8.2  Key issues and open questions

Though the research in multi-view acquisition and compression is expanding continuously, a number of key issues still needs to be addressed.

First, in order to gain acceptance of the 3D multi-view video technology in the motion picture or consumer electronics industry, simple acquisition systems should be easily accessible and ready for use. Specifically, comparing the simplicity of acquiring monocular video against the difficulty of acquiring multi-view video, it can be readily understood that there is a large complexity difference between monocular and multi-view video technology. For example, acquiring multi-view video data requires an acquisition setup composed of multiple synchronized cameras. Also, to obtain a high-quality image, the color of the multiple cameras should be calibrated, so that the multiple images show consistent colors across the views. Additionally, to enable the usage of specific features, e.g., free navigation within the scene (as discussed in Section 4.1.2), the multi-view acquisition setup should be calibrated such that the positions and orientations of all cameras are known. Finally, a high-performance system enabling the simultaneous recording of multiple input video streams, is necessary. From this discussion, it can be noticed that setting up a multi-view acquisition system requires scientific expertise and hands-on experience. Presently, this forms a high entry barrier for potential users, and thus a reduced acceptance of the multi-view technology. More generally, the problem of working on multi-view video is that it affects the complete communication chain, from acquisition through coding and to rendering. This is clearly more complicated than introducing a new compression standard such as MPEG-1 or MPEG-2.

A second issue is related to the estimation of depth data that is necessary for rendering high-quality synthetic images. As discussed in Chapter 3, depth image estimation is an ill-posed problem in many situations. Currently, the problem of depth estimation remains an open research topic for which no generic and very robust solution has emerged yet.

A final issue is the uncertainty related to the value of the potential applications of multi-view video technologies. Currently, it is not known how much value such a technology would bring to entertainment or advertisement applications. It is fairly evident that it will enhance the video production technology and improve the quality of professional video presentations, such as in the industrial design and medical system areas.