We are now working to reduce the weight and power consumption of our shutter glasses, which currently weigh more and consume more power than conventional ones.3D glasses allow a flat image to be viewed by the human eye in three dimensions. Within the acceptable angle range of head tilt, crosstalk does not increase more than 1.6%, which frees the viewer to change their head position without adversely affecting the 3D image they see. This is achieved by incorporating a tilt sensor and off-state voltage controller. They also can be tilted within ±50° without a significant increase in crosstalk. In summary, we developed 3D shutter glasses that are flicker-free with respect to ambient light.
We found experimentally that the full variation of open state transmittance within the same range does not exceed 10% in shutter with active tilt compensation. The variation of transmission with tilt angle in the ON state is far less. The contrast ratio varies between 0.0045 at zero tilt and 0.016 with ±50° tilt angle. A plot of the contrast ratios with and without active tilt compensation shows active tilt compensation results in lower crosstalk that does not increase much with tilt angle: see Figure 3. The measured contrast ratio is 0.0062 with no tilt, and >1.1 with a tilt angle of +50°. At any given tilt angle, we adjusted the voltage applied to the compensation cell to minimize the shutter's transmission in the off state. During the measurement, we varied the tilt angle between −50° and +50°. tilt angle for a shutter, both with and without tilt compensation. 2We measured the switching contrast I o#/I on for a narrow beam of green LED light. At low levels, the contrast ratio is practically equal to the stereoscopic crosstalk. The shutter can be characterized by I o#/I on, the ratio of its transmission in the off and on states. Compensating for both right and left tilt requires a second LC cell: see Figure 2(b). We add a tilt sensor to the shutter-glasses which sends information on the tilt to the LC cell's controller. In addition, when the viewer's head is tilted, the tilted quarter-wave film causes elliptical polarization of the transmitted light that can be compensated by proper control of the off-state voltage applied to the LC cell. Replacing the front polarizer with the retardation film stops the flicker effect caused by bright ambient light. We align the film's principal axis parallel to the transmission axis of the output polarizer. Incident light polarized parallel to either principal axis is unchanged, but incident light polarized between the axes is transformed to elliptically polarized light (circularly, if the incident light is polarized at 45° to each axis). This has fast and slow orthogonal principal axes. We found that a better design for the shutter replaces the front polarizer with a quarter-wave retardation film.
Shutter contrast ratio plotted against head tilt angle without (upper line) and with (lower line) active tilt compensation. One way to overcome this is to apply a tilt-dependent voltage to the LC cell.įigure 3. When the viewer's head is tilted, there is severe ghosting on the stereoscopic image caused by ‘crosstalk’ between the left and right images: the left eye receives some of the image intended for the right eye and vice versa. However, omitting the front polarizer to improve flicker creates another problem. Since the light emitted by the LCD panel is polarized, the front polarizer facing the screen can be removed without loss of functionality: see Figure 2(a). The shutter is opaque when the voltage is ON and translucent when the voltage is off.
In conventional shutter glasses, a pulsed voltage is applied to the LC cell and (via a microcontroller) synchronized with the TV set by an IR or RF signal. The shutters switch at 60Hz and the light source is modulated at 50Hz, providing perceived ‘flicker’ of 10Hz. (b) Low frequency flicker by interference of shutter and blinking light source. (a) Ambient light condition and shutter's structure.