3-D TV: Are you ready?
Mar 1, 2010 12:00 PM, By Stan Moote with Chris Lennon
Understanding the technology and communicating with vendors are key
Writing about 3-D is a bit like trying to do play-by-play commentary on a hockey game being played at twice normal speed. By the time you comment on one play, the game has moved on to such a degree that it's already irrelevant. Maybe it's not quite that bad, but it is a challenge to talk about a topic that's moving at unprecedented speed, while trying to ensure your comments remain relevant.
The main purpose of this article is to help you consider your state of readiness for 3-D TV. Even if you don't think this is going to affect you any time soon, it will be helpful to have an appreciation for what it will take if and when your boss suddenly comes to you and says, Tell me right now what it would take for us to hop on this 3-D bandwagon!
Brief background
Table 1 (Caption: Table 1. Format, compression and display types vary at different stages in 3-D workflow.)
Select figure to enlarge.
3-D TV can be characterized as the distribution of two signals (left eye and right eye) to the viewer, so that a stereoscopic view of the content is achieved. The current 3-D movement comes, naturally, out of cinema. The reason it's different from previous, abandoned attempts at 3-D is largely due to cinema's (and TV's) move to digital. Today's 3-D is of far superior quality, less prone to audience discomfort and seems much more likely to succeed than previous attempts.
With the clear ROI for 3-D releases demonstrated by studios, it's logical that this movement would get the attention of those producing and distributing content to TV viewers. Add to that the release of 3-D Blu-ray players and titles to consumers, upcoming cable and satellite 3-D offerings, and the onslaught of 3-D TVs many at relatively low incremental cost to consumers over traditional HDTVs and you have something that seems to have many of the ingredients for success.
Content drivers
Those in the TV business who specialize in sports and movie content are the first to embrace 3-D TV. Big sporting events and feature films have appeal in 3-D that goes well beyond other TV fare. For viewers, donning glasses to watch special events like these seems reasonable, but expecting them to put on and take off glasses for everything under the sun may be unrealistic. So, if you specialize in news and typical TV series, you may not have to worry as much about 3-D content today as others will, but never say never.
Let's clear up some confusion
One of the areas of frustration for broadcasters at this point is the confusion surrounding the various 3-D technologies. A quick survey of that landscape shows why 3-D can be bewildering.
The 2-D + Difference approach, which has enjoyed success in gaming and other areas, involves taking a traditional 2-D picture and adding metadata describing the difference (or depth) between the left eye and right eye view to allow TVs to render the second eye view. Blu-ray is going with MPEG's MVC (Multiview Video Coding) extension of H.264/MPEG-4 AVC, which supplements a traditional 2-D view with metadata, enabling the construction of the second eye view. This provides full-resolution pictures for each eye. Of course, bandwidth isn't as much of a consideration for Blu-ray as it is for other distribution media.
Frame-compatible approaches, such as over-under and side-by-side are favored by cable and satellite providers. There are others, such as line interleave, column-interleave and checkerboard, but those don't seem to be enjoying the uptake of the other two. Frame-compatible approaches make sense for distribution media with limited bandwidth (our current HD distribution pipes).
Frame-sequential approaches, which are based on every other frame being targeted at a different eye, offer full HD resolution but at a cost. This is the format of choice for lower-cost displays, utilizing active shutter glasses, but doesn't make sense for early distribution of broadcast material.
An easy trap to find yourself in if you're a TV person trying to sort through all of this is a tendency to confuse the transmission and display formats with the formats used to handle 3-D internally in the plant. The format used in production, post production and processing in your facility need not match that used in transmission or viewing.
Here's an example. The viewer may watch the content with a frame-sequential display running at 120Hz (or faster) with active shutter glasses. The signal may reach him via satellite in a frame-compatible, side-by-side format. However, the program may have been recorded as two distinct full HD streams and handled internally in the broadcast plant as two streams. Decoding one 3-D format and encoding it into another is just as routine as moving from any 2-D format to another, so be careful to decouple the emission and display format used from that applied in the production and transmission facilities.
Since many are still reeling from a recent investment in a digital infrastructure, expecting them to undergo another plant upgrade replacing all the associated gear with special 3-D gear is unrealistic in many cases. It is for this same reason that cable and satellite operators currently favor frame-compatible 3-D TV approaches. They may not be full HD for each eye (as they must drop half the resolution, either vertically or horizontally, to fit two views into a single frame), but these approaches allow stereoscopic content to be handled by existing infrastructure with mostly minor upgrades. And reduced resolution or not, it looks pretty darned good.
However, these frame-compatible approaches seem unlikely to be adopted internally by broadcasters, as lost resolution in the plants is something most will try to avoid. Alternatives, such as 2-D + Difference, which is now touted as requiring only a 35 percent increase in bandwidth and MVC, seem to be interesting approaches to dealing with identical 2-D and 3-D content (since 2-D + Difference and MVC are 2-D- and 3-D-compatible in a single stream and full resolution for each eye). At the moment, however, it would seem more likely that they'll instead use two full HD streams internally.
Practically, we should think about 3-D TV in a similar fashion to SD and HD signals with just a few exceptions. Figure 1 shows a typical 3-D workflow.
Post production
There is no question that preserving the two streams in the highest quality possible is most important mezzanine I-frame compression only. As for monitoring the use of 3-D TV content, active shutter glasses should be used with full-bandwidth video into the monitor.
In plant
Ideally, 3-D TV video within a broadcast facility will match up with the HD plant format. The left eye and right eye streams will be 1080i or 720p on a single 3Gb/s or two 1.5Gb/s coax. Certainly running on a single 3Gb/s coax has several advantages, similar to the change from mono into stereo audio (matched timing, switching and processing).
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