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Historically. progress in image coding tecliniqnes has been made by incorporating resnits from other fields SUCh as information theory. Most of the existing coding methods such as predictive coding. transform coding, and vector quantization belong to information-theory-based methods in which image signals are considered as ranidoni signals aiid compressed by exploiting their stochastic properties. Apart from these iiiformation-tlieoretic coding iniethods, research on new approaches such as modelbased coding (which is related to 1)0th image analysis and computer graphics) has recently intensified. An essential difference between conventional coding methods and these new approaches is the image model they assume. Contrary to conventional coding methods which efficiently represent 2-D waveforms of image signals model-based co ding represent iniage signals using structural image models which take into accomit the 3-D properties of the scene in some sense. There have been two major approaches to model-based image coding. One approach uses general niodels such as planar patches and sniooth surfaces to represent the 3-D properties of the oI)jects [11, 19, 28. 31, 33. 36, 39. 40, 43]. The other approach utilizes detailed 1)arameterized 3-D object models such as a parameterized facial model [2. 6, 13. 15. 17, 22. 24. 2G. 32, 35. 41. 47, 48. 49. 51. 54]. TIne former approach has been discussed in the context of advanced motion compensation. The latter approach is clearly different from the conventional approaches. since it uses an explicit 3—D model and encodes images with coniputer—vision— Oiieiite(il tecliniques an(I 1eJ)1()(luces iniages with colnj)uter—grapllics—oriented techniques . Both approaches will potentially achieves very low l)it rate video compression. Iii the following sectionis. unage co(ling schemes are described froni the point of view of their associated image IIli)delS. Amoiig our works related to these paradignins in the Univ. of Tokyo [2. 3, 4. 8, 9, 10, 36, 41 42. 40]. 3-D model-based coding and 2-D deforniable triangle based niotion compensation are described.
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