Hash based fast local search for Intra Block Copy (IntraBC) mode in HEVC screen content coding

The Intra Block Copy (IntraBC) mode is a very efficient coding tool for the screen content coding (SCC) extension in High Efficiency Video Coding (HEVC) due to the frequently occurrences of repeating patterns and noiseless characteristics of screen content videos. There are local search and hash search for the IntraBC mode to increase coding efficiency. However, the IntraBC mode also brings along high computational complexity for SCC as exhaustive block matching is done within the same frame. Though there are already some constraints applied to IntraBC mode to reduce its complexity, it is still very high. To further reduce the complexity, we propose to speed up the local search by checking the hash values of both current block and block candidates. With our proposed methods, the encoding time is reduced by up to 25% and 23% for YUV and RGB sequences respectively while coding efficiency can still be maintained with only negligible bitrate increased.