Adaptive temporal decimation algorithm with dynamic time window

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Decimation approaches for image processing have been widely used for various applications. For video processing, decimation refers to sampling the frame rate in order to reduce the number of processing frames. Most of these temporal decimation methods discard whole frames; as a result, some high-speed motions could be completely eliminated while some redundant frames might remain in the processing frames. An adaptive temporal decimation approach has been successfully developed by Olstad (1993) to take both spatial and temporal information into consideration and is fully compatible with some existing discrete cosine transform (DCT)-based standards, such as MPEG and H.261. Moreover, it theoretically preserves all high activity motions and discards all low activity motions. However, we found that it is still not fully adaptive due to the confinement of the size of the time window. The discontinuity detection method is quite complex and, more importantly, the efficiency of coding block position maps is fairly low. We propose to resolve the problem of the time window by a dynamic time window approach. By using variable sizes of the time window, the optimal number of remaining frames could be produced. It also enhances the visual quality of the resulting video while the compression is comparable with the conventional approach. Based on our proposed algorithm, a simple but efficient quantization process has been used to replace the highly complex temporal discontinuity detection. The conventional adaptive temporal decimation algorithm operates on the basis of block sequences, but our dynamic approach which can retain all high activity blocks operates on the spatio-temporal domain. This approach can reduce redundant planes with slow activity and give higher precision for blocks with high activity. Experimental results show that the proposed algorithm achieves the optimal number of remaining frames.