適用於無線連結系統之混合策略多層次視訊編碼演算法及架構設計

多樣化的消費性電子產品造就了前所未有的數位多媒體家庭影音整合式應用，以播放裝置為例，可攜式多媒體播放器、平面顯示器，甚至是單槍投影機都是新一代的顯示裝置。然而，若是這樣多樣化的裝置能夠連結於無線系統，必定能帶給使用者極大的便利性。無線連結系統近年來急速發展，但是在傳輸頻寬方面，仍與有線連結傳輸有一段相當大的差距。而且，基於使用者追求高畫質視訊的概念，使得視訊傳輸壓縮必須要使用無失真的方法。因此，若要在無線連結系統下進行視訊傳輸，使用無失真編碼/解碼器是無可避免的。一個應用於無線連結系統的視訊編碼必須含有下面幾項特點：其一，此編碼必須有極低的延遲時間，才可以在即時視訊傳輸上避免使用者感知的延遲；其二，此編碼必須有較高的錯誤抵抗能力以處理傳輸所造成的資料錯誤；再者，以目前常用規格而言，一個全像素，即1920×1080，每秒60張的視訊資料，若要以無線USB(480bps)傳輸的話，則此視訊編碼必須提供五至十倍的壓縮倍率。本論文提出了一個採用混合策略的多層次編碼器，其中含有三個主要的單元：辨識單元(classify unit)、內部預測單元(intra unit)、以及無失真編碼單元(JLS unit)。辨識單元能夠將視訊來源影像分解成兩部分，分別為自然影像以及人工介面，此辨識可以預先決定模式而不用等最後才決定，預先決定模式可以將分類的區域獲得更好的壓縮效率；內部預測單元以近乎無失真壓縮方式處理自然影像區域；無失真編碼單元則處理人工介面區域，這兩個單元處理後的輸出為基礎層位元流(base-layer bitstream)；此外，原本自然影像區域與重建自然影像區域的差值將會經過無失真編碼單元再次處理，形成強化層位元流(enhancement-layer bitstream)。本論文提出的多層次辨識概念是基於一個假設，即多樣化的輸入視訊多為包含自然區域及人工介面的複合式影像，這個假設可使辨識後的影像區域得到較佳的處理已達到高壓縮效率；另外，採用混合策略編碼實現了一個適合的位元流，可以有彈性的適應於無線連結頻寬多變動，即若當無線頻寬足夠時，基礎層和強化層都將接收並且解壓縮還原成一個無失真的影像，否則就單解壓縮基礎層還原成一個近乎無失真的影像；此外，為了避免大量的錯誤擴散，使編碼器不使用時間資訊做預測，同時也可以降低運算複雜度及時間延遲。我們將此編碼器實現成晶片，原型晶片利用聯電90奈米技術製程，面積為2.4×2.2mm2`，其工作頻率為216MHz，處理速度為每秒124MSamples/sec，最大支援規格為1920×1080每秒60張影像。

關鍵字

無線視訊系統；無失真壓縮；多層次

並列摘要

Variant consuming electronic products make the home digital multimedia integrations very different from the past. For Example, a display device might be a portable handout, a flat panel, or a projector. It must be much more convenient if these devices are linked in a wireless system. Wireless system has developed for years but still exists a large gap to the wire linkage, especially in bandwidth variation. Furthermore, the desire of enjoy high definition video quality makes the video raw data cannot be compression in lossy way. As the result, it is inevitable to encode the video raw data in a wireless link system. A video coding for wireless link system has some particular requirements as following. It requires low latency for real-time applications. Besides, it concerns more error robustness for wireless transmission noise. Moreover, if the Full-HD(1080p) 60fps video source would like to transmission in a wireless-USB(480Mbps), the video coding must provide a 5-10 times compression ratio. In this thesis, a multi-layer encoder with hybrid scheme is proposed. In this encoder, there are three main units, which are classify unit, intra unit, and JLS unit. The classify unit can decompose the video source frame into two layers which are natural picture layer and graphic interface layer. This can cause a previous mode decision instead of a latter one, and processing each layers in different scheme. The intra unit is near-lossless intra prediction core. It is used to encode the natural picture region , and reconstruct a near-lossless region. The JLS unit is used to encode the graphic interface region with the lossless JPEG-LS algorithm. These near-lossless natural region and graphic interface region are the base-layer bitstream of the proposed encoder. Besides, the difference of the origin natural picture region and the reconstructed one is sent to JLS unit to encode again as a enhancement-layer bitstream. The multi-layer classification is based on the assumption of the video source is usually a compound frame consisting of natural picture and graphic user interface. This assumption causes the video raw data could be compressed more efficiently. The hybrid scheme coding realizes a flexibility of adaptive bitstream for wireless bandwidth variations. The decoder can choose to decode both base-layer and enhancement-layer bitstream to reconstruct a lossless frame while the bandwidth is unlimited. It can also choose and decode only the base-layer bitstream to reconstruct a near-lossless frame in low bandwidth environment. To prevent temporal error propagations, the proposed encoder dose not use inter prediction. Besides, this can also reduce the computation complexity and latency. The proposed multi-layer encoder with hybrid scheme is implemented in this thesis. The prototype chip is fabricated using UMC 90um technology, and the chip size is 2.4×2.2mm2. The design working frequency is 216MHz, and the processing capability of the chip is 124MSamples/sec. The max specification of video processing is 1920×1080 60Hz.

並列關鍵字

wireless video system ； lossless coding ； multi-layer

參考文獻

[1] T C. Chen, S. Y. Chien, Y.W. Huang, C. H. Tsai, C. Y. Chen, T.W. Chen, and

L. G. Chen, “Analysis and architecture design of an HDTV720p 30 frames/s

H.264/AVC encoder,” in IEEE Transactions on Circuits and Systems for

[4] X. Wu and N. Memon, “Context-based, adaptive, lossless image coding,”

IEEE Transactions Communications, vol. 45, no. 4, pp. 437–444, Apr. 1997.

國際替代計量

適用於無線連結系統之混合策略多層次視訊編碼演算法及架構設計

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