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Alternate-Frame Sequencing

Build Your Own: Wall-Sized 3D Gaming, Just Like Theaters Do It
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Let's start with alternate-frame sequencing. We're not going to use this method in this article, but it's important to learn about it so that you understand the strengths and weaknesses of the two main methods of producing a stereoscopic 3D display. Alternate-frame sequencing is the stereoscopic 3D system that is positioned to be the standard in the home and almost all of the new 3D-ready TVs will rely on this method to reproduce 3D stereoscopic content.

A standard TV can provide 60 frames of video per second (60 Hz), but a 3D-ready TV can provide twice that, or 120 frames per second (120 Hz). The alternate-frame sequencing system works by alternately displaying a frame of video for each eye--first a frame of video for the left eye is shown, followed by a frame for the right eye, a frame of video for the left eye again, and so on. This changes back and forth, 120 times each second.

If you were to watch TV while it delivered 3D content this way, all you'd see would be a blur of what would appear to be two perspectives overlapped on top of each other. The key to making this system work is LCD shutter glasses. These glasses alternatively block each eye, 120 times each second (60 times a second for each eye), in order to allow only the intended frame of video to be seen by the targeted eye.

With a total 120 Hz, each eye sees every second frame and thus receives 60 frames of video per second--the same rate that we're used to seeing on conventional televisions. At this speed, you shouldn't be able to perceive any strobing or flickering, but you'd probably notice that the video seems darker than you'd expect. This makes sense since, each eye is only receiving light half of the time.

The alternate frame-sequencing method of stereoscopic 3D is used not only in upcoming 3D-ready television sets, but in some new GeForce 3D Vision-ready PC monitors.

Alternate-frame sequencing is the method of 3D realization that we used in 2007 when we put together the "Wall-Sized 3D Displays: The Ultimate Gaming Room" article. Back then, 120 Hz projectors were practically unheard of, so we settled for an 80 Hz DLP projector. This projector could display 80 FPS, delivering 40 frames for each eye. While 40 frames per eye aren’t bad, at the slower shutter speed, the strobe effect is far more pronounced. This strobe effect can make it hard to watch a 3D display for long periods of time and may cause disorientation and headaches. The issue was more acceptable three years ago when intrepid early-adopters were pioneering wall-sized 3D viewing, but it wouldn't cut it in today's mass market. It's 2010 and we expect more.

Thankfully, today there are a number of 120 Hz 3D-ready projectors on the market, and that high refresh rate makes for a far smoother experience far easier on the eyes. What's the downside to the alternate-frame sequencing method? The cost of the equipment can become increasingly prohibitive. For example, a kit including a single pair of 3D glasses and an IR emitter (required to synchronize the glasses to the proper frame of video) is about $200. Each extra pair of glasses after that will typically cost $150 each. So, if you have a family of five and you want to watch a 3D film on your new 3D Blu-ray home-theater system, it'll cost you about $800 to get the glasses alone. Invite a couple to join your family for movie night, and the cost goes up to $1,100--and that's not including the cash you've already spent on your 3D-ready television or projector.

Are there any other downsides to active LCD glasses? Well, as mentioned previously, it limits the amount of light that reaches the eye, so your TV will seem darker than it does without wearing them. The glasses will also need to be powered. Modern LCD glasses are rechargeable, but this is a minor inconvenience.

However, the advantage of alternate-frame sequencing is significant--while the 3D Blu-ray specification is said to be display-agnostic, almost all of the consumer-grade TVs that have been recently announced rely on this method. That means when films like Cloudy with a Chance of Meatballs, Monsters vs. Aliens, and Avatar become available to purchase as a 3D Blu-ray disc, it might not be practical to view them in any other way. We will have to wait until the technology arrives and matures to see if this will be the case, but alternate-frame sequencing is poised to become the de-facto standard for 3D stereoscopic displays in the home.

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Top Comments
  • 26 Hide
    MiamiU , March 30, 2010 6:32 AM
    seems like being a hardcore gamer just keeps getting more and more expensive...
  • 23 Hide
    Icehearted , March 30, 2010 6:56 AM
    As for poor folk like me, we'll just settle for those still images where we cross our eyes, and cry because $2,565 is far away from "comfortable".
  • 12 Hide
    salgado18 , March 30, 2010 1:11 PM
    I don't know if it would be possible, but it would sure be AWESOME to see some of those games on a short gif animation in "fake" 3D! Please! (a video review would be great too!) :D 

    PLEASE people, vote me up! If you do they'll try it!
Other Comments
  • 26 Hide
    MiamiU , March 30, 2010 6:32 AM
    seems like being a hardcore gamer just keeps getting more and more expensive...
  • 23 Hide
    Icehearted , March 30, 2010 6:56 AM
    As for poor folk like me, we'll just settle for those still images where we cross our eyes, and cry because $2,565 is far away from "comfortable".
  • -3 Hide
    winner4455 , March 30, 2010 7:29 AM
    I can see this becoming main stream and the next few years... In 3d too.
  • 6 Hide
    tigerwraith , March 30, 2010 7:59 AM
    2.6k now but you know things like this keep getting cheaper and cheaper. Maybe by this time next year, the 1080p 2600 lumens will drop to 500, and the drivers will better support dual projector setups.
  • -4 Hide
    tigerwraith , March 30, 2010 8:09 AM
    But I do have a question would of mattered if you used LCD projectors?
  • 0 Hide
    gti88 , March 30, 2010 9:40 AM
    Great article! Thanx a lot.
    But as I can see, 3D stereo is not there yet.
    Almost no movies are available at 3DS, and game developers don't focus on stereo optimisation. Thus, we have some glitches and inconveniences.
  • 1 Hide
    pojih , March 30, 2010 9:59 AM
    ahh, something else to cost an arm and a leg...

    not saying that many people here don't want the fastest and most expensive....

    but it was clearly shown that many people looking at this site want something that performs for what it costs, as seen by the fermi release and the comments .....
  • 2 Hide
    skora , March 30, 2010 10:24 AM
    Whats the next price bracket up for a projector with higher res?

    I like the idea of dual projectors better than the alt-image standard, but they didn't ask me.

    Here's a wild thought, soon, everyone will have their own glasses that not only do the shutter for 3D, but will also be able to be personal monitors. Connect to any computer/phone/TV with your glasses. Displays might even become unnecessary. That will be the next wireless mainstream device. The iShades. Phone, mobile pc and display, earbud is right there. Have pants that have built in keyboard. We'll all just be sitting there with our shades on and never see the person next to us as we get lost in the cloud. And it all starts with 3D glasses. :p 
  • -1 Hide
    djab , March 30, 2010 10:31 AM
    IceheartedAs for poor folk like me, we'll just settle for those still images where we cross our eyes, and cry because $2,565 is far away from "comfortable".


    No, you can at least use red/cyan paper glasses with iz3d drivers and a normal display.
    That is not that bad!
  • 0 Hide
    manitoublack , March 30, 2010 11:05 AM
    Great article, and no doubt people ask you: "why have you got 2 projectors?" The only trouble with polarized setups is that you cant view 3D laying down, eg: Lounge Lizard style, which you can do with shutter glasses (however uncomfortable that may be.)

    Still though, for $2,500USD you've built a pretty mad setup. To those winging about price, deal with it, if you want the best you've got to be prepared to buy the best. I'd suspect that a WUXGA setup would be in the $5-6,000 range using the projectors you'd want. Well worth the buy-in price. I hope for your sake (if you payed for it, not Tomshardware) that it is compatible with yet-to-be-released BR3D.

  • 0 Hide
    mjello , March 30, 2010 11:17 AM
    manitoublackGreat article, and no doubt people ask you: "why have you got 2 projectors?" The only trouble with polarized setups is that you cant view 3D laying down, eg: Lounge Lizard style, which you can do with shutter glasses (however uncomfortable that may be.)Still though, for $2,500USD you've built a pretty mad setup. To those winging about price, deal with it, if you want the best you've got to be prepared to buy the best. I'd suspect that a WUXGA setup would be in the $5-6,000 range using the projectors you'd want. Well worth the buy-in price. I hope for your sake (if you payed for it, not Tomshardware) that it is compatible with yet-to-be-released BR3D.


    Samsung display dont work lying down
  • -4 Hide
    idisarmu , March 30, 2010 11:27 AM
    What's wrong with the old school red-green glasses? It seems like a much cheaper and convenient solution. I would hate having to recharge glasses, let alone wear them if they're going to be heavier than normal.
  • -4 Hide
    d70guy , March 30, 2010 11:27 AM
    There are a lot of issues with this. The lack of resolution, difference in brightness of the images over time (no two bulbs are identical), the less than ideal projection surface, the fact that all bluray titles will be 1080p for each eye, etc.. I mean, this *is* a fun toy, but not for a serious gamer, and not for an even semi-serious home theater person. It is strictly for someone with the money to blow on a toy.
  • 0 Hide
    d70guy , March 30, 2010 11:34 AM
    idisarmuWhat's wrong with the old school red-green glasses? It seems like a much cheaper and convenient solution. I would hate having to recharge glasses, let alone wear them if they're going to be heavier than normal.


    Red blue glasses are the worst case 3D experience. Both polarized and shutter glasses are 10 times better at delivering a realistic 3D experience. The anaglyph (red/blue separation of the image distorts the color of the image, and even with high quality (eyeglass quality) red/blue glass lenses the overall effect is that of a poor quality experience. Shutter glasses these days are not that heavy, and its not like you are going to be wearing them for the length of the movie. It really doesn't factor in. Personally, I will take the shutter glasses. They block light much better thereby eliminating the ghosting issues associated with the polarized lenses. I say this as someone who has worked with linear, circular, and shutter technology since the late 1980s.
  • 1 Hide
    Artman256 , March 30, 2010 12:21 PM
    From the dual projector page - "the filters polarize the light across a plane". This is not entirely true, old systems did that, but modern systems use circular polarization, which avoids the problems caused by tilting your head.
  • 1 Hide
    JohnnyLucky , March 30, 2010 12:21 PM
    This is going to be very expensive.
  • 12 Hide
    salgado18 , March 30, 2010 1:11 PM
    I don't know if it would be possible, but it would sure be AWESOME to see some of those games on a short gif animation in "fake" 3D! Please! (a video review would be great too!) :D 

    PLEASE people, vote me up! If you do they'll try it!
  • 5 Hide
    pluripotent , March 30, 2010 1:23 PM
    But Don! I'z only gotz one eye!
  • 2 Hide
    Rehnquist- , March 30, 2010 1:53 PM
    Why on earth are all the screenshots scaled down to such a low resolution?
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