近年來，許多多媒體影像視訊諸如即時視訊會議、智慧型手機及網路視頻等等，皆致力於高解析度及高品質的發展，然而伴隨著高解析度而來的是龐大的資料量，使用HEVC(High Efficiency Video Coding)可以達到比H.264/AVC更好的壓縮率，其採用了四分樹(Quad-Tree)的編碼架構，在畫面內預測中，使用了35個預測模式來達到更精準的預測，然而為了增進編碼效能，需要計算編碼單元、預測單元(Prediction Unit , PU)及轉換單元(Transform Unit , TU)所有的組合，而編碼單元遞迴重覆地切割其深度更是造成極高的運算複雜度，因此本篇論文利用影像經由離散餘弦轉換(Discrete Cosine Transform , DCT)後在頻域上的特性提出了快速演算法：於編碼單元中，計算低頻交流值(Low- frequency AC components)來決策最佳大小，提前終止其深度的切割；於畫面內預測中，藉由DCT邊界特徵來判斷預測單元的邊界方向，篩選約略模式決策(Rough Mode Decision ,RMD)及RDO(Rate-Distortion Optimization)的候選模式個數。由實驗結果可知，我們所提出的演算法平均可節省41%的時間，並在視訊畫面上維持一定的品質。

In recent years, lots of multimedia video applications aim for higher resolution and quality, such as real-time video conference, smart phones, network video and etc. The higher resolution brings more bitrate. Using HEVC can achieve significant improvements in compression efficiency compared to H.264/AVC. In HEVC, there is a quadtree-based coding structure. To improve the coding efficiency of intra frame, the prediction mode is increased up to 35. However, it has to consider all the combination of coding unit (CU), prediction unit, and transform unit for the improving coding efficiency. The CU which recursively split into 4 CUs cause quite high computational complexity. Hence, in this thesis, we proposed a fast algorithm which employed the characters in frequency domain of image transformed by discrete cosine transform (DCT): In CU, calculate the Low- frequency AC components to determine the best CU size and early terminate the split of depth; in intra prediction, judge the edge orientation of PU and choose the candidate modes of rough mode decision and rate-distortion optimization by DCT edge features. The experimental results show that our proposed algorithm achieves 41% time saving on average without significant degradation of coding performance.

[1] “Generic coding of moving pictures and associated audio information,” ISO/IEC 13818-2: Video (MPEG-2), May 1996.
[2] “Video coding for low bit rate communication, version 1,” ITU-T recommendation H.263, 1995.
[3] “Coding of audio-visual objects - Part 2: Visual,” in ISO/IEC 14496-2 (MPEG-4 Visual Version 1), Apr. 1999.
[4] T. Wiegand, G. J. Sullivan, G. Bjontegaard and A. Luthra, “Overview of the 　 H.264/AVC video coding standard,” IEEE Transactions on Circuits and Systems for Video Technology, vol. 13, pp. 560-576, Jul. 2003.
[5] Mpeg Resource Share Project, available online at http://mpegsrc.ee.nctu.edu.tw/mpegTalk/MPEGstatus201204all.pdf
[6] JCT-VC, “High Efficiency Video Coding (HEVC) Test Model 6 Encoder Description,” JCTVC-H1002, JCT-VC Meeting, San Jose, Feb. 2012
[7] JCT-VC, “High Efficiency Video Coding (HEVC) Test Model 10 (HM10) Encoder Description,” JCTVC-L1002, JCT-VC Meeting, Geneva, Jan. 2013
[8] B. Bross, W. J. Han, J. R. Ohmn, G. J. Sullivan and T. Wiegand, “WD4: Working Draft 4 of High-Efficiency Video Coding,” JCTVC-F800, Torino, Italy, Jul. 2011.
[9] Jani Lainema, Frank Bossen, Woo-Jin Han, Junghye Min and Kemal Ugur, “Intra Coding of the HEVC Standard,” IEEE Transactions on Circuits and Systems for Video Technology, vol. 22, no. 12, pp. 1792-1801, Dec. 2012.

[10] Gary J. Sullivan, Jens-Rainer Ohm, Woo-Jin Han and Thomas Wiegand, “Overview of the High Efficiency Video Coding (HEVC) Standard,” Pre-publication Draft, To Appear in IEEE Trans. on Circuits and Systems for Video Technology, pp. 1-19, Dec. 2012.
[11] Yinyi Lin, Yu-Ming Lee and Chien-Da Wu, “Efficient Algorithm for H.264/AVC Intra Frame Video Coding,” IEEE Transactions on Circuits and Systems for Video Technology, vol. 20, no. 10, pp. 1367-1372, Oct. 2010.
[12] H. Kato, Y. Takishima and Y. Kaji, “Fast Intra Mode Decision Method for MPEG to H.264 Transcoding,” Proc. IEEE ICIP, pp. 833-836, Oct. 2006.
[13] Yilong Cheng, Guowei Teng, Xuli Shi and Huosheng Li, “A Fast Intra Prediction Algorithm for HEVC,” Proc. IFTC Communications in Computer and Information Science, vol. 331, pp. 292-298, 2012.
[14] Younhee Kim, DongSan Jun, Soon-heung Jung, Jin Soo Choi, and Jinwoong Kim, “A Fast Intra-Prediction Method in HEVC Using Rate-Distortion Estimation Based on Hadamard Transform,” ETRI Journal, Vol.35, No. 2, pp. 270-280, Apr. 2013.
[15] Wenqiang Zhao, Liquan Shen, Zhiming Cao and Zhaoyang Zhang1, “Texture and Correlation Based Fast Intra Prediction Algorithm for HEVC,” Proc. IFTC Communications in Computer and Information Science, vol. 331, pp. 284-291, 2012.
[16] Jongho Kim, Yoonsik Choe1 and Yong-Goo Kim, “Fast Coding Unit Size Decision Algorithm for Intra Coding in HEVC,” IEEE International Conference on Consumer Electronics, pp. 637-638, 2013.

[17] G. Bjontegarrd, “Calculation of average PSNR differences between RD curves,“ in ITU-T SC16/Q6 13th VCEG meeting, No.VCEG-M33, Austin, TX, Apr. 2001.
[18] Yu-Ming Lee, Yu-Ting Sun and Yinyi Lin, “SATD-Based Intra Mode Decision for H.264/AVC Video Coding,” IEEE Transactions on Circuits and Systems for Video Technology, vol. 20, no. 3, pp. 463-469, Mar. 2010.
[19] Liang Zhao, Li Zhang, Siwei Ma and Debin Zhao, “Fast Mode Decision Algorithm for Intra Prediction in HEVC,” IEEE Visual Communications and Image Processing, pp. 1-4, Nov. 2011.
[20] Daniel Palomino, Muhammad Shafique, Jorg Henkel, Luciano Agostini and Altamiro Susin, “A fast intra mode decision scheme for high efficiency video coding,” Proc. IEEE ICIP, 2013.
[21] Yongfei Zhang, Zhe Li and Bo Li, “Gradient-based Fast Decision for Intra
Prediction in HEVC,” IEEE Visual Communications and Image Processing, pp. 1-6, Nov.2012
[22] Thaisa L.da Silva, Luciano V. Agostini, Luis A. da Silva Cruz, “Fast HEVC Intra Prediction Mode Decision based on Edge Direction Information,” IEEE European Signal Processing Conference, pp. 1214- 1218, Aug. 2012.
[23] Michael Lee, Surya Nepal and Uma Srinivasan, “Role of Edge Detection in Video Semantics,” CSIRO Mathematical and Information Sciences, pp. Proc. VIP Conferences in Research and Practice in Information Technology, vol. 22, pp. 59-68, 2003.