Number 1 (2012)

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http://hdl.handle.net/11025/1055

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Showing 1 - 9 out of 9 results

Preprocessing for quantitative statistical noise analysis of MDCT brain images reconstructed using hybrid iterative (iDose) algorithm
(Václav Skala - UNION Agency, 2012) Walek, Petr; Jan, Jiří; Ouředníček, Petr; Skotáková, Jarmila; Jíra, Igor; Skala, Václav
Radiation dose reduction is a very topical problem in medical X-ray CT imaging and plenty of strategies have been introduced recently. Hybrid iterative reconstruction algorithms are one of them enabling dose reduction up to 70 %. The paper describes data preprocessing and feature extraction from iteratively reconstructed images in order to assess their quality in terms of image noise and compare it with quality of images reconstructed from the same data by the conventional filtered back projection. The preprocessing stage consists in correction of a stair-step artifact and in fast, precise bone and soft tissue segmentation. Noise patterns of differently reconstructed images can therefore be examined separately in these tissue types. In order to remove anatomical structures and to obtain the pure noise, subtraction of images reconstructed by the iterative iDose algorithm from images reconstructed by the filtered back projection is performed. The results of these subtractions called here residual noise images and are the used to further extract parameters of the noise. The noise parameters, which are intended to serve as input data for consequent multidimensional statistical analysis, are the standard deviation and power spectrum of the residual noise. This approach enables evaluation of noise properties in the whole volume of real patient data, in contrast to noise analysis performed in small regions of interest or in images of phantoms.
Interactive BRDF estimation for mixed-reality applications
(Václav Skala - UNION Agency, 2012) Knecht, Martin; Tanzmeister, Georg; Traxler, Christoph; Wimmer, Michael; Skala, Václav
Recent methods in augmented reality allow simulating mutual light interactions between real and virtual objects. These methods are able to embed virtual objects in a more sophisticated way than previous methods. However, their main drawback is that they need a virtual representation of the real scene to be augmented in the form of geometry and material properties. In the past, this representation had to be modeled in advance, which is very time consuming and only allows for static scenes. We propose a method that reconstructs the surrounding environment and estimates its Bidirectional Reflectance Distribution Function (BRDF) properties at runtime without any preprocessing. By using the Microsoft Kinect sensor and an optimized hybrid CPU & GPU-based BRDF estimation method, we are able to achieve interactive frame rates. The proposed method was integrated into a differential instant radiosity rendering system to demonstrate its feasibility.
Coupling between meshless FEM modeling and rendering on GPU for real-time physically-based volumetric deformation
(Václav Skala - UNION Agency, 2012) Movania, Muhammad Mobeen; Lin, Feng; Qian, Keman; Chiew, Wei Ming; Seah, Hock Soon; Skala, Václav
For real-time rendering of physically-based volumetric deformation, a meshless finite element method (FEM) is proposed and implemented on the new-generation Graphics Processing Unit (GPU). A tightly coupled deformation and rendering pipeline is defined for seamless modeling and rendering: First, the meshless FEM model exploits the vertex shader stage and the transform feedback mechanism of the modern GPU; and secondly, the hardware-based projected tetrahedra (HAPT) algorithm is used for the volume rendering on the GPU. A remarkable feature of the new algorithm is that CPU readback is avoided in the entire deformation modeling and rendering pipeline. Convincing experimental results are presented.
Morphometric analysis of mesh asymmetry
(Václav Skala - UNION Agency, 2012) Krajíček, Václav; Dupej, Ján; Velemínská, Jana; Pelikán, Josef; Skala, Václav
New techniques of capturing shape geometry for the purpose of studying asymmetry in biological objects bring the need to develop new methods of analyzing such data. In this paper we propose a method of mesh asymmetry analysis and decomposition intended for use in geometric morphometry. In geometric morphometry the individual bilateral asymmetry is captured by aligning a specimen with its mirror image and analyzing the difference. This involves the construction of a dense correspondence mapping between the meshes. We tested our algorithm on real data consisting of a sample of 102 human faces as well as on artificially altered meshes to successfully prove its validity. The resulting algorithm is an important methodological improvement which has a potential to be widely used in a wide variety of morphological studies.
On global MDL-based multichannel image restoration and partitioning
(Václav Skala - UNION Agency, 2012) Ivanovska, Tetyana; Hahn, Horst K.; Linsen, Lars; Skala, Václav
In this paper, we address the problem of multichannel image partitioning and restoration, which includes simultaneous denoising and segmentation processes. We consider a global approach for multichannel image partitioning using minimum description length (MDL). The studied model includes a piecewise constant image representation with uncorrelated Gaussian noise. We review existing single- and multichannel approaches and make an extension of the MDL-based grayscale image partitioning method for the multichannel case. We discuss the algorithm’s behavior with several minimization procedures and compare the presented method to state-of-the-art approaches such as Graph cuts, greedy region merging, anisotropic diffusion, and active contours in terms of convergence, speed, and accuracy, parallelizability and applicability of the proposed method.
A statistical framework for estimation of cell migration velocity
(Václav Skala - UNION Agency, 2012) Huang, Guangming; Kim, Jiwoong; Huang, Xinyu; Zheng, Gaolin; Tokuta, Alade; Skala, Václav
Migration velocity of cell populations in vitro is one of important measurements of cell behaviors. As there are massive amount of cells in one image that share similar characteristics and are highly deformable, it is often computational expensive to track every individual cell. It is also difficult to track cells over a long period of time due to propagation of segmentation and tracking errors. This paper presents an algorithm to estimate migration velocity of cell populations observed by time-lapse microscopy. Instead of tracking cells individually, our proposed algorithm computes mutual information between image blocks of consecutive frames. The migration velocity is then estimated by a linear regression, with mutual information and foreground area ratio as input. Experiments on a variety of image sequences verified that our algorithm can give accurate and robust estimation under different situations in real-time.
A hierarchical splitting scheme to reveal insight into highly self-occluded integral surfaces
(Václav Skala - UNION Agency, 2012) Brambilla, Andrea; Viola, Ivan; Hauser, Helwig; Skala, Václav
In flow visualization, integral surfaces are of particular interest for their ability to describe trajectories of massless particles. In areas of swirling motion, integral surfaces can become very complex and difficult to understand. Taking inspiration from traditional illustration techniques, such as cut-aways and exploded views, we propose a surface analysis tool based on surface splitting and focus+context visualization. Our surface splitting scheme is hierarchical and at every level of the hierarchy the best cut is chosen according to a surface complexity metric. In order to make the interpretation of the resulting pieces straightforward, cuts are always made along isocurves of specific flow attributes. Moreover, a degree of interest can be specified, so that the splitting procedure attempts to unveil the occluded interesting areas. Through practical examples, we show that our approach is able to overcome the lack of understanding originating from structural occlusion.
A study on the animations of swaying and breaking trees based on a particle-based simulation
(Václav Skala - UNION Agency, 2012) Akagi, Yasuhiro; Kitajima, Katsuhiro; Skala, Václav
In this paper, we propose a particle-based simulation method to create the animations of swaying and breaking trees. Since the shapes of trees and their realistic motions are usually complex, it is difficult for us to create an animation of a swaying tree manually. Therefore, to produce films and image contents which contain a natural scene of swaying and breaking trees, it takes a lot of work to create the animation. To solve this problem, it is important that how to calculate interactions between a tree and wind to automatically generate the swaying and breaking motions of a tree by using a physical simulation. We model both a tree and wind as particles to simulate the interactions. The advantage of the particle-based method is that the method is robust for changing of the topology of wind and the branching structure of a tree. Our results show that the proposed method can naturally represent the breaking behavior of a tree and the wind flow around the tree by using the particle-based simulation of the wind.
Caustic object construction based on multiple caustic patterns
(Václav Skala - UNION Agency, 2012) Tandianus, Budianto; Johan, Henry; Seah, Hock Soon; Skala, Václav
Inverse caustic problem, that is computing the geometry of a reflector and/or refractor based on a given caustic pattern, is currently not widely studied. In this paper, we propose a technique to solve the inverse caustic problem in which we compute the geometry of a semi-transparent homogeneous refractive object (caustic object) given a directional light source and a set of caustic patterns (each pattern is considered to be formed at a specified distance from the caustic object). We validate the results by using mental ray (software rendering). The novelty of our research is that we consider a set of caustic patterns whereas existing techniques only consider one caustic pattern. We employ a stochastic approach to simulate the refracted light beam paths that can approximately reconstruct the input caustic patterns. Working backward, from the computed refracted light beam paths we compute the geometry of the caustic object that can produce such light beam paths. Due to having multiple caustic patterns as the inputs, it is a challenge to reconstruct the input caustic patterns because of the differences in their shapes and intensities. We solve this problem by using a two-step optimization algorithm in which we adjust the position and size of the caustic regions in the first step and we adjust the caustic shapes in the second step. Our technique is able to construct a caustic object for a various types of input caustic patterns.

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