電腦已進入家庭成為人類生活的中視聽娛樂的一部分，但是，信息數據越來越複雜和所需硬碟空間也越來越大，再加上影像、視訊、聲音等資料的儲存需求也日益提升，儘管儲存空間一直成長，再龐大的硬碟空間也有不敷使用的一天。因此，隨著近年來科技的進步和網路蓬勃的發展，所有的資訊都變成非常龐大若能壓縮變小就更利於網路傳遞，影像壓縮的研究也是如此。
H.265/HEVC是目前制定的最新的影像壓縮標準，與其他標準比較，H.265/HEVC 提供了較高的壓縮效率，但是H.265/HEVC 的複雜度也相對較高。在H.265/HEVC之快速畫面內編碼，提供最高35個畫面內模式(Intra Coding)與較大的編碼單元來實現，其最佳的選擇模式方法，首先從所有可用的模式中，藉由粗糙的選擇方式做選擇，然後透過位元率失真的方式做最後的決定。在H.265/HEVC畫面內模式選擇過程中使用所有可能的深度層級和預測模式，以找到一個最小的位元率失真代價。這實現了最高的編碼編碼效率，但是需要非常高的計算複雜度，為了減輕編碼的計算量，我們在H.265/HEVC畫面內編碼中，提出了一個快速選擇的演算法。
相較於HEVC測試的模型HM 12.0編碼方案，實驗結果可以看出，提出的演算法，大約減少平均42.337%的時間，伴隨著一些BD-rate的增加和微乎其微的BD-PSNR的減少。

The computers have entered family become a part of human life. However, information data are getting complex and the storage space needed is getting larger, too. The need for image, video and audio is also increasing. Although the storage space is growing, one day it will not be enough. Therefore, in the recent years the development of technology makes all information be compressed for faster transmission through internet, so as the research of video compression.
H.265/HEVC is the latest standard of video compression. Comparing the other standards, it provides higher efficiency of video compression. However the complexity of H.265/HEVC is higher. In the intra prediction of H.265/HEVC, this is achieved by providing up to 35 intra modes with larger coding unit. The optimal mode is selected by a rough mode decision (RMD) process from all of the available modes first and then through the rate-distortion optimization (RDO) process for the final decision. The intra mode decision process in H.265/HEVC is performed by using all the possible depth levels and prediction modes to find the one with the least rate distortion (RD) cost. This achieves the highest coding efficiency but requires a very high computational complexity. To alleviate the encoder computation load, we propose a fast decision algorithm for HEVC intra coding.
Comparing with the default encoding scheme in HEVC test model HM 12.0, experimental results show that the proposed method provides almost 42.337% time savings in all intra setting on average, with a little increase in the BD-rate and a negligible reduction in BD-PSNR values.

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