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Abstract

In a low bit-rate video coder which processes the pels in each video frame on a block-by-block basis using a hybrid differential pulse code modulation and discrete cosine transformation as defined in CCITT Recommendation H.261, the blocks are processed in a sequential order, which in areas of high activity may cause the output buffer to approach its capacity level. In response, the adjoining blocks are more coarsely quantized with resultant image degradation. Improved coding performance is achieved by processing the blocks in a pseudo-random order which disperses the high activity blocks among the more quiescent blocks. As a result the buffer is less likely to reach its maximum capacity, and the quantization levels will remain essentially constant throughout coding of the frame, thereby improving image quality.

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