PU level intra block copying with flipping mode

With the development of HEVC Screen Content Coding (SCC) extension, intra block copying (IntraBC) mode have been proven to be a very efficient tool in coding of typical screen content video materials. Currently, the decision of IntraBC usage is on coding unit (or CU) level. The coding modes for all the possible partitions inside a CU should be the same. If a CU contains pixels of different objects, the whole block may not be coded efficiently in either inter mode or IntraBC mode. Also, sometimes there are some structural similarity between the current block and the one in the reconstructed area of the same picture, but the textual orientation is just in opposite direction. In this paper, two new methods are proposed to improve the IntraBC mode. The first one is PU level IntraBC decision, which allows a CU to be partitioned into combination of IntraBC coded PU and inter coded PU. The other one is the flipping mode for IntraBC, where the reference block is actually mirrored before doing compensation. Simulation results show that the proposed methods can bring noticeable coding gains on top of the current IntraBC design.