Passive 3D Projection – Part 10
This blog provides a wrap-up to the discussion of my past 9 blogs on the subject of Passive 3D Projection. Most of that discussion focused on using two consumer projectors operating in 2D mode and configured with auxiliary equipment/components such that one projector is used for the right-eye view and the second projector is used for the left-eye view as required to present a stereoscopic 3D image when viewed thru passive 3D glasses. This final blog in the series on passive 3D projection discusses a single projector solution for implementing a passive 3D projection system.
Single Projector Passive 3D
Back in PART 2 of this series of blogs, I briefly discussed the LG CF3D (Art’s full review is HERE) that was introduced in 2010 and has been the only generally available single projector passive 3D solution for home theater use. The CF3D when introduced had a list price of $14,999 which is substantially more than most current consumer 3D projectors using active 3D technology, many of which have a list price of less than $4,000. The LG CF3D is essentially two LCoS light engines fitted into a single cabinet and sharing a single projection lens. However if the LG CF3D were the only alternative for a single projector passive 3D system, then this would be a very brief blog indeed.
Taking a page from the world of digital cinema, there is a technique that is used by RealD for creating 3D presentations using a single digital projector. As I have mentioned in previous blogs in this series, RealD uses circular polarization as the means to separate the right from the left visual image streams. A RealD setup for this using a single digital projector displays 144 frames per second that alternate the right and left images (i.e., 72 Hz per eye or 144 Hz. total). The projector used in such a RealD setup is outfitted with a “ZScreen” that is an electronically controlled optical element (specifically a push-pull electro-optical liquid crystal polarization modulator) that switches the polarization of the projected light between right-hand circular and left-hand circular synchronized with the 144 Hz frame rate of the projector. Although this is a passive projection system, the image sequence reaching the viewer’s eyes is similar to active 3D projection systems where each projected image is alternately seen by only the right eye or by only the left eye. By comparison, dual projector passive 3D systems, as discussed in my recent blogs, allow both eyes to see images simultaneously. Such a single projector solution (i.e., using a polarization modulator) also means additional light loss due to the 50% duty cycle of the projected images (i.e., also similar to active 3D systems), as seen by either the right or left eye.
While some home theater hobbyists have experimented with an externally mounted electro-optical polarization modulator (i.e., similar to the ZScreen), there are now consumer oriented solutions becoming available. The most convenient of these commercial systems are intended for use with an active 3D projector. With such a setup the conventional active 3D projector has all of the responsibility for accepting the 3D signal, via its HDMI v1.4a input, decoding the 3D and projecting the 3D video as an alternating sequence of right and left images. The external electro-optical polarization modulator system then must synchronize with the projector (e.g., using the projector’s 3D sync. output that is normally used with a IR emitter for active 3D projection) and alternate the polarization orientation between the right and left image frames. Thus such an electro-optical polarization modulator system converts an active 3D projector into a passive 3D projection system. The polarization may be linear, rather than circular as used by RealD in commercial cinemas.
One such add-on filter system is being offered by the European company Volfoni (Web Site) with their “Smart Crystal Cinema” product. Volfoni describes their “polarization modulator” as (web page is HERE):
“Made up of a multi-layer stack of liquid crystal elements based on Volfoni’s Surface Switching Technology™, it allows for high-speed operation and optical efficiency, creating a crisp and bright 3D image.”
“SmartCyrstal™ Pro can be connected directly to any suitable 3D input source and works with projector strength up to 5,000 lumens. It can be connected to a computer via USB cable, allowing the user to adjust the settings of the LCD to optimize image quality for any venue.”
A YouTube video discussing the Volfoni system is located HERE. The price of the Volfoni filter system with a few pairs of compatible polarized 3D glasses is estimated at $1500.
Another supplier of polarization modulators for 3D projection is the DepthQ unit being marketed by Lightspeed Design, Inc. of Bellevue, Washington. They sell the polarization modulator as a separate item or packaged with a projector supplied in InFocus. The press release is HERE and the Art’s review, from January 2011, of the projector equipped with the DepthQ polarization modulator is HERE .
Another option for a complete projector plus polarization modulator setup comes from French manufacturer DreamVision. They are offering a projector and attached polarization modulator system where the projector appears to be based on a JVC DILA 3D model (perhaps the DLA-X90 or virtually identical DLA-RS60 model). For those of you not familiar with the company DreamVision, they offered one of the first DLP projectors marketed for the home theater market. This was back in the days when CRT projectors ruled the front projector market.
DreamVision calls their new model the “Best 3D Passive” and DreamVision web site’s description says (the full text can be found on the product web page is HERE):
“Dreamvision is proud to release the Inti BEST projector range. The BEST (Bi-level Efficiency Stereo Transmitter) module is a new concept of passive 3D which will be a milestone in the history of video-projection. The creation of the 3D effect is based on an innovating management of the light path and an optimized polarization modulator that implements high-tech materials. The result is an unprecedent optimized projection system, whose performance in 2D is equivalent to the one in 3D.”
DreamVision claims the following features for their system:
- Easy to setup and straight forward use
- Out of the box pre-calibrated for 2D and 3D modes
- Light weight glasses, cost effective and with no battery
- Highest contrast available on the market
- 50% brightness gain over Active 3D
- Similar picture quality and brightness in 2D and 3D modes
- Single-head 3D passive projection system
When considering an external polarization modulator for use with a separately purchased projector, care must be taken to select a projector that is compatible. One factor to consider it that most LCD and LCoS based projectors (but not the case for DLP projectors) output polarized light and the orientation of these projector’s polarized light must be compatible with the external polarization modulator. Also the projector must be able to integrate with the polarization modulated so that the projector and the polarization modulator are precisely synchronized in alternating the polarization orientation correctly timed with the frame transitions of the projected images. If you are considering such a setup, check with the manufacturer of the polarization modulator for projector compatibility.
A “silver screen” will be required with such a passive 3D system in order to retain the polarization of the projected light. As with any passive 3D projection system using polarization, the level of 3D crosstalk/ghosting will be greatly influenced by the ability of the projection screen to retain polarization. This was previously discussed in Part 7 of this series of blogs. In the case of using an active 3D projector equipped a electro-optical polarizing modulator, the level of 3D crosstalk will also be influenced by the ability of the projector to alternate the display of the right and left images without retaining traces of the previous image in the sequence. Virtually all active 3D projectors using LCD (e.g., Epson, Panasonic) or LCoS (e.g., JVC, Sony) micro imaging display chips will exhibit some crosstalk due to a limitation in the response time of these display technologies. Thus the level of crosstalk exhibited by these 3D projectors when used in active 3D mode will more-or-less carry over when used with a passive 3D setup where there will also be additional 3D crosstalk added from the passive portion of the system (mainly the limitations of the screen and polarizing filters). DLP projectors should not contribute any 3D crosstalk, since they do not have response time limitations that produce crosstalk. As long the electro-optical polarization modulator system is correctly synchronized with the DLP projector, then the level of 3D crosstalk should be the same as for a dual projector passive polarized projection system (i.e. with crosstalk originating only from the screen’s performance and the quality of the polarizing filters used with the projector’s polarizing modulator and the lenses of the 3D glasses).
For my next blog I will discuss the next generation HDMI specification (now under development).