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Posts Tagged ‘S3D’

3D Theatrical Projection Problems with Floating Windows – Keystoning

As noted in a prior post on “Floating Windows” there is somewhat of a problem with the theatrical screening of 3D whereby cinema screens cannot for various reasons project a full screen DCI compliant image without physical image masking. Below I outline some possible solutions to this problem.

The main problem with both the theatrical presentation of 2D and 3D Feature Films is the tendancy for a cinema to be designed where the projection device is situated at the rear upper level of the auditorium. This old model of cinema design requires that the image be projected downwards over the distance of the auditorium to the screen. The physics of this basic model there for assume that the image will be somewhat keystoned by the time it reached the screen. To then counter the effect of a trapeziod shaped projection image on the screen one would then employ cinema black masking and essentially over shoot the image into the blacks until a nice pleasing rectangle is created.

For this very reason a ‘projection safe’ or ‘action safe’ model is employed by 2D image creators whereby, just like television, images were made to be displayed with a 5% ‘masking’ tolerance. Some screens may see the full image and most would see somewhere between that and roughly 5% – 10% in.

You can see now that if in a 3D presentation you are employing the use of ‘floating windows’ to counter 3D edge violations or simply play with the 3D screen dynamics these will more than likely be lost. Unfortunately as these windowing techniques are employed to assist with the audiences comfort factor when viewing 3D materials their exclusion from the presentation will make the experience slightly more uncomfortable.

Lets look at the below screen setup.

  • Screen Width – 30 Ft Screen
  • Screen Resolution – 2048
  • Auditorium Depth / Projector Throw- 100 Ft
  • Tilt of Projector – 10 Degrees

Given the above scenario, without masking, our image is now 30 foot across on the top of the image and 29 foot along the bottom. 28/30 = 93%

Top Width = 68″9′

Bottom Width = 76″1′

Keystone % = 100 * (top width-botom width)/top width = %9

9% of 2048 = 184 pixels.

Generally FLoating Windows will not be more than the max Positive Disparity which ona 30ft screen would not be more than 28 pixels Either side.

Well…with the calculations above we just lost our floating windows.

Bugger!


The Great Gatsby – 3D

The Great Gatsby

2013

Director: Baz Luhrmann

DOP: Simon Duggan

Studio: Warner Bros

Senior Digital Intermediate Colorist and Stereoscopic Finishing Artist : Adrian Hauser

Grading Hardware: Baselight 8 & Baselight 2

Stereo Finishing  Hardware: Baselight 8 & Baselight 2

Acquisition Format – Red Epic 3D

Projection Format – DCI 2.39:1

 

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iRiS Stereoscopic Base and Disparity Calculator – 1.1.0 Update – Introducing the Roundness Factor

The Stereoscopic Base and Disparity Calculator 1.1.0 for the Android OS has just been updated and introduces a new base calculation measured around the perceived on-screen Roundness or depth of an image.

The new option allows the user to either :

  • Calculate the camera base separation using a predetermined target parallax amount
  • Calculate the camera base separation to a “Roundness Factor” of 1.0.

The Roundness Factor represents the factorial difference in depth between the photographed scene and the resultant projected 3D scene.

It is generally referred as a factor because ideally one would want to capture and project the same depth representation of photographed object, thus having a factor of 1.0.    IE: Physical scene depth/perceived 3D on-screen depth.

If the Roundness Factor is less than 1.0 then for example a round sphere will appear flat and compressed. It will have lost is dimensionality.

If the Roundness Factor is greater than 1.0 then the same sphere will appear stretched or extruded on the Z depth plane.

Consider dimensionality in filming the close-up of someones strong angular face. Captured with perfect roundness the 3D on-screen projected face will feel volumetric and proportionately correct. If the “Roundness Factor” starts getting too high the persons head and nose will begin to feel stretched toward the viewer, which is not such a flattering look.  In this sense it is better to err on the side of a factor less than 1.0.

The effect of Roundness is related very closely to Lens selection. A longer focal length lens will have a much greater impact on roundness and Parallax as the base separation in altered. On a 75mm Lens it takes only small changes in Base distance to make quite large differences in background parallax and therefor depth.   Additionally sensor size is quite an important factor to consider as the resulting 35mm Lens equivalents could be a lot higher than you think.

As always it is recommended to test Lens/Sensor configs as much as possible before entering any project.


Adrian


iRiS S3D StereoScopic Base and Disparity Calc – new Skin Released

S3D Calc New Skin - template

New skin released with a few UI improvements.

Adrian


iRiS S3D Stereo Base and Disparity Calculator Released

The S3D Base and Disparity Calculator is now officially released on the Android Market.

The S3D Calculator is divided into three Main Screens.

Navigating between the screens is performed by swiping the current page with a horizontal finger gesture.

  1. Initial Simple Base Calculation
  2. Base and Disparity Evaluation and adjustment
  3. Disparity Overview and Analysis

Simple Base Calc

Input Options Include:

  • Camera
  • Camera Active Area
  • Lens
  • Screen Size
  • Screen Resolution
  • Parallax Target
  • Distance Measurement Metric (Meters or Feet)

Base and Disparity Evaluation and adjustment

Disparity overview and analysis

Output Data Includes:

    • Base (inter occular Distance)
    • Field of View
    • Angle of View
    • Total Pixel Parallax
    • Total screen Parallax %
    • Total Screen Parallax (mm)
      • Positive Parallax
      • Negative Parallax
    • Zoom Required
    • Post Convergence Required

    Regards,

    Adrian


    s3d stereoscopic Base and parallax / divergence calculator for Android

    ScreenShots from forth coming s3D Base and Parallax Calculator for Android.


    S3D Stereoscopic Screen Parallax / Disparity Calculator

    v1.04 Excel template of my S3D Screen Parallax Calculator.

    It will end up as an OSX app and a Android Mobile Phone Application in the coming weeks.

    Measures Positive and Negative Pixel Parallax of a Stereo Scene on a given Screen Size.

    Inputs:

    • Camera Base
    • Focal Length
    • Near Distance
    • Far Distance
    • Focal Distance
    • Sensor Size
    • Projection Ratio
    • Projection Size
    • Projection Resolution
    • Floating Windows


    3D Glossary

    Accommodation

    The ability of our eyes to refocus at a new point of interest. In normal vision the processes of focusing on objects at different distances (accommodation) and converging (the angle between the lines of sight of our eyes) are linked by muscle reflex. A change in one creates a complementary change in the other. However, watching 3-D requires the viewer to break the link between accommodating at a fixed distance (the screen) while dynamically varying eye convergence and divergence (something we don’t do in life) to view objects at different stereoscopic distances. A young human eye can change focus from infinity to 7 cm in 350 milliseconds.

    Acuity

    The acuteness or clearness of vision; the level of detail perceptible at a distance (resolution). This is dependant on the sharpness of the retinal focus and the sensitivity of the interpretative faculty of the brain.

    Anachrome

    Anachrome is similar to the Anaglyph process but allows some red colour into the cyan right eye to improve the colour range. The red filter is darker than the red filter used in the Anaglyph process to help avoid retinal rivalry.

    Anaglyph

    The anaglyph process was invented in 1853 and is a time parallel process where both images are sent to the viewer at the same time. The name is derived from the Greek words ‘again’ and ‘sculpture’. Two pictures are individually coloured and then superimposed as a single image rather than two separate images. Each eye sees only the required image through the use of coloured filters (red/green or red/cyan). The right eye sees through cyan or blue filters which provide colour information. The left eye sees through the red gel where no colour range is visible just a monochromatic red cast. The issue is that the colour red is lost from the images. Cross talk and ghosting is a problem as the filters do not totally eliminate the opposite eye view. Historically the Anaglyph technique with its cardboard glasses is probably the best known 3-D display system. It has drawbacks including the inability to present true colour images and discomfort caused by prolonged viewing. Anaglyph enables wide spread viewing of 3-D on the web and TV without the need of specialist screens so is a cheap solution to create 3-D.

    Angulation

    Resulting angle between the optical axes of the 2 cameras.

    Augmented Reality

    HMD technology is used to project a computer image onto a view of the real world as an overlay. Mirrors are used to show the partial reflection of the real world. Applications include medicine, architecture and gaming.

    Autostereoscopic

    A method of displaying 3-D images that can be viewed without the use of special headgear or glasses by the user. These methods produce depth perception for the viewer even though the image is produced by a flat device. There are two methods to create autostereoscopic screens, Lenticular lens and Parallax barrier.

    Binocular Vision

    Binocular comes from two Latin roots, bini for double, and oculus for eye. The disparity between images that fall on the retinas of both eyes create retinal disparity which is a binocular cue used to perceive depth.

    Card Boarding

    The lack of 3-D modelling for objects in a scene due to the use of telephoto lenses. Objects appear flat like cardboard cut outs.

    CAVE

    Computer Assisted (or Collaborative) Virtual Environment – using projectors to display images on 3 or 4 walls and the floor to create an immersive experience.

    Convergence

    The ability of our eyes to simultaneously angle inward to focus on a near object. The convergence ‘near point’ is the closest point which is still possible to perceive one image. Our eyes can easily converge inward but have much less ability to diverge outward (no more than 1 degree beyond parallel).Toeing in cameras (angling) simulates the eyes converging inward on a depth point in the scene. The ‘convergence point’ is where the axes of the toed in cameras align on the Z-axis. Convergence can be adjusted in post by horizontal movement of the two images (alignment).

    DCI (Digital Cinema Initiatives)

    A joint venture of the major studios for the standardization and specifications of digital cinema. Version one of the specifications was released in July 2005

    DCS

    Digital Cinema Specifications created by SMPTE

    Depth budget

    A term used to refer to the combined value of positive and negative parallax and expressed as a % of screen width.

    Depth cues

    Information acquired about the depth of a scene. This is achieved using a combination of binocular cues (retinal disparity) and monocular cues (motion parallax, relative size, perspective, object motion, occlusion etc).

    Depth grading

    A post production process where negative and positive parallax, convergence and divergence are adjusted. This is a creative tool and also a way to ensure that the content can be comfortably watched on the screen size it is intended for.

    Depth of field

    DOF defines the range where vision is sharpest and how much of the subject is in focus.

    Diplopia

    Known as double vision where the eyes are uncoupled and the image of an object is not received correctly on the fovea of both eyes. Some people can uncouple their eyes voluntarily.

    Disparity

    The distance of two corresponding points on the retina, the further the points are apart the greater the disparity.

    Divergence

    Caused when the viewer looks at 3-D images that have positive parallax beyond the human interocular. Our eyes cannot diverge (rotate outward) more than a maximum of 1 degree without straining the eye muscles. If images have divergence then they can cause viewer discomfort. Also see Wall eye

    Dwarfism

    See Miniaturization

    Empty field myopia

    When there is no image on your retina (blacked out room) your eyes rest with focus set around 3-5 feet.

    Far Point

    The furthest point from the eye (or the nodal point of the camera) where the image is clear.

    Floating windows

    A device used in post production, where the perceived position of the screen is shifted into the theatre by adding black strips down the edge of the frame. This is primarily used to avoid screen violation, but can also be used for creative results such as angling, leaning or distorting the screen.

    Fovea (Centralis)

    The area of sharpest vision on the retina which has the highest concentration of cones (6-7 million mainly red and green).

    Frame violation

    The illusion of depth breaks down at the edge of the screen if an object is occluded by the screen boundary. The brain is confused if a 3-D object is supposed to be in front of the screen but then occluded by the screen. In the real world anything that is occluded is further away.

    Free viewing

    A viewing technique where no additional apparatus is required to be worn by the viewer. This can be as simple as two images placed side by side and the viewer crosses their eyes to see stereo or autostereoscopic screens.

    Ghostbusting

    The process of reducing crosstalk where parts of the left or right eye images appear in the unintended eye. Also called ghost reduction

    Ghosting

    Artefacts typically caused by signal leakage (crosstalk) between the two eyes. A secondary ‘ghost’ image can be seen. High contrast levels between an object and its background is the main cause of the problem. Ghostbusting can reduce this issue.

    Gigantism

    Confusing visual cues in a stereoscopic scene that can make an object seem enlarged. This is due to shooting with an interocular distance much less than adult human eyesight (Hypostereo).

    Handing off

    Cuts between shots with strong positive and strong negative parallax can be unsettling. This is because the eyes and brain are being asked to jump uncomfortably quickly between different depths without warning. Handing off is the technique of dynamically changing the convergence of an outgoing shot while balancing the convergence of the incoming shot so the abrupt depth jump is smoothed. Wherever possible cut between shots where the point of interest is on a similar plane.

    Horopter

    The volume centered around the fixation point that contains all points of single vision, it contains corresponding points that fall onto both retinas.

    Hyperstereo

    Using widely spaced cameras (beyond 70mm interocular) which record more stereo effect than the eyes can see. Such a large interocular distance can produce the effect of miniaturization. Also used to achieve the effect of exaggerated stereo depth. For stereo effects on very long shots (e.g. landscapes) Interocular camera set ups of several meters can been used. An extreme example of Hyperstereo is from NASA cameras mounted in space to record the Sun in 3D.

    Hypostereo

    Using closely spaced cameras (less than 50 mm interocular) which record less stereo effect than the eyes can see. Such a small interocular distance can produce the effect of gigantism. If standard cameras are used, the minimum interocular distance is typically limited by the thickness of the camera body or lenses so a mirror rig is used, enabling a separation of millimetres. For miniatures Interocular distances of 5mm or less can be used.

    Interaxial Distance

    The distance between the nodal point of the lenses of the two cameras. A distance of 65mm is often considered to be the ideal distance as it matched the distance between the eyes but it is also subject to focal length selection and the nature of the shot. The term ‘Interaxial’ is sometimes interchangeable with ‘Interocular’ or ‘Interpupillary’ but specifically relates to camera distance where the other terms relate to eye distance.

    Interoccular distance

    The distance between the centre-points of your eyes. This can range from 50-76mm in an adult.

    Inverted stereo

    See Psuedoscopic

    Keystoning

    The result arising when the film plane in a camera or projector is not parallel to the view or screen leading to a trapezoid shape. When a pair of cameras are ‘toed-in’ they can create varying vertical mismatching between the images which can be fixed by corner pinning in post.

    Miniaturization

    Confusing visual cues in a stereoscopic scene that can make an object appear to be reduced in size. This is due to shooting with an interocular distance much greater than adult human eyesight (Hyperstereo). The viewer effectively becomes a giant looking at the scene.

    Mirror Rig (Beamsplitter rig)

    Housing for two cameras one facing forward, the other facing 90 degrees down (or up) viewing through a 50% beamsplitter mirror. The cameras can be ‘overlapped’ reducing the interaxial beyond the limitations of the camera body or lenses. These rigs can be large and cumbersome.

    Monocular cues

    A series of depth cues calculated from a single eye. Cues include occlusion/relative size / motion parallax/depth from motion/atmospheric haze/texture detail etc.

    Motion parallax

    The change of angular position of two stationary objects relative to the observer caused by the movement of the observer.

    Near point

    The closest point at which an object can be brought into focus by the eye. A standard near point distance of 25cm is typically assumed.

    Orthostereoscopic

    A one-to-one condition where what is being displayed is the same as the ‘real world’. For example IMAX 3D is often shot with parallel cameras spaced at the average human adult interocular distance (approx 63.5 mm) and with wide angle lenses that closely match an audience member’s view of the screen.

    Panums Fusional Area

    The region of binocular single vision, a volume centered on the fixation point that contains all points in space that yield single vision. These points in space are imaged as identical corresponding points on the two retinas.

    Parallax

    From the Greek word parallage meaning alteration. It relates to the apparent change in angular position of an object seen from two different perspectives. Also see Screen parallax

    Photogrammetry

    Geometric properties of an object are determined from photographic images taken from different positions. The same object point must be visible within at least 2 images. Dates back to the mid 19th century. Used in topographic mapping, architecture, Vfx, geology, archaeology and police investigation.

    Pseudoscope

    A stereoscopic device that creates the opposite effect of the stereoscope by inverting the depth of objects (turning them inside out) – achieved with a series of prisms

    Pseudoscopic

    If a stereoscopic signal is reversed (each eye is being fed the opposite eye signal or if there is a one frame offset between each eyes) a strange ‘punched in’ effect appears. This is also referred to as inverted stereo or reversed stereo.

    Pulfrich Effect

    The process was invented by Carl Pulfrich in 1922. It is a psycho-optical effect where lateral motion of an object is interpreted by the brain as having depth, due to the difference in processing speed between the two eyes. The effect is induced by placing a dark filter over one eye. Depth is created by a reduction in retinal illumination compared to the other eye resulting in a delay in signal transmission creating spatial disparity in moving objects. The effect has been reported in eye diseases like cataract and multiple sclerosis where it is hard to judge the paths of oncoming vehicles. It does not work with stationary objects or objects that are moving vertically. The BBC carried out a Pulfrich test on the Doctor Who charity special (1993). It has also been used in some commercials and on an episode of ‘3D Rock from the Sun’ (1997). 6 million glasses were shipped in North America for an episode of Discovery channels shark week (2000). Nintendo tested the technique with the Orb-3D game with constantly scrolling backgrounds.

    Retinal disparity

    The difference in information viewed by each eye, the greater the disparity the closer the object is to the viewer.

    Retinal rivalry

    Where there is a difference in the information presented to each eye which can cause discomfort. In 3-D imagery this can include specular highlights, flares or rain drops which are present in one image and not the other.

    Screen parallax

    This relates to the separation of the left and right images on the projection device or display screen. Positive parallax puts an object behind the screen (on screen objects in the left eye image appear on the left of the other image). Negative puts an object in front of the screen (on screen objects in the left eye image appear on the right of the other image). Zero parallax puts an object on the screen plane with no visual separation. Also see Parallax

    Stereographer

    The senior technical/creative advisor in regards to all aspects of stereo photography. This is a highly skilled role and experience in the field on stereo projects is necessary. The stereographer works closely with the production, in particular the DOP and camera crew.

    Stereopsis

    The sense of depth resulting from the information provided by binocular disparity.

    Stereoscope

    The stereoscope is a simple optical binocular device which allows the viewer to see a photograph in 3-D. A left and right image of the scene are placed side by side and viewed though magnifying lenses to create the illusion of a single stereoscopic image.

    Stereoscopic window

    The boundary frame surrounding a stereoscopic image (TV / projection) is called the Stereo Window. Depending on the size objects will appear either in front, at or behind this window. IMAX has the largest window.

    Toe In

    When cameras are angled inward to converge on an object in the scene.

    Virtual reality

    Immersion, sensory feedback (provided by tracking systems) and interactivity within a virtual world.

    Wall eye

    Where positive parallax exceeds the ability for your eyes to rotate outward (diverge) creating a painful effect. Also see Divergence

    Window violation

    See Frame violation

    Windowed stereo

    Keeping the majority of the 3-D experience in positive parallax (behind the screen). It is more like looking though a window. Accuracy is lost in scale reproduction where characters may appear to change scale depending on scene location or from close up to wide shot.

    View Master

    A transparency viewer developed in the 1940′s.

    VRD

    Virtual Retinal Display. Separate left and right images are projected directly onto the retina of the viewer.

    Zero parallax

    See Screen parallax


    3D – How to “FreeView” 3D Stereoscopic Images

    FreeView 6

    The above is an example Stereo Pair 3D image from the 3D Feature Film “Cane Toads” . (Double Click on the images for larger versions.)

    3D FreeViewing , unlike other 3D viewing methods, does not require any other apparatus or special equipment to view an image in 3D. As a viewing method is more associated with viewing stills and 3D previs as it can be quite a strain on the eyes to view motion picture images this way for a prolonged period. The 3D FreeView method does however render a beautiful 3D scene as there is no Crosstalk between the Stereo pair that is otherwise apparent in most other electronic 3D viewing apparatus.

    Analog systems like the “3D Viewmaster” are also produce very pure viewing methods.

    3D ViewMaster

    This ‘FreeView 3D’ image is composed of stills from both the Left and Right Eye. The Right Image is from

    the Left eye and the Left Image is from the Right eye. When viewing you have to go somewhat crosseyed for your brain to fuse the two images together as a 3D image. See Below.

    How to FreeView 3D

    1. Look at the pair of images on the screen. (Double click the image for a larger version)

    2. While still Focusing on the Screen, Hold one finger in between your eyes and the image onScreen. You will see your finger as two ghost images.

    3. Still focusing on the screen, move your finger towards, or away from, the screen until the tip of your ‘ghost fingers’ align with the two circles.

    4. Now focus on your finger. You will now perceive 3 ghost circles behind your finger. The centre circle will be the fused 3D image. (You may have to rotate your head a little so that the 2 images align vertically.)

    5. Here is the tricky bit. While still focusing at the point where your finger is, move your finger away to reveal the 3D image behind it. For beginners your eye will naturally want to focus back to the screen so for a while you can help your brain fuse the 3D by leaving your finger slightly in view.

    The result will be that in this case you see the green dot sitting forward of the black circle in 3D space.

    With practice you will find it second nature. I had looked at many 1990′s stereograms or “magic eye” pictures in my youth so I picked it up quite quickly :)

    Free-View 2

    Have fun.

    Adrian Hauser


    “Cane Toads – The Conquest” 3D – Mark Lewis – 2010

    Cane Toads – The Conquest

    (2010)

    Director - Mark Lewis

    DOP’s - Paul Nichola, Toby Oliver, Kathryn Milliss

    Grading Platform - Baselight 4

    Format - SI2K 3D


    Below are stereo Pair FreeView 3D images. Click on this link for more information about viewing how to view FreeView S3D images

    FreeView 1

    FreeView 2


    FreeView 3

    FreeView 4

    FreeView 5

    FreeView 6

    FreeView 7

    FreeView 8

    FreeView 8

    FreeView 9


    Floating Windows in 3D post

    The use of Floating Windows can help aid 3D problematic sequences and shots where images with a negative parallax (forward of the screen) break the edges of the screen plane. These are called Window Violations.

    <IMAGE_1>

    By manipulating the image boarders with masks one can help reduce the breaking of the immersive illusion. These masks can serve two purposes.

    Firstly they can help reduce the curse of retinal rivalry where an object on the edge of screen is present in one eye and not the other.

    <IMAGE_2>

    Secondly they can perceptually bring the screen plane forward or backward to become inline with an object of negative parralax that is breaking the screen edge.

    <IMAGE_3>

    Depending on the camera or object motion through the shot the Floating Windows can be dynamically tracked to match.

    <IMAGE _4>

    Unfortunately there is a bit of a problem with this function in the real world theatre though. I watched a 3D kids animation feature on the weekend and noted the projected image was (as usual) projecting into the theatre blacks surrounding the screen. (In 2D cinema we can usually use a TV like 10 percent safe area to imagine worst case scenario projection masking.) Because of this the floating windows of many shots became nulified as they shot into the blacks and therefor many shots broke the screen window somewhat uncomfortably that would have been otherwise fixed with this technique.

    Additionally Floating Window effects are also masked due to keystoning of the projector itself. Most theatrical cinemas have their projector raised almost to the level of the top of the screen which naturally causes keystoning. The easy way out of this is to increase the theatre masking so that a true rectangle is projected. This will most definitely mask the Floating windows as well. Some distributors would prefer the image was left full frame in a trapezoid shape that included all floating windows.

    Adrian


    Post 3D Convergence

    The repositioning of LR convergence in post helps the stereographer to smooth the edit in terms of creating a comfortable 3D viewing experience. Convergence does not effect the Depth of the Shot (inter-ocular distance). It simply focuses the eyes attention to a particular part of the 3D volume at a particular place in the 3D z Depth of the Screen.

    By converging 2 points together of a stereo pair we are making that point in the image sit at the screen plane. Anything in front of that plane will appear to come forward of the screen. Anything behind that point will appear behind the screen.

    FreeView 1 - Behind the Screen Plane

    FreeView 2 - At the Screen Plane

    Generally speaking the convergence of an object will be set at or just behind the screen plane. If we converge behind the point of interest, say at the back of someones shoulders, this would force their faces into the auditorium (in front of the screen plane). Such 3D tricks must be carefully thought through as there are  potential problems created. More on those later.

    Dynamic convergence can be of help over cut points where there is little option to cut from a foreground image converged at the screen plane to a another shot where we are made to focus beyond the screen plane (Positive Parallax). By use of dynamic convergence we can ramp over time the convergence to push the viewers attention past the screen plane so as the incoming shot will make for a comfortable 3D edit.

    EXPLANATORY IMAGES COMING.

    Convergence tools and stereo repositioning tools can also help deal with objects that are “Breaking the Frame” and hence the potential cause of eye fatigue. These tools in conjunction with Floating Windows (See post) can hep cure cases of retinal rivalry where one image is present on the edge of screen in one eye but not on the other .

    Adrian Hauser


    Retinal Rivalry in Live action 3D cinematography

    Retinal Rivalry is when the two eyes are simultaneously or successively stimulated on corresponding retinal areas by dissimilar images (e.g. a green source to one eye and a red to the other). The effects of retinal rivalry have been discussed since at least the 192o’s.

    Retinal Rivalry can cause quite a problem with Live Action 3D sequences causing audiences to feel mild unease as their brains attempt to calculate the errors between both stereoscopic images.

    As with most 3D viewing problems a small percentage of people find such 3D visual disturbances completely acceptable and will not find it a distraction. Others will sense an optical distraction or slight discomfort but by the time the have a chance to work out what is wrong with the image the scene would have developed on to the next shot in the sequence. Such distractions are unwanted as they will consciously pull the viewers attention from the story unfolding before them.

    Some Factors causing Retinal Rivalry.

    Specular Highlights.

    Look at a piece of glass about 1 meter away from your face. Now close one eye, look at the highlights, then close that eye and look at the same highlight with your other eye. The highlights are different. Because of the interoccular distance between our eyes we actually see two different images. Normal human vision seems to smooth over this effect because we can look else where but when projected as a fixed image in 3D certain examples of this can be quite discomforting. Because the Highlights are spatially different the 3D effect then assumes this area is on a different zPlane even though we are converging on that point. This apparent depth makes that part of the image difficult for our brains to calculate.

    FreeView 1 - Highlights/Reflections Different in each image

    Free-Viewing the stereo above image feels quite normal. But when projected on screen one can feel the slight discomfort presented by the different reflections in each of the Picture Frames.

    Images forward of the screen plane sitting on the edge of frame.

    Poorly color matched LR imagery.

    Convergence Problems with mismatched screen edges.

    FreeView 3 - Convergence Problem

    The Above image is somewhat disturbing to View because of the object in the Left had side of the Right Eye. It is not noticeable in the Left eye and causes some disturbance in viewing the Stereo Pair. It could be fixed by reframing the overall image pair to the Left as seen Below.

    Fixed

    Edge Problem fixed

    Ghosting of highlights. (Cross talk)

    Particular parts of images, generally of a high contrast in content, can have highlights bleed from one eye to the other when viewed through stereotypical 3D devices*. It is apparent to the viewer as a ‘ghost’ effect.  Imagine a shot showing a hand held torch sweeping through a darkened night exterior. The torch is situated midway in the 3D depth of the overall shot and we are converged on a foreground object. On screen, without glasses, we can see, literally, that the highlights of the torch lens are diverged by about 4% of the screen width. With the glasses now on we can see that the highlight is leaking from one eye into the other by that same distance, producing a ghosting of that part of the image.

    The more the interOccular distance between the eyes the more obvious this ‘ghosting’ will be as the potential distance between the two highlights will be further apart. There are certain processes an image can go through to reduce the ghosting effect but not all instances can be fixed.

    *{Most, if not all, current (2010) 3D display devices are unable to project a pure 100% LR Stereo Pair containing 0% crosstalk. FreeViewing a LR stereo pair, is an exception. FreeViewing is where, like in the old 80′s magic eye images, the viewer looks cross-eyed at a pair of stereo images, combining them to make the 3D composite. Focus about midway between the images and your nose and you will see the two images overlap to create a 3rd in the middle}.

    Vertically misaligned LR images.

    Differing focal planes and DOF between eyes.

    Asynchronous frame recording between eyes.

    FreeView 2 - Notice the Bird on the cross to the Left of the statue in one frame but not the other.

    Adrian