Three-Stage Multi-Frame Multi-Channel In-Loop Filter of VVC

For the Versatile Video Coding (VVC) standard, extensive research has been conducted on in-loop filtering to improve encoding efficiency. However, most methods use only spatial characteristics without exploiting the content correlation across multiple frames or fully utilizing the inter-channel relational information. In this paper, we introduce a novel three-stage Multi-frame Multi-channel In-loop Filtering (3-MMIF) method for VVC that improves the quality of each encoded frame by harnessing the correlations between adjacent frames and channels. Firstly, we establish a comprehensive database containing pairs of encoded and original frames across various scenes. Then, we select the nearest frames in the decode buffer as the reference frames for enhancing the quality of the current frame. Subsequently, we propose a three-stage in-loop filtering method that leverages spatio-temporal and inter-channel correlations. The three-stage method is grounded in the recently developed Residual Dense Network, benefiting from its enhanced generalization ability and feature reuse mechanism. Experimental results demonstrate that our 3-MMIF method, with the encoder’s standard filter tools activated, achieves 2.78%/4.87%/5.13% Bjøntegaard delta bit-rate (BD-Rate) reductions for the Y, U, and V channels over the VVC 17.0 codec for random access configuration on the standard test set, outperforming other VVC in-loop filter methods.