2010 is the year that 3D Blu-ray makes into the home, writes Stephen Dawson, but how does it work?

Several of the major consumer electronics manufacturers are introducing 3D televisions this year, along with 3D Blu-ray players. All this comes as a result of dozens of 3D cinema releases in recent years, many of them truly major works.

Of course, one reason 3D cinema has recently been ramping up has been the movie industry seeking to draw people back into theatres. The idea of offering something more than can be delivered in the home dates back to the 1950s when TV was first taking off. Hollywood introduced widescreen and moved almost entirely to colour to keep the big screen viable.

Soon enough colour made it into the home as well. In the US the first colour TV became available in 1954, but it took until the late 1960s until there was broad penetration, largely because of the very high cost of the colour TVs. (1975 saw the introduction of colour TV to Australia).

In the last couple of years movie makers have seen a sizable part of their box-office take coming from the 3D versions of their movies. But now that exclusivity is drawing to an end.

The optical illusion
There is no real 3D video system. Such a thing would involve some kind of box or bubble into which you would peer. The next best thing would be some form of motion holography, but making even non-moving holograms is still a high specialised and labour intensive exercise involving lasers and mirrors.

What current 3D technologies do is replicate some elements of what your eyes see as 3D on two dimensional plane, such as a cinema or TV screen. But they do not replicate all aspects of 3D.

Much of our sense of 3D comes from the slightly different point of view each eye has upon the world. You can see this for yourself by looking at a nearby object. First, close your right eye, then open it and close your left eye. As you do this you will notice that you can see less of the left side of the object than you could before, and more of the right side.

When you look at it with both eyes you don’t ‘see’ two different views as such. Your brain integrates them into a single view, but one with a special sense of depth. Indeed, it allows you to estimate how far things are away from you with quite a bit of accuracy, so you can reach out and grab something without hesitation.

This form of depth perception only works close to you and to a medium distance. Once objects are many tens of metres away, the views from both eyes are so close to identical that they become useless for sensing depth.
All current viable 3D entertainment systems use this ‘stereoscopic’ effect as the basis of their operation. They produce two different views on the scene, and make sure that the left eye can see only one of them, and the right eye only the other.

And they cheat. Instead of using of this mode of depth perception – different views from the two eyes – to only moderate distances, they apply it to much greater distances. This is easy enough in a two camera stereoscopic system: the cameras simply need to be moved further apart. In 3D computer animation, it just means dialling different parameters into the 3D generation model.

The next part of the 3D process is what the technology is all about: how to present different views of a scene to the two eyes at the same time.

Splitting the world in two
3D technology has been around nearly as long as cinematography, dating right back to the 1890s. But it really took off, perhaps not surprisingly, at the same time as widescreen and colour as another attempt to fight off competition from TV.

It wasn’t all just whiz-bang show-off material either. Hitchcock’s Dial M for Murder was produced for both regular 2D and 3D presentation. While early 3D was delivered by means of so-called ‘anaglyph’ images, by the early 1950s when it enjoyed its first burst of popularity, it was largely based on differently polarised images for the two eyes. In both cases, both the left and right eye images were shown on the screen at the same time.

With anaglyphs they were given different colours. You watched them using eyewear with matching coloured filters so that each eye only saw the part of the image it was supposed to.

The advantage of this system was that it did not require any additional equipment, aside from cheap cardboard ‘glasses’ with coloured cellophane ‘lenses’. The film ran normally through a regular theatre projector. Indeed, this system continued to be used from time to time over the years, even after 3D largely went out of fashion by the mid-1950s. I saw a movie with 3D elements presented in this way in the early 2000s (Spy Kids 3D). It also works with TV, DVD and Blu-ray. The regular Monsters vs Aliens Blu-ray has an animated 3D short using this system, while the regular Coraline Blu-ray and DVD have the entire feature repeated in this style of 3D.

The problem with it – aside from the uncomfortable cardboard of the eyewear cutting into your nose – is that it severely limits the colour palette. This type of 3D may have been suitable as a novelty in the early decades of the twentieth century when nearly all movies were still in black and white, but colour proved to be a far more popular enhancement than 3D.

The polarising system is also used in the recent renaissance of cinema 3D. A polarised filter has extremely fine, closely spaced parallel lines in the lens. This only allows light through with the wave form in a particular orientation. By having one lens at ninety degrees to the other, and projecting two images (often some form of splitter is used on a single projector) with similarly orientated polarisation, clearly defined separate images can be delivered to each eye… this time in full colour.

These days the polarised glasses are purchased at low cost by the viewer, and can be reused for other movies.
Anaglyph 3D isn’t suitable for real home 3D because of the colour problems, and polarisation would take a major redesign of TV technology. So for the home we are seeing liquid crystal shutter glasses. These use liquid crystals to make the glass in front of one eye go opaque, then transparent while the other goes opaque. This repeats rapidly (100, 120 or 200 times per second depending on the design). Meanwhile, the display is flashing the left and right eye images up, not at the same time, but in rapid succession to each other.

Of vital importance is that the eyewear shutters stay in time with the TV’s display of the images, so the TV has an infrared transmitter producing a synchronisation signal. The eyewear has a receiver and uses this signal to keep everything aligned.

As with polarised filters, this system allows full colour. As with any system, it reduces image brightness since each eye is only permitted to see half of what is being displayed.

The main problem with these systems is likely to be ‘crosstalk’ or ‘leakage’, where one eye sees part of the other eye’s image. This manifests as ghosting.

Early experience has been variable, with some amazingly convincing demonstration material on view, but some equipment also producing clearly visible levels of ghosting, which makes it difficult to maintain the 3D illusion.

For the moment, 3D is restricted to direct view displays (both plasma and LCD models are coming on stream). But clearly this situation won’t last. Expect to see 3D home theatre projectors appearing eventually, even though there might be some engineering challenges to do with synchronising the glasses to a device that you’re not actually looking at.

Delivering it
What has made 3D now a possibility is the standardisation of a way of doing it on Blu-ray. Essentially two full images are held on the disc in format called MPEG4 MVC (for Multiview Video Coding).

This is not compatible with previous players because these files are actually held elsewhere on the disc. The data load down the HDMI cable is double what went before when it comes to movies: a boost from 24 frames per second to 48. To ensure compatibility with 3D, products specified as supporting this should be selected. It is unclear to what extent older home theatre receivers will be able to pass through 3D video via HDMI. Panasonic cater for this with its forthcoming Blu-ray player by having two HDMI outputs: one carrying 3D video and the other carrying audio intended for a home theatre receiver.

3D Blu-ray can only be used via HDMI.