Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Pattern Recognition and Machine Learning

“Unpaired Image-to-Image Translation using Cycle-Consistent Adversarial Networks”の学習報告

Hyperspectral image (HSI) classification has become a hot topic in the field of remote sensing. In general, the complex characteristics of hyperspectral data make the accurate classification of such data challenging for traditional machine learning methods. In addition, hyperspectral imaging often deals with an inherently nonlinear relation between the captured spectral information and the corresponding materials. In recent years, deep learning has been recognized as a powerful feature-extraction tool to effectively address nonlinear problems and widely used in a number of image processing tasks. Motivated by those successful applications, deep learning has also been introduced to classify HSIs and demonstrated good performance. This survey paper presents a systematic review of deep learning-based HSI classification literatures and compares several strategies for this topic. Specifically, we first summarize the main challenges of HSI classification which cannot be effectively overcome by traditional machine learning methods, and also introduce the advantages of deep learning to handle these problems. Then, we build a framework which divides the corresponding works into spectral-feature networks, spatial-feature networks, and spectral-spatial-feature networks to systematically review the recent achievements in deep learning-based HSI classification. In addition, considering the fact that available training samples in the remote sensing field are usually very limited and training deep networks require a large number of samples, we include some strategies to improve classification performance, which can provide some guidelines for future studies on this topic. Finally, several representative deep learning-based classification methods are conducted on real HSIs in our experiments.

Deep Learning for Hyperspectral Image Classification: An Overview

Underwater image enhancement has been attracting much attention due to its significance in marine engineering and aquatic robotics. Numerous underwater image enhancement algorithms have been proposed in the last few years. However, these algorithms are mainly evaluated using either synthetic datasets or few selected real-world images. It is thus unclear how these algorithms would perform on images acquired in the wild and how we could gauge the progress in the field. To bridge this gap, we present the first comprehensive perceptual study and analysis of underwater image enhancement using large-scale real-world images. In this paper, we construct an Underwater Image Enhancement Benchmark (UIEB) including 950 real-world underwater images, 890 of which have the corresponding reference images. We treat the rest 60 underwater images which cannot obtain satisfactory reference images as challenging data. Using this dataset, we conduct a comprehensive study of the state-of-the-art underwater image enhancement algorithms qualitatively and quantitatively. In addition, we propose an underwater image enhancement network (called Water-Net) trained on this benchmark as a baseline, which indicates the generalization of the proposed UIEB for training Convolutional Neural Networks (CNNs). The benchmark evaluations and the proposed Water-Net demonstrate the performance and limitations of state-of-the-art algorithms, which shed light on future research in underwater image enhancement. The dataset and code are available at https://li-chongyi.github.io/proj_benchmark.html .

An Underwater Image Enhancement Benchmark Dataset and Beyond

In this paper, we describe a novel deep convolutional neural network (CNN) that is deeper and wider than other existing deep networks for hyperspectral image classification. Unlike current state-of-the-art approaches in CNN-based hyperspectral image classification, the proposed network, called contextual deep CNN, can optimally explore local contextual interactions by jointly exploiting local spatio-spectral relationships of neighboring individual pixel vectors. The joint exploitation of the spatio-spectral information is achieved by a multi-scale convolutional filter bank used as an initial component of the proposed CNN pipeline. The initial spatial and spectral feature maps obtained from the multi-scale filter bank are then combined together to form a joint spatio-spectral feature map. The joint feature map representing rich spectral and spatial properties of the hyperspectral image is then fed through a fully convolutional network that eventually predicts the corresponding label of each pixel vector. The proposed approach is tested on three benchmark data sets: the Indian Pines data set, the Salinas data set, and the University of Pavia data set. Performance comparison shows enhanced classification performance of the proposed approach over the current state-of-the-art on the three data sets.

Going Deeper With Contextual CNN for Hyperspectral Image Classification

Dynamic Vision Sensor (DVS) is a compelling neuromorphic camera compared to conventional camera, but it suffers from fiercer noise. Due to the nature of irregular format and asynchronous readout, DVS data is always transformed into a regular tensor (e.g., 3D voxel or image) for deep learning method, which corrupts its own asynchronous properties. To maintain asynchronous, we establish an innovative asynchronous event denoise neural network, named AEDNet, which directly consumes the correlation of the irregular signal in spatial-temporal range without destroying its original structural property. Based on the property of continuation in temporal domain and discreteness in spatial domain, we decompose the DVS signal into two parts, i.e., temporal correlation and spatial affinity, and separately process these two parts. Our spatial feature embedding unit is a unique feature extraction module that extracts feature from event-level, which perfectly maintains its spatial-temporal correlation. To test effectiveness, we build a novel dataset named DVSCLEAN containing both simulated and real-world data. The experimental results of AEDNet achieve SOTA.

AEDNet: Asynchronous Event Denoising with Spatial-Temporal Correlation among Irregular Data

In this paper, we focus on subjective and objective Point Cloud Quality Assessment (PCQA) in an immersive environment and study the effect of geometry and texture attributes in compression distortion. Using a Head-Mounted Display (HMD) with six degrees of freedom, we establish a subjective PCQA database, named SIAT Point Cloud Quality Database (SIAT-PCQD). Our database consists of 303 valid distorted point clouds compressed by the MPEG point cloud encoder with the combination of 20 sequences and 17 pairs of geometry and texture quantization parameters. The impacts of contents and geometry and texture attributes are further discussed in this paper. Then, we evaluate our subjective database with current objective PCQA methods and propose an objective weighted projection-based method to improve the consistency between observers' awareness and the importance of projected views. Our subjective database and findings can be used in perception-based point cloud processing, transmission, and coding, especially for Virtual Reality applications. The subjective dataset and quality scores will be available on the public repository.

Subjective Quality Study and Database of Compressed Point Clouds with 6DoF Head-mounted Display

Learning Graph-embedded Key-event Back-tracing for Object Tracking in Event Clouds

In rate-distortion optimization, the encoder settings are determined by maximizing a reconstruction quality measure subject to a constraint on the bitrate. One of the main challenges of this approach is to define a quality measure that can be computed with low computational cost and which correlates well with the perceptual quality. While several quality measures that fulfil these two criteria have been developed for images and videos, no such one exists for point clouds. We address this limitation for the video-based point cloud compression (V-PCC) standard by proposing a linear perceptual quality model whose variables are the V-PCC geometry and color quantization step sizes and whose coefficients can easily be computed from two features extracted from the original point cloud. Subjective quality tests with 400 compressed point clouds show that the proposed model correlates well with the mean opinion score, outperforming state-of-the-art full reference objective measures in terms of Spearman rank-order and Pearson linear correlation coefficient. Moreover, we show that for the same target bitrate, rate-distortion optimization based on the proposed model offers higher perceptual quality than rate-distortion optimization based on exhaustive search with a point-to-point objective quality metric. Our datasets are publicly available at https://github.com/qdushl/Waterloo-Point-Cloud-Database-2.0 .

Reduced Reference Perceptual Quality Model With Application to Rate Control for Video-Based Point Cloud Compression

Compression of mesh-based 3-D models has been an important issue, which ensures efficient storage and transmission. In this paper, we present a very effective compression scheme specifically for expression variation 3-D face models. Firstly, 3-D models are mapped into 2-D parametric domain and corresponded by expression-invariant parameterizaton, leading to 2-D image format representation namely geometry images, which simplifies the 3-D model compression into 2-D image compression. Then, sparse representation with learned dictionaries via K-SVD is applied to each patch from sliced GI so that only few coefficients and their indices are needed to be encoded, leading to low datasize. Experimental results demonstrate that the proposed scheme provides significant improvement in terms of compression performance, especially at low bitrate, compared with existing algorithms.

Junhui Hou

Papers

AEDNet: Asynchronous Event Denoising with Spatial-Temporal Correlation among Irregular Data

Subjective Quality Study and Database of Compressed Point Clouds with 6DoF Head-mounted Display

Learning Graph-embedded Key-event Back-tracing for Object Tracking in Event Clouds

Reduced Reference Perceptual Quality Model With Application to Rate Control for Video-Based Point Cloud Compression

Expression-invariant and sparse representation for mesh-based compression for 3-D face models