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2D compatible 3D broadcasts

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Ant Miller Ant Miller | 10:00 UK time, Tuesday, 24 January 2012

The Digital Service Development group led by Phil Layton in BBC R&D was involved in the previous trial of 3D at the Wimbledon Tennis Championships this year and also the recently broadcast Strictly Come Dancing Grand Final. In this post Dr Peter Cherriman outlines the work to produce 2D compatible 3D broadcasts for Freeview and Freesat receivers.

The BBC has been trialling 3D broadcasting over the last year. While 3D content is an interesting development in television, it creates a number of challenging problems for existing 2D receivers in the market.

In order to allow the introduction of 3D broadcasting with the minimum changes to existing systems and receivers, the DVB broadcasting specifications allow 3D content to be broadcast as HD video. The stereoscopic video is merged into a single HD frame by anamorphically compressing the view for each eye into half of the HD frame. This 'frame compatible' video can then be transmitted on a separate 3D channel or broadcast as part of a 2D HD channel.

Launching a separate 3D channel does reduce some of the legacy 2D receiver issues. However, such a channel would require a significant amount of 3D content and the cost of finding additional capacity. The BBC has broadcast its 3D trials on an existing 2D channel, the BBC HD channel.

Our trial 3D broadcasts started with the Wimbledon Singles Finals and then the Strictly Come Dancing Final before Christmas. These programmes were all broadcast in 3D on the BBC HD channel. Viewers without 3D televisions were able to watch a simulcast in 2D on BBC One or BBC One HD.

However, scheduling a 2D simulcast of a 3D broadcast will not always be possible. We have been looking for solutions to allow viewers with a existing HD receiver and a 2D television to watch the 3D content in 2D. It is possible to generate a 2D view from the frame compatible 3D content, by showing the 2D viewers a stretched version of either the left or right eye view.

With the current broadcasting standards this 2D view results in a loss of resolution, to something less than HD resolution but higher than standard definition.

The 2D view could be created by new functionality in receivers or by using some low-level H.264 signalling. After testing the various options, we found that none worked successfully with all HD receivers already in the market. However, we did find a solution using "Red button" (MHEG) technology that is present in all FreeviewHD and FreesatHD receivers. This solution uses the cropping and video scaling features in the interactive MHEG engine. We originally trialled this technology on FreeviewHD receivers during our 3D Wimbledon broadcasts. We have yet to investigate whether a similar interactive application approach is possible on other platforms.

On new year's day we broadcast the film Streetdance3D, in 3D, on the BBC HD channel. This film had previously been shown in 2D on BBC One and BBC One HD. On this occasion we weren't able simulcast it in 2D on another channel. It was therefore the perfect opportunity to trial this "Red button" technology on both FreeviewHD and FreesatHD receivers. The MHEG application allowed viewers to select between a 2D and 3D view by pressing the Red Button.

Figure 1: Screen capture of MHEG application on a 2D display. The red button toggles between a 2D and 3D view. A) shows the 2D view and B) shows the 3D view.

Figure 1A 2D view of the program. Note the on screen option to switch to 3D

 

Figure 1B The 3d view- a pair of images presented side by side.

Figure 1B The 3D view- a pair of images presented side by side.

 

The "3D view" passed the video straight through, so viewers would see the normal side-by-side pictures (see Figure 1B), until either their 3D TV detected the video was 3D and switched to 3D mode or they manually switched their TV into its 3D display mode.

 

Figure 2: Screen capture of MHEG application showing its 3D view on a 3D TV. This photo represents what a viewer without glasses would see.

Figure 2: Screen capture of MHEG application showing its 3D view on a 3D TV. This photo represents what a viewer without glasses would see.

 

The application's "2D view" used the MHEG video scaling feature to take the left half of the screen and stretch it horizontally by a factor of two in order to fill the whole screen. This effectively cropped out the right half of the screen giving 2D viewers the same picture that people with a 3D television saw in their left eye when wearing 3D glasses.

When the MHEG application was in the "3D view" viewers may have noticed that two red buttons appeared (see Figure 1B). This was to ensure that the red button icon could be seen by both eyes when the television was in 3D mode and therefore did not flicker. The two red buttons were placed so they overlapped in the TV's 3D mode (see Figure 2).

The application was designed to hide the red button icon(s) after 30 seconds, once viewers had made their choice to watch in 2D or 3D.

The MHEG application initially started in the "3D view", but it is possible to configure the MHEG application to start in the "2D view". The reason we started the application in the "3D view" was that the startup time of the MHEG application varied among receivers. If the application had initialised into a "2D view", some viewers would have seen the 3D side-by-side video for a few seconds before the MHEG application loaded and changed to the "2D view". There was also a small chance a 3D television could have detected the side-by-side video as 3D during this small time window, and switched into a 3D mode, just as the MHEG application switched to 2D resulting in a undesirable and confusing display (see Figure 3).

 

Figure 3: Screen capture of MHEG application in 2D mode on a 3D TV in 3D mode

Figure 3: Screen capture of MHEG application in 2D mode on a 3D TV in 3D mode

 

Figure 3: Screen capture of MHEG application in 2D mode on a 3D TV in 3D mode.

In summary, this MHEG application allowed viewers with a FreeviewHD or FreesatHD receivers without a 3D television to watch the film in 2D. The resultant 2D picture was not HD resolution, but was still much better than a standard definition picture. Using this technology may enable the BBC to broadcast 3D content, without the complications of scheduling a 2D simulcast or requiring an extra channel. However there are also some production issues with deriving 2D content from 3D, which also need to be considered.

The BBC is working with standard bodies and in cross-industry forums to help standardise the requirements related to 3D content in both current and future receivers.

 

Comments

  • Comment number 1.

    Is there still any serious research that takes this in a different direction, such as using a full HD resolution left image that is used by all receivers whether 2D or 3D and a lower bandwidth difference signal "hidden" within it to allow a receiver to generate the right eye image?
    I don't remember where I read about this possibility but it was a couple of years ago.

  • Comment number 2.

    I believe 3D TV is a dead end. I do not want to watch 3D TV, and I do not want to be forced to watch a further degraded HD broadcast to support this gimmick.

    Chris W

  • Comment number 3.

    I was stunned that the creators of 3D TV decided to halve the horizontal resolution. From experiments I did with autostereograms when they were in fashion in the 90s, something I realised very quickly was that horizontal resolution was critical because a single pixel of horizontal resolution maps to a large depth. Surely it would be much better to compress the images vertically rather than horizontally.

  • Comment number 4.

    I think it would be be better if it was full HD main view + a difference single, a bit like Blu-ray 3D (but obviously higher frame rate at full HD), where existing 2D players can still play the main view and the 3D ones can use both. This way, unlike the method used in the blog, it wouldn't cut the resolution in half for both 2D and 3D viewers.

  • Comment number 5.

    Excellent stuff. I chopped my active plasma in for an LED passive set - and have the recording of Streetdance 3D on my Sky PVR. It looks fantastic - active just wasn't for me! As menioned on Andy Quested's blogspot - will any previous tests be available to watch via iplayer at some stage.

    Looking forward to the Olympics (and maybe the Queen's Diamond Jubillee?? hint hint) in 3D...

    Any more tests planned before the summer?

  • Comment number 6.

    First things first. The BBC needs to sort out HD picture quality first. I endured the football on BBC HD last night and it was very poor compared with Sky Sports.

    The red button 3d method is definitly a very bad idea. The BBC's low definition 1440x1080 pictures are bad enough but lowering the definition even further is unacceptable. It is likely that programs broadcast in 3D are restricted to important events and so substandard 2D would be very unpopular. In addition this would not work on Sky boxes and so would not be any use to 50% of viewers.

    I would like to see the adoption of something like MVC used for Blu-ray discs. This is backward compatable with 2D sets and so 2D will be full resolution. It would need about a 50% increase in bitrate but that is a small price to pay.

  • Comment number 7.

    Is it such a big issue to give a dedicated 3d channel. Instead of squeezing it down a pipe and making other displays worse what stops the extra channel now bandwidth has increased. Big events can used BBCHD in 3d anyway and other items on bbc one hd, question is does the bbc think that 3d will generate enough requests or is it just a fad.

  • Comment number 8.

    Very pleased with the 3D footage that I've seen (Samsung 46 D8000 + Virgin TiVo). Why does BBC HD consistently look better than BBC One HD (even with the same show). I hope the BBC choose to keep BBC HD, it's excellent (as a viewer) to be part of some of the ground breaking work you do on the channel. It really shows that you have the best engineers working on this stuff. Keep up the great r&d.

  • Comment number 9.

    Could the left eye be broadcast on BBC One HD, and the right eye using the bandwidth from BBC HD, then it's just metadata needed to use them both for the BBC HD channel. I guess to do this, you'd have to drop the DOGs (good riddance I say ;))

  • Comment number 10.

    Has any one noticed on the BBC HD Channel, the Screen they put up while the Local news is on (white writing on a deep red background with the BBC link Videos on a loop) Looks 3D to the naked Eye??? (real depth - Even my other half commented) Is this something they are playing with or just some trick of the eye caused by the colour? (This was on a plasma screen) Going to watch it again tonight to see if it looks this way every time.

  • Comment number 11.

    2 Things, why does my screen show 2 pictures on 109 tennis when it is a 3d tele and nothing happens on the red button.?So I watch 3d upgrade on 108.
    Also, has anybody noticed the differnet vol. levels on BBC HD compared to the others, watch ITV at the norm and switch to BBC it blows you out. Cannot be the set as it is only on the BBC! Any ideas.

  • Comment number 12.

    I bought a 3D tv and the quality of HD is just stunning and 3d videos I have seen are also a treat to watch. I wish 3D tv was made a higher priority. I remember when the BBC was trialing steror braodcasts, my father had the radio on one side of the room and the tv on the other, and I remember how thrilled we were to hear stereo broadcasts for the first time. Come on BBC, there are plenty of 3d TV's on the market now.

  • Comment number 13.

    Having watched 3D in showrooms I remain unconvinced that it is a viewing experience to aspire to. And no I don't want HD channels degraded to accommodate 3D thank you.

 

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