Joint Optimization for SSIM-Based CTU-Level Bit Allocation and Rate Distortion Optimization
Yang Li, Xuanqin Mou · IEEE Transactions on Broadcasting · 2021
Structural similarity (SSIM)-based distortion DSSIMis more consistent with human perception than the traditional mean squared error DMSE. To achieve better video encoding quality, many studies on optimal bit allocation (OBA) used DSSIMas the distortion metric. However, the MSE-based rate distortion optimization (RDO) was still used in these studies. The inconsistency between the optimization goals of OBA and RDO results in a non-optimal SSIM-based encoding performance. To solve this problem, we propose an accurate coding tree unit level DSSIM-DMSEmodel, which enables performing the SSIM-based RDO with simpler R-DMSEcost scaled by the SSIM-based Lagrangian parameter λSSIM. Moreover, based on this model, the R-DSSIMmodel can be accurately estimated based on the joint relationship of R-DSSIM-λSSIM. With the accurate R-DSSIMmodel, the SSIM-based OBA problem is then solved. Accordingly, the SSIM-based OBA and SSIM-based RDO are unified together in our scheme, called SOSR. Compared with the HEVC reference encoder HM16.20, SOSR saves 5%, 11%, and 17% bitrate under the same SSIM in the commonly used all-intra, hierarchical and non-hierarchical low-delay-B configurations, which is superior to existing state-of-the-art SSIM-based OBA schemes.