Rate-scalable object-based wavelet codec with implicit shape coding

In this paper, we present an embedded approach for coding image regions wit h arbitrary shapes. Our scheme takes a different approach by separating the objects in the transform domain instead of the image domain so that only o ne transform for the entire image is required. We define a new shape-adapti ve embedded zerotree wavelet coding (SA-EZW) technique for encoding the coe fficients corresponding to specific objects in gray-scale and color-image s egments by implicitly representing their shapes, thereby forgoing the need for separately coding the region boundary, At our decoder, the shape inform ation can be recovered without separate and explicit shape coding. The impl icit shape coding enables the bit stream for the object to be fully rate sc alable, since no explicit bit allocation is needed for the object shape. Th is makes it particularly suitable when content-based functionalities are de sired in situations where the user bit rate is constrained and enables prec ise bit-rate control while avoiding the problem of contour coding. We show that our algorithm sufficiently addresses the issue of content-based scalab ility and improved coding efficiency when compared with the "chroma keying" technique, an implicit shape-coding technique which is adopted by the curr ent MPEG-4 standard.