Trajectory-based Human Action Recognition

Human activity recognition has been a hot topic for some time. It has several challenges, which makes this task hard and exciting for research. The sparse representation became more popular during the past decade or so. Sparse representation methods represent a video by a set of independent features. The features used in the literature are usually lowlevel features. Trajectories, as middle-level features, capture the motion of the scene, which is discriminant in most cases. Trajectories have also been proven useful for aligning small neighborhoods, before calculating the traditional descriptors. In fact, the trajectory aligned descriptors show better discriminant power than the trajectory shape descriptors proposed in the literature. However, trajectories have not been investigated thoroughly, and their full potential has not been put to the test before this work. This thesis examines trajectories, defined better trajectory shape descriptors and finally it augmented trajectories with disparity information. This thesis formally define three different trajectory extraction methods, namely interest point trajectories (IP), Lucas-Kanade based trajectories (LK), and Farnback optical flow based trajectories (FB). Their discriminant power for human activity recognition task is evaluated. Our tests reveal that LK and FB can produce similar reliable results, although the FB perform a little better in particular scenarios. These experiments demonstrate which method is suitable for the future tests. The thesis also proposes a better trajectory shape descriptor, which is a superset of existing descriptors in the literature. The examination reveals the superior discriminant power of this newly introduced descriptor. Finally, the thesis proposes a method to augment the trajectories with disparity information. Disparity information is relatively easy to extract from a stereo image, and they can capture the 3D structure of the scene. This is the first time that the disparity information fused with trajectories for human activity recognition. To test these ideas, a dataset of 27 activities performed by eleven actors is recorded and hand labelled. The tests demonstrate the discriminant power of trajectories. Namely, the proposed disparity-augmented trajectories improve the discriminant power of traditional dense trajectories by about 3.11%

Automatic visual detection of human behavior: a review from 2000 to 2014

Due to advances in information technology (e.g., digital video cameras, ubiquitous sensors), the automatic detection of human behaviors from video is a very recent research topic. In this paper, we perform a systematic and recent literature review on this topic, from 2000 to 2014, covering a selection of 193 papers that were searched from six major scientific publishers. The selected papers were classified into three main subjects: detection techniques, datasets and applications. The detection techniques were divided into four categories (initialization, tracking, pose estimation and recognition). The list of datasets includes eight examples (e.g., Hollywood action). Finally, several application areas were identified, including human detection, abnormal activity detection, action recognition, player modeling and pedestrian detection. Our analysis provides a road map to guide future research for designing automatic visual human behavior detection systems.This work is funded by the Portuguese Foundation for Science and Technology (FCT - Fundacao para a Ciencia e a Tecnologia) under research Grant SFRH/BD/84939/2012

Vision-Based Observation Models for Lower Limb 3D Tracking with a Moving Platform

Tracking and understanding human gait is an important step towards improving elderly mobility and safety. This thesis presents a vision-based tracking system that estimates the 3D pose of a wheeled walker user's lower limbs with cameras mounted on the moving walker. The tracker estimates 3D poses from images of the lower limbs in the coronal plane in a dynamic, uncontrolled environment. It employs a probabilistic approach based on particle filtering with three different camera setups: a monocular RGB camera, binocular RGB cameras, and a depth camera. For the RGB cameras, observation likelihoods are designed to compare the colors and gradients of each frame with initial templates that are manually extracted. Two strategies are also investigated for handling appearance change of tracking target: increasing number of templates and using different representations of colors. For the depth camera, two observation likelihoods are developed: the first one works directly in the 3D space, while the second one works in the projected image space. Experiments are conducted to evaluate the performance of the tracking system with different users for all three camera setups. It is demonstrated that the trackers with the RGB cameras produce results with higher error as compared to the depth camera, and the strategies for handling appearance change improve tracking accuracy in general. On the other hand, the tracker with the depth sensor successfully tracks the 3D poses of users over the entire video sequence and is robust against unfavorable conditions such as partial occlusion, missing observations, and deformable tracking target

Improved robustness and efficiency for automatic visual site monitoring

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 219-228).Knowing who people are, where they are, what they are doing, and how they interact with other people and things is valuable from commercial, security, and space utilization perspectives. Video sensors backed by computer vision algorithms are a natural way to gather this data. Unfortunately, key technical issues persist in extracting features and models that are simultaneously efficient to compute and robust to issues such as adverse lighting conditions, distracting background motions, appearance changes over time, and occlusions. In this thesis, we present a set of techniques and model enhancements to better handle these problems, focusing on contributions in four areas. First, we improve background subtraction so it can better handle temporally irregular dynamic textures. This allows us to achieve a 5.5% drop in false positive rate on the Wallflower waving trees video. Secondly, we adapt the Dalal and Triggs Histogram of Oriented Gradients pedestrian detector to work on large-scale scenes with dense crowds and harsh lighting conditions: challenges which prevent us from easily using a background subtraction solution. These scenes contain hundreds of simultaneously visible people. To make using the algorithm computationally feasible, we have produced a novel implementation that runs on commodity graphics hardware and is up to 76 faster than our CPU-only implementation. We demonstrate the utility of this detector by modeling scene-level activities with a Hierarchical Dirichlet Process.(cont.) Third, we show how one can improve the quality of pedestrian silhouettes for recognizing individual people. We combine general appearance information from a large population of pedestrians with semi-periodic shape information from individual silhouette sequences. Finally, we show how one can combine a variety of detection and tracking techniques to robustly handle a variety of event detection scenarios such as theft and left-luggage detection. We present the only complete set of results on a standardized collection of very challenging videos.by Gerald Edwin Dalley.Ph.D

A Study on Human Motion Acquisition and Recognition Employing Structured Motion Database

九州工業大学博士学位論文 学位記番号:工博甲第332号　学位授与年月日:平成24年3月23日1 Introduction||2 Human Motion Representation||3 Human Motion Recognition||4 Automatic Human Motion Acquisition||5 Human Motion Recognition Employing Structured Motion Database||6 Analysis on the Constraints in Human Motion Recognition||7 Multiple Persons’ Action Recognition||8 Discussion and ConclusionsHuman motion analysis is an emerging research field for the video-based applications capable of acquiring and recognizing human motions or actions. The automaticity of such a system with these capabilities has vital importance in real-life scenarios. With the increasing number of applications, the demand for a human motion acquisition system is gaining importance day-by-day. We develop such kind of acquisition system based on body-parts modeling strategy. The system is able to acquire the motion by positioning body joints and interpreting those joints by the inter-parts inclination. Besides the development of the acquisition system, there is increasing need for a reliable human motion recognition system in recent years. There are a number of researches on motion recognition is performed in last two decades. At the same time, an enormous amount of bulk motion datasets are becoming available. Therefore, it becomes an indispensable task to develop a motion database that can deal with large variability of motions efficiently. We have developed such a system based on the structured motion database concept. In order to gain a perspective on this issue, we have analyzed various aspects of the motion database with a view to establishing a standard recognition scheme. The conventional structured database is subjected to improvement by considering three aspects: directional organization, nearest neighbor searching problem resolution, and prior direction estimation. In order to investigate and analyze comprehensively the effect of those aspects on motion recognition, we have adopted two forms of motion representation, eigenspace-based motion compression, and B-Tree structured database. Moreover, we have also analyzed the two important constraints in motion recognition: missing information and clutter outdoor motions. Two separate systems based on these constraints are also developed that shows the suitable adoption of the constraints. However, several people occupy a scene in practical cases. We have proposed a detection-tracking-recognition integrated action recognition system to deal with multiple people case. The system shows decent performance in outdoor scenarios. The experimental results empirically illustrate the suitability and compatibility of various factors of the motion recognition

Whole-Body Motion Capture and Beyond: From Model-Based Inference to Learning-Based Regression

Herkömmliche markerlose Motion Capture (MoCap)-Methoden sind zwar effektiv und erfolgreich, haben aber mehrere Einschränkungen: 1) Sie setzen ein charakterspezifi-sches Körpermodell voraus und erlauben daher keine vollautomatische Pipeline und keine Verallgemeinerung über verschiedene Korperformen; 2) es werden keine Objekte verfolgt, mit denen Menschen interagieren, während in der Realität die Interaktion zwischen Menschen und Objekten allgegenwärtig ist; 3) sie sind in hohem Maße von ausgeklügelten Optimierungen abhängig, die eine gute Initialisierung und starke Prioritäten erfordern. Dieser Prozess kann sehr zeitaufwändig sein. In dieser Arbeit befassen wir uns mit allen oben genannten Problemen. Zunächst schlagen wir eine vollautomatische Methode zur genauen 3D-Rekonstruktion des menschlichen Körpers aus RGB-Videos mit mehreren Ansichten vor. Wir verarbeiten alle RGB-Videos vor, um 2D-Keypoints und Silhouetten zu erhalten. Dann passen wir modell in zwei aufeinander folgenden Schritten an die 2D-Messungen an. In der ersten Phase werden die Formparameter und die Posenparameter der SMPL nacheinander und bildweise geschtäzt. In der zweiten Phase wird eine Reihe von Einzelbildern gemeinsam mit der zusätzlichen DCT-Priorisierung (Discrete Cosine Transformation) verfeinert. Unsere Methode kann verschiedene Körperformen und schwierige Posen ohne menschliches Zutun verarbeiten. Dann erweitern wir das MoCap-System, um die Verfolgung von starren Objekten zu unterstutzen, mit denen die Testpersonen interagieren. Unser System besteht aus 6 RGB-D Azure-Kameras. Zunächst werden alle RGB-D Videos vorverarbeitet, indem Menschen und Objekte segmentiert und 2D-Körpergelenke erkannt werden. Das SMPL-X Modell wird hier eingesetzt, um die Handhaltung besser zu erfassen. Das SMPL-XModell wird in 2D-Keypoints und akkumulierte Punktwolken eingepasst. Wir zeigen, dass die Körperhaltung wichtige Informationen für eine bessere Objektverfolgung liefert. Anschließend werden die Körper- und Objektposen gemeinsam mit Kontakt- und Durch-dringungsbeschrankungen optimiert. Mit diesem Ansatz haben wir den ersten Mensch-Objekt-Interaktionsdatensatz mit natürlichen RGB-Bildern und angemessenen Körper und Objektbewegungsinformationen erfasst. Schließlich präsentieren wir das erste praktische, leichtgewichtige MoCap-System, das nur 6 Inertialmesseinheiten (IMUs) benötigt. Unser Ansatz basiert auf bi-direktionalen rekurrenten neuronalen Netzen (Bi-RNN). Das Netzwerk soll die zeitliche Abhängigkeit besser ausnutzen, indem es vergangene und zukünftige Teilmessungen der IMUs zu- sammenfasst. Um das Problem der Datenknappheit zu lösen, erstellen wir synthetische Daten aus archivierten MoCap-Daten. Insgesamt läuft unser System 10 Mal schneller als die Optimierungsmethode und ist numerisch genauer. Wir zeigen auch, dass es möglich ist, die Aktivität der Testperson abzuschätzen, indem nur die IMU Messung der Smart-watch, die die Testperson trägt, betrachtet wird. Zusammenfassend lässt sich sagen, dass wir die markerlose MoCap-Methode weiter-entwickelt haben, indem wir das erste automatische und dennoch genaue System beisteuerten, die MoCap-Methoden zur Unterstützung der Verfolgung starrer Objekte erweiterten und einen praktischen und leichtgewichtigen Algorithmus mit 6 IMUs vorschlugen. Wir glauben, dass unsere Arbeit die markerlose MoCap billiger und praktikabler macht und somit den Endnutzern fur den taglichen Gebrauch näher bringt.Though effective and successful, traditional marker-less Motion Capture (MoCap) methods suffer from several limitations: 1) they presume a character-specific body model, thus they do not permit a fully automatic pipeline and generalization over diverse body shapes; 2) no objects humans interact with are tracked, while in reality interaction between humans and objects is ubiquitous; 3) they heavily rely on a sophisticated optimization process, which needs a good initialization and strong priors. This process can be slow. We address all the aforementioned issues in this thesis, as described below. Firstly we propose a fully automatic method to accurately reconstruct a 3D human body from multi-view RGB videos, the typical setup for MoCap systems. We pre-process all RGB videos to obtain 2D keypoints and silhouettes. Then we fit the SMPL body model into the 2D measurements in two successive stages. In the first stage, the shape and pose parameters of SMPL are estimated frame-wise sequentially. In the second stage, a batch of frames are refined jointly with an extra DCT prior. Our method can naturally handle different body shapes and challenging poses without human intervention. Then we extend this system to support tracking of rigid objects the subjects interact with. Our setup consists of 6 Azure Kinect cameras. Firstly we pre-process all the videos by segmenting humans and objects and detecting 2D body joints. We adopt the SMPL-X model here to capture body and hand pose. The model is fitted to 2D keypoints and point clouds. Then the body poses and object poses are jointly updated with contact and interpenetration constraints. With this approach, we capture a novel human-object interaction dataset with natural RGB images and plausible body and object motion information. Lastly, we present the first practical and lightweight MoCap system that needs only 6 IMUs. Our approach is based on Bi-directional RNNs. The network can make use of temporal information by jointly reasoning about past and future IMU measurements. To handle the data scarcity issue, we create synthetic data from archival MoCap data. Overall, our system runs ten times faster than traditional optimization-based methods, and is numerically more accurate. We also show it is feasible to estimate which activity the subject is doing by only observing the IMU measurement from a smartwatch worn by the subject. This not only can be useful for a high-level semantic understanding of the human behavior, but also alarms the public of potential privacy concerns. In summary, we advance marker-less MoCap by contributing the first automatic yet accurate system, extending the MoCap methods to support rigid object tracking, and proposing a practical and lightweight algorithm via 6 IMUs. We believe our work makes marker-less and IMUs-based MoCap cheaper and more practical, thus closer to end-users for daily usage

Articulated people detection and pose estimation in challenging real world environments

In this thesis we are interested in the problem of articulated people detection and pose estimation being key ingredients towards understanding visual scenes containing people. First, we investigate how statistical 3D human shape models from computer graphics can be leveraged to ease training data generation. Second, we develop expressive models for 2D single- and multi-person pose estimation. Third, we introduce a novel human pose estimation benchmark that makes a significant advance in terms of diversity and difficulty. Thorough experimental evaluation on standard benchmarks demonstrates significant improvements due to the proposed data augmentation techniques and novel body models, while detailed performance analysis of competing approaches on our novel benchmark allows to identify the most promising directions of improvement.In dieser Arbeit untersuchen wir das Problem der artikulierten Detektion und Posenschätzung von Personen als Schlüsselkomponenten des Verstehens von visuellen Szenen mit Personen. Obwohl es umfangreiche Bemühungen gibt, die Lösung dieser Probleme anzugehen, haben wir drei vielversprechende Herangehensweisen ermittelt, die unserer Meinung nach bisher nicht ausreichend beachtet wurden. Erstens untersuchen wir, wie statistische 3 D Modelle des menschlichen Umrisses, die aus der Computergrafik stammen, wirksam eingesetzt werden können, um die Generierung von Trainingsdaten zu erleichtern. Wir schlagen eine Reihe von Techniken zur automatischen Datengenerierung vor, die eine direkte Repräsentation relevanter Variationen in den Trainingsdaten erlauben. Indem wir Stichproben aus der zu Grunde liegenden Verteilung des menschlichen Umrisses und aus einem großen Datensatz von menschlichen Posen ziehen, erzeugen wir eine neue für unsere Aufgabe relevante Auswahl mit regulierbaren Variationen von Form und Posen. Darüber hinaus verbessern wir das neueste 3 D Modell des menschlichen Umrisses selbst, indem wir es aus einem großen handelsüblichen Datensatz von 3 D Körpern neu aufbauen. Zweitens entwickeln wir ausdrucksstarke räumliche Modelle und ErscheinungsbildModelle für die 2 D Posenschätzung einzelner und mehrerer Personen. Wir schlagen ein ausdrucksstarkes Einzelperson-Modell vor, das Teilabhängigkeiten höherer Ordnung einbezieht, aber dennoch effizient bleibt. Wir verstärken dieses Modell durch verschiedene Arten von starken Erscheinungsbild-Repräsentationen, um die Körperteilhypothesen erheblich zu verbessern. Schließlich schlagen wir ein ausdruckstarkes Modell zur gemeinsamen Posenschätzung mehrerer Personen vor. Dazu entwickeln wir starke Deep Learning-basierte Körperteildetektoren und ein ausdrucksstarkes voll verbundenes räumliches Modell. Der vorgeschlagene Ansatz behandelt die Posenschätzung mehrerer Personen als ein Problem der gemeinsamen Aufteilung und Annotierung eines Satzes von Körperteilhypothesen: er erschließt die Anzahl von Personen in einer Szene, identifiziert verdeckte Körperteile und unterscheidet eindeutig Körperteile von Personen, die sich nahe beieinander befinden. Drittens führen wir eine gründliche Bewertung und Performanzanalyse führender Methoden der menschlichen Posenschätzung und Aktivitätserkennung durch. Dazu stellen wir einen neuen Benchmark vor, der einen bedeutenden Fortschritt bezüglich Diversität und Schwierigkeit im Vergleich zu bisherigen Datensätzen mit sich bringt und über 40 . 000 annotierte Körperposen und mehr als 1 . 5 Millionen Einzelbilder enthält. Darüber hinaus stellen wir einen reichhaltigen Satz an Annotierungen zur Verfügung, die zu einer detaillierten Analyse konkurrierender Herangehensweisen benutzt werden, wodurch wir Erkenntnisse zu Erfolg und Mißerfolg dieser Methoden erhalten. Zusammengefasst präsentiert diese Arbeit einen neuen Ansatz zur artikulierten Detektion und Posenschätzung von Personen. Eine gründliche experimentelle Evaluation auf Standard-Benchmarkdatensätzen zeigt signifikante Verbesserungen durch die vorgeschlagenen Datenverstärkungstechniken und neuen Körpermodelle, während eine detaillierte Performanzanalyse konkurrierender Herangehensweisen auf unserem neu vorgestellten großen Benchmark uns erlaubt, die vielversprechendsten Bereiche für Verbesserungen zu erkennen

More is Better: 3D Human Pose Estimation from Complementary Data Sources

Computer Vision (CV) research has been playing a strategic role in many different complex scenarios that are becoming fundamental components in our everyday life. From Augmented/Virtual reality (AR/VR) to Human-Robot interactions, having a visual interpretation of the surrounding world is the first and most important step to develop new advanced systems. As in other research areas, the boost in performance in Computer Vision algorithms has to be mainly attributed to the widespread usage of deep neural networks. Rather than selecting handcrafted features, such approaches identify which are the best features needed to solve a specific task, by learning them from a corpus of carefully annotated data. Such important property of these neural networks comes with a price: they need very large data collections to learn from. Collecting data is a time consuming and expensive operation that varies, being much harder for some tasks than others. In order to limit additional data collection, we therefore need to carefully design models that can extract as much information as possible from already available dataset, even those collected for neighboring domains. In this work I focus on exploring different solutions for and important research problem in Computer Vision, 3D human pose estimation, that is the task of estimating the 3D skeletal representation of a person characterized in an image/s. This has been done for several configurations: monocular camera, multi-view systems and from egocentric perspectives. First, from a single external front facing camera a semi-supervised approach is used to regress the set of 3D joint positions of the represented person. This is done by fully exploiting all of the available information at all the levels of the network, in a novel manner, as well as allowing the model to be trained with partially labelled data. A multi-camera 3D human pose estimation system is introduced by designing a network trainable in a semi-supervised or even unsupervised manner in a multiview system. Unlike standard motion-captures algorithm, demanding a long and time consuming configuration setup at the beginning of each capturing session, this novel approach requires little to none initial system configuration. Finally, a novel architecture is developed to work in a very specific and significantly harder configuration: 3D human pose estimation when using cameras embedded in a head mounted display (HMD). Due to the limited data availability, the model needs to carefully extract information from the data to properly generalize on unseen images. This is particularly useful in AR/VR use case scenarios, demonstrating the versatility of our network to various working conditions