Posted Fri Nov 12, 2010 at 11:00 AM PST by Joshua Zyber
Editor's Note: Each Friday, High-Def Digest's own HD Advisor will answer a new round of questions from our readers. If you have home theater questions you need answered, send an email to [email protected].
Answers by Joshua Zyber
Are 3-D Blu-rays Compatible with 2-D?
Q: When you purchase a 3-D Blu-ray, do you have the option to watch the movie in 2-D? I have a Mitsubishi 3-D ready DLP and a PS3, but no glasses yet. If I buy a 3-D Blu-ray, will it be watchable in 2-D?
A: The specifications for 3-D Blu-ray contain an option for backwards compatibility with 2-D viewing. However, this must be authored onto the disc. Some of the 3-D Blu-rays released to date (such as the German import of 'Clash of the Titans') can only be watched on 3-D equipment. If you want to watch in 2-D, you have to use a separate 2-D disc. (That 'Titans' release contains both in a 2-disc set.)
[Our site's Nate Boss points out that 'Monsters vs. Aliens', 'A Christmas Carol', 'IMAX: Deep Sea', (and presumably also the other IMAX titles released on the same day) are likewise limited to only 3-D playback.]
If the disc is authored for 2-D compatibility, it should in theory be viewable on any legacy 2-D equipment. The 3-D effect is achieved by viewing a scene from two slightly different angles simultaneously. When seen together, your brain combines the views into one image with three-dimensional depth. To convert this to 2-D, all the Blu-ray player has to do is shut off (or not turn on) one of the two angles. But, again, the disc must be authored in such a way that a regular 2-D Blu-ray player can read one of the views, without the data for the other view causing compatibility errors.
With that in mind, we come to the question of how you will watch these discs in 3-D when you're ready for the full upgrade. For one, you'll need to make sure that your PS3 is up to date with the latest firmware that enables 3-D viewing. After that, you'll need not just a pair of 3-D glasses, but also a 3-D converter component for your TV. Your TV is "3-D ready," but cannot accept or process the 3-D Blu-ray signal out of the box. Once you add the converter (see your TV's manufacturer for details), the 3-D Blu-ray signal will be downconverted to the "checkerboard" 3-D format that your DLP TV uses.
Unfortunately, Mitsubishi's line of "3-D ready" DLP sets do not entirely support 3-D Blu-ray, which offers full 1080p resolution for each of the left and right eye views. The "checkerboard" 3-D format displays both the left and right views on screen within the same 1080p frame, in a pattern that equates to a resolution of approximately 1358x764.
3-D Bit Rates
These next two questions are related, so I'll address them together:
Q: There's a technical aspect of the 3-D Blu-ray standard that no one seems to talk about despite potentially being very important: bit rate. While I'm guessing (it hasn't been made very clear) that multi-view video encodes treat one of the two views (left or right eye) as a delta of the other (similar to how MP3s and MP4s use joint stereo), this undoubtedly lowers the amount of bandwidth available for each view. That being said, wouldn't 3-D releases have to be more compressed and thus be of inferior video quality? BRD media (3-D or not) is limited to 36 Mb/s, and let's not forget that you might be giving up up to 5 of those 36 MB to a lossless audio track. Now with 3-D, two video streams have to be accommodated in the same amount of space. While I understand you can get away with higher levels of compression and lower levels of detail when you're using 3-D, wouldn't it be readily apparent if you're watching a 3-D movie in 2-D since you're looking at a video-stream encoded at a lower bit rate than it would be if it were natively 2-D? Putting it as simply as possible: Logically speaking, since 3-D Blu-ray discs have to convey more video information with the same limitations imposed on 2-D media, isn't the video quality inferior?
Q: Is there any difference in picture quality between the same movie released in 3-D Blu-ray and normal (2-D) Blu-ray? I'm thinking of 'Avatar', which was released a year ago in 2-D. That was said to be the most perfect transfer of a movie on Blu-ray because it had maxed out all the free space on the disc. The creators had specifically kept the bit rates as high as possible and included no extras to ensure the best possible transfer. Now with a new version on the way which will be in 3-D, how can the same level of quality be kept when you have to put twice as many frames on the same disc?
A: While I'm not an engineer, I've heard it claimed that 3-D Blu-ray video requires approximately 1.5x the amount of disc space as a standard 2-D encoding. So, as you both say, doesn't that beg the question whether this automatically means that 3-D video is inferior in quality to 2-D?
No, it doesn't.
This goes back to a point I have discussed many times in previous columns. We in the home theater community spend too much time obsessing over bit rate statistics, which are more often than not misleading. It's easy to make the assumption that there's a direct linear relationship between bit rate and quality, as if you could judge how good a Blu-ray transfer looks just by watching how high the bit rate meter peaks. The truth of the matter is far more complicated. The bit rate required to encode any given frame is highly dependent on the complexity of the content in that frame. In many movie scenes, throwing more bits at the picture will yield only diminishing returns, and may not offer much of any tangible benefit over a lower bit rate encoding. The skill of the compressionist and the quality of the encoding are always more important than the arbitrary bit rate numbers hit.
Did 'Avatar' max out all of the available space on its disc? It came close. Did it look amazing? Yes, it did. Does that automatically mean that a lower bit rate encoding would have looked less amazing? Not necessarily. The 'Avatar' Blu-ray disc was encoded using the same principle as the old "Superbit" DVD line from Sony. Remember those? When Sony had a movie that it wanted to issue with no bonus features, the studio would crank up the bit rate to the maximum, call it a "Superbit" release, and charge extra for it. This was, more than anything else, a marketing ploy. Most Superbit discs were no better in quality than regular DVDs sold by any other studio.
The same situation applies to 'Avatar'. 20th Century Fox had no bonus features to offer with the first Blu-ray, so it bumped up the bit rate in order to advertise the disc as being "maximum quality." Now, the studio is issuing a new "Extended Collector's Edition" of 'Avatar' that includes a longer version of the movie and a bunch of supplements. And yet, somehow, I don't see anyone claiming that it's inferior to the previous disc. In fact, I was at a studio presentation last week in which James Cameron himself explicitly said – and I quote – "We didn't have to sacrifice the bit rate or quality." He said in no uncertain terms that the Collector's Edition looks just as good as the earlier disc.
But but but… How can that be? It has to have a lower bit rate to fit more material onto the same sized disc, doesn't it? Indeed, yes, it will have a lower bit rate. Is James Cameron lying? No. All this really means is that the maxed-out bit rates on the first 'Avatar' Blu-ray were mostly done for marketing purposes, not due to technical necessity. When the Collector's Edition hits, I will defy anyone to tell the difference in picture quality between it and the original release. The same goes for 3-D.
In no way am I trying to excuse certain studios from authoring discs with sloppy encodes filled with visible compression artifacts (which unfortunately does still happen). However, nor would I demand that all Blu-ray encodes hit arbitrary bit rate levels just because I want to see the meter on my player spike. We all need to spend less time watching bit rate meters (which aren't even accurate half the time, by the way), and more time judging quality by what we can actually see.
3-D Blu-ray Naming Conventions
Q: I'm about to dip my toe into the world of 3-D TV, but I'm a bit confused when it comes to the 3-D Blu-ray format – or is that Blu-ray 3D? It seems a small point, but if I'm shopping online, how do I know if 'My Bloody Valentine 3D Blu-ray' or 'Piranha Blu-ray 3D' is the actual proper 3-D disc, or the old style one which requires red/ blue (or whatever) glasses? To make things more confusing, some current 3-D films, use "3D" as part of the title! Taking 'Piranha' 2010 as an example, is it 'Piranha 3D 3D Blu-ray'? Or 'Piranha 3D Blu-ray 3D'? What is the proper naming convention for the format, and do retailers know it? I regularly import, but I'd be disappointed if I got the wrong version.
A: Unfortunately, I don't believe that there's any standardization in these naming conventions. I know that Warner Bros., for one, has made a point of tacking "3D" onto the official name of the movie for the packaging of its 3-D Blu-rays. For example, 'Cats & Dogs: The Revenge of Kitty Galore 3D' not only has "3D" at the end, but also has different cover art than the standard Blu-ray edition, which is just called 'Cats & Dogs: The Revenge of Kitty Galore'.
However, this alone doesn't always clear up the confusion. The new full-1080p 3-D Blu-ray release of 'The Polar Express 3D' sounds an awfully lot like the earlier anaglyph red/blue release of 'The Polar Express Presented in 3-D', doesn't it?
And yes, what of 'Piranha 3D' (which was the movie's proper title in theaters)? The studio press release implies that that standard Blu-ray edition will be retitled to just 'Piranha'.
How can you definitively tell what you'll be getting? I'm afraid that you're going to have to do a little research by reading reviews at sites like ours.
3-D Without Glasses
Q: I have a workmate who is telling me that he's waiting for 3-D without glasses. I keep telling him that when I watch 3-D with my glasses, not only do I get depth, but the glasses bring the 3-D right to my eyes. While I believe it's the depth that makes 3-D awesome, I don't want to lose the coolness of on-screen objects floating in suspension seemingly inches in front of me. I believe the glasses bring that effect and that non-glasses 3-D will only retain the depth part of 3-D. Am I correct or should I prepare to be surprised?
A: 3-D without glasses is technically called "autostereoscopic 3-D." In principle, this works the same way that traditional 3-D with glasses works: A 3-D image is encoded with separate left and right views, each recorded with a slight offset in position. During playback, one view must go directly to your right eye, and the other view must go directly to your left eye. Your brain will then combine them into a single image with three-dimensional depth.
When you wear 3-D glasses, the lenses filter the imagery to make sure that each eye gets the correct view, either through polarized light or by LCD shutters that rapidly open and close in sync with the signal transmitted by the TV.
An autostereoscopic display has something called a "parallax barrier" behind the screen that aims the light particles in specific directions so that, once again, one camera view will be shone towards your right eye and the other camera view will be shone towards your left eye. The most significant disadvantage to autostereoscopic screens is that they have incredibly limited viewing angles. You must be seated directly in specified "sweet spots" for the parallax barrier to effectively hit the correct eyes. If you sit at the wrong viewing angle, the 3-D effect will be lost, and you may not even be able to see any picture at all.
Regardless of whether you wear 3-D glasses or watch an autostereoscopic screen, the 3-D effect itself should be the same. If the imagery was recorded to convey a sense of depth behind the screen, that's what you'll see. If it was recorded to project objects outwards from the screen, you'll see that instead. (Or both.) How the 3-D effect is designed is at the control of the content creator (for example, the movie's director), and shouldn't be limited by the type of 3-D screen.
Check back soon for another round of answers. Keep those questions coming.
Joshua Zyber's opinions are his own and do not necessarily reflect those of this site, its owners or employees.
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