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  • 301.
    Pettersson, Johan
    Linköpings universitet, Institutionen för systemteknik.
    Real-time Object Recognition on a GPU2007Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats
    Abstract [en]

    Shape-Based matching (SBM) is a known method for 2D object recognition that is rather robust against illumination variations, noise, clutter and partial occlusion.

    The objects to be recognized can be translated, rotated and scaled.

    The translation of an object is determined by evaluating a similarity measure for all possible positions (similar to cross correlation).

    The similarity measure is based on dot products between normalized gradient directions in edges.

    Rotation and scale is determined by evaluating all possible combinations, spanning a huge search space.

    A resolution pyramid is used to form a heuristic for the search that then gains real-time performance.

    For SBM, a model consisting of normalized edge gradient directions, are constructed for all possible combinations of rotation and scale.

    We have avoided this by using (bilinear) interpolation in the search gradient map, which greatly reduces the amount of storage required.

    SBM is highly parallelizable by nature and with our suggested improvements it becomes much suited for running on a GPU.

    This have been implemented and tested, and the results clearly outperform those of our reference CPU implementation (with magnitudes of hundreds).

    It is also very scalable and easily benefits from future devices without effort.

    An extensive evaluation material and tools for evaluating object recognition algorithms have been developed and the implementation is evaluated and compared to two commercial 2D object recognition solutions.

    The results show that the method is very powerful when dealing with the distortions listed above and competes well with its opponents.

  • 302.
    Pham, Tuan
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    COMPLEMENTARY FEATURES FOR RADIOMIC ANALYSIS OF MALIGNANT AND BENIGN MEDIASTINAL LYMPH NODES2017Ingår i: 2017 24TH IEEE INTERNATIONAL CONFERENCE ON IMAGE PROCESSING (ICIP), IEEE , 2017, s. 3849-3853Konferensbidrag (Refereegranskat)
    Abstract [en]

    The importance of developing effective strategies for investigating mediastinal lymph-node metastases in non-small cell lung cancers is increasingly emphasized. It is because the precise detection of this metastatic disease is critical for optimal surgical intervention and treatment for patients with lung cancer. Existing medical image analysis is of limited power for mediastinal lymph-node staging on computed tomography (CT). Motivated by the radiomics hypothesis, this paper explored deep-learning, texture features and their combinations to ascertain subtle difference between malignant and benign mediastinal lymph nodes on CT. The radiomics-based results are found to be promising for differentiating malignant from benign mediastinal lymph nodes of patients with lung cancer.

  • 303.
    Pham, Tuan
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Scaling of Texture in Training Autoencoders for Classification of Histological Images of Colorectal Cancer2017Ingår i: ADVANCES IN NEURAL NETWORKS, PT II, SPRINGER INTERNATIONAL PUBLISHING AG , 2017, Vol. 10262, s. 524-532Konferensbidrag (Refereegranskat)
    Abstract [en]

    Autoencoding in deep learning has been known as a useful tool for extracting image features in multiple layers, which are subsequently configured for classification by deep neural networks. A practical burden for the implementation of autoencoders is the time required for training a large number of artificial neurons. This paper shows the effects of scaling of texture in the histology of colorectal cancer, which can result in significant training time reduction being approximately to an exponential function, with improved classification rates.

  • 304.
    Pham, Tuan
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    The Kolmogorov-Sinai entropy in the setting of fuzzy sets for image texture analysis and classification2016Ingår i: Pattern Recognition, ISSN 0031-3203, E-ISSN 1873-5142, Vol. 53, s. 229-237Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Kolmogorov–Sinai (K–S) entropy is used to quantify the average amount of uncertainty of a dynamical system through a sequence of observations. Sequence probabilities therefore play a central role for the computation of the entropy rate to determine if the dynamical system under study is deterministically non-chaotic, deterministically chaotic, or random. This paper extends the notion of the K–S entropy to measure the entropy rate of imprecise systems using sequence membership grades, in which the underlying deterministic paradigm is replaced with the degree of fuzziness. While constructing sequential probabilities for the calculation of the K–S entropy is difficult in practice, the estimate of the K–S entropy in the setting of fuzzy sets in an image is feasible and can be useful for modeling uncertainty of pixel distributions in images. The fuzzy K–S entropy is illustrated as an effective feature for image analysis and texture classification.

  • 305.
    Pham, Tuan D
    Bioinformatics Applications Research Centre; and the School of Mathematics, Physics and Information Technology, James Cook University, Australia.
    Cancer classification by minimizing fuzzy scattering effect2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Proteomic technology has been found promising for classifying complex diseases that leads to early prediction. However, for effective classification, the extraction of good features that can represent the identities of different classes plays the frontal critical factor for any classification problems. In addition, another major problem associated with pattern recognition is how to effectively handle a large feature space. This paper addresses these two frontal issues for mass spectrometry (MS) classification. We apply the theory of linear predictive coding to extract features and fuzzy vector quantization to reduce the large feature space of MS data. The minimization of the fuzzy scattering matrix in the setting of the fuzzy c-means algorithm provides better grouping for feature classification. The proposed methodology was tested using two MS-based cancer datasets and the results are promising.

  • 306.
    Pham, Tuan D
    Aizu Research Cluster for Medical Engineering and Informatics Center for Advanced Information Science and Technology The University of Aizu, Aizuwakamatsu, Fukushima 965-8580, Japan.
    Detecting mitochondria in intracellular images with nonstationary indicator kriging2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    The mitochondrion is a membrane-bound organelle found in most eukaryotic cells. Mitochondria are considered as the powerhouse of the cell because they function as the platform for generating the production of chemical energy. The visual information of mitochondria revealed by the recent advanced technology in nanoimaging opens doors to life-science researchers to gain insights into its spatial structure and its spatial distribution within the cell. In order to simulate and model mitochondria using a large amount of images, the first task in image processing is the automated detection of this organelle. This paper introduces a nonstationary indicator kriging model, which can model the spatial uncertainty in an image, for feature extraction. This feature can be effectively applied for the detection of mitochondria.

  • 307.
    Pham, Tuan D
    Aizu Research Cluster for Medical Engineering and Informatics, Research Center for Advanced Information Science and Technology, The University of Aizu, Aizuwakamatsu, Japan.
    Dynamic-Time-Warping Analysis of Feature-Vector Reliability for Cognitive Stimulation Therapy Assessment2015Ingår i: Information Science and Applications / [ed] Kuinam J. Kim, Springer Berlin/Heidelberg, 2015, s. 235-241Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    Cognitive stimulation therapy (CST) can help people with mental illness improve their health condition. In particular, CST provides an alternative treatment for people with mild to moderate dementia. Signal processing and pattern recognition methods are promising tools for automated assessment of the effectiveness of CST in treating individuals with dementia. This paper applies the dynamic time-warping for investigating the reliability of photoplethysmography-derived features extracted by the largest Lyapunov exponents and spectral distortion for CST evaluation.

  • 308.
    Pham, Tuan D
    Aizu Research Cluster for Medical Engineering and Informatics Research Center for Advanced Information Science and Technology.
    Image texture analysis using geostatistical information entropy2012Ingår i: Intelligent Systems (IS), 2012 6th IEEE International Conference, 2012, s. 353-356Konferensbidrag (Refereegranskat)
    Abstract [en]

    Extraction of effective features of objects is an important area of research in the intelligent processing of image data. A well-known feature in images is texture which can be used for image description, segmentation and classification. This paper presents a novel texture extraction method using the principles of geostatistics and the concept of entropy in information theory. Experimental results on medical image data have shown the superior performance of the proposed approach over some popular texture extraction methods.

  • 309.
    Pham, Tuan D
    Aizu Research Cluster for Medical Engineering and Informatics, Research Center for Advanced Information Science and Technology, The University of Aizu Aizu-Wakamatsu, Fukushima, Japan.
    Image texture analysis using geostatistical information entropy2012Ingår i: Intelligent Systems (IS), 2012 6th IEEE International Conference, IEEE , 2012, s. 353-356Konferensbidrag (Refereegranskat)
    Abstract [en]

    Extraction of effective features of objects is an important area of research in the intelligent processing of image data. A well-known feature in images is texture which can be used for image description, segmentation and classification. This paper presents a novel texture extraction method using the principles of geostatistics and the concept of entropy in information theory. Experimental results on medical image data have shown the superior performance of the proposed approach over some popular texture extraction methods.

  • 310.
    Pham, Tuan D
    Aizu Research Cluster for Medical Engineering and Informatics Center for Advanced Information Science and Technology The University of Aizu Aizu-Wakamatsu, Fukushima 965-8580, Japan.
    Modeling spatial uncertainty of imprecise information in images.2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    The description of information content in images is imprecise in nature. Quantification of uncertainty in images for pattern analysis has been addressed with the theories of probability and fuzzy sets. In this paper, an approach for modeling the spatial uncertainty of images is proposed in the setting of geostatistics and probability measure of fuzzy events. The proposed approach can be utilized to extract an effective feature for image classification.

  • 311.
    Pham, Tuan D.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    The semi-variogram and spectral distortion measures for image texture retrieval2016Ingår i: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042, Vol. 25, nr 4, s. 1556-1565Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Semi-variogram estimators and distortion measures of signal spectra are utilized in this paper for image texture retrieval. On the use of the complete Brodatz database, most high retrieval rates are reportedly based on multiple features, and the combinations of multiple algorithms; while the classification using single features is still a challenge to the retrieval of diverse texture images. The semi-variogram, which is theoretically sound and the cornerstone of spatial statistics, has the characteristics shared between true randomness and complete determinism; and therefore can be used as a useful tool for both structural and statistical analysis of texture images. Meanwhile, spectral distortion measures derived from the theory of linear predictive coding provide a rigorously mathematical model for signal-based similarity matching, and have been proven useful for many practical pattern classification systems. Experimental results obtained from testing the proposed approach using the complete Brodatz database, and the UIUC texture database suggest the effectiveness of the proposed approach as a single-feature-based dissimilarity measure for real-time texture retrieval.

  • 312.
    Pham, Tuan D
    et al.
    ADFA School of Information Technology and Electrical Engineering The University of New South Wales Canberra, Australia.
    Eisenblätter, Uwe
    ADFA School of Information Technology and Electrical Engineering The University of New South Wales Canberra, ACT 2600, Australia.
    A New Spatial Approach to Image Restoration2008Ingår i: Image Processing Theory, Tools and Applications, 2008. IPTA 2008. First Workshops on, Institute of Electrical and Electronics Engineers (IEEE), 2008, s. 1-8Konferensbidrag (Refereegranskat)
    Abstract [en]

    Study in restoring images from their degraded states has been an important research topic in image processing and has potential applications in complex pattern recognition. We propose in this paper a new adaptive image restoration method using the concept of random-function realizations in geostatistics. This conceptual framework allows us to derive the model means and variances in the context of spatial statistics. Experimental results demonstrate the superior performance of the proposed approach to other image restoration algorithms.

  • 313.
    Pham, Tuan D
    et al.
    Aizu Research Cluster for Medical Engineering and Informatics The University of Aizu, Aizu-Wakamatsu, Fukushima 965-8580, Japan.
    Tsunoyama, Taichiro
    Teikyo University, Tokyo 173-8606, Japan.
    Thang, Truong C
    Aizu Research Cluster for Medical Engineering and Informatics The University of Aizu, Aizu-Wakamatsu, Fukushima 965-8580, Japan.
    Fujita, Takashi
    Teikyo University, Tokyo 173-8606, Japan.
    Sakamoto, Takanori
    Teikyo University, Tokyo 173-8606, Japan.
    Image classification of bowel abnormalities and ischemia2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Intestinal abnormalities and ischemia are medical conditions in which inflammation and injury of the intestine are caused by inadequate blood supply. Developments of computerized systems for the automated identification of these types of complex gastrointestinal disorders are rarely reported. In this paper, we introduce a mapping model of spatial uncertainty in computed tomography images for feature extraction, which can be effectively applied for diagnostic detection. Experimental results obtained from the analysis of clinical data suggest the usefulness of the proposed uncertainty mapping model.

  • 314.
    Pham, Tuan D
    et al.
    School of Computing, University of Canberra, Canberra, Australia.
    Wagner, M
    School of Computing, University of Canberra, Canberra, Australia.
    Fuzzy kriging filter for image restoration1999Konferensbidrag (Refereegranskat)
    Abstract [en]

    Kriging and fuzzy sets are combined as a spatial filter for smoothing gray-scale images degraded by Gaussian white noise. Application of fuzzy sets allows a gradual transition between two boundaries of semi-variance levels as a criterion for smoothing the pixel values. Results which are obtained by the fuzzy kriging filter are smoother and still preserved edges compared with those by the adaptive Wiener filter

  • 315.
    Pham, Tuan D
    et al.
    Bioinformatics Applications Research Centre, James Cook University, Australia.
    Zhou, Xiaobo
    Bioinformatics Applications Research Centre, James Cook University, Australia.
    Computational Models For Life Sciences (CMLS '07)2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    This conference proceedings text features research papers that address novel applications of computer, physical, engineering and mathematical models for solving modern challenging problems in life sciences. All the papers, presented at the Computational Models for Life Sciences conference held in 2007, have been peer-reviewed. They cover a huge range of topics, including image analysis, computer vision, and pattern analysis and classification, among many others.

  • 316.
    Qiu, Li
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer.
    Polygonal models from range scanned trees2009Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    3D Models of botanical trees are very important in video games, simulation, virtual reality, digital city modeling and other fields of computer graphics. However, since the early days of computer graphics, the modeling of trees has been challenging, because of the huge dynamical range between its smallest and largest structures and their geometrical complexity. Trees are also ubiquitous which makes it even hard to model them in a realistic way, Current techniques are limited in that they model a tree either in a rule-based way or in an approximated way. These methods emphasize appearance while sacrificing its real structure. Recent development in range scanners are making 3D aquisition feasible for large and complex objects. This report presents the semi-automatic technique developed for modeling laser-scanned trees. First, the user draws a few strokes on the depth image plane generated from the dataset. Branches are then extracted through the 2D Curve detection algorithm originally developed. Afterwards, those short branches are connected together to generate the skeleton of the tree by forming a Minimum Spanning Tree (MST). Finally, the geometry of the tree skeleton is produced using allometric rules for branch thickness and branching angles.

  • 317.
    Ragnemalm, Ingemar
    Linköpings universitet, Institutionen för systemteknik, Informationskodning. Linköpings universitet, Tekniska fakulteten.
    A sub-pixel distance correction method for distance transforms of binary images.2018Ingår i: Swedish Symposium on Image Analysis, Stockholm: SSBA , 2018Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We present a method for estimating the location of edges in binary images, in order to correct the distance produced by distance transforms to sub-pixel precision. We also show that the resulting precision significantly outper- forms the precision of an uncorrected Euclidean Distance Transform.

  • 318.
    Ragnemalm, Ingemar
    et al.
    Linköpings universitet, Institutionen för systemteknik, Informationskodning.
    Hjelm Andersson, Patrik
    Shape matching on the Euclidean Distance Transform2005Ingår i: Swedish Symposium on Image Analysis, 2005, s. 21-24Konferensbidrag (Övrigt vetenskapligt)
  • 319.
    Reininghaus, Jan
    et al.
    Zuse Institue Berlin.
    Hotz, Ingrid
    Zuse Institue Berlin.
    Computational Discrete Morse Theory for Divergence-Free 2D Vector Fields2012Ingår i: Topological Methods in Data Analysis and Visualization: Theory, Algorithms, and Applications / [ed] Ronald Peikert, Helwig Hauser, Hamish Carr, Raphael Fuchs, Springer, 2012, s. 3-14Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    We present a simple approach to the topological analysis of divergence-free 2D vector fields using discrete Morse theory. We make use of the fact that the point-wise perpendicular vector field can be interpreted as the gradient of the stream function. The topology of the divergence-free vector field is thereby encoded in the topology of a gradient vector field. We can therefore apply a formulation of computational discrete Morse theory for gradient vector fields. The inherent consistence and robustness of the resulting algorithm is demonstrated on synthetic data and an example from computational fluid dynamics.

  • 320.
    Reininghaus, Jan
    et al.
    Zuse Institute Berlin, Germany.
    Kasten, Jens
    Zuse Institute Berlin, Germany.
    Weinkauf, Tino
    Saarbru¨cken, Germany.
    Hotz, Ingrid
    Zuse Institute Berlin, Germany.
    Efficient Computation of Combinatorial Feature Flow Fields2011Ingår i: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 18, nr 9, s. 1563-1573Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a combinatorial algorithm to track critical points of 2D time-dependent scalar fields. Existing tracking algorithms such as Feature Flow Fields apply numerical schemes utilizing derivatives of the data, which makes them prone to noise and involve a large number of computational parameters. In contrast, our method is robust against noise since it does not require derivatives, interpolation, and numerical integration. Furthermore, we propose an importance measure that combines the spatial persistence of a critical point with its temporal evolution. This leads to a time-aware feature hierarchy, which allows us to discriminate important from spurious features. Our method requires only a single, easy-to-tune computational parameter and is naturally formulated in an out-of-core fashion, which enables the analysis of large data sets. We apply our method to synthetic data and data sets from computational fluid dynamics and compare it to the stabilized continuous Feature Flow Field tracking algorithm.

  • 321.
    Reininghaus, Jan
    et al.
    Zuse Institute Berlin, Germany.
    Kotava, Natallia
    Kaiserslautern, Germany.
    Günther, David
    Zuse Institute Berlin, Germany.
    Kasten, Jens
    Zuse Institute Berlin, Germany.
    Hagen, Hans
    University of Kaiserslautern.
    Hotz, Ingrid
    Zuse Institute Berlin, Germany.
    A Scale Space Based Persistence Measure for Critical Points in 2D Scalar Fields2011Ingår i: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 17, nr 12, s. 2045-2052Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper introduces a novel importance measure for critical points in 2D scalar fields. This measure is based on a combination of the deep structure of the scale space with the well-known concept of homological persistence. We enhance the noise robust persistence measure by implicitly taking the hill-, ridge- and outlier-like spatial extent of maxima and minima into account. This allows for the distinction between different types of extrema based on their persistence at multiple scales. Our importance measure can be computed efficiently in an out-of-core setting. To demonstrate the practical relevance of our method we apply it to a synthetic and a real-world data set and evaluate its performance and scalability.

  • 322.
    Ringaby, Erik
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska högskolan.
    Geometric Computer Vision for Rolling-shutter and Push-broom Sensors2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Almost all cell-phones and camcorders sold today are equipped with a CMOS (Complementary Metal Oxide Semiconductor) image sensor and there is also a general trend to incorporate CMOS sensors in other types of cameras. The sensor has many advantages over the more conventional CCD (Charge-Coupled Device) sensor such as lower power consumption, cheaper manufacturing and the potential for on-chip processing. Almost all CMOS sensors make use of what is called a rolling shutter. Compared to a global shutter, which images all the pixels at the same time, a rolling-shutter camera exposes the image row-by-row. This leads to geometric distortions in the image when either the camera or the objects in the scene are moving. The recorded videos and images will look wobbly (jello effect), skewed or otherwise strange and this is often not desirable. In addition, many computer vision algorithms assume that the camera used has a global shutter, and will break down if the distortions are too severe.

    In airborne remote sensing it is common to use push-broom sensors. These sensors exhibit a similar kind of distortion as a rolling-shutter camera, due to the motion of the aircraft. If the acquired images are to be matched with maps or other images, then the distortions need to be suppressed.

    The main contributions in this thesis are the development of the three dimensional models for rolling-shutter distortion correction. Previous attempts modelled the distortions as taking place in the image plane, and we have shown that our techniques give better results for hand-held camera motions.

    The basic idea is to estimate the camera motion, not only between frames, but also the motion during frame capture. The motion can be estimated using inter-frame image correspondences and with these a non-linear optimisation problem can be formulated and solved. All rows in the rolling-shutter image are imaged at different times, and when the motion is known, each row can be transformed to the rectified position.

    In addition to rolling-shutter distortions, hand-held footage often has shaky camera motion. It has been shown how to do efficient video stabilisation, in combination with the rectification, using rotation smoothing.

    In the thesis it has been explored how to use similar techniques as for the rolling-shutter case in order to correct push-broom images, and also how to rectify 3D point clouds from e.g. the Kinect depth sensor.

    Delarbeten
    1. Rectifying rolling shutter video from hand-held devices
    Öppna denna publikation i ny flik eller fönster >>Rectifying rolling shutter video from hand-held devices
    2010 (Engelska)Ingår i: IEEE  Conference on  Computer Vision and Pattern Recognition (CVPR), 2010, Los Alamitos, CA, USA: IEEE Computer Society, 2010, s. 507-514Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a method for rectifying video sequences from rolling shutter (RS) cameras. In contrast to previous RS rectification attempts we model distortions as being caused by the 3D motion of the camera. The camera motion is parametrised as a continuous curve, with knots at the last row of each frame. Curve parameters are solved for using non-linear least squares over inter-frame correspondences obtained from a KLT tracker. We have generated synthetic RS sequences with associated ground-truth to allow controlled evaluation. Using these sequences, we demonstrate that our algorithm improves over to two previously published methods. The RS dataset is available on the web to allow comparison with other methods

    Ort, förlag, år, upplaga, sidor
    Los Alamitos, CA, USA: IEEE Computer Society, 2010
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-70572 (URN)10.1109/CVPR.2010.5540173 (DOI)978-1-4244-6984-0 (ISBN)
    Konferens
    CVPR10, San Fransisco, USA, June 13-18, 2010
    Tillgänglig från: 2011-09-13 Skapad: 2011-09-13 Senast uppdaterad: 2015-12-10
    2. Efficient Video Rectification and Stabilisation for Cell-Phones
    Öppna denna publikation i ny flik eller fönster >>Efficient Video Rectification and Stabilisation for Cell-Phones
    2012 (Engelska)Ingår i: International Journal of Computer Vision, ISSN 0920-5691, E-ISSN 1573-1405, Vol. 96, nr 3, s. 335-352Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    This article presents a method for rectifying and stabilising video from cell-phones with rolling shutter (RS) cameras. Due to size constraints, cell-phone cameras have constant, or near constant focal length, making them an ideal application for calibrated projective geometry. In contrast to previous RS rectification attempts that model distortions in the image plane, we model the 3D rotation of the camera. We parameterise the camera rotation as a continuous curve, with knots distributed across a short frame interval. Curve parameters are found using non-linear least squares over inter-frame correspondences from a KLT tracker. By smoothing a sequence of reference rotations from the estimated curve, we can at a small extra cost, obtain a high-quality image stabilisation. Using synthetic RS sequences with associated ground-truth, we demonstrate that our rectification improves over two other methods. We also compare our video stabilisation with the methods in iMovie and Deshaker.

    Ort, förlag, år, upplaga, sidor
    Springer Verlag (Germany), 2012
    Nyckelord
    Cell-phone, Rolling shutter, CMOS, Video stabilisation
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-75277 (URN)10.1007/s11263-011-0465-8 (DOI)000299769400005 ()
    Anmärkning
    Funding Agencies|CENIIT organisation at Linkoping Institute of Technology||Swedish Research Council||Tillgänglig från: 2012-02-27 Skapad: 2012-02-24 Senast uppdaterad: 2017-12-07
    3. Scan Rectification for Structured Light Range Sensors with Rolling Shutters
    Öppna denna publikation i ny flik eller fönster >>Scan Rectification for Structured Light Range Sensors with Rolling Shutters
    2011 (Engelska)Ingår i: IEEE International Conference on Computer Vision, Barcelona Spain, 2011, s. 1575-1582Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
    Abstract [en]

    Structured light range sensors, such as the Microsoft Kinect, have recently become popular as perception devices for computer vision and robotic systems. These sensors use CMOS imaging chips with electronic rolling shutters (ERS). When using such a sensor on a moving platform, both the image, and the depth map, will exhibit geometric distortions. We introduce an algorithm that can suppress such distortions, by rectifying the 3D point clouds from the range sensor. This is done by first estimating the time continuous 3D camera trajectory, and then transforming the 3D points to where they would have been, if the camera had been stationary. To ensure that image and range data are synchronous, the camera trajectory is computed from KLT tracks on the structured-light frames, after suppressing the structured-light pattern. We evaluate our rectification, by measuring angles between the visible sides of a cube, before and after rectification. We also measure how much better the 3D point clouds can be aligned after rectification. The obtained improvement is also related to the actual rotational velocity, measured using a MEMS gyroscope.

    Ort, förlag, år, upplaga, sidor
    Barcelona Spain: , 2011
    Serie
    International Conference on Computer Vision (ICCV), ISSN 1550-5499
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-77059 (URN)10.1109/ICCV.2011.6126417 (DOI)978-1-4577-1101-5 (ISBN)
    Konferens
    IEEE International Conference on Computer Vision(ICCV11), 8-11 November 2011, Barcelona, Spain
    Tillgänglig från: 2012-05-07 Skapad: 2012-05-03 Senast uppdaterad: 2015-12-10Bibliografiskt granskad
    4. Co-alignmnent of Aerial Push-broom Strips using Trajectory Smoothness Constraints
    Öppna denna publikation i ny flik eller fönster >>Co-alignmnent of Aerial Push-broom Strips using Trajectory Smoothness Constraints
    2010 (Engelska)Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
    Abstract [en]

    We study the problem of registering a sequence of scan lines (a strip) from an airborne push-broom imager to another sequence partly covering the same area. Such a registration has to compensate for deformations caused by attitude and speed changes in the aircraft. The registration is challenging, as both strips contain such deformations. Our algorithm estimates the 3D rotation of the camera for each scan line, by parametrising it as a linear spline with a number of knots evenly distributed in one of the strips. The rotations are estimated from correspondences between strips of the same area. Once the rotations are known, they can be compensated for, and each line of pixels can be transformed such that ground trace of the two strips are registered with respect to each other.

    Ort, förlag, år, upplaga, sidor
    Swedish Society for automated image analysis, 2010
    Nationell ämneskategori
    Datorseende och robotik (autonoma system)
    Identifikatorer
    urn:nbn:se:liu:diva-70706 (URN)
    Konferens
    SSBA10, Symposium on Image Analysis 11-12 March, Uppsala
    Tillgänglig från: 2011-09-15 Skapad: 2011-09-15 Senast uppdaterad: 2018-01-12Bibliografiskt granskad
    5. Co-aligning Aerial Hyperspectral Push-broom Strips for Change Detection
    Öppna denna publikation i ny flik eller fönster >>Co-aligning Aerial Hyperspectral Push-broom Strips for Change Detection
    2010 (Engelska)Ingår i: Proc. SPIE 7835, Electro-Optical Remote Sensing, Photonic Technologies, and Applications IV / [ed] Gary W. Kamerman; Ove Steinvall; Keith L. Lewis; Richard C. Hollins; Thomas J. Merlet; Gary J. Bishop; John D. Gonglewski, SPIE - International Society for Optical Engineering, 2010, s. Art.nr. 7835B-36-Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    We have performed a field trial with an airborne push-broom hyperspectral sensor, making several flights over the same area and with known changes (e.g., moved vehicles) between the flights. Each flight results in a sequence of scan lines forming an image strip, and in order to detect changes between two flights, the two resulting image strips must be geometrically aligned and radiometrically corrected. The focus of this paper is the geometrical alignment, and we propose an image- and gyro-based method for geometric co-alignment (registration) of two image strips. The method is particularly useful when the sensor is not stabilized, thus reducing the need for expensive mechanical stabilization. The method works in several steps, including gyro-based rectification, global alignment using SIFT matching, and a local alignment using KLT tracking. Experimental results are shown but not quantified, as ground truth is, by the nature of the trial, lacking.

    Ort, förlag, år, upplaga, sidor
    SPIE - International Society for Optical Engineering, 2010
    Serie
    Proceedings Spie, ISSN 0277-786X ; 7835
    Nationell ämneskategori
    Datorseende och robotik (autonoma system)
    Identifikatorer
    urn:nbn:se:liu:diva-70464 (URN)10.1117/12.865034 (DOI)978-0-8194-8353-9 (ISBN)
    Konferens
    Electro-Optical Remote Sensing, Photonic Technologies, and Applications IV, 20-23 September, Toulouse, France
    Tillgänglig från: 2011-09-13 Skapad: 2011-09-09 Senast uppdaterad: 2018-01-12Bibliografiskt granskad
  • 323.
    Ringaby, Erik
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska högskolan.
    Geometric Models for Rolling-shutter and Push-broom Sensors2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Almost all cell-phones and camcorders sold today are equipped with a  CMOS (Complementary Metal Oxide Semiconductor) image sensor and there is also a general trend to incorporate CMOS sensors in other types of cameras. The CMOS sensor has many advantages over the more conventional CCD (Charge-Coupled Device) sensor such as lower power consumption, cheaper manufacturing and the potential for onchip processing. Nearly all CMOS sensors make use of what is called a rolling shutter readout. Unlike a global shutter readout, which images all the pixels at the same time, a rolling-shutter exposes the image row-by-row. If a mechanical shutter is not used this will lead to geometric distortions in the image when either the camera or the objects in the scene are moving. Smaller cameras, like those in cell-phones, do not have mechanical shutters and systems that do have them will not use them when recording video. The result will look wobbly (jello eect), skewed or otherwise strange and this is often not desirable. In addition, many computer vision algorithms assume that the camera used has a global shutter and will break down if the distortions are too severe.

    In airborne remote sensing it is common to use push-broom sensors. These sensors exhibit a similar kind of distortion as that of a rolling-shutter camera, due to the motion of the aircraft. If the acquired images are to be registered to maps or other images, the distortions need to be suppressed.

    The main contributions in this thesis are the development of the three-dimensional models for rolling-shutter distortion correction. Previous attempts modelled the distortions as taking place in the image plane, and we have shown that our techniques give better results for hand-held camera motions. The basic idea is to estimate the camera motion, not only between frames, but also the motion during frame capture. The motion is estimated using image correspondences and with these a non-linear optimisation problem is formulated and solved. All rows in the rollingshutter image are imaged at dierent times, and when the motion is known, each row can be transformed to its rectied position. The same is true when using depth sensors such as the Microsoft Kinect, and the thesis describes how to estimate its 3D motion and how to rectify 3D point clouds.

    In the thesis it has also been explored how to use similar techniques as for the rolling-shutter case, to correct push-broom images. When a transformation has been found, the images need to be resampled to a regular grid in order to be visualised. This can be done in many ways and dierent methods have been tested and adapted to the push-broom setup.

    In addition to rolling-shutter distortions, hand-held footage often has shaky camera motion. It is possible to do ecient video stabilisation in combination with the rectication using rotation smoothing. Apart from these distortions, motion blur is a big problem for hand-held photography. The images will be blurry due to the camera motion and also noisy if taken in low light conditions. One of the contributions in the thesis is a method which uses gyroscope measurements and feature tracking to combine several images, taken with a smartphone, into one resulting image with less blur and noise. This enables the user to take photos which would have otherwise required a tripod.

    Delarbeten
    1. Rectifying rolling shutter video from hand-held devices
    Öppna denna publikation i ny flik eller fönster >>Rectifying rolling shutter video from hand-held devices
    2010 (Engelska)Ingår i: IEEE  Conference on  Computer Vision and Pattern Recognition (CVPR), 2010, Los Alamitos, CA, USA: IEEE Computer Society, 2010, s. 507-514Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a method for rectifying video sequences from rolling shutter (RS) cameras. In contrast to previous RS rectification attempts we model distortions as being caused by the 3D motion of the camera. The camera motion is parametrised as a continuous curve, with knots at the last row of each frame. Curve parameters are solved for using non-linear least squares over inter-frame correspondences obtained from a KLT tracker. We have generated synthetic RS sequences with associated ground-truth to allow controlled evaluation. Using these sequences, we demonstrate that our algorithm improves over to two previously published methods. The RS dataset is available on the web to allow comparison with other methods

    Ort, förlag, år, upplaga, sidor
    Los Alamitos, CA, USA: IEEE Computer Society, 2010
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-70572 (URN)10.1109/CVPR.2010.5540173 (DOI)978-1-4244-6984-0 (ISBN)
    Konferens
    CVPR10, San Fransisco, USA, June 13-18, 2010
    Tillgänglig från: 2011-09-13 Skapad: 2011-09-13 Senast uppdaterad: 2015-12-10
    2. Efficient Video Rectification and Stabilisation for Cell-Phones
    Öppna denna publikation i ny flik eller fönster >>Efficient Video Rectification and Stabilisation for Cell-Phones
    2012 (Engelska)Ingår i: International Journal of Computer Vision, ISSN 0920-5691, E-ISSN 1573-1405, Vol. 96, nr 3, s. 335-352Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    This article presents a method for rectifying and stabilising video from cell-phones with rolling shutter (RS) cameras. Due to size constraints, cell-phone cameras have constant, or near constant focal length, making them an ideal application for calibrated projective geometry. In contrast to previous RS rectification attempts that model distortions in the image plane, we model the 3D rotation of the camera. We parameterise the camera rotation as a continuous curve, with knots distributed across a short frame interval. Curve parameters are found using non-linear least squares over inter-frame correspondences from a KLT tracker. By smoothing a sequence of reference rotations from the estimated curve, we can at a small extra cost, obtain a high-quality image stabilisation. Using synthetic RS sequences with associated ground-truth, we demonstrate that our rectification improves over two other methods. We also compare our video stabilisation with the methods in iMovie and Deshaker.

    Ort, förlag, år, upplaga, sidor
    Springer Verlag (Germany), 2012
    Nyckelord
    Cell-phone, Rolling shutter, CMOS, Video stabilisation
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-75277 (URN)10.1007/s11263-011-0465-8 (DOI)000299769400005 ()
    Anmärkning
    Funding Agencies|CENIIT organisation at Linkoping Institute of Technology||Swedish Research Council||Tillgänglig från: 2012-02-27 Skapad: 2012-02-24 Senast uppdaterad: 2017-12-07
    3. Scan Rectification for Structured Light Range Sensors with Rolling Shutters
    Öppna denna publikation i ny flik eller fönster >>Scan Rectification for Structured Light Range Sensors with Rolling Shutters
    2011 (Engelska)Ingår i: IEEE International Conference on Computer Vision, Barcelona Spain, 2011, s. 1575-1582Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
    Abstract [en]

    Structured light range sensors, such as the Microsoft Kinect, have recently become popular as perception devices for computer vision and robotic systems. These sensors use CMOS imaging chips with electronic rolling shutters (ERS). When using such a sensor on a moving platform, both the image, and the depth map, will exhibit geometric distortions. We introduce an algorithm that can suppress such distortions, by rectifying the 3D point clouds from the range sensor. This is done by first estimating the time continuous 3D camera trajectory, and then transforming the 3D points to where they would have been, if the camera had been stationary. To ensure that image and range data are synchronous, the camera trajectory is computed from KLT tracks on the structured-light frames, after suppressing the structured-light pattern. We evaluate our rectification, by measuring angles between the visible sides of a cube, before and after rectification. We also measure how much better the 3D point clouds can be aligned after rectification. The obtained improvement is also related to the actual rotational velocity, measured using a MEMS gyroscope.

    Ort, förlag, år, upplaga, sidor
    Barcelona Spain: , 2011
    Serie
    International Conference on Computer Vision (ICCV), ISSN 1550-5499
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-77059 (URN)10.1109/ICCV.2011.6126417 (DOI)978-1-4577-1101-5 (ISBN)
    Konferens
    IEEE International Conference on Computer Vision(ICCV11), 8-11 November 2011, Barcelona, Spain
    Tillgänglig från: 2012-05-07 Skapad: 2012-05-03 Senast uppdaterad: 2015-12-10Bibliografiskt granskad
    4. Co-alignmnent of Aerial Push-broom Strips using Trajectory Smoothness Constraints
    Öppna denna publikation i ny flik eller fönster >>Co-alignmnent of Aerial Push-broom Strips using Trajectory Smoothness Constraints
    2010 (Engelska)Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
    Abstract [en]

    We study the problem of registering a sequence of scan lines (a strip) from an airborne push-broom imager to another sequence partly covering the same area. Such a registration has to compensate for deformations caused by attitude and speed changes in the aircraft. The registration is challenging, as both strips contain such deformations. Our algorithm estimates the 3D rotation of the camera for each scan line, by parametrising it as a linear spline with a number of knots evenly distributed in one of the strips. The rotations are estimated from correspondences between strips of the same area. Once the rotations are known, they can be compensated for, and each line of pixels can be transformed such that ground trace of the two strips are registered with respect to each other.

    Ort, förlag, år, upplaga, sidor
    Swedish Society for automated image analysis, 2010
    Nationell ämneskategori
    Datorseende och robotik (autonoma system)
    Identifikatorer
    urn:nbn:se:liu:diva-70706 (URN)
    Konferens
    SSBA10, Symposium on Image Analysis 11-12 March, Uppsala
    Tillgänglig från: 2011-09-15 Skapad: 2011-09-15 Senast uppdaterad: 2018-01-12Bibliografiskt granskad
    5. Anisotropic Scattered Data Interpolation for Pushbroom Image Rectification
    Öppna denna publikation i ny flik eller fönster >>Anisotropic Scattered Data Interpolation for Pushbroom Image Rectification
    Visa övriga...
    2014 (Engelska)Ingår i: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042, Vol. 23, nr 5, s. 2302-2314Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    This article deals with fast and accurate visualization of pushbroom image data from airborne and spaceborne platforms. A pushbroom sensor acquires images in a line-scanning fashion, and this results in scattered input data that needs to be resampled onto a uniform grid for geometrically correct visualization. To this end, we model the anisotropic spatial dependence structure caused by the acquisition process. Several methods for scattered data interpolation are then adapted to handle the induced anisotropic metric and compared for the pushbroom image rectification problem. A trick that exploits the semi-ordered line structure of pushbroom data to improve the computational complexity several orders of magnitude is also presented.

    Ort, förlag, år, upplaga, sidor
    IEEE, 2014
    Nyckelord
    pushbroom, rectification, hyperspectral, interpolation, anisotropic, scattered data
    Nationell ämneskategori
    Teknik och teknologier Elektroteknik och elektronik Signalbehandling
    Identifikatorer
    urn:nbn:se:liu:diva-108105 (URN)10.1109/TIP.2014.2316377 (DOI)000350284400001 ()
    Tillgänglig från: 2014-06-25 Skapad: 2014-06-25 Senast uppdaterad: 2018-09-25Bibliografiskt granskad
    6. A Virtual Tripod for Hand-held Video Stacking on Smartphones
    Öppna denna publikation i ny flik eller fönster >>A Virtual Tripod for Hand-held Video Stacking on Smartphones
    2014 (Engelska)Ingår i: 2014 IEEE INTERNATIONAL CONFERENCE ON COMPUTATIONAL PHOTOGRAPHY (ICCP), IEEE , 2014Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    We propose an algorithm that can capture sharp, low-noise images in low-light conditions on a hand-held smartphone. We make use of the recent ability to acquire bursts of high resolution images on high-end models such as the iPhone5s. Frames are aligned, or stacked, using rolling shutter correction, based on motion estimated from the built-in gyro sensors and image feature tracking. After stacking, the images may be combined, using e.g. averaging to produce a sharp, low-noise photo. We have tested the algorithm on a variety of different scenes, using several different smartphones. We compare our method to denoising, direct stacking, as well as a global-shutter based stacking, with favourable results.

    Ort, förlag, år, upplaga, sidor
    IEEE, 2014
    Serie
    IEEE International Conference on Computational Photography, ISSN 2164-9774
    Nationell ämneskategori
    Teknik och teknologier Elektroteknik och elektronik Signalbehandling
    Identifikatorer
    urn:nbn:se:liu:diva-108109 (URN)10.1109/ICCPHOT.2014.6831799 (DOI)000356494100001 ()978-1-4799-5188-8 (ISBN)
    Konferens
    IEEE International Conference on Computational Photography (ICCP 2014), May 2-4, 2014, Intel, Santa Clara, USA
    Projekt
    VPS
    Tillgänglig från: 2014-06-25 Skapad: 2014-06-25 Senast uppdaterad: 2015-12-10Bibliografiskt granskad
  • 324.
    Ringaby, Erik
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Optical Flow Computation on Compute Unified Device Architecture2008Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats
    Abstract [en]

    There has been a rapid progress of the graphics processor the last years, much because of the demands from computer games on speed and image quality. Because of the graphics processor’s special architecture it is much faster at solving parallel problems than the normal processor. Due to its increasing programmability it is possible to use it for other tasks than it was originally designed for.

    Even though graphics processors have been programmable for some time, it has been quite difficult to learn how to use them. CUDA enables the programmer to use C-code, with a few extensions, to program NVIDIA’s graphics processor and completely skip the traditional programming models. This thesis investigates if the graphics processor can be used for calculations without knowledge of how the hardware mechanisms work. An image processing algorithm calculating the optical flow has been implemented. The result shows that it is rather easy to implement programs using CUDA, but some knowledge of how the graphics processor works is required to achieve high performance.

  • 325.
    Ringaby, Erik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Ahlberg, Jörgen
    Sensor Informatics Group, Swedish Defence Research Agenc y (FOI), Linköping.
    Forssén, Per-Erik
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Wadströmer, Niclas
    Sensor Informatics Group, Swedish Defence Research Agenc y (FOI), Linköping.
    Co-alignmnent of Aerial Push-broom Strips using Trajectory Smoothness Constraints2010Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We study the problem of registering a sequence of scan lines (a strip) from an airborne push-broom imager to another sequence partly covering the same area. Such a registration has to compensate for deformations caused by attitude and speed changes in the aircraft. The registration is challenging, as both strips contain such deformations. Our algorithm estimates the 3D rotation of the camera for each scan line, by parametrising it as a linear spline with a number of knots evenly distributed in one of the strips. The rotations are estimated from correspondences between strips of the same area. Once the rotations are known, they can be compensated for, and each line of pixels can be transformed such that ground trace of the two strips are registered with respect to each other.

  • 326.
    Ringaby, Erik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Ahlberg, Jörgen
    FOI, Swedish Defence Research Agency, Linköping, Sweden.
    Wadströmer, Niclas
    FOI, Swedish Defence Research Agency, Linköping, Sweden.
    Forssén, Per-Erik
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Co-aligning Aerial Hyperspectral Push-broom Strips for Change Detection2010Ingår i: Proc. SPIE 7835, Electro-Optical Remote Sensing, Photonic Technologies, and Applications IV / [ed] Gary W. Kamerman; Ove Steinvall; Keith L. Lewis; Richard C. Hollins; Thomas J. Merlet; Gary J. Bishop; John D. Gonglewski, SPIE - International Society for Optical Engineering, 2010, s. Art.nr. 7835B-36-Konferensbidrag (Refereegranskat)
    Abstract [en]

    We have performed a field trial with an airborne push-broom hyperspectral sensor, making several flights over the same area and with known changes (e.g., moved vehicles) between the flights. Each flight results in a sequence of scan lines forming an image strip, and in order to detect changes between two flights, the two resulting image strips must be geometrically aligned and radiometrically corrected. The focus of this paper is the geometrical alignment, and we propose an image- and gyro-based method for geometric co-alignment (registration) of two image strips. The method is particularly useful when the sensor is not stabilized, thus reducing the need for expensive mechanical stabilization. The method works in several steps, including gyro-based rectification, global alignment using SIFT matching, and a local alignment using KLT tracking. Experimental results are shown but not quantified, as ground truth is, by the nature of the trial, lacking.

  • 327.
    Robinson, Andreas
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska högskolan.
    Implementation and evaluation of a 3D tracker2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Many methods have been developed for visual tracking of generic objects. The vast majority of these assume the world is two-dimensional, either ignoring the third dimension or only dealing with it indirectly. This causes difficulties for the tracker when the target approaches or moves away from the camera, is occluded or moves out of the camera frame.

    Unmanned aerial vehicles (UAVs) are increasingly used in civilian applications and some of these will undoubtedly carry tracking systems in the future. As they move around, these trackers will encounter both scale changes and occlusions. To improve the tracking performance in these cases, the third dimension should be taken into account.

    This thesis extends the capabilities of a 2D tracker to three dimensions, with the assumption that the target moves on a ground plane.

    The position of the tracker camera is established by matching the video it produces to a sparse point-cloud map built with off-the-shelf structure-from-motion software. A target is tracked with a generic 2D tracker and subsequently positioned on the ground. Should the target disappear from view, its motion on the ground is predicted. In combination, these simple techniques are shown to improve the robustness of a tracking system on a moving platform under target scale changes and occlusions.

  • 328.
    Robinson, Andreas
    et al.
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska fakulteten.
    Persson, Mikael
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska fakulteten.
    Felsberg, Michael
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska fakulteten.
    Robust Accurate Extrinsic Calibration of Static Non-overlapping Cameras2017Ingår i: Computer Analysis of Images and Patterns: 17th International Conference, CAIP 2017, Ystad, Sweden, August 22-24, 2017, Proceedings, Part II / [ed] Michael Felsberg, Anders Heyden and Norbert Krüger, Springer, 2017, Vol. 10425, s. 342-353Konferensbidrag (Refereegranskat)
    Abstract [en]

    An increasing number of robots and autonomous vehicles are equipped with multiple cameras to achieve surround-view sensing. The estimation of their relative poses, also known as extrinsic parameter calibration, is a challenging problem, particularly in the non-overlapping case. We present a simple and novel extrinsic calibration method based on standard components that performs favorably to existing approaches. We further propose a framework for predicting the performance of different calibration configurations and intuitive error metrics. This makes selecting a good camera configuration straightforward. We evaluate on rendered synthetic images and show good results as measured by angular and absolute pose differences, as well as the reprojection error distributions.

  • 329.
    Romu, Thobias
    et al.
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Borga, Magnus
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Tekniska högskolan.
    Dahlqvist Leinhard, Olof
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Hälsouniversitetet.
    MANA - Multi scale adaptive normalized averaging2011Ingår i: 2011 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, IEEE conference proceedings, 2011, s. 361-364Konferensbidrag (Refereegranskat)
    Abstract [en]

    It is possible to correct intensity inhomogeneity in fat–water Magnetic Resonance Imaging (MRI) by estimating a bias field based on the observed intensities of voxels classified as the pure adipose tissue. The same procedure can also be used to quantify fat volume and its distribution which opens up for new medical applications. The bias field estimation method has to be robust since pure fat voxels are irregularly located and the density varies greatly within and between image volumes. This paper introduces Multi scale Adaptive Normalized Average (MANA) that solves this problem bybasing the estimate on a scale space of weighted averages. By usingthe local certainty of the data MANA preserves details where the local data certainty is high and provides realistic values in sparse areas.

  • 330.
    Romu, Thobias
    et al.
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Dahlqvist Leinhard, Olof
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Hälsouniversitetet.
    Forsgren, Mikael
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Almer, Sven
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Gastroenterologi och hepatologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Endokrin- och magtarmmedicinska kliniken US.
    Dahlström, Nils
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiologi. Linköpings universitet, Hälsouniversitetet.
    Kechagias, Stergios
    Linköpings universitet, Institutionen för medicin och hälsa, Internmedicin. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Endokrin- och magtarmmedicinska kliniken US.
    Nyström, Fredrik
    Linköpings universitet, Institutionen för medicin och hälsa, Internmedicin. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Endokrin- och magtarmmedicinska kliniken US.
    Smedby, Örjan
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Diagnostikcentrum, Röntgenkliniken i Linköping.
    Lundberg, Peter
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Borga, Magnus
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Tekniska högskolan.
    Fat Water Classification of Symmetrically Sampled Two-Point Dixon Images Using Biased Partial Volume Effects2011Ingår i: Proceedings of the annual meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2011), 2011., 2011Konferensbidrag (Refereegranskat)
  • 331.
    Rowa, Per
    et al.
    Linköpings universitet, Institutionen för systemteknik. Linköpings universitet, Tekniska högskolan.
    Antonsson, Dan
    Linköpings universitet, Institutionen för systemteknik. Linköpings universitet, Tekniska högskolan.
    Automated Malaria Parasite Detection1977Rapport (Övrigt vetenskapligt)
    Abstract [en]

    A system for malaria parasite detection in thin blood-smears is presented. Sample slides prepared with standard methods are accepted. A low-cost TV-camera mounted on an ordinary microscope with a computer controlled stage is used as a picture sensor. Frames, digitized in windows of 64 x 64 pixels are fed into a special purpose picture processor at normal frame rate (25 frames/sec). In the picture processor measurements are made on the images at high speed. The classification problem is split into different levels each having different characteristics such as different sampling density. Four classes, three of which are different types of malaria parasites, are recognized. As a whole the classification is best labelled as a sequential pattern recognition procedure.

    In its preliminary version the system has been run at a speed comparable to that of a human operator, that is l 500 cells per minute. A test on 80 000 cells gave 25 false negatives out of 283 parasites (9%) and 41 false positives (0.05%).

  • 332.
    Rudol, Piotr
    Linköpings universitet, Institutionen för datavetenskap, UASTECH – Teknologier för autonoma obemannade flygande farkoster. Linköpings universitet, Tekniska högskolan.
    Increasing Autonomy of Unmanned Aircraft Systems Through the Use of Imaging Sensors2011Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    The range of missions performed by Unmanned Aircraft Systems (UAS) has been steadily growing in the past decades thanks to continued development in several disciplines. The goal of increasing the autonomy of UAS's is widening the range of tasks which can be carried out without, or with minimal, external help. This thesis presents methods for increasing specific aspects of autonomy of UAS's operating both in outdoor and indoor environments where cameras are used as the primary sensors.

    First, a method for fusing color and thermal images for object detection, geolocation and tracking for UAS's operating primarily outdoors is presented. Specifically, a method for building saliency maps where human body locations are marked as points of interest is described. Such maps can be used in emergency situations to increase the situational awareness of first responders or a robotic system itself. Additionally, the same method is applied to the problem of vehicle tracking. A generated stream of geographical locations of tracked vehicles increases situational awareness by allowing for qualitative reasoning about, for example, vehicles overtaking, entering or leaving crossings.

    Second, two approaches to the UAS indoor localization problem in the absence of GPS-based positioning are presented. Both use cameras as the main sensors and enable autonomous indoor ight and navigation. The first approach takes advantage of cooperation with a ground robot to provide a UAS with its localization information. The second approach uses marker-based visual pose estimation where all computations are done onboard a small-scale aircraft which additionally increases its autonomy by not relying on external computational power.

  • 333. Russ, Christoph
    et al.
    Kubisch, Christoph
    Qiu, Feng
    Hong, Wei
    Ljung, Patric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten. Siemens Corporation.
    Real-time Surface Analysis and Tagged Material Cleansing for Virtual Colonoscopy.2010Ingår i: Volume Graphics, 2010, s. 29-36Konferensbidrag (Refereegranskat)
    Abstract [en]

    The most common representation of volumetric models is a regular grid of cubical voxels with one value each, from which a smooth scalar field is reconstructed. However, common real-world situations include cases in which volumes represent physical objects with well defined boundaries separating different materials, giving rise to models with quasi-impulsive gradient fields. In our split-voxel representation, we replace blocks of N 3 voxels by one single voxel that is split by a feature plane into two regions with constant values. This representation has little overhead over storing precomputed gradients, and has the advantage that feature planes provide minimal geometric information about the underlying volume regions that can be effectively exploited for volume rendering. We show how to convert a standard mono-resolution representation into a out-of-core multiresolution structure, both for labeled and continuous scalar volumes. We also show how to interactively explore the models using a multiresolution GPU raycasting framework. The technique supports real-time transfer function manipulation and proves particularly useful for fast multiresolution rendering, since accurate silhouettes are preserved even at very coarse levels of detail.

  • 334.
    Saläng, Björn
    et al.
    Linköpings universitet, Institutionen för systemteknik.
    Salomonsson, Henrik
    Linköpings universitet, Institutionen för systemteknik.
    Vision based pose estimation for autonomous helicopter landing2008Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats
    Abstract [sv]

    Marknaden for obemannade autonoma luftburna farkoster (UAV:er) växer snabbt. För att möta behovet av marina tillämpningar har CybAero AB nyligen startat ett projekt som kallas Mobil Automatisk Start- och Landningsstation (MALLS). Syftet med malls är att möjliggöra autonom start och landning på objekt i rörelse, som till exempel ett fartyg. I det här examensarbetet studeras ett system för att bestämma position och attityd för en helikopter relativt en helikopterplatta, för att möjliggöra landning på ett ojekt i rörelse.

    Fokus har främst legat på att utveckla ett positionerings- och attitydbestämningssystem. Ett datorseende positionerings- och attitydbestämningssystem har utvecklats. Två olika metoder har undersökts, ett system som bygger på homografi och ett annat som bygger på Extended Kalman Filter (EKF). Båda metoderna har testats med verklig data från en kamera monterad på en RC helikopter. Noggrannheten i positionsbestämmelsen har undersökts med hjälp av data från en industrirobot. Testresultaten visar att det EKF-baserade systemet är mindre bruskänsligt än det homografibaserade systemet. En nackdel med det ekf-baserade systemet är däremot att det kräver initialvillkor vilket det homografibaserade systemet inte gör. Noggrannheten på båda systemen finner vi tillfredsställande för syftet.

    Ett enkelt styrsystem med styrlagar för att genomföra landningar på ett rörligtobjekt har utvecklats. Styrsystemet har dock inte testats under verklig flygning.

  • 335.
    Sandberg, David
    Linköpings universitet, Institutionen för systemteknik, Datorseende.
    Model-Based Video Coding Using a Colour and Depth Camera2011Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    I detta examensarbete har en modellbaserad videokodningsalgoritm utvecklats som använder data från en djup- och färgkamera, exempelvis Microsoft Kinect. Det finns flera fördelar med en modellbaserad representation av en video över den mer vanligt förekommande blockbaserade varianten, vilket används av bland annat H.264. Några exempel är möjligheten att rendera videon i 3D samt från alternativa vyer, placera in objekt i videon samt möjlighet för användaren att interagera med scenen.

    Detta examensarbete påvisar en väldigt effektiv metod för komprimering av scengeometri. Resultaten av den presenterade algoritmen visar att möjligheten att uppnå väldigt låg bithastighet med jämförelsebara resultat med H.264-standarden.

  • 336.
    Schlemmer, Michael
    et al.
    Kaiserslautern, Germany.
    Hagen, Hans
    Kaiserslautern, Germany.
    Hotz, Ingrid
    Universtiy of California, Davis.
    Hamann, Bernd
    University of California, Davis, USA.
    Clifford Pattern Matching for Color Image Edge Detection2006Ingår i: Visualization of Large and Unstructured Data Sets: first workshop of the DFG's International Research Training Group Visualization of Large and Unstructured Data Sets - Applications in Geospatial Planning, Modeling, and Engineering, June 14-16, 2006, Dagstuhl Castle, Germany / [ed] Hans Hagen, Andreas Kerren, Peter Dannenmann, GI-Edition , 2006, s. 47-58Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Feature detection and pattern matching play an important role in visualization.Originally developed for images and scalar fields, pattern matching methods become increasingly interesting for other applications, e.g., vector fields. To apply pattern matching to vector fields the basic concepts of convolution and fast Fourier transform (FFT) have to be generalized to vector fields. A formalism supporting an elegant generalization of these concepts is provided by the Clifford Algebra, originally developed for describing geometry and geometric operations. We discuss an application of the Clifford Pattern Matching (CPM). We apply CPM to images for ”Clifford Color Edge Detection” (C2ED), an approach for detecting edges and other features in color images. The basic idea is to treat color value tripels as vectors and apply the pattern matching algorithm to the resulting vector field. We introduce vector-valued filters for edge detection and present results.

  • 337.
    Schlemmer, Michael
    et al.
    University of Kaiserslautern.
    Hotz, Ingrid
    Universtiy of California, Davis.
    Natarajan, Vijay
    University of California, Davis.
    Hamann, Bernd
    University of California, Davis, USA.
    Hagen, Hans
    University of Kaiserslautern.
    Fast Clifford Fourier transfor- mation for unstructured vector field data.2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    Vector fields play an important role in many areas of computational physics and engineering. For effective visualization of vector fields it is necessary to identify and extract important features inherent in the data, defined by filters that characterize certain “patterns”. Our prior approach for vector field analysis used the Clifford Fourier transform for efficient pattern recognition for vector field data defined on regular grids [1,2]. Using the frequency domain, correlation and convolution of vectors can be computed as a Clifford multiplication, enabling us to determine similarity between a vector field and a pre-defined pattern mask (e.g., for critical points). Moreover, compression and spectral analysis of vector fields is possible using this method. Our current approach only applies to rectilinear grids. We combine this approach with a fast Fourier transform to handle unstructured scalar data [6]. Our extension enables us to provide a feature-based visualization of vector field data defined on unstructured grids, or completely scattered data. Besides providing the theory of Clifford Fourier transform for unstructured vector data, we explain how efficient pattern matching and visualization of various selectable features can be performed efficiently. We have tested our method for various vector data sets.

  • 338.
    Schöndell, Andreas
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling.
    Evaluation of methods for segmentation of 3D range image data2011Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    3D-kameror som levererar höjddata kan användas för kvalitetskontroll av varor på ett löpande band.

    Det är då av intresse att urskilja de viktiga delarna av bilden från bakgrund och brus samt även att dela upp dessa intressanta delar i segment med stark korrelans till objekten på bandet.

    Segmentering kan utföras genom tröskling i det enkla fallet. I mer komplexa situationer då objekt vidrör eller överlappar varandra blir det svårare.

    I detta examensarbete presenteras forskning och utvärdering av några olika metoder för segmentering av höjdbildsdata. Fokus ligger på att finna en noggrann metod för segmentering av mjuka släta oregelbundna objekt som grönsaker och skaldjur.

    I utvärderingssyfte har en databas bestående höjdbilder föreställande lite olika typer av sådana organiska objekt samlats in.

    Vi visar i uppstatsen att en konventionell gradientlängdsmetod är svår att slå i det generella fallet. Om objekten som ska segmenteras är kraftigt icke-konvexa å andra sidan, med en mängd krön och dalar inom varje objekt, kan man göra bättre i att välja en normaliserad minstakvadratfelsmetod.

  • 339.
    Schöneich, Mark
    et al.
    University Saarbrücken, Saarbrücken, Germany.
    Kratz, Andrea
    Zuse Institute Berlin, Berlin, Germany.
    Zobel, Valentin
    Universität Leipzig, Leipzig, Germany .
    Scheuermann, Gerik
    Universität Leipzig, Leipzig, Germany.
    Stommel, Markus
    University Dortmund, Dortmund, Germany.
    Hotz, Ingrid
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Tensor lines in engineering: success, failure, and open questions2015Ingår i: Visualization and Processing of Tensors and Higher Order Descriptors for Multi-Valued Data / [ed] Ingrid Hotz, Thomas Schultz, Cham: Springer, 2015, s. 339-351Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Today, product development processes in mechanical engineering are almost entirely carried out via computer-aided simulations. One essential output of these simulations are stress tensors, which are the basis for the dimensioning of the technical parts. The tensors contain information about the strength of internal stresses as well as their principal directions. However, for the analysis they are mostly reduced to scalar key metrics. The motivation of this work is to put the tensorial data more into focus of the analysis and demonstrate its potential for the product development process. In this context we resume a visualization method that has been introduced many years ago, tensor lines. Since tensor lines have been rarely used in visualization applications, they are mostly considered as physically not relevant in the visualization community. In this paper we challenge this point of view by reporting two case studies where tensor lines have been applied in the process of the design of a technical part. While the first case was a real success, we could not reach similar results for the second case. It became clear that the first case cannot be fully generalized to arbitrary settings and there are many more questions to be answered before the full potential of tensor lines can be realized. In this chapter, we review our success story and our failure case and discuss some directions of further research.

  • 340.
    Schötz, Susanne
    et al.
    Lund University.
    van de Weijer, Joost
    Lund University.
    Eklund, Robert
    Linköpings universitet, Institutionen för kultur och kommunikation, Avdelningen för språk och litteratur. Linköpings universitet, Filosofiska fakulteten.
    Phonetic Characteristics of Domestic Cat Vocalisations2017Ingår i: Proceedings of the 1st International Workshop on Vocal Interactivity in-and-between Humans, Animals and Robots, VIHAR 2017 / [ed] Angela Dassow, Ricard Marxer & Roger K. Moore, 2017, s. 5-6Konferensbidrag (Refereegranskat)
    Abstract [en]

    The cat (Felis catus, Linneaus 1758) has lived around or with humans for at least 10,000 years, and is now one of the most popular pets of the world with more than 600 millionindividuals. Domestic cats have developed a more extensive, variable and complex vocal repertoire than most other members of the Carnivora, which may be explained by their social organisation, their nocturnal activity and the long period of association between mother and young. Still, we know surprisingly little about the phonetic characteristics of these sounds, and about the interaction between cats and humans.

    Members of the research project Melody in human–cat communication (Meowsic) investigate the prosodic characteristics of cat vocalisations as well as the communication between human and cat. The first step includes a categorisation of cat vocalisations. In the next step it will be investigated how humans perceive the vocal signals of domestic cats. This paper presents an outline of the project which has only recently started.

  • 341.
    Selin, Magnus
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Artificiell intelligens och integrerade datorsystem. Linköpings universitet, Tekniska fakulteten. Royal Institute of Technology, Stockholm Sweden.
    Tiger, Mattias
    Linköpings universitet, Institutionen för datavetenskap, Artificiell intelligens och integrerade datorsystem. Linköpings universitet, Tekniska fakulteten.
    Duberg, Daniel
    Royal Institute of Technology, Stockholm Sweden.
    Heintz, Fredrik
    Linköpings universitet, Institutionen för datavetenskap, Artificiell intelligens och integrerade datorsystem. Linköpings universitet, Tekniska fakulteten.
    Jensfelt, Patric
    Royal Institute of Technology, Stockholm Sweden.
    Efficient Autonomous Exploration Planning of Large Scale 3D-Environments2019Ingår i: IEEE Robotics and Automation Letters, ISSN 2377-3766, E-ISSN 1949-3045Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Exploration is an important aspect of robotics, whether it is for mapping, rescue missions or path planning in an unknown environment. Frontier Exploration planning (FEP) and Receding Horizon Next-Best-View planning (RH-NBVP) are two different approaches with different strengths and weaknesses. FEP explores a large environment consisting of separate regions with ease, but is slow at reaching full exploration due to moving back and forth between regions. RH-NBVP shows great potential and efficiently explores individual regions, but has the disadvantage that it can get stuck in large environments not exploring all regions. In this work we present a method that combines both approaches, with FEP as a global exploration planner and RH-NBVP for local exploration. We also present techniques to estimate potential information gain faster, to cache previously estimated gains and to exploit these to efficiently estimate new queries.

  • 342.
    Shimoni, Michal
    et al.
    Signal and Image Centre, Dept. of Electrical Engineering (SIC-RMA), Brussels, Belgium.
    Tolt, Gustav
    FOI Swedish Defence Research Agency, Linköping, Sweden.
    Perneel, Christiaan
    Dept. of Mathematics, Royal Military Academy, Brussels, Belgium.
    Ahlberg, Jörgen
    FOI Swedish Defence Research Agency, Linköping, Sweden.
    Detection of vehicles in shadow areas2011Ingår i: 2011 3rd Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS), IEEE , 2011, s. 1-4Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a new method to automatically detect occluded vehicle in semi or deep shadow areas using combined very high resolution (VHR) 3D LIDAR and hyperspectral data. The proposed shape/spectral integration (SSI) decision fusion algorithm was shown to outperform the spectral based anomaly algorithm mainly in deep shadow areas. The fusion of LIDAR DSM data with spectral data is useful in the detection of vehicles in semi and deep shadow areas. The utility of shape information was shown to be a way to enhance spectral target detection in complex urban scene.

  • 343.
    Shimoni, Michal
    et al.
    Signal and Image Centre, Dept. of Electrical Engineering (SIC-RMA), Brussels, Belgium.
    Tolt, Gustav
    FOI Swedish Defence Research Agency, Linköping, Sweden.
    Perneel, Christiaan
    Dept. of Mathematics, Royal Military Academy, Brussels, Belgium.
    Ahlberg, Jörgen
    FOI Swedish Defence Research Agency, Linköping, Sweden.
    Detection of vehicles in shadow areas using combined hyperspectral and LIDAR data2011Ingår i: 2011 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), IEEE , 2011, s. 4427-4430Konferensbidrag (Refereegranskat)
    Abstract [en]

    In an effort to overcome the limitations of small target detection in complex urban scene, complementary data sets are combined to provide additional insight about a particular scene. This paper presents a method based on shape/spectral integration (SSI) decision level fusion algorithm to improve the detection of vehicles in semi and deep shadow areas. A four steps process combines high resolution LIDAR and hyperspectral data to classify shadow areas, segment vehicles in LIDAR data, detect spectral anomalies and improves vehicle detection. The SSI decision level fusion algorithm was shown to outperform detection using a single data set and the utility of shape information was shown to be a way to enhance spectral target detection in complex urban scenes.  

  • 344.
    Sigfridsson, Andreas
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Multidimensional MRI of Cardiac Motion: Acquisition, Reconstruction and Visualization2006Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Methods for measuring deformation and motion of the human heart in-vivo are crucial in the assessment of cardiac function. Applications ranging from basic physiological research, through early detection of disease to follow-up studies, all benefit from improved methods of measuring the dynamics of the heart. This thesis presents new methods for acquisition, reconstruction and visualization of cardiac motion and deformation, based on magnetic resonance imaging.

    Local heart wall deformation can be quantified in a strain rate tensor field. This tensor field describes the local deformation excluding rigid body translation and rotation. The drawback of studying this tensor-valued quantity, as opposed to a velocity vector field, is the high dimensionality of the tensor. The problem of visualizing the tensor field is approached by combining a local visualization that displays all degrees of freedom for a single tensor with an overview visualization using a scalar field representation of the complete tensor field. The scalar field is obtained by iterated adaptive filtering of a noise field.

    Several methods for synchronizing the magnetic resonance imaging acquisition to the heart beat have previously been used to resolve individual heart phases from multiple cardiac cycles. In the present work, one of these techniques is extended to resolve two temporal dimensions simultaneously, the cardiac cycle and the respiratory cycle. This is combined with volumetric imaging to produce a five-dimensional data set. Furthermore, the acquisition order is optimized in order to reduce eddy current artifacts.

    The five-dimensional acquisition either requires very long scan times or can only provide low spatiotemporal resolution. A method that exploits the variation in temporal bandwidth over the imaging volume, k-t BLAST, is described and extended to two simultaneous temporal dimensions. The new method, k-t2 BLAST, allows simultaneous reduction of scan time and improvement of spatial resolution.

    Delarbeten
    1. Tensor Field Visualisation using Adaptive Filtering of Noise Fields combined with Glyph Rendering
    Öppna denna publikation i ny flik eller fönster >>Tensor Field Visualisation using Adaptive Filtering of Noise Fields combined with Glyph Rendering
    2002 (Engelska)Ingår i: IEEE Visualization 2002 Conference, IEEE , 2002, s. 371-378Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    While many methods exist for visualising scalar and vector data, visualisation of tensor data is still troublesome. We present a method for visualising second order tensors in three dimensions using a hybrid between direct volume rendering and glyph rendering.

    An overview scalar field is created by using three-dimensional adaptive filtering of a scalar field containing noise. The filtering process is controlled by the tensor field to be visualised, creating patterns that characterise the tensor field. By combining direct volume rendering of the scalar field with standard glyph rendering methods for detailed tensor visualisation, a hybrid solution is created.

    A combined volume and glyph renderer was implemented and tested with both synthetic tensors and strain-rate tensors from the human heart muscle, calculated from phase contrast magnetic resonance image data. A comprehensible result could be obtained, giving both an overview of the tensor field as well as detailed information on individual tensors.

    Ort, förlag, år, upplaga, sidor
    IEEE, 2002
    Nyckelord
    Tensor, Visualisation, Volume rendering, Glyph rendering, Hybrid rendering, Strain-rate
    Nationell ämneskategori
    Medicin och hälsovetenskap Medicinsk laboratorie- och mätteknik
    Identifikatorer
    urn:nbn:se:liu:diva-14011 (URN)
    Tillgänglig från: 2006-10-04 Skapad: 2006-10-04 Senast uppdaterad: 2013-09-03Bibliografiskt granskad
    2. Five-dimensional MRI Incorporating Simultaneous Resolution of Cardiac and Respiratory Phases for Volumetric Imaging
    Öppna denna publikation i ny flik eller fönster >>Five-dimensional MRI Incorporating Simultaneous Resolution of Cardiac and Respiratory Phases for Volumetric Imaging
    2006 (Engelska)Ingår i: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 25, nr 1, s. 113-121Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Purpose

    To develop a new volumetric imaging method resolved over both the cardiac and respiratory cycles, to enable future physiological and pathophysiological studies of respiratory-related cardiac motion.

    Materials and Methods

    An acquisition scheme is proposed whereby the k-space acquisition order is controlled in real-time by the current cardiac and respiratory phases. To reduce eddy-current effects induced by sudden jumps in k-space, the acquisition order is further optimized by the use of a Hilbert curve trajectory in the ky-kz plane. A complete three-dimensional (3D) k-space is acquired for all combinations of cardiac and respiratory phases, yielding a five-dimensional (5D) data set after retrospective reconstruction.

    Results

    Left (LV) and right ventricular (RV) wall excursion was measured in a healthy volunteer. Diastolic LV diameter was shown to increase during expiration and decrease during inspiration, as expected from previous echocardiography studies. The LV volume was estimated for all cardiac and respiratory phases with the use of a fully 3D segmentation tool. The results confirmed that the diastolic LV volume increased during expiration and decreased during inspiration.

    Conclusion

    With its ability to measure motion anywhere in the heart, the described technique provides a promising approach for in-depth description of interventricular coupling, including 3D ventricular volumes, during both the cardiac and respiratory cycles.

    Nyckelord
    respiration, septal motion, interventricular coupling, volumetric MRI, cine imaging
    Nationell ämneskategori
    Medicin och hälsovetenskap Medicinsk laboratorie- och mätteknik
    Identifikatorer
    urn:nbn:se:liu:diva-14012 (URN)10.1002/jmri.20820 (DOI)000243250800014 ()
    Tillgänglig från: 2006-10-04 Skapad: 2006-10-04 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
    3. k-t2 BLAST: Exploiting spatiotemporal structure in simultaneously cardiac and respiratory time-resolved volumetric imaging
    Öppna denna publikation i ny flik eller fönster >>k-t2 BLAST: Exploiting spatiotemporal structure in simultaneously cardiac and respiratory time-resolved volumetric imaging
    2007 (Engelska)Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 58, nr 5, s. 922-930Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Multidimensional imaging resolving both the cardiac and respiratory cycles simultaneously has the potential to describe important physiological interdependences between the heart and pulmonary processes. A fully five-dimensional acquisition with three spatial and two temporal dimensions is hampered, however, by the long acquisition time and low spatial resolution. A technique is proposed to reduce the scan time substantially by extending the k-t BLAST framework to two temporal dimensions. By sampling the k-t space sparsely in a lattice grid, the signal in the transform domain, x-f space, can be densely packed, exploiting the fact that large regions in the field of view have low temporal bandwidth. A volumetric online prospective triggering approach with full cardiac and respiratory cycle coverage was implemented. Retrospective temporal interpolation was used to refine the timing estimates for the center of k-space, which is sampled for all cardiac and respiratory time frames. This resulted in reduced reconstruction error compared with conventional k-t BLAST reconstruction. The k-t2 BLAST technique was evaluated by decimating a fully sampled five-dimensional data set, and feasibility was further demonstrated by performing sparsely sampled acquisitions. Compared to the fully sampled data, a fourfold improvement in spatial resolution was accomplished in approximately half the scan time.

    Nyckelord
    Cine imaging, k-t BLAST, Respiration, Volumetric MRI
    Nationell ämneskategori
    Teknik och teknologier Medicinsk laboratorie- och mätteknik
    Identifikatorer
    urn:nbn:se:liu:diva-47833 (URN)10.1002/mrm.21295 (DOI)000250560000009 ()
    Tillgänglig från: 2009-10-11 Skapad: 2009-10-11 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
  • 345.
    Simberg, Gustav
    et al.
    Linköpings universitet, Institutionen för systemteknik.
    Viggeborn, Björn
    Linköpings universitet, Institutionen för systemteknik.
    Utveckling av mobiltelefonapplikation för kommunikation i ad-hoc nätverk med Bluetoothteknik2005Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats
    Abstract [en]

    The purpose of this thesis is to develop an application for mobile phones that simplifies communication. The company Doberman wanted to look at possibilities to develop such an application that uses Bluetooth™ technol-ogy to communicate in ad-hoc networks. The aim has been an application to run on mobile phones in which you can send messages and files to other devices and also add a user profile with personal information to share with others. The communication will take place in temporary networks created when Bluetooth enabled devices is in range of each other.

    The market for mobile phones has grown rapidly over the past years and is still growing. There are many differ-ent phone models and it is difficult to find a developer platform that covers many phone models. In the beginning of this thesis an inquiry of different developer platforms has been made. The Java™ platform is supported by most phones but has limitations in accessing functions on the device. The best alternative was Symbian C++ for devices with Symbian OS. This alternative does not have the same limitations as Java and is still supported by relatively many devices. The application was then developed in Symbian C++. There are a number of different versions of Symbian OS and different GUI-platforms that runs on Symbian OS which leads to other issues in the development. We have limited the development of the application to the Series 60 platform for Symbian OS v7.0s. During design and implementation portability to other GUI-platforms has been considered.

    We have tested the application on emulator compatible with Symbian OS v7.0s and Symbian OS v8.0a and found some compatibility problems between the two versions. We have also tested the application on mobile phones and between emulator and the phone with corresponding OS-version no new problems occurred

  • 346.
    Sjanic, Zoran
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Simultaneous Navigation and Synthetic Aperture Radar Focusing2015Ingår i: IEEE Transactions on Aerospace and Electronic Systems, ISSN 0018-9251, E-ISSN 1557-9603, Vol. 51, nr 2, s. 1253-1266Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Synthetic aperture radar (SAR) equipment is a radar imaging system that can be used to create high-resolution images of a scene by utilizing the movement of a flying platform. Knowledge of the platforms trajectory is essential to get good and focused images. An emerging application field is real-time SAR imaging using small and cheap platforms where estimation errors in navigation systems imply unfocused images. This contribution investigates a joint estimation of the trajectory and SAR image. Starting with a nominal trajectory, we successively improve the image by optimizing a focus measure and updating the trajectory accordingly. The method is illustrated using simulations using typical navigation performance of an unmanned aerial vehicle. One real data set is used to show feasibility, where the result indicates that, in particular, the azimuth position error is decreased as the image focus is iteratively improved.

  • 347.
    Sjöholm, Alexander
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska högskolan.
    Closing the Loop: Mobile Visual Location Recognition2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Visual simultaneous localization and mapping (SLAM) as field has been researched for ten years, but with recent advances in mobile performance visual SLAM is entering the consumer market in a completely new way. A visual SLAM system will however be sensitive to non cautious use that may result in severe motion, occlusion or poor surroundings in terms of visual features that will cause the system to temporarily fail. The procedure of recovering from such a fail is called relocalization. Together with two similar problems localization, to find your position in an existing SLAM session, and loop closing, the online reparation and perfection of the map in an active SLAM session, these can be grouped as visual location recognition (VLR).

    This thesis presents novel results by combining the scalability of FabMap and the precision of 13th Lab's tracking yielding high-precision VLR, +/- 10 cm, while maintaining above 99 % precision and 60 % recall for sessions containing thousands of images. Everything functional purely on a normal mobile phone.

    The applications of VLR are many. Indoors, where GPS is not functioning, VLR can still provide positional information and navigate you through big complexes like airports and museums. Outdoors, VLR can improve the precision of GPS tenfold yielding a new level of navigational experience. Virtual and augmented reality applications are other areas that benefit from improved positioning and localization.

  • 348.
    Skoglund, Johan
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Robust Real-Time Estimation of Region Displacements in Video Sequences2007Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The possibility to use real-time computer vision in video sequences gives many opportunities for a system to interact with the environment. Possible ways for interaction are e.g. augmented reality like in the MATRIS project where the purpose is to add new objects into the video sequence, or surveillance where the purpose is to find abnormal events.

    The increase of the speed of computers the last years has simplified this process and it is now possible to use at least some of the more advanced computer vision algorithms that are available. The computational speed of computers is however still a problem, for an efficient real-time system efficient code and methods are necessary. This thesis deals with both problems, one part is about efficient implementations using single instruction multiple data (SIMD) instructions and one part is about robust tracking.

    An efficient real-time system requires efficient implementations of the used computer vision methods. Efficient implementations requires knowledge about the CPU and the possibilities given. In this thesis, one method called SIMD is explained. SIMD is useful when the same operation is applied to multiple data which usually is the case in computer vision, the same operation is executed on each pixel.

    Following the position of a feature or object in a video sequence is called tracking. Tracking can be used for a number of applications. The application in this thesis is to use tracking for pose estimation. One way to do tracking is to cut out a small region around the feature, creating a patch and find the position on this patch in the other frames. To find the position, a measure of the difference between the patch and the image in a given position is used. This thesis thoroughly investigates the sum of absolute difference (SAD) error measure. The investigation involves different ways to improve the robustness and to decrease the average error. One method to estimate the average error, the covariance of the position error is proposed. An estimate of the average error is needed when different measurements are combined.

    Finally, a system for camera pose estimation is presented. The computer vision part of this system is based on the result in this thesis. This presentation contains also a discussion about the result of this system.

  • 349.
    Solli, Martin
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Digitala Medier. Linköpings universitet, Tekniska högskolan.
    Color Image Retrieval with Bags-of-Emotions2009Ingår i: Proceedings of SSBA 2009, Symposium on image analysis, 2009 / [ed] Josef Bigun, Antanas Verikas, Halmstad, Sweden: Halmstad University , 2009, s. 37-40Konferensbidrag (Övrigt vetenskapligt)
  • 350.
    Solli, Martin
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för teknik och naturvetenskap, Digitala Medier.
    Topics in Content Based Image Retrieval: Fonts and Color Emotions2009Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Two novel contributions to Content Based Image Retrieval are presented and discussed. The first is a search engine for font recognition. The intended usage is the search in very large font databases. The input to the search engine is an image of a text line, and the output is the name of the font used when printing the text. After pre-processing and segmentation of the input image, a local approach is used, where features are calculated for individual characters. The method is based on eigenimages calculated from edge filtered character images, which enables compact feature vectors that can be computed rapidly. A system for visualizing the entire font database is also proposed. Applying geometry preserving linear- and non-linear manifold learning methods, the structure of the high-dimensional feature space is mapped to a two-dimensional representation, which can be reorganized into a grid-based display. The performance of the search engine and the visualization tool is illustrated with a large database containing more than 2700 fonts.

    The second contribution is the inclusion of color-based emotion-related properties in image retrieval. The color emotion metric used is derived from psychophysical experiments and uses three scales: activity, weight and heat. It was originally designed for single-color combinations and later extended to include pairs of colors. A modified approach for statistical analysis of color emotions in images, involving transformations of ordinary RGB-histograms, is used for image classification and retrieval. The methods are very fast in feature extraction, and descriptor vectors are very short. This is essential in our application where the intended use is the search in huge image databases containing millions or billions of images. The proposed method is evaluated in psychophysical experiments, using both category scaling and interval scaling. The results show that people in general perceive color emotions for multi-colored images in similar ways, and that observer judgments correlate with derived values.

    Both the font search engine and the emotion based retrieval system are implemented in publicly available search engines. User statistics gathered during a period of 20 respectively 14 months are presented and discussed.

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