Improvement of HEVC Inter-coding Mode Using Multiple Transforms

Multiple transforms have received considerable attention recently, especially in the course of an exploration conducted by MPEG and ITU toward the standardization of the next generation video compression algorithm. This joint team has developed a software, called the Joint Exploration Model (JEM) which outperforms by over 25% the HEVC standard. The transform step in JEM consists in Adaptive Multiple Transforms (AMT) and Non-Separable Secondary Transforms (NSST) which are designed and adapted to the intra-coding modes. In inter-coding, only the AMT is allowed and it is restricted to a single set of five transforms. In this paper, adaptive transforms schemes suitable for inter-predicted residuals are designed and proposed to improve the coding efficiency. Two configurations are evaluated for the proposed designs, providing an average bitrate saving of roughly 1% over HEVC with unchanged decoding time.