Adjustable Memory-efficient Image Super-resolution via Individual Kernel Sparsity

Though single image super-resolution (SR) has witnessed incredible progress, the increasing model complexity impairs its applications in memory-limited devices. To solve this problem, prior arts have aimed to reduce the number of model parameters and sparsity has been exploited, which usually enforces the group sparsity constraint on the filter level and thus is not arbitrarily adjustable for satisfying the customized memory requirements. In this paper, we propose an individual kernel sparsity (IKS) method for memory-efficient and sparsity-adjustable image SR to aid deep network deployment in memory-limited devices. IKS performs model sparsity in the weight level that implicitly allocates the user-defined target sparsity to each individual kernel. To induce the kernel sparsity, a soft thresholding operation is used as a gating constraint for filtering the trivial weights. To achieve adjustable sparsity, a dynamic threshold learning algorithm is proposed, in which the threshold is updated by associated training with the network weight and is adaptively decayed with the guidance of the desired sparsity. This work essentially provides a dynamic parameter reassignment scheme with a given resource budget for an off-the-shelf SR model. Extensive experimental results demonstrate that IKS imparts considerable sparsity with negligible effect on SR quality. The code is available at: https://github.com/RaccoonDML/IKS.