ESVAE: An Efficient Spiking Variational Autoencoder with Reparameterizable Poisson Spiking Sampling

In recent years, studies on image generation models of spiking neural networks (SNNs) have gained the attention of many researchers. Variational autoencoders (VAEs), as one of the most popular image generation models, have attracted a lot of work exploring their SNN implementation. Due to the constrained binary representation in SNNs, existing SNN VAE methods implicitly construct the latent space by an elaborated autoregressive network and use the network outputs as the sampling variables. However, this unspecified implicit representation of the latent space will increase the difficulty of generating high-quality images and introduces additional network parameters. In this paper, we propose an efficient spiking variational autoencoder (ESVAE) that constructs an interpretable latent space distribution and design a reparameterizable spiking sampling method. Specifically, we construct the prior and posterior of the latent space as a Poisson distribution using the firing rate of the spiking neurons. Subsequently, we propose a reparameterizable Poisson spiking sampling method, which is free from the additional network. Comprehensive experiments have been conducted, and the experimental results show that the proposed ESVAE outperforms previous SNN VAE methods in reconstructed & generated images quality. In addition, experiments demonstrate that ESVAE's encoder is able to retain the original image information more efficiently, and the decoder is more robust. The source code is available at https://github.com/QgZhan/ESVAE.

Sparse Label Smoothing for Semi-supervised Person Re-Identification

Person re-identification (re-id) is a cross-camera retrieval task which establishes a correspondence between images of a person from multiple cameras. Deep Learning methods have been successfully applied to the problem and achieved impressive results. However, these methods require large amounts of labeled training data. Current labeled datasets in person re-id are limited in scale and manually acquiring such large-scale dataset in surveillance camera is a tedious and labor-intensive task. In this paper, we propose a semi-supervised framework that performs Sparse Label Smoothing Regularization (SLSR) by considering similarities between unlabeled sample and training sample in the same feature space. Our approach first exploits the clustering property of existing person re-id datasets to create groups of similar objects that model the correlation among view. We make use of the training set to create cluster of similar objects using the intermediate feature representation of a CNN model. Each cluster is used to generate synthetic data samples using a generative adversarial model. We finally defined a sparse smoothing regularization term and train the network with join supervision of cross-entropy loss. The proposed approach tackles two problems (1) how to efficiently use the generated data and (2) how to address the over-smoothness problem found in current regularization. We solve these two problems by using a generative model for data augmentation and by maintaining and propagating similarities across the network through the concatenation of training images and generated images into one homogeneous feature space. Extensive experiments on four large-scale datasets show that our regularization method significantly improves the Re-ID accuracy compared to existing semi-supervised methods.

Self Attention Grid for Person Re-Identification

In this paper, we present an attention mechanism scheme to improve person re-identification task. Inspired by biology, we propose Self Attention Grid (SAG) to discover the most informative parts from a high-resolution image using its internal representation. In particular, given an input image, the proposed model is fed with two copies of the same image and consists of two branches. The upper branch processes the high-resolution image and learns high dimensional feature representation while the lower branch processes the low-resolution image and learn a filtering attention grid. We apply a max filter operation to non-overlapping sub-regions on the high feature representation before element-wise multiplied with the output of the second branch. The feature maps of the second branch are subsequently weighted to reflect the importance of each patch of the grid using a softmax operation. Our attention module helps the network learn the most discriminative visual features of multiple image regions and is specifically optimized to attend feature representation at different levels. Extensive experiments on three large-scale datasets show that our self-attention mechanism significantly improves the baseline model and outperforms various state-of-art models by a large margin.