Event-based Vision, Event Cameras, Event Camera SLAM

Event cameras, such as the Dynamic Vision Sensor (DVS), are bio-inspired vision sensors that output pixel-level brightness changes instead of standard intensity frames. They offer significant advantages over standard cameras, namely a very high dynamic range, no motion blur, and a latency in the order of microseconds. However, because the output is composed of a sequence of asynchronous events rather than actual intensity images, traditional vision algorithms cannot be applied, so that new algorithms that exploit the high temporal resolution and the asynchronous nature of the sensor are required.


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Asynchronous, Photometric Feature Tracking using Events and Frames

We present a method that leverages the complementarity of event cameras and standard cameras to track visual features with low latency. Event cameras are novel sensors that output pixel-level brightness changes, called "events". They offer significant advantages over standard cameras, namely a very high dynamic range, no motion blur, and a latency in the order of microseconds. However, because the same scene pattern can produce different events depending on the motion direction, establishing event correspondences across time is challenging. By contrast, standard cameras provide intensity measurements (frames) that do not depend on motion direction. Our method extracts features on frames and subsequently tracks them asynchronously using events, thereby exploiting the best of both types of data: the frames provide a photometric representation that does not depend on motion direction and the events provide low latency updates. In contrast to previous works, which are based on heuristics, this is the first principled method that uses raw intensity measurements directly, based on a generative event model within a maximum-likelihood framework. As a result, our method produces feature tracks that are both more accurate (subpixel accuracy) and longer than the state of the art, across a wide variety of scenes.


References

Asynchronous, Photometric Feature Tracking using Events and Frames

D. Gehrig, H. Rebecq, G. Gallego, D. Scaramuzza

Asynchronous, Photometric Feature Tracking using Events and Frames

European Conference on Computer Vision (ECCV), Munich, 2018.

Oral Presentation.

PDF YouTube


Semi-Dense 3D Reconstruction with a Stereo Event Camera

Event cameras are bio-inspired sensors that offer several advantages, such as low latency, high-speed and high dynamic range, to tackle challenging scenarios in computer vision. This paper presents a solution to the problem of 3D reconstruction from data captured by a stereo event-camera rig moving in a static scene, such as in the context of stereo Simultaneous Localization and Mapping. The proposed method consists of the optimization of an energy function designed to exploit small-baseline spatio-temporal consistency of events triggered across both stereo image planes. To improve the density of the reconstruction and to reduce the uncertainty of the estimation, a probabilistic depth-fusion strategy is also developed. The resulting method has no special requirements on either the motion of the stereo event-camera rig or on prior knowledge about the scene. Experiments demonstrate our method can deal with both texture-rich scenes as well as sparse scenes, outperforming state-of-the-art stereo methods based on event data image representations.


References

Semi-Dense 3D Reconstruction with a Stereo Event Camera

Y. Zhou, G. Gallego, H. Rebecq, L. Kneip, H. Li, D. Scaramuzza

Semi-Dense 3D Reconstruction with a Stereo Event Camera

European Conference on Computer Vision (ECCV), Munich, 2018.

PDF YouTube


Continuous-Time Visual-Inertial Odometry for Event Cameras

In this paper, we leverage a continuous-time framework to perform visual-inertial odometry with an event camera. This framework allows direct integration of the asynchronous events with micro-second accuracy and the inertial measurements at high frequency. The event camera trajectory is approximated by a smooth curve in the space of rigid-body motions using cubic splines. This formulation significantly reduces the number of variables in trajectory estimation problems. We evaluate our method on real data from several scenes and compare the results against ground truth from a motion-capture system. We show that our method provides improved accuracy over the result of a state-of-the-art visual odometry method for event cameras. We also show that both the map orientation and scale can be recovered accurately by fusing events and inertial data. To the best of our knowledge, this is the first work on visual-inertial fusion with event cameras using a continuous-time framework.

References

TRO18_Mueggler

E. Mueggler, G. Gallego, H. Rebecq, D. Scaramuzza

Continuous-Time Visual-Inertial Odometry for Event Cameras

IEEE Transactions on Robotics, 2018.

PDF


A Unifying Contrast Maximization Framework for Event Cameras, with Applications to Motion, Depth and Optical Flow Estimation

We present a unifying framework to solve several computer vision problems with event cameras: motion, depth and optical flow estimation. The main idea of our framework is to find the point trajectories on the image plane that are best aligned with the event data by maximizing an objective function: the contrast of an image of warped events. Our method implicitly handles data association between the events, and therefore, does not rely on additional appearance information about the scene. In addition to accurately recovering the motion parameters of the problem, our framework produces motion-corrected edge-like images with high dynamic range that can be used for further scene analysis. The proposed method is not only simple, but more importantly, it is, to the best of our knowledge, the first method that can be successfully applied to such a diverse set of important vision tasks with event cameras.


References

A Unifying Contrast Maximization Framework for Event Cameras

G. Gallego, H. Rebecq, D. Scaramuzza

A Unifying Contrast Maximization Framework for Event Cameras, with Applications to Motion, Depth and Optical Flow Estimation

IEEE Conference on Computer Vision and Pattern Recognition (CVPR), Salt Lake City, 2018.

Spotlight Presentation.

PDF YouTube


Event-based Vision meets Deep Learning on Steering Prediction for Self-driving Cars

Event cameras are bio-inspired vision sensors that naturally capture the dynamics of a scene, filtering out redundant information. This paper presents a deep neural network approach that unlocks the potential of event cameras on a challenging motion-estimation task: prediction of a vehicle's steering angle. To make the best out of this sensor-algorithm combination, we adapt state-of-the-art convolutional architectures to the output of event sensors and extensively evaluate the performance of our approach on a publicly available large scale event-camera dataset (~1000 km). We present qualitative and quantitative explanations of why event cameras allow robust steering prediction even in cases where traditional cameras fail, e.g. challenging illumination conditions and fast motion. Finally, we demonstrate the advantages of leveraging transfer learning from traditional to event-based vision, and show that our approach outperforms state-of-the-art algorithms based on standard cameras.


References

Event-based Vision meets Deep Learning on Steering Prediction for Self-driving Cars

A.I. Maqueda, A. Loquercio, G. Gallego, N. Garcia, D. Scaramuzza

Event-based Vision meets Deep Learning on Steering Prediction for Self-driving Cars

IEEE Conference on Computer Vision and Pattern Recognition (CVPR), Salt Lake City, 2018.

PDF YouTube


Ultimate SLAM? Combining Events, Images, and IMU for Robust Visual SLAM in HDR and High Speed Scenarios

In this paper, we present the first state estimation pipeline that leverages the complementary advantages of a standard camera with an event camera by fusing in a tightly-coupled manner events, standard frames, and inertial measurements. We show on the Event Camera Dataset that our hybrid pipeline leads to an accuracy improvement of 130% over event-only pipelines, and 85% over standard-frames only visual-inertial systems, while still being computationally tractable.

Furthermore, we use our pipeline to demonstrate - to the best of our knowledge - the first autonomous quadrotor flight using an event camera for state estimation, unlocking flight scenarios that were not reachable with traditional visual inertial odometry, such as low-light environments and high dynamic range scenes.


References

RAL18_VidalRebecq

T. Rosinol Vidal, H.Rebecq, T. Horstschaefer, D. Scaramuzza

Ultimate SLAM? Combining Events, Images, and IMU for Robust Visual SLAM in HDR and High Speed Scenarios

IEEE Robotics and Automation Letters (RA-L), 2018.

PDF YouTube ICRA18 Video Pitch


EMVS: Event-Based Multi-View Stereo - 3D Reconstruction with an Event Camera in Real-Time

We introduce the problem of event-based multi-view stereo (EMVS) for event cameras and propose a solution to it. Unlike traditional MVS methods, which address the problem of estimating dense 3D structure from a set of known viewpoints, EMVS estimates semi-dense 3D structure from an event camera with known trajectory. Our EMVS solution elegantly exploits two inherent properties of an event camera: (1) its ability to respond to scene edges - which naturally provide semi-dense geometric information without any preprocessing operation - and (2) the fact that it provides continuous measurements as the sensor moves. Despite its simplicity (it can be implemented in a few lines of code), our algorithm is able to produce accurate, semi-dense depth maps, without requiring any explicit data association or intensity estimation. We successfully validate our method on both synthetic and real data. Our method is computationally very efficient and runs in real-time on a CPU.

References

3D reconstruction with an Event-based camera in real-time

H. Rebecq, G. Gallego, E. Mueggler, D. Scaramuzza

EMVS: Event-Based Multi-View Stereo - 3D Reconstruction with an Event Camera in Real-Time

International Journal of Computer Vision, 2017.

PDF YouTube


Event-based, 6-DOF Camera Tracking from Photometric Depth Maps

We present an event-based approach for ego-motion estimation, which provides pose updates upon the arrival of each event, thus virtually eliminating latency. Our method is the first work addressing and demonstrating event-based pose tracking in six degrees-of-freedom (DOF) motions in realistic and natural scenes, and it is able to track high-speed motions. The method is successfully evaluated in both indoor and outdoor scenes.

References

Pose tracking with an Event-based camera

G. Gallego, Jon E. A. Lund, E. Mueggler, H. Rebecq, T. Delbruck, D. Scaramuzza

Event-based, 6-DOF Camera Tracking from Photometric Depth Maps

IEEE Transactions on Pattern Analysis and Machine Intelligence, 2017.

PDF YouTube


Real-time Visual-Inertial Odometry for Event Cameras using Keyframe-based Nonlinear Optimization

We propose a novel, accurate tightly-coupled visual-inertial odometry pipeline for event cameras that leverages their outstanding properties to estimate the camera ego-motion in challenging conditions, such as high-speed motion or high dynamic range scenes. Our pipeline can output poses at a rate proportional to the camera velocity and runs in real-time on a CPU.

The method tracks a set of features (extracted on the image plane) through time. To achieve that, we consider events in overlapping spatio-temporal windows and align them using the current camera motion and scene structure, yielding motion-compensated event frames. We then combine these feature tracks in a keyframe-based, visual-inertial odometry algorithm based on nonlinear optimization to estimate the camera's 6-DOF pose, velocity, and IMU biases.

We evaluated the proposed method quantitatively on the public Event Camera Dataset and it significantly outperforms the state-of-the-art, while being computationally much more efficient: our pipeline can run much faster than real-time on a laptop and even on a smartphone processor. Furthermore, we demonstrate qualitatively the accuracy and robustness of our pipeline on a large-scale dataset, and an extremely high-speed dataset recorded by spinning an event camera on a leash at 850 deg/s.


References

BMVC17_Rebecq

H.Rebecq, T. Horstschaefer, D. Scaramuzza

Real-time Visual-Inertial Odometry for Event Cameras using Keyframe-based Nonlinear Optimization

British Machine Vision Conference (BMVC), London, 2017.

Oral Presentation. Acceptance Rate: 5.6%

PDF PPT YouTube Oral Presentation


Fast Event-based Corner Detection

Inspired by frame-based pre-processing techniques that reduce an image to a set of features, which are typically the input to higher-level algorithms, we propose a method to reduce an event stream to a corner event stream. Our goal is twofold: extract relevant tracking information (corners do not suffer from the aperture problem) and decrease the event rate for later processing stages. Our event-based corner detector is very efficient due to its design principle, which consists of working on the Surface of Active Events (a map with the timestamp of the latest event at each pixel) using only comparison operations. Our method asynchronously processes event by event with very low latency. Our implementation is capable of processing millions of events per second on a single core (less than a micro-second per event) and reduces the event rate by a factor of 10 to 20.

References

BMVC17_Mueggler

E. Mueggler, C. Bartolozzi, D. Scaramuzza

Fast Event-based Corner Detection

British Machine Vision Conference (BMVC), London, 2017.

PDF Poster YouTube Open-Source Code


EVO: Event-based, 6-DOF Parallel Tracking and Mapping in Real-Time

We present EVO, an Event-based Visual Odometry algorithm. Our algorithm successfully leverages the outstanding properties of event cameras to track fast camera motions while recovering a semi-dense 3D map of the environment. The implementation runs in real-time on a standard CPU and outputs up to several hundred pose estimates per second. Due to the nature of event cameras, our algorithm is unaffected by motion blur and operates very well in challenging, high dynamic range conditions with strong illumination changes. To achieve this, we combine a novel, event-based tracking approach based on image-to-model alignment with a recent event-based 3D reconstruction algorithm in a parallel fashion. Additionally, we show that the output of our pipeline can be used to reconstruct intensity images from the binary event stream, though our algorithm does not require such intensity information. We believe that this work makes significant progress in SLAM by unlocking the potential of event cameras. This allows us to tackle challenging scenarios that are currently inaccessible to standard cameras.

References

EVO

H. Rebecq, T. Horstschaefer, G. Gallego, D. Scaramuzza

EVO: A Geometric Approach to Event-based 6-DOF Parallel Tracking and Mapping in Real-time

IEEE Robotics and Automation Letters (RA-L), 2016.

PDF PPT YouTube


Accurate Angular Velocity Estimation with an Event Camera

We present an algorithm to estimate the rotational motion of an event camera. In contrast to traditional cameras, which produce images at a fixed rate, event cameras have independent pixels that respond asynchronously to brightness changes, with microsecond resolution. Our method leverages the type of information conveyed by these novel sensors (that is, edges) to directly estimate the angular velocity of the camera, without requiring optical flow or image intensity estimation. The core of the method is a contrast maximization design. The method performs favorably against round truth data and gyroscopic measurements from an Inertial Measurement Unit, even in the presence of very high-speed motions (close to 1000 deg/s).

References

EVO

G. Gallego and D. Scaramuzza

Accurate Angular Velocity Estimation with an Event Camera

IEEE Robotics and Automation Letters (RA-L), 2016.

PDF PPT YouTube


The Event Camera Dataset and Simulator: Event-based Data for Pose Estimation, Visual Odometry, and SLAM

We present the world's first collection of datasets with an event-based camera for high-speed robotics. The data also include intensity images, inertial measurements, and ground truth from a motion-capture system. An event-based camera is a revolutionary vision sensor with three key advantages: a measurement rate that is almost 1 million times faster than standard cameras, a latency of 1 microsecond, and a high dynamic range of 130 decibels (standard cameras only have 60 dB). These properties enable the design of a new class of algorithms for high-speed robotics, where standard cameras suffer from motion blur and high latency. All the data are released both as text files and binary (i.e., rosbag) files. Find out more on the dataset website!

References

DAVIS dataset paper

E. Mueggler, H. Rebecq, G. Gallego, T. Delbruck, D. Scaramuzza

The Event-Camera Dataset and Simulator: Event-based Data for Pose Estimation, Visual Odometry, and SLAM

International Journal of Robotics Research, Vol. 36, Issue 2, pages 142-149, Feb. 2017.

Dataset Page PDF YouTube


EMVS: Event-based, Multi-View Stereo

We introduce the problem of Event-based Multi-View Stereo (EMVS) for event cameras and propose a solution to it. Unlike traditional MVS methods, which address the problem of estimating dense 3D structure from a set of known viewpoints, EMVS estimates semi-dense 3D structure from an event camera with known trajectory. Our EMVS solution elegantly exploits two inherent properties of an event camera: (i) its ability to respond to scene edges that naturally provide semidense geometric information without any preprocessing operations and (ii) the fact that it provides continuous measurements as the sensor moves. Despite its simplicity (it can be implemented in a few lines of code), our algorithm is able to produce accurate, semidense depth maps. We successfully validate our method on both synthetic and real data. Our method is computationally very efficient and runs in real-time on a laptop CPU and even on a smartphone processor.

References

EMVS paper

H. Rebecq, G. Gallego, D. Scaramuzza

EMVS: Event-based Multi-View Stereo

British Machine Vision Conference (BMVC), York, 2016.

Best Industry Related Paper (sponsored by nvidia and BMVA)

PDF PPT YouTube


Low-Latency Visual Odometry using Event-based Feature Tracks


We develop an event-based feature tracking algorithm for the DAVIS sensor and show how to integrate it in an event-based visual odometry pipeline. Features are first detected in the grayscale frames and then tracked asynchronously using the stream of events. The features are then fed to an event-based visual odometry pipeline that tightly interleaves robust pose optimization and probabilistic mapping. We show that our method successfully tracks the 6-DOF motion of the sensor in natural scenes (see video above).

References

Low-Latency Visual Odometry using Event-based Feature Tracks

B. Kueng, E. Mueggler, G. Gallego, D. Scaramuzza

Low-Latency Visual Odometry using Event-based Feature Tracks

IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Daejeon, 2016.

Best Application Paper Award Finalist! Highlight Talk: Acceptance Rate 2.5%

PDF PPT YouTube


Feature Detection and Tracking with the Dynamic and Active-pixel Vision Sensor (DAVIS)

D. Tedaldi, G. Gallego, E. Mueggler, D. Scaramuzza

Feature Detection and Tracking with the Dynamic and Active-pixel Vision Sensor (DAVIS)

International Conference on Event-Based Control, Communication and Signal Processing (EBCCSP), Krakow, 2016.

PDF PPT YouTube


ELiSeD

C. Braendli, J. Strubel, S. Keller, D. Scaramuzza, T. Delbruck

ELiSeD - An Event-Based Line Segment Detector

International Conference on Event-Based Control, Communication and Signal Processing (EBCCSP), Krakow, 2016.

PDF


Continuous-Time Trajectory Estimation for Event-based Vision Sensors

In this paper, we address ego-motion estimation for an event-based vision sensor using a continuous-time framework to directly integrate the information conveyed by the sensor. The DVS pose trajectory is approximated by a smooth curve in the space of rigid-body motions using cubic splines and it is optimized according to the observed events. We evaluate our method using datasets acquired from sensor-in-the-loop simulations and onboard a quadrotor performing flips. The results are compared to the ground truth, showing the good performance of the proposed technique.

References

RSS2015_Mueggler

E. Mueggler, G. Gallego, D. Scaramuzza

Continuous-Time Trajectory Estimation for Event-based Vision Sensors

Robotics: Science and Systems (RSS), Rome, 2015.

PDF PPT Poster


Event-based Camera Pose Tracking using a Generative Event Model

We tackle the problem of event-based camera localization in a known environment, without additional sensing, using a probabilistic generative event model in a Bayesian filtering framework. Our main contribution is the design of the likelihood function used in the filter to process the observed events. Based on the physical characteristics of the sensor and on empirical evidence of the Gaussian-like distribution of spiked events with respect to the brightness change, we propose to use the contrast residual as a measure of how well the estimated pose of the event-based camera and the environment explain the observed events. The filter allows for localization in the general case of six degrees-of-freedom motions.

References

arXiv15 paper

G. Gallego, C. Forster, E. Mueggler, D. Scaramuzza

Event-based Camera Pose Tracking using a Generative Event Model

arXiv:1510.01972, 2015.

PDF


Lifetime Estimation of Events from Dynamic Vision Sensors

We develop an algorithm that augments each event with its "lifetime", which is computed from the event's velocity on the image plane. The generated stream of augmented events gives a continuous representation of events in time, hence enabling the design of new algorithms that outperform those based on the accumulation of events over fixed, artificially-chosen time intervals. A direct application of this augmented stream is the construction of sharp gradient (edge-like) images at any time instant. We successfully demonstrate our method in different scenarios, including high-speed quadrotor flips, and compare it to standard visualization methods.

References

ICRA2015_Mueggler

E. Mueggler, C. Forster, N. Baumli, G. Gallego, D. Scaramuzza

Lifetime Estimation of Events from Dynamic Vision Sensors

IEEE International Conference on Robotics and Automation (ICRA), Seattle, 2015.

PDF PPT Code


Event-based, 6-DOF Pose Tracking for High-Speed Maneuvers

In the last few years, we have witnessed impressive demonstrations of aggressive flights and acrobatics using quadrotors. However, those robots are actually blind. They do not see by themselves, but through the "eyes" of an external motion capture system. Flight maneuvers using onboard sensors are still slow compared to those attainable with motion capture systems. At the current state, the agility of a robot is limited by the latency of its perception pipeline. To obtain more agile robots, we need to use faster sensors. In this paper, we present the first onboard perception system for 6-DOF localization during high-speed maneuvers using a Dynamic Vision Sensor (DVS). Unlike a standard CMOS camera, a DVS does not wastefully send full image frames at a fixed frame rate. Conversely, similar to the human eye, it only transmits pixel-level brightness changes at the time they occur with microsecond resolution, thus, offering the possibility to create a perception pipeline whose latency is negligible compared to the dynamics of the robot. We exploit these characteristics to estimate the pose of a quadrotor with respect to a known pattern during high-speed maneuvers, such as flips, with rotational speeds up to 1,200 degrees a second. Additionally, we provide a versatile method to capture ground-truth data using a DVS.

References

IROS2014_Mueggler

E. Mueggler, B. Huber, D. Scaramuzza

Event-based, 6-DOF Pose Tracking for High-Speed Maneuvers

IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Chicago, 2014.

PDF PPT YouTube


Low-Latency Event-Based Visual Odometry

This paper presents the first visual odometry system based on a DVS plus a normal CMOS camera to provide the absolute brightness values. The two sources of data are automatically spatiotemporally calibrated from logs taken during normal operation. We design a visual odometry method that uses the DVS events to estimate the relative displacement since the previous CMOS frame by processing each event individually. Experiments show that the rotation can be estimated with surprising accuracy, while the translation can be estimated only very noisily, because it produces few events due to very small apparent motion.

References

ICRA2014_Censi

A. Censi, D. Scaramuzza,

Low-Latency Event-Based Visual Odometry

IEEE International Conference on Robotics and Automation (ICRA), Hong Kong, 2014.

PDF


Low-latency localization by Active LED Markers tracking using a DVS

This paper presents a method for low-latency pose tracking using a DVS and Active Led Markers (ALMs), which are LEDs blinking at high frequency (>1 KHz). The sensor's time resolution allows distinguishing different frequencies, thus avoiding the need for data association. This approach is compared to traditional pose tracking based on a CMOS camera. The DVS performance is not affected by fast motion, unlike the CMOS camera, which suffers from motion blur.

References

IROS2013_Censi

A. Censi, J. Strubel, C. Brandli, T. Delbruck, D. Scaramuzza,

Low-latency localization by Active LED Markers tracking using a Dynamic Vision Sensor

IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Tokyo, 2013.

PDF PPT