Wyniki wyszukiwania - BazTech

1

A Particle-Based Method for Large-Scale Breaking Wave Simulation

Darles E., Crespin B., Ghazanfarpour D.

Machine Graphics and Vision

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2011

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Vol. 20, No. 1

3-25

EN

In this paper we address the problem of particle-based simulation of breaking waves. We present a new set of equations based on oceanographic research which allow us to deal with several types of breaking waves and multiple wave trains with full control over the governing parameters. Sprays are generated by explicitly computing sub-particle systems depending on the local motion caused by plunging. In order to reduce computations in non-significant areas, we also describe a simple and efficient multiresolution scheme based on the properties of our breaking wave model.

2

Hexagonal discrete global GRID systems for geospatial computing

Sahr K.

Archiwum Fotogrametrii, Kartografii i Teledetekcji

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2011

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Vol. 22

363--376

EN

Advanced geospatial applications often involve complex computing operations performed under sometimes severe resource constraints. These applications primarily rely on traditional raster and vector data structures based on square lattices. But there is a significant body of research that indicates that data structures based on hexagonal lattices may be a superior alternative for efficient representation and processing of raster and vector data in high performance applications. The advantages of hexagonal rasters for image processing are discussed, and hexagonal discrete global grid systems for location coding are introduced. The combination provides an efficient, unified approach to location representation and processing in geospatial systems.

3

Template matching by means of correlation coefficient for detecting cancerous masses in mammograms

Bator M., Nieniewski M.

Machine Graphics and Vision

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2007

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Vol. 16, No. 3/4

329-345

EN

The paper presents the authors' experiences with the detection of cancerous masses in mammograms. The described detection method is based on the use of multiscale template matching and multiresolution. As a measure of similarity, the correlation coefficient is adapted. The main conclusion drawn from the conducted experiments is that by sufficiently dense scaling of the templates one can achieve FROC (Free Response Operating Characteristics) curves of the same quality as the curves obtained in the literature with considerably more sophisticated methods. The results were calculated for full mammograms of the entire MIAS database, in contrast to the literature, where the results are often given for regions of interest or for selected images. Several options for the templates were investigated, including three variants based on the hemispherical gray level distribution, as well as the optimal choice of the increasing scale of templates covering the whole range of diameters of masses.

4

The Haar-wavelet transform in digital image processing: its status and achievements

Porwik P., Lisowska A.

Machine Graphics and Vision

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2004

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Vol. 13, No. 1/2

79-98

EN

Image processing and analysis based on continuous or discrete image transforms are classic techniques. The image transforms are widely used in image filtering, data description, etc. Nowadays, wavelet theorems make up very popular methods of image processing, denoising and compression. Considering that Haar functions are the simplest wavelets, these forms are used in many methods of discrete image transforms and processing. The image transform theory is a well known area characterized by a precise mathematical background, but in many cases some transforms have particular properties which have not been investigated yet. This paper presents graphic dependences between parts of Haar and wavelets spectra for the first time. It also presents a method of image analysis by means of the wavelet-Haar spectrum. Some properties of the Haar and wavelet spectrum are investigated. Extraction of image features directly from spectral coefficients distribution is presented. The paper shows that two-dimensional products of both Haar and wavelet functions can be treated as exstractors of particular image features. Furthermore, it is also shown that some coefficients from both the spectra are proportional, which simplifies computations and analyses to some degree.

5

Extended wedgelets : geometrical wavelets in efficient image coding

Lisowska A.

Machine Graphics and Vision

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2004

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Vol. 13, No. 3

261-273

EN

In the modern world, image coding, and especially image compression, plays a very important role. There are well known and recognized theories concerning this topic, such as, for example, Fourier and wavelets theories. Both of these theories allow for representation of images in a sparse way. Unfortunately wavelets, though very good in catching point discontinuities, cannot properly catch line discontinuities often present in images, that is, edges. As a remedy for this problem, the new theory of geometrical wavelets has arisen. In the paper we present a new and fashionable, hence well known, theory of geometrical wavelets called wedgelets, which allows us to code images with edges in a very efficient way. Moreover, we present the new improvement in the wedgelets theory. This improvement - the theory of extended wedgelets - allows us to represent images in a more sparse and efficient way than in the case of the known wedgelets. Such representation allows us to get a higher compression ratio, together with better visual effects. Furthermore, the application to image coding is also presented. The performance of the improvement has been confirmed both theoretically and experimentally.

6

Approaches dedicated to the modelling of complex shapes application to medical data

Mari J. L.

Journal of Medical Informatics & Technologies

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2004

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Vol. 7

IP3--16

EN

The way to model complex shapes has a significant influence depending on the context. Handling an object can be considerably increased if a good underlying model is used. On the contrary, preponderant problems can appear if an unsuited model is associated to the object. The main criterion to discriminate existing models is to determine the balance between: their ability to control global characteristics and the possibility to handle local features of the shape. The fact is very few models are adapted both to structure and to geometrical modelling. In this paper, we first describe an overview of existing approaches. They can be classified principally in two groups: skeleton based models, used to control the global aspect of the shape, and free form models, used to control local specificities of the object. Then, trying to keep the advantages of both techniques in mind, we present an original approach based on a multi-layer model to represent a 3D object. We focus on the ability to take into account both global and local characteristics of a complex shape, on topological and morphological levels, as well as on the geometric level. To do that, the proposed model is composed of three layers. We call the boundary mesh the external layer, including a multi-resolution feature. We enhance this representation by adding an internal structure: the inner skeleton, which is topologically equivalent to the input object. In addition to that, a third layer links the structural entity and the geometrical crust, to induce an intermediary level of representation. This approach is applied to classical and medical data through a specific algorithm.

7

Ternary wavelets and their applications to signal compression

Mustafa G., Chen F., Huang Z.

International Journal of Applied Mathematics and Computer Science

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2004

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Vol. 14, no 2

233-240

EN

We introduce ternary wavelets, based on an interpolating 4-point C2 ternary stationary subdivision scheme, for compressing fractal-like signals. These wavelets are tightly squeezed and therefore they are more suitable for compressing fractal-like signals. The error in compressing fractal-like signals by ternary wavelets is at most half of that given by four-point wavelets (Wei and Chen, 2002). However, for compressing regular signals we further classify ternary wavelets into 'odd ternary' and 'even ternary' wavelets. Our odd ternary wavelets are better in part for compressing both regular and fractal-like signals than four-point wavelets. These ternary wavelets are locally supported, symmetric and stable. The analysis and synthesis algorithms have linear time complexity.

8

Rola kompresji obrazów w internetowych publikacjach kartograficznych

Pyka K.

Roczniki Geomatyki

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2003

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T. 1, z. 1

103-108

PL

Dzisiejsi użytkownicy internetu oczekują aby działające on-line, interaktywne publikacje kartograficzne prezentowały mapy o wysokiej jakości. Jedną z barier stosowania rastrowych map podkładowych w przeglądarkach GIS są ich duże rozmiary przy relatywnie małej prędkości transmisji. Artykuł analizuje przydatność kompresji obrazów dla hybrydowych publikacji kartograficznych. Porównuje się dotychczasowe metody kompresji z metodą falkową. Wskazuje się zalety i wady tej kompresji oraz proponuje rozwiązanie łączące system piramid obrazowych z kompresją falkową.

EN

The Internet users of today expect online interactive GIS to provide high quality maps. Large image data sets with a relatively low speed network are the principal barrier for online GISviewers, especially of base maps. This paper analyses usefulness of image compression to design hybrid GIS browsers. It is compared some known compression method with wavelet technology. Advantage and disadvantage of this new technology are discussed and an integration of image pyramid system and wavelet technology is suggested as a solution.

9

Fully spatial and SNR scalable, SPIHT-based image coding for transmission over heterogenous networks

Danyali H., Mertins A.

Journal of Telecommunications and Information Technology

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2003

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nr 2

92-98

EN

This paper presents a fully scalable image coding scheme based on the set partitioning in hierarchical trees (SPIHT) algorithm. The proposed algorithm, called fully scalable SPIHT (FS-SPIHT), adds the spatial scalability feature to the SPIHT algorithm. It provides this new functionality without sacrificing other important features of the original SPIHT bitstream such as: compression efficiency, full embeddedness and rate scalability. The flexible output bitstream of the FS-SPIHT encoder which consists of a set of embedded parts related to different resolutions and quality levels can be easily adapted (reordered) to given bandwidth and resolution requirements by a simple parser without decoding the bitstream. FS-SPIHT is a very good candidate for image communication over heterogenous networks which requires high degree of scalability from image coding systems.

10

Multiresolution image denosing based on wavelet transform

Hassanien A. E., El Henawy I., Own H.

Machine Graphics and Vision

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2001

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Vol. 10, No. 2

221-230

EN

Wavelet-based image denoising is a very attractive tool for analysis and syntesis of functions. It enables us to divide a complicated function into several simpler ones and study them individually. In this paper, we presents a new image-denoising algorithm based on multiresolution local contrast entropy of wavelet coefficients. Depending on the propability distribution of the noise in the wavelet coeficients, a new adaptive threshold estimation algorithm is introduced. This threshold enables the proposed algorithm to adapt unknown smoothness of denoised images. The experiments performed confirm that the proposed algorithm is capable of achieving good results for additive white guassian noise.