Palette Mode Coding in HEVC Screen Content Coding Extension

Palette mode is a new coding tool included in the HEVC screen content coding extension (SCC) to improve the coding efficiency for screen contents such as computer generated video with substantial amount of text and graphics. It is observed that a local area in screen content typically has a few colors separated by sharp edges. To exploit such characteristics, palette mode represents samples in a block with indexes pointing to the color entries in a palette table. This paper provides a detailed overview of the palette mode in HEVC SCC in terms of palette generation, coding of the palette, and coding of the palette indexes for the samples in the palette block. Several improvements to palette mode coding, which have been proposed but not included in HEVC SCC, are also described. Simulation results are presented to quantify the bitrate savings provided by the palette mode for equal distortions.