Joint wavelet packets for groups of frames in MCTF

Wavelet packets provide a flexible representation of data, which has been proved to be very useful in a lot of applications in signal, image and video processing. In particular, in image and video coding, their ability to best capture the input content features can be exploited by designing appropriate optimization criteria. In this paper, we introduce joint wavelet packets for groups of frames, allowing to provide a unique best basis representation for several frames and not one basis per frame, as classically done. Two main advantages are expected from this joint representation. On the one hand, bitrate is spared, since a single tree description is sent instead of 31 per group of frames (GOP) - when a GOP contains, for example, 32 frames. On the other hand, this common description can characterize the spatio-temporal features of the given video GOP and this way can be exploited as a valuable feature for video classification and video database searching. A second contribution of the paper is to provide insight into the modifications necessary in the best basis algorithm (BBA) in order to cope with biorthogonal decompositions. A computationally efficient algorithm is deduced for an entropy-based criterion.