Improved Deep Image Compression with Joint Optimization of Cross Channel Context Model And Generalized Loop Filter

Abstract

Among the recent deep image compression frameworks, transform coding together with a context-adaptive entropy model is the most representative approach to achieve the best coding performance. For entropy model, 2D mask convolution is widely utilized to capture the spatial context, which omits the correlations along channel dimension. To complement to the spatial context, a cross channel context model is proposed. For transform, if given more network layers to improve its representation ability, how to allocate these network layers in forward and inverse transform is investigated. After analyzing the scheme of deep image compression connected with loop filter, we find this investigation can be regarded as a more generalized loop filter. The proposed cross channel context model and generalized loop filter (CCCMGLF) are integrated into the deep image compression framework and jointly optimized to improve the coding performance. Experimental results demonstrate that, using PSNR as distortion metric, the proposed CCCMGLF outperforms VTM-11.0 by 1.20%, 10.82% and 5.38% in terms of BD-rate reductions for Y, U and V components, respectively, for the Kodak dataset. For the JVET CTC sequences, the proposed method outperforms VTM-11.0 by 1.44% for Y but has a coding performance loss of 24.74% and 11.91% for U and V, respectively. Over the baseline deep compression framework, the proposed method provides 7.80%, 12.66% and 11.15% performance improvement for Y, U, and V, respectively, for the Kodak dataset; 9.10%, 12.27%, and 12.68% performance improvement for Y, U and V, respectively, for the JVET CTC sequences. The proposed approaches are applicable in both image compression and intra coding in video compression.