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In this paper, we propose a coding tree unit (CTU)-level rate control scheme from the perspective of SSIM-based rate-distortion optimization to improve the coding efficiency. First, we establish the SSIM-based rate-distortion model based on the divisive normalization scheme, which characterizes the relationship between the local visual quality and the coding bits. Then, the established model is applied to the CTU-level rate control and transformed into a global optimization problem solved by convex optimization. Finally, a new model parameter updating strategy for the CTU-level rate control is presented that is robust to scene variations. Our algorithm can achieve optimal CTU-level bit allocation given the bit-rate budget. The experimental results show that our algorithm substantially enhances the coding performance and consistently outperforms both the rate control scheme in the HEVC reference software and existing algorithms in terms of rate-perceptual distortion performance using different test configurations. [ABSTRACT FROM AUTHOR]

Different from the conventional calculative methods, a learning-based initial quantization parameter (LIQP) method is proposed in this paper to improve rate control of high efficiency video coding (H.265). First, the framework for initial quantization parameter (QP) learning is proposed, where a novel equivalent approach to build the benchmark labels is proposed using the single rate-distortion (R-D) pair in each initial QP testing. With the criterion of maximizing the prediction accuracy of initial QPs, features and parameters of the learning model are refined. Instead of the traditionally used target bits per pixel (bpp) for intraframe, the target bpp for all remaining frames is proposed to avoid the empirical setting on intracoding bits, and thus the related inaccuracy can be prevented. We clearly present the motivations of the proposed LIQP method, as well as the reasons for the extracted features and model parameters. The proposed LIQP method outperforms the latest HM-16.14 by achieving significant gains on R-D performance (−15.48% BD-BR and 0.782 dB BD-PSNR gains), quality smoothness (1.581 dB versus 2.598 dB), and more stable buffer occupancy control, with similar high bit rate accuracy (99.84% versus 99.87%), and can also work well for scene change cases. [ABSTRACT FROM AUTHOR]