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17 results on '"Lie, Johan"'

4. Piecewise Constant Level Set Methods and Image Segmentation

Author

Lie, Johan, Lysaker, Marius, Tai, Xue-Cheng, Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Dough, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Kimmel, Ron, editor, Sochen, Nir A., editor, and Weickert, Joachim, editor

Published
2005
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7. A binary level set model and some applications to Mumford-Shah image segmentation

Author

Lie, Johan, Lysaker, Marius, and Xue-Cheng Tai

Subjects
Image processing -- Analysis, Iterative methods (Mathematics) -- Usage, Business, Computers, Electronics, Electronics and electrical industries
Abstract

Piecewise constant level set methods including the method proposed by Mumford-Shah for capturing interface are presented. The methods are tested for image segmentation and simple gradient methods are used for the iterative algorithms.

Published
2006

9. (Wanting to do) Ethical research in a shifting context

Author

Eikset, Andrea, Fosse, Trude, Lange, Troels, Lie, Johan, Lossius, Magni, Meaney, Tamsin, Severina, Elena, Dooley, Therese, and Bergen University College

Subjects
Ethical research, learning, ICT, multilingual children, [MATH] Mathematics [math], [SHS] Humanities and Social Sciences, [MATH]Mathematics [math], play, [SHS]Humanities and Social Sciences
Abstract

International audience; 1 trl@hvl.no; 2 tme@hvl.no This paper describes the features of ethical research and how we attempted to undertake this kind of research. Our contention is that the aim of ethical research should be to produce action for change. Our understandings of ethical research led us to pause our negotiations for setting up two new projects, in kindergartens in Norway. By taking seriously our potential collaborators' concerns, we were alerted to how kindergartens were simultaneously seen as both the cause and the salvation for several issues. In media discussions, which often originated with the Minister for Education, there was a perception that there was a need for more learning, particularly of mathematics and language, to overcome difficulties that children, especially immigrant children, may have when they begin school. These discussions were often contradictory with kindergartens being placed in an invidious position of navigating these discussions for their work with children. Ethical research In August 2016, we were in the early stages of setting up two projects involving dialogue between ourselves, as mathematics education researchers, and the parents and teachers of multilingual children in kindergartens in Norway. As described in the next section, our initial discussions with an organisation about one project made us stop and reconsider what we wanted to do and why. To do this, we clarified our ideas about the kind of research, ethical research, which we wanted to undertake. In this paper, we discuss how implementing its principles resulted in us investigating the shifting landscape of priorities in Norwegian kindergarten policies.

Published
2017

11. Total variation regularization of matrix-valued images

Author

Christiansen, Oddvar, Lee, Tin Man, Lie, Johan, Sinha, Usha S., Chan, Tony F., Christiansen, Oddvar, Lee, Tin Man, Lie, Johan, Sinha, Usha S., and Chan, Tony F.

Abstract

We generalize the total variation restoration model, introduced by Rudin, Osher, and Fatemi in 1992, to matrix-valued data, in particular, to diffusion tensor images (DTIs). Our model is a natural extension of the color total variation model proposed by Blomgren and Chan in 1998. We treat the diffusion matrix D implicitly as the product D=LLT, and work with the elements of L as variables, instead of working directly on the elements of D. This ensures positive definiteness of the tensor during the regularization flow, which is essential when regularizing DTI. We perform numerical experiments on both synthetical data and 3D human brain DTI, and measure the quantitative behavior of the proposed model.

Published
2007

16. Piecewise Constant Level Set Methods and Image Segmentation.

Author

Kimmel, Ron, Sochen, Nir, Weickert, Joachim, Lie, Johan, Lysaker, Marius, and Xue-Cheng Tai

Abstract

In this work we discuss variants of a PDE based level set method. Traditionally interfaces are represented by the zero level set of continuous level set functions. We instead use piecewise constant level set functions, and let interfaces be represented by discontinuities. Some of the properties of the standard level set function are preserved in the proposed method. Using the methods for interface problems, we minimize a smooth locally convex functional under a constraint. We show numerical results using the methods for image segmentation. [ABSTRACT FROM AUTHOR]

Published
2005
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17. A Binary Level Set Model and Some Applications to Rumford -- Shah Image Segmentation.

Author

Lie, Johan, Lysaker, Marius, and Xue-Cheng Tai

Subjects
*SET functions, *COMPUTER interfaces, *STOCHASTIC convergence, *DIGITAL images, *REAL variables, *ASYMPTOTIC expansions
Abstract

In this paper, we propose a PDE-based level set method. Traditionally, interfaces are represented by the zero level set of continuous level set functions. Instead, we let the interfaces be represented by discontinuities of piecewise constant level set functions. Each level set function can at convergence only take two values, i.e., it can only be 1 or -1; thus, our method is related to phase-field methods. Some of the properties of standard level set methods are preserved in the proposed method, while others are not. Using this new method for interface problems, we need to minimize a smooth convex functional under a quadratic constraint. The level set functions are discontinuous at convergence, but the minimization functional is smooth. We show numerical results using the method for segmentation of digital images. [ABSTRACT FROM AUTHOR]

Published
2006
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