MixBin: Towards Budgeted Binarization

Binarization has proven to be amongst the most effective ways of neural network compression, reducing the FLOPs of the original model by a large extent. However, such levels of compression are often accompanied by a significant drop in the performance. There exist some approaches that reduce this performance drop by facilitating partial binarization of the network, however, a systematic approach to mix binary and full-precision parameters in a single network is still missing. In this paper, we propose a paradigm to perform partial binarization of neural networks in a controlled sense, thereby constructing budgeted binary neural network (B2NN). We present MixBin, an iterative search-based strategy that constructs B2NN through optimized mixing of the binary and full-precision components. MixBin allows to explicitly choose the approximate fraction of the network to be kept as binary, thereby presenting the flexibility to adapt the inference cost at a prescribed budget. We demonstrate through experiments that B2NNs obtained from our MixBin strategy are significantly better than those obtained from random selection of the network layers. To perform partial binarization in an effective manner, it is important that both the full-precision as well as the binary components of the B2NN are appropriately optimized. We also demonstrate that the choice of the activation function can have a significant effect on this process, and to circumvent this issue, we present BinReLU, that can be used as an effective activation function for the full-precision as well as the binary components of any B2NN. Experimental investigations reveal that BinReLU outperforms the other activation functions in all possible scenarios of B2NN: zero-, partial- as well as full binarization. Finally, we demonstrate the efficacy of MixBin on the tasks of classification and object tracking using benchmark datasets.