As mentioned in the previous chapter, displacement vector measurement and its usage in motion compensation in interframe coding for a TV signal can be traced back to the 1970s. Netravali and Robbins (1979) developed a pel-recursive technique, which estimates the displacement vector for each pixel recursively from its neighboring pixels using an optimization method. Limb and Murphy (1975), Rocca and Zanoletti (1972), Cafforio and Rocca (1976), and Brofferio and Rocca (1977) developed techniques for the estimation of displacement vectors of a block of pixels. In the latter approach, an image is first segmented into areas with each having an approximately. | 11 Block Matching As mentioned in the previous chapter displacement vector measurement and its usage in motion compensation in interframe coding for a TV signal can be traced back to the 1970s. Netravali and Robbins 1979 developed a pel-recursive technique which estimates the displacement vector for each pixel recursively from its neighboring pixels using an optimization method. Limb and Murphy 1975 Rocca and Zanoletti 1972 Cafforio and Rocca 1976 and Brofferio and Rocca 1977 developed techniques for the estimation of displacement vectors of a block of pixels. In the latter approach an image is first segmented into areas with each having an approximately uniform translation. Then the motion vector is estimated for each area. The segmentation and motion estimation associated with these arbitrarily shaped blocks are very difficult. When there are multiple moving areas in images the situation becomes more challenging. In addition to motion vectors the shape information of these areas needs to be coded. Hence when moving areas have various complicated shapes both computational complexity and coding load will increase remarkably. In contrast the block matching technique which is the focus of this chapter is simple straightforward and yet very efficient. It has been by far the most popularly utilized motion estimation technique in video coding. In fact it has been adopted by all the international video coding standards ISO MPEG-1 and MPEG-2 and ITU and . These standards will be introduced in detail in Chapters 16 17 and 19 respectively. It is interesting to note that even nowadays with the tremendous advancements in multimedia engineering object-based and or content-based manipulation of audiovisual information is still very demanding particularly in audiovisual data storage retrieval and distribution. The applications include digital library video on demand audiovisual databases and so on. Therefore the coding of arbitrarily shaped objects has attracted great
