Fast HEVC screen content coding by skipping unnecessary checking of intra block copy mode based on CU activity and gradient

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) by finding the repeating patterns within the same frame. Yet, it also brings along impractically high computational complexity for SCC, which can be a double of the conventional HEVC, as exhaustive block matching is done within the same frame even though there are already some constraints applied to the IntraBC mode. To reduce the complexity, we propose to skip the unnecessary IntraBC mode checking based on the activity and gradient within the coding unit (CU). With our proposed methods, the increased encoding time compared with the conventional HEVC is reduced from 90.0% to 62.2% on average while the coding efficiency can still be maintained with only negligible bitrate increased.