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Thörnberg, Benny
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Publications (10 of 63) Show all publications
Alqaysi, H., Lawal, N., Fedorov, I., Thörnberg, B. & O'Nils, M. (2019). Design Exploration of Multi-Camera Dome. In: ICDSC 2019 Proceedings of the 13th International Conference on Distributed Smart Cameras: . Paper presented at 13th InternationalConference on Distributed Smart Cameras (ICDSC 2019), Trento, Italy, 9-11 September, 2019. New York, NY: ACM Digital Library, Article ID Article No. 7a.
Open this publication in new window or tab >>Design Exploration of Multi-Camera Dome
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2019 (English)In: ICDSC 2019 Proceedings of the 13th International Conference on Distributed Smart Cameras, New York, NY: ACM Digital Library, 2019, article id Article No. 7aConference paper, Published paper (Refereed)
Abstract [en]

Visual monitoring systems employ distributed smart cameras toeffectively cover a given area satisfying specific objectives. Thechoice of camera sensors and lenses and their deployment affectsdesign cost, accuracy of the monitoring system and the ability toposition objects within the monitored area. Design cost can bereduced by investigating deployment topology such as groupingcameras together to form a dome at a node and optimize it formonitoring constraints. The constraints may include coverage area,number of cameras that can be integrated in a node and pixelresolution at a given distance. This paper presents a method foroptimizing the design cost of multi-camera dome by analyzing tradeoffsbetween monitoring constraints. The proposed method can beused to reduce monitoring cost while fulfilling design objectives.Results show how to increase coverage area for a given cost byrelaxing requirements on design constraints. Multi-camera domescan be used in sky monitoring applications such as monitoring windparks and remote air-traffic control of airports where all-round fieldof view about a point is required to monitor.

Place, publisher, year, edition, pages
New York, NY: ACM Digital Library, 2019
Keywords
Distributed smart cameras, sky monitoring, volumetric surveillance.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-36762 (URN)10.1145/3349801.3349808 (DOI)2-s2.0-85073333209 (Scopus ID)978-1-4503-7189-6 (ISBN)
Conference
13th InternationalConference on Distributed Smart Cameras (ICDSC 2019), Trento, Italy, 9-11 September, 2019
Projects
SMART
Available from: 2019-07-29 Created: 2019-07-29 Last updated: 2019-11-14Bibliographically approved
Vilar, C., Thörnberg, B. & Krug, S. (2019). Evaluation of embedded camera systems for autonomous wheelchairs. In: VEHITS 2019 - Proceedings of the 5th International Conference on Vehicle Technology and Intelligent Transport Systems: . Paper presented at 5th International Conference on Vehicle Technology and Intelligent Transport Systems, VEHITS 2019, Heraklion, Crete, Greece, 3 May 2019 through 5 May 2019 (pp. 76-85). SciTePress
Open this publication in new window or tab >>Evaluation of embedded camera systems for autonomous wheelchairs
2019 (English)In: VEHITS 2019 - Proceedings of the 5th International Conference on Vehicle Technology and Intelligent Transport Systems, SciTePress , 2019, p. 76-85Conference paper, Published paper (Refereed)
Abstract [en]

Autonomously driving Power Wheelchairs (PWCs) are valuable tools to enhance the life quality of their users. In order to enable truly autonomous PWCs, camera systems are essential. Image processing enables the development of applications for both autonomous driving and obstacle avoidance. This paper explores the challenges that arise when selecting a suitable embedded camera system for these applications. Our analysis is based on a comparison of two well-known camera principles, Stereo-Cameras (STCs) and Time-of-Flight (ToF) cameras, using the standard deviation of the ground plane at various lighting conditions as a key quality measure. In addition, we also consider other metrics related to both the image processing task and the embedded system constraints. We believe that this assessment is valuable when choosing between using STC or ToF cameras for PWCs.

Place, publisher, year, edition, pages
SciTePress, 2019
Keywords
Autonomous Wheelchair, Embedded Camera System, RANSAC, Stereo Camera, Time-of-Flight, Cameras, Embedded systems, Intelligent systems, Intelligent vehicle highway systems, Quality control, Traffic control, Wheelchairs, Camera systems, Stereo cameras, Time of flight, Stereo image processing
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-36685 (URN)2-s2.0-85067542836 (Scopus ID)9789897583742 (ISBN)
Conference
5th International Conference on Vehicle Technology and Intelligent Transport Systems, VEHITS 2019, Heraklion, Crete, Greece, 3 May 2019 through 5 May 2019
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Available from: 2019-07-09 Created: 2019-07-09 Last updated: 2019-09-09Bibliographically approved
Rydblom, S., Thörnberg, B. & Olsson, E. (2019). Field Study of LWC and MVD Using the Droplet Imaging Instrument. IEEE Transactions on Instrumentation and Measurement, 68(2), 614-622
Open this publication in new window or tab >>Field Study of LWC and MVD Using the Droplet Imaging Instrument
2019 (English)In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 68, no 2, p. 614-622Article in journal (Refereed) Published
Abstract [en]

The droplet imaging instrument (DII) is a new instrument for cost-effective in situ measurements of the size and concentration of water droplets. The droplet size distribution and the concentration of atmospheric liquid water are important for the prediction of icing on structures, such as wind turbines. To improve the predictions of icing, there is a need to explore cost-effective working solutions. Through imaging, a wide range of droplet sizes can be measured. This paper describes a study of the atmospheric liquid water content and the median volume diameter using the DII and a commercial reference instrument--the cloud droplet probe 2 from Droplet Measurement Technologies Inc. The measurement is done at a weather measurement station in mid-Sweden. For a second validation, the result is compared with predictions using a numerical weather prediction model. The size measurement of the DII is verified using polymer microspheres of four known size distributions. The study shows that the DII measurement is precise, but there is a systematic difference between the two compared instruments. It also shows that droplets larger than 50 μm in diameter are occasionally measured, which we believe is important for the prediction of icing.

Place, publisher, year, edition, pages
IEEE, 2019
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-34304 (URN)10.1109/TIM.2018.2843599 (DOI)000454332000030 ()
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Note

Date of Publication: 20 June 2018

Available from: 2018-08-28 Created: 2018-08-28 Last updated: 2019-11-07Bibliographically approved
Nyström, J., Gradin, P. & Thörnberg, B. (2018). An experimental study of the chipping process with focus on energy consumption and chipping angles. Nordic Pulp & Paper Research Journal, 33(3), 460-467
Open this publication in new window or tab >>An experimental study of the chipping process with focus on energy consumption and chipping angles
2018 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 3, p. 460-467Article in journal (Refereed) Published
Abstract [en]

A series of chipping experiments were performed under both dynamic and quasi-static conditions in a laboratory wood chipper (dynamic) and in a MTS-servohydraulic testing machine (quasi-static). One aim with the experiments was to investigate the rate dependency of the energy consumption during chipping. Another aim was to try to determine the load per unit knife edge length required to initiate cutting. The experiments were carried out using different combinations of spout and edge angles. It was found that for large edge angles (keeping the spout angle constant at 30 °30^\circ ) there was a slight rate dependency such that the energy consumption was larger at higher cutting rates which is quite in opposite of what is expected if wood is assumed to be a viscoelastic material. It was also found that to determine the force at initiation of cutting, is not a trivial task. Both Acoustic Emission monitoring and visual inspection was used to this end. The wood species used in this study was pine (Pinus silvestris). 

Keywords
energy consumption, rate dependency, wood chipping
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-34599 (URN)10.1515/npprj-2018-3055 (DOI)000450923900012 ()2-s2.0-85052632762 (Scopus ID)
Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2018-12-11Bibliographically approved
Rydblom, S. & Thörnberg, B. (2018). Particle Measurement Volume and Light Intensity in a Shadowgraph Imaging System. In: IST 2018 - IEEE International Conference on Imaging Systems and Techniques, Proceedings: . Paper presented at 2018 IEEE International Conference on Imaging Systems and Techniques, IST 2018; Krakow; Poland; 16 October 2018 through 18 October 2018. IEEE, Article ID 8577170.
Open this publication in new window or tab >>Particle Measurement Volume and Light Intensity in a Shadowgraph Imaging System
2018 (English)In: IST 2018 - IEEE International Conference on Imaging Systems and Techniques, Proceedings, IEEE, 2018, article id 8577170Conference paper, Published paper (Refereed)
Abstract [en]

A method is sought to find the measurement volume of an optical instrument for particle measurement is sought. The study shows that the measurement volume depends on a combination of the optical homogeneity of the illumination light and the camera system. The result from a mix of illumination cases and positions shows that, if the true size and the background brightness are known, the measurement volume can be determined with an average precision of four percent using adual term exponential fit. Using a lens with lower magnification increases the measurement volume since both the field of viewand the depth of field increase. However, a larger field of view increases the required amount of light as well as the sensitivity to other optical errors.

Place, publisher, year, edition, pages
IEEE, 2018
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-34825 (URN)10.1109/IST.2018.8577170 (DOI)000455657200028 ()2-s2.0-85060703908 (Scopus ID)978-1-5386-6628-9 (ISBN)
Conference
2018 IEEE International Conference on Imaging Systems and Techniques, IST 2018; Krakow; Poland; 16 October 2018 through 18 October 2018
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2019-11-07Bibliographically approved
Fedorov, I., Lawal, N., Thörnberg, B., Alqaysi, H. & O'Nils, M. (2018). Towards calibration of outdoor multi-camera visual monitoring system. In: ACM International Conference Proceeding Series: . Paper presented at ICDSC'18 Proceedings of the 12th International Conference on Distributed Smart Cameras, Eindhoven, Netherlands, 3-4 September 2018.. New York, NY, US: ACM Digital Library
Open this publication in new window or tab >>Towards calibration of outdoor multi-camera visual monitoring system
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2018 (English)In: ACM International Conference Proceeding Series, New York, NY, US: ACM Digital Library, 2018, , p. 6Conference paper, Published paper (Refereed)
Abstract [en]

This paper proposes a method for calibrating of multi-camera systems where no natural reference points exist in the surrounding environment. Monitoring the air space at wind farms is our test case. The goal is to monitor the trajectories of flying birds to prevent them from colliding with rotor blades. Our camera calibration method is based on the observation of a portable artificial reference marker made out of a pulsed light source and a navigation satellite sensor module. The reference marker can determine and communicate its position in the world coordinate system at centimeter precision using navigartion sensors. Our results showed that simultaneous detection of the same marker in several cameras having overlapping field of views allowed us to determine the markers position in 3D world coordinate space with an accuracy of 3-4 cm. These experiments were made in the volume around a wind turbine at distances from cameras to marker within a range of 70 to 90 m.

Place, publisher, year, edition, pages
New York, NY, US: ACM Digital Library, 2018. p. 6
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-34643 (URN)10.1145/3243394.3243695 (DOI)000455840700017 ()2-s2.0-85056618979 (Scopus ID)978-1-4503-6511-6 (ISBN)
Conference
ICDSC'18 Proceedings of the 12th International Conference on Distributed Smart Cameras, Eindhoven, Netherlands, 3-4 September 2018.
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Available from: 2018-10-05 Created: 2018-10-05 Last updated: 2019-09-09Bibliographically approved
Amir, Y. M. & Thörnberg, B. (2017). High Precision Laser Scanning of Metallic Surfaces. International Journal of Optics, Article ID 4134205.
Open this publication in new window or tab >>High Precision Laser Scanning of Metallic Surfaces
2017 (English)In: International Journal of Optics, ISSN 1687-9384, E-ISSN 1687-9392, article id 4134205Article in journal (Refereed) Published
Abstract [en]

Speckle noise, dynamic range of light intensity, and spurious reflections are major challenges when laser scanners are used for 3D surface acquisition. In this work, a series of image processing operations, that is, Spatial Compound Imaging, High Dynamic Range Extension, Gray Level Transformation, and Most Similar Nearest Neighbor are proposed to overcome the challenges coming from the target surface. A prototype scanner for metallic surfaces is designed to explore combinations of these image processing operations. The main goal is to find the combination of operations thatwill lead to the highest possible robustness andmeasurement precision at the lowest possible computational load. Inspection of metallic tools where the surface of its edge must be measured at micrometer precision is our test case. Precision of heights measured without using the proposed image processing is firstly analyzed to be +/- 7.6 mu m at 68% confidence level. The best achieved height precision was +/- 4.2 mu m. This improvement comes at 24 times longer processing time and five times longer scanning time. Dynamic range extension of the image capture improves robustness since the numbers of saturated or underexposed pixels are substantially reduced. Using a high dynamic range (HDR) camera offers a compromise between processing time, robustness, and precision.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-31363 (URN)10.1155/2017/4134205 (DOI)000405332500001 ()2-s2.0-85024488897 (Scopus ID)
Available from: 2017-08-10 Created: 2017-08-10 Last updated: 2017-11-29Bibliographically approved
Rydblom, S. & Thörnberg, B. (2016). Droplet Imaging Instrument Metrology Instrument for Icing Condition Detection. In: 2016 IEEE INTERNATIONAL CONFERENCE ON IMAGING SYSTEMS AND TECHNIQUES (IST): . Paper presented at IEEE International Conference on Imaging Systems and Techniques (IST) / IEEE International School on Imaging, OCT 04-06, 2016, Chania, GREECE (pp. 66-71). IEEE, Article ID 7738200.
Open this publication in new window or tab >>Droplet Imaging Instrument Metrology Instrument for Icing Condition Detection
2016 (English)In: 2016 IEEE INTERNATIONAL CONFERENCE ON IMAGING SYSTEMS AND TECHNIQUES (IST), IEEE, 2016, p. 66-71, article id 7738200Conference paper, Published paper (Refereed)
Abstract [en]

An instrument for measuring water droplets is described and constructed. It is designed to measure the volume concentration and the size distribution of droplets in order to detect icing conditions in a natural fog. The instrument works by shadowgraph imaging, with a collimated blue LED as background illumination. We show how to use a reference object to obtain a calibration of the droplet size and the measurement volume. These properties are derived from a measurement of the object's shadow intensity and its edge second derivative. From the size of every measured droplet and its expected detection volume, a measure of the liquid water content (LWC) and the median volume diameter (MVD) can be estimated. The instrument can be used for continuous measurement in a remote weather-exposed location and is tested in a small environment chamber. We also describe this chamber and how we can change the LWC using an ultrasonic fog generator and a fan.

Place, publisher, year, edition, pages
IEEE, 2016
Series
IEEE International Conference on Imaging Systems and Techniques, ISSN 2471-6162
Keywords
atmospheric measurements, fog chamber, image analysis, liquid water content, machine vision
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-29765 (URN)10.1109/IST.2016.7738200 (DOI)000388735200012 ()2-s2.0-85004010273 (Scopus ID)STC (Local ID)978-1-5090-1817-8 (ISBN)STC (Archive number)STC (OAI)
Conference
IEEE International Conference on Imaging Systems and Techniques (IST) / IEEE International School on Imaging, OCT 04-06, 2016, Chania, GREECE
Available from: 2016-12-22 Created: 2016-12-22 Last updated: 2019-11-07Bibliographically approved
Rydblom, S. & Thörnberg, B. (2016). Liquid Water Content and Droplet Sizing Shadowgraph Measuring System for Wind Turbine Icing Detection. IEEE Sensors Journal, 16(8), 2714-2725, Article ID 7384444.
Open this publication in new window or tab >>Liquid Water Content and Droplet Sizing Shadowgraph Measuring System for Wind Turbine Icing Detection
2016 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 16, no 8, p. 2714-2725, article id 7384444Article in journal (Refereed) Published
Abstract [en]

This study shows that the liquid water content (LWC) and the median volume diameter (MVD) can be derived from images of water droplets using a shadowgraph imaging system with incoherent LED illumination.

Icing on structures such as a wind turbine is the result of a combination of LWC and MVD and other parameters like temperature, humidity and wind speed. Today, LWC and MVD are not commonly measured for wind turbines. Systems for measuring these properties are often expensive or impractical in terms of location or remote reading. The aim of this study is to gain knowledge about how to design a single instrument based on imaging that has the ability to measure these properties with enough precision and accuracy to detect icing conditions for wind turbines.

A method to calculate both the LWC and the MVD from the same images is described in this paper. The size of one droplet is determined by measuring the shadow created by the droplet in background illumination. The concentration is calculated by counting the measured droplets and estimating the volumes in which these droplets can be observed.

In the described study, the observation volume is shown to be dependent on the particle size and the signal to noise ratio (SNR) for each measured particle. An expected coefficient of variation of the LWC depending on the droplet size is shown to be 2.4 percent for droplets 10 µm in diameter and 1.6 percent for 25 µm droplets. This is based on an error estimation of the laboratory measurements calibrated using a micrometer dot scale.

Place, publisher, year, edition, pages
IEEE Sensors Council, 2016
Keywords
LWC, MVD, Icing, Clouds, Image processing, Machine vision, Meteorology, Optical microscopy, Wind power generation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-27321 (URN)10.1109/JSEN.2016.2518653 (DOI)000372419100061 ()2-s2.0-84962128668 (Scopus ID)STC (Local ID)STC (Archive number)STC (OAI)
Funder
Swedish Energy Agency
Available from: 2016-03-22 Created: 2016-03-22 Last updated: 2019-11-07Bibliographically approved
Imran, M., O'Nils, M., Munir, H. & Thörnberg, B. (2015). Low complexity FPGA based background subtraction technique for thermal imagery. In: ACM International Conference Proceeding Series: . Paper presented at 9th International Conference on Distributed Smart Cameras, ICDSC 2015; Seville; Spain; 8 September 2015 through 11 September 2015; Code 117454 (pp. 1-6). Association for Computing Machinery (ACM)
Open this publication in new window or tab >>Low complexity FPGA based background subtraction technique for thermal imagery
2015 (English)In: ACM International Conference Proceeding Series, Association for Computing Machinery (ACM), 2015, p. 1-6Conference paper, Published paper (Refereed)
Abstract [en]

Embedded smart camera systems are gaining popularity for a number of real world surveillance applications. However, there are still challenges, i.e. variation in illumination, shadows, occlusion, and weather conditions while employing the vision algorithms in outdoor environments. For safety-critical surveillance applications, the visual sensors can be complemented with beyond-visual-range sensors. This in turn requires analysis, development and modification of existing imaging techniques. In this work, a low complexity background modelling and subtraction technique has been proposed for thermal imagery. The proposed technique has been implemented on Field Programmable Gate Arrays (FPGAs) after in-depth analysis of different sets of images, characterizing poor signal-to-noise ratio challenges, e.g. motion of high frequency background objects, temperature variation and camera jitter etc. The proposed technique dynamically updates the background on pixel level and requires a single frame storage as opposed to existing techniques. The comparison of this approach with two other approaches show that this approach performs better in different environmental conditions. The proposed technique has been modelled in Register Transfer Logic (RTL) and implementation on the latest FPGAs shows that the design requires less than 1 percent logics, 47 percent block RAMs, and consumes 91 mW power consumption on Artix-7 100T FPGA.

Place, publisher, year, edition, pages
Association for Computing Machinery (ACM), 2015
Keywords
Background modelling; subtraction; FPGA; architecture; smart camera, thermal imaging.
National Category
Embedded Systems
Identifiers
urn:nbn:se:miun:diva-25997 (URN)10.1145/2789116.2789121 (DOI)2-s2.0-84958251961 (Scopus ID)STC (Local ID)978-145033681-9 (ISBN)STC (Archive number)STC (OAI)
Conference
9th International Conference on Distributed Smart Cameras, ICDSC 2015; Seville; Spain; 8 September 2015 through 11 September 2015; Code 117454
Available from: 2015-09-28 Created: 2015-09-28 Last updated: 2016-12-23Bibliographically approved
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