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>> European satellite broadcasters we are working with are already using this cropping rectangle feature to distribute backward-compatible 3D content, and by using the bandwidth for a single HD video stream they are reaching both audiences. The terrestrial broadcasters experiencing the format, such as Quartarete in Italy, are using it to mix 2D and 3D on the same channel – some 3D and some 2D is mixed in the schedule seamlessly, with users only noticing the start of a 3D content if they are equipped with a 3D decoder: others simply see 2D at all times. What else does the 3D Tile Format offer? Besides the save of bandwidth another advantage of the 3D Tile Format is the improved resolution. With the Side- by-side and Top-and-bottom methods, you have to reduce the resolution of the video either horizontally or vertically in order to squeeze the two into a single HD frame. The 3D Tile Format uses a different approach, composing two 720p frames (left and right) in a 1080p container. This does not require any loss of resolution because the area of the 1080p container is higher than the sum of the two component 720p video frames. The format only requires one of the images to be sliced into parts and this is reconstructed by the 3D decoder to make the left or right frame, while 2D decoders may discard it and use one of the frames for an HD 2D image. The key quality difference is that no information is lost in composing the packed format, so to reconstruct the 3D image, no re-creation of pixels is required – unlike in the other formats where half of the pixels have to be recreated, either by interpolation of extra pixels, or by scaling the size of the existing pixels, making rectangular pixels from the square originals. This technique introduces a lot of artifacts into the image and leads to a degraded picture quality. The DVB Project is already working on the specification for the second phase of 3D broadcasting because many of the broadcasters transmitting 3D are not happy with current quality and are willing to adopt a better method for the next phase of the standard. The 3D Tile Format is one of the candidates for this new phase. There are others, such as MVC (multi-view video coding), the principles for which are included in an annex to the H264 specification. There is a drawback to this technology, in that MVC is able to encode the two views with full HD quality but broadcasters would have to carry two independent video streams across the production infrastructure, which is difficult for current broadcasters because of the use of so-called ‘single-wire infrastructure’. MVC would require doubling of the existing production and contribution infrastructure, which of course would entail a huge investment. Another approach may be the ‘frame- compatible compatible’ approach, currently under study by the MPEG consortium. The idea here is to use the existing frame-compatible formats as a base layer and then to encode several enhancement layers, so that existing decoders receive plain side-by-side, but new encoders will be able to detect and use the enhancement layers to make up the full HD resolution of the image. As with MVC, however, there is at least one major drawback: at this point there is no encoding ASK OUR EXPERTS 38 | TV-BAY MAGAZINE standard efficient enough to make this approach feasible within the existing broadcast structures – you end up with a bitrate comparable with simulcasting two independent views. So it’s not attractive to broadcasters unless a new generation of encoding technology is developed to make it more efficient. (this also applies to MVC – it’s not that efficient). MPEG is already working on next generation encoding standards that will outperform current standard by 40 percent, but until this is available broadcasters are unlikely to adopt either standard. Therefore the 3D Tile Format allows broadcasters to use their existing infrastructure, but delivers a better quality image. It’s therefore a good compromise that will allow the 3D broadcast market to grow organically, without requiring a lot of speculative investment up-front. How and where is a new format likely to be adopted? The idea of adapting broadcast technology for 3D originated at least 30 years ago, with the innovator Lenny Lipton laying the theoretical foundations in the 1980. These ideas become the current de facto standards of Side-by-side and Top-and-bottom. In recent years, the development of large LCD and plasma screens with fast refresh rates is the key enabler for 3D content distribution, allowing the presentation of the alternating frames at speeds fast enough to avoid causing flicker or other unpleasant effects. This has made 3D broadcasting feasible. The formats proposed in the 1980s were a practical solution, but not good enough to provide an acceptable image quality to the viewers used to HD. There are also non-broadcast applications for the format. The 3D Tile Format is neutral in respect of networking technologies used for distribution, so it’s also applicable for VOD or distribution over IP networks. 3D content for portable gaming consoles is another market we are discussing with manufacturers. One possible area of development for the future would be to allow the viewer to moderate the ‘strength’ of the 3D effect; some users find that 3D causes them headaches, and would feel more comfortable ‘dialing down’ the perceived amount of 3D. Enabling this feature would require some extra depth maps carried to the encoder together with video content, and with the 3D Tile Format, the black part of the frame could be used to carry this type of information. POST YOUR QUESTION ONLINE: Search ‘tvbay’ Tel. +44 (0)1635 237 237 Email. questions@tv-bay.com