We recently had the opportunity of putting a few questions to Texas Instruments (TI) on the 3D world at the cinema and at home and gained a better understanding of how their products work and their position on the market. Here are their answers (in italics) with additional info from us.

- What is the frequency used for 3D in DLP Cinema?

TI : 144 fps (triple flash) - 144 Hz.

Triple Flash technology is used by DLP projectors to improve 3D viewing perception of films at the cinema. 3D films are currently distributed at 48 frames per second: 24 for the right eye and 24 for the left. If 3D glasses, necessary for seeing in relief, functionned at this frequency, you would see images alternating between both eyes with unpleasant results. In the space of one image, alternance between the right eye and the left eye happens 6 times instead of 2. This is how we get to 144 Hz (48x3), giving a better sensation of 3D perception. For more information, take a look at this excellent article Choice in 3-D Digital Cinema.

3 types of glasses (and therefore technologies) currently exist at the cinema (see this pdf).

• Polarisation : the left and right images projected for each eye are encoded with light polarity in opposite directions to each other. This technology means the viewer can tilt their head without upsetting decoding quality. It is also subject to ghosting effects due to electronic interference. To combat effects of ghosting, Real D uses circular polarisation and ghost busting, a method to prevent crosstalk between left- and right-eye images. For more information see this link to a PDF from the European Digital Cinema Forum on the REAL D 3D projection system.

• Spectral division : left and right images are encoded each with a differently filtered spectrum of light. In the Infitec spectral division technique licensed by Dolby Laboratories, the light is filtered such that the left spectrum appears as white light (or near-white light), as does the right spectrum. In this way, this technique is importantly differentiated from the older, much lower quality, anaglyph method of using red filters for one eye and blue filters for the other, as found in cereal packets. The light path in the projector is modified with a filter wheel to achieve spectral division of the stereoscopic images. The glasses are curved to allow for eye movement without losing decoding quality. For more information, see the Dolby Digital site.

• LCD screens (active shutter): this is the technology used by NVIDIA for its 3D Vision glasses. Each of the lenses is an LCD screen that is switched on and off to synchronize with the images displayed on screen. When the left eye image is displayed, the right eye is switched off and only the left eye sees the image and vice verse. The frequency is fixed to that of the screen, 120 Hz for the NVIDIA solution and 144 Hz for cinema.

- What is the frequency used for home theatre projectors? Would it be possible to update existing projectors with new 3D firmware?

There is no "home theatre" 3D projector available on the market, however business/classroom projectors will be 120 Hz (60 per eye). To get 3D you only need one computer and a game – be sure to change the setting on the game to enable 3D viewing – which turns it from 60 Hz to 120 Hz.

ViewSonic do have a projector, the PJD6220-3D, that can display video flow at 120 Hz. One drawback is that this frequency is only accessible with 1024x768 pixel definition (XGA), a step down from standard HD Ready, at 1280x720 pixels. Mitsubishi also have the XD600U with XGA definition.

- Compatibility between technologies: will it be possible to use NVIDIA glasses with 3D DLP technology?

Yes it is possible.

- What about connectivity? Will it be possible to have a 120 Hz signal in 1080p with existing HDMI and cables currently on the market?

HDMI 1.4 will support 1080p 3D at 24 Hz but this is not supported in any DLP projector at this time. We are plannning end of year support for 1080p with DLP Link.

If we base ourselves on the principle applied in cinemas (triple flash), current HDMI cables should be able to send a 1080p signal at 48 Hz (24 Hz for each eye). The problem is that your projector will need to be able to triple these images (as we explain in the first paragraph) and display them at 144 Hz and you will need to have the right glasses. Projectors like the Sanyo PLV-Z3000, which function at 120 Hz,could use a 60 Hz signal (2 x 30 Hz) and double it to display at 120 hz. Unfortunately this hasn’t been planned by the manufacturer, who have already confirmed that this projector will not be adapted for 3D.

It would seem that we are currently leaning towards 120 Hz with cables capable of transiting a 1080p 120 Hz (2x60Hz) signal. This will only be possible, according to the HDMI consortium, with HDMI version 1.4. In other words the products that are currently on the market will not be 3D compatible and you’ll need to reinvest if you want to view in 3D.