Theory and Practice of Temporal Scalability
نویسندگان
چکیده
This paper evaluates two temporally scalable video coding techniques, temporal subband coding (TSB) and predictive coding, both theoretically and in practice to provide comparisons of compression and visual quality at differing frame rates. An emphasis is placed on evaluating only the visual effects caused by the temporal coding technique rather than those introduced by any spatial coding. Results demonstrate that TSB coding has a higher coding gain at full frame rate than predictive coding if both algorithms use either no motion compensation (MC) or MC that can be modeled as an invertible pre-distortion of the video sequence. However, MC techniques often exploit local motion of many different regions in a scene, and therefore must contend with covered and uncovered regions. Often in TSB schemes using regional MC (e.g. block-based MC), these covered or uncovered regions are coded with “open-loop” prediction, instead of subband coding, to maintain the ability to fully reconstruct coded video. Since quantization errors are propagated in open-loop prediction, this is less efficient than “closed-loop” prediction used in motion compensated prediction (MCP) coding. Thus, MCP coding outperforms TSB coding at full frame rate with block-based MC for sequences containing regions being covered and uncovered, even if there are only a small number of these regions. In addition, visual results for lower-frame-rate video using TSB coding are unacceptable due to significant distortions from temporal filtering. These results are demonstrated through both mathematical evaluation of rate-distortion based coding gains and simulated coding of real video sequences.
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تاریخ انتشار 1997