Abstract

A video compression system comprises a pre-processing section, an encoder, and a post-processing section. The pre-processing section employs a median decimation filter which combines median filtering and decimation process. The preprocessing section also employs adaptive temporal filtering and content adaptive noise reduction filtering to provide images with proper smoothness and sharpness to match the encoder characteristics. The encoder employs a two pass look-ahead allocation rate buffer control scheme where the numbers of bits allocated and subsequently generated for each block may differ. In the first pass, the means square error for each block is estimated to determine the number of bits assigned to each block in a frame, In the second pass, the degree of compression is controlled as a function of the total number of bits generated for all the preceding blocks and the sum of the bits allocated to such preceding blocks. The DCT coefficients are vector coded by scanning the coefficients using three different scan paths, and the one providing the most compact path is chosen. Each scan vector is divided into eight zones and coded using variable length coding. An all vector module is employed to take advantage of the low rate coding. Background information is employed in addition to the previous frame for prediction to achieve better coding gain. The post-processing section filters block boundaries to remove blocking artifacts. Depending on the image characteristic (average quantization applied), different kinds of filtering is applied to enhance the images.

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