A low bit rate hybrid coding scheme based on new classes of block overlap transforms

Summary form only given. An approach to the development of low-bit-rate video coding algorithms operating at rates below 2 Mb/s, for providing videophone/videoconferencing services over emerging ISDN networks, is reported. Two new classes of block overlap transform have been applied and their performances compared. A lapped orthogonal transform (LOT), which can also be viewed as an efficient quadrature mirror filter bank implementation in which analysis synthesis filters have identical finite impulse responses, has been applied. Although experimental results have shown a reduction in blocking effect, they have also shown an increase in the so-called mosquito effect (i.e. image degradation visible in the moving area of the picture). To reduce the latter effect and also implementation complexity, a new block overlap transform with short overlap (e.g. typically one to two adjacent pixels) has been applied. This is a simple nonorthogonal transform that uses discrete-cosine transform basis functions in combination with appropriately designed window functions