Generative Refinement for Low Bitrate Image Coding Using Vector Quantized Residual

Despite the significant progress in recent deep learning-based image compression, the reconstructed visual quality still suffers at low bitrates due to the lack of high-frequency information. Existing methods deploy the generative adversarial networks (GANs) as an additional loss to supervise the rate-distortion (R-D) optimization, capable of producing more high-frequency components for visually pleasing reconstruction but also introducing unexpected fake textures. This work, instead, proposes to generate high-frequency residuals to refine an image reconstruction compressed using existing image compression solutions. Such a residual signal is calculated between the decoded image and its uncompressed input and quantized to proper codeword vectors in a learnable codebook for decoder-side generative refinement. Extensive experiments demonstrate that our method can restore high-frequency information given images compressed by any codecs and outperform the state-of-the-art generative image compression algorithms or perceptual-oriented post-processing approaches. Moreover, the proposed method using vector quantized residual exhibits remarkable robustness and generalizes to both rules-based and learning-based compression models, which can be used as a plug-and-play module for perceptual optimization without re-training.