D-ILATM Based 3D Projectors
This is the second part of my blog on using LCoS 3D projection technology. We are currently talking about 3D projection using sequentially alternating right/left images and where viewers must wear active shutter 3D glasses. For this blog I will focus on the JVC D-ILA approach used for 3D.
The currently lineup of 3D-ready projectors from JVC includes their DLA-RS40 (and equivalent DLA-X3), DLA-RS50 (and equivalent DLA-X7), and DLA-RS60 (and equivalent DLA-X9). JVC has two different divisions that market their projectors with the DLA-X series being marketed by their consumer products division and the DLA-RS series being marketed by their professional products division. The RS and the equivalent X series model are functionally identical and differ only by a very minor cosmetic difference. The main differences in features among these models are:
- The entry-level RS40 and X3 models have presets for the color profile, including a preset that is fairly close to ITU Recommendation 709 (the HDTV standard). but lack a full color management system (CMS). As a result, these entry-level models can be professionally calibrated for grey scale, 6500K color temperature and gamma, but cannot be calibrated for precise ITU Rec. X.709 gamut (i.e., correct color saturation and hue for the primary and secondary colors based on the HD video standard). Based on test results from multiple sources these entry-level models generally seem to have higher lumens output than the higher-end models.
- The mid-level RS50 and X7 models add a full CMS and THX certification. They also include a second manual iris within the light engine. All of the JVC models include a manual iris in the lens assembly and these mid and high-end models add a second iris between the light source and the LCoS panels while. This dual iris setup will produce a higher native dynamic on/off contrast ratio when both irises are stopped down as compared to the single iris models. Of course stopping down an iris will result is lower lumens output from the projector, and thus a dimmer image on the screen. The most appropriate setting for the iris depends on many factors, such as screen size, screen gain, room lighting control, etc. These models also have a THX preset mode and also add Xenon color temperature modes to approximate the spectrum from projectors that use Xenon lamps. Selecting a Xenon color temperature mode causes an internal color correction filter to be moved in to the light path, but this does reduce the light output of the projector.
- The flagship RS60 and X9 models are essentially identically to the RS50 and X7 models except the LCoS display chips (and perhaps a few other components within the light engine) have been hand selected to use only the best performing of the production components.
When projecting 3D all of the current JVC models have similar features and limitations. However, the RS50/X7 and RS60/X9 models include an additional internal video processor that handles the CMS functions as well as certain of the 3D processing functions. All of the current 3D JVC projectors are advertised as providing a 120 Hz refresh rate. However, in 3D mode the 120 Hz refresh rate only applies to video sources using 30 Hz or 60 Hz rates, while for 24 Hz 3D sources, such as Blu-ray 3DTM movies using the full resolution 1080p/24 frame packing signal format, the projector’s refresh rate is 96 Hz, or 48 Hz per eye. These JVC projectors do not offer frame interpolation (ie., for smooth motion) in 3D mode so for 24 Hz 3D sources each input frame is simply repeated 2 times (i.e., 2:2 pulldown) to produce 48 Hz for each the right and left frames, or 96 Hz total for all frames. Likewise 2:2 pulldown is applied to 30 Hz 3D sources and 60 Hz 3D sources are displayed directly thus displaying these latter types of sources at 60 Hz per eye or 120 Hz total for all frames. While displaying 24 Hz 3D source material at 96 Hz (48 Hz per eye) is less than ideal for eliminating visible flicker in the projected image, this has proven to not be a significant issue with most viewers, but those that are especially sensitive to flicker may have an issue with this limitation of the JVC projectors when operated in 3D mode.
Like virtually all of the first generation LCoS 3D ready projectors, these JVC projectors when operated in 3D mode have marginal light output for supporting larger screens, especially those with a gain of 1.0 or less. JVC recommends, based on the THX certification for the RS50/X7 and RS60/X9 models, a maximum screen size of 90 inches (diagonal 16 x 9 screen with a gain of 1.0). However, use of higher gain screens may be used to accommodate larger screen sizes. For reasons still unexplained by JVC, the RS40/X3 series seem to generally provide 10% to 30% more lumens output, using similar preset modes or with calibration, than the more expensive series, although they all use the same lamp and similar light engine design. Further, after calibration the 2D lumens output measured from my RS40 was substantially higher than reported in Arts review of the RS60. My own experience with a RS40 is the 3D brightness is adequate when used with a 120 inch screen with a gain of 1.4. By adequate brightness for 3D I mean as bright as typical 3D presentations seen in most commercial movie theaters. Image brightness when operated in 2D mode with this same setup is much better. In fact to reach the frequently recommended (e.g., SMPTE and THX) 16 foot-lambert luminance level on the screen in a fully light controlled theater, the projector can be used in normal lamp mode and with the manual iris (aperture) stopped down somewhat.
Other 3D related attributes/limitations of these projectors are they do not offer the vertical stretch feature when in 3D mode (it is offered in 2D mode) that would be needed for use in combination an external anamorphic lens for displaying widescreen ‘scope’ movies on a 2.35:1 aspect ratio screen. Finally these projectors support the HDMI 1.4a mandatory 3D signal formats generally not the optional formats. This has created a compatibility issue with some programmed be provided via Directv. Specifically, Directv has elected to use an optional 3D format (half resolution 720p side-by-side format) for their distribution of ESPN 3D programming and some occasional 3D programming on their other 3D channels. While Directv does not conform to the requirements of the HDMI 1.4a specification, some other 3D TV manufacturers have elected to support this optional format in order to have compatibility with the Directv 3D offerings.
In my previous blog in describing how Sony LCoS (SXRD) 3D projectors use a 240 Hz. refresh but and insert a blanking frame between each actual video frame to provide an effective 120 Hz. overall rate with 60 Hz. per eye of actual video content. It is during this 1/240 second blanking interval that the Sony projectors update the information of their LCoS display chips for the next video frame. JVC’s D-ILA variation of LCoS, unlike the SXRD variation, can update the full frame of video information on the LCoS display simultaneously. However, the actual response time limitations of the LCoS display chips means that a new image cannot instantaneously replace the previous image. Due to the way in which the D-ILA display chips work, the JVC implementation for their 3D projectors is able to first force the display to black then to write the new video frame onto the LCoS display. While this is functionally similar to inserting a black frame between each frame with video content, the JVC approach is able to keep the “pseudo black frame” to shorter duration than the normal video frame. Thus for each 1/120 second (or 1/96 second) interval the information on the display chip if forced toward black as the previous image quickly fades away, then the next video frame is loaded and displayed. This approach results in a little less light lost as compared to inserting full black frames having the same duration as the actual video frames. In more technical terms the projected video has a somewhat higher duty cycle with the JVC approach as compared to the approach described in my previous blog that is used by Sony with their 1st generation SXRD 3D projector.
Another characteristics of LCoS (and LCD) technology is when the display is cold the response time slows down. Too slow a response time can lead to the remnants of a previous image (e.g., a frame from the right eye video stream) not be fully cleared from the display when the next image needs to displayed (e.g., a frame from the left eye video stream). Such a situation is the major cause of 3D crosstalk (ghosting) with LCoS and LCD display technology. With the JVC projectors increased crosstalk is more visible when the projector is first turned on and as the projector’s internal temperature and the temperature of the LCoS display chips increases the level of crosstalk decreases. Generally, the level of crosstalk will stabilize within 15 to 20 minutes. Also it is suggested to always operate these projectors in high lamp mode during the warm up period and while projecting 3D video so as to keep up the temperature of the projector’s LCoS display chips. This is not an issue for normal 2D projection.
For my next Blog I plan to discuss 3D glasses and what projection screen characteristics you need to consider when setting up a home theater for 3D. After that blog I’ll go on to discuss DLP 3D projectors.