vhd: a system for directing real-time virtual...

1 Introduction

VHD: a system fordirecting real-time virtualactors

Gaël Sannier1, Selim Balcisoy2,Nadia Magnenat-Thalmann1,Daniel Thalmann2

1 MIRALab, University of Geneva, 24 rue du GeneralDufour, CH 1211 Geneva, Switzerland2 Computer Graphics Laboratory, Swiss FederalInstitute of Technology, EPFL, LIG, CH 1015Lausanne, Switzerland

In this paper, we present a new system dedi-cated to the real-time production of multime-dia products and TV shows involving mul-tiple virtual actors and presenters. This sys-tem, named VHD (Virtual Human Director),may also be used for character animation onhigh-level systems and interaction with Web-based applications. The user can create vir-tual stories by directing all actions in realtime. It is similar to a movie producer di-recting actors during filming but with morecontrol given to the director in the sense thateverything is decided and controlled by thesame person. To make this complicated taskpossible, in a useable way, we based the in-teraction on the high-level control of the vir-tual actor.

Key words: Authoring tool – Virtual hu-mans – Real-time facial animation – Bodyanimation – Motion capture – Virtual speech– Virtual presenter

Though virtual human models have been in exis-tence for many years (Badler et al. 1993; Magnenat-Thalmann and Thalmann 1991), they have beenmainly used for research purposes to enable the sim-ulation of human movements and behaviors. Onlyrecently has there been any encouraging interestfrom outside the academic world, especially for mul-timedia products and TV applications. Traditionalcharacter animation techniques are time-consumingtasks without any real-time possibilities. Design andanimation of such characters is a time-demandingoperation as it is done using a general-purpose an-imation system like Softimage, Alias-Wavefront,Maya, or 3D StudioMax. Furthermore, characteranimation systems developed for high quality graph-ical output cannot interact with any other mediaspaces such as web-based applications, television, ortelecommunication.Traditional multimedia systems are systems thathandle different forms of data, such as text, audio,or video. Until recently, the Web has represented thetypical traditional multimedia system with HTMLtext, gif images, and movies. Then came VRML theVirtual Reality Modeling Language: a way of cre-ating 3D scenes allowing the Web users to walkthrough 3D spaces. VRML supports the integrationof virtual reality with the World Wide Web withthe goal of broadening access to VR environmentsvia the WWW infrastructure. Generally, virtual en-vironments define a new interface for networkedmultimedia applications. Users will be able to movein virtual spaces where they can find many virtualobjects, including virtual humans. These virtual ob-jects should be multimedia objects. For example,a virtual human should not only be a 3D graphi-cal object, but also an object able to speak or emitsound. A virtual dog should not only be able tomove, but also to bark. Virtual humans have po-tential applications in entertainment and businessproducts such as film, computer games, and as TVtalk-show hosts. New applications are involved withnew ways of interacting between real and virtualentities.VHD is a system which aims to provide interac-tive control of real-time virtual humans. In thispaper, after giving an overview of the system, wepresent the body and facial animation modules. Thenwe describe the user-friendly interface, and finallywe present some results, where we tested VHDwith broadcasting partners of the European ProjectVISTA.

The Visual Computer (1999) 15:320–329c© Springer-Verlag 1999

G. Sannier et al.: VHD: a system for directing real-time virtual actors 321

2 System overview

Controlling virtual humans is still a tedious task.A lot of work has been done in the area of providingeasy control of their behavior in the virtual environ-ment. Nevertheless, if typical systems are mainlyfocussed on the immersive aspects, just a few areinterested in controlling the virtual actors for the pur-pose of “virtual story” elaboration. However, withThe JACK system, Badler et al. (1993) focussed theirwork on providing realistic behavioral control ofhuman models. Based on a similar framework, Mo-tivate (http://www.motion-factory.com/home.html)was developed for the creation of 3D games. In Im-prov (Perlin and Goldberg 1996) provide tools todefine the behavior of their animated actors. Theirgoal is more to “educate” virtual actors, being able toreact by themselves to real humans or virtual events,than to give to the user the possibility of having spe-cific control of each virtual human. The goal of oursystem is to provide tools that will allow a user tocreate any scenario involving realistic virtual hu-mans. One other key aspect is to keep the ability toreact in real-time to some external events (for ex-ample, a virtual presenter interviewing a real guest)while showing a high-quality rendered virtual hu-man. This system is very similar to what is used bya real puppeteer, except that more control is given tothe user due to the complexity of animation that canbe triggered.In this paper, we do not discuss animation techniquesas in (Kalra et al. 1998), but we present a new kind ofsystem dedicated to the real-time production of mul-timedia products and TV shows. This system, namedVHD may also be used for character animation onhigh-end systems and interaction with Web-basedapplications.VHD focuses on two important issues:

- Fully integrated virtual humans with facial andbody animation, and speech.

- A straightforward user interface for designers anddirectors.

VHD system provides a range of virtual human an-imation and interaction capabilities integrated intoone single environment. Our software architectureallows the addition of different interfaces from dis-tinct environments. VHD actors can be controlled viaa standard TCP/IP connection over any network byusing our virtual human message protocol as shown

Fig. 1. System overview

in Fig. 1. Using this protocol, possible high-levelAI software can also be coded to control multipleactors.

3 Real-time animation modules forbody

In VHD, we have two types of body motion: prede-fined gestures and task-oriented motion. Predefinedgestures are prepared using keyframe animation andmotion capture. For task oriented motions like walk-ing we use motion motors.

3.1 Motion capturing and predefinedpostures

A traditional way of animating virtual humans isplaying keyframe sequences. We can record specifichuman body postures or gestures with a magneticmotion capturing system and an anatomical con-verter (Molet et al. 1996), or we can design hu-man postures or gestures using the TRACK system(Boulic et al. 1994).Motion capturing can be best achieved by usinga large number of sensors to register every degreeof freedom of the real body. Molet et al. (1996)consider that a minimum of 14 sensors are requiredto manage a biomechanically correct posture. Theraw data coming from the trackers has to be fil-tered and processed to obtain a usable structure.Our software permits the conversion of raw trackerdata into joint angle data for all 75 joints in theskeleton.

322 G. Sannier et al.: VHD: a system for directing real-time virtual actors

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Fig. 2. Keyframe examples with user interfaceFig. 3. Walking example with walking interface

TRACK is an interactive tool for the visualiza-tion, editing and manipulation of multiple track se-quences. To record an animation sequence we createkey positions from the scene, then store the 3D pa-rameters as 2D tracks of the skeleton joints. Thestored keyframes, from the TRACK system or mag-netic tracker, can be used to animate the virtualhuman in real time. We use predefined postures andgestures to perform realistic hand and upper bodygestures for interpersonal communications. Figure 2presents some predefined postures and a body ani-mation part of the user interface.Users can trigger gestures and postures from a liston the main interface. Moreover, users can automatethe activation of gestures and postures from the inter-face. A good example is automating “neutral” pos-tures: usually when nothing is happening, e.g., whenan actor is not performing any animation, the actorlooks “frozen”. It is not easy for a user to activaterandom postures to move the actor slightly every fewseconds. To overcome this problem we developeda programmable posture trigger, where a user can de-cide the interval and randomness of a posture. Theright-most image in Fig. 1 shows details from theuser interface. The upper slider “Weight” defines theweight of current active keyframe in case of a motionmerge with other body animation. Under the sliderthere is a selectable list of available keyframes.

3.2 Motion motors

We used one motion motor (Boulic et al. 1990) forthe body locomotion. Current walking motors en-able virtual humans to travel in the environment us-ing instantaneous velocity of motion. One can com-pute the walking cycle-length and time from whichthe necessary skeleton joint angles can be calculatedfor animation. This instantaneous speed-oriented ap-proach has influenced VHD user interface design,where user is directly changing the speed. On theother hand VHD also supports another module forcontrolling walking, where users can control walk-ing with simple commands like “WALK_FASTER”or “TURN_LEFT”. This simple interface allows spe-cific user interfaces to talk with VHD more easily.A possible user interface is a touch phone to con-trol walking. In this case setting speed and directionis impossible with our first method. The latter onesolves this problem in a natural way where we canmap our commands to each key on the number pad.Figure 3 includes snapshots from a walking sessionin one picture.In many cases actors are expected to perform mul-tiple body motions like waving while walking. Ouragent-based software (Boulic et al. 1992) coordi-nates multiple AGENTS with multiple ACTIONS.AGENTLib also manages natural motion blending.


VHD is built on the AGENTLib library for body an-imation, motion planning and motion blending.

4 Real-time animation and speech forface

For virtual actors and presenters, facial animation isessential. In this section we will describe our methodfor animating a 3D-face model. The animation isdriven by high-level actions such as “smile”, “sur-prise”, which also control the head deformations. Forthe speech part, different approaches have been pro-posed. Pearce et al. (1986) use a string of phonemesto generate the corresponding animation of the 3Dface, while Cohen and Massaro (1993) start withan English text as input to generate the speech. Inour system we combine both elements to generatespeech. We extended our facial animation model tospeech capabilities by combining these facial anima-tions with the output of a text-to-audio system at thephoneme level.

4.1 Real-time facial animation system

Globally, the process of face animation is decom-posed into several layers of information as shown inFig. 4.

• The high-level actions concern the emotions, thesentences and the head movements of the virtualactor. The animator completely directs the virtualclone with actions from this level.Emotions are interpreted as an evolution of faceover time. It is defined as starting from a neu-tral state, passing through a sequence of visiblechanges, and returning to a neutral state. A libraryof standard emotions can be defined, includingsmile, anger, surprise, fear, etc., but specific emo-tions like “virtual twitch” can also be created topersonalize the virtual human.For speech animation, each sentence is decom-posed into phonemes. To each phoneme corre-sponds a viseme, which is the phoneme coun-terpart in terms of facial animation. A total of44 visemes are used. Examples of visemes aregiven in Fig. 5. From the animation point of view,a sentence is a sequence of temporized visemes.Nevertheless, during a conversation, a humanmouth is not able to articulate precisely eachphoneme: visemes are blended with one another

Fig. 4. Layer of information to perform facial animation

through time. In order to smooth the animation,we mix the beginning of a viseme with the end ofthe previous one.Finally, the head movements can be controlled bysetting the intensity of motion over time.

• The mid-level actions can be defined as expres-sions of the face. They are considered as a facialsnapshot modulated in time and intensity to makethe high-level actions. A facial snapshot is com-posed by a set of low-level action units.

• The low-level actions are defined as 63 face re-gions. Each region corresponds to a facial mus-cle. An intensity value is associated to each re-gion describing its deformation. These intensitiesare called ‘Minimum Perceptible Actions’ (MPA).For each frame of the facial animation, an array of63 MPAs is provided, defining the state of the faceat this frame.

• The deformation of the face is performed usingRational Free Form Deformation (RFFD) appliedon regions of the mesh corresponding to the fa-cial muscles (Kalra et al. 1992). The role of ourfacial animation library is to compute, at every ac-tivation of high-level action, a list of MPA frames.To get the face deformation at a given time, thislibrary composes, one by one, every MPA of thetime-right frame of each activated action. It al-lows the mixing of high-level actions in real-time(for example smiling while speaking). The result-


Fig. 5. A virtual head model with its corresponding visemes for the indicated words

ing array of MPA is transmitted to the face ani-mation module that computes the deformation ofthe mesh. This regions-based method is totallymesh/head independent, as long as the 63 regionsare well defined for each object.

4.2 Speech

The input text is converted into temporized phon-emes using a text-to-speech synthesis system. In thiscase we are using the Festival Speech Synthesis Sys-tem that is being developed at the University of Edin-burgh (Black and Taylor 1997). It also produces theaudio stream that will be subsequently played backin synchronization with the facial animation system.Using the temporized phonemes, we are able to cre-ate the facial animation by concatenating the corre-sponding visemes through time. Most of time, weuse the set of phonemes present in the Oxford En-glish Dictionary. Nevertheless, an easy extension toany language could be done by designing the corre-sponding visemes. As a case study, we also extendour model to the German language.The synchronization of face movement with soundis initially done by starting the two processes at thesame time. In order to keep synchronization duringall the speech, we use the sound playback as a timereference. By knowing beforehand the total lengthof the sound, the number of frames of the animation(given by the temporized visemes), and the currenttime, the synchronization can be done easily by skip-ping frames in case of delay.

5 Software issues on integration

In order to be able to optimize quality, a computercan be completely dedicated to the rendering usingIRIS Performer (Rohlf and Helman 1994) libraries,while another one is used only for the interface. Theconstraint, for the interface, is to remotely control theanimation in real time.For that purpose, a very simplified client-server pro-tocol was established as shown in Fig. 6. The in-terface communicates directly with the 3D applica-tion using TCP/IP sockets over a network. It al-lows the computing of a real-time full-screen ren-dered animation while also having a whole screendedicated to the interface. In order to make the con-nection possible between the interface and the 3Dapplication, a communication protocol has been es-tablished. As a consequence, any interface using thesame protocol for communication is able to controlthe 3D environment.A new concept can be developed based on the idea ofa networked PC-based interface as shown in Fig. 7.Each client of this network will have control of oneactor. A simplified lower-quality rendering could bedisplayed on each PC. A specific client would con-trol the cameras. The server of this network, ob-taining all the data from all its clients, could usethe communication protocol for directing the 3Dapplication in order to render a high quality out-put of the scene in real time. Such a PC connec-tion is planned for the near future using a JAVAserver with VRML worlds, where home users con-nect to a multi-user VRML media space. VHD can


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Fig. 6. Simplified client-server system between the interface and the 3D application

Fig. 7. A client-server network linked with VHD output

be used as a flying camera over a multi-user world.The Director can shoot interesting interactions witha virtual camera.

6 Interface design issues

In the previous sections, we described a system foranimating virtual humans with regard to quality con-straints. We will now present aspects of interactivitydeveloped in this system.The issue of easily controlling a virtual face wasraised in (Magnenat-Thalmann et al. 1998). The goalof the VHD interface is an extension of this concept.VHD provides an easy way to control multiple actorsand cameras in real time. Thus, the user can cre-ate virtual stories by directing all the actions in realtime. It is similar to a producer directing actors dur-

ing shooting but with more control given to the pro-ducer in the sense that everything is decided and con-trolled by the same person. To make this complicatedtask possible and useable, we provide high-level con-trol of the virtual actors. Tools were developed tobe able to predefine actions in advance so that dur-ing real-time playing, the producer can concentrateon the main guidelines of his scenario (sentences forexample).Only high-level actions can be used with the inter-face. It allows control of the speech by typing/select-ing simple text-based sentences. The facial anima-tion is controlled by pre-recorded sequences. Thesefacial animations can be mixed in real time and alsomixed with speech. Control of the body is donethrough keyframing and motion motors for walking.As soon as we have many virtual actors to control,the number of available actions will make the task


Fig. 8. Interface setting the camera position to “General View”

of the director more and more complex. In order toease this complicated task for real-time interaction,we provide several tools for pre-programming ac-tions in advance. The user can give a time after whichthe action will be played. Nevertheless, the idea ismore useful for repeating actions. For example, wecan program the eye blinking of an actor every fiveseconds. However, not all the actions can be pro-grammed this way. As the goal is to be able to playthe scenario in real time, we want to let the con-trol of the main actions to be in the hands of thedirector. Nevertheless, a lot of actions result froma few main events. Let’s consider the sentence “Iam very pleased to be here with you today”. Theuser may want to have the virtual actor smiling aftersomething like one second (while saying: “pleased”)and move the right hand after 1.5 seconds (saying:“here”). So the idea is to pre-program actions to beplayed after the beginning of a main event which isthe sentence. Then, just by selecting the main ac-tions, complex behavior of the virtual actors will becompletely determined. However, the user will stillbe able to mix other actions to the pre-programmedones.Basic virtual camera tools are also given to theuser. New camera positions can be fixed interac-tively from the interface. Cameras can be attachedto virtual humans, so that we can have a total shotand a close-up of a virtual actor whatever his/herposition is on the virtual scene. During real time,the list of camera positions is available on the in-terface, and the user can switch from one camerato the other just by clicking on it. An interpola-tion time can be easily set to provide zooming and

traveling options between two camera positions.Figure 8 shows a snapshot of camera control in-terface. The cameras are also considered as an ex-tension of the actions. They can be programmed inadvance so when an actor says a sentence, the cam-era can be programmed to go directly to a givenposition.In order to improve the building of virtual stories,a scripting tool was developed for recording all theactions being directed to an actor. Each action isrecorded into a file with its activation time. Then,the user can adjust the timing of the sequence andplay it again in real time. During playback, new ac-tions can be triggered. As the saving is done inde-pendently for each actor and for the cameras, onecan program each actor separately. At the end, allthe scripts can be played at once. The other impor-tant aspect is to be able to program background ac-tors. Then, only important actors will be directed“live”.

7 Results

We tested our software extensively within the Euro-pean project VISTA, with broadcasting partners, toproduce TV programs. After several tests with de-signers and directors, our concept of one single in-tegrated platform for virtual humans obtained goodfeedback. Our interface has a straightforward con-cept and the high level of control allows designers tocontrol virtual humans in a natural way. We includedseveral traditional camera operations into our inter-face to allow directors to use VHD without a steeplearning curve.This case study presents how VHD can be used tomake interactive events. The first stage is compila-tion of the scenario. Designers then create virtualhumans. According to the scenario, the produc-tion team records necessary predefined body ges-tures, facial animations and sentences. After this, thefirst trials may start with VHD. The director gen-erates specific camera shots and checks all partsof the scenario. The director and the productionteam record and edit the complete scenario withthe scripting capabilities of VHD. Some complexparts of a real-time show can be recorded as a scriptto have a perfectly synchronized result. Today, themain interest is in the mixing of real and virtual el-ements in the same environment. Production housesuse several virtual set applications to attract view-


Fig. 9. Examples of the interface controlling virtual actors

ers by using mixed environments. Virtual sets in-clude multiple components like a rendering system,an animation management system and a cameracalibration system. In our work with broadcast-ing companies we had to embed VHD into sucha large system. Preset positions for static camerashots and other environmental parameters are setby the interface. A major problem was synchro-nization of real and virtual cameras (when the realcamera switches from position A to B). To havecorrect synchronization we developed a serial portinterface for VHD. Through this interface a realcamera switch sends the number of the active realcamera to VHD. As such a connection can be usedfor dynamic cameras, we are planning to developa dynamic camera tracking protocol in the nearfuture.Figure 9 displays snapshots from a VHD sessionwhere designers are testing a conversation betweentwo virtual actors.In all the design steps of VHD we tried to keep realtime as our main target. We used multiple processesfor communication, sound rendering (speech) and

animation. We used a 4-processor SGI Onyx2 witha single Infinite Reality Pipe for timings in the firstdiagram of Table 1. VHD renders and animates up to4 actors at acceptable rates. The frame size is fixed toPAL size.We also tested VHD with a close-up virtual headmade of 2313 triangles and fully textured. The sec-ond diagram in Table 1 presents the number offrames per second we got on our trials on the follow-ing computers using full screen (1280×1024) anda 400×500 pixel window:

1- O2 R5000 at 200 MHz2- Octane R10000 at 195 MHz3- Onyx2 2x R10000 at 195 MHz

8 Conclusion and future work

In this paper we have presented a novel system forintegrated virtual human animation. Our software,VHD, has been developed to enable a non-computerscientist to interact with virtual humans in several


Table 1. Real-time performance diagrams

ways. A designer can create a full story by directing,and animating several virtual actors. A home usercan get connected via their home PC to a studio andcontrol one virtual actor (this option requires specialPC software). A director and a team of artists cancreate a complex event, where virtual actors interactwith real actors.For many AI programs VHD can be used to createa visual environment. VHD also provides an openplatform to extend the capabilities of virtual humanswithout any major difficulties.In the near future we are planning to add new ca-pabilities to VHD. Several high-level motion/taskcontrols and editing facilities will be integrated tocreate mini scripts. Automatic grasping of virtual ob-jects will be included. We have already started tointegrate an AI system to trigger reactions to facialemotions, sentences, and pre-recorded keyframes forthe body. We will also look for integration with com-puter vision-based tracker software to have a fullyintegrated augmented reality system. In order to im-prove the audio control of our virtual actors, we areworking for direct-speech animation control with theuse of a microphone.

Acknowledgements. The authors would like to thank MIRALab andLIG teams for their support, and Frank Alsema from VPro for his in-tuitive ideas and constructive criticism. We would also like to thankChris Joslin for proof-reading this document. The European ProjectVISTA and the Swiss National Foundation for Scientific Research sup-ported this research.

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DANIEL THALMANN isa pioneer in research on virtualhumans. His current research in-terests include real-time virtualhumans in virtual reality, net-worked virtual environments, ar-tificial life, and multimedia. Heis coeditor-in-chief of the Jour-nal of Visualization and Com-puter Animation, member of theeditorial board of the VisualComputer, the CADDM Journal(China Engineering Society) andComputer Graphics (Russia). Heis cochair of the EUROGRAPH-

ICS Working Group on Computer Simulation and Animationand member of the Executive Board of the Computer GraphicsSociety. Daniel Thalmann was member of numerous ProgramCommittees, Program Chair of several conferences and chairof the Computer Graphics International ’93, Pacific Graph-ics ’95, and ACM VRST ’97 conferences. He has also organized4 courses at SIGGRAPH on human animation. He has pub-lished more than 200 papers in Graphics, Animation, andVirtual Reality. He is coeditor of 25 books, and coauthor ofseveral books including: Computer Animation: Theory andPractice and Image Synthesis: Theory and Practice. He is alsocodirector of several computer-generated films with syntheticactors including a synthetic Marilyn Monroe shown on numer-ous TV channels all over the world.

NADIA MAGNENAT–THAL-MANN has pioneered researchinto virtual humans over the last20 years. She studied psychol-ogy, biology and chemistry atthe University of Geneva andobtained her PhD in computerscience (cum laude) in 1977.In 1989 she founded MIRAlab,an interdisciplinary creative re-search laboratory at the Uni-versity of Geneva. Some recentawards for her work include the

1992 Moebius Prize for the best multimedia system awarded bythe European Community, “Best Paper” at the British ComputerGraphics Society congress in 1993, election to the Academy ofImage by the Belgium Television in Brussels in l993, and elec-tion as a Member at the Swiss Academy of Technical Sciences,in l997. She is president of the Computer Graphics Society andchair of the IFIP Working Group 5.10 in computer graphics andvirtual worlds.

GAEL SANNIER is a com-puter scientist who has studiedin Lyon (master degree in Com-puter Graphics in 1996). Heis now working at the Univer-sity of Geneva as a researchassistant in MIRALab partici-pating in research being donethere. His main tasks are user-friendly texture-fitting methodsand virtual presenters for TVapplications.

SELIM BALCISOY is cur-rently research assistant in theComputer Graphics Laboratoryat Swiss Federal Institute ofTechnology (EPFL). He gradu-ated from ETHZ in Electronicsin 1996. His research interestsinclude mixing real and syn-thetic worlds, augmented realityand vision, and human actionrecognition.

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