螢幕內容編碼技術(SCC)是一個基於高效能視訊編碼技術(HEVC)的擴展標準。這個編碼標準 可以針對一些螢幕分享應用，諸如雲端遊戲、螢幕畫面分享、遠端桌面操作及無線顯示內容等， 提供更有效率的編碼壓縮方法。可調式色彩轉換(Adaptive Color Transform；ACT)是螢幕內容編 碼技術其中一項編碼工具，被用於冗餘值(residue)的色彩空間轉換，它能夠有效地降低色彩空間 組成之間的相關性， 並因此而提升編碼效果。然而，要評估目前這個編碼單元(coding unit)是否 該啟用ACT需要額外的碼率失真函數(rate-distortion optimization)計算， 因而花費大量的編碼時 間。我們將在本文裡介紹一個更有效率的ACT編碼流程，它藉由判斷目前這個編碼單元的尺寸大 小，來決定是不是要提前終止轉換單元(transform unit)的分割流程。根據實驗模擬結果顯示， 我 們提出的方法能夠在幾乎不犧牲編碼效益的情況下，最多縮短了8%的編碼時間。

Screen Content Coding(SCC) is an extension of High Efficiency Video Coding(HEVC). It targets to further improve the coding efficiency for the applications, such as cloud gaming, screen sharing, remote computer desktop control and wireless display of content . Adaptive color transform (ACT) is one of the new coding tools in SCC extension. ACT is a color space transform applied to residual data of a coding unit. It could effectively de-correlate color components of pixel samples and accordingly improve the resulting coding performance. However, when ACT is enabled, the encoder currently needs to perform additional rate-distortion checks which are extremely time-consuming. In this article, we propose an optimal ACT coding flow for SCC. The proposed methods can reduce the encoding complexity by early terminating the recursive transform unit(TU) splitting. The early termination is activated while the current CU size is greater than a pre-defined threshold. The experimental results show that the proposed methods can reach up to 8% encoding time saving with negligible coding gain loss.