A Novel Derived Mode for Block Partitioning Structure in Video Coding

In the exploration of the next video coding standard, the quadtree plus binary tree block structure (QTBT) has been adopted in the joint video exploration team. QTBT splits a block into sub-blocks following a structure of quadtree or binary tree. However, all the split modes of QTBT are symmetrical, which is less efficient in coding asymmetrical motion. In addition, the lower signaling efficiency of side information occurs when a successive binary split in the same direction is selected. Motivated by these observations, the derived mode (DM) based on QTBT is proposed in this letter, where six novel DMs are introduced. The DM further splits a QTBT node into several sub-blocks, and each sub-block can be predicted independently. Among the DMs, four asymmetrical split modes are introduced to improve the capability of coding asymmetrical motion, and two 4-split modes are designed to improve signaling efficiency. Moreover, higher efficiency than QTBT, a 0.99% BD-rate saving on average, is verified by extensive experiments.