Stereoscopy and 3D cinema

Stereoscopy - 3D CInema3D / stereoscopic film historyStereo vision and depth perception

Why is 3D so much fun?Satisfying an innate human instinct• Predatory nature of the species– FOV - Field of view– Predators require depth to hunt – eyes to the front– Prey require wide angled vision – eyes to the side• Playing with our personal space?

3D AND THEFILM INDUSTRY

1950s Golden Age of ‘Naturalvision’– Multicamera filming– 2 film stocks to be played back simultaneously (synced in theprojectors)– Skilled projectionists for effective 3D viewing– Image quality problems

1960 / 70s revival– Multicamera filming– 2 film stocks to be played back simultaneously (synced in theprojectors)– Skilled projectionists for effective 3D viewing– Image quality problems

1980s• The IMAX cinema theatres• Enhanced the viewingexperience

1990s– Film with digitisation– A digital workflow– Full digital FX

2000’s...• Digital ‘lens to lens’ workflow• Synthetic digital movie making (fully CGI)

Economics of 3D• A certain amount of 3D projectors are needed to break even on presenting3D movies• Film companies still require 2D simultaneous releaseto be economically viable• Aside from projector limitations, 3D is in itself economically viable– The polar express 3D (2003)• Released in 2D• Released in 70 IMAX cinemas• Revenue (per copy 3D:2D) - 14:1

Avatar – Economic milestone2,351,605,000 worldwide box office takings (15 February 2010)81% of that is from the 3D version• 64% regular 3D cinema• 17% IMAX cinema

Stereo vision and stereo imageryHow 3D works

In Short…• Our brain sees one image but it is made up of information from twoimages• These two images (from left and right eye) are almost the same• The slight differences tell us a lot about the depth of a scene• These differences become more obvious the closer things are to us– (Fingers example)• Stereoscopic photography uses two cameras representing our eyes, torecord (see) the scene for us• When we watch a stereoscopic film with 3D glasses, we extract the twoimages from it and our brain does the rest…….

Stereopsis and stereoscopyStereopsis (natural stereo vision)• Our eyes see the world as 2 individual images (left / right)• Their difference is referred to as disparity• Our 2 ‘eye-images’ are fused into a single stereo imagein our brainsStereoscopy (stereo camera imagery)• the production of 2 separate digital images• The digital images are taken at a distance of 2.7” (the same disparity asour eyes)

Shooting StageTwo cameras are placed sideby side, roughly the distancebetween an adults eyes (2.7inches)The images from each camera willhave a slightly different picture

Mixing the viewsThe two separate images arecolourised (left – red, rightcyan)The colourised images arecomposited (mixed together)Where the two images are thesame, the colours are naturallookingWhere the images are different,coloured edges are visible

Viewing Stage3D glasses filter the redcomponents to the left eyeand the cyan components tothe rightNatural stereo vision can nowtake place because the vieweris seeing the scene as twoimagesThe brain re-assembles the twoimages into one stereo image(STEREOPSIS)

Visualizing and using disparity

Convergence and Accomodation (focusing)• Convergence (coming together)– Our eyes rotate inwards (cross) when looking at an object that is close to us– Our eyes are in parallel when looking into the distance (infinity)• Accomodation (Sharpening)– The muscles that focus the lens of the eye at a particular distance– Accomodating - at a distance(USE FINGER EXAMPLE TO CONVERGE AND ACCOMMODATE)• In 3D cinema, we are converging on objects as if they were between us and thescreen or behind the screen but accomodating on the screen

The disparity is forcing eyes to convergeat a point close to usThe brain thinks the object is in front ofthe screen

There is little or no disparityThe brain thinks the object is atthe screen

The disparity is forcing the eyes to converge at adistanceThe object appears to recede behind the screen

InfinityThe left / right disparity doesn’t force anyconversionThe eyes are relaxed and facing out in parallelThe brain thinks it is looking at infinityStereopsis doesn’t work at such agreat distance (40Meteres +) and we must instead usemonoscopic depth cues to gauge relativedistance

The stereoscopic comfort zoneToo much disparity can beuncomfortableAnd sometimes painful!

Bad 3DRetinal Rivalry• The on screen disparity is so wide that your brain can no longer fuse theviewpoints into one stereo image• Your eyes (retinas) compete over who gets to look at the image• The image flickers between each view point (L – R)Vertical Disparity• Where the images are not aligned horizontally• Our eyes cannot resolve them vertically (our eyes are horizontally aligned)• 3D effect fails

Stereoptic depthOcclusion revelation (hiding and revealing)• Our eyes see two distinct images• When viewing a scene where one object overlaps anotherwe see a tiny strip of the object throughone eye that is not visible with the other• This strip is the ’occlusion revelation’• Occlusion revelation is key in assessing objectsrelative distance from each other in z space

How is the 3D effect enhanced?• Traditional film depth + stereoscopic depth• Stereopsis is just one of many ways that we perceive depth• Human adults can still perceive depth with one eye closed• Monoscopic photography can also indicate depth• Monoptic depth cues involve extracting depth information from a 2D view

Monoscopic depth cuesRelative size– Distant = small– Near = big• Dependant on existing knowledge of scale and proportion• A small house next to a big person indicates that the person is in the foregroundand the house is in the backgroundOverlap• Objects obscured by other objects areperceived as background objects– Distant = behind– Near = on front

Monoscopic depth cuesPerspective• Aerial - colours become faded and grey as they recede• Linear - Lines converge in the distance• Pattern - Objects get smaller as they recede(Crowd scene)

Monoscopic depth cuesLight and shade• Sculpting depth with light• Objects surfaces catch and hide from light– Light fades away from its source– Curves gradually fade from light to dark

Monoscopic depth cuesMotion Parallax• Example - The view from a train window (Point Of View Parallax)– The hedges fly past in a blur– The houses move past quite fast– The distant trees move more slowly– The mountains in the background do not seem to move at all– Train video with parallax• Every time you move your head you are experiencing subtle but crucial POVMotion Parallax

Object movement parallax• The farther away an object is, the slower it seems to move– A plane about to take off will seem extremely fast to a nearby viewer– As it takes off at the end of the runway it will appear slower– As it flies off into the distance it will seem slower again– In full flight it will seem to be almost stopped (flying x3 the runway speed)