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Published: 2010-05-06 - 01:04:32
Home Theater : News and Show Reports

3D TV: The Myth of 3D Glasses Compatibility

By Chris Boylan

We read the reports yesterday in Home Cinema Choice (repeated by Gizmodo and elsewhere) about the miracle of 3D glasses interoperability (e.g., using Samsung 3D glasses to watch a Panasonic 3D TV) and had to laugh.  Yes, the picture of a guy with 3D glasses on upside down was fairly amusing, but what made me laugh was the explanation given as to why this works and the implication that a) the glasses have to be upside down for compatibility and b) that it would work in the real world (neither of which is true, but I'll get to that).

It was reported that for Samsung 3D glasses to work with Panasonic 3D TVs (and vice versa) that all you need to do is flip your 3D glasses upside down. But the truth is that Samsung glasses will "work" with Panasonic 3D TVs even right side up, if you understand how the technology works and know which settings on the 3D TV are important.  But even so, this doesn't make them compatible.

The reason that this little trick works (sometimes) is because the Panasonic and Samsung TVs in the test environment were 180 degrees out of synch from each other.  In the US market, 3D TVs' synchronication signal (the signal that tells the left and right shutters on the glasses when to open and close) is locked at 120 Hz -- 60 blinks of the left eye alternated with 60 blinks of the right eye.  To get the 3D effect, your left eye needs to get that left eye information while your right eye needs the right eye information.  This is how your brain sees the illusion of 3D, by putting the two images back together to form one.  When the right eye gets left eye information (and vice versa), you get an inverted 3D image, which looks very strange indeed.  People are going when they should be coming (and yes, I know how that sounds).

When you fire up two different 3D TVs, one TV may start up with the synch signal for left eye first, locking the same-branded glasses into a left eye/right eye pattern, but the second TV may begin transmitting the left eye/right eye image later -- exactly 1/120th of a second later, to be precise -- which causes the second TV to be "out of phase" from the first.  You basically have a 50/50 chance as to whether the second TV will be in synch or out of synch with the first.  When it's out of synch, the second TV displays a right eye image on screen when the first TV displays a left eye image (and vice versa).  When this happens, turning the glasses upside down will allow you to see a proper 3D image on the second TV.  But if you go into the menu of a Samsung 3D TV and hit the "3D Picture Correction" button (or "Left/Right Swap" on a Panasonic 3D TV), the TV will shift the phase of its left/right broadcast, thereby locking to the same 3D sequence as the first TV.  Voila - one pair of 3D glasses works with two different branded 3D TVs!  Or does it?

Rose Colored Lenses?  Well, No... More Like Amber

The problems here, not discussed in any of the earlier posts, are two-fold: a) Samsung 3D glasses will not even turn on without a Samsung TV broadcasting a 3D signal (and vice versa for Panasonic) and b) the Samsung and Panasonic 3D glasses have slightly different colored lenses which correct for the different TV's color shifts in 3D mode.  The first issue means that you will not be able to bring your Panasonic 3D glasses over to a friend's house who has a Samsung TV, because the Samsung TV won't turn them on ("it's not you, it's me!").  The second issue means that even if you can get your 3D glasses on and synchronized to your friend's TV, the colors won't be accurate as you're using the wrong color filter in the lenses.

samsung and panasonic 3d glasses
Not just an illusion, Samsung's (left) and Panasonic's (right) 3D glasses have different colored lenses to compensate for color shifts in 3D mode.

XPand has announced that they will offer "universal" 3D glasses this Summer.  Our assumption is that they will rig the glasses to respond to the power on codes from multiple manufacturers.  But how they are planning to handle the different color shifts, we're not sure.  Will they use flip-down or interchangeable lenses?  Will they offer a tint that falls between those used by current manufacturers and hope that no one notices the color shift (admittedly, it is relatively slight, but measurable).  We shall see when they actually reveal their product.

Until then, the quest for universal 3D glasses goes on... for those few thousand people who actually own a 3D TV that is.

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