Corner-to-Center Long-range Context Model for Efficient Learned Image Compression
This work addresses the efficiency and performance trade-off in learned image compression for real-world applications, representing an incremental improvement over existing parallel methods.
The paper tackles the performance degradation in parallel context models for learned image compression by analyzing information quantity and quality, proposing a Corner-to-Center transformer-based Context Model (C³M) with logarithmic prediction order and a Long-range Crossing Attention Module (LCAM) to enhance context and latent predictions, resulting in improved rate-distortion performance that outperforms state-of-the-art parallel methods.
In the framework of learned image compression, the context model plays a pivotal role in capturing the dependencies among latent representations. To reduce the decoding time resulting from the serial autoregressive context model, the parallel context model has been proposed as an alternative that necessitates only two passes during the decoding phase, thus facilitating efficient image compression in real-world scenarios. However, performance degradation occurs due to its incomplete casual context. To tackle this issue, we conduct an in-depth analysis of the performance degradation observed in existing parallel context models, focusing on two aspects: the Quantity and Quality of information utilized for context prediction and decoding. Based on such analysis, we propose the \textbf{Corner-to-Center transformer-based Context Model (C$^3$M)} designed to enhance context and latent predictions and improve rate-distortion performance. Specifically, we leverage the logarithmic-based prediction order to predict more context features from corner to center progressively. In addition, to enlarge the receptive field in the analysis and synthesis transformation, we use the Long-range Crossing Attention Module (LCAM) in the encoder/decoder to capture the long-range semantic information by assigning the different window shapes in different channels. Extensive experimental evaluations show that the proposed method is effective and outperforms the state-of-the-art parallel methods. Finally, according to the subjective analysis, we suggest that improving the detailed representation in transformer-based image compression is a promising direction to be explored.