建構於 H.264 無損幀內編碼的變動長度編碼法

Abstract

視窗內容係指經由電腦或者其他數位裝置所產生之圖像與影音，其實際應用的例子有: 遠端桌面、桌面分享、視訊會議以及遠端教學等等。這些視窗內容通常都包含了大量的文字與圖示部分，然而這些部分並不適合利用當前的圖像壓縮規格以及H.264/AVC中的幀內編碼方式進行壓縮。

因此，於本篇論文中我們針對視窗內容中的文字部分，提出一個新的變動長度編碼用於H.264/AVC無失真幀內編碼中。我們利用文字區塊之特性，基於適應性變動長度編碼法而設計新的無失真編碼方法，並且利用位元率失真最佳化決定區塊壓縮的模式。實驗結果顯示提出之方法相較於H.264/AVC編碼方式不僅能夠降低編碼位元率，並且能夠增進編碼效率以及視覺品質。

Screen content image and video were generated by computer or other digital devices in the real applications such as remote desktop, desktop sharing, video conferencing, and remote education. However, screen content normally contains numerous texts and graphic part which are not appropriate to be encoded by the state-of-the-art image compression standards and intra frame coding in H.264/advanced video coding (AVC).

Therefore, in this paper we proposed a new variable length coding in H.264/AVC lossless intra-coding for text part in screen content images or videos. We utilize the characteristics of text blocks to design the new lossless coding method based on context adaptive variable length coding (CAVLC), and determine the block compression mode by rate-distortion optimization (RDO) selector. Experiment results show that, compared to H.264/AVC coding, the proposed method not only reduce the coding bitrates, but also enhance the coding efficiency and visual quality on text content.