基於影像於網路或無線通訊傳輸的需求，在有限的頻寬條件下我們希望能使壓縮後影像資料串流大小能符合頻寬的限制，同時又期望影像品質能夠達到最佳的水準，因此在視訊壓縮系統中加入位元率控制機制是必要的。在本論文中提出一種基於餘弦轉換量化係數的模型，此模型可在編碼時根據不同的DCT係數進行調整，提供較為精確的位元估測。經由此位元率控制模型，我們可從已限制位元率條件下輕易的得到量化參數大小。本方法實現於MPEG-4簡易版，實驗結果顯示本方法在位元率控制或是影像品質方面，都能同時達到不錯的水準。

Due to the requirement of video transmission in Internet or wireless, in the condition of limited bandwidth, we anticipate that not only the compressed bitstream size could fit with the channel bandwidth, but also the video frames could reach the optimal quality in the finite bandwidth. For the sake of achieving this goal, we have to add the rate control mechanism in the video compression system inevitably. In this thesis, we propose a model, which is based on the indices of quantized DCT coefficients. The proposed model, adjusting the during encoding processing which relies on the different DCT indices, provides more precise rate estimation than the traditional approaches. Based on the model of the proposed rate control, the quantization parameter size can be easily obtained from a given bit-rate constraint. Realized in MPEG-4 Simple Profile, the simulation results show that the proposed algorithm achieves superior rate control ability and improves PSNR of the reconstructed video signal at the same time.

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