Vol. 8 (1999): Abstracts of Papers | Machine Graphics and Vision

No. 1
No. 2: Special Issue on Graph Transformations in Pattern Generation and CAD
No. 3
No. 4: Special Issue on Image Processing Methods in Applied Mechanics

Machine GRAPHICS & VISION, Vol. 8 (1999), No. 1:

Neumann L., Neumann A., Szirmay-Kalos L.:
Reflectance models by pumping up the albedo function.
MGV vol. 8, no. 1, 1999, pp. 3-17.

The paper introduces a method, called the albedo pumping-up, to derive new, physically plausible BRDFs from an existing one or from any symmetric function. This operation can be applied recursively arbitrary number of times. An important application of this operation is the transformation of the Phong and Blinn models in order to make them produce metallic effects. The paper also examines the albedo function of reflectance models and comes to the conclusion that widely used models violate energy balance at grazing angles.
Key words: reflectance function, BRDF representation, albedo function, energy balance, metal models, perceptual based fitting.

Wang Y., Bhattacharya P.:
Hierarchical correspondence of gray connected components in stereo images using epipolar geometry.
MGV vol. 8, no. 1, 1999, pp. 19-54.

In this paper, we propose a new feature-based method for stereo matching. The matching primitives that we use are the boundaries of certain parameter-dependent connected components of images. Under certain assumptions, there is a one-to-one correspondence between subsets of the points on the boundaries of connected components of stereo pairs. This correspondence can be identified using the epipolar geometry. Using matched boundaries, we can identify the corresponding connected components determined by the boundaries. By changing the values of the parameters, we obtain a hierarchy of connected components in a gray image, which in turn provides us with a hierarchical stereo correspondence method.
Key words: stereo correspondence, hierarchy, connected component, gray image, epipolar geometry.

Van Sint Jan S., Clapworthy G., Rooze M.:
A computer graphics system for the analysis of joint kinematics.
MGV vol. 8, no. 1, 1999, pp. 55-62.

The paper describes a system to diagnose disorders related to joint kinematics. By the use of a multidisciplinary approach, including medical imaging, three-dimensional reconstruction, kinematics and computer graphics, the system provides simultaneous visualization of both the three-dimensional morphology and the three-dimensional motion of a joint for which the kinematics parameters have been experimentally interpolated from medical imaging. Applications planned for the future include both an interactive diagnosis system for joint disorders and a system to illustrate normal and pathological joint kinematics to medical students.
Key words: medical imaging, 3D reconstruction, diagnose disorders, joint kinematics.

Li X., Zheng N.:
Warping-based interactive visualization on PC.
MGV vol. 8, no. 1, 1999, pp. 63-76.

Image-based rendering produces realistic-looking 3D graphics at relatively low cost. In this paper, an original post-warping rendering system using more than two sample views to derive a new view is presented. Owing to the warp-based compression and incremental computation, the computational expense is less or no more than conventional two-image synthesis approaches. The procedure consists of three steps. First, a set of sample images is selectively acquired with conventional geometry rendering or volume rendering or from photographs of the real scene. Next each of the neighboring image pair is compressed by warping transformation based on redundant pixels between them. Finally, the compressed sample images are directly re-projected to produce new images. In order to improve the speed more, an incremental warping flow is developed, which is computationally less expense. With the method described above, animation faster than fifty frames (300$\times$ 300) per second is achieved on PC.
Key words: image-based rendering (IBR), warping transformation, field of view (FOV), compressing data.

Bisoi A.K., Mishra J.:
Fractal images with inverse replicas.
MGV vol. 8, no. 1, 1999, pp. 77-82.

Fractals are famous for their beauty and fractal techniques are employed for less storage space requirement while storing images. The fractals contain their scaled down, rotated and skewed replicas embedded in them. The concept of multiple reduction copy machine (MRCM) has been used for creating fractals since long. A modified MRCM has been designed to generate fractal images having inverse replicas embedded in them along with the scaled down, rotated, translated and skewed replicas. We restrict our experiments only to binary images in order to compare the results with the existing regular fractals. This paper only demonstrates the generation of fractal images with inverse replicas.
Key words: multiple reduction copy machine, fractals, inverse replica.

Zheng N., Song W., Li W.:
Image coding based on flexible contour model.
MGV vol. 8, no. 1, 1999, pp. 83-94.

This paper presents a new scheme of model-based image coding method. First a new image model called Flexible Contour Model that can extract features of nonrigid objects in images is proposed, then we deduce the fast algorithms for calculating the parameters of the model and for matching the model to images. Furthermore the combination of the model with multiscale analysis and the triangulation of the model has been studied. As a result, reconstruction of original images with high compression rate and unnoticeable distortion was obtained.
Key words: image compression, facial image compression, flexible contour model, model based image coding.

Starosolski R.:
Fast, robust and adaptive lossless image compression.
MGV vol. 8, no. 1, 1999, pp. 95-116.

For applications like image transmission or storage we need fast and adaptive lossless compression algorithms. A speed improvement must not be achieved at the expense of significant compression ratio deterioration or too big memory requirements. The robustness, which may be defined as a performance on the worst case of data, is very important in practical applications.
Presented algorithm uses the traditional decorrelation-statistical compression scheme of adaptive image compression. We introduce many modifications to improve speed and robustness of the algorithm. Firstly, we vastly increase the processing speed by altering the traditional statistical compression scheme. Instead of coding each symbol and updating the data model each time a symbol is coded, we update the model only after coding some symbols. We construct a robust family of codes based on the Golomb codes and adapted to the real image data - that is to the finite alphabet of not ideally exponential symbol distribution. In order to quickly adapt to the specific image data characteristic the data model uses a variable number of context buckets and is updated with a variable frequency -- starting with a single collective context bucket and a full model update.
The introduced modifications allow us to increase the processing speed by a factor of two or more at no or negligible compression ratio deterioration. Our algorithm limits worst-case local and global data expansion and has strictly bounded memory requirements. We present the experimental results of introduced modifications and the comparison to some well-known algorithms.
Key words: lossless image compression, image coding, adaptive algorithms, O(n), statistical compression.

Szkodzik A., Materka A.:
Automatic generation of nearly optimal decision trees for handwritten character recognition.
MGV vol. 8, no. 1, 1999, pp. 117-126.

This paper presents results of applying decision trees to printed and handwritten character recognition. An automatic feature generation method was employed during the construction of the trees, which improved the recognition rate for the testing set. This learning technique significantly reduces the drawback of the tree classifiers that is their rapid error accumulation with depth, while it does not influence the size of trees. It was shown that the proposed approach gives better results than increasing the size of the training sets used for construction of the trees. The recognition rate above 97% was obtained by means of a parallel classifier built of multiple decision trees despite no advanced preprocessing of input characters (like skeletonization or slant reduction) was performed.
Key words: optical character recognition, automatic feature generation, feature extraction, decision tree, parallel classifier.

Stapor K.:
Recognition of cartographic symbols based on a structural model of a shape.
MGV vol. 8, no. 1, 1999, pp.129-142.

This paper presents a method for recognition of cartographic symbols that is based on a structural model of a general 2D-curve. The presented method utilizes an algebraic description of a curve structure described in [7]. Feature extraction is based on the vectorized skeleton generated by the non-pixelwise thinning algorithm, [14]. From such representation, a structural description of a cartographic symbol is obtained. Finding a match between a model and a given, unknown 2D-shape, is performed through the devised, hybrid procedure, consisting of the structural matching algorithm with followed distance calculation in a parameter space. Experimental results shows that the method gives satisfying recognition rates.
Key words: cartographic symbol recognition, feature extraction, structural description, shape analysis, matching.

Titov V., Tevs S., Shirabakina T.:
Optical recognition system for radioelectronic products.
MGV vol. 8, no. 1, 1999, pp. 143-152.

Nowadays optical recognition systems (ORS) are widely used in recognition and inspection of various radioelectronic products. In this paper the principles of ORS creation are presented. The principles of fuzzy adaptation and fuzzy recognition are also reported. Our fuzzy algorithms yield new insight into design of optical systems. These algorithms can process the low contrast images in real-time mode. They can recognise the multicontour object, which can be turned around, moved from the frame centre and scale changed.
Key words: optical inspection systems, recognition, primary image processing, product quality control.

Machine GRAPHICS & VISION, Vol. 8 (1999), No. 2:

Special Issue on Graph Transformations in Pattern Generation and CAD.
Special Issue Editor: Ewa Grabska.

Salotti M.:
Graph representation for the description and recognition of patterns: some issues.
MGV vol. 8, no. 2, 1999, pp. 155-168.

We propose a new approach for the representation and recognition of patterns. The primitives extraction process is based on the properties of an original contour profile. Corners, curves and line segments can easily be detected. The main characteristic of the method is the possible overlap among primitives, which allows multiple descriptions of ambiguous parts. The relation "is followed by" is the most important of the graph. As the graph representation is very simple, model graphs can be intuitively defined by hand. The recognition stage consists in finding the greatest common structure between a model graph and an input graph. Some results illustrate the method.
Key words: pattern representation and recognition, primitives extraction, model graph, input graph.

Pariès A., Wendling L.:
Directed acyclic graph compression of labelled trees.
MGV vol. 8, no. 2, 1999, pp. 169-174.

A new algorithm for compressing labelled trees is proposed in this paper. This algorithm allows to obtain a Directed Acyclic Graph (DAG) from a labelled tree in linear time. An experimental study is also given.
Key words: algorithms, labelled tree, compression.

Göttler H., Liu X.:
A programming environment for graphics based on graph grammars and Java.
MGV vol. 8, no. 2, 1999, pp. 175-194.

The paper reports on the system OOPAGGDE which can be used in a wide area of visual programming. This field encompasses diagram techniques in the field of software engineering and the generation of "nice" patterns as well. The theoretical basis of OOPAGGDE are graph grammars enriched with features like object-orientation, programmability, and attributes. How OOPAGGDE works is shown by a small example, the creation of "Lindenmayer trees".
Key words: programmed attributed graph grammars, object orientation, graphical modelling.

Lladós J., Martí E.:
A graph-edit algorithm for hand-drawn graphical document recognition and their automatic introduction into CAD systems.
MGV vol. 8, no. 2, 1999, pp. 195-211.

In this work, a graph-based algorithm for symbol recognition in hand-drawn architectural plans has been described. The algorithm belongs to a prototype of man-machine interface consisting in the introduction of hand-drawn designs to a CAD system. Documents and symbol prototypes are represented in terms of a Region Adjacency Graph (RAG) structure. Hence, the localization of symbol instances in documents is performed by an error-tolerant subgraph isomorphism algorithm that looks for the minimum cost edit sequence that transforms a model graph to an input one. In this paper we describe this algorithm and the set of graph edit operations designed to transform RAGs. The main idea of the algorithm is to formulate the distance between two RAGs in terms of the string edit distance between the boundary strings of the corresponding graph regions. The main advantage of the algorithm is its ability to cope with distorted structures and its invariance to rotation, translation and scaling.
Key words: graphics recognition, graph matching, edit distance, CAD systems, structural pattern recognition.

Strug B.:
Application of attributed graph grammars to the synthesis of visual models of plants.
MGV vol. 8, no. 2, 1999, pp. 213-229.

Over the last years a rapid development of modelling and visualization methods of biological structures has taken place. In this paper I propose a method based on graph grammars. A method of modelling as well as of visualization is described. The implementation of this method is also presented. The implementation and a number of examples are shown for the selected case of two families of cactuses.
Key words: graph transformation, design, modelling plants, rendering.

Lumini A., Maio D., Maltoni D.:
Inexact graph matching for fingerprint classification.
MGV vol. 8, no. 2, 1999, pp. 231-248.

In this work we introduce a new structural approach to automatic fingerprint classification. The fingerprint directional image is partitioned into homogeneous connected regions according to the fingerprint topology. A relational graph is constructed in order to compactly summarize the fingerprint macro-structure resulting from the partitioning process. An inexact graph matching technique is adopted to compare this graph with a set of prototype graphs which have been a-priori derived starting from a well-known classification scheme.
Key words: fingerprint classification, directional image, partitioning algorithms, relational graph, inexact graph matching.

Stapor K., Skabek K., Tomaka A.:
Model-based recognition of polyhedral objects from single intensity image using aspect graph.
MGV vol. 8, no. 2, 1999, pp. 249-264.

The method for recognition of polyhedral objects composed of blocks and pyramids from a single 2D--image is presented. The knowledge of an object appearance is provided by an explicit model of a shape composed of a graph representation of aspects, faces and boundary groups. The recognition of an unknown object is performed through graph matching. To avoid a combinatorial expolosion in the search process during recognition statistical properties of the chosen primitives have been used.
Key words: 3-D shape recognition, aspect modelling, recognition by parts.

Yadohisa H.:
Graphical representation of asymmetry in three-way dissimilarity data.
MGV vol. 8, no. 2, 1999, pp. 265-279.

Vector models for representation of asymmetry in three-way (dis)similarity data are proposed. We evaluate several different data matrices corresponding to observations, individuals and so on. We then propose models for representation of asymmetry on the basis of the INDSCAL (Carroll and Chang, 1970) and GEMSCAL (Young, 1984) models.
Key words: asymmetry, data visualization, (dis)similarity, GEMSCAL, INDSCAL, MDS.

Machine GRAPHICS & VISION, Vol. 8 (1999), No. 3:

Gorelik A. G.:
Logical functions of arbitrary vicinities of geometric objects.
MGV vol. 8, no. 3, 1999, pp. 285-294.

For Constructive Solid Geomety (CSG) models of the complex geometric objects, the definition of the logical functions of arbitrary vicinities is proposed. These functions are equal to the initial functions in some vicinities from the viewpoint of membership tests. The new functions are much simpler than initial ones and allow to significantly accelerate basic membership tests on CSG models.
Key words: constructive solid geometry, boundary representation, three-valued calculus.

Rataj A.:
Finding outlines of objects in raster images.
MGV vol. 8, no. 3, 1999, pp. 295-312.

The object of the presented method is to extract structural information about a raster image. The structural information consists of strings of pixels describing outlines of objects. Various definitions of an object areused.
Key words: outline extraction from color images.

Rataj A.:
Approximating outlines of objects in raster images.
MGV vol. 8, no. 3, 1999, pp. 313-339.

The object of the presented method is to approximate outlines of objects found in a raster image. The input outlines are represented by strings of pixels, and the approximated output outlines are represented by curves. This method is meant to reduce distortion of outlines of objects, caused by a raster structure of an image.
Key words: raster curve approximation, outlines in color images.

Stapor K.:
A vectorized thinning algorithm for handwritten symbols recognition.
MGV vol. 8, no. 3, 1999, pp. 341-352.

In this paper a non-pixelwise thinning algorithm of binary line images, called vectorized thinning is proposed. The presented algorithm produces a skeleton of a 2D-object which is performed in three steps: (1) links finding and simple region extraction, (2) complex region extraction and multiple points finding, (3) transformation into vectorized skeleton. As opposed to other thinning algorithms, the obtained skeleton is obtained in vector form, particularly suitable for further structural recognition of an object. The proposed vectorized thinning algorithm has been used at the feature extraction in the cartographic symbol recognition from scanned, geodesic maps, with much better results than using other, pixelwise thinning methods. The main advantages of the proposed thinning algorithm lie in better extraction of multiple points representing corners, branch or crossing regions of 2D objects, and less sensitivity to a boundary noise which is one of the main problems in pixelwise thinning algorithms.
Key words: hinning algorithm, skeleton, medial axis, feature extraction, shape analysis.

Xu Z., Toncich D., Stefani S.:
Adaptive edge-preserving filtering.
MGV vol. 8, no. 3, 1999, pp. 353-365.

The research, upon which this paper is based, focused upon the accurate acquisition of images that could be used for precision measurement processes. These precision measurements would either be used as a part of an inspection system or as a feedback mechanism to improve process quality. In this paper, a novel adaptive filtering method is proposed for the purpose of reducing noise and removing spurious pixel values on images, acquired within a manufacturing environment without blurring edges or displacing identified boundaries. The paper documents the experimental outcomes derived from testing this novel filtering technique.
Key words: vision systems, image processing, filtering.

Borkowski A., Grabska E., Hliniak G.:
Function-structure computer-aided design model.
MGV vol. 8, no. 3, 1999, pp. 367-381.

This paper considers defining functional requirements of the designed object and transforming them into the object structure. The proposed Function Structure Editor (FSE) enables to bridge the gap between the design specification and the object structure. When utilising FSE the designer uses graph operations which are automatically transformed into graph rules allowing one to generate potential solutions of a given design problem. Relations between graph operations and graph rules are formulated in the form of certain statements. The proposed methodology is illustrated by examples of designing the teapot and the floor-layout of the house.
Key words: design problem, object structure, design specification, graph rules, graph operations, function structure editor.

Mayoh B.:
Evolutionary pattern grammars in artificial intelligence and design.
MGV vol. 8, no. 3, 1999, pp. 383-394.

Evolutionary algorithms are a creative way of finding new designs. Grammars are a precise, concise way of describing the structure of possible designs. Patterns capture the required symmetries in designs. In this paper we show that these three ideas fit neatly together and give a powerful tool for design and other AI problems.

Toppano E.:
Using graph transformations to support multilevel reasoning in engineering design.
MGV vol. 8, no. 3, 1999, pp. 395-425.

It is generally admitted that expert designers work with design entities - specifications and design solutions - described at different levels of abstraction, detail or generality and can switch from one representation level to another in a very effective and flexible way. Moreover, they often use graphic representations such as sketches and diagrams to externalize their ideas about the designed artefact during the course of a design process. The paper proposes a general framework for multilevel representation of design products based on the use of plex structures. In this frame we illustrate a set of graph transmutations that can be used to generate or modify design solutions during the design development stage. Our aim is to address these issues with the expectation that the results would provide insights into what sort of computational tool should support the cognitive need for multilevel reasoning and how. It is argued that by providing ICAD systems a stronger cognitive foundation we can guarantee to them a greater success among end users.
Key words: conceptual schemes, model transmutations, design.

Nieniewski M.:
Morphological method for extraction of microcalcifications in mammograms for breast cancer diagnosis.
MGV vol. 8, no. 3, 1999, pp. 427-448.

The paper presents a new morphological method for extraction of microcalcifications in mammograms for breast cancer diagnosis. The proposed method is based on the use of the morphological detector together with morphological pyramid for detection of local irregularities of brightness in a wide range of sizes and shapes. The binary maps obtained from the pyramid indicate locations of the candidates for microcalcifications in the mammogram. Independently, the gray level reconstruction of the original mammogram is carried out in order to obtain the exact shape of h-domes, which depict regional maxima (hills) of brightness in the image. By thresholding the image of h-domes, one obtains a binary map of h-domes. Subsequently, a binary reconstruction is carried out, in which the binary map of h-domes is used as a mask, and the map obtained from the pyramid after some modification is used as the marker. As a result of the reconstruction, the required map of microcalcifications is extracted. A number of tests of the proposed method on various mammograms are presented.
Key words: breast cancer diagnosis, mammograms, microcalcification detection, microcalcification extraction, morphological pyramid, morphological reconstruction.

Nowinski W.L.:
Analysis of medical images by means of brain atlases.
MGV vol. 8, no. 3, 1999, pp. 449-468.

This paper: (i) introduces the taxonomy of the use of electronic brain atlases, (ii) identifies representations, features and tools available at various levels of this taxonomy structure, and (iii) demonstrates how the brain atlases can be applied for analysis of medical images focusing on stereotactic functional neurosurgery and human brain mapping.
Key words: brain atlas, neuroimaging, stereotactic functional neurosurgery, human brain mapping.

Vilanova A., König A., Gröller E. :
VirEn: a virtual endoscopy system.
MGV vol. 8, no. 3, 1999, pp. 469-487.

Virtual endoscopy systems are promising tools for the simplification of daily clinical procedures. In this paper, a conceptual framework for a virtual endoscopy system (VirEn) is proposed, which is intended to be an interactive system. So far, our efforts have concentrated on some elements of the system. The generation of an optimal path for the automated navigation is one of them. Extensions to existing thinning algorithms used to generate the optimal path are presented and discussed. First results produced with VirEn are shown.
Key words: volume visualization, virtual endoscopy, navigation, thinning.

Machine GRAPHICS & VISION, Vol. 8 (1999), No. 4:

Special Issue on Image Processing Methods in Applied Mechanics.
Special Issue Editor: Tomasz A. Kowalewski.

Excerpt from the Guest Editorial of the Special Issue:

This special issue of Machine GRAPHICS & VISION presents a selection of 16 papers, preliminary versions of which were presented during the Euromech 406 colloquium on Image Processing Methods in Applied Mechanics held in Warsaw on May 6-8, 1999. Intention of the colloquiium was to create a forum in which both fluid and solid mechanics groups, working separately on the development and application of the same image processing and acquisition methods, would find a common ground.

Reinecke H., Mo M., Grant I.:
Image processing problems in fluid dynamics: selected digital procedures.
MGV vol. 8, no. 4, 1999, pp. 493-507.

Image processing in fluid dynamics, often in conjunction with quantitative flow visualisation, is an important tool used, in both computational and experimental studies, for analysis and data presentation. The development of inexpensive, powerful image capture and processing hardware is being complemented by imaginative software development, utilising ideas often evolved from earlier analogue, optical, and electronic image processing methods while evolving new concepts based on advances in computation and digital image processing.
Key words: image filtering, colour, the Fourier transform, wavelet transform, flow visualisation.

Carlomagno G.M.:
Quantitative infrared thermography and convective heat transfer measurements.
MGV vol. 8, no. 4, 1999, pp. 509-528.

When using infrared thermography to perform convective heat transfer measurements, it is necessary to restore the thermal images because of their degradation which is due to the heat flux sensor, the environment and the temperature sensor. This problem is addressed herein. Besides, infrared thermography is employed to study three different fluid flow configurations; in particular: the heat transfer to a jet centrally impinging on a rotating disk; the complex heat transfer pattern associated with a jet in cross-flow; and the heat transfer distribution along a 180 degree turn channel. Attention is focused on the capability of the infrared thermography to deal with complex flow dynamics, the interaction between the jet and the boundary layer linked to the disk rotation, heat transfer developing in the wake region of a jet in cross-flow, high heat transfer regions and recirculation bubbles in a 180 degree turn channel.
Key words: image restoration, infrared thermography, convective heat transfer.

Aanen L., Telesca A., Westerweel J.:
Measurement of turbulent mixing using PIV and LIF.
MGV vol. 8, no. 4, 1999, pp. 529-543.

Experimental investigation of turbulent mixing requires the simultaneous measurement of the instantaneous velocity and concentration fields. The velocity is measured by means of particle image velocimetry (PIV), and the concentration by means of laser induced fluorescence (LIF). A combined measurement technique was developed in which we use PIV and LIF simultaneously, without influencing each other. To test the reliability and precision of the technique we took measurements on the mixing of a point source placed at the centerline of a fully-developed turbulent pipe flow. The experimental results are compared against results of a direct numericalsimulation, and against the analytical result for the mixing of a point source in homogeneous turbulence. The agreement with the experimental results is satisfactory, although there remains a small deficit in the mass-balance equation. It is conjectured that this is due to the finite resolution of the experimental data and the high intermittency of the concentration.
Key words: PIV, LIF, turbulent mixing, velocity and concentration measurement.

Cenedese A., Pocecco A., Querzoli G.:
Principal components analysis for PIV applications.
MGV vol. 8, no. 4, 1999, pp. 545-552.

An application of the PIV technique based on cross-correlation method is described. In order to obtain single-exposed images from a double-exposed colour image, the separation in RGB components is performed and the effects on the PIV analysis are evaluated. A method to obtain uncorrelated colour bands, based on Principal Components Analysis, is proposed for PIV applications which utilises colour codes information.
Key words: RGB images, color PIV, cross-correlation.

Verestóy J., Chetverikov D., Nagy M.:
Digital particle image velocimetry: a challenge for feature based tracking.
MGV vol. 8, no. 4, 1999, pp. 553-569.

Motion tracking is an important step of the analysis of flow image sequences. However, Digital Particle Image Velocimetry (DPIV) methods rarely use tracking techniques developed in computer vision: FFT and correlation are usually applied. Two major types of motion estimation algorithms exist in computer vision, namely, the optical flow and the feature based ones. Promising results have been recently obtained by optical flow techniques. In this paper, we examine the applicability of feature tracking algorithms to digital PIV. Two feature based and one optical flow based tracking algorithms are compared. Flow measurement and visualisation results for standard DPIV sequences are presented.
Key words: digital PIV, computer vision, feature based motion tracking, optical flow.

Fei R., Gui L., Merzkirch W.:
Comparative study of correlation-based PIV evaluation methods.
MGV vol. 8, no. 4, 1999, pp. 571-578.

Several correlation-based PIV evaluation methods are compared by applying them to the evaluation of simulated PIV recordings, in which the particle images are distributed stochastically and have a Gaussian gray value distribution. The influence of particle image displacement and the influence of interrogation window size on the evaluation accuracy in uniform and in non-uniform flow were investigated. In all these cases the best results in terms of a statistical error are obtained with the MQD method.
Key words: PIV evaluation algorithm, cross-corelation.

Camussi R., Stella A., Guj G., Kowalewski T.A.:
Large-scale structures forming in a cross flow: particle image velocimetry conditional analysis.
MGV vol. 8, no. 4, 1999, pp. 579-595.

A conditional Particle Image Velocimetry (PIV) acquisition technique and averaging procedure are developed to study coherent structures formed by the interaction between a jet and a cross-stream. The experiment is conducted in a water tunnel, the water transversal jet is perturbed by a mechanical device. Measurements are performed at Reynolds number 100 and cross-flow velocity ratio ranging from 2.0 to 4.5. Sequences of images are acquired synchronously to the perturbation so that a statistical process may be applied to obtain average velocity and vorticity in a selected cross-section of the flow. The averaged fields and the instantaneous images together with flow visualizations by Laser Induced Fluorescence (LIF) technique are used to interpret behaviour of the large-scale vortices generated in the cross-flow experiment.
Key words: PIV, cross flow, coherent flow structures.

Fornalik E., Nakabe K., Yamamoto Y., Chen W., Suzuki K.:
Visualization of heat transfer enhancement regions modified by the interaction of inclined impinging jets into crossflow.
MGV vol. 8, no. 4, 1999, pp. 597-609.

Visualization of heat transfer enhancement regions was made for a pair of jets obliquely discharged into a crossflow. The examination of interaction between the two oblique jets and the comparison of different flow patterns caused by the vertically and obliquely issued jets were provided. The temperatures of the target surface were visualized with thermochromic liquid crystal sheets. The colours of the liquid crystal images taken by a CCD camera were transformed accurately and effectively into the temperatures by means of the neural network technique to obtain Nusselt number distributions on the target surface. Fluorescent dyes were added to the jet fluid to visualize the cross-sectional flow patterns with the light sheet of a laser. The most important parameter used in the present study was the velocity ratio VR of the jet to the crossflow besides the crossflow Reynolds number.
Key words: heat transfer, impinging jet, visualization, neural network, thermochromic liquid crystal.

Kreis T.M.:
Digital holography and holographic interferometry.
MGV vol. 8, no. 4, 1999, pp. 611-624.

Holography is a method for three-dimensional imaging frequently used in metrology and nondestructive testing. Up to now both the generation of the holograms as well as the reconstruction of the wavefields was performed optically. In digital holography optically generated Fresnel or Fraunhofer holograms are recorded by a CCD array. The reconstruction of the wavefields is done digitally by image processing methods based on the mathematical concept of the diffraction integral. Two approaches to its numerical solution are the finite discrete Fresnel transform and a procedure employing the convolution theorem. Both approaches result in a complex field from which intensity and phase can be determined. In digital holographic interferometry the sign-correct interference phase distribution is computed with high accuracy by subtraction of two numerically reconstructed phase distributions.
Key words: digital holography, holographic interferometry, Fresnel transform, diffraction integral, three-dimensional imaging.

Andrés N., Arroyo M.P., Quintanilla M.:
Interferometric techniques for measuring flow velocity fields.
MGV vol. 8, no. 4, 1999, pp. 625-636.

Holographic interferometry and digital speckle pattern interferometry as techniques for measuring out-of-plane velocity fields are presented. The feasibility of introducing phase shifting techniques in order to improve the accuracy of holographic interferometry is investigated. The techniques are demonstrated in a Rayleigh-Bènard convective flow.
Key words: fluid velocimetry, holographic interferometry, speckle pattern interferometry.

Vuskovic V., Kauer M., Dual J., Bajka M.:
Method and device for in-vivo measurement of elasto-mechanical properties of soft biological tissues.
MGV vol. 8, no. 4, 1999, pp. 637-654.

We present a method to determine elasto-mechanical properties of soft biological tissues, and a device able to perform the required measurements in-vivo. The device permits the controlled application of vacuum to small spots of organic tissue and registers the small deformation caused, during the whole measurement process. Deformation is measured with a vision based technique and the grabbed images are processed in real-time to avoid storage problems. We model biological tissue with a hyperelastic quasilinear viscoelastic material law and determine the unknown material parameters via inverse finite element methods.
Key words: contour extraction, in-vivo measurement, elasto-mechanical properties, soft tissue aspiration, inverse finite element, hyperelastic.

Gourinat Y., Pramono A.S.:
Educational applications of photoelastodynamics for solid dynamics and dynamics of structures.
MGV vol. 8, no. 4, 1999, pp. 655-666.

This paper presents developments performed on photoelastodynamic bench of ENSICA's Department of Mechanical Engineering. Classical wave, vibrating, shock and rotating parts theories, were compared with colour pictures of isochromatic lines obtained with rapid camera and urethane resin specimens. For nonlinear shock and large deflection, explicit code LSDYNA has been used. Then, the facility has been used to analyse dynamic work of gears for power transmission, in comparison with numerical computations. These developments have lead to demonstrations, now included in engineering general courseware, about stress analysis, theory of elasticity and dynamics of structures. Gear visualisations have been included in integrated France-Canada developments concerning dynamics of transmission, as a complement to theoretical models and experimental acoustic analysis of functioning gears.
Key words: dynamic photoelasticity, dynamics of solids, dynamics of plates, dynamics of beams gears.

Lörcher M., Schmitz D., Mewes D.:
Tomographic measurement techniques - visualization of multiphase flows.
MGV vol. 8, no. 4, 1999, pp. 667-679.

A tomographic measurement technique is applied for visualization of the local void fraction in the two phase flow of air and water in the mixing chamber of a two-phase-nozzle. With this measurement technique a high spatial and temporal resolution can be achieved. The measured physical property is the electric conductivity of the water. The conductivity is measured with pairs of wires strained in the investigated cross section. The measurement values are proportional to the relative liquid fraction. With an algebraic reconstruction technique (ART) the field of the liquid fraction in the investigated cross-section is calculated from the measurement values. The quality of the reconstruction is increased by a-priori-knowledge.
Key words: tomographic measurement, multiphase flow, void fraction, wire-mesh sensor.

West R.M., Bennett M.A., Jia X., Ostrowski K.L., Williams R.A.
Flow-regime discrimination in bubble columns using electrical capacitance tomography .
MGV vol. 8, no. 4, 1999, pp. 681-690.

Electrical capacitance tomography has been used to image a bubble column. Sets of linear back projection tomograms are then analysed to yield gas hold-up values and to determine flow regime in a traditional manner. Further analysis is performed producing a statistic (heterogeneity index for tomograms) that is independent of the average hold-up. This is used to provide an alternative and superior means to determine flow regime.
Key words: electrical capacitance tomography, heterogeneity index for tomograms.

Lorang T., Schuster E., Gengler M., Prinz M.:
Optimising ray tracing for visualisation of volumetric medical image data.
MGV vol. 8, no. 4, 1999, pp. 691-697.

The presented optimizations provide an approach to fast rendering of medical volume data. They are based on the ray casting algorithm, which is substantially speeded up with regard to voxel addressing and interpolation.
Key words: interpolation, volume rendering, volumetric medical data.

Nieniewski M., Chmielewski L., Jozwik A., Sklodowski M.:
Morphological detection and feature-based classification of cracked regions in ferrites.
MGV vol. 8, no. 4, 1999, pp. 699-712.

Automatic quality inspection of ferrite products is difficult as their surfaces are dark and in many cases covered with traces of grinding. A two-stage vision system for detection and measurement of crack regions was devised. In the first stage the regions with strong evidence for cracks are found using a morphological detector of irregular brightness changes with subsequent morphological reconstruction. In the second stage the feature-based k-Nearest Neighbors classifier analyzes the pixels indicated in the first stage. The classifier is optimized by using procedures of reclassification and replacement carried out on the reference set of pattern pixels to achieve a low error rate and a maximum speed of computation.
Key words: morphological defect detection, surface defects, morphological reconstruction, defect classification, k-Nearest Neighbors classification, parallel classifier.

Furtak J.:
Space orientation based on image from mobile camera.
[Dissertation Abstract]
MGV vol. 8, no. 4, 1999, p. 713.

Zorski W.:
Segmentation methods of digital images based on the Hough transform.
[Dissertation Abstract]
MGV vol. 8, no. 4, 1999, p. 714.

Hliniak G.:
Graph operations and graph rewriting in graphic design.
[Dissertation Abstract]
MGV vol. 8, no. 4, 1999, p. 715.

Revievers' index

Authors' index

Contents of volume 8, 1999