Cross talk is caused by the incomplete isolation of the left and right image channels, and one image leaks into the other. The effect makes it look like a double exposure.
Crosstalk
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Cross talk is caused by the incomplete isolation of the left and right image channels, and one image leaks into the other. The effect makes it look like a double exposure.
The definition provided uses two versions of the term: “crosstalk” and “cross talk”. The most common usage in the scientific literature is “crosstalk” (with out the intermediate space) so I recommend that version be used normally.
Crosstalk is the result of incomplete cross-cancellation of opposite eye-view images, also sometimes referred to as “ghosting”. Whatever you call it, the artifact is undesirable, but common in many recent digital cinema screenings.
It actually began in many instances with the inception of the stereoscopic digital cinema. Not that it is caused by digital projection, per se, but because it was coincidental. The wide use of circular polarizers with a low extinction ratio began at that time. The reason was twofold: the very low light output of the projectors, and the ability to advertise a purported advantage of circular: that you could tilt your head.
You can tilt your head with high extinction ratio linear up to about 10 degrees without incurring as much crosstalk as with circular at any angle. More than that is undesirable, regardless of the type of polarizer, because the vertical displacement then becomes excessive, resulting in discomfort, and even headaches. In fact, linear polarizers are safer than circular, because you quickly become aware if you are tilting your head excessively for viewing comfort.
A little-know fact is that for any polarizer, circular or linear, passive or active, increasing the overall density two times by increasing the herapathite crystal concentration, will result in an increase in the extinction ratio of about ten times. This is only true if you increase the concentration (as during manufacture), NOT if you attempt to put two sheets of polarizer together, as if you wore two pair of glasses, one over the other.
Therefore, if you have much more light to start out with, you can use slightly darker polarizers (as manufactured) and get a tremendous gain in cross-cancellation, ergo no visible ghosting or crosstalk, even with extreme high contrast images, such as widely displaced white text on a black background. This is not likely to happen until projectors become much brighter. The new laser projectors are capable of 14 ft. Lamberts, but they are expensive. As such, they are not likely to replace the equipment in many theaters for another 5 to ten years.
Comparing with the past, you did have much more light in the 1950’s. Today, typical theater projection results in 3 ft. Lamberts on the screen from a single projector (6 for two projectors, still not that common). Back in the 1950’s (and even before), you had 16 ft. Lamberts from each of two projectors, for a total of 32 ft. Lamberts on the screen. Even with double-density linear polarizers, you were looking at 3D images that were over four times as bright as today, with no visible crosstalk.
Over 100,000 people saw this at the 1939 World’s Fair, some 74 years ago. My, how we have progressed.