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3D TV Buyer's Guide - Picture Formats

John Archer


3D TV Buyer's Guide - Picture Formats

Introduction and Frame Packing

As hopefully became clear during our look at 3D display hardware a couple of weeks ago, not all home 3D signals are equal.

People with a long-held interest in AV technology won’t be at all surprised to hear this; after all, ‘experimental’ 3D broadcasts used to pop up even on our old CRT TVs from time to time, when all the HD flat TV technologies we’ve got nowadays were just wistful twinkles in manufacturers’ eyes.

If you’ve been following our review coverage of the first generation of new 3D products, from Sky boxes to TVs and projectors, you will hopefully also have taken on board that Sky’s 3D broadcasting system is radically different to the new Blu-ray 3D system.

However, we’ve never made a concerted effort to explain in one place all the key 3D formats out there - so here goes! Starting with the one that first kick-started all the new interest in 3D...

Frame Packing - As seen in: 3D Blu-ray discs

The key point about the so-called Frame Packing 3D picture format is that it enables the transmission of full HD 3D images to display devices able to ‘decode’ them. Other current 3D formats cap resolutions at somewhere below the 1,920 x 1,080 pixel full HD level.

The frame packing approach sends both the left and right eye image information at the same time, with one full HD image sitting on top of the other and a small 'gap' to separate them. The display device then splits the single super-sized frame into its two constituent parts, ready to transmit sequentially - left eye, right eye, left eye, right eye - to a pair of active shutter glasses.

Passive 3D TVs can take in full HD frame packed 3D signals too, but they have to halve the resolution for output.

While this format sounds fairly straightforward in principal, it has two ‘catches’. First, in order for it to be guaranteed to work properly, with full HD resolution, it needs HDMI v1.4 connectivity. This most recent of many HDMI connection evolutions is essentially designed to handle much higher data bandwidths than earlier incarnations, and clearly, transmitting two full HD images stacked on top of each other like 3D Blu-ray players do is a pretty data-intensive process.

The other issue with frame packing is that it requires a display that can unpack the single 3D signal into separate frames. And for now, at least, the displays that can do this tend to be considerably more expensive than ‘normal’ TVs and projectors.

Adding a big layer of confusion to all this is the PS3. As you all surely know, the PS3 has a built-in Blu-ray player. And actually, thanks to a big software update last September, this Blu-ray player can play frame-packed 3D Blu-ray discs. Yet it only has a v1.3 HDMI output. So how does it get round the supposed HDMI v1.4 restriction?

The answer, in short, is that it compromises the disc’s audio. Basically, since the v1.3 output prevents the PS3 from being able to push out all the data required for a full 3D home cinema experience, the console keeps the 1080 line resolution of the disc’s pictures, but won’t/can’t pass out at the same time the HD audio mixes that usually accompany today’s 3D Blu-ray movies. Instead, you have to make do with a normal-resolution Dolby Digital 5.1 or DTS mix.

Sony also admits that the bandwidth restrictions imposed by its v1.3 HDMI socket could cause issues with things like subtitles and fancy disc menu designs. Though we haven’t had any of these problems so far.

Another issue for the PS3 where 3D is concerned relates to games. For while the console can output 1080p 3D at 24 frames per second, most games naturally need to run at frame rates considerably higher than that to work - 50 or 60fps, ideally. So Sony’s preferred solution is to cap 3D games to a 720p resolution, at which level 50/60fps transmissions can be handled by the 3D hardware and cables.

One final issue we’ve found with the PS3 is that while most people seem to get it working with their 3D TVs and projectors OK, it doesn’t always ‘handshake’ properly with AV receivers - even some 3D Ready receivers.

If you’re having trouble with this, one thing to try is to connect the PS3 directly to your 3D-capable TV rather than looping it through your receiver, so that the PS3 can have its 3D talents ‘woken up’ by acknowledging a connection with a 3D TV. Then when you plug it back into your receiver, it should retain its newfound 3D sensibility.

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