Jan Cornelis - Academia.edu (original) (raw)

Papers by Jan Cornelis

ABSTRACT Despite their theoretical limitations and numerically often disappointing performance, O... more ABSTRACT Despite their theoretical limitations and numerically often disappointing performance, Output-Least-Squares (OLS) algorithms retain a dominant role in solving the inverse problem of Electrical Impedance Tomography. We present a new approach based on a double-constrained variational formulation of the problem. The method relies on a nonlinear integral transform, which relates the conductivity in the interior of a closed domain to the dissipated power as computed from the Cauchy data on the boundary. The kernel of this transform involves the unknown electric potential field at the target conductivity function, which on the boundary is constrained by the Dirichlet conditions. A first-order Taylor series approximation, centred at a known prior, leads to a bilinear residual expression, which is then used to define a Tikhonov regularized misfit measure on the discrete Lp norm, where p = 1, 2, inf. Unlike for the error measure in OLS, the misfit function is defined over the entire domain, and not restricted to the boundary. What emerges is an iterative algorithm requiring the solution of a sequence of sparse matrix problems, the structure of which is retained during the entire calculation. For p = 2 the iteration essentially reduces to a Gauss-Newton method. To the expense of computing the misfit measure also over the interior of the domain, the algorithm lends itself particularly well for accelerated implementations, exploiting the sparse structure demonstrated by the constitutive matrix problems.

2008 16th European Signal Processing Conference, 2008

Signal Process Image Commun, 1999

This paper describes some new algorithms for Segmented Still Image and Image Sequence Coding. A n... more This paper describes some new algorithms for Segmented Still Image and Image Sequence Coding. A new filter is introduced for reducing the number of contour points produced by segmentation, and also the number of bits needed to code them, leading to higher compression ratios without visible subjective degradation of the image quality. The impact of using such a contour points' reduction filter in image sequence compression is studied. The inclusion of the filter in a new video codec scheme leads to higher frame rates for almost the same subjective video quality, especially when coding complex scenes. A simple way to control the video bit-rate is also described.

Proceedings of Spie the International Society For Optical Engineering, 2006

ABSTRACT

Lecture Notes in Computer Science, 2006

ABSTRACT

Abstract—This paper describes two schemes that combine JPEG and Segmented Image Coding (SIC) for ... more Abstract—This paper describes two schemes that combine JPEG and Segmented Image Coding (SIC) for progressive image transmission. Compared to JPEG-based progressive transmission schemes, the new schemes produce reconstructed images of better quality during all the stages of transmission and never transmit more bits. Also, the computational complexity of the new schemes is lower than that of the SIC-only approach.

We study global optimization (GOP) in the framework of non-linear inverse problems with a unique ... more We study global optimization (GOP) in the framework of non-linear inverse problems with a unique solution. These problems are in general ill-posed. Evaluation of the objective function is often expensive, as it implies the solution of a non-trivial forward problem. The ill-posedness of these problems calls for regularization while the high evaluation cost of the objective function can be addressed with response surface techniques. The global optimization using Radial Basis Function (RBF) as presented by Gutmann (2001) is a response surface global optimization technique with regularizing aspects. Alternatively, several publications put forward global optimization using a probabilistic approach based upon Kriging as an efficient technique for non-linear multi modal objective functions, thereby providing a credible stopping rule (Jones2001). After comparing both concepts, we argue that in case of non-linear inverse problems an adaptation of the RBF algorithm seems to be the most promis...

A scalable multiple description scalar quantizer (SMDSQ) is a quantization based framework used f... more A scalable multiple description scalar quantizer (SMDSQ) is a quantization based framework used for scalable multiple description coding (SMDC). In this paper, we introduce a novel generalization of the Lloyd-Max algorithm to realize locally optimal SMDSQs. Both level-constrained and entropy-constrained cases are considered. For both cases, locally optimal solutions are realized by iterative execution of the centroid and the modified nearest-neighbor conditions. Experimental results confirm that, for a zero-mean unit-variance Gaussian source, the optimization algorithm enables a significant reduction in distortion for the level-constrained case. Moreover, relatively lesser but still significant distortion-rate (D-R) gains are viable for the entropy-constrained case. It is shown that, for a packetized transmission of Gaussian as well as wavelet-decomposed images, the obtained optimization gains translate into an average improvement in the decoder's signal-to-noise-ratio (SNR) for...

Algorithms and Parallel VLSI Architectures III, 1995

ABSTRACT. This paper describes the parallel implementation of the 2-D Fast Cosine Transform (FCT)... more ABSTRACT. This paper describes the parallel implementation of the 2-D Fast Cosine Transform (FCT). The examined algorithms are: Row-Column (RC) FCT and Vector-Radix (VR) FCT. A SUN SPARC 10 with 4 processors and shared-memory is considered. It is observed that the parallel approach provides considerable gain for block sizes of more than 128x128 pixels. For smaller sizes there is no speed-up: by using more than one processor, the execution times are larger than on one processor due to the time required for the ...

IFMBE Proceedings, 2010

This paper introduces a system for monitoring physical activity of elderly. The position based mo... more This paper introduces a system for monitoring physical activity of elderly. The position based monitoring system requires accurate calibration methods mapping the camera coordinate system onto a room based system. An algorithm mapping a coordinate system defined by ...

Biochimica et biophysica acta, Jan 21, 1978

The elimination of cyclobutane pyrimidine dimers from the nuclear DNA of ultraviolet irradiated H... more The elimination of cyclobutane pyrimidine dimers from the nuclear DNA of ultraviolet irradiated HeLa cells has been examined by means of chromatography and immunoautoradiography. The extent and duration of the process was similar when dimers were assayed by both methods, proving that the anti-sera recognized pyrimidine dimers. The rate of dimer excision did not differ through the cell cycle with the exception of mitosis during which no dimers were removed. Dimer excision is a relatively fast process which is terminated within a few hours, but it leaves many dimers in the DNA. Excision is depressed by inhibitors of semiconservative DNA synthesis that affect the DNA precursor pool or DNA polymerases. Cells whose DNA is partly substituted with bromodeoxyuridine instead of thymidine, repair single-strand breaks and remove dimers at the same rate but to different extents. On the other hand, inhibitors limit repair of breaks and removal of dimers to the same degree suggesting that the rep...

Applications of Digital Image Processing XXIII, 2000

ABSTRACT

Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1992

Two algorithms for medical image processing are discussed: CAVITY DETECTOR, which solves the segm... more Two algorithms for medical image processing are discussed: CAVITY DETECTOR, which solves the segmentation problem of regions which are not completely surrounded by walls and EDGMENTATION, which is used for (i) preprocessing before segmentation, (ii) boundary refinement before edge detection, (iii) segmentation based on a modified split-and-merge approach, and (iiii) data reduction. In this paper, we describe the principles of

Journal of Medical Imaging and Health Informatics, 2012

ABSTRACT Given that the number of patients suffering from chronic heart failure is increasing exp... more ABSTRACT Given that the number of patients suffering from chronic heart failure is increasing exponentially over the last years, ambulatory monitoring systems capable of providing an advanced warning of pulmonary congestion at a presymptomatic stage, have the potential to drastically reduce the costs of (re-)hospitalization for acute decompensation, and substantially improve the living quality of these patients. Unfortunately this has not been possible up to now because no suitable methods have been available. However, recent advances in the development of ECT (electrical capacitance tomography) have the potential to become the driving force behind future approaches to the ambulatory monitoring and therapeutic remediation of gradually unfolding cardiogenic edema. ECT makes it possible to literally look into the lungs during prolonged ambulatory monitoring periods. In this way, ECT provides a continuous view of the regional distribution and retention of fluids throughout the pulmonary volume. This opens completely new ways for clinicians to accurately follow up gradually developing heart failure decompensation. The ECT technology is completely non-invasive and non-hazardous, and connects to the patient via an array of surface electrodes mounted on an elastic strap that attaches around the thorax. In this first paper we report on the development of a realistic morphological simulation model capable of replicating to high accuracy the bioelectrical response of the human thorax to external electrical measurement stimuli.

2008 IEEE 10th Workshop on Multimedia Signal Processing, 2008

Abstract A novel coding approach, applying open-loop coding principles in predictive coding syste... more Abstract A novel coding approach, applying open-loop coding principles in predictive coding systems is proposed in this paper. The proposed approach is instantiated with an intra-frame video codec employing the transform and spatial prediction modes from H. 264. ...

Proceedings 15th International Conference on Pattern Recognition. ICPR-2000, 2000

ABSTRACT

ABSTRACT Despite their theoretical limitations and numerically often disappointing performance, O... more ABSTRACT Despite their theoretical limitations and numerically often disappointing performance, Output-Least-Squares (OLS) algorithms retain a dominant role in solving the inverse problem of Electrical Impedance Tomography. We present a new approach based on a double-constrained variational formulation of the problem. The method relies on a nonlinear integral transform, which relates the conductivity in the interior of a closed domain to the dissipated power as computed from the Cauchy data on the boundary. The kernel of this transform involves the unknown electric potential field at the target conductivity function, which on the boundary is constrained by the Dirichlet conditions. A first-order Taylor series approximation, centred at a known prior, leads to a bilinear residual expression, which is then used to define a Tikhonov regularized misfit measure on the discrete Lp norm, where p = 1, 2, inf. Unlike for the error measure in OLS, the misfit function is defined over the entire domain, and not restricted to the boundary. What emerges is an iterative algorithm requiring the solution of a sequence of sparse matrix problems, the structure of which is retained during the entire calculation. For p = 2 the iteration essentially reduces to a Gauss-Newton method. To the expense of computing the misfit measure also over the interior of the domain, the algorithm lends itself particularly well for accelerated implementations, exploiting the sparse structure demonstrated by the constitutive matrix problems.

2008 16th European Signal Processing Conference, 2008

Signal Process Image Commun, 1999

This paper describes some new algorithms for Segmented Still Image and Image Sequence Coding. A n... more This paper describes some new algorithms for Segmented Still Image and Image Sequence Coding. A new filter is introduced for reducing the number of contour points produced by segmentation, and also the number of bits needed to code them, leading to higher compression ratios without visible subjective degradation of the image quality. The impact of using such a contour points' reduction filter in image sequence compression is studied. The inclusion of the filter in a new video codec scheme leads to higher frame rates for almost the same subjective video quality, especially when coding complex scenes. A simple way to control the video bit-rate is also described.

Proceedings of Spie the International Society For Optical Engineering, 2006

ABSTRACT

Lecture Notes in Computer Science, 2006

ABSTRACT

Abstract—This paper describes two schemes that combine JPEG and Segmented Image Coding (SIC) for ... more Abstract—This paper describes two schemes that combine JPEG and Segmented Image Coding (SIC) for progressive image transmission. Compared to JPEG-based progressive transmission schemes, the new schemes produce reconstructed images of better quality during all the stages of transmission and never transmit more bits. Also, the computational complexity of the new schemes is lower than that of the SIC-only approach.

We study global optimization (GOP) in the framework of non-linear inverse problems with a unique ... more We study global optimization (GOP) in the framework of non-linear inverse problems with a unique solution. These problems are in general ill-posed. Evaluation of the objective function is often expensive, as it implies the solution of a non-trivial forward problem. The ill-posedness of these problems calls for regularization while the high evaluation cost of the objective function can be addressed with response surface techniques. The global optimization using Radial Basis Function (RBF) as presented by Gutmann (2001) is a response surface global optimization technique with regularizing aspects. Alternatively, several publications put forward global optimization using a probabilistic approach based upon Kriging as an efficient technique for non-linear multi modal objective functions, thereby providing a credible stopping rule (Jones2001). After comparing both concepts, we argue that in case of non-linear inverse problems an adaptation of the RBF algorithm seems to be the most promis...

A scalable multiple description scalar quantizer (SMDSQ) is a quantization based framework used f... more A scalable multiple description scalar quantizer (SMDSQ) is a quantization based framework used for scalable multiple description coding (SMDC). In this paper, we introduce a novel generalization of the Lloyd-Max algorithm to realize locally optimal SMDSQs. Both level-constrained and entropy-constrained cases are considered. For both cases, locally optimal solutions are realized by iterative execution of the centroid and the modified nearest-neighbor conditions. Experimental results confirm that, for a zero-mean unit-variance Gaussian source, the optimization algorithm enables a significant reduction in distortion for the level-constrained case. Moreover, relatively lesser but still significant distortion-rate (D-R) gains are viable for the entropy-constrained case. It is shown that, for a packetized transmission of Gaussian as well as wavelet-decomposed images, the obtained optimization gains translate into an average improvement in the decoder's signal-to-noise-ratio (SNR) for...

Algorithms and Parallel VLSI Architectures III, 1995

ABSTRACT. This paper describes the parallel implementation of the 2-D Fast Cosine Transform (FCT)... more ABSTRACT. This paper describes the parallel implementation of the 2-D Fast Cosine Transform (FCT). The examined algorithms are: Row-Column (RC) FCT and Vector-Radix (VR) FCT. A SUN SPARC 10 with 4 processors and shared-memory is considered. It is observed that the parallel approach provides considerable gain for block sizes of more than 128x128 pixels. For smaller sizes there is no speed-up: by using more than one processor, the execution times are larger than on one processor due to the time required for the ...

IFMBE Proceedings, 2010

This paper introduces a system for monitoring physical activity of elderly. The position based mo... more This paper introduces a system for monitoring physical activity of elderly. The position based monitoring system requires accurate calibration methods mapping the camera coordinate system onto a room based system. An algorithm mapping a coordinate system defined by ...

Biochimica et biophysica acta, Jan 21, 1978

The elimination of cyclobutane pyrimidine dimers from the nuclear DNA of ultraviolet irradiated H... more The elimination of cyclobutane pyrimidine dimers from the nuclear DNA of ultraviolet irradiated HeLa cells has been examined by means of chromatography and immunoautoradiography. The extent and duration of the process was similar when dimers were assayed by both methods, proving that the anti-sera recognized pyrimidine dimers. The rate of dimer excision did not differ through the cell cycle with the exception of mitosis during which no dimers were removed. Dimer excision is a relatively fast process which is terminated within a few hours, but it leaves many dimers in the DNA. Excision is depressed by inhibitors of semiconservative DNA synthesis that affect the DNA precursor pool or DNA polymerases. Cells whose DNA is partly substituted with bromodeoxyuridine instead of thymidine, repair single-strand breaks and remove dimers at the same rate but to different extents. On the other hand, inhibitors limit repair of breaks and removal of dimers to the same degree suggesting that the rep...

Applications of Digital Image Processing XXIII, 2000

ABSTRACT

Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1992

Two algorithms for medical image processing are discussed: CAVITY DETECTOR, which solves the segm... more Two algorithms for medical image processing are discussed: CAVITY DETECTOR, which solves the segmentation problem of regions which are not completely surrounded by walls and EDGMENTATION, which is used for (i) preprocessing before segmentation, (ii) boundary refinement before edge detection, (iii) segmentation based on a modified split-and-merge approach, and (iiii) data reduction. In this paper, we describe the principles of

Journal of Medical Imaging and Health Informatics, 2012

ABSTRACT Given that the number of patients suffering from chronic heart failure is increasing exp... more ABSTRACT Given that the number of patients suffering from chronic heart failure is increasing exponentially over the last years, ambulatory monitoring systems capable of providing an advanced warning of pulmonary congestion at a presymptomatic stage, have the potential to drastically reduce the costs of (re-)hospitalization for acute decompensation, and substantially improve the living quality of these patients. Unfortunately this has not been possible up to now because no suitable methods have been available. However, recent advances in the development of ECT (electrical capacitance tomography) have the potential to become the driving force behind future approaches to the ambulatory monitoring and therapeutic remediation of gradually unfolding cardiogenic edema. ECT makes it possible to literally look into the lungs during prolonged ambulatory monitoring periods. In this way, ECT provides a continuous view of the regional distribution and retention of fluids throughout the pulmonary volume. This opens completely new ways for clinicians to accurately follow up gradually developing heart failure decompensation. The ECT technology is completely non-invasive and non-hazardous, and connects to the patient via an array of surface electrodes mounted on an elastic strap that attaches around the thorax. In this first paper we report on the development of a realistic morphological simulation model capable of replicating to high accuracy the bioelectrical response of the human thorax to external electrical measurement stimuli.

2008 IEEE 10th Workshop on Multimedia Signal Processing, 2008

Abstract A novel coding approach, applying open-loop coding principles in predictive coding syste... more Abstract A novel coding approach, applying open-loop coding principles in predictive coding systems is proposed in this paper. The proposed approach is instantiated with an intra-frame video codec employing the transform and spatial prediction modes from H. 264. ...

Proceedings 15th International Conference on Pattern Recognition. ICPR-2000, 2000

ABSTRACT