Here’s a quick tutorial on 3D program and transport formats, all coming to a TV near you.

Probably not. Samsung and Panasonic are long out of the gate, while LG just started its advertising campaign for INFINIA LCD TVs during the NCAA Men’s Basketball Tournament.  And there will be more companies following with 3D TVs, Blu-ray players, and a host of accessories.

One question I’ve gotten repeatedly is this: “How do they pack a 3D signal into a conventional cable TV channel?” Another one: “How can DirecTV send out 3D, which is progressive scan? They’re not broadcasting in 1080p!”

Time to wheel out the whiteboard! In a nutshell, here’s how the different 3D transmission formats work.

Earlier this month, the 3D amendments for the HDMI 1.4 standard were released. These standards include a host of broadcast 3D formats, along with the Blu-ray top/bottom packed 1080p frame format. (I’ll touch on that, too.) These mandatory 3D formats must be supported if the HDMI interface is a ‘true’ 3D connection.

That’s not to say that a TV manufacturer won’t support other formats: They can, and they are! Examples of ‘other formats’ include checkerboard, interlaced 3D, line-by-line, and alternate frame. There are even 2D+ depth and other ‘overlay’ formats (think of the FM subcarrier for stereo from the 1950s) that are backwards-compatible with older TVs.

What we’re interested in is what DirecTV, Dish, Comcast, Cox, Discovery, and possibly major TV networks like CBS, NBC, and Fox are doing, and might do. Here’s the short list:

Side by side: This is the format that DirecTV will launch in June. It’s also likely to be used by Comcast, Dish, Cox, and any other multi-channel video system. In the side-by-side system, the left eye and right eye images are anamorphically squeezed to fit into a single 1920x1080i/30 frame. (Figure 1)

That means that each image has half the horizontal resolution, or 960×1080 pixels, when expanded back to its normal shape and presented sequentially. Does this look bad? Not really, considering there’s still over 1 million pixels in each eye. As it turns out, HDMI 1.4a calls for side-by-side exclusively with 1920x1080i video content.

Top + Bottom: This format is more likely to be used by stations transmitting progressive scan signals. Once again, the left and right eye images are anamorphically squeezed and packed into a single frame, except they are aligned one atop the other. This is the standard for 1280x720p/60 and 1920x1080p/24 transmissions. (Figure 2)

In this case, each image has half the vertical resolution of a full HD video frame. For a 1080p program, that’s no big deal – each eye works out to 1920×540 pixels. But 720p comes up short, with an effective resolution of 1280×360 pixels in each eye.

The thinking here is that it’s better to sacrifice vertical resolution in a progressive scan TV system than horizontal resolution. I don’t think it makes much of a difference with 1080p content, but 720p? It may not look as good as it should.

What about the alternative? Using a side-by-side format, this would reduce the resolution of each left and right eye image to 640×720 pixels – not much more than a regular DVD. As a result, adopting 720p as an HD format may leave something to be desired with respect to 3D.

HDMI 1.4a: There are two formats here. One uses a top/bottom dual-frame structure (Figure 3) with a total of 1920×2205 pixels. (45 pixels are a blanking or metadata interval.) This retains full 1080p resolution and the frame rate is 24 (23.98) Hz. The other format is for video games, and oddly enough, it’s at a lower resolution – 1280×720 pixels, with either a 50Hz or 60 (59.94) Hz refresh. (Figure 3)

Figure 3. The HDMI 1.4 Blu-ray frame packing structure.

To summarize, these are the ‘mandatory’ HDMI 1.4a 3D formats. A compatible 3D TV will support all of them. On the other hand, set-top boxes and media players only have to provide one of these signals (for Blu-ray players, it’s the full 1080p top + bottom format exclusively), based on the content being served up.

It’s important to remember that, not matter what delivery (transport) format is used, the 3D TV will present ALL of these as sequential left eye/right eye images, using the same active shutter glasses. Only the physical resolution of the images will vary, along with frame rates.

And now you know the rest of the story…to quote the late, great Paul Harvey.