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 Digital Cinema Report does it again: This website is a source of great info.


Basic 3D Perception Concepts

By Phil Lelyveld

[email protected]


1) Looking at an image on a 3D display (cinema, TV, laptop) is not the same for your eyes as

looking at the real world.

One reason relates to the mismatch between the object appearing to be in front of or

behind the screen while the object is in focus onto the surface of the screen.

2) When producing 3D content, define and work within a "safe" depth budget in-front of and

behind the screen.

There are guidelines and limits for a comfortable viewing experience based on screen

size and viewing distance. It would be useful for the industry to develop standards and

guidelines that optimize the depth budget(s) for consistent digital workflows and

consumer experiences.

3) Some effects simply don't work the same way in 3D as they do in 2D.

We should aim to provide guidelines on what works well in 3D and what doesn't. This is

the emerging language of 3D. The ETC is developing a Standard Test and Evaluation

Material (STEM) reel for this purpose.

4) Audience members will vary in their response to 3D. While most will find 3D easy to watch

and more engaging than 2D, research has found that a small percentage of the population will

either not see the 3D effect or find it uncomfortable. Some individuals who are in that small

percentage are vocal critics of 3D.

It would be useful to provide resources to inform the public of this issue, and develop

tools that individuals can use to self-identify and avoid a disappointing and possibly

unpleasant experience. The ETC is researching the criteria for this self-identifying tool.

© 2009 Entertainment Technology Center at USC all rights reserved

Consumer 3D Experience – basic concepts and guidelines

This is a brief executive primer on 3D movies and human perception. It is intended to cover the

basic terms and concepts behind how we see 3D movies and what to watch out for when they are

created and displayed. Links and references are provided at the end for those who want a more

detailed overview (ref. 1 and 2).

Binocular vision

Our brain gets its visual information about the real world through our eyes. Because the eyes are

approximately two inches apart, each eye “sees” and sends a slightly different signal/angle to the

brain. The brain understands the difference between those two views as cues for depth, and

automatically fuses those two images to get a “center” view, which was not actually seen by

either eye. Hold a finger in front of your face and alternate between two eyes open and one eye

shut to see this process in action.

Two key terms used by vision researchers for how our eyes capture three-dimensional

information are vergence and accommodation.

Vergence is the angle one of your eyes turns relative to the other eye so that they both look at

(aka converge on) the object that you want to see. When you look at the horizon the vergence is

zero. When you look at something close to your face the vergence is significant.

Accommodation is the act of focusing your eyes so that you see what you are looking at clearly.

Vergence-accommodation conflict

In the natural environment, the distance at which your eyes converge is the same as the distance

at which your eyes should focus. This is not the case with stereoscopic 3D, where the images for

both eyes are projected as two separate images on a screen.

Assume we project a 3D object that is meant to appear to be in front of the screen. Your left eye

turns to look at the left-eye image of the object, and your right eye turns to look at the right-eye

image of the object. Put together, your eyes converge (vergence) as if the object exists in front

of the screen.

As your eyes converge, your brain sends instructions to the eyes to focus the way they normally

would for a real object at that convergence distance (accommodation). But in 3D movies the

“object” is in focus on the screen, which is behind this convergence point. So your brain keeps

working your eyes until the “object” is in focus. That inescapable difference between how we

naturally see the real world and how we see 3D movies is called the vergence-accommodation


© 2009 Entertainment Technology Center at USC all rights reserved

The vergence-accommodation conflict also occurs if the object is meant to appear behind the

screen. Only when the 3D object is meant to appear on the screen itself is there no vergenceaccommodation

conflict, because your eyes converge on the point where the image is indeed in


An audience member’s ability to deal with this vergence-accommodation conflict over the

duration of a movie is impacted by how flexible the lenses of their eyes are (ref. 3) and how well

his/her brain reacts to the conflict. To maximize the enjoyment of 3D for the entire audience, one

guideline is to recognize that this conflict exists, and to give considerable thought to the impact

on the audience before having objects jump or scenes cut rapidly and repetitively in and out of

the screen.

Research has been done to quantitatively define the comfort zone for the vergenceaccommodation

conflict. Eye flexibility, often a function of age, is a factor (ref. 3).

Comfortable viewing and vergence-accommodation conflict

According to Prof. Martin Banks, Professor of Optometry and Vision Science at U.C. Berkeley,

the vergence-accommodation conflict should be kept at less than ½ to 1/3 diopters for the

majority of a 3D viewing experience to avoid discomfort and fatigue.

Diopter is a term that is widely used in vision science research. It is useful for understanding

how the depth component of 3D content works. We normally think in terms of distance from the

person to the screen. Diopter is the inverse of that; 1/distance (in meters) to the screen.

The practical impact of keeping the vergence-accommodation conflict less than 1/3 diopters is

that for a person sitting 10 meters (32.8 feet) from the screen, the effect should come no closer

than 2.31 meters (7.6 feet) from the person.

Diopters help us understand how the comfortable viewing range changes as a function of

viewing distance. For the same 1/3 diopter limit;

How far the person is from

the screen

How close to the person the

object appears

How far in front of the screen

the object appears

5 meters (16.4 feet) 1.875 meters (6.2 feet) 3.125 meters (10.2 feet)

10 meters (32.8 feet) 2.31 meters (7.6 feet) 7.69 meters (25.2 feet)

20 meters (65.6 feet) 2.61 meters (8.6 feet) 17.39 meters (57.0 feet)

Laptop distance from person

to screen

0.25 meters (9.8 inches) 0.23 meters (9.1 inches) 0.02 meters (0.8 inches)

0.5 meters (19.7 inches) 0.43 meters (16.9 inches) 0.07 meters (2.8 inches)

This table shows that the comfortable viewing range is larger for a person sitting further away

from the screen than for a person sitting closer to the screen. The same 3D effect that extends

from just barely in front of the screen to infinity when viewed on a laptop appears to be from 57

feet or more in front of the screen to infinity when viewed from the back of the theatre.

© 2009 Entertainment Technology Center at USC all rights reserved

Perceptual distortion due to incorrect viewing angle

Your brain compensates for the distortions caused by viewing a 2D image (e.g., a painting) at an

oblique angle by using the images from both of your eyes to recognize and compensate for the

angle of the surface of the image.

Assume that you are sitting in the best viewing position in the theatre or your home and watching

3D content. As you move away from the centerline of the screen, either to the left or the right,

the 3D object becomes increasingly distorted. Different seating positions provide a different 3D

viewing experience! Your brain cannot compensate for viewing a 3D projected object at an

extreme angle to the screen (ref. 4). This may be an inescapable attribute of physics and human

visual perception.

Interpupillary distance (IPD)

Interpupillary distance is the lateral separation between the left and right eyes. The majority of

adults have an IPD of between 5.5 and 7.0 cm. Children have a narrower IPD, with the majority

greater than 4.0 cm (ref. 5).

As objects move from up close to infinitely far away, your eyes move from converging on a

point to looking in parallel toward infinity.

Part of the emerging language of stereography will be establishing recommended practices for

the offsets to use when establishing the deep/distance portion of the 3D image. This decision

will be influenced by assumptions of both the measured distance of the offset on the screen and

the viewer’s distance from the screen. If the offset is too great, as might be the case for a person

sitting too close to a theatre screen that is larger than the screen size anticipated by the

stereographer, then the 3D effect will induce that person’s eyes to diverge (e.g. turn outward in

opposite directions) to see the image clearly. This is unnatural and uncomfortable, and some

people are completely incapable of doing it. Yet the same offset will provide a pleasant viewing

experience for someone sitting farther away from the screen in the same theatre. And the same

offset in the source material, when displayed on a home theatre screen that is a fraction of the

theatre screen size, will produce a shallower image. A recommended practice may be something

as simple as developing a table of screen size versus minimum distance from the screen to the

front row for a given screen size and telling the theatre owner to only allow audience members to

sit at or further than X feet from the screen.

Depth of field

The previous section on IPD flows into the question of how to handle the distant background in

3D images. Often, filmmakers working in traditional 2D will use shallow depth of field to draw

audience attention to an actor or object, while leaving the rest of the scene blurry/out of focus.

Some researchers believe that people are more likely to explore a 3D image than they are a 2D

image. Shallow depth of field could exacerbate eyestrain and fatigue if viewers attempt to focus

on parts of the screen that they cannot bring into focus no matter how hard the brain tries to

accommodate. On the other hand, increasing the depth of field in a 3D movie increases the work

you are encouraging the audiences’ brains and eyes to do. The director of the 3D movie Coraline

made the artistic decision to selectively use shallow depth of field in the depth script (ref. 6).

From the vision science perspective, research is needed on the relationship between depth of

field, stereoscopic 3D imagery, and discomfort and fatigue. Part of developing the language of

3D stereography for filmmaking will be learning how to use depth of field. The language will

© 2009 Entertainment Technology Center at USC all rights reserved

evolve as audiences get past the novelty of 3D and become familiar with the conventions of the

3D experience.

Depth budget is the amount of depth in and out of the screen that you plan to or are able to use.

Depth script is a script/score/timeline describing how the 3D space is used over time; how to

pace the action in the third dimension. It is here that you would map out where to use an

extreme 3D effect relative to the ambient 3D depth value, and how to block scenes so that cuts

between shots do not draw attention to the 3D effect and take the audience out of the story.

Image-pair balancing

If the displayed image-pairs are not perfectly aligned and matched, they will contain visual

information beyond the parallax needed to produce the 3D effect, and will contribute to viewer

discomfort and fatigue over time. Here are some image-pair balancing concerns to keep in mind.

• There may be creative or technical reasons to have the cameras ‘toe in’ rather than point

forward in parallel. When the two images are combined, the ‘toe in’ introduces a

keystone effect that must be corrected.

• Vertical misalignment, where one camera is slightly tilted ‘up’ relative to the other, and

rotational misalignment, where one camera is capturing an image at a slight clockwise

rotation to the other, must both be corrected.

There is software to correct for these problems (ex. Nuke compositing software from The

Foundry, Binocle.com showed prototyped tools for live 3D shoots at 2009 NAB).

• Magnification must match between the images. This is especially critical during zoom


• Illumination and color balance of the image pairs must match.

• Temporal balancing; Multiple camera-pairs used during live action filming should have

lens- and camera-pair imperfections that produce images that edit together well.

Research needed

To advance the language of 3D filmmaking, accelerate the development of 3D products and

tools, and expand the market for 3D content and experiences, research to answer these

fundamental questions should be conducted;

- Can fundamental principles emerge so that we can produce a trailer with the tag line; ‘if you

find viewing this to be an unpleasant experience, then you are among the segment of the

population that will not enjoy a 3D movie experience [in a theatre, at home, on a personal

device, etc.], so please do not watch movies in 3D.’ We know there are people out there

who, for any number of reasons, will have a bad experience or will not see the 3D effect.

Anything we can do that will help those people self-identify and avoid an unpleasant

experience will be extremely useful in sustaining support for 3D entertainment.

Stereographers will use whatever fundamental principles emerge creatively, and build on

them as they learn how to incorporate 3D into the language of storytelling.

- Will stereographers author once for all display situations, or will there be more granularity

based on expected display device (ex. will there be “home version”) or some other

© 2009 Entertainment Technology Center at USC all rights reserved

parameter? Studios are working on digital workflow, archiving policies, etc. Recommended

practices, which may emerge naturally as the industry gains more experience, will be useful.

- People have trouble resolving a 3D image as the horizontal pan rate increases. Filmmakers

need more quantitative information regarding pan rate, the brain’s ability to resolve the stereo

image, and frame rate. Some research in this area is being done by Martin Banks and his

students at UC Berkeley.

- Does increasing the amount of light that reaches the eyes significantly impact the vergenceaccommodation


- How does depth of field impact the way people explore a stereoscopic 3D image? Does the

impact change with time, both during the viewing of long-form content and over years of

viewing experience? Research is needed on the relationship between depth of field,

stereoscopic 3D imagery, and discomfort and fatigue.

Additional Resources:

1. “Foundations of the Stereoscopic Cinema” by Lenny Lipton, is available as a free pdf

download at http://www.stereoscopic.org/library

2. Prof. Nick Holliman of the University of Durham, UK, has posted an excellent overview

of 3D concepts, including shooting 3D images, at http://www.binocularity.org

3. Decline in accommodation with age is plotted in Fig. 3 of “Ocular and Refractive

Considerations for the Aging Eye” by Kathryn Richdale, at

4. Marty Banks’ NAB presentation slides will be posted on his website
http://bankslab.berkeley.edu/ . They are currently available at
http://www.etcenter.org/files/public...anks_NAB09.pdf )

5. Neil Dodgson of the University of Cambridge Computer Lab, UK, has aggregated data

on the range and average of human interpupillary distance (IPD). His paper is available

at http://www.cl.cam.ac.uk/~nad10/pubs/EI5291A-05.pdf .

6. Perception and the Art of 3D Storytelling, by Brian Gardner, Creative Cow Magazine, the

June, 09 Stereoscopic 3D issue, at http://magazine.creativecow.net/issue/stereoscopic-3d

7. Research on visual fatigue from vergence-accommodation conflict is laid out very well in

this paper; “Vergence-accommodation conflicts hinder visual performance and cause

visual fatigue”, by David Hoffman, Ahna Girshick, Kurt Akeley, and Martin Banks, at

Author: Phil Lelyveld is an Entertainment Technology and Business Development Consultant

( www.ReelWord.com ). He is currently developing the Consumer 3D Experience Lab and

program at USC’s Entertainment Technology Center ( www.etcenter.org ). Phil spent 10 years

developing and implementing Disney’s digital media strategy as the corporate Vice President of

Digital Industry Relations. He has been involved in new and emerging media for almost 20


Contributors: the following contributed text, feedback, and edits to this paper:

© 2009 Entertainment Technology Center at USC all rights reserved

Martin Banks is Professor of Optometry and Vision Science; Affiliate Professor of Psychology

and Bioengineering, UC Berkeley. He and his team have done research into stereoscopic surface

perception, virtual reality, binocular correspondence, binocular visual direction, picture

perception, self-motion perception, multisensory interactions, and infant spatial vision (
http://bankslab.berkeley.edu/ ). He frequently presents his research to both professional and lay

audiences, including the recent Society for Information Display’s 3D Technology Update for

Display Professionals conference in Costa Mesa, CA ( www.sid.org/ ), and the Digital Cinema

Summit (ref. 4) coproduced by the ETC and SMPTE at NAB 2009.

Neil Dodgson is Reader in Graphics & Imaging in the Computer Laboratory at the University of

Cambridge (UK), where he is a co-leader of the Graphics & Interaction Research Group

( http://www.cl.cam.ac.uk/Research/Rainbow/ ). His research interests are in computer graphics,

3D display technology, human-figure animation and image processing. He is on the program

committee of the annual Stereoscopic Displays and Applications (SD&A) conference

( www.stereoscopic.org ).

Nick Holliman is Senior Lecturer, Department of Computer Science, Durham University,

Durham, England ( http://www.dur.ac.uk/n.s.holliman/ ). His research into digital imaging

covers 3D computer graphics, computer vision and visualization technologies. He specializes in

interdisciplinary research investigating the theory, human factors and application of (auto-)

stereoscopic 3D displays. The Durham Visualization Laboratory, which he founded in

January 2004, supports these and other inter-disciplinary 3D research themes. It contains a wide

range of 3D displays, tracking/interaction devices and 3D capture systems

( http://www.dur.ac.uk/n.s.holliman/3dDurhamDisplays.html ). He is cochair of the annual

Stereoscopic Displays and Applications (SD&A) conference ( www.stereoscopic.org ).

Phil Captain 3D McNally is the Stereoscopic Supervisor for Dreamworks’ Kung Fu Panda,

Monsters vs Aliens, How to Train Your Dragon, and Shrek Goes Fourth. Prior to that he was

Stereoscopic Supervisor for Disney’s Meet the Robinsons, and has worked on other features at

Disney and ILM. He is a graduate of the Royal College of Art in London and has over 15 years

of 3D experience. In the 1990s he legally changed his middle name to Captain 3D.

John Merritt is CTO of The Merritt Group ( http://www.merritt.com/ ), A Fellow of the Society

of Photo-optical Instrumentation Engineers (SPIE), and cochair of the annual Stereoscopic

Displays and Applications (SD&A) conference ( www.stereoscopic.org ).

David Wertheimer is the CEO and Executive Director of the ETC (Entertainment Technology

Center) at USC. Prior to ETC, David was president of Paramount Digital Entertainment, CEO of

WireBreak Networks, and worked with Steve Jobs at NeXT and Larry Ellison at Oracle.

Andrew Woods is a Research Engineer at Curtin University of Technology's Centre for Marine

Science and Technology (CMST) (Australia). His research interests include Stereoscopic

Imaging, Stereoscopic Video, Underwater Technology and Remotely Operated Vehicles (ROVs)

( http://3d.curtin.edu.au/ ). He is cochair of the annual Stereoscopic Displays and Applications

(SD&A) conference ( www.stereoscopic.org ).

Ray Zone is a leading champion of 3D ( www.ray3dzone.com/ ). For 25 years, through his

company The 3-D Zone, Ray has been converting flat art to 3-D for every conceivable

application. The client list includes Warner Brothers, Walt Disney Company, A&M Records,

Saban Entertainment, Galoob Toys, and many others.
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