The performance of a hybrid videoconferencing coder using displacement estimation in the transform domain

In this paper we extend the transform domain oriented estimation algorithm introduced in [1] in which the calculation of the displacement vector was obtained from the transform domain coefficients. The performance of the algorithm is verified within a hybrid coding configuration. In this paper only transform domain block matching algorithms are considered. The block-match procedure makes use of the displacement matrix H defined in [1]. A matrix decomposition method is described in order to show that a practical implementation is very well possible. The properties of the translation invariant matrices are explained by using the ordered Walsh Hadamard transform as an example. The procedure however enables the use any other orthogonal transform. An important issue with respect to the hardware complexity of this motion compensated hybrid coder is the use of only one transform. The performance of the proposed new algorithm is shown and a video tape containing a very critical videoconferencing scene (i.e. split screen and a hard switch to full screen with heavy motion) will be presented. The sequences are coded at a bitrate of 384 kbit/s and 64 kbit/s respectively. Results of the compensation in the pixel domain and in the transform domain are compared and it is shown that the latter approach results in an improved performance of the estimation procedure.