but rather a prolificperiod of advancement of uisual liteMCJ), with the science of optics providing thesyntllx upon which new spatial understandings were constructed. As Greenstein(1997, p. 682) states:

Because vision is a cognitive process involving inner sense and intellect,optics links sight with semantics, semiotics, and theories of the soul. It makesuse of such fundamental 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 scientists on visual artistsKlein (1961, p.212) states, "'We may observe the widespread conviction that therewas a close connection between their disciplines, reaily an identity". He furtherstates, "If one can believe Rafaello Maffei, the ancient science of Alhazen andVitellio now included artistic applications and was almosr identified with the finearts" (Klein, 1961, p. 212). Kemp (2005) remains cautious of considerations that

122 C.M. Falca, A.L. Wdntz Allen

superimpose perspectivist theories of vision directiy upon the development oflinear 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 Renaissance art wds the expres-sion of a u'orltl r'ieu, inrplicir in the Perspectivist anall,sis of sight, a world vie*.based upon the 'georretrization' of visual space. If, l-rou'ever-, Alhacen and hisPelspectivist follou'ers taught Renaissance artists to 'see' the \,,,orld in such spatial terms, those aflists in turl taught early modem thinkers to see tl,e rvorld intl-rose same terns and thus to conccivc oli it lrs a Euclidean coltinuum.

l . r c .5

Il lustrarion of Albcrtis picturc plane, intemrpting the visrral ravsor rDe persPecarvrst pyrarxd,

\Written evidcnce of this 'Luclidean contiltuunr' is interpretable in the rvritings of such well knou'n Renaissancc masters as Alberti, Ghiberti and da Vinci,and equally important visual evidence is evident in the actual inages createdthroughout the peliod. Alberti's most notable rvork, On Painting, c1415, for ex-ample, errtploys a model for vision taken directly fi-om Ibn al-I{aythan.r. Greenstein (1997, p. 682) valid21s5 a paraijelism between Ibn al Haytham and Alberti'srespective models of vision by stating, "Alberti's viewer first sees under aspectslalpecimusla then recognizes by intuition llntuentes. . . dign oscirzza.rl ; and finallydiscerns with greater discrimination [arp iciefttes dittinct:ius... discernitnus]" .Thesestages of visual succession imply that Alberti understood spatial perception ds a

Ibn al-Haytham's Contributions. . .

layered and complex cognitive process; one that must account for the perceptualtendencies the viewer applies as a means for interpreting any given scene. Thereis support for the idea as well that the 'Euclidean continuum' informed Alberti'sunderstanding of the visual pyramid (Lindberg, 1981).

Kemp (1990, p. 345) however, is conservative in his estimate o{the influenceoptics had on transitions in visual art practice evident in painting stating, "Medieval optical science created far more problems than it solved for Renaissance art'ists". For example, that Alberti is explicit about having composed, On Paintingforartists and demonstrates indifference to debates about which direction visual raysmight reach the eye of the viewer, i.e. intromission vs. extromission, is interpretedby Kemp (1997) as a break in Alberti with scientific tradition. Kempt conclu-sions, however, do not wholly consider the practical implications which occurwhen the visual system is oriented and applied to visual art practice, and pre'datethe discoveries of the Hockney-Falco thesis by a decade.

Alberti was aware of the debate born out of the perspectivist optical tradition about visual rays; aware enough to put forth that such considerations are'useless' for artistic purposes (Kemp, 1997). Subsequendy, Alberti focuses his at-tention instead on concepts relative to spatial disposition and composition, andhow these two principles are translated and reoriented as objects on a two dimen-sional picture plane. In short, Alberti was the first to interrupt (in writing) thevisual pyramid by placing the canvas perpendicular to the visual rays, specificallyat the vertex of the pyramid. \X/hether Brunelleschi's panel expedments at thePiazza del Duomo or the Piazza della Signoria, in Florence, were actually the firstexperimental illustration of this effect, will not be discussed here. Howeveq thelatter certainly informed the former (Arnheim, 1978; Kemp 1990). The neces-sary level of understanding for providing audiences with instruction of these ad-vanced visual considerations subsequently required a new form of erudition andlanguage, namely pe$pective.

Lorenzo Ghiberti's efforts to make a contribution to the discussion aoDear adecade or so after Oa Paintingwas first published and immediately translaied intoItalian. Ghiberti attempted a theoretical understanding of the arts, relying heavilyon the optical theories of Pecham, \X/itelo and others, which in turn relied on Ibnal'Haytham. Ghiberti certainly had access to a 14,b century Italian translation ofIbn al-Haytham, given that entire portions of it are incorporated in Book 3 of hisCommentari (Fragenberg, 1986; Greenstein, 1997, etc.). The book was incompleteat the time of Ghiberti's death but is described by Lindberg (1981, p. 152) as:

The most transparent case of the influence ofmedieval visual theory c'rr aquattrccentro afiist... he lGhiberti] presents a complete survey of the mathe-matical tradition in optics consisting mainly of excerpts and paraphrases drawnfrom the perspectivists.

Subsequently, by the time da Vinci v'ould consider the wotks of these sameoptical scientists, he too would be forced to reconcile for himself the relationshipbetween vision. perception. and pictoriaJ representation.

t23

124 C.M. Falco, A.L. \Veintz Allen

Kemp's (1977, p. 147) research on da Vinci makes it clear that the arrisr es-tablished an "Increasingly sharp separation bet\veen perspective as the science ofvision and percpective as a geomerical means for constructing a rational pictufespace", which da Vinci refers to respectively as 'perspective made by nature' and'perspective made b y art' , ot

'prospettiua naturale' and 'plospettittt accidentdle' .Itis also clear that Alberti and Ghiberti's shortcomings in affirming or denying thefunction ofthe visual pyramid are too laconic in the mind of da Vinci, who subse-quently embarks on an intense period of experimentation, applying a methodology and conducting experiments remarkably similar to those of Ibn al-Haytham(Smi th ,2001) .

Given the progression of events outlined throughout the preceding sectionsit seems unusual that an artist like Alberti was so familiar with the perspectivisrtradition, and yet so little is known about how he arrived at the principles oflinearperspective. Nevertheless, a clear language ofvisual literacy has been established,beginning most significantly with the work of Ibn al Haytham and culn.rinatir.rgwith Alberti's visual pyramid for artistic production during the Renaissance.

5. Conclusion

Consideration of the lineage of medieval optical theories leading up to andthroughout the Renaissance is necessary for understanding the methodologyHockney and Falco developed, centuries later, for analyzing well known European paintings, as well as the larger impact of the perspectivist tradition as it relatesto realist image production. This methodology is one based on a framework ofvisual understanding, i.e. visual literacy; one that dates back to the perspecrivisttradition and explicitly recognizes the optical principles evident within artificialand natural representations of space.

Smith eloquently and accurately iliusrates the complex relationship that ex-ists between visual literacy and reading by interpreting Ibn al Haytham:

In likening spatial perception to reading, Alhacen underscores that theease with which u'e read 'space', like the ease with whicl we read words, masksthe arduousness of acquiring that reading skill in the 6rst place. Reading space,in short, is far more intellectual than it is tactile (Smith, 2005, p. 2005).

That the mind of a painter is as intrinsically involved in the oeative process,as is his hand in creating paintings, makes original works of art highly complex subjects to analyze. Hockney and Falco however, demonstrated that optical evidenceexists within the visual compositions of certain pahtings. This evidence is thereforesubject to visual (qualitative) as well as optical (quantitative) interpretation.

Such 'optical evidence' might consist of visual elements observed within apainting that do not reflect the perspectivist world-view of the age in which theimage 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 thescenc it is vierving. As a coDsequence, humans do not simultaoeously see partof a scene in focus and part of it out of focus. Although modeln humiurs haveobscrved the effect of scenes depictcd out of focus countless tinres in the form ofphotographs, in novics, and on televisior.r, it is not an effect that is part of naturalhuman vision. IIence, a simple example of the indirect use of optics is if an artisthas pair.rted d distant portion of zr scene as if it were out of focus, replicating thedepth-of-field ofan image projected by a lens.'fhis is precisely the effect Hocknel,and Falco identified from their observatiols of Lorenzo L otto's Poltrdit of d Mdrried Cc.tuple, c152,1-5 (Hockney & Falco,2005).

t Ic, b

Llusbattl antl Vzfe, Lorenzo Lotto, c.1521.1. 96cm x 116cm. flockney and Falcoobserve that the octag_onal pattem in the center of the rablecloth appears to go ouroffocus - one piece oT the oqtical cvidenc.e fiat Lotto used oprics ;hen conj osing

tnls portlon ol the pamtmg-

While optically assisted techniques for artistic production are known to havebecome 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 praciceas a verifiable form of research affirms this belief, and suggests that Hockney

..,!.::\ : l

126 C.M. Falco, A.L. \Veintz Allen

and Falco's approach for observation and deduction, essentially born out of theirpractice of art and optics respectively, might account for why their theones wererejected, at least initially, by some art historians (2005).

Additionally, lack of detailed understanding of optics and the history ofoptics continues to affect interpretation of historic realist images. For example,despite documentary evidence showing that concave lenses and mirrors of highenough quality were available in the first quarter of the 15th century (Ilardi, 2007),such evidence has done little to achieve wide acceptance by historians that a con-cave mirror can, in fact, project useful images for artists (Campbell, Syson, Falo-mir. & Fletcher. 2008).

I IG, /

Roger Bacon! diagrams relating to the scientific srudy ofoptics, from Pe$pectiod,B r i r i sh L i b :a r y , n . . Ro ) , r l / L V i l l , i . i 4 \ .

Despite these challenges, recent study of Hockney and Falco's collaborativeprocess highlights the specific manner in which their respective practice ofart andoptics enabled them to identify optical evidence within a number of Renaissancepaintings, and ultimately demonstrate that artists as eady asJan van Eyck (c1425)

Ihn al Haytham's ContributioLts. . .

used optical projections as aids for producing portions of their paintings (Allen,2007). Hockney and Falco's methodology of visually interpreting optics,based images stipulates that visually evident compositional details qualify certain paintingsas 'photorepresentations' composed both by the hand and mind of the artists, butresulting from optical geometry as well.

Hockney and Falco's methodology and findings have implications for thehistories of science and art, as u'ell as science and art education. This unique ap-proach for analyzing works of art is within the long, interdisciplinary, progressiontowards a new visual language; one historically informed by the science of medieval optics, but put into action by visual artists during the Renaissance.

Acknowledgements

We gratefully acknowledge David Hockney for his invaluable insights onpainting through his investigation of over 1000 years of European arr. These in,sights provided the foundation for ongoing work subsequently being pursuedwithDar'ld Graves, resulting in locating documents reiated to the eady use of optics byartists, the origin of which we have raced to the writings of Ibn al Haytham.

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