Journal articles

1. Estimation of the pore volume at the interface between paper web and press felt
   Authors: Axelsson, M.; Östlund, C.(1); Vomhoff, H.(1); Svensson, S.
   (1) STFI Packforsk, Stockholm
   Journal: Nordic Pulp and Paper Research Journal 21(3), 2006
   Abstract: A method for determining the water content at the interface between a press felt and a paper web has been developed. The water content was obtained by subtracting the estimated volume of the indented fibre web from the measured felt surface porosity of the press felt. The felt surface porosity was calculated from a topography map that was imaged with a Confocal Laser Scanning Microscope (CLSM) method. Here, the press felt was compressed against a smooth surface using a stress in the range of 0 to 10 MPa. Artefacts in the CLSM images were reduced using an image analysis method. The indentation of paper webs into the measured felt surface pores at different applied pressures was estimated using another image analysis method, simulating a rolling ball, with different radii of curvature for the different pressures and grammages, rolling over the felt surface. The ball radii were determined for a low and a high grammage web using the STFI-Packforsk Dewatering model.

   The method was evaluated in a case study with four press felts that had batt fibre diameters in a range between 22 and 78 $\mu m$. The indentation was calculated for webs with a low (15 $g/m^2$) and a high grammage (105 $g/m^2$), respectively. The evaluation showed that a considerable amount of porespace is available at the interface between the web and the felt. In most cases, the volume of the water-filled pores accounted for approximately 50% of the total surface porosity of the felt. Assuming a complete water saturation of the web/felt interface, approximately 10 $g/m^2$ of water for the finest felt surface up to 40 $g/m^2$ for the coarsest felt surface, could be located at the interface between the press felt and the paper web at a load of 10 MPa. This implies that a considerable amount of water is available for separation rewetting.

2. Two preprocessing techniques based on grey level and geometric thickness to improve segmentation results
   Author: Eriksson, M.
   Journal: Pattern Recognition Letters 27(3):160-166, 2006
   Abstract: Two different techniques of performing preprocessing of an image to improve segmentation results are presented. The methods use the grey level thickness of the objects, in order to find the resulting image, by varying the size of a neighbourhood depending on the sum of the included grey levels. The first method, RW, uses the random walk of a particle, defined in the neighbourhood of the position of the particle. The resulting image holds the number of times the particle visits a pixel. Instead of randomization to find the number of visits, the second method, IP, scans the image iteratively and calculates the expected value of the same number. Three different kinds of real world applications are demonstrated to get better segmentation results with the preprocessing techniques included than without.

3. Surface glyphs for efficient visualization of multivariate data
   Authors: Forsell, C.(1); Seipel, S.; Lind, M.(1)
   (1) Dept. of Information Science, UU
   Journal: Information Visualization 5(2):112-124, 2006
   Abstract: We present a first effort to evaluate the possible utility of a new type of surface glyphs intended for visualizations of multivariate spatial data. The glyphs are based on results from vision research suggesting that our perception of metric 3D structure is distorted and imprecise relative to the actual scene before us; only a class of qualitative properties of the scene is perceived with accuracy. These properties are best characterized as being invariant over affine but not Euclidean transformations. A large number of possible 3D glyphs for the visualization of spatial data can be constructed using such properties. One group of such glyphs is based on the local sign of surface curvature. We investigated this group in two visualization experiments. The results show that available sources of 3D structural information were sufficient for our subjects to make fast and accurate judgments. Some implications for visualization are also discussed.

4. Volume-wise application of principal component analysis on masked dynamic PET data in sinogram domain
   Author: Razifar, P.; Axelsson, J.(1); Schneider, H.(1); Långström, B.(1); Bengtsson, E; Bergström, M.(1)
   (1) Uppsala Imanet
   Journal: IEEE Transactions on Nuclear Science 53(5):2759-2768, 2006
   Abstract: Most of the methods used for analyzing PET data are applied in the spatial domain (image domain), in which reconstructed images contain all different types of effects and errors caused by the reconstruction algorithm such as correlation in-between pixels, correlations in-between frames, and streak-artifacts. In this paper, we have investigated a new, pixel wise, noise prenormalization method used for transformation of input data followed by volume-wise application of principal component analysis (PCA) on masked dynamic PET data in the sinogram domain. We are aiming to improve the performance of PCA and to provide images with improved quality and signal extraction. We compare the performance of PCA and the image quality obtained with the new method with previously published approaches. The results show improvement of performance of PCA with respect to image quality, signal extraction, precision, and visualization.

5. A new application of pre-normalized principal component analysis for improvement of image quality and clinical diagnosis in human brain PET studies-clinical brain studies using [11C]-GR205171, [11C]-L-deuterium-deprenyl, [11C]-5-Hydroxy-L-Tryptophan, [11C]-L-DOPA and Pittsburgh Compound-B.
   Author: Razifar, P.; Axelsson, J.(1); Schneider, H.(1); Långström, B.(1); Bengtsson, E; Bergström, M.(1)
   (1) Uppsala Imanet
   Journal: Neuroimage 33(2):588-598, 2006
   Abstract: Principal component analysis (PCA) is one of the most applied multivariate image analysis tool on dynamic Positron Emission Tomography (PET). Independent of used reconstruction methodologies, PET images contain correlation in-between pixels, correlations in-between frame and errors caused by the reconstruction algorithm including different corrections, which can affect the performance of the PCA. In this study, we have investigated a new approach of application of PCA on pre-normalized, dynamic human PET images. A range of different tracers have been used for this purpose to explore the performance of the new method as a way to improve detection and visualization of significant changes in tracer kinetics and to enhance the discrimination between pathological and healthy regions in the brain. We compare the new results with the results obtained using other methods. Images generated using the new approach contain more detailed anatomical information with higher quality, precision and visualization, compared with images generated using other methods.

6. Parameterizations of digital surfaces homeomorphic to a sphere using discrete harmonic functions
   Author: Weistrand, O.
   Journal: Pattern Recognition Letters 27(16):1934-1941, 2006
   Abstract: We discuss how to map simply connected digital surfaces to the unit sphere using discrete harmonic functions. This technique is well known for constructing parametrizations of surfaces onto simpler domains. A common problem is the creation of dense clusters of vertices, which leads to numerical instability of methods operating on this mapping. By an explicit calculation, we quantify the cluster density for a simple model example. This example shows that distances between mapped vertices can decrease exponentially in regions on the sphere. By numerical examples, we show that severe clustering often occurs for natural objects. A computationally inexpensive algorithm, based on a bijective transformation of the unit sphere, is suggested for post-processing of clusters. Experiments indicate that this algorithm often improves the mapping such that convergence of a non-linear optimization program is achieved. The program aims at optimizing the parameterization, making it useful for global shape analysis. Examples of approximations in terms of spherical harmonics functions are presented.