In this work a novel image coding scheme and a generalized video codec are presented which is based on optimal filter design for subband coding. The proposed image coding scheme does not suffer from block artifacts which are prevalent in JPEG at higher compressions and achieves better compression, than the later. In this approach, an image is decomposed into subbands using an optimal filter in conjunction with generalized perfect reconstruction scheme so as to give flexibility to optimal filter design. The optimality of the subband coding scheme is formulated with subband entropy as the objective function. The subband entropy is represented as explicit function of the subband impulse filter response and optimum filter is derived by optimizing the objective function. The subbands are cod...[ Read more ]

In this work a novel image coding scheme and a generalized video codec are presented which is based on optimal filter design for subband coding. The proposed image coding scheme does not suffer from block artifacts which are prevalent in JPEG at higher compressions and achieves better compression, than the later. In this approach, an image is decomposed into subbands using an optimal filter in conjunction with generalized perfect reconstruction scheme so as to give flexibility to optimal filter design. The optimality of the subband coding scheme is formulated with subband entropy as the objective function. The subband entropy is represented as explicit function of the subband impulse filter response and optimum filter is derived by optimizing the objective function. The subbands are coded using vector quantization with varying bit strategy followed by lossless Lempel-Ziv (LZ77) coding. A significant compression ratio of 4O:l is achieved for gray scale images and 80: 1 for colored images.

The stages in the video codec originates by splitting the video frames into optimal subbands which is similar to the image compression scheme. Temporal information is explored by classifying the co-sited blocks of the subbands into temporal activity (TA) blocks or no temporal activity (NTA) blocks. The TA blocks are coded using vector quantization followed by Lempel-Ziv coding. The NTA-blocks (except in the anchor frame) are transmitted as a special signal. The designed video codec has great potential for several popular applications such as broadcast television, digital television and video telephones. Video codec experiments are performed for very low bit rate applications. A bit rate of 15.2 kbits per second at ten frames per second for QCIF format is obtained. Comparisons are made with other video coding methods, including the H.261 and MPEG standards.