10 research outputs found
Self-supervised Learning of Interpretable Keypoints from Unlabelled Videos
We propose KeypointGAN, a new method for recognizing the pose of objects from
a single image that for learning uses only unlabelled videos and a weak
empirical prior on the object poses. Video frames differ primarily in the pose
of the objects they contain, so our method distils the pose information by
analyzing the differences between frames. The distillation uses a new dual
representation of the geometry of objects as a set of 2D keypoints, and as a
pictorial representation, i.e. a skeleton image. This has three benefits: (1)
it provides a tight `geometric bottleneck' which disentangles pose from
appearance, (2) it can leverage powerful image-to-image translation networks to
map between photometry and geometry, and (3) it allows to incorporate empirical
pose priors in the learning process. The pose priors are obtained from unpaired
data, such as from a different dataset or modality such as mocap, such that no
annotated image is ever used in learning the pose recognition network. In
standard benchmarks for pose recognition for humans and faces, our method
achieves state-of-the-art performance among methods that do not require any
labelled images for training.Comment: CVPR 2020 (oral). Project page:
http://www.robots.ox.ac.uk/~vgg/research/unsupervised_pose
Shape Consistent 2D Keypoint Estimation under Domain Shift
Recent unsupervised domain adaptation methods based on deep architectures
have shown remarkable performance not only in traditional classification tasks
but also in more complex problems involving structured predictions (e.g.
semantic segmentation, depth estimation). Following this trend, in this paper
we present a novel deep adaptation framework for estimating keypoints under
domain shift}, i.e. when the training (source) and the test (target) images
significantly differ in terms of visual appearance. Our method seamlessly
combines three different components: feature alignment, adversarial training
and self-supervision. Specifically, our deep architecture leverages from
domain-specific distribution alignment layers to perform target adaptation at
the feature level. Furthermore, a novel loss is proposed which combines an
adversarial term for ensuring aligned predictions in the output space and a
geometric consistency term which guarantees coherent predictions between a
target sample and its perturbed version. Our extensive experimental evaluation
conducted on three publicly available benchmarks shows that our approach
outperforms state-of-the-art domain adaptation methods in the 2D keypoint
prediction task
Relation-Based Associative Joint Location for Human Pose Estimation in Videos
Video-based human pose estimation (HPE) is a vital yet challenging task.
While deep learning methods have made significant progress for the HPE, most
approaches to this task detect each joint independently, damaging the pose
structural information. In this paper, unlike the prior methods, we propose a
Relation-based Pose Semantics Transfer Network (RPSTN) to locate joints
associatively. Specifically, we design a lightweight joint relation extractor
(JRE) to model the pose structural features and associatively generate heatmaps
for joints by modeling the relation between any two joints heuristically
instead of building each joint heatmap independently. Actually, the proposed
JRE module models the spatial configuration of human poses through the
relationship between any two joints. Moreover, considering the temporal
semantic continuity of videos, the pose semantic information in the current
frame is beneficial for guiding the location of joints in the next frame.
Therefore, we use the idea of knowledge reuse to propagate the pose semantic
information between consecutive frames. In this way, the proposed RPSTN
captures temporal dynamics of poses. On the one hand, the JRE module can infer
invisible joints according to the relationship between the invisible joints and
other visible joints in space. On the other hand, in the time, the propose
model can transfer the pose semantic features from the non-occluded frame to
the occluded frame to locate occluded joints. Therefore, our method is robust
to the occlusion and achieves state-of-the-art results on the two challenging
datasets, which demonstrates its effectiveness for video-based human pose
estimation. We will release the code and models publicly
Landmarks Augmentation with Manifold-Barycentric Oversampling
The training of Generative Adversarial Networks (GANs) requires a large
amount of data, stimulating the development of new augmentation methods to
alleviate the challenge. Oftentimes, these methods either fail to produce
enough new data or expand the dataset beyond the original manifold. In this
paper, we propose a new augmentation method that guarantees to keep the new
data within the original data manifold thanks to the optimal transport theory.
The proposed algorithm finds cliques in the nearest-neighbors graph and, at
each sampling iteration, randomly draws one clique to compute the Wasserstein
barycenter with random uniform weights. These barycenters then become the new
natural-looking elements that one could add to the dataset. We apply this
approach to the problem of landmarks detection and augment the available
annotation in both unpaired and in semi-supervised scenarios. Additionally, the
idea is validated on cardiac data for the task of medical segmentation. Our
approach reduces the overfitting and improves the quality metrics beyond the
original data outcome and beyond the result obtained with popular modern
augmentation methods.Comment: 11 pages, 4 figures, 3 tables. I.B. and N.B. contributed equally.
D.V.D. is the corresponding autho
From Anecdotal Evidence to Quantitative Evaluation Methods:A Systematic Review on Evaluating Explainable AI
The rising popularity of explainable artificial intelligence (XAI) to
understand high-performing black boxes, also raised the question of how to
evaluate explanations of machine learning (ML) models. While interpretability
and explainability are often presented as a subjectively validated binary
property, we consider it a multi-faceted concept. We identify 12 conceptual
properties, such as Compactness and Correctness, that should be evaluated for
comprehensively assessing the quality of an explanation. Our so-called Co-12
properties serve as categorization scheme for systematically reviewing the
evaluation practice of more than 300 papers published in the last 7 years at
major AI and ML conferences that introduce an XAI method. We find that 1 in 3
papers evaluate exclusively with anecdotal evidence, and 1 in 5 papers evaluate
with users. We also contribute to the call for objective, quantifiable
evaluation methods by presenting an extensive overview of quantitative XAI
evaluation methods. This systematic collection of evaluation methods provides
researchers and practitioners with concrete tools to thoroughly validate,
benchmark and compare new and existing XAI methods. This also opens up
opportunities to include quantitative metrics as optimization criteria during
model training in order to optimize for accuracy and interpretability
simultaneously.Comment: Link to website added: https://utwente-dmb.github.io/xai-papers
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Learning to See with Minimal Human Supervision
Deep learning has significantly advanced computer vision in the past decade, paving the way for practical applications such as facial recognition and autonomous driving. However, current techniques depend heavily on human supervision, limiting their broader deployment. This dissertation tackles this problem by introducing algorithms and theories to minimize human supervision in three key areas: data, annotations, and neural network architectures, in the context of various visual understanding tasks such as object detection, image restoration, and 3D generation.
First, we present self-supervised learning algorithms to handle in-the-wild images and videos that traditionally require time-consuming manual curation and labeling. We demonstrate that when a deep network is trained to be invariant to geometric and photometric transformations, representations from its intermediate layers are highly predictive of object semantic parts such as eyes and noses. This insight offers a simple unsupervised learning framework that significantly improves the efficiency and accuracy of few-shot landmark prediction and matching. We then present a technique for learning single-view 3D object pose estimation models by utilizing in-the-wild videos where objects turn (e.g., cars in roundabouts). This technique achieves competitive performance with respect to existing state-of-the-art without requiring any manual labels during training. We also contribute an Accidental Turntables Dataset, containing a challenging set of 41,212 images of cars in cluttered backgrounds, motion blur, and illumination changes that serve as a benchmark for 3D pose estimation.
Second, we address variations in labeling styles across different annotators, which leads to a type of noisy label referred to as heterogeneous label. This variability in human annotation can cause subpar performance during both the training and testing phases. To mitigate this, we have developed a framework that models the labeling styles of individual annotators, reducing the impact of human annotation variations and enhancing the performance of standard object detection models. We have also applied this framework to analyze ecological data, which are often collected opportunistically across different case studies without consistent annotation guidelines. Through this application, we have obtained several insightful observations into large-scale bird migration behaviors and their relationship to climate change.
Our next study explores the challenges of designing neural networks, an area that lacks a comprehensive theoretical understanding. By linking deep neural networks with Gaussian processes, we propose a novel Bayesian interpretation of the deep image prior, which parameterizes a natural image as the output of a convolutional network with random parameters and random input. This approach offers valuable insights to optimize the design of neural networks for various image restoration tasks.
Lastly, we introduce several machine-learning techniques to reconstruct and edit 3D shapes from 2D images with minimal human effort. We first present a generic multi-modal generative model that bridges 2D images and 3D shapes via a shared latent space, and demonstrate its applications on versatile 3D shape generation and manipulation tasks. Additionally, we develop a framework for joint estimation of 3D neural scene representation and camera poses. This approach outperforms prior works and allows us to operate in the general SE(3) camera pose setting, unlike the baselines. The results also indicate this method can be complementary to classical structure-from-motion (SfM) pipelines as it compares favorably to SfM on low-texture and low-resolution images
Towards accurate multi-person pose estimation in the wild
In this thesis we are concerned with the problem of articulated human pose estimation and pose tracking in images and video sequences. Human pose estimation is a task of localising major joints of a human skeleton in natural images and is one of the most important visual recognition tasks in the scenes containing humans with numerous applications in robotics, virtual and augmented reality, gaming and healthcare among others. Articulated human pose tracking requires tracking multiple persons in the video sequence while simultaneously estimating full body poses. This task is important for analysing surveillance footage, activity recognition, sports analytics, etc. Most of the prior work focused on the pose estimation of single pre-localised humans whereas here we address a case with multiple people in real world images which entails several challenges such as person-person overlaps in highly crowded scenes, unknown number of people or people entering and leaving video sequences. The first contribution is a multi-person pose estimation algorithm based on the bottom-up detection-by-grouping paradigm. Unlike the widespread top-down approaches our method detects body joints and pairwise relations between them in a single forward pass of a convolutional neural network. Multi-person parsing is performed by optimizing a joint objective based on a multicut graph partitioning framework. Secondly, we extend our pose estimation approach to articulated multi-person pose tracking in videos. Our approach performs multi-target tracking and pose estimation in a holistic manner by optimising a single objective. We further simplify and refine the formulation which allows us to reach close to the real-time performance. Thirdly, we propose a large scale dataset and a benchmark for articulated multi-person tracking. It is the first dataset of video sequences comprising complex multi-person scenes and fully annotated tracks with 2D keypoints. Our fourth contribution is a method for estimating 3D body pose using on-body wearable cameras. Our approach uses a pair of downward facing, head-mounted cameras and captures an entire body. This egocentric approach is free of limitations of traditional setups with external cameras and can estimate body poses in very crowded environments. Our final contribution goes beyond human pose estimation and is in the field of deep learning of 3D object shapes. In particular, we address the case of reconstructing 3D objects from weak supervision. Our approach represents objects as 3D point clouds and is able to learn them with 2D supervision only and without requiring camera pose information at training time. We design a differentiable renderer of point clouds as well as a novel loss formulation for dealing with camera pose ambiguity.In dieser Arbeit behandeln wir das Problem der Schätzung und Verfolgung artikulierter menschlicher Posen in Bildern und Video-Sequenzen. Die Schätzung menschlicher Posen besteht darin die Hauptgelenke des menschlichen Skeletts in natürlichen Bildern zu lokalisieren und ist eine der wichtigsten Aufgaben der visuellen Erkennung in Szenen, die Menschen beinhalten. Sie hat zahlreiche Anwendungen in der Robotik, virtueller und erweiterter Realität, in Videospielen, in der Medizin und weiteren Bereichen. Die Verfolgung artikulierter menschlicher Posen erfordert die Verfolgung mehrerer Personen in einer Videosequenz bei gleichzeitiger Schätzung vollständiger Körperhaltungen. Diese Aufgabe ist besonders wichtig für die Analyse von Video-Überwachungsaufnahmen, Aktivitätenerkennung, digitale Sportanalyse etc. Die meisten vorherigen Arbeiten sind auf die Schätzung einzelner Posen vorlokalisierter Menschen fokussiert, wohingegen wir den Fall mehrerer Personen in natürlichen Aufnahmen betrachten. Dies bringt einige Herausforderungen mit sich, wie die Überlappung verschiedener Personen in dicht gedrängten Szenen, eine unbekannte Anzahl an Personen oder Personen die das Sichtfeld der Video-Sequenz verlassen oder betreten. Der erste Beitrag ist ein Algorithmus zur Schätzung der Posen mehrerer Personen, welcher auf dem Paradigma der Erkennung durch Gruppierung aufbaut. Im Gegensatz zu den verbreiteten Verfeinerungs-Ansätzen erkennt unsere Methode Körpergelenke and paarweise Beziehungen zwischen ihnen in einer einzelnen Vorwärtsrechnung eines faltenden neuronalen Netzwerkes. Die Gliederung in mehrere Personen erfolgt durch Optimierung einer gemeinsamen Zielfunktion, die auf dem Mehrfachschnitt-Problem in der Graphenzerlegung basiert. Zweitens erweitern wir unseren Ansatz zur Posen-Bestimmung auf das Verfolgen mehrerer Personen und deren Artikulation in Videos. Unser Ansatz führt eine Verfolgung mehrerer Ziele und die Schätzung der zugehörigen Posen in ganzheitlicher Weise durch, indem eine einzelne Zielfunktion optimiert wird. Desweiteren vereinfachen und verfeinern wir die Formulierung, was unsere Methode nah an Echtzeit-Leistung bringt. Drittens schlagen wir einen großen Datensatz und einen Bewertungsmaßstab für die Verfolgung mehrerer artikulierter Personen vor. Dies ist der erste Datensatz der Video-Sequenzen von komplexen Szenen mit mehreren Personen beinhaltet und deren Spuren komplett mit zwei-dimensionalen Markierungen der Schlüsselpunkte versehen sind. Unser vierter Beitrag ist eine Methode zur Schätzung von drei-dimensionalen Körperhaltungen mittels am Körper tragbarer Kameras. Unser Ansatz verwendet ein Paar nach unten gerichteter, am Kopf befestigter Kameras und erfasst den gesamten Körper. Dieser egozentrische Ansatz ist frei von jeglichen Limitierungen traditioneller Konfigurationen mit externen Kameras und kann Körperhaltungen in sehr dicht gedrängten Umgebungen bestimmen. Unser letzter Beitrag geht über die Schätzung menschlicher Posen hinaus in den Bereich des tiefen Lernens der Gestalt von drei-dimensionalen Objekten. Insbesondere befassen wir uns mit dem Fall drei-dimensionale Objekte unter schwacher Überwachung zu rekonstruieren. Unser Ansatz repräsentiert Objekte als drei-dimensionale Punktwolken and ist im Stande diese nur mittels zwei-dimensionaler Überwachung und ohne Informationen über die Kamera-Ausrichtung zur Trainingszeit zu lernen. Wir entwerfen einen differenzierbaren Renderer für Punktwolken sowie eine neue Formulierung um mit uneindeutigen Kamera-Ausrichtungen umzugehen