Basis Scaling and Double Pruning for Efficient Transfer Learning

Transfer learning allows the reuse of deep learning features on new datasets with limited data. However, the resulting models could be unnecessarily large and thus inefficient. Although network pruning can be applied to improve inference efficiency, existing algorithms usually require fine-tuning and may not be suitable for small datasets. In this paper, we propose an algorithm that transforms the convolutional weights into the subspaces of orthonormal bases where a model is pruned. Using singular value decomposition, we decompose a convolutional layer into two layers: a convolutional layer with the orthonormal basis vectors as the filters, and a layer that we name "BasisScalingConv", which is responsible for rescaling the features and transforming them back to the original space. As the filters in each transformed layer are linearly independent with known relative importance, pruning can be more effective and stable, and fine tuning individual weights is unnecessary. Furthermore, as the numbers of input and output channels of the original convolutional layer remain unchanged, basis pruning is applicable to virtually all network architectures. Basis pruning can also be combined with existing pruning algorithms for double pruning to further increase the pruning capability. With less than 1% reduction in the classification accuracy, we can achieve pruning ratios up to 98.9% in parameters and 98.6% in FLOPs.