A CNN-Based Post-Processing Algorithm for Video Coding Efficiency Improvement

Lossy compression algorithms are widely used in video coding. However, lossy compressed videos exist some annoying distortion and artifacts, such as blocking, blurring, and ringing. Thus, coding efficiency improvement is a steady-state topic in the domain of video coding. High Efficiency Video Coding (HEVC), a recent video standard, adopts two in-loop filters for the improvement of the coding efficiency, including deblocking (DB) and sample adaptive offset (SAO). In a certain extent, traditional in-loop filters reduce the distortion and improve the video quality. But the reduction of the distortion is a nonlinear problem that is difficult to be solved by traditional linear filters. Recently, the progress of deep learning shows the possibility to settle the complex problems in the computer vision field. Meanwhile, according to the compressive sensing theory, the post-processing method at the decoder end can further enhance the coding efficiency. In this paper, we propose a variable-filter-size Residue-learning convolutional neural network with batch normalization layer (VRCNN-BN). Our model is an end-to-end model. We feed the decoded pictures to the model at the decoder end. Different from previous methods, we apply the model to luma pictures and chroma pictures, respectively. In order to comprehensively evaluate the coding performance of both luma and chroma components, the color-sensitivity-based combined PSNR (CS-PSNR) is exploited to measure the effectiveness of the proposed method. Compared to HEVC baseline, our approach achieves an average BD-rate reduction of 10.3%, 8.9%, 13.1% and 11.8% in terms of CS-PSNR for random access, all intra, low delay P and low delay B configurations, respectively. Abundant experimental results indicate that our method is better than existing similar methods.