Intra-Prediction Mode Propagation for Video Coding

Intra-prediction and inter-prediction are two major ways of prediction in video coding. In the state-of-the-art video coding schemes such as joint exploration model (JEM), these two kinds of prediction are performed independently as different modes. An inter-coded coding unit (CU) is only assigned with the motion information, without an intra-prediction mode (IPM). To capture the texture direction in an inter-coded CU with low complexity, we present an IPM propagation approach in this paper. In the proposed scheme, each $4\times 4$ sub-block in an inter-coded CU is assigned with a propagated IPM, which is fetched from a reference block, located by a motion vector. The propagated IPM is utilized in two aspects. First, the propagated IPM can help to perform inter–intra-prediction in the inter-coded CU. Inter-prediction controlled by the motion information and intra-prediction controlled by the propagated IPM are both performed. The final prediction is generated by a position-dependent weighted sum of the two kinds of prediction. Second, the propagated IPMs of neighboring inter-coded blocks can help to predict the IPM of the intra-coded CU in an inter-picture. The propagated IPM of an inter-coded neighboring block can also be treated as a most probable mode. Simulation results show that BD rate savings of 0.5%, 1.0%, and 1.0% on average for Y, Cb, and Cr components, respectively, are achieved in random access configurations under the common test condition, compared with JEM-7.1. On ultra-high definition sequences, the BD rate savings can reach 1.0%, 1.7%, and 2.3% for Y, Cb, and Cr components, respectively.