In part one (PLSN, Oct. 2009), we took a trip down memory lane, with a refresher course on digital cinema and the evolution of 3D projection. From its beginnings in the 1890s through its “golden age” in the 1950s, 3D stereoscopic projection expanded and matured.
However, the genre was generally regarded as a novelty, and due to electro-mechanical limitations 3D never achieved the audience numbers required to sustain extended theatre runs.
This paradigm completely changed circa 2004, when digital cinema came of age and when the studios started releasing fantastic 3D films such as The Polar Express and Chicken Little. In addition, 3D technology became easier due to the advent of server-based digital projection.
More importantly, the long lines at the box offices sent a clear message to the studios: this 3D stuff simply delights audiences – let’s make a few more! In fact, as you read this, James Cameron’s new 3D sci-fi epic Avatar should be starting to create the illusion of depth at a cinema near you.
Add-on Components to Fool the Brain
Regardless of the digital cinema projector manufacturer (of which there are three – Barco, Christie and NEC), in order to transform a 2D projector into a 3D projector a few important add-on components are required. It ain’t rocket science, but it is complex.
First, the content has to be produced in 3D with separate images created exclusively for the left and right eye, and played out in an alternating left-right sequence which progresses continuously throughout the film. To complete the stereoscopic illusion, you need a pair of 3D glasses capable of separating the left and right images (and fooling the brain). And finally, you need to create an electronic shutter – one that turns off the left eye when the right eye’s frame is being projected, and vice-versa.
Passive and Active
There are two types of 3D glasses; passive and active. Passive glasses are designed with polarized lenses and the left lens is polarized differently than the right. With this method, the shutter is created in the projector, either with a third-party polarizer placed in front of the lens (similar to a filter), or a third-party color modulator placed inside the projector – electronically upstream of the projector’s DLP (Digital Light Processing) chip.
Active lenses, on the other hand, have a built-in electronic shutter, which makes them more expensive. These glasses are synchronized to the projector via an infra-red beam emanating from the screen. No additional hardware is required in the projector.
Both processes are driven by frame pulses in the movie’s digital file (as stored on the server). The pulses identify the left and right frames. For the “passive” method, the pulses tell the third-party polarizer which frames to turn on and off, in the proper sequence, thus creating the shutter. When this “pre-polarized” light reaches the passive glasses, the left eye only sees the left frame, and the right eye is blanked. In the next frame the right eye sees the right frame, and the left eye is blanked – and so on, throughout the movie.
In the case of “active” glasses, the pulses drive an infra-red beam which synchronizes the frame sequence to the glasses. When a “left” frame is projected, the beam tells the glasses to open the left eye and shutter the right. When a “right” frame is projected, the glasses’ open the right eye and shutter the left – and so on. Study up; there’s a pop-quiz tomorrow.
The 3D Players
In addition to the big three manufacturers, there are four major players in the 3D “add-on” game for single projector solutions as shown in the table. Each company has a proprietary method for completing the illusion – with either active or passive glasses, silver or white screens, and internal or external shuttering.
At the next 3D movie you see, take a close look at the glasses – that’s your first clue as to which method is being employed up in the projection booth.
No Headaches, Please
The default rate for film projection is 24 frames per second, which is just dandy for 2D. But when you’re alternating left and right frames with an electronic shutter, a highly noticeable flicker occurs at that rate, and everyone in the audience gets an instant headache. To solve this dilemma, the wizards at Texas Instruments (inventors of the DLP chip) set a new digital cinema standard for digital cinema projector manufacturers; 144 frames per second (72 frames per eye), effectively tripling the 2D frame rate and eliminating the flicker.
Light is King
One additional item is giving the digital cinema industry fits and serious money is being poured into the remedy. 3D is a very light-hungry technology. Of the light that leaves the projector, only about 14 to 18 percent reaches your eye. This is why some 3D screenings appear noticeably dim as compared to their 2D counterparts. As we track the path from lens to eye, light is lost to the 3D shuttering device, the viewport in the projection booth, the screen “bounce” and the 3D glasses.
Currently there are two solutions: brighter projector lamps or double-stacking. All digital cinema projectors are designed with the ability to swap the “light engines” – some with a greater degree of ease than others. Double-stacking projectors doubles the light output, but the efficiency factor isn’t affected. Both of these are considered short-term fixes. The ultimate solution will most likely be a combination of increased brightness and increased efficiency of the 3D shuttering methods. Research in this area is underway, guaranteed.
From the Theatre to the Arena
The final topic on our 3D agenda brings us back to our industry. With the success of 3D in the theatre (with audiences typically numbering from 200 to 300), many enterprising touring companies have pondered how to bring 3D to the concert arena (with audiences ranging up to 15,000 customers plus). Prior to his untimely passing, 3D projection was to be a component in Michael Jackson’s comeback tour.
In order to take 3D into the concert arena, you’d need to cut the fog machines, install as many double-stacked projectors as required to get the desired brightness and audience coverage, create 3D content exclusively for the tour, order truckloads of 3D glasses and educate our already highly-skilled projection techs in the intricacies and quirks of 3D. Whew! It’s quite a task, but not an impossible one. And just picture the art of the touring gag taken to the next level. I mean, if U2 can use 500,000 pixels of video in their remarkable 360° structure, certainly someone can be the first to go 3D.
In the meantime, two tickets to Avatar, please.
