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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.


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.


One Response to “Retinal Rivalry in Live action 3D cinematography”

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