1 Introduction. Swiss Federal Institute of Technology Zurich Center of Product Development

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1 Appeared in he Immersive Projecion Technology and Virual Environmens 2001, pp ; May, ; Sugar (Germany); ISBN ; Springer-Verlag Wien/New York Novel Shuer Glass Conrol for Simulaneous Projecion and Picure Acquisiion Andreas M. Kunz Chrisian P. Spagno Swiss Federal Insiue of Technology Zurich Cener of Produc Developmen Absrac. Virual realiy offers compleely new possibiliies for collaboraive work over disribued environmens. To enable collaboraive work, i is necessary ha boh, virual objecs as well as he oher users, can be seen simulaneously in real-ime. A novel echnique is necessary o overcome he conradicion of darkness and ligh for image projecion and video acquisiion, respecively. A sroboscopic ligh and a camera sysem are added o he exising VR-sysem and a few modificaion are made o exising shuer glasses. In such a soluion, he mehod of projecion in he VR-sysem remains unmodified. This paper describes how o resolve his conradicion wih he consrain o make as few changes as possible o exising VR-sysems. Furhermore he iming of he differen devices is discussed. 1 Inroducion More and more VR insallaions are se up worldwide [1], [2]. Mos of hese insallaions are sand-alone, where he user is shown synheic, compuer-generaed objecs. Alhough presen compuing ools suppor informaion exchange and simple communicaion fairly well, collaboraion on complex issues - be i models of funcions, form or behavior - is no well suppored. Curren VR sysems use projecors o display full-color, compuer-generaed sereoscopic images on he walls of a cube. Sofware synchronizes all he devices and calculaes he correc perspecive for each wall. In he CAVE [5]; [6] all perspecives are calculaed from he user s poin of view. Offse images are calculaed for each eye o creae he sereoscopic effec. The user can only experience his sereoscopic effec by wearing acive sereo glasses, which alernaely block he lef and righ eye. Sand-alone insallaions lack he funcionaliy for collaboraive work among neworked users and are hus no well suied for disribued eamwork. Mos sysems oday do no allow ineracions beween muliple users and an objec under design. In virual meeings, humans are represened inadequaely and disembodied hrough ex, voice, or wo-dimensional video projecions. By inegraing human represenaions in compuer modeling environmens, many of oday s simulaion echniques can be improved and new ones invened. Furhermore, he projecs ha use picure acquisiion for rendering and gesure recogniion no only face he problem of creaing an effecive eam-working environmen, bu usually do no make use of a nework [7];

2 [8]; [9]. In order o enable collaboraive work in a disribued environmen, a picure acquisiion of he person mus work ogeher wih he projecion of boh, he virual objecs and he oher users, all in real-ime [3], [4]. A new projec called blue-c" [10] proposes o build a sysem ha achieves he following wo major goals. The firs goal is o enable a number of paricipans o inerac in a virual meeing and a collaboraive seing, where he represenaion of people and objecs is as complee as possible, in oher words all objecs and persons are fully rendered in hree-dimensions wih real-ime movemen and speech. The second goal is o provide an ineracion beween all he users and he simulaed arifacs, be hey models of funcion, form, behavior or heir combinaion. The advanage of such simulaions is he improvemen of elepresence in conference meeings and he creaion of immersive, virual muli-user environmens. The key problem wih simulaneous projecion and picure acquisiion is he illuminaion of he scene. On he one hand, o achieve a high qualiy image acquisiion, a well-lighed scene is necessary. On he oher hand, he projecion sysem requires dark surroundings for a brigh and sharp picure. In order o overcome hese conflicing lighing requiremens, a new approach is used in he blue-c"-projec. The basic idea is o illuminae he blue-c" acively wih a sroboscopic ligh source during video image acquisiion. The sroboscope is synchronized wih he cameras, he projecors and he shuer glasses, ha are needed o generae sereoscopic views in such VR Caves. 2 Conribuions In order o simulaneously provide a good projecion and a good image acquisiion, wo differen illuminaion phases are necessary. In a dark phase he specaor can wach he projecion and in a ligh phase he camera can acquire he person s exure. Our approach uses a flash o illuminae he person in order o ge he exure. During he flash, he specaors eyes are covered by a new, hird phase of he shuer glasses, where he glasses become opaque. If he phase sequence is done fas enough, human percepion fails o follow he oscillaion from ligh o dark. Thus, he basic idea of he presened concep is o make as few changes as possible o an exising echnical seup. The projecion sysem is he mos criical par in a VR seup and so i should no be modified o accommodae he video acquisiion. Furhermore, sereoscopic viewing should sill be possible and no be affeced by he sroboscopic illuminaion. These consrains lead o a soluion shown in Figure 1. The original wo saes of he shuer glasses are hus supplemened by a hird sae, which darkens boh he lef and he righ lenses simulaneously. This dark phase is used o shield he user s eye from he sroboscopic illuminaion. Each of he original saes, one for he lef and he oher for he righ eye, is shorened in order o creae a hird sae. If his hird sae is kep very shor, i will no be deeced by he specaor s eye. However, regardless of how shor he new sae is, he overall picure will appear slighly darker because of he decreased ligh inegraion (exposure) ime for he lef and he righ eye. Consequenly, he dark phase is made o be as shor as possible. The acual value for he dark phase is consrained by he following aspecs:

3 he minimum required ime (o grab a video frame) for a picure (dicaed by he shuer speed) he maximum swiching frequency of he shuer glasses he minimum ime of he flash (including he aferglow ime) he maximum rise ime of he flash he laency ime of he addiional elecronical circuiry These consrains were verified by he preliminary, basic measuremens. Sync. lef dark righ lef dark righ Figure 1 Time muliplexing diagram 3 Basic measuremens The shuer glasses and heir riggering via he infrared link is he only par of he whole VR-sysem ha has o be changed. Therefore, he following basic measuremens have been made o verify ha he requiremens, lised in he above, can be fulfilled by he shuer glasses and he acive illuminaion. Shuer glasses (LCD): Firs of all, he ime behavior of he glasses mus be examined in order o ge he maximum usable frequency and he shores swiching ime from ransparency o opaciy. The measuremen gave he following resuls: he LCD-shuers are fas enough o work on he required frequencies up o 60 Hz increasing he driving volage has no effec on he opaciy of he glasses i is possible o shoren he ransparency phase of he glasses Shuer glasses (elecronic): In a nex sep he driving signals for he glasses iself have o be analyzed. Figure 2 shows he wo channels for he lef and he righ lens. The decoding and signal-processing uni wihin he shuer glasses generaes a bipolar signal ha is used o operae he LCD shuers. This bipolar signal is used o charge and discharge he LCD shuers since hey behave like a capacior. This implies ha only he absolue value of he signal is used o darken he LCD shuers. In order o use he already exising circuiry wihin he glasses ha decodes he emier s infrared signals, an addiional elecronic circui was added o delay he rising edge for he lef eye impulse and o sar he falling edge of he righ eye impulse earlier. This modificaion of he pulse widhs causes an overlap and hus creaes he hird, dark phase. Acive illuminaion: Nex, a suiable sroboscopic illuminaion was chosen and i s performance was measured. To provide such a high flash frequency only

4 semiconducors or gas-filled ligh bulbs can be used. In he es seup a sroboscope and an array of whie ligh emiing diodes (LEDs) were used. This illuminaion is brigh enough o overpower he normal projecion making changes o he projecion sysem unnecessary. The ess gave he following resuls: he sroboscope has sufficien ligh inensiy. he pulse-widh of he scope-flash is very small. acive illuminaion using a sroboscopic ligh is very noisy. whie ligh emiing diodes have lower inensiy and need a wider pulse-widh of he flash. Figure 2 Driving signal for he glasses 4 Generaing he hird phase For human percepion, i is imporan ha he new dark phase is symmerical o he original phases for he lef and he righ eye. This mus be aken ino accoun when placing a hird sae ino he operaional cycle of he shuer glasses. In order o reain he sysem s symmery, he hird phase is placed during he ransiion from he original dark phase of he lef eye o he dark phase of he righ eye. Figure 3 shows he iming diagram of he prolonged signal for boh glasses, compared o he original signal. In he chosen example, he picure refresh frequency is f w = 60 Hz. Therefore, each eye will see 60 picures per second and he dark phases for he lef and he righ eye can be calculaed as: T D T L T D = T L =1/(2* f w ) = 8,33 ms = period of he dark phase = period of he ligh phase In order o keep he symmery, he frequency f 3 of he hird phase mus be eiher an inegral muliple or an inegral facor of fw. The following opions are available for he period lengh T 3 of he dark phase:

5 f 3 = 2*n*f w ; 0 T 3 1/(2*n*f w ); 1n = 1, 2, 3,... (case 1) In case 1, he dark phase can be placed anywhere wihou disorion of he symmery, since he hird phase akes an equal amoun of ime from he righ and he lef eye. f 3 = f w ; 0 T 3 1/f w (case 2) In order o use he same amoun of ime from he lef and he righ eye in case 2, he dark phase mus be placed symmerically during he ransiion from he lef o he righ eye. f 3 = f w /n; 0 T 3 1/f w ; n = 2, 3,... (case 3) In case 3, he dark phase mus be placed symmerically during he change from he lef o he righ eye, as well. Especialy case 3 was furher examined. A higher frequency f3 did no give beer resuls han case 2, because he person will sill see he lower screen refresh frequency. lef shuer glass wihou hird sep 8.33 ms 8.33 ms dark ligh righ shuer glass wihou hird sep ligh dark hird sep dark ligh lef shuer glass wih hird sep dark ligh righ shuer glass wih hird sep ligh dark Figure 3 Signal diagrams for he shuer glasses 5 Modificaions on he exising sysem Firs experimens have been done wih he CrysalEyes shuer glasses. This shuer glasses work wih wo LCDs. The addiional circui for he hird phase is inegraed beween he original circui of he shuer glasses and he wo LCDs. Figure 4 shows he block diagram for his addiional circui. The original bipolar signal coming from he shuer glasses is given o a recifier sage since only unipolar signals will be processed. In he following, pulse-duraion sage

6 100K 50K 2.2 nf 50K 500K 50K 10K he recified pulses are modified. The couner sage conrols he number of pulses o be prolonged. This number can be chosen from one prolonged pulse wihin every period o one prolonged pulse only every 15 h period. The hird phase signal is combined wih he original signals for he lef and he righ lens o generae he new signal for he glasses. Finally he signal passes o a flip-flop sage, which generaes he bipolar signal. Couner lef bipolar signal Signalrecifier Timer for pulse duraion Third sep generaion Symmery Combinaion wih original signal righ bipolar signal Figure 4 Block diagram for he addiional circui Figure 5 shows he signal recifier, he couner and he imer. Sig 1 is he signal coming in from he shuer glasses. The couner and he imer define when and how ofen he hird phase is generaed. The duraion and he iming of he hird sae (he dark phase of he shuer glasses) are generaed wihin his sage. The signal, sig 3, coming ou of his sage corresponds o only a half of he hird phase and will be compleed in he following sage. 74HC163 +5V +5V 4538 sig 1 50K 100K 50K 50K 4013 sig 3 sig 2 sig 4-5V -5V Figure 5 Signal recifier, couner and imer In he nex sage, he symmery of he hird phase is generaed. In Figure 6, signal sig 3 is coming in from he previous sage and sig 5 corresponds o he hird phase. To creae he required symmery, a capacior is charged and discharged wih a consan DC curren. The inpu (sig 3) is a 0 V when charging he capacior and a + 5 V when discharging he capacior. The posiive inpu of he firs op-amp is regulaed o 2.5 V. The capacior is charged and discharged over he resisor ha is conneced o

The alernaion beween posiive and negaive volage prevens he LCDs from showing a memory effec.

7 60K 100K 100K 100K 60K signal sig 3. A diode is conneced in parallel o he capacior o ensure ha he op-amp does no saurae. In he las sage, he hird phase signal sig 5 is combined wih he original signals for he lef and he righ LCDs as shown in Figure 6 The new signals are hen amplified. The alernaion beween posiive and negaive volage prevens he LCDs from showing a memory effec. The LCDs for he lef eye is conneced o he signals sig 6 and sig 7 while he one for he righ eye is conneced o sig 8 and sig 9. sig 6 sig 3 0.1nF sig 2 sig sig 7 sig 4 sig sig 9 Figure 6 Symmery generaor of hird phase and r oupu signal 6 Tes seup In order o verify he funcionaliy he sysem, is componens were assembled and inegraed ino a es seup as shown in Figure 7. Box Monior Objec 1 Objec 2 Flash Shuerglasses Figure 7 Tes seup The es seup is a chamber, which can be compleely darkened. Inside he chamber, here is a monior o provide a sereoscopic projecion, combined wih a sandard infrared ransmier. The sereoscopic image can be viewed from ouside hrough he modified shuer glasses, which are riggered via he infrared emier. The chamber can be illuminaed by sroboscopic ligh o illuminae he objecs found inside. These objecs can be acquired via a camera, which is insalled in he chamber.

demonsrae he effeciveness of he modificaions, he illuminaion of he objec was viewed wih and wihou a hird phase. Figure 8 shows he difference beween hese wo resuls.

8 7 Experimenal resuls The chamber was used o es he feasibiliy of he whole sysem. The following poins were of main ineres: he subjecive impression o he user he inerference beween he video image an he flash he need o synchronize he flash wih he picure acquisiion In order o demonsrae he effeciveness of he modificaions, he illuminaion of he objec was viewed wih and wihou a hird phase. Figure 8 shows he difference beween hese wo resuls. Boh images have been aken hrough he shuer glasses. In he lef image, he shuer glasses were no modified, while in he righ image he hird phase was added. The illuminaion was he same for boh images, i.e. he lef objec was illuminaed wih a flash while he righ was illuminaed wih diffuse ligh. Figure 8 Illuminaion viewed wihou (lef) and wih he hird phase (righ) Figure 8 shows ha he flash illuminaion fades ou almos compleely. Tess wih lower inensiy flashes brough even beer resuls in fading ou he illuminaion. In boh cases, he video image is brigh enough o acquire good exure of he objec. Several ess were made in order o find ou if he camera needs o be synchronized. A CCD-camera was insalled wihin he es-seup of Figure 7. The camera was able o ake video picures every 1/50 s and was no synchronized wih he sroboscopic flash, running a 48 Hz. Figure 9 shows ypical resuls of such video acquisiion. Figure 9 Typical video acquisiion sequence wih a CCD-camera and a sroboscopic flash I can be seen from Figure 9 ha here is one picure frame wih poor illuminaion. This frame repeas afer 0.5 s. Figure 10 Typical video acquisiion sequence wih a CCD-camera and a LED flash

9 Using a LED s insead of he flash gives much beer resuls. I can be seen from Figure 10, ha he illuminaion differs. However, here is no picure frame wihou illuminaion. The period of he flash is slighly longer han he period of picure acquisiion. Assuming he flash illuminaion is a dirac impulse, here will be frames wihou illuminaion. The widh of he sroboscopic flash is very similar o such a dirac impulse, while he LED illuminaion is no. This causes ha every 25 h picure appears dark when he sroboscopic flash is used. In order o avoid inerference beween he flash frequency and he picure frequency of he camera, he camera mus be synchronized wih he flash frequency. This iniial es se-up proved ha he sroboscopic ligh could be used ogeher wih he video acquisiion sysem. Furhermore, i has been shown ha he hird phase of he shuer glasses shields he user s eyes sufficienly from exposure o acive scene illuminaion. 8 Conclusions The basic measuremens and he firs es resuls from he seup proved ha i is possible o inegrae acive illuminaion ino a sereoscopic viewing sysem and perform exure acquisiion of objecs and people inside he sysem. A hird phase (dark phase for boh eyes) wihin he shuer glass proecs he user s eyes from his addiional illuminaion. The iming frequency of his hird phase can be chosen o be fas enough so ha he human eye canno resolve i. The new echnology is compaible wih exising VR-sysems and incurs low addiional coss from he modified shuer glasses. This basic echnology will allow he developmen of new applicaions of virual realiy wihin a collaboraive framework. 9 Fuure work In addiion o he small es chamber, he sysem needs o be esed wihin a full-size es seup. This will give he user a beer impression of a modified VR-sysem. The ess have shown ha he sroboscopic illuminaion is needed a every display cycle. Therefore he couner in he elecronic circui is no longer necessary. Furher work will also be focused on he sroboscopic illuminaion. The sroboscope used in he iniial se-up was very noisy; a semiconducor flash could be used insead. This semiconducor flash can be made from a number of LED s placed all over he projecion room. This will creae sufficienly diffuse ligh, as required. In addiion we will work on an illuminaion wih infrared ligh, ha can be used in parallel o he projecion and he acive illuminaion. The infrared ligh ogeher wih specialized cameras will allow an easy silhouee exracion of he person inside he sysem.

10 10 Acknowledgemens The research work is funded by he ETH research conrac We would like o hank all members of he projec eam. 11 References 1. C. Cruz-Neira, D.J. Sandin, and T.A. DeFani, Surround-screen projecion-based virual realiy: The design and implemenaion of he cave." Proceedings of SIGGRAPH 93, pages , Augus E: Lanz. The fuure of virual realiy: head mouned displays versus spaially immersive displays (panel)." In Proceedings of SIGGRAPH 96, Compuer Graphics Proceedings, pages , Aug V.D. Lehner and T.A. DeFani. Disribued virual realiy: supporing remoe collaboraion in vehicle design." Compuer Graphics & Applicaions, 17(2): 13-17, R. Raskar, G. Welch, M. Cus, A. Lake; L. Sesin, and H. Fuchs. The office of he fuure: A unified approach o image-based modeling and spaially immersive displays." Proceedings of SIGGRAPH 98, pages , July C. Cruz-Neira, D. J. Sandin, T. A. DeFani, R. V. Kenyon, and J. C. Har. The cave: Audio visual experience auomaic virual environmen." Communicaions of he ACM, 35(6): 65 72, June T. Disz, M. Papka, M. Pellegrino, and R. Sevens. Sharing visualizaion experiences among remoe virual environmens." In Proceedings of he Inernaional Workshop on High Performance Compuing for Compuer Graphics and Visualizaion, July J. W. Davis and A. F. Bobick. Sideshow: A silhouee-based ineracive dualscreen environmen." Technical Repor 457, MIT Media Lab, H. Fuchs, G. Bishop, K. Arhur, L. McMillan, R. Bajcsy, S. Lee, H. Farid, and T. Kanade. Virual space eleconferencing using a sea of cameras." Technical Repor TR94-033, The Universiy of Norh Carolina a Chapel Hill, Deparmen of Compuer Science, T. Kanade, P. J. Narayanan, and P. W. Rander. Virualized realiy: Conceps and early resuls." In Proceedings of he IEEE Workshop on he Represenaion of Visual Scenes, June W. Elspass, L. VanGool, M. H. Gross, A. Kunz, M. Meier, G. Schmi, O. Saad, P. Sucki The BlueCave"; ETHZ-inernal research proposal; Swiss Federal Insiue of Technology (ETH) Zurich, Swizerland and Universiy of Zurich, Swizerland 11. A. Kunz, C. Spagno Modified Shuer Glasses for Projecion and Picure Acquisiion in Virual Environmens.", exended absrac o appear in IEEE VR 2001

4 20mA Interface-IC AM462 for industrial µ-processor applications

4 20mA Interface-IC AM462 for industrial µ-processor applications Because of he grea number of indusrial buses now available he majoriy of indusrial measuremen echnology applicaions sill calls for he sandard analog curren nework. The reason for his lies in he fac ha