There is a growing interest in using compressed video in a wide variety o f areas. Besides its use for communication over mobile networks, the main area where very low bit-rate video will be used in the years to come is assumed to be connected to the PC environment. For both applications, computational complexity w ill be a vital factor for their practical implementation. Hence, future research for these applications should be aimed for low complexity algorithms. Moreover, for mobile communication where bit errors in the transmission is a major problem, error resilient coding, which is currently being intensively investigated, is worth investigating.
A t the moment, much compression activity is taking place in MPEG4, a new video coding standard based on object-oriented concept. The coding structure is a merge between the segmentation-based scheme and the current block transform coding scheme. As a result o f being object oriented, coding the contour and texture o f arbitrary-shaped regions is necessary. Contour coding is a relatively mature area, several efficient coding methods exist. However, most o f them belong to the lossless approach which is unnecessary in lossy video coding for communication applications. Therefore, new techniques which result in lower bit-rate by allowing some distortion in the contours w ill be preferred. As for texture coding, a number o f techniques have been proposed but it is coded in very much the same way as in H.263 using DCT coding. A fairly computationally intensive padding technique [67] is used for padding
those blocks that contain the contour into a 8x8 block. Therefore, more effort can be spent on developing new techniques which are much simpler and efficient. Moreover, the motion estimation approach is only a small modification o f the block matching technique. Hence, future work should also include the design o f new techniques which allow interframe prediction o f the contour and texture information o f arbitrarily shaped regions in order to reduce the temporal redundancy.
On the other hand, the IT U group that developed H.263 have been collaborating closely with MPEG4 for the last two years. This led to the results o f additional functionalities being added to the core H.263. These functionalities, like the 4 optional modes described in section 3.7.4, are optional and their performance is sequence dependent. Further work in the direction o f mode selection strategy for achieving optimum performance is worthwhile.
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