Posted on March 21, 2011

Crosstalk harms 3D realism


Researchers at Canada’s York University claimed to have demonstrated a link between the amount of crosstalk involved in 3D displays and the realism of the stereoscopic effect. Crosstalk, in which separate left or right eye images ‘leak’ into each other, is a phenomenon that occurs in all 3D cinema projection and 3D TV displays.

To minimise such visual distortions, crosstalk should be kept at levels of four percent or lower, the study recommends. Currently few systens have crosstalk below 4 percent.

“Our study found that the more interference from crosstalk, the less depth you’ll see. This reduction in depth can make 3D images appear less realistic,” says Inna Tsirlin (pictured), a psychology PhD student in York’s Centre for Vision Research.

The study showed that crosstalk was detrimental at even the smallest depths tested, and became more disruptive as depth increased.

“For example, instead of seeing two objects at 10cm apart in depth, you would see them at 5cm apart if the crosstalk is high enough,” reports Tsirlin. “We also found that the detrimental effect of crosstalk on the perceived amount of depth is stronger when there is a larger depth range in a 3D image. So, there will be a more disruption for objects at 1mm apart then for objects at 10cm apart in depth.”

Previous research has established that crosstalk causes viewing discomfort, which can include eye strain, headaches and dizziness. The study reccommends optimising hardware for a crosstalk level below four percent may resolve these issues as well.

Several companies including Dolby 3D and RealD use ghostbusting pre-processing software techniques to reduce crosstalk which is most effective for high contrast white on black imagery.

RealD’s projection systems have crosstalk around 1-2 percent. Austostereoscopic displays are particularly susceptible with crosstalk up to 5-10 percent, the study found. Anaglyph systems can yield crosstalk as high as 50 percent.

According to York Professor Dr. Laurie Wilcox; “It is safe to say that many current 3D projection and 3D TV technologies can reach acceptably low levels of crosstalk under ideal viewing conditions. However vigilance is required to ensure that these ideals are met… if they are not the viewing experience will suffer.”

Minimising the distortion includes improving the hardware (glasses and displays). Some software solutions also exist to manipulate the images of the two eyes. “Zero percent crosstalk is great, since this will be closest to natural images we see every day,” adds Tsirlin. “However, 1-2 percent crosstalk is not likely to reduce the quality of the images and the 3D depth significantly.”

The research was conducted as part of the 3D Film Innovation Consortium (3D FLIC), a collaborative venture whose partners include Cinespace Studios, IMAX, Christie Digital, and Starz Animation.

Wilcox is co-principal investigator on Depth in Motion in York’s Faculty of Fine Arts’ Department of Film and recipient of a recent $1m grant to assess human responses to moving content in stereoscopic 3D film, believed to be the first such investigation.