liu.seSök publikationer i DiVA
Ändra sökning
Avgränsa sökresultatet
1234567 151 - 200 av 400
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 151.
    Hedlund, Martin
    et al.
    n/a.
    Granlund, Gösta H.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Image Filtering and Relaxation Procedures using Hierarchical Models1981Ingår i: Proceedings of the 2nd Scandinavian Conference on Image Analysis: Finland, 1981Konferensbidrag (Refereegranskat)
  • 152.
    Hemmendorff, M.
    et al.
    Linköpings universitet, Institutionen för systemteknik. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Kronander, T.
    SECTRA, Teknikringen 2, SE-583 30 Linköping, Sweden.
    Motion compensated digital subtraction angiography1999Konferensbidrag (Refereegranskat)
    Abstract [en]

    Digital subtraction angiography, whether based on traditional X-ray or MR, suers from patient motion artifacts. Until now, the usual remedy is to pixel shift by hand, or in some cases performing a global pixel shift semi-automatically. This is time consuming, and cannot handle rotations or local varying deformations over the image. We have developed a fully automatic algorithm that provides for motion compensation in the presence of large local deformations. Our motion compensation is very accurate for ordinary motions, including large rotations and deformations. It does not matter if the motions are irregular over time. For most images, it takes about a second per image to get adequate accuracy. The method is based on using the phase from lter banks of quadrature lters tuned in dierent directions and frequencies. Unlike traditional methods for optical ow and correlation, our method is more accurate and less susceptible to disturbing changes in the image, e.g. a moving contrast bolus. The implications for common practice are that radiologists' time can be significantly reduced in ordinary peripheral angiographies and that the number of retakes due to large or local motion artifacts will be much reduced.

  • 153.
    Hemmendorff, Magnus
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik.
    Andersson, Mats
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik.
    Knutsson, Hans
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik.
    Accurate registration and motion estimation based on canonical correlation2001Ingår i: Scandinavian conference on image analysis SCIA,2001, 2001Konferensbidrag (Övrigt vetenskapligt)
  • 154.
    Hemmendorff, Magnus
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Kronander, T.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Phase-based Multidimensional Volume Registration2000Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a method for accurate image registration and motion estimation in multidimensional volumes, such as 3D CT and MR images. The method is based on phase from quadrature filters, which makes it insensitive to variations in luminance and other disturbance in the images. The theory is not restricted to any particular kind of motion model or number of dimensions. Experimental results for affine motions in 3D show high accuracy.

  • 155.
    Hemmendorff, Magnus
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Kronander, Torbjörn
    SECTRA AB, Linköping, Sweden.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Phase-based multidimensional volume registration2002Ingår i: IEEE Transactions on Medical Imaging, ISSN 0278-0062, E-ISSN 1558-254X, Vol. 21, nr 12, s. 1536-1543Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a method for accurate image registration and motion compensation in multidimensional signals, such as two-dimensional (2-D) X-ray images and three-dimensional (3-D) computed tomography/magnetic resonance imaging volumes. The method is based on phase from quadrature filters, which makes it robust to noise and temporal intensity variations. The method is equally applicable to signals of two, three or higher number of dimensions. We use parametric models, e.g., affine models, finite elements or local affine models with global regularization. Experimental results show high accuracy for 2-D and 3-D motion compensation.

  • 156.
    Hemmendorff, Magnus
    et al.
    n/a.
    Andersson, Mats T.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Phase-based Image Motion Estimation and Registration: Phoenix, AZ, USA1999Ingår i: International Conference on Acoustics, Speech, and Signal Processing (ICASSP), 1999, 1999Konferensbidrag (Refereegranskat)
    Abstract [en]

    Conventional gradient methods (optical flow), for motion estimation assume intensity conservation between frames. This assumption is often violated in real applications. The remedy is a novel method that computes constraints on the local motion. These constraint are given on the same form as in conventional methods. Thus, it can directly substitute the gradient method in most applications. Experiments indicate a superior accuracy, even on synthetic images where the intensity conservation assumption is valid. The conventional gradient methods seem obsolete.

  • 157.
    Hemmendorff, Magnus
    et al.
    n/a.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats T.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Kronander, Torbjörn
    n/a.
    Motion compensated digital subraction angiography1999Ingår i: Proceedings of SPIE's International Symposium on Medical Imaging, vol 3661,  1999: San Diego, USA, 1999, Vol. 3661 Image ProcessingKonferensbidrag (Refereegranskat)
    Abstract [en]

    Digital subtraction angiography, whether based on traditional X-ray or MR, suffers from patient motion artifacts. Until now, the usual remedy is to pixel shift by hand, or in some cases performing a global pixel shift semi-automatically. This is time consuming, and cannot handle rotations or local varying deformations over the image. We have developed a fully automatic algorithm that provides for motion compensation in the presence of large local deformations. Our motion compensation is very accurate for ordinary motions, including large rotations and deformations. It does not matter if the motions are irregular over time. For most images, it takes about a second per image to get adequate accuracy. The method is based on using the phase from filter banks of quadrature filters tuned in different directions and frequencies. Unlike traditional methods for optical flow and correlation, our method is more accurate and less susceptible to disturbing changes in the image, e.g. a moving contrast bolus. The implications for common practice are that radiologists' time can be significantly reduced in ordinary peripheral angiographies and that the number of retakes due to large or local motion artifacts will be much reduced.

  • 158.
    Herberthson, Magnus
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Tillämpad matematik.
    Brun, Anders
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Knutsson, Hans
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Pairs of orientation in the plane2006Ingår i: SSBA Symposium on Image Analysis,2006, 2006, s. 97-100Konferensbidrag (Övrigt vetenskapligt)
  • 159.
    Herberthson, Magnus
    et al.
    Linköpings universitet, Matematiska institutionen, Tillämpad matematik. Linköpings universitet, Tekniska högskolan.
    Brun, Anders
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    P-averages of diffusion tensors2007Ingår i: SSBA 2007, Symposium on image analysis,2007, Linköping, 2007Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    For positive semi-definite tensors like diffusion tensors in the plane it is possible to calculate several different means or p-averages. These are related to p-norms for functions, but produce mappings rather than numbers as means. We compare these means for various values of the real parameter p. One important future application is the filtering and interpolation of tensor fields in Diffusion Tensor Magnetic Resonance

  • 160.
    Herberthson, Magnus
    et al.
    Linköpings universitet, Matematiska institutionen, Tillämpad matematik. Linköpings universitet, Tekniska högskolan.
    Brun, Anders
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Representing Pairs of Orientations in the Plane2007Ingår i: Image Analysis: 15th Scandinavian Conference, SCIA 2007, Aalborg, Denmark, June 10-14, 2007 / [ed] Bjarne Kjær Ersbøll, Kim Steenstrup Pedersen, Springer Berlin/Heidelberg, 2007, s. 661-670Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this article we present a way of representing pairs of orientations in the plane. This is an extension of the familiar way of representing single orientations in the plane. Using this framework, pairs of lines can be added, scaled and averaged over in a sense which is to be described. In particular, single lines can be incorporated and handled simultaneously.

  • 161.
    Herberthson, Magnus
    et al.
    Linköpings universitet, Matematiska institutionen, Matematik och tillämpad matematik. Linköpings universitet, Tekniska fakulteten.
    Yolcu, Cem
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Westin, Carl-Fredrik
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten. Harvard Med Sch, MA 02115 USA.
    Özarslan, Evren
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Orientationally-averaged diffusion-attenuated magnetic resonance signal for locally-anisotropic diffusion2019Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikel-id 4899Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Diffusion-attenuated MR signal for heterogeneous media has been represented as a sum of signals from anisotropic Gaussian sub-domains to the extent that this approximation is permissible. Any effect of macroscopic (global or ensemble) anisotropy in the signal can be removed by averaging the signal values obtained by differently oriented experimental schemes. The resulting average signal is identical to what one would get if the micro-domains are isotropically (e.g., randomly) distributed with respect to orientation, which is the case for "powdered" specimens. We provide exact expressions for the orientationally-averaged signal obtained via general gradient waveforms when the microdomains are characterized by a general diffusion tensor possibly featuring three distinct eigenvalues. This extends earlier results which covered only axisymmetric diffusion as well as measurement tensors. Our results are expected to be useful in not only multidimensional diffusion MR but also solid-state NMR spectroscopy due to the mathematical similarities in the two fields.

  • 162.
    Herberthson, Magnus
    et al.
    Linköpings universitet, Matematiska institutionen, Matematik och tillämpad matematik. Linköpings universitet, Tekniska fakulteten.
    Özarslan, Evren
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Westin, Carl-Fredrik
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten. Harvard Medical Sch, MA 02215 USA.
    Dynamics of local magnetization in the eigenbasis of the Bloch-Torrey operator2017Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, nr 12, artikel-id 124201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider diffusion within pores with general shapes in the presence of spatially linear magnetic field profiles. The evolution of local magnetization of the spin bearing particles can be described by the Bloch-Torrey equation. We study the diffusive process in the eigenbasis of the non-Hermitian Bloch-Torrey operator. It is possible to find expressions for some special temporal gradient waveforms employed to sensitize the nuclear magnetic resonance (NMR) signal to diffusion. For more general gradient waveforms, we derive an efficient numerical solution by introducing a novel matrix formalism. Compared to previous methods, this new approach requires a fewer number of eigenfunctions to achieve the same accuracy. This shows that these basis functions are better suited to the problem studied. The new framework could provide new important insights into the fundamentals of diffusion sensitization, which could further the development of the field of NMR. Published by AIP Publishing.

  • 163.
    Janerot-Sjöberg, Birgitta
    et al.
    Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärtcentrum, Fysiologiska kliniken. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Image processing renders tissue doppler obsolete?2002Ingår i: ASE Conference,2002, 2002Konferensbidrag (Refereegranskat)
  • 164.
    Jilken, L.
    et al.
    n/a.
    Bäcklund, J.
    n/a.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Automatic Fatigue Threshold Value Testing1978Ingår i: Conf. on Mechanisms of Deformation and Fracture: Luleå, Sweden, 1978Konferensbidrag (Refereegranskat)
  • 165.
    Johansson, Björn
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Borga, Magnus
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Learning Corner Orientation Using Canonical Correlation2001Ingår i: Proceedings of the SSAB Symposium on Image Analysis: Norrköping, 2001, s. 89-92Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper shows how canonical correlation can be used to learn a detector for corner orientation invariant to corner angle and intensity. Pairs of images with the same corner orientation but different angle and intensity are used as training samples. Three different image representations; intensity values, products between intensity values, and local orientation are examined. The last representation gives a well behaved result that is easy to decode into the corner orientation. To reduce dimensionality, parameters from a polynomial model fitted on the different representations is also considered. This reduction did not affect the performance of the system.

  • 166.
    Johansson, Björn
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för systemteknik, Bildbehandling.
    Knutsson, Hans
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för systemteknik, Bildbehandling.
    Granlund, Gösta
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för systemteknik, Bildbehandling.
    Detecting Rotational Symmetries using Normalized Convolution2000Ingår i: Proceedings of the 15th International Conference on Pattern Recognition,2000, IEEE , 2000, s. 496-500 vol.3Konferensbidrag (Refereegranskat)
    Abstract [en]

    Perceptual experiments indicate that corners and curvature are very important features in the process of recognition. This paper presents a new method to detect rotational symmetries, which describes complex curvature such as corners, circles, star, and spiral patterns. It works in two steps: 1) it extracts local orientation from a gray-scale or color image; and 2) it applies normalized convolution on the orientation image with rotational symmetry filters as basis functions. These symmetries can serve as feature points at a high abstraction level for use in hierarchical matching structures for 3D estimation, object recognition, image database retrieval, etc

  • 167.
    Johansson, Gustaf
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Tekniska högskolan.
    Motion Field Regularization for Sliding Objects using Global Linear Optimization2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    In image registration it is often necessary to employ  regularization in one form or another to be able to find a plausible  displacement field. In medical applications, it is useful to define  different constraints for different areas of the data. For instance  to measure if organs have moved as expected after a finished  treatment. One common problem is how to find plausible motion  vectors far away from known motion. This paper introduces a new  method to build and solve a Global Linear Optimizations (GLO)  problem with a novel set of terms which enable specification of  border areas to allow a sliding motion. The GLO approach is  important especially because it allows simultaneous incorporation of  several different constraints using information from medical atlases  such as localization and properties of organs. The power and  validity of the method is demonstrated using two simple, but  relevant 2D test images. Conceptual comparisons with previous  methods are also made to highlight the contributions made in this  paper. The discussion explains important future work and experiments  as well as exciting future improvements to the GLO framework.

  • 168.
    Johansson, Gustaf
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Regularization in Medical Image Registration using Global Linear OptimizationManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Common problems in image registration include having large parts of the images contain noisy, uncertain, missing or impossible motion. Regularization is the field that aims to overcome these problems. In this article, we propose a novel framework : Global Linear Optimization (GLO) which we demonstrate has the capabilities to simultaneously and globally regularize with respect to : (1) anisotropic certainty of prior motion field, (2) sliding of organ boundaries and (3) incompressibility of organ interiors. The power of the presented framework consists of being able to spatially adapt which subsets of the data each constraint should affect and then solve a large sparse linear equations system which automatically propagates a solution over the data set through an overlapping localized metric. We demonstrate the validity of the methods and the power of the GLO framework on relevant test cases and on medical data from the DIR-lab.

  • 169.
    Johansson, Gustaf
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Tekniska högskolan.
    Forsberg, Daniel
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Tekniska högskolan.
    Globally Optimal Displacement Fields Using Local Tensor Metric2012Ingår i: Image Processing (ICIP), 2012 19th IEEE International Conference on, 2012, s. 2957-2960Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In this paper, we propose a novel algorithm for regularizing displacement fields in image registration. The method uses the local structure tensor and gradients of the displacement field to impose a local metric, which is then used optimizing a global cost function. The method allows for linear operators, such as tensors and differential operators modeling the underlying physical anatomy of the human body in medical images. The algorithm is tested using output from the Morphon image registration algorithm on MRI data as well as synthetic test data and the result is compared to the initial displacement field. The results clearly demonstrate the power of the method and the unique features brought forth through the global optimization approach.

  • 170.
    Karlholm, Jörgen
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Westelius, Carl-Johan
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Object Tracking Based on the Orientation Tensor Concept1995Ingår i: SCIA9, Uppsala, 1995Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A scheme for performing generalized convolutions is presented. A flexibleconvolver, which runs on standard workstations, has been implemented. It isdesigned for maximum throughput and flexibility. The implementation incorporatesspatio-temporal convolutions with configurable vector combinations. Itcan handle general multi-linear operations, i.e. tensor operations on multidimensionaldata of any order. The input data and the kernel coefficients canbe of arbitrary vector length. The convolver is configurable for IIR filters inthe time dimension. Other features of the implemented convolver are scatteredkernel data, region of interest and subsampling. The implementation is doneas a C-library and a graphical user interface in AVS (Application VisualizationSystem).A scheme for performing generalized convolutions is presented. A flexible convolver, which runs on standard workstations, has been implemented. It is designed for maximum throughput and flexibility. The implementation incorporates spatio-temporal convolutions with configurable vector combinations. It can handle general multi-linear operations, i.e. tensor operations on multidimensional data of any order. The input data and the kernel coefficients can be of arbitrary vector length. The convolver is configurable for IIR filters in the time dimension. Other features of the implemented convolver are scattered kernel data, region of interest and subsampling. The implementation is done as a C-library and a graphical user interface in AVS (Application Visualization System).

  • 171.
    Karlholm, Jörgen
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Westelius, Carl-Johan
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Westin, Carl-Fredrik
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Object Tracking Based on the Orientation Tensor Concept1994Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We apply the 3D-orientation tensor representation to construct an object tracking algorithm. 2D-line normal flow is estimated by computing the eigenvector associated with the largest eigenvalue of 3D (two spatial dimensions plus time) tensors with a planar structure. Object's true 2D velocity is computed by averaging tensors with consistent normal flows, generating a 3D line representation that corresponds to a 2D point in motion. Flow induced by camera rotation is compensated for by ignoring points with velocity consistent with the ego-rotation. A region-of-interest growing process based on motion consistency generates estimates of object size and position.

  • 172. Karlholm, Jörgen
    et al.
    Westelius, Carl-Johan
    n/a.
    Westin, Carl-Fredrik
    n/a.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Object Tracking Based on the Orientation Tensor Concept1995Ingår i: Theory and Applications of Image Analysis II / [ed] Gunilla Borgefors, Singapore: World Scientific Publishing , 1995, s. 267-278Kapitel i bok, del av antologi (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    We apply the 3D-orientation tensor representation to construct an object tracking algorithm. 2D-line normal flow is estimated by computing the eigenvector associated with the largest eigenvalue of 3D (two spatial dimensions plus time) tensors with a planar structure. Object's true 2D velocity is computed by averaging tensors with consistent normal flows, generating a 3D line represention that corresponds to a 2D point in motion. Flow induced by camera rotation is compensated for by ignoring points with velocity consistent with the ego-rotation. A region-of-interest growing process based on motion consistency generates estimates of object size and position.  Introduction The literature on optical flow estimation is wast. Descriptions and performance studies of a number of different techniques are given in  and the monographs by Fleet  and Jahne. We will only briefly describe the particular methods used in the present study. Details on the tensor field represention a...

  • 173.
    Knutsson, H.
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Andersson, M.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Morphons: Segmentation using Elastic Canvas and Paint on Priors 2004Rapport (Övrigt vetenskapligt)
  • 174.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    3-D Reconstruction by Fourier Techniques with Error Estimates1978Rapport (Övrigt vetenskapligt)
  • 175.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    A Tensor Representation of 3-D Structures1987Ingår i: 5th IEEE-ASSP and EURASIP Workshop on Multidimensional Signal Processing: Noordwijkerhout, The Netherlands, 1987Konferensbidrag (Refereegranskat)
  • 176.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Filtering and reconstruction in image processing1982Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Image processing is a broad field posing a wide range of problems. The Work presented in this dissertation is mainly concerned with filter design subjectto different criteria and constraints.

    The first part describes the development of a new radiographic reconstruction method designated Ectomography. The method is novel in that it allows reconstruction of an arbitrarily thick layer of an object using limited viewing angle.

    The subject of the second partis estimation and filtering of local image information. Quadrature filters are designed enabling accurate orientation and frequency estimates. The extracted information is shown to provide a good basis fo r efficient image enhancement and coding procedures.

    Delarbeten
    1. Ectomography: A New Radiographic Method for Reproducing a Selected Slice of Varying Thickness
    Öppna denna publikation i ny flik eller fönster >>Ectomography: A New Radiographic Method for Reproducing a Selected Slice of Varying Thickness
    1980 (Engelska)Ingår i: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 21, nr 4, s. 433-442Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The mathematical basis is described of a new radiographic method by which an arbitrarily thick layer of the patient may be reconstructed. The reconstruction is performed from at least 60 images of the volume under examination. Each of these images, which have to be in digital form, is subjected to a special filtration process of its spatial frequencies. The combination of all the images will form the resulting image of the layer--the ectomogram. The method has been analysed and tested in experiments simulated with a computer.

    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-21580 (URN)7457172 (PubMedID)
    Tillgänglig från: 2009-10-04 Skapad: 2009-10-04 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
    2. Ectomography. A New Radiographic Reconstruction Method: I. Theory and Error Estimates
    Öppna denna publikation i ny flik eller fönster >>Ectomography. A New Radiographic Reconstruction Method: I. Theory and Error Estimates
    1980 (Engelska)Ingår i: IEEE Transactions on Biomedical Engineering, ISSN 0018-9294, E-ISSN 1558-2531, Vol. BME--27, nr 11, s. 640-645Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Radiographic technology has advanced considerably during the last years with the advent of reconstruction techniques allowing visualization of slices through the body. In spite of the advantage of computed tomography compared to conventional radiographic methods, there are still some shortcomings with the method If a different section of the body is desired, another recording has to be made, the width of the dice reconstructed is fixed, and a full 1800 view angle is required.

    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-21571 (URN)10.1109/TBME.1980.326704 (DOI)
    Tillgänglig från: 2009-10-04 Skapad: 2009-10-04 Senast uppdaterad: 2017-12-13
    3. Ectomography. A New Radiographic Reconstruction Method: II. Computer Simulated Experiments
    Öppna denna publikation i ny flik eller fönster >>Ectomography. A New Radiographic Reconstruction Method: II. Computer Simulated Experiments
    1980 (Engelska)Ingår i: IEEE Transactions on Biomedical Engineering, ISSN 0018-9294, E-ISSN 1558-2531, Vol. BME--27, nr 11, s. 649-655Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    In a special radiographic process, ectomography, an image of a slice is produced by simple summation of a set of specially filtered component images, of which each represents one of at least 60 different projections of the object. After being digitized, they are stored, filtered, and summed in a computer. Images representing any slice of any thickness in the object may be produced from the same set of component images. All details within the slice are pictured correctly while details outside are almost completely eliminated.

    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-21581 (URN)10.1109/TBME.1980.326705 (DOI)
    Tillgänglig från: 2009-10-04 Skapad: 2009-10-04 Senast uppdaterad: 2017-12-13
    4. Design of Convolution Kernels
    Öppna denna publikation i ny flik eller fönster >>Design of Convolution Kernels
    1982 (Engelska)Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Operators for extraction of local information are essential components in an image processing system. This paper concentrates on the design and evaluation of convolution kernel sets enabling easy estimation of local orientation and frequency.

    Consideration of interpolation properties and the limiting effects of the uncertainty principle leads to the definition of an "i deal" quadrature filter function. An optimization procedure is utilized to produce pairs of convolution kernels which implement an approximation of the desired function. A number of optimization results are presented.

    To evaluate the performance of the optimized kernels in an image processing task, a series of experiments have been carried out. Examples are given of local orientation and frequency estimates for images with different signal to noise ratios. An angle deviation measure is defined and avector averaging scheme is introduced to increase angle estimation accuracy. Using a OdB SNR testimage, orientation estimates are produced having an expected deviation of less than 7 degrees.

    Förlag
    s. 61
    Serie
    LiTH-ISY-I, ISSN 8765-4321 ; 0557
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-56437 (URN)LiTH-ISY-I-0557 (ISRN)
    Tillgänglig från: 2010-05-12 Skapad: 2010-05-12 Senast uppdaterad: 2010-05-12Bibliografiskt granskad
    5. Anisotropic Non-Stationary Image Estimation and its Applications: Part I. Restoration of Noisy Images
    Öppna denna publikation i ny flik eller fönster >>Anisotropic Non-Stationary Image Estimation and its Applications: Part I. Restoration of Noisy Images
    1983 (Engelska)Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. COM--31, nr 3, s. 388-397Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    A new form of image estimator, which takes account of linear features, is derived using a signal equivalent formulation. The estimator is shown to be a nonstationary linear combination of three stationary estimators. The relation of the estimator to human visual physiology is discussed. A method for estimating the nonstationary control information is described and shown to be effective when the estimation is made from noisy data. A suboptimal approach which is computationally less demanding is presented and used in the restoration of a variety of images corrupted by additive white noise. The results show that the method can improve the quality of noisy images even when the signal-to-noise ratio is very low.

    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-21582 (URN)10.1109/TCOM.1983.1095832 (DOI)
    Anmärkning
    ©2009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Hans Knutsson, Roland Wilson and Gösta H. Granlund, Anisotropic Non-Stationary Image Estimation and its Applications: Part I. Restoration of Noisy Images, 1983, IEEE Transactions on Communications, (COM--31), 3, 388-397. http://dx.doi.org/10.1109/TCOM.1983.1095832 Tillgänglig från: 2009-10-04 Skapad: 2009-10-04 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
    6. Anisotropic Non-Stationary Image Estimation and its Applications: Part II. Predictive Image Coding
    Öppna denna publikation i ny flik eller fönster >>Anisotropic Non-Stationary Image Estimation and its Applications: Part II. Predictive Image Coding
    1983 (Engelska)Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 31, nr 3, s. 398-406Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    A new predictive coder, based on an estimation method which adapts to line and edge features in images, is described. Quantization of the prediction error is performed by a two-level adaptive scheme: an adaptive transform coder, and a threshold coding in both transform and spatial domains. Control information, which determines the behavior of the predictor, is quantized using a simple variable rate technique. The results are improved by pre- and post-filtering using a related noncausal form of the estimator. Acceptable images have been produced in this way at bit rates of less than 0.5 bit/pixel.

    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-21587 (URN)
    Tillgänglig från: 2009-10-04 Skapad: 2009-10-04 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
  • 177.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Kernel Optimizatioin1995Ingår i: Signal Processing for Computer Vision / [ed] Gösta H. Granlund and Hans Knutsson, Dordrecht: Kluwer , 1995, s. 199-218Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This chapter presents a method for obtaining an optimal n-dimensional set of filter coefficients for any given frequency response. An optimality criterion is defined that enables different frequencies to be given individual weights. Appropriate forms of frequency weight functions are discussed and a number of optimization examples are given.

  • 178.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Producing a Continuous and Distance Preserving 5-D Vector Representation of 3-D Orientation1985Ingår i: IEEE Computer Society Workshop on Computer Architecture for Pattern Analysis and Image Database Management - CAPAIDM: Miami Beach, Florida, 1985, s. 175-182Konferensbidrag (Refereegranskat)
  • 179.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Representing and Estimating 3-D Orientation Using Quadrature Filters1986Ingår i: Conference Publication No. 265, Second Int. Conf. on Image Processing and Its Applications: London, 1986, s. 87-91Konferensbidrag (Refereegranskat)
  • 180.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Representing Local Structure Using Tensors1989Ingår i: Proceedings of the 6th Scandinavian Conference on Image Analysis, Linköping: Linköping University Electronic Press , 1989, s. 244-251Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The fundamental problem of finding a suitable representation of the orientation of 3D surfaces is considered. A representation is regarded suitable if it meets three basic requirements: Uniqueness, Uniformity and Polar separability. A suitable tensor representation is given.

    At the heart of the problem lies the fact that orientation can only be defined mod 180± , i.e the fact that a 180± rotation of a line or a plane amounts to no change at all. For this reason representing a plane using its normal vector leads to ambiguity and such a representation is consequently not suitable. The ambiguity can be eliminated by establishing a mapping between R3 and a higherdimensional tensor space.

    The uniqueness requirement implies a mapping that map all pairs of 3D vectors x and -x onto the same tensor T. Uniformity implies that the  mapping implicitly carries a definition of distance between 3D planes (and lines) that is rotation invariant and monotone with the angle between the planes. Polar separability means that the norm of the representing tensor T is rotation invariant. One way to describe the mapping is that it maps a 3D sphere into 6D in such a way that the surface is uniformly uniformly stretched and all pairs of antipodal points maps onto the same tensor.

    It is demonstrated that the above mapping can be realized by sampling the 3D space using a specified class of symmetrically distributed quadrature filters. It is shown that 6 quadrature filters are necessary to realize the desired mapping, the orientations of the filters given by lines trough the vertices of an icosahedron. The desired tensor representation can be obtained by simply performing a weighted summation of the quadrature filter outputs. This situation is indeed satisfying as it implies a simple implementation of the theory and that requirements on computational capacity can be kept within reasonable limits.

    Noisy neigborhoods and/or linear combinations of tensors produced by the mapping will in general result in a tensor that has no direct counterpart in R3. In an adaptive hierarchical signal processing system, where information is flowing both up (increasing the level of abstraction) and down (for adaptivity and guidance), it is necessary that a meaningful inverse exists for each levelaltering operation. It is shown that the point in R3 that corresponds to the best approximation of a given tensor is  given by the largest eigenvalue times the corresponding eigenvector of the tensor.

  • 181.
    Knutsson, Hans
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    The meaninglessness of `Sit-and-stare' -- How Vision-Action-Understanding is inseparable1992Ingår i: Workshop on Vision: Ruzenagaard, Själlands Udde, 1992, s. 9-20Konferensbidrag (Refereegranskat)
  • 182.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Andersson, Magnus
    n/a.
    Robust N-Dimensional Orientation Estimation using Quadrature Filters and Tensor Whitening1994Ingår i: ICASSP: Adelaide, Australia, 1994Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper it is shown how estimates of local structure and orientation can be obtained using a set of spherically separable quadrature filters. The method is applicable to signals of any dimensionality the only requirement being that the filter set spans the corresponding orientation space. The estimates produced are 2:nd order tensors, the size of the tensors corresponding to the dimensionality of the input signal. A central part of the algorithm is an operation termed Tensor Whitening reminiscent of classical whitening procedures. This operation compensates exactly for any biases introduced by non-uniform filter orientation distributions and/or non-uniform filter output certainties. Examples of processing of 2D-images, 3D-volumes and 2D-image sequences are given. Sensitivity to noise and missing filter outputs are analyzed in different situations. Estimation accuracy as a function of filter orientation distributions are studied. The studies provide evidence that the algorithm is robust and preferable to other algorithms in a wide range of situations.

  • 183.
    Knutsson, Hans
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Andersson, Mats
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Implications of invariance and uncertainty for local structure analysis filter sets2005Ingår i: Signal processing. Image communication, ISSN 0923-5965, E-ISSN 1879-2677, Vol. 20, nr 6, s. 569-581Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper discusses which properties of filter sets used in local structure estimation that are the most important. Answers are provided via the introduction of a number of fundamental invariances. Mathematical formulations corresponding to the required invariances leads up to the introduction of a new class of filter sets termed loglets. Loglets are polar separable and have excellent uncertainty properties. The directional part uses a spherical harmonics basis. Using loglets it is shown how the concepts of quadrature and phase can be defined in n-dimensions. It is also shown how a reliable measure of the certainty of the estimate can be obtained by finding the deviation from the signal model manifold. Local structure analysis algorithms are quite complex and involve a lot more than the filters used. This makes comparisons difficult to interpret from a filter point of view. To reduce the number 'free' parameters and target the filter design aspects a number of simple 2D experiments have been carried out. The evaluation supports the claim that loglets are preferable to other designs. In particular it is demonstrated that the loglet approach outperforms a Gaussian derivative approach in resolution and robustness. (c) 2005 Elsevier B.V. All rights reserved.

  • 184.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Loglets: Generalized quadrature and phase for local spatio-temporal structure estimation2003Ingår i: Image Analysis: 13th Scandinavian Conference, SCIA 2003 Halmstad, Sweden, June 29 – July 2, 2003 Proceedings / [ed] Josef Bigun and Tomas Gustavsson, Springer Berlin/Heidelberg, 2003, Vol. 2749, s. 741-748Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    The question of which properties of a local structure estimator are important is discussed. Answers are provided via the introduction of a number of fundamental invariances. Mathematical formulations corresponding to the required invariances leads up to the introduction of a new class of filter sets termed loglets. Using loglets it is shown how the concepts of quadrature and phase can be defined in n-dimensions. A number of experiments support the claim that loglets are preferable to other designs. In particular it is demonstrated that the loglet approach outperforms a Gaussian derivative approach in resolution and robustness to variations in object illumination. It is also shown how a measure of the certainty of the estimate can be obtained using the consistency of the generalized phase with respect to orientation.

  • 185.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Morphones: Paint on priors and elastic canvas for segmentation and registration2005Ingår i: Image Analysis: 14th Scandinavian Conference, SCIA 2005, Joensuu, Finland, June 19-22, 2005. Proceedings, Springer Berlin/Heidelberg, 2005, s. 292-301Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a new robust approach for registration and segmentation. Segmentation as well as registration is attained by morphing of an N-dimensional model, the Morphon, onto the Ndimensional data. The approach is general and can, in fact, be said to encompass much of the deformable model ideas that have evolved over the years. However, in contrast to commonly used models, a distinguishing feature of the Morphon approach is that it allows an intuitive interface for specifying prior information, hence the expression paint on priors. In this way it is simple to design Morphons for specific situations.

    The priors determine the behavior of the Morphon and can be seen as local data interpreters and response generators. There are three different kinds of priors: – material parameter fields (elasticity, viscosity, anisotropy etc.), – context fields (brightness, hue, scale, phase, anisotropy, certainty etc.) and – global programs (filter banks, estimation procedures, adaptive mechanisms etc.).

    The morphing is performed using a dense displacement field. The field is updated iteratively until a stop criterion is met. Both the material parameter and context fields are addressed via the present displacement field. In each iteration the neighborhood operators are applied, using both data and the displaced parameter fields, and an incremental displacement field is computed.

    An example of the performance is given using a 2D ultrasound heart image sequence where the purpose is to segment the heart wall. This is a difficult task even for trained specialists yet the Morphon generated segmentation is highly robust. Further it is demonstrated how the Morphon approach can be used to register the individual images. This is accomplished by first finding the displacement field that aligns the morphon model with the heart wall structure in each image separately and then using the displacement field differences to align the images.

  • 186.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Morphons: Segmentation using elastic canvas and paint on priors2005Ingår i: Image Processing, 2005. ICIP 2005. IEEE International Conference on  (Volume:2 ), 2005, s. 1226-1229Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a new robust approach for segmentation. The segmentation is attained by morphing of an TV-dimensional model, the Morphon, onto the TV-dimensional data. The approach is general and can, in fact, be said to encompass much of the deformable model ideas that have evolved over the years. However, in contrast to commonly used models, a distinguishing feature of the Morphon approach is that it allows an intuitive interface for specifying prior information, hence the expression paint on priors. In this way it is simple to design Morphons for specific situations. The priors determine the behavior of the Morphon and can be seen as local data interpreters and response generators. There are three different kinds of priors: material parameter fields (elasticity, viscosity, anisotropy etc.), context fields (brightness, hue, scale, phase, anisotropy, certainly etc.) and global programs (filter banks, estimation procedures, adaptive mechanisms etc.). The morphing is performed using a dense displacement field. Both the material parameter and context fields are addressed via the present displacement field. An example of the performance of is given using 2D ultrasound images of a heart where the purpose is to segment the heart wall.

  • 187.
    Knutsson, Hans
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Andersson, Mats
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Morphons: Segmentation using elastic canvas and paint on priors2005Rapport (Övrigt vetenskapligt)
  • 188.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Optimization of Sequential Filters1995Ingår i: Proceedings of the SSAB Symposium on Image Analysis: Linköping, Sweden, 1995, s. 87-90Konferensbidrag (Refereegranskat)
    Abstract [en]

    A recursive method for separation of spherically separable quadrature filters into simple kernels with mainly one dimensional extent has been worked out. The resulting filter responses are mapped to a non biased tensor representation where the local tensor constitutes a robust estimate of both the shape and the orientation (velocity) of the neighbourhood. The performance of this General Sequential Filter concept has exceeded the authors most optimistic expectations. A qualitative evaluation results in no detectable loss in accuracy when compared to conventional FIR (Finite Impulse Response) filters but the computation is performed 20-30 times faster. The magnitude of the attained speed-up implies that complex spatio-temporal analysis can be performed using standard hardware, such as a powerful workstation, in close to real time. Due to the soft implementation of the convolver and the tree structure of the sequential filtering approach the processing is simple to optimize for most standard hardware. The method used in the examples was implemented in AVS (Application Visualization System) using modules written in C.

  • 189.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    What's so good about quadrature filters?2003Ingår i: Image Processing, 2003. ICIP 2003. Proceedings. 2003 International Conference on  (Volume:3 ), IEEE Signal Processing Society, 2003, s. 61-64Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper argues for the use of quadrature filters for local structure tensor and motion estimation. The question of which properties of a local motion estimator are important is discussed. Answers are provided via the introduction of a number of fundamental invariances that are required in object motion estimation. A combination of statistical and deterministic modeling leads to mathematical formulations corresponding to the required invariances. The discussion leads up to the introduction of a new class of filter sets loglets. A number of experiments support the claim that loglets are preferable to other designs. In particular it is demonstrated that the loglet approach outperforms a Gaussian derivative approach in resolution and robustness to variations in object illumination.

  • 190.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Borga, Magnus
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Wigström, Lars
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet.
    Respiratory Arifact Reduction in MRI using Dynamic Deformation Modelling2002Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a novel magnetic resonance imaging (MRI) reconstruction method that will reconstruct an object correctly despite the presence of respiratory-type motions. The basis for the method is the observation that affine deformations of an object will correspond to a different but unique affine coordinate transform of the Fourier representation (k-space) of the object. The resulting sample points will be irregularly distributed prohibiting the use of standard IFFT to reconstruct the object. The object can however be reconstructed through the use of a weighted regularized pseudo inverse. Short computing times are obtained using a novel fast sequential pseudo inverse algorithm.

     

  • 191.
    Knutsson, Hans
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik.
    Andersson, Mats
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik.
    Borga, Magnus
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik.
    Wiklund, Johan
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för systemteknik, Bildbehandling.
    Automated generation of representations in vision2000Ingår i: International Conference on Pattern Recognition ICPR,2000, Barcelona, Spain: IEEE , 2000, s. 59-66 vol.3Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a general strategy for automated generation of efficient representations in vision. The approach is highly task oriented and what constitutes the relevant information is defined by a set of examples. The examples are pairs of situations that are dependent through the chosen feature but are otherwise independent. Particularly important concepts in the work are mutual information and canonical correlation. How visual operators and representations can be generated from examples are presented for a number of features, e.g. local orientation, disparity and motion. Interesting similarities to biological vision functions are observed. The results clearly demonstrates the potential of combining advanced filtering techniques and learning strategies based on canonical correlation analysis (CCA).

  • 192.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Tekniska högskolan.
    Haglund, Leif
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Wiklund, Johan
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Orientation and Velocity1995Ingår i: Signal Processing for Computer Vision / [ed] Gösta H. Granlund and Hans Knutsson, Dordrecht: Kluwer , 1995, s. 219-258Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This chapter introduces the use of tensors in estimation of local structure and orientation. The tensor representation is shown to be crucial to unambiguous and continuous representation of local orientation in multiple dimensions. In addition to orientation the tensor representation also conveys the degree and type of local anisotropy. The orientation estimation approach is developed in detail for two, three and four dimensions and is shown to be extendable to higher dimensions. Examples and performance measures are given for processing of images, volumes and time sequences.

  • 193.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats T.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Kronander, Torbjörn
    n/a.
    Hemmendorff, Magnus
    n/a.
    Digital Adaptive Angiocardiography1998Ingår i: Proceedings of the SSAB symposium on image analysis: Uppsala, Sweden, 1998, s. 65-68Konferensbidrag (Refereegranskat)
  • 194.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats T.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Kronander, Torbjörn
    SECTRA AB, Linköping, Sweden.
    Hemmendorff, Magnus
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Spatio-temporal filtering of digital angiography image data1998Ingår i: Computer Methods and Programs in Biomedicine, ISSN 0169-2607, E-ISSN 1872-7565, Vol. 57, nr 1-2, s. 115-123Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As welfare diseases become more common all over the world the demand for angiography examinations is increasing rapidly. The development of advanced medical signal processing methods has with few exceptions been concentrated towards CT and MR while traditional contrast based radiology depend on methods developed for ancient photography techniques despite the fact that angiography sequences are generally recorded in digital form. This article presents a new approach for processing of angiography sequences based on advanced image processing methods. The developed algorithm automatically processes angiography sequences containing motion artifacts that cannot be processed by conventional methods like digital subtraction angiography (DSA) and pixel shift due to non uniform motions. The algorithm can in simple terms be described as an ideal pixelshift filter carrying out shifts of different directions and magnitude according to the local motions in the image. In difference to conventional methods it is fully automatic, no mask image needs to be defined and the manual pixelshift operations, which are extremely time consuming, are eliminated. The algorithm is efficient and robust and is designed to run on standard hardware of a powerful workstation which excludes the need for expensive dedicated angiography platforms. Since there is no need to make additional recordings if the patient moves, the patient is exposed to less amount of radiation and contrast fluid. The most exciting benefits by this method are, however, that it opens up new areas for contrast based angiography that are not possible to process with conventional methods e.g. nonuniform motions and multiple layers of moving tissue. Advanced image processing methods provide significantly better image quality and noise suppression but do also provide the means to compute flow velocity and visualize the flow dynamics in the arterial trees by e.g. using color. Initial tests have proven that it is possible to discriminate capillary blood flow from angiography data which opens up interesting possibilities for estimating the blood flow in the heart muscle without use of nuclear methods.

  • 195.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Wigström, Lars
    Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Borga, Magnus
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Sigfridsson, Andreas
    Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Motion artifact reduction in MRI through generalized DFT2004Ingår i: Biomedical Imaging: Nano to Macro, 2004. IEEE International Symposium on, IEEE , 2004, s. 896-899 vol.1Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a method that dramatically reduces artifacts caused by respiratory (and similar types of) patient motion in magnetic resonance imaging (MRI). The basis for the method is the observation that affine deformations of an object will correspond to a different but unique affine coordinate transform (plus phase shift) of the Fourier representation of the object. The resulting sample points will be irregularly distributed prohibiting the use of standard IFFT to reconstruct the object. The object can however be reconstructed through the use of a weighted regularized pseudo inverse. A standard pseudo inverse is, however, not possible due to excessive computational demands. For this reason a novel fast sequential pseudo inverse algorithm is also presented. Significantly improved results are obtained on both synthetic and clinical data.

  • 196.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Wiklund, Johan
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Advanced Filter Design1999Ingår i: Proceedings of the 11th Scandinavian Conference on Image Analysis: Greenland, SCIA , 1999, s. 185-193Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a general approach for obtaining optimal filters as well as filter sequences. A filter is termed optimal when it minimizes a chosen distance measure with respect to an ideal filter. The method allows specification of the metric via simultaneous weighting functions in multiple domains, e.g. the spatio-temporal space and the Fourier space. Metric classes suitable for optimization of localized filters for multidimensional signal processing are suggested and discussed.

    It is shown how convolution kernels for efficient spatio-temporal filtering can be implemented in practical situations. The method is based on applying a set of jointly optimized filter kernels in sequence. The optimization of sequential filters is performed using a novel recursive optimization technique. A number of optimization examples are given that demonstrate the role of key parameters such as: number of kernel coefficients, number of filters in sequence, spatio-temporal and Fourier space metrics.

    The sequential filtering method enables filtering using only a small fraction of the number of filter coefficients required using conventional filtering. In multidimensional filtering applications the method potentially outperforms both standard convolution and FFT based approaches by two-digit numbers.

  • 197.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik. Linköpings universitet, Tekniska högskolan.
    Andersson, Mats
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Wiklund, Johan
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Multiple Space Filter Design1999Ingår i: Proceedings of the SSAB symposium on image analysis: Gothenburg, 1999Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a general approach for obtaining optimal filters as well as filter sequences. A filter is termed optimal when it minimizes a chosen distance measure with respect to an ideal filter. The method allows specification of the metric via simultaneous weighting functions in multiple domains, e.g. the spatio-temporal space and the Fourier space. It is shown how convolution kernels for efficient spatio-temporal filtering can be implemented in practical situations. The method is based on applying a set of jointly optimized filter kernels in sequence. The optimization of sequential filters is performed using a novel recursive optimization technique. A number of optimization examples are given that demonstrate the role of key parameters such as: number of kernel coefficients, number of filters in sequence, spatio-temporal and Fourier space metrics. In multidimensional filtering applications the method potentially outperforms both standard convolution and FFT based approaches by two-digit numbers.

  • 198.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Borga, Magnus
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Learning Visual Operators from Examples: A New Paradigm in Image Processing1999Ingår i: Proceedings of the 10th International Conference on Image Analysis and Processing (ICIAP'99): Venice, Italy, 1999Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a general strategy for designing efficient visual operators. The approach is highly task oriented and what constitutes the relevant information is defined by a set of examples. The examples are pairs of images displaying a strong dependence in the chosen feature but are otherwise independent. Particularly important concepts in the work are mutual information and canonical correlation. Visual operators learned from examples are presented, e.g. local shift invariant orientation operators and image content invariant disparity operators. Interesting similarities to biological vision functions are observed.

  • 199.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Borga, Magnus
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Landelius, Tomas
    n/a.
    Generalized Eigenproblem for Stochastic Process Covariances1996Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a novel algorithm for finding the solution of the generalized eigenproblem where the matrices involved contain expectation values from stochastic processes. The algorithm is iterative and sequential to its structure and uses on-line stochastic approximation to reach an equilibrium point. A quotient between two quadratic forms is suggested as an energy function for this problem and is shown to have zero gradient only at the points solving the eigenproblem. Furthermore it is shown that the algorithm for the generalized eigenproblem can be used to solve three important problems as special cases. For a stochastic process the algorithm can be used to find the directions for maximal variance, covariance, and canonical correlation as well as their magnitudes.

  • 200.
    Knutsson, Hans
    et al.
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Borga, Magnus
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Landelius, Tomas
    n/a.
    Learning Canonical Correlations1995Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a novel learning algorithm that finds the linear combination of one set of multi-dimensional variates that is the best predictor, and at the same time finds the linear combination of another set which is the most predictable. This relation is known as the canonical correlation and has the property of being invariant with respect to affine transformations of the two sets of variates. The algorithm successively finds all the canonical correlations beginning with the largest one. It is shown that canonical correlations can be used in computer vision to find feature detectors by giving examples of the desired features. When used on the pixel level, the method finds quadrature filters and when used on a higher level, the method finds combinations of filter output that are less sensitive to noise compared to vector averaging.

1234567 151 - 200 av 400
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf