White PaPer3-D for Cinema

anD television

Document created under the sponsorship ofFicam, the CST, UP3D, the HD-Forum and the AFC

White PaPer3-D for Cinema

anD television

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Editorial Coordination : Marc Bourhis (Ficam) and Olivier Amato (Smartjog)Editorial Coordination : Marc Bourhis (Ficam) and Olivier Amato (Smartjog)

Document created under the sponsorship ofFicam, the CST, UP3D, the HD-Forum and the AFC

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The Ficam (Fédération des Industries du Cinéma, de l’Audiovisuel et du Multimédia), presided over by Thierry de Segonzac, is a professional organization bringing together 180 enterprises whose activity covers all the professions and technical know-how dealing with image and sound. Always proposing strong measures, the Ficam represents, promotes and defends the national and international interests of technical industries dealing with audiovisual creation.

The Commission Supérieure Technique de l’Image et du Son (CST), presided over by Pierre-William Glenn is an association grouping professionals in cinema and the audiovisual and multimedia fields, as well as technicians and technical artists. The CST brings together today close to 700 members. Its goals are to defend the quality of the production and distribution of images and sound, defend creativity and technological and artistic innovation in cinema and the audiovisual fields, as well as to defend the independence and freedom of action and expression in our professional activities.

UP3D (Union des professionnels de la 3Ds) is an association whose objectives are: to bring together and animate the 3-D professional community, inform and communicate on the professions, know-how and equipment specific to the 3-D world, and to promote and develop 3-D in Europe.

Partners for this white paper :

The AFC (Association Française des Directeurs de la Photographie Cinématographique), co-presided over by Matthieu Poirot-Delpech, Michel Abramowicz and Remy Chevrin, brings together most of the directors of French cinematic photography at the highest artistic and technical level of French and foreign productions. The AFC promotes the existence of quality cinematic images, tests new techniques and affirms the competence of photography directors as creative collaborators of film directors, in the best tradition of French cultural and artistic discourse.

Originally composed of 17 members, the HD Forum, presided over by Jean-Pierre Lacotte, now has 51 members, all professionals as stated in the statutes. The diversity of the questions to resolve around HD has led the HD Forum to create two commissions: the “technical commission” and the “communication and marketing commission”, which are themselves divided into work groups that regularly collaborate with the work of the Ficam and the CST.

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Special thanks :

To Pascal Buron (associate president of Ficam in charge of the Research and Innovation technical commission, and to Olivier Amato (Smartjog) for all the coordination work they did on this project as they have done on so many others. A big thank you to Yves Pupulin (Bincole) for his contribution to all the chapters of this white paper. Thank you also to Olivier Cahen (Stéréo-Club Français) for having shared with us his encyclopedic knowledge of 3-D and for his editorial contribution to the visual comfort chapter, as well as to Philippe Gérard (3DLized), who, through his commitment to research on 3-D visual comfort, permitted us to be at the forefront of ideas on this question. A big thank you, too, to Marc Léger (INA Sup) for the writing of the chapter on the main principles of 3-D and the updating of the chapter on codecs and modes of TV distribution.Many thanks to the late Alain Derobe (stereographer and photography director) who passed away on 11 March 2012, for having accepted in due course the taking up again of his contribution made to the CST concerning the adapting of 3-D to the size of the broadcast screen, as well as to the members of the CST for their contribution to the part on 3-D projection for cinema. Thanks as well to Laurent Verduci (stereographer) for his educational aids on 3-D which we used as a common theme and for his active participation in our work groups. Thanks also to Alain Chaptal (Sonovision), Franck Montagné (Imagie), Michel Chabrol (Eutelsat), Thierry Gruszka (NDS/CISCO), Eric Martin (Technicolor), Charles de Cayeux (France Télévisions), Pascal Charpentier (UP3D) and Benoit Michel (stereoscopynews.com) for their active participation. Finally, we wish to thank all those who attentively reread the final document. Thanks also to David Steiner and Cédric-Alexandre Saudinos (Parallell Cinéma) for their contribution on the techniques of preproduction and filming, as well as to Philippe Ros (photo AFC director)..

TOMORROWstarts here.

Today, it s easy to marvel at how ar we ve come.

Our phones talk to our TVs to record our avorite shows. Doctors in Estonia diagnosepatients in Denmark. Social networks help companies improve customer service.

And yet, up to now, more than 99% o our world is not connected to the Internet.

But we re working on it.

And tomorrow, we ll wake up pretty much everything else you can imagine.

Trees will talk to networks will talk to scientists about climate change.

Stoplights will talk to cars will talk to road sensors about increasing tra ic e iciency.

Ambulances will talk to patient records will talk to doctors about saving lives.

It s a phenomenon we call the Internet o Everything an unprecedented opportunity

or today s businesses.

Tomorrow?

We re going to wake the world up. And watch, with eyes wide, as it gets to work.

#tomorrowstartshere

©2012 Cisco Systems, Inc. All Rights Reserved

Why a White PaPer on stereosCoPiC 3-D* (3Ds)?? PaGe 8

funDamental PrinCiPles of stereosCoPy PaGe 10

riGs anD stereosCoPiC Cameras PaGe 20

live multi-Camera 3Ds CaPturinG PaGe 24

3Ds PostProDuCtion: CorreCtions anD WorKfloW PaGe 25

2-D/3Ds Conversion: the neeD for KnoW-hoW PaGe 30

visual Comfort With 3Ds PaGe 32

3Ds ProJeCtion for films PaGe 34

3-D tv DisPlay PaGe 36

aDaPtinG 3-D to the siZe of the BroaDCast sCreen PaGe 40

3Ds Glossary PaGe 45

aPPenDiX 1: Definition of 3Ds Professions PaGe 47

aPPenDiX 2: 3-D filminG teChniQues PaGe 49

aPPenDiX 3: CoDeCs anD DistriBution moDes PaGe 54

SOMMAIRE

FICAM (Fédération des Industries du Cinéma, de l’Audiovisuel et du Multimédia)11/17, rue de l'Amiral Hamelin-75783 Paris Cedex 16-Tel : + 33 (0)1 45 05 72 55-Fax : + 33 (0)1 45 05 72 50

FÉDÉRER ET PROMOUVOIR LES INDUSTRIES TECHNIQUESDU CINÉMA, DE L’AUDIOVISUEL ET DU MULTIMÉDIA

With over 180 member companies,the Ficam represents and promotesthe technical industries of Cinema,

Audiovisual and Multimedia.

www.ficam.fr

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ever since movie theaters have been equipped with digital 3-D pro-jectors, a number of 3-D feature-length films have been shown with often disparate processing quality. The television market has

also decided to respond rapidly to the desire of the public for 3-D films. The television manufacturers, quick to participate in this technological craze, now make flat television screens on a grand scale equipped with display systems “in 3-D”, allowing the viewer to watch 3Ds TV programs in conditions of quite acceptable visual comfort. Moreover, some smart-phones have recently appeared in the mass market which are capable of generating autostereoscopic 3-D. However, the market for mobile, TV and cinema broadcast hardware is much in advance, chronologically speaking, of the produc-tion capacity of stereoscopic 3-D content by the audiovisual and cinema industry. Up to now, there does not exist enough natively produced 3Ds content to furnish all the ad hoc broadcast media. The barrier is mainly economic and technological, but it is also a result of a lack of informa-tion on the practical conditions in which it is possible today to create film in 3-D for television and cinema. Due to the current deficiency in 3Ds content, it should be noted that many 3-D films and programs broadcast in movie theaters, or on the first 3Ds television channels, use procedures that create 3-D from 2-D automated images. These do not sufficiently take into account the main principles of visual comfort for the viewer and put into question the notion of respect for the original work. Given this enthusiasm for 3-D, it seemed necessary for diffe-rent professional organizations of the cinematographic and television industries (Ficam, CST, UP3D, AFC, HD-Forum, etc.) to produce a white paper laying out the current state of stereoscopic 3-D. The goal of this white paper is to point out the different technical and narrative issues tied to the filming, postproduction, visual comfort, 2-D/3Ds conversion and display on a cinema and/or television screen. Stereoscopic 3-D is an artistic and technical mechanism requi-ring a mental reconstruction of images, which is chosen by the director and limited by the physiological laws specific to most viewers. As such, it is crucial to put in place, at every step in the manu-facturing chain, 3-D monitoring and quality procedures supervised by qualified personnel and trained in this new mode of creation and post-

Why a White PaPer

production. In fact, stereoscopic 3-D, if it adds new possibilities on the narrative level, also includes new obligations on the technical level tied to the cerebral acceptance of cinema and television viewers. This is why, in this 3Ds white paper, our objective is not to constrain the creativity of directors, who should remain free in their artistic content, but to set a framework for their being better able to get around in the additional production possibilities specific to stereoscopic 3-D. It is also important to specify that the study of stereoscopy, already quite old, has allowed the visual comfort zones–inside which a viewer will have no discomfort or, not to say headaches–to be empiri-cally defined. Scientific studies are now taking place to refine these pa-rameters.We say also that the art of 3Ds is only at its beginnings. There will no doubt be the possibility for directors of films or television broadcasts to go beyond this technical framework, at least from time to time, in order to provoke quite new emotions in the viewer. Finally, it should be noted that the perception of the depth of an object in a 3Ds scene is modified according to the size of the display of the images (movie theater screens or televisions). This white paper thus describes the different display technologies and defines the technical contours of future 3Ds programs to be provided for television and the cinema. In fact, in order to summarize the main objective of this white paper, we would say that it consists of sufficiently informing audiovi-sual and cinema professionals on the possibilities of 3Ds so that they can appropriate this new language as much as possible, and that public disappointment can be avoided for this new artistic and technical field, as might have been the case during the first wave of infatuation for 3-D films in the 1950’s.

This white paper on 3-D refers to the state of the art in May 2012. It is the second version of the document that takes into account the remarks of French professionals and updates the generic ideas on the subject.

* rather than use the terms “relief” or “3-D”, quite imprecise for the former and source of confusion with computer generated images for the latter, we recommend using the term “3Ds” for stereoscopic 3-D.

on stereosCoPiC 3-D* (3Ds) ?

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let’s look at a close object: for example the index finger of our hand. Naturally, the optic axes of our eyes convergent

towards the object being looked at. We thus become slightly cross-eyed. The more the ob-ject is close to us, the more we become cross-eyed: the angle of convergence increases. The more the object moves away, the more the angle of convergence decreases. The angle of convergence is a very important indication for our brain: knowing the distance between the two eyes, it can deduce the distance of the object, like a range-finder. The brain allows us to perceive the depth of the scene by way of the differen-ces between the angles of convergence of the different ob-jects being observed. Now let us examine the images formed by our two eyes: as the optic axes of our eyes converge towards our finger, the image of our finger is formed at the same place on our two retinas (Figure 1). We call the same points of the objects in the left and right images “homologous points”. It is said in this case that the homologous points are fused and that our finger is in the “plane of conver-gence” of our eyes.

Now, while continuing to look at the tip of our finger, let us consider the objects situated behind our finger (Figure 2). On which side to they seem to be placed when we close one eye and then the other? We notice that they are more to the left seen from the left eye and more to the right seem from the right eye. It is what is called parallax. It is said that for objects situated behind the plane of conver-gence, the parallax is positive. Let us observe again our finger and now consider the objects

that are closer (Figure 3). The p h e n o m e n o n is inversed: the object is more to the right seem from the left eye and more to the left seem from the right eye. For objects situated in front of the plane of

convergence, the parallax is negative. In sum, the parallax is zero for all the objects situated in the plane of convergence, positive for all the objects si-tuated behind the plane of convergence and negative for all the objects situated in front of the plane of convergence.The more an object is distant, the more the perception of its distance is imprecise. When the distance of the object goes beyond several dozen meters, the two optic axes of our eyes

funDamental PrinCiPles of stereosCoPy

hoW Do We PerCeive 3-D ?

are then practically parallel and the angle of convergence becomes too small to inform us sufficiently as to the distance of the object. Be-ginning from a 100 meters, the distance of an

object can hardly be perceived. Happily, other indications inform us of the depth: occultation, relative size of the objects, perspective, the ef-fect of mist, etc.

figure 1 figure 2 figure 3

figure 4

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hoW is 3-D reConstruCteD?

We now take two cameras in pla-ce of our two eyes along with a 3-D screen system whose role

is to make each eye see only the image that is intended for it. In Figure 4, the left and right homologous points are repre-sented respectively in red and cyan. If the homologous points are superimposed du-ring projection, the view will converge on the screen and the object will be seen on the plane of the screen. That is how one sees films in 2-D.If the parallax is positive, the view will converge towards a point situated behind the screen: the viewer will thus have the impression that the object is situated behind the screen (as if seen through a window). Finally, if the parallax is nega-tive, the view will converge towards a point situated in front of the screen, and the object will thus seem to be in front of the screen (as if popping out).In sum:• Objects situated on the plane of conver-gence during filming will be reconstructed on the plane of the screen (parallax zero).• Objects situated behind the plane of convergence during filming will be re-constructed behind the screen: window effect (positive parallax).• Objects situated in front of the plane of convergence during filming will be recons-tructed in front of the screen: popping-out effect (negative parallax).

the fundamental difference between attempts in the past and the present growth of 3Ds comes from the tech-

nical mastery of 3-D in the entire chain of the manufacturing and image broadcasting process. The use of computer tools during shooting and the possibilities of modifying images pixel by pixel up to broadcasting are steps that from now on are indispensa-ble and in constant evolution. They guaran-tee the quality of the 3Ds image necessary for the visual comfort of the viewer.Digital tools take part in the mastery of stereoscopic production. Being more knowledgeable from this experience, we wish today to support the emergence of a new cinematographic and television lan-guage tied to the usage of 3Ds.A purely technical conception of 3Ds is a risky bet. It is preferable to rely on the savoir-faire, both technical and artistic, of the stereographers and technical service companies, which have both a solid theo-retical knowledge and experience in 3Ds.The production of a sequence in 3Ds can-not be summed up in an automatic algo-rithm for creating 3-D effects, however sophisticated it may be, or do without the onsite experience of specialized professio-nals who know how to adapt to particular filming conditions, very often full of unfo-reseen events. The creation of a 3Ds scene requires a perfectly regulated production with the camera angles completely maste-red. If the production teams are not sup-ported by competent people in this way, they risk having their possibilities limited as to the creation of emotions in the viewer specifically tied to 3-D effects of depth or of popping out, or even in certain cases, to provoke visual discomfort in the public.

Stereography : a new production languageCreating for the cinema or for television is not tied only to the techniques of produc-tion or broadcasting, but also to the emo-tional connection that these images foster in the human brain. From this standpoint, 3Ds requires that this connection be re-considered so as to adapt the conditions of creating a cinematographic or televi-sion project to this question. 3Ds induces a rupture with the practices of production and which modifies the interpretation of the space as imagined by the director. One should also note that, in studying certain filming parameters such as lighting and framing, if there is a rupture between 2-D and 3Ds, it is situated more on the side of acceptance by the viewer’s brain than that of artistic practice.In 2-D as in 3Ds, the director remains the main judge of the use of 3-D in order to serve his narrative, whether it is a question of a film, a telefilm or a televised program. In the same way that he decides a produc-tion in 2-D, he formulates a particular re-quest to the stereographer who will see to its completion. The working together of the director and the stereographer thus aims to establish “3-D behavior” (modulation of the stereoscopic range), done through a graphic image or annotations on the script or storyboard, which then serves as a guide for the team doing the shooting. 3-D that is too strong can lead to visual discomfort over time, while 3-D that is too weak risks frustrating the viewer. It is mainly within these limits that the director can choose the depths he wants. The streographer translates these choices using the tools at his disposal, tools which he will super-vise in their practical use. Given this, he is responsible for the adjustment of the angulation and the inter-axial distance between the center of the camera lenses according to the chosen focal length, and

consequently the placing of the plane of convergence as well as the amplitude of the “scenic box” (see Appendix 2).It should be noted that the size of the 3Ds monitoring screen during filming does not necessarily correspond to that of the fi-nal broadcast. The stereographer should clearly inform the production team of the differences in the sense of depth according to the dimensions of the film’s intended screen and to justify his “not visual” but “provisional” adjustments.The parameters of “depth” can be in-creasingly modified in postproduction. Gi-ven this fact, just as the color calibration gives the tone of the scenes in a film, the “3Ds calibration” becomes an important step after the film has been edited. It al-lows for the perception of reality in 3-D to be given a general tonality and to provide 3Ds continuity between shots according to the final intention of the director.

Think about 3Ds before filmingIf you want to have a quality 3-D effect, it would be useful to verify beforehand the pertinence of the choice of 3Ds for this or that film or television program from the beginning of the synopsis or scenario. In this way, a story unfolding in an aerial or aquatic universe lends itself totally to a popping-out effect, for the objects can be “unglued” from any support, like levita-ting in a fluid or a vacuum. Furthermore, longer shots and/or rather slow and fluid movements of the cameras also favor the perception of a more comfortable 3-D ef-fect. They leave time for the public to dis-cover and enter into the depth of the ima-ge. In the same way, wide compositions with framing using high-angle or low-an-gle shots favor 3-D effects and intensify sensations of dizziness. Geometric forms, buildings for example, are more quic-kly identified by our brain and contribute to the quick immersion into 3-D. As for

3Ds aPPlieD to Cinema anD television

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Creating a 3-D SCene

From the beginning of writing the scenario, 3-D can be taken into account and used as a narrative tool. It is possible to imagine scenes whose dramatic intensity will be amplified if one plays with the depth, the popping-out effect and the effects of gigantic size and minia-turization. The scriptwriters can think about 3-D effects in advance, sometimes integrating their ideas directly into the scenario. These can be indicated in capital letters (in the Anglo-Saxon world, they are sometimes preceded by the term “3DFX”). Nevertheless, the logical process of creating a film lends to entrusting the control of stereoscopic effects to the director and/or stereographer. For example, in Océanosaures (Sea Rex), a 3-D IMAX© film written and directed by the Frenchmen Pascal Vuong and Ronan Chapalain, the stereoscopic filming proposals appear right from the storyboard.

It should be noted in the case of this film that Pascal Vuong created the storyboard himself and Ronan Chapalain supervised the stereography, thus allowing each shot to be conceived very early in all its depth and not as a 2-D image. In this storyboard extract, the colored markings added to the initial drawing permit one to quickly loca-te the elements to be popping out and the position of individuals in relation to the plane of the screen. This stereoscopic pro-duction information, added to the framing and cropping choices, allows the director and film crew to better prepare the shoo-ting and postproduction of the images and prevent certain pitfalls of stereography en-visaged too late in the process.

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streaming programs, among the first ex-periments taking place today using 3Ds in retransmission of sporting events, football is looked on as the favorite due to the high number of viewers and a public potentially interested by the fact of viewing matches in 3-D. Nevertheless, the current produc-tions of this sport on television, centered on lateral panoramas and a depth of field often difficult to master, is not necessarily the best adapted to retransmission in 3D, unless the camera angles and the pano-ramas are comple-tely rethought out with respect to a 2-D retrans-mission. A fur-ther constraint comes from the fact that the ac-tion takes place most of the time far from the ca-meras, thus re-quiring the use of a long focal length on the basis of wide 3-D shots that could create a “maquette” effect. On the other hand, certain inside sports, such as basketball, where one can be clo-ser to the action, offers 3-D that reinforces the viewer’s emotions.

PreproductionPreparation is essential in order for fil-ming in 3Ds to be successful. Researching particularly meticulous points (measuring distances, verification of distant objects, taking into account the size of the 3Ds rig) permits many problems to be avoided in advance. Creating a 3Ds storyboard is ad-vised. Without help from software, this sto-ryboard could show, for each shot, at least two or more views for the most complica-

ted cases:- The shot itself, as in a classic film. Ideal-ly, the storyboard creator should create a storyboard that is optically correct.- A view “from the side”. Starting from the principle that the 3Ds window is projec-ted onto the plane of the screen, this side view will mark the location of the plane of the screen so as to distinguish the objects that should be in front of the plane of the screen (popping out) and those that should be behind it (in depth).

- In the most complex cases, a view from above, with the location of the plane of the screen, could also be useful. Beyond these general rules, it could also be advisable to use previsualization software that si-mulates what the shot or perspec-tive will be in or-der to define the camera angles

and movements in 3Ds. Such software al-lows computer-generated images to preci-sely reconstitute each filming location and the camera position (whatever the type of rig). It allows the frame, the inter-axial dis-tance, and the angles to be calculated and previsualized during filming and in post-production. All the parameters, such as the focal length, the diaphragm, the depth of field, the movements, etc., can also be predetermined.

The importance of checking volumesDuring the work of identifying certain para-meters and of preparing a film in 3Ds, it is necessary for the director and the head of

Screen capture of 3Ds previsualization software

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photography to check the frames by taking into account the development and distri-bution of volumes relating to depth. They rely on the stereographer who helps them in looking for homogeneity in the choice of angles and focal length in relation to 3Ds. This step should allow the position of the objects to be determined within the “scenic box” containing the volumes of the scene in three dimensions. This checking is of major im-portance.At this step, a warning is neces-sary to point out that, as opposed to 2-D images, s t e r e o s c o p i c viewing provides the viewer with the perception of the position in depth of each object, and thus their sizes. The choice therefore of the 3Ds fil-ming parameters can lead to a si-tuation in which a person can be perceived as a giant (magnifi-cation) or like a drawing on card-board (flattening), or like its opposite (a maquette or stretching effect).Finally, it is useful to note that, as a ge-neral rule, 3-D is best appreciated when the scene is in movement, close to the ob-ject and with a rather short focal length. Nevertheless, it is difficult to produce a whole film without close-up shots. For shots resorting to medium and long focal

lengths, the establishing of the position of the massive forms of the film set becomes even more decisive in determining the po-sition of the actors and the viewpoint of the camera in terms of the depth and the edge of the frame. The sensation of 3-D, even if it appears realistic or admissible for a single shot, might no longer be so during the editing of several shots one af-ter another. For example, during filming in

2-D, it is normal to “cheat” in the po-sitioning of the actors (to make a shot or perspective easier). This prac-tice should arouse the greatest vigi-lance when using 3Ds.

FramingThe precision of the cinematogra-phic frame is one of the essential parameters of 2-D filming. Yet, with stereoscopy, whe-re we are nearer to low and/or high 3-D effects, the frame shows a slight uncertainty in relation to the two shots being

filmed, which only overlap completely on the plane of convergence or the plane of the screen. Furthermore, the notion of the immersion of the viewer for certain ste-reoscopic productions is often emphasi-zed even before the notion of framing, in IMAX© for example. But for most cinema-tographic productions, the frame remains

Visualization of the benchmark visual comfort zone as regards 3Ds.

one of the fundamental parameters. It is what happens within the shot or out of it that justifies the movement of the camera according to the director’s decision. In streaming programs, the frame is deter-mined much more by following the action, which in sports for example, is generally centered.

A camera in movementMoving shots reinforce the perception of the succession of volumes within the sce-ne. This emphasis of volumes is obtained, of course, by the movement of the actors in relation to the objects in the frame. It is equally increased by the camera’s view-point, which reinforces the presence of the actors. Perhaps this could be a new type of space between cinema and theater?

Lighting in 3DsIf, in 2-D cinematography, light and its contrast are only limited by the projection standards and, in this context, the power of the projector, it is quite otherwise in stereoscopy. Strong contrasts, in particu-lar at the edges of the shot, through fo-liage against the sunlight or between dif-ferent parts of the subject, can lead to real cerebral discomfort for the viewer.The lowering of contrast is often advised, without us knowing how to precisely quantify it today. This being so, shots for which the lighting and contrast levels are not controllable require sensors covering a large range in order to obtain images capable of conserving 3-D in high and low lighting. This also allows a better adjust-ment of contrast during the calibration of stereoscopic films and TV programs. Likewise, it is advised to pay attention to clipping of strong lighting, for such lighting can produce a disparity of form between the two stereoscopic images, such as

when there is a blurred background with backlit foliage.

Using visual indications of depth for 3Ds productionsCreating a shot in 3-D does not only mean adjusting the stereoscopy, but also to use information that is going to ease the un-derstanding of the depth of the image.It is thus necessary to know how to use both stereoscopic and non-stereoscopic information.Painting and photography remind us that in 2-D numerous factors allow the brain to analyze and understand the depth of an image. This faculty is conserved, moreo-ver, when one eye is closed. The utiliza-tion of this non-stereoscopic information makes the understanding of space, and the participation of the sensation of 3-D, easier to experience. Among these fac-tors, we can cite the following:-An object up close masks an object far away. This effect, which can be obtained by the movement of the actors or the objects in the depth of the scene, is reinforced by the movement of the camera’s viewpoint. The dollies, the movements of the cra-nes or steadicams, or the movements of a shoulder-held camera, emphasize the relative position of objects in relation to each other.-The size of objects decreases with distan-ce. This can be used to “cheat” in certain shots, provided that a likeness is preser-ved with the effects of reduction in size, if a realistic image is to be conserved.-The gradation of textures: bricks, gras-ses, pavements, etc., become less defined with distance.-The “atmospheric dispersion” (mist ef-fect): it is due to the pollution of the mi-lieu being passed through according to its thickness. It works for infinite distances

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Managing the PoPPing-out effeCt

Popping out is one of the effects belonging to 3-D. It gives the feeling that the objects pop out of the screen towards the viewer.However, there are rules to follow so that this effect does not cause any visual discomfort. The elements or parts of elements that pop out must be contained within the field of the cameras. The speed of the appearance of popping out must not be too slow or too fast. A sufficient time must be left for the viewer’s brain to get accustomed to this effect. To preserve the visual comfort, it must be fast if the intensity

is to be weak and slow if the intensity is to be strong. The same popping out can vary in intensity and be produced twice: first weak then strong, in order to reinforce the final effect. The total length of the effect cannot be too long. For reasons of visual comfort and of concern for a narrative balance, the frequency of popping out throughout a film or a TV program must be an intelligent dose between the repetition of popping out and their differences in intensity.Finally, it has been noticed empirically that there is a phenomenon of learning in

the capacity of the viewer to “read” comfortably the effects of popping out: at the beginning of a film, around three seconds are necessary for the brain to submit to the interval between convergence and accommodation that is imposed on it, whereas after ten minutes of a film in 3-D stereoscopy, this accommodation time is reduced to half a second. It is thus strongly advised against abusing the effects of brutal popping out at the beginning of a film, for they can become painful and wrongly interpreted by viewers’ brains..

as well as for a smoke-filled room.-The effect of perspective is very important information: as we look, we search in per-manence for a scene’s convergence lines to understand its perspective by using roads, railways and buildings.-3-D is above all comparative. The brain performs better in comparing, for exam-ple, colors than in analyzing them. It’s the same thing for stereoscopy. A distribution of volumes in the depth of a scene will fa-vor the impression of viewing in 3-D. It will be more difficult if there is only one ele-ment in the foreground separated from another element placed at infinity without any intermediary volume. For example: a bee popping out on a background of infi-nitely distant mountains will not favor the impression of viewing in 3-D.-Furthermore, it is sometimes preferable to have titles popping out on a textured background rather than on a black one.-Textures and shadows are stereoscopic objects, supplementary “information” for

understanding depth. This is why certain head operators prefer using light that is more directional than in 2-D in order to emphasize the shadows. Regions without detail of an image—for example a comple-tely white sky or an interior scene with to-tally black zones—are less favorable to the comprehension of 3-D than a cloudy sky or an interior in which half-light allows the subtlety of the details to be seen.-One must also attend to the consistency of the screen depths and avoid the “collision” of a title placed on the plane of the screen with an object that is popping out. As for a “window violation”, it is characterized by the collision of the edge of the screen with an object that is popping out.

It is important to use all of this information to enrich the stereoscopic production parameters. In a general way, the least contradiction between monocular and binocular (that is, parallax) depth information cannot be allowed.

Modulation example of the stereoscopic range for the length of a film

Stereoscopic range and modulation of stereosco-pic rangesThe stereoscopic range is a measure of the quantity of 3-D in an image. It is the difference between the interval of the most distant object and the interval of the closest object in a shot.The stereoscopic range can vary within a shot, between two shots and during the length of a film. Within all these cases, one can speak of “modulation of stereoscopic ranges”.The stereoscopic range (histogram of disparities) is a quantifiable data for each image in percentage of its size or in pixels.The term “depth budget” is sometimes used to designate either a stereo range or the modulation of stereo ranges, which can lead to confusion.The same stereo range gives a weak impression of 3-D on a small screen, stronger on a movie screen and very powerful on a giant screen such as IMAX©. The acceptance by the viewer of a stereo range chosen for a given screen

is, moreover, variable according to the individual.Some scientific studies are, however, still going on in France (3-D Acceptance & Comfort) and in the United States (BanksLab, University of California at Berkeley) to clear up the relation between stereoscopic range and visual comfort. Without 100% reliable reference points in this domain, we recommend, during the production of a teaser or a test, to examine, case by case, the contentious shots that deviate from the “acceptable” limits of stereoscopy.In general, it is customary to moderate the exceeding of these limits in favor of the production.It should be noted that there already exists technical recommendations defining the acceptable limits of stereoscopic ranges for 3Ds TV broadcasting (ex: BSkyB 3-D). The establishment of technical recommendations is currently under study in France.

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Ensuring the continuity of the modulation of the stereoscopic range during a whole filmIt is indispensable to think of a 3Ds film or TV program in its entire continuity. For ci-nema in 3Ds, like in 2-D, the order of se-quences and shots at different steps in the making of a film are often modified, and particularly when it is being edited.The modulation of the stereoscopic range may be modified by the inversion of shots during editing. For example, a close-up with much popping out will correspond ba-dly with a wide landscape shot having a lot of depth: this alternation tires the viewer. It is thus necessary to take care in the or-ganization of the shots to ensure smooth transitions of depth for the public.

riGs anD stereosCoPiC

Cameras

a “rig” is an adjustable support on which movie cameras can be arranged and set up. There are two types according

to whether the cameras are placed side-by-side or as a mirror (beam-splitter). It is the need to obtain or not a small or large inter-axial distance that determines the choice of a rig. If a large inter-axial distance is desired, usually for helicopter or distance shots, a si-de-by-side rig is used.The sophistication of side-by-side or mirror rigs is not linked to the device but to the definition made by the manufacturer. Certain manufacturers make rigs that are versatile and are simply assembled differently to be installed either as a side-by-side or mirror rig.

Side-by-side rigsTwo identical cameras are placed next to

each other on more or less sophisticated mechanical or motorized rigs. The advantage of this arrangement is that it is often more rigid and avoids the aberrations linked to the mirror set up.Its inconvenience is that it imposes wide inter-axial distances which results in a “maquette” effect tied to the apparent miniaturization of the objects being filmed. It is not known how to avoid this effect today, but it comes into play from the moment one goes beyond the inter-axial distance of human vision. It can be put up with, or even looked for, according to how the director wants his production to be.In any case, there is no other solution when one films from far away, with objects in the foreground situated far from the camera and one wishes to have 3-D. This is the case, for example, for certain shots taken from a helicopter.

Semi-transparent mirror rigsThe cameras are placed vertically at a 90° an-gle to each other and find themselves in opti-cal concurrence in a semi-aluminized mirror. This mirror, also called a “beam splitter”, al-lows one camera to film through the mirror and the other to film by reflection on the re-flecting side of it.For this process, the transmission through, and the reflection from, the mirror is equal to 50% each so that the loss of a diaphragm, induced for the camera filming through the mirror, is identical, or almost so, to the other one. The mirror thus permits filming with an inter-axial distance equal to 0 and thus be freed from the problems related to the space used by the cameras and lenses.It is thus possible to reduce the inter-axial distance to 0 mm, which allows for the ca-meras to be perfectly aligned. The mirror rig mainly permits small inter-axial distances, indispensable for filming close to the sub-ject, which is the case in a large majority of

shots in a fiction film.Mirror rigs are used with steadicams, shoul-der-held cameras and most classic machi-nery. Mirror rigs are conceived or arranged in two ways when they can be turned around the optical axis:-The first, called zenithal, favors the protection of the mirror. The vertical camera is placed under the optical axis and directed upwards. This arrangement allows for a simpler protec-tion from lights interfering with the mirror.-The second, called “crane position”, has the

advantage of having its vertical camera placed above the mirror, allowing the optical axis to be brought very close to the ground for ma-king large vertical low-angle shots.

Integrated 3Ds cameraAlso appearing on the market are professio-nal video cameras that record two views of the same scene through two optical axes in-tegrated within the same camera body. This type of wholly integrated technology has the advantage of limiting problems of dis-

Binocle

Binocle

Two types of side-by-side rigs

Simplified schema of a semi-transparent rig

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A stereoscopic shot requires paired equipment (cameras and lenses) and the stereographer’s utmost attention to the adjustment of the rig during shooting. Not being able to have perfect alignment once the shooting starts, it is necessary to continue working thanks to real-time correction algorithms for television, and in postproduction for cinema. It is a question of bringing to the viewer two images perfectly aligned vertically pixel by pixel.Factors provoking troublesome vertical disparities:- Difference in height of the optical axes (whether they are parallel or cross verti-cally)- Difference in the placement of one camera in relation to the other- Difference, even minimal, between the focal lengths of the cameras and the focusing of the lenses- Different optical aberrations between the lenses- Trapezoid effect resultant in vergence on the object. It’s a question of minimizing as much as possible these disparities when filming. On a side-by-side rig, the optical axes are placed in parallel aiming at infinity, and a test card is used at 3 meters to verify that the altitudes have been respected. On a mirror rig, the same procedure is used in placing the inter-axial distances at 0. In both cases, test cards and a 3Ds monitor is used to precisely adjust the alignment, if possible to the size of a pixel. Likewise, that the colorimetry and luminosity of the cameras are identical should be watched over closely. Certain tools on the 3Ds monitor allow this to be precisely monitored.Synchronization of the camera sensors at the pixel level is indispensable. The non-respect of this rule on moving images leads to visual fatigue by the viewer. For the timecode, the cameras must be connected with one camera as TC “master” and the other as “slave”. As to scanning, putting one camera in Genlock master and the other in Genlock slave is not precise enough, except for certain miniature cameras or cameras conceived for this purpose. It is preferable therefore to have recourse to an external synchronization camera body in Tri-level Sync, connected to the camera Genlock inputs. Cameras without the Genlock input, such as digital photo cameras, are problematic. Certain 3Ds monitors allow, however, scanning to be viewed and to try “manual” or “on the fly” synchronization by triggering the cameras simulta-neously. But this does not provide the indispensable guarantees need for a feature film project or for live television.

MethoDS for aLigning anD SYnChroniZing 3DS CaMeraS

Two examples of integrated 3-D cameras

DR

parity between the two stereoscopic points of view to be superimposed, especially pro-blems of alignment, differences in focusing, of zooming, etc. However, the integrated 3Ds camera has the drawback of generally offering only a single setting for the inter-axial distance and a limited adjustment of vergence. These restrictions result in heavy constraints when filming a close-up scene in 3-D, and, more generally, does not allow for complete control of stereoscopic production through adjustment of the two parameters inter-axial distance and vergence.

Progress of 3Ds rigs and monitoring of disparitiesWhatever the talent of the stereographer, involuntary disparities between the two viewpoints of the cameras remain. It is indispensable to correct them when filming live. For fiction, these defaults can also be corrected on the film site so that rushes can be viewed comfortably. In postproduction, if these defaults are very minor and do not bother the editing process, certain stereographers prefer to usefully make these corrections during the “3-D calibration” stage. This consists in adjusting the 3-D values for a shot or between two shots. It ensures the consistency of the 3-D effect for the length of the film.

To this end, technical creation industries have seen, since the end of the 90’s, the rise of motion control rigs capable of being precisely paired electronically via a computer. More recently, 3Ds image analysis instruments have arrived with, notably, the possibility of making a precise real-time drawing out of problems of disparity between two stereoscopic images and correcting them in real time.All these factors make it so that today one sees hardware and software solutions appear from several components manufacturers for processing 3Ds shots in real time, which allows certain corrections—such as vertical disparities, detection of rotation and trapezoid deformation—to be automated. Certain software also permits automation of the inter-axial distance and convergence. Solutions of this kind, conceived in France or elsewhere, which allow these problems to be corrected or parameters to be monitored in real time, are already being used on film sites, particularly in live sports productions. 3-D correctors are also being integrated into visualization tools used in fiction or for capturing in order to judge the effects obtained without mental strain for the team.

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live multi-Camera 3Ds

CaPturinG

live multi-camera 3Ds capturing implies ac-tions in real time in order to preserve 3-D ho-mogeneity. The first action consists in analy-zing new actors and organizing them into the production team’s hierarchy. The director is the one who conceives the stereoscopy of a project that puts the stereographer and all the technicians to work.A single stereographer guarantees the qua-lity of 3-D capturing. He works in concert with the director of photography. He is assis-ted by the convergence operators who are in charge of the stereoscopy of one or two axes. He continuously regulates the inter-axial distance and vergence according to the va-riations of frame, focal length and focus.By analogy with photography, it is necessary to integrate this team into the live production unit in order to make discussion easy and guarantee a consistent program.

A modification of workflow should be consi-dered in the 3Ds production unit. In fact, each stereoscopic source should undergo 3-D cor-rection before being integrated into the grid or the mixer. This correction can be multiple and specific to each rig. It encompasses the flip image in the case of a mirror rig, geo-metric correction, compensation for opti-cal centering, etc. Whatever the nature and number of corrections applied, they should be done in a very short time since this period comes before mixing. Today, this processing time varies from 40 to 120 ms.The quality and number of 3Ds visualizations is a key element of a 3Ds production tool. Two cases are possible for the production: to propose a multiviewer which includes all the sources as well as the program and preview in 3Ds. This requires a certain vigilance in or-der to exclude from the mosaic any camera being adjusted. The second option consists of keeping the sources in 2-D visualization and to put only the program and preview in 3Ds.

As a general rule, it should be noted that all the actors who intervene in the live stream should have 3Ds visualization: slow motion operators, synthesizer operators, special ef-fects technicians, etc.

The difficulty of live 3Ds multi-cameras today is not only related to technical problems, but also to the calling into question of the pro-duction. It is quite clear that the acceptance of 3-D is directly dependent on the quality of the stereoscopy, but it is also necessary to provide the necessary information for a good narrative. Due to this fact, live broadcasting is a dangerous exercise in 3Ds. For example, if one wishes to bring information captured by a 2-D camera into a 3Ds stream, one can resort to a real-time 2-D/3-D transfer, or if one wishes to provide a score or a time, one would proceed by inserting 3Ds elements into a 3Ds image. These techniques are to-lerable for the viewer as long as they are mastered.

3Ds PostProDuCtion:

CorreCtions anD WorKfloW

accomplishing postproduction in 3Ds is not very different from traditional postproduction, if only that it is neces-

sary to manage file volumes twice as large. It is also necessary to ensure the continuity of depth in 3Ds scenes, by watching over the sequence of their stereoscopic ranges and by correcting the disparities between the left and right images. When filming fiction, these defaults can also be corrected, of course, before reaching the postproduction stage. However, if these defaults are very minor and do not interfere with editing, certain stereographers prefer to make these adjust-ments during 3-D calibration, or, in any case, these 3-D adjustments are reviewed in terms of consistency over the length of the film.

Viewing is at the heart of the process of 3Ds editingThe postproduction of 3-D images requires

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a return to more rigorous methods of work than before, and to a more precise definition of each person’s task, from preparation of filming to postproduction. These precau-tions, taken before the various operations, limit the alternation of inconsistent 3-D se-quences.However, even if a stereographer has per-fectly adjusted the rigs and taken care to limit the “bad” connections between shots, the editor, will in all likelihood, as in the case of 2-D, change the editing order that was planned at the beginning. Due to this fact, it will be necessary to again verify the conti-nuity between shots during each viewing of the 3Ds already-edited rushes.Furthermore, following the planned post-production method and the production bud-get, it might be useful to take some time to correct the involuntary disparities between images. This would mean to correct the-se geometric and colorimetric disparities between the left and right images such that each of the homologous pixels is situated at the same altitude. It must be kept in mind that these corrections, necessarily made for a live capture, should become a postproduc-tion operation for fiction.This operation could be made on the rushes before editing, but today it is generally done

after editing, during or just before the stage of calibrating the 3-D of the film. It is done by a stereograph technician having experience with the correction tools, under the direction of the stereographer who has already wor-ked on it during filming.

Continuity of shots during editing of 3Ds imagesThe rhythm of shots edited in stereoscopy is logically slower than that of editing of 2-D images, for when there is a change of shot, it is necessary for the brain to have one second to appreciate the new universe to be explo-red. Learning to watch 3-D by the viewer can, however, reduce the accommodation time necessary for each change of shot. But as of today this is only a supposition.In order to limit mental discomfort and re-duce adaptation time between each shot, it is also possible to use the “3-D dissolve” method which smoothes the passage from one 3-D shot to another when the 3-D ef-fects are obviously too different.Because of these constraints, it would be more practical in the absolute for stereos-copic editing to take place “online”, directly from already-corrected stereoscopic ima-ges. However, for reasons of visual fatigue over time, but also for the sake of economy and/or the non-availability of online 3Ds edi-

ting tools, this is rarely the case.For this reason, during “offline” editing of 3Ds films or programs, it is imperative to view 3Ds edited shots and to validate them regularly on a stereoscopic screen having a size near to the one that will be used for the final showing. In this way it is possible to identify at once the visual discomfort resul-ting from the non-corrected stereoscopic disparities or the different 3-D values used in different shots.If possible, it is even desirable that the conti-nuity of the shots be studied during the pre-paration phase of filming in order to make the 3-D space consistent before and after the transition by reducing to the maximum the differences in distance and convergence of the cameras. Nevertheless, adjustments are often to be planned in postproduction through horizontal transfer of the left and right images.The change in location of the space to whe-re the viewer is attracted, from one shot to another, can also cause visual discomfort. Thus the necessity of an appropriate script and a specific “3-D calibration”, making the

stereoscopic range at the end of the prece-ding plan consistent with the beginning of the next one.

Flare: a source of visual discomfort

Example of correcting geometric disparities

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oroPtiMiZing LiVe 3Ds CoStS iS PoSSiBLe !

Concerning the additional costs related to 3Ds capturing, the figure of 25 to 30%more than 2-D capturing is often put forward, but according to those in charge of AMP VISUAL TV these figures are relative. The additional costs greatly depend on the length of the capturing itself, and AMP VISUAL TV hopes to have, in the end, enough production streams in 3Ds to be able to have economies of scale. What is most important today is to find methods for reducing the installation and preparation times. If it is possible, for example, to have two cameras/lenses used only for 3Ds capturing, it would then be possible to considerably reduce the preparation time before shooting. But for this to happen, it would be necessary to have a greater volume of production than there is today.

aDaPting ConVergenCe anD eDiting: 3-D ContinuitY Between two ShotS

In 3Ds, convergence between two successive shots must be adjusted. Usually, the convergence shots will be brought closer during cropping in postproduction if they are too different. Otherwise, the viewer may feel visual discomfort. The time this adjustment takes can also vary. Experiences that took place during the production of Legend of the Guardians: The Owls of Ga’Hoole (2010) brought to light the fact that the softest transition in 3Ds is obtained when the vergence of entrances into a shot is progressively adjusted according to the previous shot. In this film, the length of the vergence adaptation time between shots varied from one sequence to another from 8 to 40 images. Further-more, rather than making the depth characteristics of each shot exactly correspond to the level of the cropping point, it was noticed that for most of the sequences, it was possible to eliminate only 50% of the difference in depth between shots, and to leave a slight upsurge in 3Ds when cropping. Of course, nothing prevents one from using a brutal 3Ds connection between shots to provoke a particular sensation in the viewer.

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Two types of 3-D according to objects entering into the shotThe viewer feels visual discomfort if one of his eyes sees part of an element that the other eye does not yet see coming into the shot from the side. A wise compromise between the intensity of the 3-D effect and the speed of entering into the shot will need to be determined. This does not pose a pro-blem, on the contrary, when this entering into the shot is made either on the plane of convergence (plane of the screen) or verti-cally (from the top or bottom of the screen), for in these cases both eyes see the same element appear at the same instant.

Speed, acceleration and the trajectory of the camerasThe movements should preferably be fluid and slow, with slow accelerations and dece-lerations and trajectories in wide curves. If the scenario imposes rapid effects far from such recommendations, reduced 3-D should be chosen: in the extreme, the optical axes of the left and right cameras can be blended little by little so that one films in quasi-mo-noscopy, thus preserving visual comfort. It must be added that rapid movements, espe-cially towards the observer, can give rise to ocular fatigue.

Hunting down contrasts that are too strongSince 3Ds broadcasting systems (polarizing filters and glasses, liquid crystal glasses, etc.), do not have an absolute separating power, each eye more or less perceives a phantom of the image destined for the other eye. It is thus necessary to limit contrasts that are too strong between foreground and background elements according to the intensity of the 3-D effects and the created horizontal disparities.

Adjusting the light for popping-out effectsTo reinforce the sensation of immersion, the visual field of the viewer must be filled. The best thing is to progressively dim the zones of the popping-out object that cut the edges of the frame. To do this, a method consists in reducing the light of a scene progressively towards the edges of the screen. The volume of the filmed scene then seems to be entirely centered on the viewer.

Matte painting in 3DsMatte painting is a technique that can always be used in 3Ds for distant scenery, in bac-kgrounds toward infinity, where the 3-D set-tings are closest to human vision and without real perception of 3-D. However, it is indis-pensable in this case to create a matte pain-ting that is very precisely integrated into the “composite” 3-dimensional space.The distinguishing of composite stereosco-pic 3-D elements by the viewer is in fact is much more keen than within a 2-D image. An imprecise composition of a 3-D image will be immediately seen as incoherent by the viewer, and even more so when the size of the broadcasting screen is large.

Compositing in 3DsIn order to precisely composite the different elements of the final scene, it is necessary to acquire the tools for viewing and modifying

the parameters of each element in real time, and, if possible, on the size of a screen clo-sest to that of the definitive broadcasting size in order to take into account the magnifica-tion factor.The special effects person must be trained in 3-D and know how to measure and precisely place the different elements of a composite image in a stereoscopic 3-D scene. The pla-cing of these elements must necessarily be very precise. The objective of the visual effect is to modify the perception of the 3-D space of each element to be integrated by using:• The horizontal transfer of the left and right images, modifying the convergence point and thus the depth location of each object in the scene (“horizontal shift”).• The resizing of the images after the removal of the parts that are not common to the left and right views (“crop” and “resize”).• The correction of the vertical disparities, especially trapezoid effects (“keystone”) due to the convergence of the two cameras.

Adjusting convergence in postproductionIt is important to note that 3Ds convergence can be adjusted in postproduction and espe-cially for special effects sequences contai-ning visual effects (see box). In this case, filming often takes place in “parallel” mode, and convergence is done in postproduction, which is much simpler.It is no longer convergence that is adjusted, but the position of the image according to the depth: the whole image being brought closer or set farther back, and this without deformations. It should be noted that a small part of the side of the images will be lost, while the vergence on the set will lead to a rather slight loss at the top and bottom of the image during the elimination of the trapezoid effects.

Management of 3Ds files More and more shootings in 3Ds use cameras

the CaSe of a fiLM haVing “heaVY” DigitaL ViSuaL effeCtS?

Concerning geometric and colorimetric defaults, there is a tolerance threshold beyond which the viewer gets tired, and it must be admitted that there is a certain imprecision in the correction of these defaults. On the other hand, the fine tuning of different elements of a composite image must be accomplished with “zero tolerance”. It is for this reason that the SFX supervisor takes charge of all the image’s 3-D manipulations:1 - Correction of geometric and colorimetric defaults as well as putting the image filmed in convergence in simultaneous parallel mode.2 - Creation and assembly of the composite image’s elements.3 - 3-D fine tuning of these elements, in particular in the case of assembling live and computer-generated images.4 - Putting the composite image in convergence, and 3-D calibrating for the projection screen. Important note: when there is filming for a composite image (special effects), it is not recommended to correct the defaults of the 3-D image before the special effects, because this step produces a destructive “filtering” that harms the quality of the special effects at the end.Besides the SFX supervisor, a certain number of positions can be identified whose work methods should be adapted to 3-D images:-rotoscopy-tracking-compositing-matte painting and all work of changing the palette-computer-generated graphicsThe computer graphics artist in charge of this work must be labeled “3-D ready” in order to guarantee the quality and productivity of his work.

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that record in “file mode”. It then becomes very important to recover the X and Y infor-mation from the cameras to integrate them into the metadata. In 3Ds postproduction, one of the main questions is the management of storing these files, which becomes crucial. The best thing is to opt for regular backups of the images as production proceeds, for the quantity of data to be processed is doubled.The method that consists of editing online directly in 3Ds is most often used for short programs (publicity, corporate films, docu-mentaries, etc.). This method assumes that there are enough editing stations sufficiently powerful to process 3Ds images in full reso-lution and in real time. Longer editingThe editing of a 3Ds project is accomplished in certain cases from a single point of view, for example, the left image. To appreciate the consistency of the final editing, it will be necessary to make regular conformations in 3Ds, allowing the editor to modify the struc-ture and rhythm of the film according to the 3-D effects obtained.

Lengthening the calibration timeThe calibration of the 3Ds calibration screen should be made according to the technology of the glasses used (passive or active). Besides, it is difficult to plan the calibration (colorimetry and density) with 3Ds glasses being used for numerous consecutive hours without having ocular fatigue. Usually, calibration is done in 2-D. Then, during viewing in 3Ds, a correction is applied on the viewing screen (LUT) to com-pensate for the effect of using glasses when viewing the images.At this stage, it is necessary to adjust the ste-reoscopic range of the film, also called “3-D calibration”, or to modify the colorimetric calibration according to the 3Ds perception constraints.

2-D/3Ds Conversion

the neeD for KnoW-hoW

Choosing conversion according to filming conditionsToday, several American blockbus-

ters shown in movie theaters in 3Ds are the result of conversion of 2-D images into 3Ds in postproduction. The main reason is econo-mic and comes from the fact that producers, in front of the obstacles related to filming in 3Ds, prefer to respond to the demand of the 3-D digital movie theater market through 2-D/3Ds conversion, often easier to manage when it has to do with films integrating a large number of digital special effect shots.For example, for the needs of creating 3-D it is possible to cut out persons who have been filmed with a green background and to re-process scenery in 3Ds that has been trac-ked by a virtual camera. Usually, this sce-nery will have been stretched out in matte painting with computer-generated images of creatures inserted into the scene and, in this case, the stereoscopic processing of the film can become more expensive and more difficult to manage than a 2-D/3Ds conver-sion in postproduction.It is also possible to mix techniques within the same film. Such “composite” projects then consist of shots filmed in 3Ds and others converted from 2-D to 3-D when the sequences are easier to process by 2-D/3Ds conversion rather than by filming. This is the case, for example, of sequences filmed with long focal lengths in stereoscopic mode that can give the effect of successive “slabs”. This flattening effect, due to filming with long focal lengths, is especially irritating when filming a close-up portrait shot. Then the simplest and most economical thing to do is to film the sequence in 2-D and then add contours to the face using rotoscopy of the person such that the viewer is given the

illusion that he sees from two different view-points.

Filming in 2-D while respecting 3-D constraintsHowever, when filming in 2-D in view of converting to 3Ds in postproduction, it is im-perative to film while already extrapolating the 3-D effects and in keeping in mind the constraints pertaining to 3-D. This is how the beginning shots, when characters are often cut off during filming in 2-D by the edges of the frame, can prevent using popping-out ef-fects in the scene. One can slightly cheat to have a slight popping-out effect, but with the risk of generating the beginning of visual dis-comfort in a section of the public, especially if this choice is repeated throughout the film. More generally, shots could have superb popping-out effects provided that the frame is kept “airy”, which requires the cameras to pull back or to have the foreground charac-ters moved back or recentered.Certain transitions and dissolves already in place in a film or TV program shot in 2-D are going to have to be adapted to the constraints of the transitions between 3-D spaces, or else there will be volumes overlapping each other without any spatial coherence.Consequently, putting 2-D images into 3-D is a technical process demanding the grea-test care to prevent visual discomfort or even rejection by the viewer, all the while respecting a certain realism in 3-D. During 2-D/3Ds conversion, the 3-D should be set up essentially to ensure the visual comfort of the viewers, with beautiful window effects but with few effective and comfortable pop-ping-out effects given the difficulties in set-ting them up.

Correcting disparities2-D/3Ds conversion, accomplished automa-tically with the help of postproduction ma-chines, is certainly becoming more and more efficient, but it is no less clear that manual

steps and intervention of a specialist remain indispensable without which the possibility exists of providing insufficient visual comfort. A number of disparities between the image’s two viewpoints must be corrected manually.Likewise, when distant objects are blurred in the original 2-D image, the infinite in the re-constituted 3Ds image must be redefined. It is also necessary to recreate some 3Ds ma-terial in zones where the 3-D effect is pro-nounced.

Automatic 2-D/3Ds conversion: an aberration…Most of the current automatic conversion systems provide stereoscopy processed only in the sense of depth and immersion without popping-out effects. These machines work with the help of algorithms resting, among other things, on a principle of color recogni-tion, with distribution organized on the fact that warm tones are mostly in the foreground of a scene and cool tones in the back far away. The only problem with this so-called “natural” rule is that it includes many excep-tions, for the simple reason that one is in an artificially lit universe where, when someone has some clothing with a cold tone in the fo-reground, warm tones may be observed in the background. Due to this fact, automatic conversion generates many visual artifacts and ambiguities. These ambiguities are going to quickly turn the viewer away from this type of image which gives a truncated view of reality.

…needed for 3Ds program processingHowever, TV broadcasters will be quickly constrained to use automatic conversion from 2-D to 3Ds in order to accomplish pro-gram continuity between different programs in 3Ds sufficiently smooth and acceptable to the viewer, such as, for example, between trailers and publicity that have been made with different 3-D settings.

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Animation in computer-generated graphics, matte painting and stereoscopyAll the shots of a film or a TV program using matte painting for background scenery should be studied before postproduction if conversion from 2-D to 3Ds is desired. It is especially indispensable to determine which matte-painting elements should be recrea-ted by 3-D computer-generated graphic models in order to obtain a second camera viewpoint that is visually consistent.For matte painting of background scenery to-wards infinity, it is possible in fact to “cheat” by creating 3-D through compositing. Our human perception of 3-D towards infinity is, in reality, almost nonexistent (due to the small distance between our two pupils com-pared to the distance separating them from observed objects). It is thus possible to easily fool the brain through this type of composi-ting operation.For matte painting and digital visual effects closer to stereoscopic virtual cameras, one must, on the contrary, model the scenery in 3D computer-generated graphics in order to

truly have two viewpoints of the objects (one for the left eye and the other for the right eye). For this type of precise shot, a classic output of a film or TV program in 2-D can-not be recovered to be used as a basis for 3-D. It is thus necessary to take up again all the 3-D files used in compositing with matte paintings and digital visual effects.

visual Comfort With 3Ds

it often happens that viewers of 3-D films complain of visual fatigue, nausea or dis-comfort. This dissatisfaction can have two

main causes:-defaults during the making and/or broad-casting of 3Ds content-rejection of the artistic means (rejection of its use or disinterest)In-depth studies on the main causes of visual discomfort with 3Ds for the viewer are made from samples of representative groups.The 3-D Comfort & Acceptance project, fi-nanced by the Agence Nationale de la Re-

reLation Between aCCoMoDation anD VergenCe in 3Ds

The zone in blue corresponds to the zone of ordinary, sharp binocular vision of a normal subject (ZVBSN). This diagram shows how in natural vision the demand for ac-commodation and vergence in the human ocular system are covariant in a way that can be predicted according to a linear relation (demand line). In 3-D vision (3Ds), this coupling is no longer in perfect concordance and can lead to convergence accommodation conflicts causing stinging and/or irritation of the eyes, headaches, etc. (asthenopic symptoms).

cherche (France), has the goal, among other things, of corroborating the results of labo-ratory tests with a more restricted panel of 3Ds viewers. A vast study using the general public should be published during 2012. A small sample of people has already been put under visual constraints that are supposed to provoke problems in order to objectively de-fine certain indications of discomfort. Some examples are: loss of visual acuity, increased movement of the eyelids, contraction of the pupil, slowing of the change in orientation of the ocular axes, loss of binocular fusion, etc.Among the diverse causes of visual discom-fort with 3Ds, most of the studies concentra-ted on the visual disparity between the two viewpoints in relation to convergence and accommodation. While in natural vision our ocular system converges and accommodates on the same object, the viewer of a 3Ds film accommodates on the plane of the screen, but converges towards the objects that at-tracts his attention and can be situated just as easily on the plane of the screen, in front of it or behind it.

Wide variability according to the personBut the effective limits noticed are extremely variable from one person to the next: a small proportion of people are less sensible to dis-parities in the lower limit of this “comfort zone”, whereas another small proportion will only feel discomfort more than five times the higher limit.The most well-known causes of visual dis-comfort with 3Ds are mainly:- divergence of the ocular axes (heteropho-ry)- amplitude of variations of angular parallax- vertical disparities- “orphan” elements in the image, that is, vi-sible in one eye and not the other, especially if they attract the attention (very bright, for example)

- flicker, when the left and right views are al-ternately shown too slowly- when the colors or brightness of the left and right views of the same element in the image are too unequal- the contradictions between monocular and binocular indications of depth, particularly those that result from a default in synchro-nization during rapid side movements, or “window violations” that make it so that an element of the image is both, because of its parallax, seen in front of the window, but hid-den by it- images that are too complicated (high spa-tial frequencies)- movements that are too quick by certain elements in the image so that the viewer does not have time for binocular fusion to take place before the image completely changesEach of the visual discomfort factors acts in a very different way from one person to ano-ther. When creating 3Ds content, one must be very vigilant concerning each of these pa-rameters.We hope that the current scientific studies will establish clear physiological thresholds, and in so doing define more precisely the possibilities of creating 3-D that is agreeable to watch.

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3Ds ProJeCtion for films

the 3Ds projection technology currently used in movie theaters is based on the sending of two distinct and successive

image streams, and a system allowing each eye to only receive information intended for it.Three technological solutions are proposed to accomplish this separation:• Polarization of light• Spectral filtering of light• Active shutteringAll of them come up against a real problem of light output, for on average between 75 and 85% of the light stream is lost in the systems (filters, glasses). The power of xenon burners being limited (currently a maximum of 7000W), the dimensions of a lightable image using 3Ds projection with a single projector are necessarily limited (14 to 15 meters in cinemascope format). Beyond that, it is recommended to use two superimposed projectors. The luminosity of the images is a fundamental factor in the perception of stereoscopic effects.Another difficulty is the fluidity of the pro-jection. In order to improve this problem, and thus to improve the perception of 3-D, each image is projected three times (triple flash) in the space of one image, that is six images altogether in 1/24th of a second (three images per eye).The last difficulty in 3-D projection is in

adjusting the synchronization. To not tire a person’s vision, it is important that the synchroniza-tion of the display of the images, using the switching of separator systems for each eye, is perfect. These adjustments are to be made for each installation.

Polarization of lightFor the record, this principle has also been used for a long time with 35mm projection.A light polarization system is placed in front of the projection lens. It is a question of al-ternately polarizing light in opposite circu-lar states. All the images intended for the left eye are thus projected with a polariza-tion in one direction, and those intended for the right eye with polarization in the oppo-site direction. To accomplish this, systems of liquid-crystal filters (RealD solution) or rotating disks (MasterImage) are placed in front of the lens. A connection to the GP/IO port of the projector ensures the synchro-nization of these filters with the display of the images.Problems could appear with the projection window, since most glass integrates light depolarization layers for security (espe-cially fire).The light is reflected by the surface of a type of “metalized” screen. In fact, it is a screen painted with a paint containing aluminum elements. This paint has the distinctive fea-ture of keeping the polarization of the light when it is reflected, which is not the case with classic mat white canvas.On the other hand, these metalized canva-ses are very directional, that is, they reflect most of the light according to the effective/reflection axes.This results in a “hot point” whose loca-tion varies according to where one is in the

Polarization of light

theater. Uniform values of lighting are thus obtained that are very inferior to the recent standards for digital projection (ISO, Afnor). While acceptable for 3Ds projection whose qualitative characteristics are not standar-dized, this particularity is very damaging for the quality of 2-D projections. It is thus recommended that theaters so equipped be dedicated to 3Ds. Furthermore, this method is not very appropriate for wide theaters with little depth.To perceive the images separately, the viewer wears glasses having a filter for each eye, each only allowing light to pass according to its polarity. This filtering is not perfect, and each eye perceives a little of the image intended for the other eye, thus generating a slight double image called “ghosting”. In order to get around this problem, DCP files called “ghost images” can be used, that is, integrating an inverse image of the parasite image for each eye. The glasses are sold to the viewer (very low cost) who can keep and reuse them for other projections using the same technology.The two main providers of this type of tech-nology are RealD and MasterImage.

Active shutteringConcerning the projector, there is no mo-dification. An infrared transmitter is simply connected to the GP/IO port, generally pla-ced behind the cabin window. This transmit-

ter sends a synchronization signal, reflected by the screen’s canvas, which easily allows all the seats to be covered. Several transmitters can be placed in large theaters.The classic movie theater screen can be kept. The less the gain is high, the better the result will be in terms of quality (in particular the uniformity of the luminosity).The viewer has “active” glasses. The-

se glasses are equipped with liquid crystals whose orientation can be modified. Accor-ding to the eye and the synchronization si-gnal sent by the infrared transmitter, these liquid crystals will alternately block the viewer’s vision or let the light pass through. Each eye thus sees the image intended for it, and only this image (no “ghost” effect).The glasses should be supplied with elec-tricity to activate the LCD command circuits. These glasses are relatively expensive and also quite fragile. They are usually “rented” to the viewer for the time of the film, which requires logistics for recovering and clea-ning them. The main suppliers are Xpand, Volfoni and E3S.

Color filteringThe principle of this technology is to filter by bands using a wavelength comb filter. Two techniques have been developed, one by Dolby (based on an Infitec patent) and one by Panavision.The Dolby solution inserts a color filtering wheel into the light path, between the lamp and the matrices (three bands per eye, sli-ghtly offset for each). The rotation of this wheel is synchronized with the alternate display of images for each eye. A colorime-tric processing must be made at the server level in order to reinforce the chromatic se-paration of the two images. This requires a server able to do this processing.The Panavision solution requires that the

Active shuttering

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whole lens be replaced and a fixed filter be inserted behind the back interior lens. This filter separates the light spectrum for each eye (five bands per eye).The classic movie theater screen can be kept. The less the gain is high, the better the result will be in terms of quality (in par-ticular the uniformity of the luminosity).The viewers are furnished with glasses that filter the light spectrum and allow each eye to only view the images formed from the color triplets intended for it. This filtering must be very precise and requires the stac-king of around 50 layers of colored plastic film. Furthermore, as these chromatic fil-ters require the light to pass through at an angle of 90°, the glasses are specially sha-ped to allow the eye to move without losing the 3-D effect.The glasses are very costly (less than ac-tive ones). They are usually “rented” to the viewer for the time of the film, which re-quires logistics for recovering and cleaning them.

Displaying the imagesFor all these systems, the display of left/

right images is successive. Concerning the projector, the same lens can be used. It is also possible to display two images “top-and-bottom” or “side-by-side” on the matrix (for example, if it is 4K). In this case, it is necessary to replace the lens by a double-lens system. This is the solution taken by 4K Sony projectors. The polarizing passive systems are used in front of these double lenses. Recently, it is also possible to use active glasses.

The technological battle between passive and ac-tive systems

3Ds cinema projection systems use a wide variety of different technological principles. It is the sign of an emerging market which is in the process of clo-sing in today on a battle between the

principle of passive projection of the type RealD or Dolby and the active system of the type XpanD. This competition in the movie theaters between two competing techno-logies, each having its advantages and in-conveniences, will no doubt be influenced by the arrival of new light sources in the D-Cinema (Laser) projectors, which clearly improve the quality of comfort when 3-D projection is used. Likewise, the techno-logical rivalry in movie theaters is likely to be decided in the course of time by choices taken by large electronic manufacturers in the mass television market, which little by little propose for both technologies more and more refined and comfortable techni-cal solutions for the viewer.

3-D tv DisPlay

With the passage to stereoscopic 3-D, the development in terms of visual sensation for the viewer is much more pronounced than during the passage of standard definition TV

Color filtering

to High Definition TV. It is what all the televi-sion manufactures say and which explains the very rapid marketing of 3-D televisions in 2010, even if the content does not exist to-day in sufficient quantity.The other explanation for the rapid deve-lopment of 3Ds televisions comes from the improvement of the quality of the display technologies and in particular the frequency of refreshing flat screens that allow this to take place above 200 Hz. Given this fact, it is possible to propose quality 3-D while crea-ting a minimum number of undesirable ef-fects for the viewer.To really understand, however, the problems of displaying 3-D images on a television, it is first necessary to recall the main technolo-gies and to provide information on specific rules related to this new mode of television display.

Exit anaglyphsAs an introduction, we note that it is possible to visualize 3Ds images on a traditional televi-sion through the transmission of an anaglyph image filtered in red and cyan. This already old possibility is still used sometimes on today’s televisions, but broadcasting in ana-glyph has only a single advantage from now on: from the encoding of the video up to its display on the television it is not necessary to have a specific broadcasting infrastructure.On the other hand, this technique suffers from serious limits concerning visual com-fort. It intrinsically generates a loss of color fidelity. In particular, depth information is lost in those parts of the image having the same colors as the red-cyan filters. Even lost sometimes is the capacity of the eyes to fuse. Also noted is discomfort due to the disparity of luminosity between the left and right filters of the glasses.To be quite complete, it must be emphasized that the anaglyph process has been refined these last years by companies like Trioviz and

ColorCode, who, thanks to a system of ma-naging the separation of colors, allows this already old principle of creating stereoscopic images on television to remain alive a bit lon-ger.

Polarized panels and passive glassesThe principle of passive TV3Ds glasses with a polarized screen surface placed on a classic LCD panel is a technology used by certain consumer electronic brands. The principle of its display is based on a filter ha-ving a circular polarization in one direction for even lines and a polarization in the oppo-site direction for odd lines. In this way, each eye only sees the lines corresponding to its direction of polarization.The main advantage of passive glasses re-sides in the fact that no electronics are embedded in them since the glass only has “static” polarization. These glasses are li-ght, the colors are quite correct and there is no flickering effect. On the other hand, with passive glasses each eye only receives a half an image on the vertical resolution plane. Furthermore, with this display technology, when the head is inclined in relation to the television screen, diaphonic effects appear like in the technology used with “active” glasses. Here, the circular polarization al-lows the head to be inclined up to a certain point, after which the polarization of the li-ght causes loss of luminosity and colorime-tric changes.

TV3Ds with active glassesIn 2010, most of the television manufacturers accepted a TV3Ds display technology using active glasses. This technology is based on flat screens having at least a double refresh frequency (even frequencies of 400 and 600 Hz), that are combined with 3-D active glas-ses. The shutter frequency of active glasses is synchronized with the display of images on a flat screen. In this way, each viewer’s

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eye only sees alternately the image that is intended for it.This technology is for the moment almost the only one to offer a 3-D image with full resolution for television, even if companies like RealD, JVC and Samsung now market a Full HD passive TV3Ds technology near to the Z-screen system used in movie thea-ters. This new approach should permit the polarization direction to be alternated on the whole image, thus offering a Full HD polarized system for TV.The only drawback to the “active” glas-ses technology is, for example, when the synchronization me-chanism of the glas-ses is defective. In this case, double images (ghosting) can appear, which is a nuisance for the viewer. The problem also results in diaphonic image information of the left eye onto the right eye and vice-versa, while the periods of each eye being open for too short a time can lead to a reduction in luminosity.

AutostereoscopyThe principle of autostereoscopy is based on two distinct processes:- An LCD panel in front of which a lenticular network is placed so that an ob-server only sees, for each eye, one column of pixels at once. One simply has to use a matrix of two images together (one pixel out of two) so that each eye receives a different image in real time and so the stereoscopic effect is produced.- The parallax barrier is the other important autostereoscopic technology. Its

principle is essentially the same as lenti-cular network autostereoscopy in which a filter (the barrier) alternately distributes the points of view intended for each eye. In contrast to lenticular networks, the lateral positions for seeing the whole image are all at the same distance from the plane of the image. It thus permits switching more easily from 2-D mode to 3Ds mode, which is not so evident with a physical lenticular network.These two technologies represent a strong p o t e n t i a l for development

in the future of TV3Ds display technology in so far as they allow the viewer to do without glasses. Autostereoscopy, as 3-D immedia-tely visible without glasses, already represents, mo-reover, a convin-cing medium for marketing and

communication ap-plications: public places, dynamic dis-

play, museums, airport halls, etc.On the other hand, autostereoscopy is for now still reserved for events and corporate communications or even as a display inten-ded for a single individual (telephone and video game consoles, smartphones, etc.). It has, in fact, two major constraints: the viewer must be in front of the screen and/or to not move too much in front of it to keep a comfortable stereoscopic effect. Further-more, to allow the viewers to be freely pla-ced in front of an autostereoscopic screen, it is necessary to display eight different came-ra views enmeshed in a single image. This therefore implies the production of complex

Panasonic P55VT50 3Ds television

3-D images to be made and thus limits de facto, on a technical and economical level, the production of content in this display mode, at least for now.

A single connection for 3Ds: HDMI 1.4aThe new HDMI 1.4a (High Definition Multi-media Interface) connection defines the new formats and timings for stereoscopic image information furnished to televisions through readers and decoders. The HDMI 1.4a stan-dard, launched on 4 March 2010, has impro-ved several functions of the HDMI connec-tors, including the possibility of conveying most of the stereoscopic 3-D signals used for broadcasting today. Among these si-gnals, there are the “Compatible Frame” modes based on classic image resolutions, where the two images share the horizontal (side-by-side) or vertical (top-and-bottom) resolution.These broadcasting modes are intended, above all, for the TV transmission of 3-D content, while the existing infrastructure can be used for the transmission in high-de-finition (HD). Thus, where HDMI 1.3 allows only one HD image to be transmitted, which means all diffusion modes of type side-by-side, top-and-bottom and checkerboard, that is 3Ds with loss of resolution, the HDMI 1.4 standard allows the transmission of two HD images, or 3Ds in full HD.As examples, there are several image for-mats compatible with the HDMI 1.4a interfa-ce: 3-D field alternative (interlaced), frame packaging (top-and-bottom format with full resolution by view), complete alternation of lines, half side-by-side, full side-by-side and the principle of 2-D broadcasting plus depth metadata. It should be noted that HDMI 1.4 works with 3-D flat screens that support definitions and broadcasting frequencies as different as 720p50, 1080p25, 720p60 and 1080p24, but also horizontal side-by-side mode in 1080i50 or in 1080i60, as well as

top-and-bottom in 720p50, 1080p25, 720p60 and 1080p24.

2-D/3Ds conversion in the television setDans la mesure où le relief créé par un réalIt will be several years before TV3Ds natively-produced 3-D content becomes widespread, especially due to the high additional costs of production and postproduction generated by this new technology. From now on, television manufacturers, far in advance of the native 3Ds content production market, have deci-ded to integrate real-time converters of 2-D images to stereoscopic 3-D images in their latest generation of televisions.This conversion function for the viewer is usually accessible with the help of a simple remote control. It acts only in the sense of the depth of the image through a heighte-ned sensation of immersion in the scene. 2-D/3Ds conversion in the television set is not conceived so as to produce objects that pop out from the screen. Such automatic 2-D/3Ds conversion in the home also causes frequent artifacts, exaggerations of 3-D on parts of the image that may quickly gene-rate visual fatigue in the viewer.So, even if it has yet to be proven by an epidemiological study, it is already known with certainty that such on-the-fly 2-D/3Ds conversion of video sources that have not been conceived using native support or in postproduction to be broadcast in 3-D (ra-pidity of editing, continuity of shots, para-sitic objects in the foreground, etc.) leads to enough parasitic effects so that the in-terpretation of the 3-D by the human brain becomes quickly uncomfortable with heada-ches eventually occurring.

Adjusting the intensity of 3-D in the televisionIn so far as 3-D created by a director is more or less comfortable for the viewer accor-ding to his own visual perception and the

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size of his screen, certain television and 3Ds decoder manufacturers are beginning to offer manual or automatic adjustment of the depth of 3Ds scenes. Whatever the electronic system used, it is clear that such adjustments made by the viewer cannot be proposed at a level of 3-D going beyond that conceived at the beginning of the program’s production, the minimum level being, of course, a flat image in 2-D.

The placing of subtitles and their presentation on the airThe placing of subtitles and graphic elements in a 3-D television program is a technological and artistic feature that must be taken into account before the program is to be broadcast. It is re-commended that scenarios should be built for the placing of subtitles and/or graphic elements based on an ana-lysis of human perception so that they do not interfere with the 3Ds effects in the program’s scenes. Two options are possible: either the subtitles are always inserted in front of the video content (fixed depth positioning) and the rest of the scene is sent to the background, or their position dynamically adapts to the stereography of the program so that they are always in front of the content, while avoiding too great of a parallax between the scene and the text.

aDaPtinG 3-D to the siZe of

the BroaDCast sCreen

there exists several phenomena and rules that govern the viewing of ste-reoscopic 3-D images that we have

summarized in the following diagrams, and which should serve as a guiding thread when creating the preproduction of a TV program or film.

Depth represented on the screen: a “scenic box”The real depth and the depth represented on the screen in a 3Ds project are very dif-ferent things, and trying to show the actual dimensions of the subject on the screen is a completely vain undertaking. The depth shown on the screen is called the “scenic box”. It obeys laws belonging to represen-tations in movie theaters or on a television and above all to the image shown (see dia-grams below).Nevertheless, one must be vigilant, becau-se sharing foreground objects (popping-out effects) and backgrounds (depths, distant objects) by specifying a precise position for the plane of convergence is only valid for a given screen size. In particular, this plane of convergence makes no sense with giant screens of the IMAX© type, for with them, all the represented volume can only be in the theater itself. In fact, 6.5 cm on the basis of a screen of 30 m is so nonsensical that it is no longer taken into account (0.2%, that is, 8 pixels out of an image of 4K). The im-portance and exact positioning of the plane of convergence decrease steadily with the increase in the size of the screen.Inversely, small screens are perfectly si-tuated in terms of depth, and consequently adapt to most of the image in back of the surface. This leads to a stereoscopic win-dow that is more in front within the volume of the scenic box, just as during filming convergence would be made a little closer

to the camera. It is thus possible to recali-brate all the stereoscopy of a production by making a simple side offset of the stereos-copic images.

Calibration of 3-D according to the size of the projection screenIf one considers that the perception of 3-D depends on the size of the image and posi-tion of the viewer, the adjustments of 3-D depth and popping out must be fine-tuned according to whether one is watching a mo-vie theater or television screen.In a stereoscopic image, space is subdivi-ded into two volumes, one part in front of the screen and the other in back. Between large movie theaters and the living room of the average man for example, this propor-tion between what is in front and what is in back changes.For all that, is it necessary to “calibrate” the 3-D according to the size of the television or cinema screen? Is it necessary to adopt a median screen value for both these broad-cast vectors? Is it also necessary to take into account an “ideal” distance of the viewer in relation to the television screen?One of the first basic rules consists in ca-librating the 3-D of a TV program or a film according to the largest screen size able

to broadcast the film, because the content created for a large screen will always be viewable on a smaller screen, even if the 3-D will be more subdued, whereas in the oppo-site situation, content planned for a small screen cannot be viewed on a large screen without provoking visual discomfort due to divergence.Therefore, a film planned for a screen of 20 meters at its base can always be projected on a screen of 2 meters at its base, at the cost of a weaker 3-D effect, but the opposite creates too large left-right horizontal spa-cing so that the 3-D can no longer be fused, necessarily creating visual discomfort.So if the same film is projected on a larger screen, the distance between the “homolo-gous” points of the “distant objects” (ele-ments discernible the farthest towards infi-nity) is going to increase quasi-proportional to the base of the screen and thus go beyond the average inter-ocular distance of human beings (65 mm).The limit resides in the fact that the homo-logous points of objects located the farthest towards infinity on two stereoscopic images should not be more than 65 mm apart, on pain of provoking ocular divergence in the viewer.

PrinCiPLe of the fLoating winDow

The floating window is an arrangement of the stereoscopic image such that the window is seen in front of the screen. It is obtained by the creation of a virtual screen frame that is closer to the viewer than the real screen frame in order to entirely or partially hide the violations of the stereoscopic window.The floating window appears as black vertical bands on the left (in the left view) and on the right (in the right view), which reduces the horizontal visual field all the more a virtual frame close to the viewer is desired. The floating window can be dynamic and thus constantly change to adapt to the scene being broadcast. It is frequently used in animation films.

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Relation between 3Ds parallax and the size of the screen

The CST, in collaboration with Alain Derobe, created a table establishing the average settings of distant objects viewed on different screen sizes: by percentage, fraction and screen discrepancies, measured in cm or in number of pixels of the 2K image.Experiments have been made on the rendering of distant objects for them to be as agreeable as possible for an audience of spectators at common viewing distances.For example, if a film is calibrated for a screen of 10 m at its base, thus involving distant objects offset by a maximum 16 pixels, it will be necessary, aided by a general offset of the image, to reduce them by 10 pixels for a presentation valid for a screen of 26 m at its base; and inversely, to increase the offset by 11 pixels to go to a screen of 4 m at its base.

Explication du tableauExcept for small screens, the table is based on the viewpoint of an average spectator situated at a distance equal to the width of the screen for viewing a “normal” scene. So as an example, the first pro-ducers of television channels to broadcast in 3-D considered the size of an average television image to be 42 inches with a viewing distance of about 3 meters.A true proportionality between the offset of distant objects and the size of the screen is only exact for a screen having

a base of around 6.5 meters. With larger screens, a bit larger offset of distant objects is possible, which will lead to a divergence of only a fraction of a degree, even for the first rows of a movie theater. For a screen larger than 6.5 me-ters at its base, another phenomenon comes into play: the synchrony that links convergence to the accommodation of the eyes. This phenomenon systematically goes against the effort of parallelism, which allows seeing beyond the surface of the screen, so that the distant offsets are limited to a maximum of 2.5% of the image’s width.

Screen width (base) % offset Offset for distant objects Correspondence in pixels

Screen of 26 m 0,25% 6,5 to 10 cm on the screen 5/7 pixels 2K or HD

Screen of 19,5 m 0,33 % 6,5 to 9 cm on the screen 7/8 pixels 2K or HD

Screen of 13 m 0,5% 6,5 to 8 cm on the screen 10/12 pixels 2K or HD

Screen of 9,85 m 0,66 % 6,5 to 7 cm on the screen 15/16 pixels 2K or HD

Screen of 6,5 m 1 % 6,5 cm on the screen 20 pixels 2K or HD

Screen of 5 m 1,1 % 5,6 to 6 cm on the screen 22 pixels 2K or HD

Screen of 4 m 1,3 % 5 to 5,5 cm on the screen 27 pixels 2K or HD

Screen of 3m 1,6 % 4,8 to 5,3 cm on the screen 32 pixels 2K or HD

Screen of 2 m 2 % 4 to 4,5 cm on the screen 40 pixels 2K or HD

Screen of 1,5 m 2,25 % 3,4 to 4 cm on the screen 45 pixels 2K or HD

Screen of 1 m 2,5 % 2,5 to 3 cm on the screen 50 pixels 2K or HD

Screen of 65 cm 2,3 % 1,5 to 3 cm on the screen 45 pixels 2K or HD

Screen of 50 cm 2,2 % 1 to 1,3 cm on the screen 42 pixels 2K or HD

Screen of 30 cm 2,25% 6 millimeters on the screen 40 pixels 2K or HD

Screen of 26 cm 2,3 % 5 millimeters on the screen 46 pixels 2K or HD

Screen of 13 cm 2,5% 3 millimeters on the screen 50 pixels 2K or HD

Sources : Alain D

erobe-CST Janvier 2009

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Accommodation: Modification of the curvature of the lens of the eye due to the action of the muscles of the ciliary body in order to form a clear image on the retina of objects obser-ved at different distances.Angular disparity: See “Parallax angle”.Automultiscopy: 3Ds visualization without glasses with N viewpoints (N being greater than 2).Autostereoscopy: 3Ds visualization without glasses, with two viewpoints.Binocular rivalry: The perception of diffe-rences between the left and right views, in particular with geometric and colorimetric asymmetry.Convergence point: A point in space at the in-tersection of the optical axes of the eyes or cameras that converge towards it.Convergence: Rotation of both eyes (binocular convergence) or of two cameras, aiming at the same point in 3-D space.Cristalline lens: Biconvex lens of the eye, behind the pupil, instrumental in the conver-gence of light rays towards the retina on which near or far observed objects are brou-ght to a focus.Crossed disparity: Retinal disparity corres-ponding to the crossing of the optical rays of each eye in front of the horopter or the plane of convergence.Cross-talk: Imperfect physical dissociation of images respectively intended for the left and right eyes during viewing of 3Ds content on a plano-stereoscopic screen.Depth range: The limits of the depth of 3Ds content coming from the left and right image shots displayed on a screen or a stereosco-pic projection.Diopter A unit of homogenous vergence op-posite the length.Diplopia: A disorder of vision characterized by the absence of fusion of the image perceived by each eye and provoking a double vision of the observed object.

Disparity: Distance between the homologous points of the same object observed on the images or the left and right retinas.Focusing: An operation that consists of concentrating light rays coming from one point onto another point.Ghosts: “Ghosting”, perception of “cross-talk” physical phenomena.Homologous points: The corresponding points of the same object viewed by the left and ri-ght eyes, and whose distance between the eyes displayed on the retinas constitutes the retinal disparity. These corresponding points of the same object are also present on the left and right images displayed on the plane of the broadcast screen and whose distance between them constitutes the parallax.Horizontal shifting: The horizontal movement of stereoscopic cameras made parallel du-ring filming, or the displacement of two left and right images in postproduction to set a null parallax and thus recompose the depth of the scene.Horopter A virtual arc of a circle of a person’s visual environment formed by all the conver-gence points coming from the observation of object-points located at the same distance from the eyes. All the points situated on this curve correspond to identical places on each retina. The retinal disparity is thus zero on this curve. The disparity of objects observed inside the horopter is called “crossed dispa-rity”, the disparity of objects situated outside is called “non-crossed disparity”.Hyperstereoscopy: Stereoscopy produced from a wide stereoscopic base, usually well beyond the inter-ocular distance.Infinite stereoscopy: The greatest distance between the object and the viewer in bino-cular vision where the effect of depth is still discernible, usually estimated at 200 me-ters.Inter-axial distance: See “Stereoscopic base”.Inter-ocular distance: The distance between

Glossary 3Ds

3-D professional monitoringMonitoring on a small size screen is useful for validating errors in producing simple 3-D effects such as inversion of the left and right eyes, but it could never be used as a way of appreciating 3-D in a feature film.All the graphic artists and technicians in charge of an audiovisual and cinematogra-phic project must be able to appropriate stereoscopic production techniques and to regularly view rushes of their work, in par-ticular during editing to adjust the 3-D and solve “depth continuity” problems, which results in retakes of the framing. What would thus be ideal would be to have a 3-D screen available for each of the main pro-duction and postproduction stages in order to be able to validate the advancement of work in progress. It is also indispensable to regularly test on “real-size” screens, that is, the same as those that viewers will be watching, for here also the impact of 3-D

directly depends on the size of the screen it will be viewed on.For example, on an editing monitor 1 me-ter wide with the viewer at a distance of 2 meters, if the offset of the distant objects is adjusted from 40 to 50 pixels (2.5 %), the 3-D image could seem pleasant to watch, but re-sult in a false setting according to the size of the screen that the public will finally view in a movie theater or a living room. It will then be impossible for the images to be fused for the eyes of a viewer who looks at a 13-meter screen (50 pixels instead of 10 pixels recom-mended in the table above represents five times the ideal inter-ocular distance, that is 32.5 cm on the screen).However, it should be noted that the figures on the table represent an observed average and depend on the quality of the restitution of the environment. Thus, a very good reso-lution of a monitor allows the figures in the table to be slightly exceeded.

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the pupils of each eye, generally considered for an adult male as being by default about 65 mm.Keystone or trapezoid effect: The consequence of a shot with two cameras in convergence.Macrostereoscopy: Stereoscopy obtained from a small stereoscopic base, below the intra-ocular distance, having virtually several mil-limeters between each camera.Magnification factor: The relation between the rendered or captured image and the final size of this image on the broadcast screen.Maquette effect: A 3-D effect where objects are perceived, during 3-D broadcasting, as being smaller than in real life. This sensation is due to the chosen size of the stereoscopic base. The cameras being separated beyond the inter-ocular distance, the real world is perceived through the eyes of a giant and the humans observed appear as ants.Motion control stereoscopy: Usage of the left and right cameras, especially to modify the stereoscopic base, convergence, focusing, zoom, time synchronization, calibration of placement, and so on.Negative parallax: 3-D objects perceived in front of the broadcast screen (for the retinal visual system, it is called “crossed disparity”.Non-crossed disparity: Retinal disparity cor-responding to the crossing of optical rays of each eye in back of the horopter or the plane of convergence.Orthostereoscopy: The ideal position of the viewer in relation to the broadcast screen, where the 3-D image of the filmed objects conforms to the real objects. The 3-D is per-ceived without depth distortion (flattened or stretched).Panum’s fusional area: A virtual region situated around the horopter where the retinal dispa-rities can be fused by the visual system into a tridimensional image. Outside of this region fusion is no longer possible, the images ap-pearing doubled (in reality, the non-fused left

and right images), and one sees with diplopia vision.Parallax angle: The angle starting from the point of convergence observed by each eye and forming a triangle with them.Parallax: The offset between the apparent positions of an object due to the distance between the eyes of the observer. It is also the space between the left and right homolo-gous points of the same object observed on a plano-stereoscopic screen. This space is due to the distance between the viewpoints of the observed scene.Plane of convergence: When shooting in ste-reoscopy, the “depth” plane that is determi-ned by making the homologous points of a scene’s object coincide, and where the came-ras have their optical axes in parallel. The po-sitioning is achieved by horizontal movement of the two cameras or by horizontal shifting in postproduction.Plano-stereoscopic screen: A screen from which the perception of 3-D depth comes from the display of viewpoints for the left and right eyes on exactly the same planar surface of this screen.Plano-stereoscopic display: A display where 3-D images intended for the left and right eyes form on the same surface of a screen.Popping-out effect: When the stereoscopic win-dow is shown on the plane of the screen, it has to do with the 3-D effect in which objects are seen in front of the physical broadcast screen. It corresponds to a negative parallax.Positive parallax: 3-D objects perceived in back of the broadcast screen (for the retinal visual system, it is called “non-crossed disparity”).Pseudoscopy: The inversion of the left and right images respectively intended for the left and right eyes. The left eye perceives the image intended for the right eye (and vice-versa). The 3-D is inversed and the objects normally situated in back of the scene are viewed in front, which causes visual discomfort.

With the increase in 3-D experien-ce of teams on filming sites or in postproduction, as well as with the

continuous training courses in stereogra-phy for professionals, the stereographer will be increasingly less necessary for trai-ning everyone onsite. However, the stereo-grapher will remain the one who ensures the continuity of 3-D on a film or television program in relation with the entire team working on a production.During postproduction, the stereographer also ensures the follow-up on 3-D cor-

rections, the positioning of the plane of convergence according to the editing being made, as well as the management of floa-ting windows.It should be noted that the definition of 3-D management positions are different accor-ding to the genres (feature film, live broa-dcasts or TV programs). The methodology and, above all, the teams will vary according to the budget allocated to the production. This is where the greatest difficulty lies: in making definitions of positions too defini-tive. In spite of all that, we are attached to

aPPenDiX 1: Definition of 3Ds Professions

Retinal disparity: Disparity between homolo-gous points of the same object formed on the retina of each eye.Stereopsis: Sensation of depth given by bino-cular vision.Stereoscopic base: The distance between the optical axes of two lenses of a single camera or lenses of two cameras, with stereoscopic shooting.Stereoscopic binocular acuity: The depth reso-lution limit perceived by each eye. It repre-sents the capacity to distinguish several planes of depth close to each other, planes defined by different parallax angles also close together.Stereoscopic fusion: A phenomenon that com-bines in the brain the views coming from each eye, allowing the perception of one tri-dimensional image.Stereoscopic window: The 3Ds region of the image in three dimensions represented by the outer limits of the left and right views. A horizontal movement between these left and right views modifies the position of the stereoscopic window in space.Stereoscopy: Principles and methods that allow the observation and/or restitution of

binocular vision. It allows the creation of left and right dual images and the perception of 3-D when broadcasting.Vergence: The size characterizing the focu-sing properties of a system.Viewer: The observer, adult or child. Accor-ding to the difference in their respective in-ter-ocular distances, adults and children do not have the same perception of 3-D depth and do not feel the same sensations of visual discomfort. It is thus necessary to take into account different distances to the screen (children closer to a 3Ds screen than adults), a distance to be specified according to the left and right view separation technology specific to each type of 3Ds screen, and to verify the inter-ocular distance hypotheses taken into account by each manufacturer.Zero parallax: A surface plane, physically re-presented by the broadcast screen, on which are situated all the left and right homolo-gous points of the scene.

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this exercise in order to better understand these new professions.

On stock TV and feature film programs: “Stereographer” or “Director of Stereography”On a feature film, the stereographer has for the most part the role of “stereo-supervisor” who determines with the director the “3-D shot” and the amplitude of the depth appro-priate for each sequence of the whole film. He also determines, with the photo direc-tor, the most appropriate hardware for the shoot. On productions having a large budget and high artistic ambitions, the stereogra-pher can be supported by a “stereographic technician” dedicated to the operational ma-nagement of the 3Ds settings and monito-ring as well as the 3Ds rushes.The stereographer must ensure the stereos-copic “guarantee of good end results” of a production. The hierarchy remains unchan-ged, but the stereographer is the same as a director of special effects under the director and director of photography.- With the director, he studies the stereosco-pic variations for the entire film.- With the chief operator, he studies the lat-ter’s demands to guarantee that the tools are used well and to respond to the specific demands of the director of photography. He also participates, as outside personnel, in how the scenes are shot and in how the ca-mera is positioned. He then supervises the work of installing and setting up the came-ras and stereoscopic modules.- For the production as a whole, he studies the necessary means for getting started in terms of teams and hardware.- With all the production technicians, he answers their precise questions on adapting their professions to 3-D.- With the manager of postproduction, he studies the specific demands related to workflow. To ensure the consistency of all the 3-D effects, he might supervise postpro-

duction stages such as correcting conver-gence errors, the continuity of depth in the shots, compositing, calibrating, correction of disparities, etc.

Stereographic technicianWhen the means of production allow it, the stereographer can be assisted by a stereo-graphic technician in charge of physical adjustments of, or the 3-D systems used, in shooting. He thus takes the initiative in setting up the rig and the camera, the ver-gence of the inter-axial distance and the involuntary disparity problems. When there are several teams shooting on a feature film or several cameras on the same film set, the different stereographic technicians can ap-pear as generic “stereographers”, because in this case they have much more autonomy than in a usual shooting environment.

3-D postproduction supervisor

The “3-D postproduction supervisor” belongs to the laboratory team. He is responsible for the adjustment of the settings of the digital postproduction machines. He will be working hand-in-hand with the stereographer as well as the editor and/or calibrator during 3-D ca-libration (depth grading). It also happens that the stereographer intervenes in a film as a “3-D supervisor” from one end to the other of the production chain and thus takes on the task of supervising the control of 3-D consis-tency at different stages of postproduction. It should be recalled that in postproduction it is necessary to correct both “visual disparities” (keystone, alignment, optical aberrations, etc.) and to bring “corrections to stereoscopic settings” resulting from shooting errors, but also from brutal 3-D variations introduced during editing by inverting shots planned for in the beginning.

Stereoscopic offset

De Stereoscopic offsets appear when the image filmed by the right camera and the image filmed by the left ca-

mera are superimposed. The stereoscopic offset of an object, or parallax, is the dis-tance to the image between left and right images of an object. It is expressed in the percentage of the width of the image, or in pixels: an offset is said to be positive when the left image of an object is to the left and

its right image to the right. In this case, the object seems to be in the distance, behind the plane of the screen, “in depth”.An offset is said to be null (0%) when the two images of an object are perfectly superim-posed. In this case, the object appears on the plane of the screen (exactly at the depth of projection screen).An offset is said to be negative (-1% for example) when the left image of an object is to the right and its right image to the left. In

aPPenDiX 2: 3-D filminG teChniQues : From “Filming in relieF: the Complete anD interaCtive Course”, parallell Cinema

For live shooting:

StereographerOn streaming TV programs being shot in 3Ds, the stereographer is usually employed on the same level as the director or the head of photography. He conceives the general stereographic options in collaboration with the production and directing teams as well as the photography director and the chief ca-meraman (framing supervisor). He also par-ticipates, as outside personnel, in conceiving the filming of shots and in the positioning of the camera. He then supervises the work of installing and adjusting the cameras and stereoscopic modules. He directs and super-vises the work of the “convergence-pullers” (also sometimes called “assistant stereo-graphers”) in order to obtain 3-D consistency between cameras. He also assists the pro-duction in making choices that influence 3-D effects. At the stereographer’s side is some-times found one or several stereographic technicians who adjust the production rigs. Also found there are 3-D vision engineers in the control room.

3-D vision engineerBased in the control room, the 3-D vision en-

gineer deals with 3-D vision and with supervi-sing the tools used for creating 3-D. He works under the direction of the stereographer and is in charge of monitoring the angulation and the inter-axial distance through the remote control commands of 3-D assessment tools. He should not be confused with the traditio-nal image vision engineer who ensures the control of the image in agreement with the head of photography by acting on the came-ras’ commands (diaphragm, level of blacks, whites and gammas, corrections of details and contours, matrices, etc.).

Stereographic technicianIn a large 3Ds multi-camera set-up (five to 6 rigs), there is generally a stereographer who supervises all the filming, two 3-D vision engineers in the control room and a stereo-graphic technician per active rig (or for seve-ral rigs). The vision engineer has a role very near to the one he has in 2-D, except that in addition he must pair (match) both cameras on the same rig. It should be noted that tech-nologies evolve very quickly in terms of 3-D filming and the convergence settings, regu-lated today by the stereographic technician, could in the end become operations that are more and more automated.

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Adjustment of distant objects on an artificial

horizon

Distant objects in divergence (diplopy)

Positive offset: the object seems behind the screen

Zero offset: the object seems on the plane of the screen

Zero offset: the object seems on the plane of the screen

this case, the object seems near, in front of the plane of the screen, “popping out”. An offset can be expressed, it should be noted, in percentage or in number of pixels.

First step in shooting: adjusting distant objectsOne of the basic rules to be respected during shooting in 3-D is to ensure that the viewer will really have the sensation that an object placed in the background of a scene is really positioned in the “depth” of the screen. For example, the space existing between the eyes is on average 6.5 cm for an adult male. Therefore, if the image of a distant object intended for the left eye is offset 6.5 cm in relation to the image intended for the right

eye, the eyes will look straight in front of them and be perfectly parallel in terms of view.On the other hand, if the two images on the screen are now offset 13 cm, then the left eye must look to the left and the right eye to the right: the viewing enters into divergence. Now this situation is not natural for the human eye, and at best it is tiring, or at worst painful, provoking nausea and headaches.It can thus be deduced that an offset (po-sitive) on the screen of 6.5 cm between the two images of an object is the maxi-mum that we can tolerate.For this reason, this offset value is of-ten called the “artificial horizon”. It is naturally a question of an absolute va-lue, which means that the same film is not necessarily adapted to every screen size. On a small screen (for example, 1 m wide), if an offset is, for example, 1 cm (that is, 1% of the width of the image), it will be 13 cm when it is projected on a screen of 13 m. It will be 26 cm on an IMAX© having a base of 26 m (see table on page 44: the relation between the 3Ds parallax and the size of the screen).Therefore, distant objects offset +1% of the width of the image will be perfectly adapted to a screen of 6.5 m (since our +1% will make exactly 6.5 cm), but they

Effect of “angulation” or “vergence” on the placement of the scenic box in relation to the

plane of the screen

Effect of inter-axial distance (distance between the optical axes of the cameras) on the stereoscopic range (amplitude of the scenic box)

will often be horrible on a screen of 13 m. They will give a weaker sensation of depth on a screen of 2 or 3 m.Adjusting the distant objects according to the planned screen size is thus very important from the beginning, even if it is possible to make adjustments in postproduction.• The artificial horizon of a 6.5 m screen is thus +1% (the “+” meaning a positive offset).• The artificial horizon of a 13 m screen is +0.5%.• The artificial horizon of a 26 m screen is +0.25%.The case where small screens are used is special: in fact, experience shows that the majority of viewers tolerate more easily an

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artificial horizon situated between +1.8% and +2.5%, the latter value already being quite large. Beyond this, the shot generally beco-mes too long to be superimposed. The artifi-cial horizon of a small screen is thus around +2% (with photos, the tolerance is greater be-cause the image does not move).It should be noted that with negative offsets (that govern popping-out effects), no artificial horizon really exists, convergence posing less problems than divergence. However, it must be kept in mind that an offset of -1% makes an object pop out at ½ the viewer’s distance to the screen on a screen of 6.5 m, and at 2/3 this distance on one of 13 m, a very strong ef-fect.

Filming in strict parallel tFilming in strict parallel, without angulation or offset of an image in relation to another one in postproduction, hardly takes place anymore except in IMAX© format, where it adapts well. For all smaller screens (cine-ma, television), this type of filming generally gives disappointing results, since it is cha-racterized by the absence of positive offsets: everything is popping out, nothing is behind the screen and distant objects are on the plane of the screen.In strict parallel, without postproduction off-sets or angulation, as soon as a film is looked at on a screen smaller than that of IMAX©, popping out effects are not very comfortable due to the proximity of the screen, which for-ces the eyes to take quite large convergence angles.

Filming in parallel with offsets in postproduction (“shift”)For this reason, on screens smaller than IMAX©, it is necessary to offset (“shift”) an image in relation to another one to create positive offsets: this pushes all the 3-D in a single block towards the back without touching the amount of depth; everything

seems farther away.This method is used to adapt the 3-D image to different screen sizes: an image is shifted in relation to another until distant objects correspond to the artificial horizon of each screen size, that is:• About +2% for small screens• +1% for 6.5 m screens• +0.5% for 13 m screens• +0.25% for a 26 m IMAX© screenWhile shooting, it is useful to determine the 3-D effect obtained by visualizing before-hand the effect of the offset by using a 3-D monitor that allows an image to be shifted in relation to another.

Filming with convergenceAnother method exists for adjusting distant objects, which is preferred by certain stereo-graphers because it avoids the loss of a band of several pixels on the left and right of the image when an image is shifted in relation to another in postproduction. Rather than shift or offset an image in relation to another, a camera, or both, can be angled, that is, to have them make a small panorama of less than one degree, which is also called the vergence of the cameras.When a camera is angled, a small panorama is made. Now, unlike a travelling, in a pano-rama the perspective does not change.Mathematically, it is the same thing as a postproduction offset (shift): with an angu-lation, like in a postproduction offset, all the pixels of the image are shifted to the left or to the right. This is why filming in parallel with postproduction offset and filming with convergence are mathematically equiva-lent—even if the two methods have practical differences (keystone problems or loss of pixels on the left and right of the image).When filming with convergence, since one camera is angled, in reality one camera films a rectangle and the other, by compari-son, a trapezoid. Thus are introduced slight

deformations of perspective in the angles of the image, called “keystoning”. These de-formations, negligible in most shots, never-theless require certain shots to be corrected in postproduction using morphing effects to “make up for” the deformations of perspec-tive, which otherwise would create visual fatigue.There exists two types of rigs: those that only converge on one axis and those that conver-ge on both so as to apportion the trapezoid or “keystone” effect over both images.The convergence of the cameras defines the plane of the screen and adjusts the distant objects. It is necessary to locate the most distant object in the scene on a 3-D monitor and to angle a camera until both images of this object have the desired offset: for exam-ple, +1%.

Second step: adjust the inter-axial distanceThe inter-axial distance is often adjusted once the distant objects have been set. The inter-axial distance is the distance separa-ting the centers of each camera’s lens. This should not be confused with the inter-ocular distance separating the optical axes of the eyes (6.5 cm on average). The inter-ocular and inter-axial distances are independent, the inter-axial distance being used to adjust the “stereoscopic range” of an image, which also depends on the focal length and the po-sitioning of the first and last object.The inter-axial distance varies according to the shots: when a large inter-axial distance is needed (landscape shots, miniaturization effects), rigs are used side-by-side. But the-se do not allow the cameras to get very close. When small inter-axial distances are needed (for most shots), mirror rigs are used.As the inter-axial distance is used to adjust the stereoscopic range, it is set according to the scene in order to obtain the stereoscopic range desired. But since the vergence of the cameras was set to define the offset of dis-

tant objects, the adjusting of the inter-axial distance will also allow the position of the plane of the screen to be determined. There exists several methods for determining the inter-axial distance necessary according to the scene being filmed.

Method for determining the inter-axial distance by calculating the stereoscopic rangeIf the farthest object in the image has an offset of +1% and the closest object has an offset of -2%, then the stereoscopic range of this image is 3%, for +1-(-2)=3. Likewise, if the farthest object has an offset of +2% and the nearest an offset of 0%, the stereoscopic range of the image is 2%, for 2-0=2.For small screens, a stereoscopic range of 1.5% to 3% is often recommended. For lar-ger screens, smaller stereoscopic ranges are usually recommended: 0.75% to 1.5%.Of course, the exact stereoscopic range depends on each shot and the effect one wishes to obtain. For certain shots (popping-out effects, for example), one might want to precisely control the stereoscopic range.Starting from an inter-axial distance of 0 cm, first the distant objects are set by using angulation (for example, +1%). Then the in-ter-axial distance is progressively increased until the left and right images of the closest object reach the value of the desired stereos-copic offset. This is directly controlled on the 3Ds monitor (in our example, the inter-axial distance would be increased until a value of -2% is reached for the closest object if a ste-reoscopic range of 3% is desired).But another method can be used that has the advantage of not needing a 3Ds monitor thanks to the following formula:

L x G = Ewhere:L is the width (in meters) of the frame at the level of the closest object (measured on the set, for example: 1.5 m).

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Horizontal decimation (one pixel out of two is kept on each line)

Decimation in staggered rows (checkerboard sampling)

Vertical decimation (one pixel out of two is kept in each column)

two major technological families can be distinguished that allow stereoscopic content to be broadcast. The first, called

“Frame Compatible”, has the advantage that it can be used on existing broadcast networks. This technology spatially compresses the left and right views into a single image, but has the inconvenience of reducing by half the ori-ginal resolution. Furthermore, a Frame Com-patible image appears as two anamorphic images placed one beside the other, thus ma-king the operator broadcast the 2-D version of the same program on a separate channel.As for the “Service Compatible” mode, it al-lows one and the same signal to be broadcast to all receivers. Using this type of approach, 2-D televisions only use that part of the signal that they need, but the 3Ds models are capa-ble of displaying the left and right views in full definition.Whatever the method being considered, the broadcast of a 3Ds signal requires a band-width much greater that its monoscopic equivalent. The Frame Compatible modes ge-nerally require between 15% to 35% supple-mentary throughput because of the increase in high frequencies in the image that solicits the encoders more.As for the Service Compatible modes of distri-bution, they require an even higher through-put, in the order of 50% to 70% in comparison with the 2-D version. From a strictly technical point of view, this increase of throughput re-

aPPenDiX 3: CoDeCs anD DistriBution moDes

G is the stereoscopic range desired in percent (for example: 2%)E is the inter-axial distance in centimeters.For example:1.5 x 2% = 3 cm

Method for determining the inter-axial distance by positioning the plane of the screenFor other shots, where the stereoscopic ran-ge does not reach critical values, the precise

position of the plane of the screen is the most important parameter. This allows, among other things, to avoid irritating window er-rors.Once the distant objects are set through an-gulation, the inter-axial distance is progres-sively increased until the plane of the screen (that is, objects having an offset of 0%) is pla-ced where one wants.

mains beneficial for the operator, since a sin-gle channel is enough to broadcast 2-D and 3Ds images. But the necessity of a different grammar makes editorial compatibility so-mewhat delicate (axes and settings of the shots, rhythm of editing, etc.). New produc-tion methods need therefore to be invented in order to optimize the technical capabilities, all the while guaranteeing the artistic quality of the 2-D and 3Ds versions of the same pro-gram.

Frame Compatible modes of distributionThe main principle of the Frame Compatible modes is to reduce the resolution of the left and right images by half in order to group them in one and the same HD image. This spatial compression (horizontal or vertical anamorphosis) generates a 2-D signal that can be processed and transmitted by existing equipment.During decoding, each of these two views is made “deanamorphic” and displayed on the screen in order to recreate the sensation of 3-D. To compose a Frame Compatible image, it is first necessary to select those pixels to be retained in the left and right original views. This step is called “decimation” and there exists several ways of proceeding: one can choose to only retain one pixel out of two on each line, in each column or in staggered rows. Moreover, the position of the retained pixels can be identical for both images, or else offset (by one line or one column).Once the pixels to be retained have been se-lected in both views, then the way to arrange them within one and the same image must be determined, which is called “packing”. Here again, several solutions exist: Side-by-Side, Top-and-Bottom, Checkerboard, etc. Although it is theoretically possible to choo-se different decimation packing modes, it is generally understood that these two steps follow a certain logic.

Side-by-Side

The left and right views are made anamorphic and placed side by side. This method induces a theoretical horizontal loss of definition of 50% for each eye, but the work done by the brain to recreate the sensation of 3-D usually attenuates this loss of real definition.

Top-and-Bottom

The left and right views are made anamor-phic and placed one above the other. This method induces a theoretical vertical loss of definition of 50% for each eye, but, as for the Side-by-Side mode, the visual discomfort felt by the viewer is not necessarily very great.

Line-by-LineIn this system, the lines coming from one eye are placed on the even lines of the final

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image and those coming from the other eye on the odd lines. The “Line-by-Line” mode is not very well adapted to video compression because its structure solicits the encoders more, and it works badly with color sub-sampling (4:2:0).

CheckerboardEach source image is sampled according to a checkerboard structure and in a comple-mentary way for each view. The loss of defi-nition felt is less than with horizontal or ver-

tical decimation.However, the Checkerboard mode is not at all adapted to video compression and will practically never be used such as it is for broadcasting. On the other hand, decimation by Checkerboard associated with Side-by-Side packing has been shown to be a very efficient method for spatial compression (Sensio proprietary codec, for example).at the international level, but companies such as Dolby and Sensio are already proposing pro-prietary methods.

DvB BroaDCastinG in 3Ds

DVB-3DTV phase 1 The DVB European consortium, which propo-ses TV broadcasting standards, defined 3Ds TV broadcasting modes in Frame Compatible format in February 2011. This broadcasting can thus take place from now on using existing HD infrastructures that make use of DVB stan-dards.This standard recommends H264 compression as well as the use of the following display for-mats:

Side by side Top and Bottom1080i/25 720p/501080i/29.97 720p/59.941080i/30 720p/60 1080p/23.98

The standard describes the transmission of signaling information that allows the decoder to know which type of Frame Compatible it is receiving, and thus to choose the appropriate processing. This information is conveyed in the SI (Service Information) tables of the DVB sys-tem as well as in the MPEG elementary packets. It has been planned that a channel can broad-cast 2-D at certain moments and 3Ds at others: in this case, the 2-D commutation to 3Ds and inversely can be automatically generated by the decoder. Likewise, the electronic program guide (EPG) will be able to say which programs are in 3Ds. The standard foresees the dynamic management of subtitle and graphics paral-lax so as to avoid conflicts of depth indications (a subtitle placed farther away than an object that it is hiding). This also allows visual fatigue to be avoided caused by the juxtaposition of a

subtitle placed too near on a very deep bac-kground. The standard allows this background to be managed differently according to the re-gion of the image where the subtitles become inserted.

DVB-3DTV Phase 2Les normes DVB-3DTV phase2 sont encore eThe DVB-3DTV Phase 2 standards are still being developed. They will permit a Service Compatible approach, that is, backward com-patible with older television receivers:- DVB-3DTV Phase 2a, whose specifications should appear in the summer of 2012, will allow TV viewers equipped with a 2-D screen to watch programs broadcast in 3Ds. This is done by broadcasting the left image plus an improvement layer which will only be decoded for 3-D screens. The 2-D televisions will not decode this and will only display the left eye. The MVC codec can no doubt be used for this. Even so, this technique does not settle all pro-duction problems: a production planned for 3Ds could turn out to be bad in 2-D.- DVB-3DTV Phase 2b corresponds to ano-

ther form of backward compatibility: it allows full resolution 3Ds programs to be broadcast while remaining readable by a DVB-3D Phase 1 decoder. The principle here is to transmit a Frame Compatible image accompanied by supplementary information that allows the left and right views to be displayed in their full resolution. With this system, the first-genera-tion 3Ds decoders will process the 3-D images in half resolution per eye, whereas the new decoders will be capable of interpreting the improvement layer and to reproduce the native definition of the original images. The improve-ment layer transports, in fact, the spatial in-formation not present in the base layer. Taking into account the strong correlation between these two streams of data, the improvement layer proves to be very light (in the order of 10% of the base layer in current encoders). This approach has not yet been standardized at the international level, but companies such as Dolby and Sensio are already proposing proprietary methods.

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