Shape-adaptive discrete wavelet transforms for arbitrarily shaped visual object coding

This paper presents a shape-adaptive wavelet coding technique for coding arbitrarily shaped still texture. This technique includes shape-adaptive discrete wavelet transforms (SA-DWTs) and extensions of zerotree entropy (ZTE) coding and embedded zerotree wavelet (EZW) coding. Shape-adaptive wavelet coding is needed for efficiently coding arbitrarily shaped visual objects, which is essential for object-oriented multimedia applications. The challenge is to achieve high coding efficiency while satisfying the functionality of representing arbitrarily shaped visual texture. One of the features of the SA-DWTs is that the number of coefficients after SA-DWTs is identical to the number of pixels in the original arbitrarily shaped visual object. Another feature of the SA-DWT is that the spatial correlation, locality properties of wavelet transforms, and self-similarity across subbands are well preserved in the SA-DWT. Also, for a rectangular region, the SA-DWT becomes identical to the conventional wavelet transforms. For the same reason, the extentions of ZTE and EZW to coding arbitrarily shaped visual objects carefully treat "don't care" nodes in the wavelet trees. Comparison of shape-adaptive wavelet coding with other coding schemes for arbitrarily shaped visual objects shows that shape-adaptive wavelet coding always achieves better coding efficiency than other schemes. One implementation of the shape-adaptive wavelet coding technique has been included in the new multimedia coding standard MPEG-4 for coding arbitrarily shaped still texture. Software implementation is also available.