On prediction techniques for palette coding

Screen content video coding is becoming increasingly important in various applications, such as desktop sharing, video conferencing, and remote education. In January 2014, the ITU-T and ISO/IEC MPEG jointly issued call for proposals for screen content coding as an extension of HEVC. In general, compared to natural camera-captured video content, screen content has different characteristics, e.g., sharper edges, and fewer unique colors on a block-by-block basis. Palette coding for screen content has been recently proposed in the ongoing HEVC Range Extensions standardization. Palette coding utilizes the fact that there are few unique colors in screen content video blocks, and tries to send palettes of these unique colors. However, the size of these palettes can expand, especially in highresolution video. Therefore, to reduce the overall bits for palette transmission, we present various palette prediction techniques in this paper. We first analyze the characteristics of palettes in screen content, and then propose various palette prediction techniques. Our experiments on HEVC test sequences in state-of-the-art HM range extensions software for HEVC show significant improvements over palette coding without any prediction, at almost negligible additional complexity.