Hardware-friendly Scalable Image Super Resolution with Progressive Structured Sparsity

Single image super-resolution (SR) is an important low-level vision task, and the dynamic SR trading off performance and efficiency are increasingly in demand. The existing dynamic SR methods are divided into two classes: the structured pruning and non-structured compressing methods. The former removes redundant structures in the network, which often leads to significant performance degradation, and the latter searches for extremely sparse parameter masks, achieving promising performance, but they are not deployable in hardware platforms with irregular memory access. In order to solve the mentioned problems, we propose Hardware-friendly Scalable SR (HSSR) with progressively structured sparsity. The superiority of our method is that with only a single scalable model it covers multiple SR models with different sizes, without extra retraining or post-processing. HSSR contains the forward and backward processing. In the forward process, we gradually shrink the SR networks with structured iterative sparsity where grouping convolution together with knowledge distillation is conducted to reduce the amount of SR parameters and the computational complexity while keeping the performance, and in the backward process, we gradually expand the compressed SR networks with structured iterative recovery. Comprehensive experiments on benchmark datasets show that HSSR is perfectly compatible with common convolution baselines. Compared with the Slimmable method, our model is superior in performance, flops, and model size. Experimental results demonstrate that HSSR achieves significant compression, saving up to 1500K parameters and 100 GFlops calculation compared to the original model in real-world applications.