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研究生:張至穎
研究生(外文):Chang, Ji-Ying
論文名稱:應用於動態影像壓縮的分類餘弦函式轉換動態補償編碼法
論文名稱(外文):Edge-Based Classified DCT With Quadtree For Image Sequence Coding
指導教授:張瑞峰張瑞峰引用關係
指導教授(外文):Chang, Ruey-Feng
學位類別:碩士
校院名稱:國立中正大學
系所名稱:資訊工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:1995
畢業學年度:83
語文別:英文
論文頁數:50
中文關鍵詞:動態影像壓縮動態補償編碼法
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  近年來,動態影像壓縮方法受到相當大的重視,其可以用來傳輸或儲存動態的影像。動態影像壓縮基本目的是希望降低傳輸或儲存所需要的位元率,同時更希望影像品質能夠不下降太多。動態影像是藉由減少空間及時間方向的重覆性,而達成壓縮之目的。一般靜態影像是藉由像素之間的關係達到壓縮的目的,而動態影像則可再利用相鄰畫面之關係提高壓縮效果。動態影像壓縮的應用範圍相當廣泛,如高畫質電視的傳播、視訊會議、視訊電話、視訊郵件、衛星影像傳輸、醫學影像、多媒體系統、電子出版業、及娛樂電影等。目前一般常見的動態影像壓縮方法,為了保持影像的品質,大部份壓縮率並不是相當高,亦及位元率仍不夠低,因此無法使用目前相當普及的電話線、行動電話或低速網路作為傳送即時動態影像的媒介,所以超低位元率動態影像壓縮(Very-low-Bit-Rate Image SequenceSequence Coding),正是目前工業界與學術介共同努力的目標。一般為了降低位元率,通常只使用較小128x128畫面,每秒則只有10張畫面,可作為視訊電話或視訊會議之用途。在本論文中,我們將研究超低位元率動態影像壓縮,所提出的方法將使用動態補補編碼法。傳統動態補償邊碼法,對每一個區塊都加以編碼而不論其與相鄰畫面所對應這區塊的差異量,顯得很沒效率,分類餘弦函式轉換動態補償邊碼法則在人眼無法辨識的情況下,捨去差異太小的區塊而不加以邊碼,並利用四元樹節構表示所有區塊的類別,使得資料量和編碼時間更加降低。同時為了提高畫質和壓縮率,更針對不同的edge來分類處理餘弦函式轉換所產生的係數和編碼,因此我們所提出的分類餘弦函式轉換動態補償邊碼法傳統的動態補償編碼法比較,我們所提出的方法在影像的畫質上和壓縮率均為最高。


  The motion compensated discrete cosine transform coding(MCDCT) is an efficient image sequence coding technique. The motion compensated technique can remove the temporal redundancy between the current frame and the previous reconstructed frame. The spatial redundancy of the motion compensated predicted errors can be removed using the discrete consine transform (DCT). For reducing the bit rate, we can classify the blocks into the moving or nonmoving. Only the moving blocks have to be encoded using the motion compensated DCT. That is, the motion vector and the predicted error for the moving blocks are transmitted to the decoder. The nonmoving blocks are not encoded and predicted by the same blocks in the previous frame. This method can be called the adaptive motion compensated discrete consine transform coding. (AMCDCT).
  In AMCDCT, each block needs one more bit for the moving information. Hence, we propose a new adaptive quadtree motion compensated discrete consine transform coding (AQMCDCT) to further reduce the bit rate. In our proposed AQMCDCT algorithm, the overhead information is encoded by a quadtree structure. Each leaf of the quadtree represents the moving information of a variable size block. As will to be shown, the improvement of AQMCDCT over the AMCDCT is up to 0.71 dB at nearly the same bit rate.
  Im order to further reduce the bit rate for the quantizied DCT coefficients and keep the visual quality, we propose an adaptive edge-based quadtree motion compensated desecrate cosine transform (AEBQMCDCT) By a 2-step selection scheme, the nonedge blocks will be encoded at lower bit rate but the edge blocks will be encoded at higher bit rate. Hence, the edge information is preserved and the image quality is improved. The edge information is not only used for classifying the edge blocks and the nonedge blocks, but also used for selecting the important DCT coefficients that will be encoded. That is, only part of the DCT coefficients, not all the DCT coefficient, is encoded to reduce the number of encoded DCT coefficients. The edge blocks will be further classified into four different classes according to the orientaion and location of the edges. Each class of edge blocks selects the different set of the DCT coefficients to be encoded. By this method, we can just preserve and encode a few DCT coefficients, but still maintain the visual quality of the images. In the proposed AEBQMCDCT image sequence coding scheme, the average bit rate of each frame is reduced to 0.072 bit/pixel and the average PSNR value is 32.11 dB.

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