Nonlinear Transforms in Learned Image Compression From a Communication Perspective

Recently, remarkable progress has been made in learned image compression (LIC), in which nonlinear transforms (NTs) play a crucial role. Although there are many NT methods for improving the rate distortion performance, all the existing methods sacrifice the computational complexity and the number of parameters of the transformation. This paper provides a fundamental novel viewpoint on nonlinear transforms from a communication perspective, and shows how this idea can be extended to design efficient NT methods. In particular, the nonlinear transforms are inferred as signal modulation modules. Under this extrapolation, the current NTs are generalized as amplitude modulation that only varies the amplitude of the carrier wave. Therefore, a nonlinear modulation-like transform (NMLT) which varies the phase angle of the carrier is proposed. Moreover, this concept is extended by introducing In-phase/Quadrature (IQ) modulation, which is a boosting technique in communication field, in order to enhance NMLT. Furthermore, the Bit-interleaved technique in communication is used to guide the optimization of NTML with IQ. The experimental results on different datasets and backbone architectures verify the efficiency and robustness of the proposed methods. For example, when backbone architecture is hyperprior model, our method achieves 19.37% BD-rate reduction over GDN on the Kodak dataset. In addition, our method with channel wise autoregressive model leads to the state-of-the-art rate-distortion performance.