Real-time 3D human body pose estimation from monocular RGB input

Human motion capture finds extensive application in movies, games, sports and biomechanical analysis. However, existing motion capture solutions require cumbersome external and/or on-body instrumentation, or use active sensors with limits on the possible capture volume dictated by power consumption. The ubiquity and ease of deployment of RGB cameras makes monocular RGB based human motion capture an extremely useful problem to solve, which would lower the barrier-to entry for content creators to employ motion capture tools, and enable newer applications of human motion capture. This thesis demonstrates the first real-time monocular RGB based motion-capture solutions that work in general scene settings. They are based on developing neural network based approaches to address the ill-posed problem of estimating 3D human pose from a single RGB image, in combination with model based fitting. In particular, the contributions of this work make advances towards three key aspects of real-time monocular RGB based motion capture, namely speed, accuracy, and the ability to work for general scenes. New training datasets are proposed, for single-person and multi-person scenarios, which, together with the proposed transfer learning based training pipeline, allow learning based approaches to be appearance invariant. The training datasets are accompanied by evaluation benchmarks with multiple avenues of fine-grained evaluation. The evaluation benchmarks differ visually from the training datasets, so as to promote efforts towards solutions that generalize to in-the-wild scenes. The proposed task formulations for the single-person and multi-person case allow higher accuracy, and incorporate additional qualities such as occlusion robustness, that are helpful in the context of a full motion capture solution. The multi-person formulations are designed to have a nearly constant inference time regardless of the number of subjects in the scene, and combined with contributions towards fast neural network inference, enable real-time 3D pose estimation for multiple subjects. Combining the proposed learning-based approaches with a model-based kinematic skeleton fitting step provides temporally stable joint angle estimates, which can be readily employed for driving virtual characters.Menschlicher Motion Capture findet umfangreiche Anwendung in Filmen, Spielen, Sport und biomechanischen Analysen. Bestehende Motion-Capture-Lösungen erfordern jedoch umständliche externe Instrumentierung und / oder Instrumentierung am Körper, oder verwenden aktive Sensoren deren begrenztes Erfassungsvolumen durch den Stromverbrauch begrenzt wird. Die Allgegenwart und einfache Bereitstellung von RGB-Kameras macht die monokulare RGB-basierte Motion Capture zu einem äußerst nützlichen Problem. Dies würde die Eintrittsbarriere für Inhaltsersteller für die Verwendung der Motion Capture verringern und neuere Anwendungen dieser Tools zur Analyse menschlicher Bewegungen ermöglichen. Diese Arbeit zeigt die ersten monokularen RGB-basierten Motion-Capture-Lösungen in Echtzeit, die in allgemeinen Szeneneinstellungen funktionieren. Sie basieren auf der Entwicklung neuronaler netzwerkbasierter Ansätze, um das schlecht gestellte Problem der Schätzung der menschlichen 3D-Pose aus einem einzelnen RGB-Bild in Kombination mit einer modellbasierten Anpassung anzugehen. Insbesondere machen die Beiträge dieser Arbeit Fortschritte in Richtung drei Schlüsselaspekte der monokularen RGB-basierten Echtzeit-Bewegungserfassung, nämlich Geschwindigkeit, Genauigkeit und die Fähigkeit, für allgemeine Szenen zu arbeiten. Es werden neue Trainingsdatensätze für Einzel- und Mehrpersonen-Szenarien vorgeschlagen, die zusammen mit der vorgeschlagenen Trainingspipeline, die auf Transferlernen basiert, ermöglichen, dass lernbasierte Ansätze nicht von Unterschieden im Erscheinungsbild des Bildes beeinflusst werden. Die Trainingsdatensätze werden von Bewertungsbenchmarks mit mehreren Möglichkeiten einer feinkörnigen Bewertung begleitet. Die angegebenen Benchmarks unterscheiden sich visuell von den Trainingsaufzeichnungen, um die Entwicklung von Lösungen zu fördern, die sich auf verschiedene Szenen verallgemeinern lassen. Die vorgeschlagenen Aufgabenformulierungen für den Einzel- und Mehrpersonenfall ermöglichen eine höhere Genauigkeit und enthalten zusätzliche Eigenschaften wie die Robustheit der Okklusion, die im Kontext einer vollständigen Bewegungserfassungslösung hilfreich sind. Die Mehrpersonenformulierungen sind so konzipiert, dass sie unabhängig von der Anzahl der Subjekte in der Szene eine nahezu konstante Inferenzzeit haben. In Kombination mit Beiträgen zur schnellen Inferenz neuronaler Netze ermöglichen sie eine 3D-Posenschätzung in Echtzeit für mehrere Subjekte. Die Kombination der vorgeschlagenen lernbasierten Ansätze mit einem modellbasierten kinematischen Skelettanpassungsschritt liefert zeitlich stabile Gelenkwinkelschätzungen, die leicht zum Ansteuern virtueller Charaktere verwendet werden können

Ensemble based on randomised neural networks for online data stream regression in presence of concept drift

The big data paradigm has posed new challenges for the Machine Learning algorithms, such as analysing continuous flows of data, in the form of data streams, and dealing with the evolving nature of the data, which cause a phenomenon often referred to in the literature as concept drift. Concept drift is caused by inconsistencies between the optimal hypotheses in two subsequent chunks of data, whereby the concept underlying a given process evolves over time, which can happen due to several factors including change in consumer preference, economic dynamics, or environmental conditions. This thesis explores the problem of data stream regression with the presence of concept drift. This problem requires computationally efficient algorithms that are able to adapt to the various types of drift that may affect the data. The development of effective algorithms for data streams with concept drift requires several steps that are discussed in this research. The first one is related to the datasets required to assess the algorithms. In general, it is not possible to determine the occurrence of concept drift on real-world datasets; therefore, synthetic datasets where the various types of concept drift can be simulated are required. The second issue is related to the choice of the algorithm. The ensemble algorithms show many advantages to deal with concept drifting data streams, which include flexibility, computational efficiency and high accuracy. For the design of an effective ensemble, this research analyses the use of randomised Neural Networks as base models, along with their optimisation. The optimisation of the randomised Neural Networks involves design and tuning hyperparameters which may substantially affect its performance. The optimisation of the base models is an important aspect to build highly accurate and computationally efficient ensembles. To cope with the concept drift, the existing methods either require setting fixed updating points, which may result in unnecessary computations or slow reaction to concept drift, or rely on drifting detection mechanism, which may be ineffective due to the difficulty to detect drift in real applications. Therefore, the research contributions of this thesis include the development of a new approach for synthetic dataset generation, development of a new hyperparameter optimisation algorithm that reduces the search effort and the need of prior assumptions compared to existing methods, the analysis of the effects of randomised Neural Networks hyperparameters, and the development of a new ensemble algorithm based on bagging meta-model that reduces the computational effort over existing methods and uses an innovative updating mechanism to cope with concept drift. The algorithms have been tested on synthetic datasets and validated on four real-world datasets from various application domains

Implicit Object Pose Estimation on RGB Images Using Deep Learning Methods

With the rise of robotic and camera systems and the success of deep learning in computer vision, there is growing interest in precisely determining object positions and orientations. This is crucial for tasks like automated bin picking, where a camera sensor analyzes images or point clouds to guide a robotic arm in grasping objects. Pose recognition has broader applications, such as predicting a car's trajectory in autonomous driving or adapting objects in virtual reality based on the viewer's perspective. This dissertation focuses on RGB-based pose estimation methods that use depth information only for refinement, which is a challenging problem. Recent advances in deep learning have made it possible to predict object poses in RGB images, despite challenges like object overlap, object symmetries and more. We introduce two implicit deep learning-based pose estimation methods for RGB images, covering the entire process from data generation to pose selection. Furthermore, theoretical findings on Fourier embeddings are shown to improve the performance of the so-called implicit neural representations - which are then successfully utilized for the task of implicit pose estimation

Using ensembles for accurate modelling of manufacturing processes in an IoT data-acquisition solution

The development of complex real-time platforms for the Internet of Things (IoT) opens up a promising future for the diagnosis and the optimization of machining processes. Many issues have still to be solved before IoT platforms can be profitable for small workshops with very flexible workloads and workflows. The main obstacles refer to sensor implementation, IoT architecture, and data processing, and analysis. In this research, the use of different machine-learning techniques is proposed, for the extraction of different information from an IoT platform connected to a machining center, working under real industrial conditions in a workshop. The aim is to evaluate which algorithmic technique might be the best to build accurate prediction models for one of the main demands of workshops: the optimization of machining processes. This evaluation, completed under real industrial conditions, includes very limited information on the machining workload of the machining center and unbalanced datasets. The strategy is validated for the classification of the state of a machining center, its working mode, and the prediction of the thermal evolution of the main machine-tool motors: the axis motors and the milling head motor. The results show the superiority of the ensembles for both classification problems under analysis and all four regression problems. In particular, Rotation Forest-based ensembles turned out to have the best performance in the experiments for all the metrics under study. The models are accurate enough to provide useful conclusions applicable to current industrial practice, such as improvements in machine programming to avoid cutting conditions that might greatly reduce tool lifetime and damage machine components.Projects TIN2015-67534-P (MINECO/FEDER, UE) of the Ministerio de Economía Competitividad of the Spanish Government and projects CCTT1/17/BU/0003 and BU085P17 (JCyL/FEDER, UE) of the Junta de Castilla y León, all of them co-financed through European-Union FEDER funds

Resource-Aware Predictive Models in Cyber-Physical Systems

Cyber-Physical Systems (CPS) are composed of computing devices interacting with physical systems. Model-based design is a powerful methodology in CPS design in the implementation of control systems. For instance, Model Predictive Control (MPC) is typically implemented in CPS applications, e.g., in path tracking of autonomous vehicles. MPC deploys a model to estimate the behavior of the physical system at future time instants for a specific time horizon. Ordinary Differential Equations (ODE) are the most commonly used models to emulate the behavior of continuous-time (non-)linear dynamical systems. A complex physical model may comprise thousands of ODEs that pose scalability, performance and power consumption challenges. One approach to address these model complexity challenges are frameworks that automate the development of model-to-model transformation. In this dissertation, a state-based model with tunable parameters is proposed to operate as a reconfigurable predictive model of the physical system. Moreover, we propose a run-time switching algorithm that selects the best model using machine learning. We employed a metric that formulates the trade-off between the error and computational savings due to model reduction. Building statistical models are constrained to having expert knowledge and an actual understanding of the modeled phenomenon or process. Also, statistical models may not produce solutions that are as robust in a real-world context as factors outside the model, like disruptions would not be taken into account. Machine learning models have emerged as a solution to account for the dynamic behavior of the environment and automate intelligence acquisition and refinement. Neural networks are machine learning models, well-known to have the ability to learn linear and nonlinear relations between input and output variables without prior knowledge. However, the ability to efficiently exploit resource-hungry neural networks in embedded resource-bound settings is a major challenge.Here, we proposed Priority Neuron Network (PNN), a resource-aware neural networks model that can be reconfigured into smaller sub-networks at runtime. This approach enables a trade-off between the model's computation time and accuracy based on available resources. The PNN model is memory efficient since it stores only one set of parameters to account for various sub-network sizes. We propose a training algorithm that applies regularization techniques to constrain the activation value of neurons and assigns a priority to each one. We consider the neuron's ordinal number as our priority criteria in that the priority of the neuron is inversely proportional to its ordinal number in the layer. This imposes a relatively sorted order on the activation values. We conduct experiments to employ our PNN as the predictive model in a CPS application. We can see that not only our technique will resolve the memory overhead of DNN architectures but it also reduces the computation overhead for the training process substantially. The training time is a critical matter especially in embedded systems where many NN models are trained on the fly

S-Rocket: Selective Random Convolution Kernels for Time Series Classification

Random convolution kernel transform (Rocket) is a fast, efficient, and novel approach for time series feature extraction using a large number of independent randomly initialized 1-D convolution kernels of different configurations. The output of the convolution operation on each time series is represented by a partial positive value (PPV). A concatenation of PPVs from all kernels is the input feature vector to a Ridge regression classifier. Unlike typical deep learning models, the kernels are not trained and there is no weighted/trainable connection between kernels or concatenated features and the classifier. Since these kernels are generated randomly, a portion of these kernels may not positively contribute in performance of the model. Hence, selection of the most important kernels and pruning the redundant and less important ones is necessary to reduce computational complexity and accelerate inference of Rocket for applications on the edge devices. Selection of these kernels is a combinatorial optimization problem. In this paper, we propose a scheme for selecting these kernels while maintaining the classification performance. First, the original model is pre-trained at full capacity. Then, a population of binary candidate state vectors is initialized where each element of a vector represents the active/inactive status of a kernel. A population-based optimization algorithm evolves the population in order to find a best state vector which minimizes the number of active kernels while maximizing the accuracy of the classifier. This activation function is a linear combination of the total number of active kernels and the classification accuracy of the pre-trained classifier with the active kernels. Finally, the selected kernels in the best state vector are utilized to train the Ridge regression classifier with the selected kernels

BagStack Classification for Data Imbalance Problems with Application to Defect Detection and Labeling in Semiconductor Units

abstract: Despite the fact that machine learning supports the development of computer vision applications by shortening the development cycle, finding a general learning algorithm that solves a wide range of applications is still bounded by the ”no free lunch theorem”. The search for the right algorithm to solve a specific problem is driven by the problem itself, the data availability and many other requirements. Automated visual inspection (AVI) systems represent a major part of these challenging computer vision applications. They are gaining growing interest in the manufacturing industry to detect defective products and keep these from reaching customers. The process of defect detection and classification in semiconductor units is challenging due to different acceptable variations that the manufacturing process introduces. Other variations are also typically introduced when using optical inspection systems due to changes in lighting conditions and misalignment of the imaged units, which makes the defect detection process more challenging. In this thesis, a BagStack classification framework is proposed, which makes use of stacking and bagging concepts to handle both variance and bias errors. The classifier is designed to handle the data imbalance and overfitting problems by adaptively transforming the multi-class classification problem into multiple binary classification problems, applying a bagging approach to train a set of base learners for each specific problem, adaptively specifying the number of base learners assigned to each problem, adaptively specifying the number of samples to use from each class, applying a novel data-imbalance aware cross-validation technique to generate the meta-data while taking into account the data imbalance problem at the meta-data level and, finally, using a multi-response random forest regression classifier as a meta-classifier. The BagStack classifier makes use of multiple features to solve the defect classification problem. In order to detect defects, a locally adaptive statistical background modeling is proposed. The proposed BagStack classifier outperforms state-of-the-art image classification techniques on our dataset in terms of overall classification accuracy and average per-class classification accuracy. The proposed detection method achieves high performance on the considered dataset in terms of recall and precision.Dissertation/ThesisDoctoral Dissertation Computer Engineering 201

Behaviour Profiling using Wearable Sensors for Pervasive Healthcare

In recent years, sensor technology has advanced in terms of hardware sophistication and miniaturisation. This has led to the incorporation of unobtrusive, low-power sensors into networks centred on human participants, called Body Sensor Networks. Amongst the most important applications of these networks is their use in healthcare and healthy living. The technology has the possibility of decreasing burden on the healthcare systems by providing care at home, enabling early detection of symptoms, monitoring recovery remotely, and avoiding serious chronic illnesses by promoting healthy living through objective feedback. In this thesis, machine learning and data mining techniques are developed to estimate medically relevant parameters from a participant‘s activity and behaviour parameters, derived from simple, body-worn sensors. The first abstraction from raw sensor data is the recognition and analysis of activity. Machine learning analysis is applied to a study of activity profiling to detect impaired limb and torso mobility. One of the advances in this thesis to activity recognition research is in the application of machine learning to the analysis of 'transitional activities': transient activity that occurs as people change their activity. A framework is proposed for the detection and analysis of transitional activities. To demonstrate the utility of transition analysis, we apply the algorithms to a study of participants undergoing and recovering from surgery. We demonstrate that it is possible to see meaningful changes in the transitional activity as the participants recover. Assuming long-term monitoring, we expect a large historical database of activity to quickly accumulate. We develop algorithms to mine temporal associations to activity patterns. This gives an outline of the user‘s routine. Methods for visual and quantitative analysis of routine using this summary data structure are proposed and validated. The activity and routine mining methodologies developed for specialised sensors are adapted to a smartphone application, enabling large-scale use. Validation of the algorithms is performed using datasets collected in laboratory settings, and free living scenarios. Finally, future research directions and potential improvements to the techniques developed in this thesis are outlined