3D Crosstalk is Always and Everywhere a Timing Phenomenon

Sorry about the title. I’ve lately been listening to a lot of economics podcasts, and the phrase (attributed to Milton Friedman) ‘Inflation is always and everywhere a monetary phenomenon’ popped into mind.

But like Friedman’s aphorism, I’m increasingly convinced that my title is largely true.

Over at HighDefDigest Josh Zyber was struggling with the causes of crosstalk a few months ago. He thought that maybe it was due to content, maybe to the display tech.

I am pretty confident that it is not the content, assuming that the content is competently done. Sure some content seems more subject to crosstalk than other content, but that’s because different 3D display techs are better at eliminating crosstalk from some colour and brightness combinations than others.

Remember, crosstalk is a simple phenomenon: it is where part of the image intended only for the left eye leaks through to the right eye, and some of that for the right eye leaks through to the left eye.

There are only two ways that can happen, as I explained here. One is by content leaking through the filter on the eyewear if it is insufficiently opaque to the other eye’s image. The other is due to timing: where, for example, some part of the left eye image is still being shown on the screen after the liquid crystal shutters in the glasses have switched over to letting the right eye see.

There is some of both. Passive LCD TVs don’t have the timing issue at all, so any crosstalk is entirely due to insufficient opacity. And there is no doubt about it: passive TVs perform enormously better on crosstalk than active TVs (although with our current state of technology, they lose half their resolution). But they still have a very low level of ghosting, so there is some leakage through the polarisation system.

But even better than passive direct view TVs are active DLP front projectors. These have virtually no crosstalk at all (I have reviewed four models from three brands, so I know).

Now what distinguishes DLP projectors from LCD and LCoS ones? Pixel response time. To quote from a recent review of mine:

[A] Digital Micro-mirror Device … has 2,073,600 tiny, yet moving, mirrors on its surface. This seems like a ludicrous proposition, compared to the solid state alternatives. But, perhaps strangely, these tiny mirrors are a hell of a lot more responsive than solid state panels. LCoS and LCD panels take time in the order of milliseconds to change their state from black to white, or grey to grey. The DMD is two orders of magnitudes faster, at around 16 microseconds.

It’s the timing! When a pixel on a DMD in a DLP projector snaps shut, it does it fast. When a pixel on an LCD panel goes opaque, or one on an LCoS chip goes non-reflective, it takes its time getting there, and in order to allow sufficient brightness, the active glasses have to reveal its state before it has completely gone. Remember, in an active system with 24fps 3D content, the total display time for each frame for one eye is just 20.8ms. Two, three, four or more milliseconds off that, and you’re losing a lot of display time and brightness.

Here is a demo. I haven’t done this with DLP, just active and passive. But it shows the gulf in performance, and believe me, DLP is even better on crosstalk while not having the lost resolution problem of passive LCD.

So what we have here are two TVs, same brand, the top one is active (ie, using shutter glasses), the bottom one is passive (ie. using reverse circular polarisation on alternate lines):

Werner Bloos ghosting test: Active 3D top, Passive 3D bottom

This shows a segment of a still test pattern developed by Werner Bloos (Caution, site in German). I photographed this through the left lens of the respective eyewear of both TVs, so it’s the left eye view we’re interested in. The vertical bar under the yellow line marked ‘White Ghosting, Left Eye’ should be perfectly black. That marked ‘Black Ghosting, Left Eye’ should be perfectly white.

As you can see, the passive TV (bottom) isn’t too far off, but the active TV has tremendous amounts of breakthrough.

So, to summarise, it isn’t the content. It is the ability of the hardware to keep the left and right eye images separate all the way into your eyeballs. And that is mostly due to timing, or at least, the smearing of image reproduction over time.

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16 Responses to 3D Crosstalk is Always and Everywhere a Timing Phenomenon

  1. Ryan Sandford says:

    Extremely interesting yet again. I was wondering though, with the small amount of leakage in passive due to the insufficient opacity, would this mean a better quality lens (eye-wear)or in my case clip-on’s,make my image possibly better? And if so, do you have a reccomendation for the best circular polarised lens or glasses?

    I would also like to make the point, that using the clip-on lenses, as I have to wear my glasses anyway, feels like the closest thing to glasses free 3D possible. Very convenient.Even though some conversions may not look the best, I have become used to watching normal foxtel converted,and really love it.

    Another thing, I can clearly see the raster lines in your & other display pics of passive 3D tv’s, but I honestly no matter how close I go,cannot see them on my Soniq tv in 3D.
    I have gone close enough to see the little black outlines (boxes) of what I think are the individual pixels, but still can’t see what I know is the major hang-up,along with the lost resloution per eye, that most who prefer active point to. I wonder if the software update I had to apply for it to recognise SBS mode also updated the firmware with the new algorthym of LG’s which is supposed to work for their Cinema 3D. Soniq makes no mention of this but does make it clear it uses the LG Cinema technology and panels in their tellys. Do you think this is possible?
    Thanks again.

  2. Haven’t tested any glasses. I doubt that there would be much difference in quality anyway. Just go for comfort.

    I have no idea about the Soniq’s algorithm. You could try creating test patterns like I did in that other post to see what happens.

    I’m not much of a fan of 2D to 3D conversions because they will inevitably produce weird results from time to time. Their detection algorithms are trying to work out what’s in the foreground and what’s in the background based on very approximate heuristics. They are very frequently fooled.

  3. Ryan Sandford says:

    Thankyou Stephen for your quick response & advice.That’s actually the point I was making in regard to the clip-on lenses, as they simply attach to my glasses I need all the time and do not need removing,it makes it extremely comforatble.

    I have also confirmed that they do not leak or bleed any image meant for the other lens. Since last posting I have actually come across a test patterns and calibration for 3D( including ghosting &crosstalk) and home theatre settings in,incredibly, the Toy Story 3D blu-ray. -http://www.amazon.com/Toy-Story-Four-Disc-Combo-Blu-ray/dp/B005GSVFBE/ref=sr_1_3?ie=UTF8&qid=1336627799&sr=8-3 .

    It is really useful and has helped me in my settings and confirmed that the 3D in the Soniq is working perfectly. I would encourage others to check these tools out as they are very useful.

    Also thankyou for your earlier advice regarding the sharpness settings, bringing it back to about 30,from the pre-set of 50 has helped my picture significantly.

  4. Brad says:

    Hi Stephen;
    I’m a new 3D owner. I feel like my head is going to explode.

    Initially, I bought a Sony Passive set. It quickly developed background leakage and I had to return it.

    I ended up with a series 6 Samsung LED set which is Active. And, you guessed it, first movie watched, “What’s that?” Crosstalk. It drives me nuts.

    Here’s a simple question, I think. Without thinking, I just used the HDMI cables I had. They’re good quality, but I doubt that they are 1.4 spec. Could it be that cables not up to 1.4 spec could throw timing off and aggravate the crosstalk problem?

  5. Hi Brad

    Sorry, it’s not your cables. HDMI cables can’t introduce crosstalk issues. The first sign of their inadequacy will be little sparkles on the screen. If the cable is a bit worse then there will be obvious problems, like streaks, big sections of the picture missing or misaligned and so on.

    What you’re seeing is crosstalk due to the way the TV presents the picture. If it is intolerable and you love 3D, then the better option is an LG passive set.

  6. Aurelio Heredia says:

    Hello,

    Little late with the entry, but I thought I’d add to it and my findings. I have an oppo 103 and Epson 3020. 3d is good, crosstalk was noticeable on some movies more than others, but I found I was always looking for it so it definitely was a distraction. I did some research and then some tinkering. First set the oppo to RGB out. Second turned off 2 to 3 converter on epson, turned the 3d brightness from high to low (biggest difference in ghosting), turned on super white, and turned off the iris (it did add cross talking and audible noise). After these setting, big improvement, only a slight off setting on the menu screen and txt, so my last adjustment was the HDMI. Now everywhere I read, said this doesn’t make a difference, hogwash. I went from an older HDMI ($300 AQ HDMI3) to a newer Audioquest HDMI (Forest 3d on sleeve) and shazam, the small bit of offsetting which could not be adjusted, was GONE. Even the 3d was better, deeper and sharper. Put on a converted 3-d movies, just beautiful. Movies that had issues before are just sublime. Thought I would have to change out projector, not on your life! Hope this helps out any frustrated Epson 3020, Oppo owners.

  7. Mike says:

    Although in spanish, please read and translate this article, it will help you to reduce ghosting/crosstalk in 3D viewing:

    http://teorizen.blogspot.com.es/2014/01/reduce-el-ghosting-o-crosstalk-consejos.html

    You are welcome!

  8. Sorry Mike, I didn’t notice this one queued for moderation.

    I checked out the link and as far as I could tell, using Google Translate, it offers quite a bit of pretty useless advice. Adjust the frame rates? With most equipment you can’t do that, nor do you need to. 3D gear will run all the appropriate frame rates. Blu-ray 3D is overwhelmingly 23.976fps. All 3D players handle that. All 3D TVs handle that. No need for any adjustment.

    One caveat: I think some Blu-ray players still come with 24fps playback switched off by default, so clearly that should be enabled.

  9. Bob Dobbs says:

    Regarding the latest, 2014 model, LG 49UB8500 …49″ 3D Ultra-HD 4K TV … which utilizes a passive (horizontal polarization) type 3D … I’ve found there’s NO viewing angle (‘sweet spot’) to completely eliminate the crosstalk (‘ghosting’)! Especially in the vertical axis. Viewers are forced to pick one or the other; crosstalk at the top of the image … or … crosstalk at the bottom of the image. Honestly LG, what we wanted was NEITHER one, but you’ve forced us to choose. Even if seated 10′ to 15′ away, crosstalk is still noticeable. So, it looks like I’ll have to wait for Dolby 3D or some other whiz-bang solution to become affordable… : (

  10. Thanks Bob. The same, I’m afraid, for the 55 inch version. My guess is that the narrower lines make it harder to get the alternate polarisations right.

  11. salah says:

    thanks Stephen for this good article, which i didn’t understand that much, but pretty understood that the problem isn’t about the content….so, i got samsung h6400 3d tv and trying all 3d content i got, some movies have crosstalk, some don’t. so, how to resolve that issue, especially that some of the movies i got are 20 Giga and more…thanks

  12. Hi Salah. Really there isn’t a solution, other to than to buy a TV or display with better crosstalk performance. The differences between movies depends on two things: 1) which colours are overlaying which other colours, because the performance varies according to those combinations; and 2) how wide the separation is between the left and right images.

  13. Ed says:

    I had a Samsung 40″ 2013 model and 3D was excellent!!! I sold it and bought the same model but bigger (48″) and 2014 year. 3D sucks in many films, :/ crosstalk in many scenes.

  14. Shane says:

    I have found that there is a big quality difference between circular polarised glasses they sell for $1 at the cinema and the $5 glasses that came with my soniq 3D TV. The theatre glasses are like looking at the screen through s smoke haze by comparison to the soniq glasses that are crystal clear. So there is some difference between brands. I also have a Samsung 27″ 3D monitor with active glasses that suffers extreme ghosting and is very dark in 3D, but it is the best 2D monitor I have ever owned.

  15. Kevin says:

    I have a JmGO G1 DLP projector, and did not expect much from the 3D, but tried it anyway. Absolutely no crosstalk. The 3D glasses have an optical sensor which synchronizes with the projected image itself, and that combined with the speed of the DMD insures perfect timing. The only fault would be that 50% of the time when the movie starts, the 3D is reversed and must be swapped left for right by pushing a button on the glasses.

  16. Carl says:

    Hi Kevin..do you mean the JmGO G1s model ? Also what brand of 3d glasses u have ?

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