The US is still trying to decide what kind of system to use for ATSC 3D.  A while back MPEG-4 was added to ATSC, so perhaps they’ll go with a full-frame L/R standard using MPEG-4 to fit both frames in the bandwidth of a single MPEG-2 frame.  Or we may end up with 2D+Depth or something like that.

Any of these systems can do 2D – in a system that uses two full frames, you just show one frame.  Either one is viable on its own.  In any of the 2D+X systems the 2D frame is used.

The US is still trying to decide what kind of system to use for ATSC 3D.  A while back MPEG-4 was added to ATSC, so perhaps they’ll go with a full-frame L/R standard using MPEG-4 to fit both frames in the bandwidth of a single MPEG-2 frame.  Or we may end up with 2D+Depth or something like that.

Any of these systems can do 2D – in a system that uses two full frames, you just show one frame.  Either one is viable on its own.  In any of the 2D+X systems the 2D frame is used.

Comcast is requiring users to switch to MPEG-4 capable boxes (Pace ones) to receive 3D channels, so its certainly an option.  They’re willing to do this of course because 3D really isn’t that popular.  If they had to replace everyones boxes they probably wouldn’t be doing this.

And MPEG-4 really can do the same quality in about half the bandwidth, so that 15Mbps they normally use for HD could handle a full HD 3D signal in the same bandwidth using h.264.

As far as 2D+Delta the stuff I’ve seen suggests it really wouldn’t save much bandwidth, given that your stereo vision is apparently very sensitive to the high frequency components so high levels of compression on the Delta tend to suppress the stereo image. 

Of course they’ll have to go with one of these approaches if 3D becomes popular, since they can’t keep allocating separate bandwidth for the 2D and 3D channels in the long run if that happens (seems unlikely at this point).  Any of these other approaches could produce a 2D or 3D image out of the 3D channel at least.

Plasmas are often considered better than LCD for 3D, but I think it is something of a matter of taste – and not all LCDs are created equal.  A 240Hz set is going to perform better than a 120Hz set.  Just as some people see flicker on a 2D 60Hz panel but 2D 120Hz looks OK.  Faster is better when it comes to refresh rates.

As always, it is worth doing your research first.  Before I bought my DLP I did a LOT of research, quite a bit of it on AVSForum, and went to look at different sets in person.  (Remember the way they’re adjusted in the store is NOT how you set them at home though.)  Some people say they always see the rainbow problem on DLPs, at least the older color wheel models like mine.  (Many newer sets switched to colored LED light sources instead of a lamp and wheel.) But I’ve only seen in on some cheaper sets, and never on mine.  Different people may perceive different things on the same set.

As for HDTV – yeah, I didn’t want to get into even more detail in the already huge post.  A lot of broadcasts are handled in side-by-side format where they cram two frames into one.  So yes, you get 1080×960 left & right frames instead of 1080×1920.  So you will lose even more in today’s passive 3D HDTV.   You lose 50% to start when you pack two frames into one, then 50% of the 50% that is left when you display it – so you end up with 75% loss from the original image.  Ouch.

Top-and-bottom packing is actually better for passive displays.  A 1080p source will be 540×1920 – which is the same resolution as each ‘eye’ on the display.  So that’s what it does, it just displays each frame on every other line, interleaved.  No loss in resolution – aside from the 50% loss you started with. 

The problem is bandwidth – there isn’t enough in one channel to broadcast the full 1080p left & right frames, like Blu-ray can handle.  At least not using the MPEG-2 codec that is standard today for ATSC & cable.  They’re still hashing out future standards for improved 3D broadcast support, but possibilities are using MPEG-4, other ways of encoding 3D like 2D+Delta (One full eye plus only the differences for the other eye), 2D+Depth (One full eye plus a ‘depth map’ the receiver can use to reconstruct the 3D effect), and others.

And one more thing–since active systems require the TV to alternate between left and right eyes 120 times a second, they require much faster reaction times than typical TV content.  As a result current 3D LCD TV sets, which have slower reaction times than plasma, often have visible ‘ghosting’ of the images between the two eyes.  Which is why if you’re going to buy an active 3D set right now, you should probably be looking at a Panasonic plasma.  Personally I’m a big LCD guy, but if you’re buying an active 3D TV right now, I’d stick with plasma.  Of course plasma TVs already consume too much power even without the 3D brightness problem…

And one more thing–since active systems require the TV to alternate between left and right eyes 120 times a second, they require much faster reaction times than typical TV content.  As a result current 3D LCD TV sets, which have slower reaction times than plasma, often have visible ‘ghosting’ of the images between the two eyes.  Which is why if you’re going to buy an active 3D set right now, you should probably be looking at a Panasonic plasma.  Personally I’m a big LCD guy, but if you’re buying an active 3D TV right now, I’d stick with plasma.  Of course plasma TVs already consume too much power even without the 3D brightness problem…

You left out one more bit of detail–that while Blu-Ray 3D may be full resolution 1920×1080, current 3D TV channels are not.  They’re already half resolution, typically 1/2 horizontal for 1080i and 1/2 vertical for 720p.  They do this in order to transmit the 3D signal in a ‘frame compatible’ format that allows them to avoid increasing the bandwidth for the channel and also allows them to make the channel work with the existing STBs the cable company has deployed. 

While most people find this trade-off acceptable, I think one of the issues with passive 3D today (e.g. half resolution) is that it halves the resolution AGAIN on top of the already-half resolution of 3D TV channels.  So while it might look acceptable when you watch a passive 3D Blu-Ray movie, it might not look so great when you watch a 3D movie on cable.  Half the horizontal resolution was tossed to create a frame compatible signal, and half the vertical lines are tossed to create the passive 3D.  Which takes your beautiful 1920×1080 frames down to 960×540.  Given that even DVDs run 720×480 you may not consider 960×540 exactly ‘hi def’.

You left out one more bit of detail–that while Blu-Ray 3D may be full resolution 1920×1080, current 3D TV channels are not.  They’re already half resolution, typically 1/2 horizontal for 1080i and 1/2 vertical for 720p.  They do this in order to transmit the 3D signal in a ‘frame compatible’ format that allows them to avoid increasing the bandwidth for the channel and also allows them to make the channel work with the existing STBs the cable company has deployed. 

While most people find this trade-off acceptable, I think one of the issues with passive 3D today (e.g. half resolution) is that it halves the resolution AGAIN on top of the already-half resolution of 3D TV channels.  So while it might look acceptable when you watch a passive 3D Blu-Ray movie, it might not look so great when you watch a 3D movie on cable.  Half the horizontal resolution was tossed to create a frame compatible signal, and half the vertical lines are tossed to create the passive 3D.  Which takes your beautiful 1920×1080 frames down to 960×540.  Given that even DVDs run 720×480 you may not consider 960×540 exactly ‘hi def’.