To us, the idea that passive screens can produce a full HD image seems the most controversial of the passive camp’s claims. For using a filter across the screen to send half the screen real estate to one eye while the other half goes to the other eye seems to require an inevitable reduction in the resolution of the source image. There are only so many pixels in a screen, after all, so it seems logical that passive screens can only manage effectively half the resolution of an active 3D TV, which delivers full HD frames to each eye in sequence.
To be fair, most if not all of 2011’s passive 3D screens will be using a new thin film rather than glass substrate to ‘split’ the two 3D frames, so we’re dealing with a potentially different 3D ‘animal’ to last year’s passive 3D TVs. But actually watching HD 3D images from Blu-ray on our two 55in contenders, it certainly looked to us as if the active set had the higher resolution. This appears as more texture in foreground objects, and increased clarity over background areas.
Turning next to the other most controversial of passive 3D’s claims, we dutifully stretched ourselves out on our sofa and tried to watch both 3D screens lying down. And we guess that on one level the passive camp’s claims are borne out, for while the 3D picture disappears completely on the Samsung active 3D TV, it’s definitely still there on the passive TV.
That does not mean, however, that the passive set’s ‘prone’ pictures are remotely watchable. In fact they suffer with no less than three severe issues: extreme amounts of crosstalk (double ghosting); a pinkish colour tone ‘wash’ caused by the fact that the polarising system in the screen/glasses is designed horizontally, not vertically; and areas of extreme colour bleed/polarisation errors. In other words, you actually can’t watch passive 3D pictures while lying down unless you want to get an almighty headache.
This is one area where you would expect passive screens to enjoy a resounding victory. And it is certainly true that if you’re sat right opposite a passive screen, with your head more or less level with it, then it does suffer less with crosstalk. The difference is much less profound than it was last year, though, thanks to the considerable improvements Samsung has delivered with crosstalk on its 2011 Active 3D TVs.
However, the passive screen isn’t completely free of crosstalk. For a start, we noticed more evidence of crosstalk when using our passive test set’s 2D-3D conversion mode than we did on the Samsung – though this may say more about the relative quality of the conversion processing each TV uses than passive/active differences per se.
More alarming, though, is what we saw when we stood up to make a get a cup of tea. For at this point, with our heads above the screen, the passive 3D picture suddenly becomes crippled by crosstalk.
A bit of bobbing up and down suggests that a vertical viewing angle of barely 15 degrees is enough to cause significant crosstalk in a passive 3D picture.
Obviously this won’t be a big deal to everyone, as for the most part you’ll be sat still while you watch whatever 3D programme you’re interested in. But it needs to be considered if you’re thinking of positioning your TV quite high – above a fireplace, say. And we can’t help but think it must present problems in a pub or club environment, where it’s likely many of the people watching will be standing up.
The active 3D screen seems to suffer no significant issues at all with its vertical viewing angle, until you get to far more extreme positions than you would encounter in any remotely typical viewing environment.
While there are all sorts of debates and issues around finding the ideal depth balance and focal point with 3D images, our tests revealed that there’s a clear difference in the 3D effect created by our active and passive 3D screens, with the active 3D screen producing a greater sense of depth.
Some of this could be down to the active screen’s more detailed and sharper 3D images, but this doesn’t seem to be the whole story.
Horizontal viewing angle
Connected with the above finding, it also transpired during our tests that the passive screen lost its ‘3Dness’ much more than the active screen if you watch from down the TVs’ sides. The effect starts as soon as you get to an angle of around 30 degrees from directly opposite the passive screen, and the image depth reduction reduces markedly with every degree further you go beyond that.
While the active 3D screen loses depth too from wide angled viewing, the extent of the reduction is much smaller.
This issue is potentially quite important given that passive 3D is sold as being the option of choice for large families/social viewing occasions, where some viewers will probably find they have to sit at quite an angle to the screen.