A discussion on the validation tests employed to compare human action recognition methods using the MSR Action3D dataset

This paper aims to determine which is the best human action recognition method based on features extracted from RGB-D devices, such as the Microsoft Kinect. A review of all the papers that make reference to MSR Action3D, the most used dataset that includes depth information acquired from a RGB-D device, has been performed. We found that the validation method used by each work differs from the others. So, a direct comparison among works cannot be made. However, almost all the works present their results comparing them without taking into account this issue. Therefore, we present different rankings according to the methodology used for the validation in orden to clarify the existing confusion.Comment: 16 pages and 7 table

Human action recognition and mobility assessment in smart environments with RGB-D sensors

Questa attività di ricerca è focalizzata sullo sviluppo di algoritmi e soluzioni per ambienti intelligenti sfruttando sensori RGB e di profondità. In particolare, gli argomenti affrontati fanno riferimento alla valutazione della mobilità di un soggetto e al riconoscimento di azioni umane. Riguardo il primo tema, l'obiettivo è quello di implementare algoritmi per l'estrazione di parametri oggettivi che possano supportare la valutazione di test di mobilità svolta da personale sanitario. Il primo algoritmo proposto riguarda l'estrazione di sei joints sul piano sagittale utilizzando i dati di profondità forniti dal sensore Kinect. La precisione in termini di stima degli angoli di busto e ginocchio nella fase di sit-to-stand viene valutata considerando come riferimento un sistema stereofotogrammetrico basato su marker. Un secondo algoritmo viene proposto per facilitare la realizzazione del test in ambiente domestico e per consentire l'estrazione di un maggior numero di parametri dall'esecuzione del test Timed Up and Go. I dati di Kinect vengono combinati con quelli di un accelerometro attraverso un algoritmo di sincronizzazione, costituendo un setup che può essere utilizzato anche per altre applicazioni che possono beneficiare dell'utilizzo congiunto di dati RGB, profondità ed inerziali. Vengono quindi proposti algoritmi di rilevazione della caduta che sfruttano la stessa configurazione del Timed Up and Go test. Per quanto riguarda il secondo argomento affrontato, l'obiettivo è quello di effettuare la classificazione di azioni che possono essere compiute dalla persona all'interno di un ambiente domestico. Vengono quindi proposti due algoritmi di riconoscimento attività i quali utilizzano i joints dello scheletro di Kinect e sfruttano un SVM multiclasse per il riconoscimento di azioni appartenenti a dataset pubblicamente disponibili, raggiungendo risultati confrontabili con lo stato dell'arte rispetto ai dataset CAD-60, KARD, MSR Action3D.This research activity is focused on the development of algorithms and solutions for smart environments exploiting RGB and depth sensors. In particular, the addressed topics refer to mobility assessment of a subject and to human action recognition. Regarding the first topic, the goal is to implement algorithms for the extraction of objective parameters that can support the assessment of mobility tests performed by healthcare staff. The first proposed algorithm regards the extraction of six joints on the sagittal plane using depth data provided by Kinect sensor. The accuracy in terms of estimation of torso and knee angles in the sit-to-stand phase is evaluated considering a marker-based stereometric system as a reference. A second algorithm is proposed to simplify the test implementation in home environment and to allow the extraction of a greater number of parameters from the execution of the Timed Up and Go test. Kinect data are combined with those of an accelerometer through a synchronization algorithm constituting a setup that can be used also for other applications that benefit from the joint usage of RGB, depth and inertial data. Fall detection algorithms exploiting the same configuration of the Timed Up and Go test are therefore proposed. Regarding the second topic addressed, the goal is to perform the classification of human actions that can be carried out in home environment. Two algorithms for human action recognition are therefore proposed, which exploit skeleton joints of Kinect and a multi-class SVM for the recognition of actions belonging to publicly available datasets, achieving results comparable with the state of the art in the datasets CAD-60, KARD, MSR Action3D

Human action recognition and mobility assessment in smart environments with RGB-D sensors

openQuesta attività di ricerca è focalizzata sullo sviluppo di algoritmi e soluzioni per ambienti intelligenti sfruttando sensori RGB e di profondità. In particolare, gli argomenti affrontati fanno riferimento alla valutazione della mobilità di un soggetto e al riconoscimento di azioni umane. Riguardo il primo tema, l'obiettivo è quello di implementare algoritmi per l'estrazione di parametri oggettivi che possano supportare la valutazione di test di mobilità svolta da personale sanitario. Il primo algoritmo proposto riguarda l'estrazione di sei joints sul piano sagittale utilizzando i dati di profondità forniti dal sensore Kinect. La precisione in termini di stima degli angoli di busto e ginocchio nella fase di sit-to-stand viene valutata considerando come riferimento un sistema stereofotogrammetrico basato su marker. Un secondo algoritmo viene proposto per facilitare la realizzazione del test in ambiente domestico e per consentire l'estrazione di un maggior numero di parametri dall'esecuzione del test Timed Up and Go. I dati di Kinect vengono combinati con quelli di un accelerometro attraverso un algoritmo di sincronizzazione, costituendo un setup che può essere utilizzato anche per altre applicazioni che possono beneficiare dell'utilizzo congiunto di dati RGB, profondità ed inerziali. Vengono quindi proposti algoritmi di rilevazione della caduta che sfruttano la stessa configurazione del Timed Up and Go test. Per quanto riguarda il secondo argomento affrontato, l'obiettivo è quello di effettuare la classificazione di azioni che possono essere compiute dalla persona all'interno di un ambiente domestico. Vengono quindi proposti due algoritmi di riconoscimento attività i quali utilizzano i joints dello scheletro di Kinect e sfruttano un SVM multiclasse per il riconoscimento di azioni appartenenti a dataset pubblicamente disponibili, raggiungendo risultati confrontabili con lo stato dell'arte rispetto ai dataset CAD-60, KARD, MSR Action3D.This research activity is focused on the development of algorithms and solutions for smart environments exploiting RGB and depth sensors. In particular, the addressed topics refer to mobility assessment of a subject and to human action recognition. Regarding the first topic, the goal is to implement algorithms for the extraction of objective parameters that can support the assessment of mobility tests performed by healthcare staff. The first proposed algorithm regards the extraction of six joints on the sagittal plane using depth data provided by Kinect sensor. The accuracy in terms of estimation of torso and knee angles in the sit-to-stand phase is evaluated considering a marker-based stereometric system as a reference. A second algorithm is proposed to simplify the test implementation in home environment and to allow the extraction of a greater number of parameters from the execution of the Timed Up and Go test. Kinect data are combined with those of an accelerometer through a synchronization algorithm constituting a setup that can be used also for other applications that benefit from the joint usage of RGB, depth and inertial data. Fall detection algorithms exploiting the same configuration of the Timed Up and Go test are therefore proposed. Regarding the second topic addressed, the goal is to perform the classification of human actions that can be carried out in home environment. Two algorithms for human action recognition are therefore proposed, which exploit skeleton joints of Kinect and a multi-class SVM for the recognition of actions belonging to publicly available datasets, achieving results comparable with the state of the art in the datasets CAD-60, KARD, MSR Action3D.INGEGNERIA DELL'INFORMAZIONECippitelli, EneaCippitelli, Ene

Human Action Recognition Based on Temporal Pyramid of Key Poses Using RGB-D Sensors

Human action recognition is a hot research topic in computer vision, mainly due to the high number of related applications, such as surveillance, human computer interaction, or assisted living. Low cost RGB-D sensors have been extensively used in this field. They can provide skeleton joints, which represent a compact and effective representation of the human posture. This work proposes an algorithm for human action recognition where the features are computed from skeleton joints. A sequence of skeleton features is represented as a set of key poses, from which histograms are extracted. The temporal structure of the sequence is kept using a temporal pyramid of key poses. Finally, a multi-class SVM performs the classification task. The algorithm optimization through evolutionary computation allows to reach results comparable to the state-of-the-art on the MSR Action3D dataset.This work was supported by a STSM Grant from COST Action IC1303 AAPELE - Architectures, Algorithms and Platforms for Enhanced Living Environments

Differential Recurrent Neural Networks for Human Activity Recognition

Human activity recognition has been an active research area in recent years. The difficulty of this problem lies in the complex dynamical motion patterns embedded through the sequential frames. The Long Short-Term Memory (LSTM) recurrent neural network is capable of processing complex sequential information since it utilizes special gating schemes for learning representations from long input sequences. It has the potential to model various time-series data, where the current hidden state has to be considered in the context of the past hidden states. Unfortunately, the conventional LSTMs do not consider the impact of spatio-temporal dynamics corresponding to the given salient motion patterns, when they gate the information that ought to be memorized through time. To address this problem, we propose a differential gating scheme for the LSTM neural network, which emphasizes the change in information gain caused by the salient motions between the successive video frames. This change in information gain is quantified by Derivative of States (DoS), and thus the proposed LSTM model is termed differential Recurrent Neural Network (dRNN). Based on the energy profiling of DoS, we further propose to employ the State Energy Profile (SEP) to search for salient dRNN states and construct more informative representations. To better understand the scene and human appearance information, the dRNN model is extended by connecting Convolutional Neural Networks (CNN) and stacked dRNNs into an end-to-end model. Lastly, the dissertation continues to discuss and compare the combined and the individual orders of DoS used within the dRNN. We propose to control the LSTM gates via individual order of DoS and stack multiple levels of LSTM cells in increasing orders of state derivatives. To this end, we have introduced a new family of LSTMs, expanding the applications of LSTMs and advancing the performances of the state-of-the-art methods

Architectures d'apprentissage profond pour la reconnaissance d'actions humaines dans des séquences vidéo RGB-D monoculaires. Application à la surveillance dans les transports publics

Cette thèse porte sur la reconnaissance d'actions humaines dans des séquences vidéo RGB-D monoculaires. La question principale est, à partir d'une vidéo ou d'une séquence d'images donnée, de savoir comment reconnaître des actions particulières qui se produisent. Cette tâche est importante et est un défi majeur à cause d'un certain nombre de verrous scientifiques induits par la variabilité des conditions d'acquisition, comme l'éclairage, la position, l'orientation et le champ de vue de la caméra, ainsi que par la variabilité de la réalisation des actions, notamment de leur vitesse d'exécution. Pour surmonter certaines de ces difficultés, dans un premier temps, nous examinons et évaluons les techniques les plus récentes pour la reconnaissance d'actions dans des vidéos. Nous proposons ensuite une nouvelle approche basée sur des réseaux de neurones profonds pour la reconnaissance d'actions humaines à partir de séquences de squelettes 3D. Deux questions clés ont été traitées. Tout d'abord, comment représenter la dynamique spatio-temporelle d'une séquence de squelettes pour exploiter efficacement la capacité d'apprentissage des représentations de haut niveau des réseaux de neurones convolutifs (CNNs ou ConvNets). Ensuite, comment concevoir une architecture de CNN capable d'apprendre des caractéristiques spatio-temporelles discriminantes à partir de la représentation proposée dans un objectif de classification. Pour cela, nous introduisons deux nouvelles représentations du mouvement 3D basées sur des squelettes, appelées SPMF (Skeleton Posture-Motion Feature) et Enhanced-SPMF, qui encodent les postures et les mouvements humains extraits des séquences de squelettes sous la forme d'images couleur RGB. Pour les tâches d'apprentissage et de classification, nous proposons différentes architectures de CNNs, qui sont basées sur les modèles Residual Network (ResNet), Inception-ResNet-v2, Densely Connected Convolutional Network (DenseNet) et Efficient Neural Architecture Search (ENAS), pour extraire des caractéristiques robustes de la représentation sous forme d'image que nous proposons et pour les classer. Les résultats expérimentaux sur des bases de données publiques (MSR Action3D, Kinect Activity Recognition Dataset, SBU Kinect Interaction, et NTU-RGB+D) montrent que notre approche surpasse les méthodes de l'état de l'art. Nous proposons également une nouvelle technique pour l'estimation de postures humaines à partir d'une vidéo RGB. Pour cela, le modèle d'apprentissage profond appelé OpenPose est utilisé pour détecter les personnes et extraire leur posture en 2D. Un réseau de neurones profond est ensuite proposé pour apprendre la transformation permettant de reconstruire ces postures en trois dimensions. Les résultats expérimentaux sur la base de données Human3.6M montrent l'efficacité de la méthode proposée. Ces résultats ouvrent des perspectives pour une approche de la reconnaissance d'actions humaines à partir des séquences de squelettes 3D sans utiliser des capteurs de profondeur comme la Kinect. Nous avons également constitué la base CEMEST, une nouvelle base de données RGB-D illustrant des comportements de passagers dans les transports publics. Elle contient 203 vidéos de surveillance collectées dans une station du métro incluant des événements "normaux" et "anormaux". Nous avons obtenu des résultats prometteurs sur cette base en utilisant des techniques d'augmentation de données et de transfert d'apprentissage. Notre approche permet de concevoir des applications basées sur des techniques de l'apprentissage profond pour renforcer la qualité des services de transport en commun.This thesis is dealing with automatic recognition of human actions from monocular RGB-D video sequences. Our main goal is to recognize which human actions occur in unknown videos. This problem is a challenging task due to a number of obstacles caused by the variability of the acquisition conditions, including the lighting, the position, the orientation and the field of view of the camera, as well as the variability of actions which can be performed differently, notably in terms of speed. To tackle these problems, we first review and evaluate the most prominent state-of-the-art techniques to identify the current state of human action recognition in videos. We then propose a new approach for skeleton-based action recognition using Deep Neural Networks (DNNs). Two key questions have been addressed. First, how to efficiently represent the spatio-temporal patterns of skeletal data for fully exploiting the capacity in learning high-level representations of Deep Convolutional Neural Networks (D-CNNs). Second, how to design a powerful D-CNN architecture that is able to learn discriminative features from the proposed representation for classification task. As a result, we introduce two new 3D motion representations called SPMF (Skeleton Posture-Motion Feature) and Enhanced-SPMF that encode skeleton poses and their motions into color images. For learning and classification tasks, we design and train different D-CNN architectures based on the Residual Network (ResNet), Inception-ResNet-v2, Densely Connected Convolutional Network (DenseNet) and Efficient Neural Architecture Search (ENAS) to extract robust features from color-coded images and classify them. Experimental results on various public and challenging human action recognition datasets (MSR Action3D, Kinect Activity Recognition Dataset, SBU Kinect Interaction, and NTU-RGB+D) show that the proposed approach outperforms current state-of-the-art. We also conducted research on the problem of 3D human pose estimation from monocular RGB video sequences and exploited the estimated 3D poses for recognition task. Specifically, a deep learning-based model called OpenPose is deployed to detect 2D human poses. A DNN is then proposed and trained for learning a 2D-to-3D mapping in order to map the detected 2D keypoints into 3D poses. Our experiments on the Human3.6M dataset verified the effectiveness of the proposed method. These obtained results allow opening a new research direction for human action recognition from 3D skeletal data, when the depth cameras are failing. In addition, we collect and introduce in this thesis, CEMEST database, a new RGB-D dataset depicting passengers' behaviors in public transport. It consists of 203 untrimmed real-world surveillance videos of realistic "normal" and "abnormal" events. We achieve promising results on CEMEST with the support of data augmentation and transfer learning techniques. This enables the construction of real-world applications based on deep learning for enhancing public transportation management services

Action classification using a discriminative multilevel HDP-HMM

We classify human actions occurring in depth image sequences using features based on skeletal joint positions. The action classes are represented by a multi-level Hierarchical Dirichlet Process – Hidden Markov Model (HDP-HMM). The non-parametric HDP-HMM allows the inference of hidden states automatically from training data. The model parameters of each class are formulated as transformations from a shared base distribution, thus promoting the use of unlabelled examples during training and borrowing information across action classes. Further, the parameters are learnt in a discriminative way. We use a normalized gamma process representation of HDP and margin based likelihood functions for this purpose. We sample parameters from the complex posterior distribution induced by our discriminative likelihood function using elliptical slice sampling. Experiments with two different datasets show that action class models learnt using our technique produce good classification results

Evolutionary joint selection to improve human action recognition with RGB-D devices

Interest in RGB-D devices is increasing due to their low price and the wide range of possible applications that come along. These devices provide a marker-less body pose estimation by means of skeletal data consisting of 3D positions of body joints. These can be further used for pose, gesture or action recognition. In this work, an evolutionary algorithm is used to determine the optimal subset of skeleton joints, taking into account the topological structure of the skeleton, in order to improve the final success rate. The proposed method has been validated using a state-of-the-art RGB action recognition approach, and applying it to the MSR-Action3D dataset. Results show that the proposed algorithm is able to significantly improve the initial recognition rate and to yield similar or better success rates than the state-of-the-art methods.This work has been partially supported by the European Commission under project “caring4U – A study on people activity in private spaces: towards a multisensor network that meets privacy requirements” (PIEF-GA-2010-274649) and by the Spanish Ministry of Science and Innovation under project “Sistema de visión para la monitorización de la actividad de la vida diaria en el hogar” (TIN2010-20510-C04-02). Alexandros Andre Chaaraoui and José Ramón Padilla-López acknowledge financial support by the Conselleria d’Educació, Formació i Ocupació of the Generalitat Valenciana (fellowships ACIF/2011/160 and ACIF/2012/064 respectively)

Deep Learning-Based Action Recognition

The classification of human action or behavior patterns is very important for analyzing situations in the field and maintaining social safety. This book focuses on recent research findings on recognizing human action patterns. Technology for the recognition of human action pattern includes the processing technology of human behavior data for learning, technology of expressing feature values ​​of images, technology of extracting spatiotemporal information of images, technology of recognizing human posture, and technology of gesture recognition. Research on these technologies has recently been conducted using general deep learning network modeling of artificial intelligence technology, and excellent research results have been included in this edition