Event Cameras Research Articles

Turbulence mitigation in imagery including moving objects from a static event camera

Long-range horizontal path imaging through atmospheric turbulence is hampered by spatiotemporally randomly varying shifting and blurring of scene points in recorded imagery. Although existing software-based mitigation strategies can produce sharp and stable imagery of static scenes, it remains highly challenging to mitigate turbulence in scenes with moving objects such that they remain visible as moving objects in the output. In our work, we investigate if and how event (also called neuromorphic) cameras can be used for this challenge. We explore how the high temporal resolution of the event stream can be used to distinguish between the apparent motion due to turbulence and the actual motion of physical objects in the scene. We use this to propose an algorithm to reconstruct output image sequences in which the static background of the scene is mitigated for turbulence, while the moving objects in the scene are preserved. The algorithm is demonstrated on indoor experimental recordings of moving objects imaged through artificially generated turbulence.

MVF-Net: A Multi-View Fusion Network for Event-Based Object Classification

Event-based object recognition has drawn increasing attention for event cameras’ distinguished advantages of low power consumption and high dynamic range. For this new modality, previous works based on customizing low-level descriptors are vulnerable to noise and with limited generalizability. Although recent works turn to design various deep neural networks to extract event features, they either suffer from data insufficiency to fully train the event-based model or fail to encode spatial and temporal cues simultaneously with their single view network. In this work, we address these limitations by proposing a multi-view attention-aware network, in which an event stream is projected to multi-view 2D maps to utilize well-trained 2D models and explore spatio-temporal complements. Besides, the attention mechanism is used to boost the complements in different streams for better joint inference. Comprehensive experiments show the large superiority of our model over state-of-the-art methods as well as the efficacy of our multi-view fusion framework for event data.

Event-Based Near-Eye Gaze Tracking Beyond 10,000 Hz.

The cameras in modern gaze-tracking systems suffer from fundamental bandwidth and power limitations, constraining data acquisition speed to 300 Hz realistically. This obstructs the use of mobile eye trackers to perform, e.g., low latency predictive rendering, or to study quick and subtle eye motions like microsaccades using head-mounted devices in the wild. Here, we propose a hybrid frame-event-based near-eye gaze tracking system offering update rates beyond 10,000 Hz with an accuracy that matches that of high-end desktop-mounted commercial trackers when evaluated in the same conditions. Our system, previewed in Figure 1, builds on emerging event cameras that simultaneously acquire regularly sampled frames and adaptively sampled events. We develop an online 2D pupil fitting method that updates a parametric model every one or few events. Moreover, we propose a polynomial regressor for estimating the point of gaze from the parametric pupil model in real time. Using the first event-based gaze dataset, we demonstrate that our system achieves accuracies of 0.45°-1.75° for fields of view from 45° to 98°. With this technology, we hope to enable a new generation of ultra-low-latency gaze-contingent rendering and display techniques for virtual and augmented reality.

Combining Events and Frames Using Recurrent Asynchronous Multimodal Networks for Monocular Depth Prediction

Event cameras are novel vision sensors that report per-pixel brightness changes as a stream of asynchronous “events”. They offer significant advantages compared to standard cameras due to their high temporal resolution, high dynamic range and lack of motion blur. However, events only measure the varying component of the visual signal, which limits their ability to encode scene context. By contrast, standard cameras measure absolute intensity frames, which capture a much richer representation of the scene. Both sensors are thus complementary. However, due to the asynchronous nature of events, combining them with synchronous images remains challenging, especially for learning-based methods. This is because traditional recurrent neural networks (RNNs) are not designed for asynchronous and irregular data from additional sensors. To address this challenge, we introduce Recurrent Asynchronous Multimodal (RAM) networks, which generalize traditional RNNs to handle asynchronous and irregular data from multiple sensors. Inspired by traditional RNNs, RAM networks maintain a hidden state that is updated asynchronously and can be queried at any time to generate a prediction. We apply this novel architecture to monocular depth estimation with events and frames where we show an improvement over state-of-the-art methods by up to 30% in terms of mean absolute depth error. To enable further research on multimodal learning with events, we release EventScape, a new dataset with events, intensity frames, semantic labels, and depth maps recorded in the CARLA simulator.

The GRIFFIN Perception Dataset: Bridging the Gap Between Flapping-Wing Flight and Robotic Perception

The development of automatic perception systems and techniques for bio-inspired flapping-wing robots is severely hampered by the high technical complexity of these platforms and the installation of onboard sensors and electronics. Besides, flapping-wing robot perception suffers from high vibration levels and abrupt movements during flight, which cause motion blur and strong changes in lighting conditions. This paper presents a perception dataset for bird-scale flapping-wing robots as a tool to help alleviate the aforementioned problems. The presented data include measurements from onboard sensors widely used in aerial robotics and suitable to deal with the perception challenges of flapping-wing robots, such as an event camera, a conventional camera, and two Inertial Measurement Units (IMUs), as well as ground truth measurements from a laser tracker or a motion capture system. A total of 21 datasets of different types of flights were collected in three different scenarios (one indoor and two outdoor). To the best of the authors' knowledge this is the first dataset for flapping-wing robot perception.

Autonomous Quadrotor Flight Despite Rotor Failure With Onboard Vision Sensors: Frames vs. Events

Fault-tolerant control is crucial for safety-critical systems, such as quadrotors. State-of-art flight controllers can stabilize and control a quadrotor even when subjected to the complete loss of a rotor. However, these methods rely on external sensors, such as GPS or motion capture systems, for state estimation. To the best of our knowledge, this has not yet been achieved with only onboard sensors. In this paper, we propose the first algorithm that combines fault-tolerant control and onboard vision-based state estimation to achieve position control of a quadrotor subjected to complete failure of one rotor. Experimental validations show that our approach is able to accurately control the position of a quadrotor during a motor failure scenario, without the aid of any external sensors. The primary challenge to vision-based state estimation stems from the inevitable high-speed yaw rotation (over 20 rad/s) of the damaged quadrotor, causing motion blur to cameras, which is detrimental to visual inertial odometry (VIO). We compare two types of visual inputs to the vision-based state estimation algorithm: standard frames and events. Experimental results show the advantage of using an event camera especially in low light environments due to its inherent high dynamic range and high temporal resolution. We believe that our approach will render autonomous quadrotors safer in both GPS denied or degraded environments. We release both our controller and VIO algorithm open source.

Real-time face & eye tracking and blink detection using event cameras

Event cameras contain emerging, neuromorphic vision sensors that capture local-light​ intensity changes at each pixel, generating a stream of asynchronous events. This way of acquiring visual information constitutes a departure from traditional frame-based cameras and offers several significant advantages — low energy consumption, high temporal resolution, high dynamic range and low latency. Driver monitoring systems (DMS) are in-cabin safety systems designed to sense and understand a drivers physical and cognitive state. Event cameras are particularly suited to DMS due to their inherent advantages. This paper proposes a novel method to simultaneously detect and track faces and eyes for driver monitoring. A unique, fully convolutional recurrent neural network architecture is presented. To train this network, a synthetic event-based dataset is simulated with accurate bounding box annotations, called Neuromorphic-HELEN. Additionally, a method to detect and analyse drivers’ eye blinks is proposed, exploiting the high temporal resolution of event cameras. Behaviour of blinking provides greater insights into a driver level of fatigue or drowsiness. We show that blinks have a unique temporal signature that can be better captured by event cameras.

Data-Driven Technology in Event-Based Vision

Event cameras which transmit per-pixel intensity changes have emerged as a promising candidate in applications such as consumer electronics, industrial automation, and autonomous vehicles, owing to their efficiency and robustness. To maintain these inherent advantages, the trade-off between efficiency and accuracy stands as a priority in event-based algorithms. Thanks to the preponderance of deep learning techniques and the compatibility between bio-inspired spiking neural networks and event-based sensors, data-driven approaches have become a hot spot, which along with the dedicated hardware and datasets constitute an emerging field named event-based data-driven technology. Focusing on data-driven technology in event-based vision, this paper first explicates the operating principle, advantages, and intrinsic nature of event cameras, as well as background knowledge in event-based vision, presenting an overview of this research field. Then, we explain why event-based data-driven technology becomes a research focus, including reasons for the rise of event-based vision and the superiority of data-driven approaches over other event-based algorithms. Current status and future trends of event-based data-driven technology are presented successively in terms of hardware, datasets, and algorithms, providing guidance for future research. Generally, this paper reveals the great prospects of event-based data-driven technology and presents a comprehensive overview of this field, aiming at a more efficient and bio-inspired visual system to extract visual features from the external environment.

DSEC: A Stereo Event Camera Dataset for Driving Scenarios

Once an academic venture, autonomous driving has received unparalleled corporate funding in the last decade. Still, operating conditions of current autonomous cars are mostly restricted to ideal scenarios. This means that driving in challenging illumination conditions such as night, sunrise, and sunset remains an open problem. In these cases, standard cameras are being pushed to their limits in terms of low light and high dynamic range performance. To address these challenges, we propose, DSEC, a new dataset that contains such demanding illumination conditions and provides a rich set of sensory data. DSEC offers data from a wide-baseline stereo setup of two color frame cameras and two high-resolution monochrome event cameras. In addition, we collect lidar data and RTK GPS measurements, both hardware synchronized with all camera data. One of the distinctive features of this dataset is the inclusion of high-resolution event cameras. Event cameras have received increasing attention for their high temporal resolution and high dynamic range performance. However, due to their novelty, event camera datasets in driving scenarios are rare. This work presents the first high resolution, large scale stereo dataset with event cameras. The dataset contains 53 sequences collected by driving in a variety of illumination conditions and provides ground truth disparity for the development and evaluation of event-based stereo algorithms.

Visualization and noise reduction algorithm based on event camera

Visualization and noise reduction algorithm based on event camera

An Asynchronous Real-Time Corner Extraction and Tracking Algorithm for Event Camera.

Event cameras have many advantages over conventional frame-based cameras, such as high temporal resolution, low latency and high dynamic range. However, state-of-the-art event- based algorithms either require too much computation time or have poor accuracy performance. In this paper, we propose an asynchronous real-time corner extraction and tracking algorithm for an event camera. Our primary motivation focuses on enhancing the accuracy of corner detection and tracking while ensuring computational efficiency. Firstly, according to the polarities of the events, a simple yet effective filter is applied to construct two restrictive Surface of Active Events (SAEs), named as RSAE+ and RSAE−, which can accurately represent high contrast patterns; meanwhile it filters noises and redundant events. Afterwards, a new coarse-to-fine corner extractor is proposed to extract corner events efficiently and accurately. Finally, a space, time and velocity direction constrained data association method is presented to realize corner event tracking, and we associate a new arriving corner event with the latest active corner that satisfies the velocity direction constraint in its neighborhood. The experiments are run on a standard event camera dataset, and the experimental results indicate that our method achieves excellent corner detection and tracking performance. Moreover, the proposed method can process more than 4.5 million events per second, showing promising potential in real-time computer vision applications.

Experimental Comparison between Event and Global Shutter Cameras.

We compare event-cameras with fast (global shutter) frame-cameras experimentally, asking: “What is the application domain, in which an event-camera surpasses a fast frame-camera?” Surprisingly, finding the answer has been difficult. Our methodology was to test event- and frame-cameras on generic computer vision tasks where event-camera advantages should manifest. We used two methods: (1) a controlled, cheap, and easily reproducible experiment (observing a marker on a rotating disk at varying speeds); (2) selecting one challenging practical ballistic experiment (observing a flying bullet having a ground truth provided by an ultra-high-speed expensive frame-camera). The experimental results include sampling/detection rates and position estimation errors as functions of illuminance and motion speed; and the minimum pixel latency of two commercial state-of-the-art event-cameras (ATIS, DVS240). Event-cameras respond more slowly to positive than to negative large and sudden contrast changes. They outperformed a frame-camera in bandwidth efficiency in all our experiments. Both camera types provide comparable position estimation accuracy. The better event-camera was limited by pixel latency when tracking small objects, resulting in motion blur effects. Sensor bandwidth limited the event-camera in object recognition. However, future generations of event-cameras might alleviate bandwidth limitations.

Experiments and Analysis for Measuring Mechanical Motion with Event Cameras

Event cameras—which detect pixelized, spatiotemporal changes asynchronously as opposed to frame-based triggered cameras—are commercially available and the topic of considerable research recently for computer vision and robotics applications. We hypothesize that these novel devices can be of utility in understanding mechanical motion by performing functions similar to high speed cameras, but with reduced bandwidth and simpler processing. To test this hypothesis, we applied multiple measurement modalities to a simple high-speed mechanical tool, including accelerometer, acoustic, and event-camera images. We also explore the utility of onboard inertial measurement units which are often integrated into these devices. Our analysis shows that these measurements are possible and consistent across modalities, possibly leading to novel new architectures for image and sensor based measurements.

Learning to Reconstruct HDR Images from Events, with Applications to Depth and Flow Prediction

Event cameras have numerous advantages over traditional cameras, such as low latency, high temporal resolution, and high dynamic range (HDR). We initially investigate the potential of creating intensity images/videos from an adjustable portion of the event data stream via event-based conditional generative adversarial networks (cGANs). Using the proposed framework, we further show the versatility of our method in directly handling similar supervised tasks, such as optical flow and depth prediction. Stacks of space-time coordinates of events are used as the inputs while the proposed framework is trained to predict either the intensity images, optical flows, or depth outputs according to the target task. We further demonstrate the unique capability of our approach in generating HDR images even under extreme illumination conditions, creating non-blurred images under rapid motion, and generating very high frame rate videos up to the temporal resolution of event cameras. The proposed framework is evaluated using a publicly available real-world dataset and a synthetic dataset we prepared by utilizing an event camera simulator.

Range Imaging and Video Generation using Generative Adversarial Network

Latency, high temporal pixel density, and dynamic range are just a few of the benefits of event camera systems over conventional camera systems. Methods and algorithms cannot be applied directly because the output data of event camera systems are segments of synchronization events and experiences rather than precise pixel intensities. As a result, generating intensity photographs from occurrences for other functions is difficult. We use occurrence camera-based contingent deep convolutional connections to establish images and videos from a variable component of the occasion stream of data in this journal article. The system is designed to replicate visuals based on spatio-temporal intensity variations using bundles of spatial coordinates of occurrences as input data. The ability of event camera systems to produce High Dynamic Range (HDR) pictures even in exceptional lighting circumstances, as well as non-blurry pictures in rapid motion, is demonstrated. Furthermore, because event cameras have a transient response of about 1 s, the ability to generate very increased frame rate video content has been evidenced, conceivably up to 1 million arrays per second. The implementation of the proposed algorithms are compared to density images recorded onto a similar gridline in the image of events based on the application of accessible primary data obtained and synthesized datasets generated by the occurrence camera simulation model.

Globally-Optimal Contrast Maximisation for Event Cameras.

Event cameras are bio-inspired sensors that perform well in challenging illumination conditions and have high temporal resolution. However, their concept is fundamentally different from traditional frame-based cameras. The pixels of an event camera operate independently and asynchronously. They measure changes of the logarithmic brightness and return them in the highly discretised form of time-stamped events indicating a relative change of a certain quantity since the last event. New models and algorithms are needed to process this kind of measurements. The present work looks at several motion estimation problems with event cameras. The flow of the events is modelled by a general homographic warping in a space-time volume, and the objective is formulated as a maximisation of contrast within the image of warped events. Our core contribution consists of deriving globally optimal solutions to these generally non-convex problems, which removes the dependency on a good initial guess plaguing existing methods. Our methods rely on branch-and-bound optimisation and employ novel and efficient, recursive upper and lower bounds derived for six different contrast estimation functions. The practical validity of our approach is demonstrated by a successful application to three different event camera motion estimation problems.

Low-Latency and Scene-Robust Optical Flow Stream and Angular Velocity Estimation

Event cameras are bio-inspired sensors that capture intensity changes of pixels individually, and generate asynchronous and independent “events”. Due to the fundamental difference from the conventional cameras, most research on event cameras builds a global event frame by grouping events according to their timestamps or their number to employ traditional computer vision algorithms. However, in order to take advantage of event cameras, it makes sense to generate asynchronous output on an event-by-event basis. In this paper, we propose an optical flow estimation algorithm with low latency and robustness to various scenes to utilize the advantage of the event camera by enhancing the existing optical flow algorithm. Furthermore, we estimate angular velocity with low latency using the proposed optical flow stream. For the validation of algorithms, we evaluate the accuracy and latency of optical flow with publicly available datasets. Moreover, we assess the performance of the proposed angular velocity estimation in comparison to the existing algorithms. Both validations suggest that our asynchronous optical flow shows comparable accuracy to the existing algorithms and the latency is reduced by half compared to the existing block matching algorithm on average. Also, our angular velocity estimation is superior to the existing algorithms in terms of accuracy and robustness while showing low latency within 15 ms consistently.

Event-Stream Representation for Human Gaits Identification Using Deep Neural Networks.

Dynamic vision sensors (event cameras) have recently been introduced to solve a number of different vision tasks such as object recognition, activities recognition, tracking, etc. Compared with the traditional RGB sensors, the event cameras have many unique advantages such as ultra low resources consumption, high temporal resolution and much larger dynamic range. However, these cameras only produce noisy and asynchronous events of intensity changes, i.e., event-streams rather than frames, where conventional computer vision algorithms can't be directly applied. In our opinion the key challenge for improving the performance of event cameras in vision tasks is finding the appropriate representations of the event-streams so that cutting-edge learning approaches can be applied to fully uncover the spatio-temporal information contained in the event-streams. In this paper, we focus on the event-based human gait identification task and investigate the possible representations of the event-streams when deep neural networks are applied as the classifier. We propose new event-based gait recognition approaches basing on two different representations of the event-stream, i.e., graph and image-like representations, and use graph-based convolutional network (GCN) and convolutional neural networks (CNN) respectively to recognize gait from the event-streams. The two approaches are termed as EV-Gait-3DGraph and EV-Gait-IMG. To evaluate the performance of the proposed approaches, we collect two event-based gait datasets, one from real-world experiments and the other by converting the publicly available RGB gait recognition benchmark CASIA-B. Extensive experiments show that EV-Gait-3DGraph achieves significantly higher recognition accuracy than other competing methods when sufficient training samples are available. However, EV-Gait-IMG converges more quickly than graph-based approaches while training and shows good accuracy with only few number of training samples (less than ten). So image-like presentation is preferable when the amount of training data is limited.

Event Camera Based Real-Time Detection and Tracking of Indoor Ground Robots

This paper presents a real-time method to detect and track multiple mobile ground robots using event cameras. The method uses density-based spatial clustering of applications with noise (DBSCAN) to detect the robots and a single k-dimensional (k-d) tree to accurately keep track of them as they move in an indoor arena. Robust detections and tracks are maintained in the face of event camera noise and lack of events (due to robots moving slowly or stopping). An off-the-shelf RGB camera-based tracking system was used to provide ground truth. Experiments including up to 4 robots are performed to study the effect of i) varying DBSCAN parameters, ii) the event accumulation time, iii) the number of robots in the arena, and iv) the speed of the robots on the detection and tracking performance. The experimental results showed 100% detection and tracking fidelity in the face of event camera noise and robots stopping for tests involving up to 3 robots (and upwards of 93% for 4 robots).

SPADE-E2VID: Spatially-Adaptive Denormalization for Event-Based Video Reconstruction.

Event-based cameras have several advantages over traditional cameras that shoot videos in frames. Event cameras have a high temporal resolution, high dynamic range, and almost non-existence of blurriness. The data that is produced by event sensors forms a chain of events when a change in brightness is reported in each pixel. This feature makes it difficult to directly apply existing algorithms and take advantage of the event camera data. Due to the developments in neural networks, important advances were made in event-based image reconstruction. Even though these neural networks achieve precise reconstructions while preserving most of the properties of the event cameras, there is still an initialization time that needs to have the highest possible quality in the reconstructed frames. In this work, we present the SPADE-E2VID neural network model that improves the quality of early frames in an event-based reconstructed video, as well as the overall contrast. The SPADE-E2VID model improves the quality of the first reconstructed frames by 15.87% for MSE error, 4.15% for SSIM, and 2.5% in LPIPS. In addition, the SPADE layer in our model allows training our model to reconstruct videos without a temporal loss function. Another advantage of our model is that it has a faster training time. In a many-to-one training style, we avoid running the loss function at each step, executing the loss function at the end of each loop only once. In the present work, we also carried out experiments with event cameras that do not have polarity data. Our model produces quality video reconstructions with non-polarity events in HD resolution (1200 × 800). The Video, the code, and the datasets will be available at: https://github.com/RodrigoGantier/SPADE_E2VID.