Passive 3D vs. active 3D: Hands-on TV comparison

CNET compares the 3D picture quality of two HDTVs, one equipped with active and one with passive glasses technology.

We compare a pair of 65-inch TVs, one with active and one with passive 3D TV technology. David Katzmaier/Joseph Kaminsky

In late 2010, Vizio quietly released the 65-inch XVT3D650SV ($3,700), the first mainstream TV equipped with so-called "passive" 3D technology for the U.S. market. Earlier this week our review sample arrived, so in advance of the full review I'd like to present some initial impressions.

This is the first time we've had a chance to really sit down and watch a passive 3D TV, so of course our first order of business was to set it up in the lab next the other 65-inch 3D TV we had on hand: the 2010 Editors' Choice-winning Panasonic TC-P65VT25 ($4,300). Like nearly all other TV makers, Panasonic has embraced "active" technology for its 3D TVs, and for 2011, it didn't announce any passive 3D TVs.

For this initial look, I chose not to include comparisons with other TVs, for the simple reason that the Panasonic is the best comparison model to the Vizio I have available. It's the only 65-incher in our lab at the moment, its 3D performance is excellent, and its overall picture quality was the best of 2010. The Vizio, as the only shipping passive TV, is by default the "best" of its kind available.

I'm also not going to get into the technical differences between active and passive 3D, except to remind new readers that active requires expensive liquid crystal shutter glasses (at least $100 per pair in Panasonic's case; the VT25 ships with one pair free) that are relatively heavy and bulky; passive calls for cheap circular polarized glasses (Vizio's TV ships with four pairs) that feel like light sunglasses. Most U.S. theaters use passive technology, and in fact many theater 3D glasses will work with the Vizio.

So, seriously, which one is better?
Between the two, I definitely preferred active 3D in our side-by-side comparison, and my colleague and fellow video-quality evaluator Matthew Moskovciak agreed.

Between us we watched a few hours of various 3D materials with the TVs set up side-by-side in our darkened lab, switching between each set of eyewear and rewinding as needed to review certain segments. I used the Cinema picture setting on the Panasonic, and since the Vizio lacks picture presets for 3D, I simply reduced its backlight all the way to zero and chose the "Normal" color temperature mode to come as close as possible to a quick-and-dirty level playing field between the two.

The most obvious difference between the two TVs to us was, as expected, their apparent resolutions. Watching the 3D Blu-ray "IMAX: Under the Sea," the Vizio's picture looked softer, with less detail, a difference particularly visible in areas like the coral reefs and sandy sea bottoms. Compared with the Panasonic, the Vizio seemed almost standard-def, especially from our relatively close seating distance (8 feet, which is the minimum recommended by Panasonic for 3D viewing on their 65-incher). Even from a farther seating distance of 12 feet, the softness difference was apparent.

We expected this difference because, as Vizio, LG, and other purveyors of 2011 passive 3D TVs admit, the system they use halves the effective 1080p resolution, delivering only 540 lines to each eye. We just didn't expect it to be so obvious. As Matt said, it makes you appreciate how good "1080p to each eye" looks.

In this close-up photo of a paused 3D image on the Vizio, you can clearly see the separation between the lines with passive 3D. Of course the effect is more subtle from normal seating distances, but it still contributes to some visible artifacts. David Katzmaier

As a result, in addition to the softness, you can actually see individual horizontal lines on the Vizio's big 65-inch screen, and in bright, flat fields they were visible from as far as 12 feet. For me these "scan lines" did blend together and become less noticeable over time, but nothing of the sort was visible on the Panasonic.

One other major flaw in the Vizio's image, and the worst in my opinion, took the form of "jaggies" that reminded us of nothing so much as the interlace artifacts seen on low-resolution, interlaced (480i) TVs. The small bodies of white fish in schools provided a good example, breaking into jagged edges on the Vizio and looking smooth and natural on the Panasonic.

Graphics like the Imax 3D logo also had jagged edges along the curves, and we saw the effects of the jaggies in numerous other areas that included any semistraight moving lines. A tennis match from the U.S. Open provided an even more glaring example: the lines of the court were jagged and the jaggies moved distractingly as the camera tracked player movement.

Both of the above issues with passive 3D in its current, half-resolution iteration, e.g. softness and visible artifacts, will be less noticeable at smaller screen sizes than 65 inches. The actual pixels and lines on smaller TVs shrink in size, and so it will be interesting to see how much less bothersome they become on, say, a 47- or 55-inch passive 3D TV (thanks to commenter HowardRourke for reminding me about this).

A few other differences should be screen size/seating distance independent. In a scene showing a field of wriggling worms receding into the distance, Matt also noticed that the apparent depth of field seemed shallower on the Vizio. Perhaps this difference has more to do with the TVs' different implementation than anything inherent to passive or active technology, but it was noticeable nonetheless.

The Imax disc has some areas of extreme crosstalk, or a ghostly double-image around objects. One of the worst was another field of worm-shaped things against a black background. In these scenes and others both displays showed crosstalk, and between the two we agreed it was worse on the Vizio. Its crosstalk was tinted blue, whereas the Panasonic's was amber, so that may have affected our impressions, but in the material we watched, passive 3D definitely didn't provide an advantage in crosstalk reduction. Interestingly, we also tried a pair of RealD passive 3D glasses and they reduced the Vizio's crosstalk quite a bit, although it was still worse than on the Panasonic.

When we moved off-angle, the active system also preserved the 3D effect better. We noticed no major drop-off in 3D fidelity when we moved to extreme angles on the Panasonic. On the Vizio, the 3D effect deteriorated and the formerly fused 3D image separated into its two parts (which looked similar to crosstalk, but was visible everywhere in the image) when we watched from extreme angles. Within a "normal" viewing angle, however, like anywhere on our three-seat couch perched at a close 8-foot distance, the Vizio's 3D image remained intact, so we don't think this difference will have a big impact on most people's enjoyment. You'll have to move pretty far off-angle for the passive 3D effect to start failing, and even then it's a gradual process.

In its favor, the passive image on the Vizio was quite a bit brighter than the Panasonic's active one, but in our view, the Panasonic's 3D was plenty bright for most dim and darker rooms. For bright rooms, however, the extra light output allowed by passive is a distinct advantage.

We also noted numerous other differences between the two that had little to do with 3D technology, including uniformity issues with the Vizio's edge-lit backlight, less accurate color on the Vizio--namely purplish blues, maybe fixable via calibration but I doubt it--and more. We'll wait for the full review to get into that, as well as any effect passive 3D has on 2D picture quality (although I haven't noticed anything obvious so far).

A question of comfort
Even with all of these flaws, passive 3D has a lot going for it beyond cheap glasses. Wearing a pair of today's active 3D specs, which generally feel more like heavy safety goggles than light prescription eyeglasses, for example, is definitely less comfortable over long periods of time (although companies like Samsung have announced lighter active glasses for 2011, and Panasonic has also lightened its new glasses design). Vizio's passive glasses fit easily over my eyeglasses, and I simply forgot they were there while I watched.

Vizio and LG used the term "flicker-free" to describe passive 3D at CES, a marketing-heavy reference to the fact that active glasses strobe on and off very rapidly (60 times each second per eye). In my experience the "flicker" of active glasses is impossible to discern directly when watching a 3D TV. It does cause some weird effects when you look through active glasses at certain light sources--like your laptop screen or some fluorescent lights--but that's not a big deal for critical, theaterlike viewing. The only obvious effect passive glasses have is a subtle dimming, like a cheap pair of sunglasses, so they're much more suitable for casual 3D viewing.

Advocates of passive say it's more comfortable over a 2-hour movie. In my experience active is comfortable enough, aside from the heavier glasses, although my judgment is still out on this one--I need more extended viewing sessions with both 3D technologies (nobody ever said reviewing TVs was easy) to say one way or the other for sure.

At least one CNET staffer to whom I showed the two TVs, however, did find passive more comfortable to watch beyond merely the weight of the glasses. He complained of a slight flickery effect with active, especially during fast motion, and said he would, based on the 15 minutes comparing between the two, buy the passive TV if 3D performance was his only consideration. As I've said before, 3D perception varies from viewer to viewer more widely than 2D.

Can passive be the MP3 of 3D?
Despite all of the picture quality issues I note above, the real question for TV buyers will be whether half-resolution passive 3D is still "good enough." When MP3 first came along, many of the audio-centric tech geeks I knew derided it as too low-quality to catch on. Now it's the de facto standard for digital audio, despite having lower audio quality than CD.

Vizio placed all of its 3D eggs in the passive basket in 2011, and given the cheapness of the eyewear, the fact that the technology "just works" without having to rely on syncing or powering up the glasses, and the improved comfort level imparted by lighter specs, it may not be a bad bet. For the next year at least, however, active and passive will battle it out for your 3D TV dollar, and if you're in the market, you owe it to yourself to audition both.

And just to complicate the 3D TV technology picture further, I'll note that full-resolution 3D using passive glasses is not only possible, it was demonstrated at CES. Real-D and Samsung's RDZ system promises full-rez 3D that's compatible with the same passive glasses Real-D uses in theaters. My guess is that it will be quite expensive at first, however.

I'll have more when the full review of the Vizio XVT3D650SV posts next week.

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