Some Folks Really *Need* 8K
There is one group of device makers that have been very clear in their desire to see more pixels and 8K on smaller displays such as those on the desktop, and that group is those that make 3D displays. It has been interesting to see at CES this month that Samsung has moved further in that direction by introducing 6K 2D and 3D displays. Moving to 3D is, arguably, another stage in the long term evolution of imaging.
Why is this group so keen? Simply, to deliver 3D effectively, you have to exploit stereopsis, the ability of humans to see depth in a scene based on the stereo vision of two eyes. Slightly different images in each eye are fused (for most people) in the brain to create one view with depth. So, if you want to deliver high resolution and 3D, you need to send twice as many pixels as with 2D. Further, you need to ensure that the different images to each eye are separated and correctly aligned. Left must go to left and right to the right eye.
Send the Correct Image to Each Eye
There are several ways of doing this. The crudest and simplest way has generally been to use different colors, with different colored spectacles for each eye. That usually destroys any chance of color accuracy, although if you use more expensive glasses with high class filters and subtle color shifts, as has been used in 3D cinema, the color shifts may not be obvious.
Another way is to use the polarisation of light and this has been used in the cinema. It was also used by LG in its 3D TVs which had a special filter on top of an LCD to polarize alternate horizontal lines in the display differently. Spectacles were provided that allowed the correctly polarized light to reach each eye. This method allowed the use of low cost passive glasses for viewing. The system has also been used with projectors, although the right kind of projection screen has to be in place to avoid changing the polarization when the light is reflected off the screen.
Send One After Another
Another way to split the left and right images is to use ‘time multiplexing’, that is to say, sending one frame with the left image and the next with the right. If you combine this kind of display with special ‘shutter glasses’ that are synchronized with the display, then you can get good 3D. This technique was used for 3D in the days of CRTs and was also used by Samsung and Sony when the idea of 3D TVs was a hot topic some years ago. Unfortunately, there were no standards for 3D TV glasses, so the different brands had their own ways of doing this. As glasses were relatively expensive and needed some power, consumers weren’t keen. You couldn’t use Samsung glasses on Sony TVs or vice versa, for example.
Each of these techniques had different impacts on the visual image quality, causing color degradation, loss of brightness (a significant complaint in 3D cinema) and with shutter glasses, possible flicker as well.
It is generally considered that the need to wear special glasses also hampered the experience. The LG method had the cheapest and lightest passive glasses, but the 3D really only works if your head is reasonably vertical. That’s acceptable in a movie theater, but not so much if you like to lie on a couch to watch TV!
Autostereo 3D Technology
So, the best solution seems to be to avoid the need for glasses altogether. To make 3D without any glasses (called autostereo 3D or AS3D), you have to beam the correct image to the viewer’s eyes using some kind of optical system. The first way this was successfully done in electronics was on CRT monitors using thin lenticular lenses that were bonded onto the screen. That was tricky to do as you had to accurately align the image created by the cathode ray beam and the phosphor dots that created the image. However, it was possible.
Flat Panels Help
Once flat panel displays came along, with their very accurate and evenly distributed pixels, the alignment issues became much less demanding. However, if you use fixed lenses, they could cause challenges if you wanted to sometimes look at 2D content and use the monitor for something other than 3D. For this reason, companies developed switchable lenses based on liquid crystal material that allow the lens effect to be switched off when 2D is required.
Another approach is to use parallax barriers. If you have a single viewer and you know where they will be looking from, you can design a display to allow each eye to only see every other pixel using an optical barrier. You can also use ‘backlight steering’ to get light from an LCD backlight to go through the imaging layer in a particular direction. You can’t do this easily on an OLED.
One or Many Viewers
One of the challenges for AS3D displays is that they really work best when there is a single viewer. In an ideal world, you would also know exactly where the eyes of the viewer are, so that you can present images that take that into account. If you do that, you can simulate looking around objects and getting different views.
Although you can make AS3D displays for multiple viewers, the resolution tends to be limited as you have to create multiple image pairs and there are often artifacts when the viewer moves between the different pairs of views. This multiviewer limitation makes 3D TV difficult, but is less of a challenge for a desktop monitor which is typically viewed by a single user.
Where are You Looking From?
Working out exactly where they viewer’s eyes were used to be very difficult. This writer’s first experience of this technique was at Sharp’s Research Labs in the UK in the 1990s – when, for the system to understand where the viewer was, a reflective dot had to be stuck onto the forehead! These days, however, camera and processing have improved so that the viewer’s eyes can be detected without using too much processor power. If you know where the viewer’s eyes are, you can adjust the scene as the head and eyes move, making the experience much more realistic than simply presenting a fixed view.
This article was triggered by the promotion at CES by Samsung of its new 6K Odyssey 3D monitor which uses a switchable lenticular lens system and eye-tracking to create an immersive 3D experience aimed mainly at gamers.
It’s More Than ‘Just’ Stereo
The human perception system uses more than just stereopsis to understand depth. The best 3D content (such as Avatar, the movie) exploit the other factors that give a feeling depth as well as stereo. The question of developing and getting access to good 3D content is a significant one and we’ll leave that for another article.
