Dual-Tree Wavelet Packet CNNs for Image Classification
Authors: Hubert Leterme, Kévin Polisano, Valérie Perrier, Karteek Alahari
Keywords: convolutional neural networks, wavelet packet transform, dual-tree wavelet packet transform, image classification, deep learning, image processing
Abstract: In this paper, we target an important issue of deep convolutional neural networks (CNNs) — the lack of a mathematical understanding of their properties. We present an explicit formalism that is motivated by the similarities between trained CNN kernels and oriented Gabor filters for addressing this problem. The core idea is to constrain the behavior of convolutional layers by splitting them into a succession of wavelet packet decompositions, which are modulated by freely-trained mixture weights. We evaluate our approach with three variants of wavelet decompositions with the AlexNet architecture for image classification as an example. The first variant relies on the separable wavelet packet transform while the other two implement the 2D dual-tree real and complex wavelet packet transforms, taking advantage of their feature extraction properties such as directional selectivity and shift invariance. Our experiments show that we achieve the accuracy rate of standard AlexNet, but with a significantly lower number of parameters, and an interpretation of the network that is grounded in mathematical theory.