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1

Per-pixel extrusion mapping with correct silhouette

Chahdi Adnane Ouazzani, Ragragui Anouar, Halli Akram, Satori Khalid

Computer Science

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2021

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T. 22 (3)

403–428

EN

Per-pixel extrusion mapping consists of creating a virtual geometry that is stored in a texture over a polygon model without increasing its density. There are four types of extrusion mapping; namely, basic extrusion, outward extru sion, beveled extrusion, and chamfered extrusion. These different techniques produce satisfactory results in the case of plane surfaces; however, when it is about curved surfaces, a silhouette is not visible at the edges of the extruded forms on the 3D surface geometry, as they not take the curvatures of the 3D meshes into account. In this paper, we present an improvement that consists of using curved ray-tracing to correct the silhouette problem by combining per-pixel extrusion-mapping techniques with a quadratic approximation that is computed at each vertex of a 3D mesh.

2

Flat Knitting Loop Deformation Simulation Based on Interlacing Point Model

Jiang G., Lu Z., Cong H., Zhang A., Dong Z., Jia D.

Autex Research Journal

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2017

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Vol. 17, no. 4

361--369

EN

In order to create realistic loop primitives suitable for the faster CAD of the flat-knitted fabric, we have performed research on the model of the loop as well as the variation of the loop surface. This paper proposes an interlacing point-based model for the loop center curve, and uses the cubic Bezier curve to fit the central curve of the regular loop, elongated loop, transfer loop, and irregular deformed loop. In this way, a general model for the central curve of the deformed loop is obtained. The obtained model is then utilized to perform texture mapping, texture interpolation, and brightness processing, simulating a clearly structured and lifelike deformed loop. The computer program LOOP is developed by using the algorithm. The deformed loop is simulated with different yarns, and the deformed loop is applied to design of a cable stitch, demonstrating feasibility of the proposed algorithm. This paper provides a loop primitive simulation method characterized by lifelikeness, yarn material variability, and deformation flexibility, and facilitates the loop-based fast computer-aided design (CAD) of the knitted fabric.

3

Teksturowanie modeli obiektów o złożonej geometrii na podstawie danych z naziemnego skaningu laserowego

Kolecki J., Słota M.

Archiwum Fotogrametrii, Kartografii i Teledetekcji

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2012

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Vol. 24

145--154

PL

Obrazy pozyskane podczas rejestrowanej w trakcie skanowania laserowego chmury punktów pozwalają na tworzenie tekstur modelowanego obiektu, co zwiększa jego zawartość informacyjną. Generowanie tekstur bezpośrednio z pozyskanych obrazów wymaga znajomości parametrów odwzorowania, w którym powstaje zdjęcie. Jednak także informacja o kolorze zapisana jako atrybuty punktów chmury może być wykorzystana do tworzenia tekstur modelowanego obiektu. W takim przypadku chmura punktów może pośredniczyć w tworzeniu obrazów tekstur a cały proces teksturowania odbywa się bez bezpośredniego udziału zdjęć. Celem niniejszych badań było opracowanie metody teksturowania modeli obiektów o złożonej geometrii na podstawie kolorowej chmury punktów pochodzącej z naziemnego skaningu laserowego. Wynikiem pracy jest autorski program do tworzenia tekstur, bezpośrednio w oparciu o kolory RGB chmury punktów. Danymi wejściowymi do programu są chmury punktów w formacie tekstowym oraz obiekty 3D w formacie VRML. W celu przyspieszenia obliczeń w pierwszym kroku wykonywana jest automatyczna segmentacja chmur punktów. Następnie pozyskiwana jest informacja o geometrii płaszczyzn obiektu na podstawie pliku VRML. W efekcie analiz przestrzennych pomiędzy położeniem pikseli na teksturowanych płaszczyznach i chmurą punktów, pozyskiwane są informacje o kolorze pikseli oraz tworzone są tekstury obiektu. Uzyskane wyniki pokazują, że tworzone w ramach prac testowych tekstury mogą posiadać artefakty, będące efektem niedopasowania radiometrycznego zdjęć pozyskiwanych z różnych stanowisk skanowania.

EN

Images taken during point cloud acquisition using laser scanning can be subsequently utilized for generating textures of 3D models. As a result the final amount of information associated with produced model is increased. Automatic texture generation using captured images directly, demands the knowledge about parameters describing image projection. However using the information about color stored as point cloud attributes allows texture generation without using the images directly. The addressed researches aim to develop a method of model texturing. As the final result a simple GUI application has been created in C++. Point clouds in text format and VRML models are used as the input data. In order to speed up the calculation process, in the first step the automatic segmentation of the point clouds is performed. Secondly the information about the object surfaces is obtained based on VRML file and then textures are defined. After performing spatial analysis between pixels position on textured surfaces and point cloud, the pixels color information is computed and texture images are generated. The results show that the test objects textures may be affected by noise resulting from radiometric discrepancies between images acquired from different standpoints.

4

Detection of windows in building textures from airborne and terrestrial infrared image sequences

Iwaszczuk D., Hoegner L., Stilla U.

Archiwum Fotogrametrii, Kartografii i Teledetekcji

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2011

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Vol. 22

215--225

EN

Infrared (IR) images depict thermal radiation of physical objects. Imaging the building façades and the roofs with an IR camera, thermal inspections of the buildings can be carried out. In such inspections a spatial correspondence between IR-images and the existing 3D building models can be helpful. Texturing 3D building models with IR images this spatial correspondence can be created. Furthermore in textures heat leakages can be detected and the heat bridges can be stored together with 3D building data. However, before extracting leakages, the windows should be located. In IR images glass reflects the surrounding and shows false results for the temperature measurements. Consequently, the windows should be detected in IR images and excluded for the inspection. The most common algorithms for window detection were developed for the images in the visual band. In this paper, an algorithm for window detection in textures extracted from terrestrial IR images is proposed. In the first step, small objects have to be removed by scaling down the image (texture). Then in the scaled image, regions are detected using a local dynamic threshold. Morphological operations are used to remove false detections and unify substructures of the windows. For every extracted region, which is a candidate for a window, the center of gravity is calculated. It is assumed that windows on façades are ordered in regular rows and columns. First the points are grouped into rows using histogram of height created from extracted gravity centers. Then masked correlation is used to detect the position and size of the windows. Finally, the gaps in the grid of windows are completed. For the first experiments we use a dataset from densely build urban area captured in Munich, Germany. The IR image sequences were taken from a vehicle driving on the street around the test area. Camera was directed to the building in oblique view. According to the acquisition geometry, no façade could be completely seen in one frame. Therefore, we combine the textures from many frames. To these textures we applied our algorithm for window detection. First results are promising. Applying the method for our test dataset, 79% completeness and 80% correctness could be achieved.

5

Teksturowanie danych z naziemnego skaningu laserowego obrazami termalnymi

Walczykowski P., Dębski W., Kędzierski M.

Archiwum Fotogrametrii, Kartografii i Teledetekcji

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2008

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Vol. 18b

643--650

PL

Przedmiotem artykułu jest połączenie danych ze skaningu laserowego ze zobrazowaniami termalnymi. Obiektem badań wykorzystanym w eksperymencie był monitor komputerowy LG Flatron F900P. Do pozyskania danych przestrzennych wykorzystano skaner laserowy Leica ScanStation 2, a obrazów termalnych kamerę termalną ThermaCam PM575. W wyniku przetworzenia pozyskanych danych uzyskano chmurę punktów powierzchni monitora. Każdy z punktów oprócz współrzędnych X, Y, Z posiadał również informację o temperaturze oraz intensywności odbicia w zakresie długości fali skanera laserowego. Możliwa była więc budowa modelu przestrzennego wzbogaconego o informacje o intensywności odbicia w zakresie widzialnym jak również termalnym. Wykorzystana w eksperymencie metoda łączenia danych ze skaningu laserowego z danymi obrazowymi pozyskanymi w termalnym zakresie widma elektromagnetycznego znacznie rozszerza zakres zastosowań skanerów laserowych i kamer termalnych. Daje możliwość dokładnego pomiaru i analizy obiektów niedostępnych dla człowieka lub takich, gdzie przebywanie człowieka wiąże się z dużym zagrożeniem dla niego.

EN

Terrestrial laser scanning is becoming increasingly widely used in those fields in which it is necessary to obtain fast and precise measurements of complex objects. The essence of the laser scanner function is the measurement of a large quantity of points located in close proximity of each other. The measurement takes place owing to the use of a laser with a defined wavelength and a rotating mirror, by means of which the laser radiation can be pointed in any direction around the instrument. The automated measurement of angles and distances allows determination of spatial coordinates of the measured points of the object. Scanner measurements result in the so-called “point cloud” which usually consists of a few million points. Each of these points possesses very precisely determined spatial coordinates X, Y, Z. Apart from the spatial coordinates, each point contains information about its reflection intensity. This information has many applications, but it has to be borne in mind that it refers only to a very narrow radiation band, equal to the laser wavelength, e.g., for the Leica ScanStation2 the laser is green. Additional, very useful information can be found on digital images, acquired by inbuilt digital cameras. However, the electromagnetic spectrum considered is still in the visible range. The paper presents a possibility of using imagery acquired by means of external sensors (not integrated with the scanner). Imagery acquired with a thermal camera, which represents the temperature distribution of the given object, has been deemed most useful. Thermal images, properly acquired and processed to a unified temperature scale, are placed onto a three dimensional model of the object to create a 3D thermal model. The objective of the paper was to present a connection between laser scanning data and thermal imagery. As a result, a point cloud of the objects surface is obtained. Each point, apart from its X, Y, Z coordinates, includes information about its temperature. This greatly broadens the existing range of applications of laser scanning, as measurements and analyses of inaccessible objects or those posing hazard to humans can be carried out, Doubtless, the advantages of laser scanning combined with the possibility of acquiring images representing spatial distribution of the temperature of the object, greatly broaden the existing range of applications. Novel application include, i.a., aiding the design of new installations, e.g., those sensitive to external thermal conditions. It seems that surveys of technical conditions and wearing rate of installations and other types of industrial objects could be completed with the thermal model much faster and more accurately than by using separate thermograms. By combining thermal images with laser scanning data it is possible to not only read the temperature at any given point of the image, but also to take measurements of length and area.

6

A proposition of mobile fractal image decompression

Nikiel S.

International Journal of Applied Mathematics and Computer Science

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2007

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Vol. 17, no 1

129-136

EN

Multimedia are becoming one of the most important elements of the user interface with regard to the acceptance of modern mobile devices. The multimodal content that is delivered and available for a wide range of mobile telephony terminals is indispensable to bind users to a system and its services. Currently available mobile devices are equipped with multimedia capabilities and decent processing power and storage area. The most crucial factors are then the bandwidth and costs of media transfer. This is particularly visible in mobile gaming, where textures represent the bulk of binary data to be acquired from the content provider. Image textures have traditionally added visual realism to computer graphics. The realism increases with the resolution of textures. This represents a challenge to the limited bandwidth of mobile-oriented systems. The challenge is even more obvious in mobile gaming, where single image depicts a collection of shots or animation cycles for sprites and a backdrop scenery. In order to increase the efficiency of image and image texture transfer, a fractal based compression scheme is proposed. The main idea is to use an asymmetric server-client architecture. The resource demanding compression process is performed on the server side while the client part decompresses highly packed image data. The method offers a very high compression ratio for pictures representing image textures for natural scenes. It aims to minimize the transmission bandwidth that should speed up the downloading process and minimize the cost and time of data transfer. The paper focuses on the implementation of fractal decompression schemes suitable for most mobile devices, and opens a discussion on fractal image models for limited resource applications.

7

Creating entirely textured 3D models of real objects using surface flattening

Jankó Z., Kós G., Chetverikov D.

Machine Graphics and Vision

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2005

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Vol. 14, No. 4

379-398

EN

We present a novel method to create entirely textured 3D models of real objects by combining partial texture mappings using surface flattening (surface parametrisation). Texturing a 3D model is not trivial. Texture mappings can be obtained from optical images, but usually one image is not sufficient to show the whole object; multiple images are required to cover the surface entirely. Merging partial texture mappings in 3D is difficult. Surface flattening coverts a 3D mesh into 2D space preserving its structure. Transforming optical images to flattening-based texture maps allows them to be merged based on the structure of the mesh. In this paper we describe a novel method for merging texture mappings using flattening and show its results on synthetic and real data.