3D Displays
Significant interest has been shown in 3D displays in a variety of configurations, with many stereoscopic 3D-ready back projection and plasma screens already sold in the US market, and 3D-equipped cinemas now using DLP projectors with, usually, polarizing glasses. 3D displays may be divided into a number of different categories:
1) Stereoscopic displays present two views, one for each eye, and are the major market at present. There is a variety of different techniques.
- Barrier or micro-lens based techniques, essentially the same technology as multi-view displays, but with only two views, where the viewer is required to keep their head still, but does not need to wear special glasses.
- Glasses-mounted micro-displays, with individual displays dedicated to each eye.
- Spectral separation with glasses, the simplest form is the old-fashioned red/green anaglyph, but more sophisticated versions giving better colour reproduction are now being demonstrated. It is possible to obtain full colour reproduction by using two spectrally-separated primaries for each of red, green and blue, with notch filters or interleaved comb filters in the glasses matched to separate pairs of primaries. Currently the preserve of digital 3D cinema systems, such a technique could be applied to domestic installations.
- Polarization separation, either diagonally or circularly polarized for each view, with appropriate polarization in the glasses. Zalman (in the games area) and Hyundai/Arisawa (for TV) are the most readily-available polarizing displays. These are usually based on LCD technology.
- Time-sequential with synchronized shuttered glasses, such as those from LG, Mitsubishi and Samsung. Early displays of this type were back-projection DLPs, but now plasma is dominant in the domestic environment, with a substantial number (a few million) such displays sold in the USA.
The last two types of stereoscopic display, both with glasses, are the most common types in the market at present, although not yet widely marketed in Europe. In both cases the quality of the 3D effect depends largely on the level of perceived crosstalk between views (i.e. visibility of the right view to the left eye and vice-versa), and is dependent on the display and the glasses, in combination. If the display knows the characteristics of the glasses, then some cross-talk can, to an extent, be pre-corrected in the signal.
2) Auto-stereoscopic displays fall into two varieties, both allowing the viewer to see “parallax” as the head is moved.
- Multi-view displays, allow the users to move their head within a certain zone, and their eyes see different views depending on where they are within that zone. Until displays become available with vastly greater pixel counts than are available at present, multi-view systems suffer from relatively low resolution in each view. Philips has had a 9-view product in this area, and has shown a 46-view prototype based on a 4k horizontal-resolution panel. However Philips has announced that it is ending commercial activity in this area, but is continuing with collaborative research projects in this field.
- Head-tracking displays, provide an image to each eye appropriate to the viewer’s head position. Head-tracking displays for a single user are already feasible, and research on tracking and providing images for multiple viewers is advancing. Fraunhofer’s Heinrich- Hertz Institut (HHI) is heavily involved in leading the collaborative work in this area.
3) Volumetric displays – a real image is formed in 3D space, providing an infinite number of simultaneous views. This avoids many of the issues with 3D viewing which are frequently experienced with other technologies, but is a very difficult technique to use for television.
- Wave-front reproduction (often called a holographic display) might be thought of as the ultimate form of 3D display, but practical implementations which are able to give high-quality images are some way into the future.
- Integral Imaging is part-way towards this, and is essentially a multi-view display with a very large number of views, of which HoloVizio is one example.
By Richard Salmon, EBU Technical Review
