An SSIM-motivated LCU-level rate control algorithm for HEVC

The rate control model used in the HEVC reference software HM10.0 is a R-λ model. In this model the distortion is measured by Mean Squared Error (MSE) and Sum of Absolute Difference(SAD). However, MSE and SAD are not correlated well with perceptual image quality. In this paper, we propose an improved LCU-level rate control algorithm based on the structural similarity (SSIM) index which was proved to be a better indicator of perceived image quality than MSE. What's more, we use the the structural similarity index to decide the weight of LCU-level bit allocation in the R-λ model and incorporate it to the rate-distortion optimization. Experiments show that the proposed scheme can achieve significant gain in terms of rate-SSIM performance and better subjective quality when compared with HEVC.