• Journal of Korea Multimedia Society
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• v.5 no.4
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• pp.458-467
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• 2002

There has been proposed many simplification algorithms for effectively decreasing large-volumed polygonal surface data. These algorithms apply their own cost function for collapse to one of fundamental simplification unit, such as vertex, edge and triangle, and minimize the simplification error occurred in each simplification steps. Most of cost functions adopted in existing works use the error estimation method based on distance optimization. Unfortunately, it is hard to define the local characteristics of surface data using distance factor alone, which is basically scalar component. Therefore, the algorithms cannot preserve the characteristic features in surface areas with high curvature and, consequently, loss the detailed shape of original mesh in high simplification ratio. In this paper, we consider the vector component, such as surface orientation, as one of factors for cost function. The surface orientation is independent upon scalar component, distance value. This means that we can reconsider whether or not to preserve them as the amount of vector component, although they are elements with low scalar values. In addition, we develop a simplification algorithm based on half-edge collapse manner, which use the proposed cost function as the criterion for removing elements. In half-edge collapse, using one of endpoints in the edge represents a new vertex after collapse operation. The approach is memory efficient and effectively applicable to the rendering system requiring real-time transmission of large-volumed surface data.

• Journal of the Korea Computer Graphics Society
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• v.14 no.3
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• pp.11-17
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• 2008

Many methods which represent complex surfaces using height map without a number of vertex have been researched. However, a single layer height map cannot present more complex objects because it has only one height value on each position. In this paper, we introduce the new approach to render more complex objects, which are not generated by single layer height map, using multi layer height map. We store height values of the scene to each texture channel by the ascending order. A pair of ordered height values composes a geometry block and we use this property. For accurate ray search, we store the highest value in odd channels and the lowest value in even channels to generate quad tree height map. Our ray search algorithm shows accurate intersections between viewing ray and height values using quad tree height map. We solve aliasing problems on grazing angles occurred in previous methods and render the result scene on real-time.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.7
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• pp.629-638
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• 2000

The main difference between mono-volume rendering and multi-volume rendering is data intermixing. In this paper, we first propose a selective rendering method for fast visualizing specific volume according to the surface level and then present data intermixing method for multiple volumes. The selective rendering method is to generate distance transformed volume using a distance transform to determine the minimum distance to the nearest interesting part and then render it. The data intermixing method for multiple volumes is to combine several volumes using intensity weighted intermixing method, opacity weighted intermixing method, opacity weighted intermixing method with depth information and then render it. We show the results of selective rendering of left ventricle and right ventricle generated from EBCT cardiac images and of data intermixing for combining original volume and left ventricular volume or right ventricular volume. Our method offers a visualization technique of specific volume according to the surface level and an acceleration technique using a distance transformed volume and the effective visual output and relation of multiple images using three different intermixing methods in three-dimensional space.

• Journal of Korea Multimedia Society
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• v.8 no.4
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• pp.554-568
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• 2005

We suggest the dynamic stroke generation algorithm that provides frame-to-frame coherence in 3D non-photorealistic animations. We use 3D particle system to eliminate the visual popping effect in the animated scene. Since we have located particles on the 3D object's surface, the coherence is maintained when the object or the camera is moving in the scene. Also, this algorithm maintains the coherence when camera is zooming in/out. However, the brush strokes on the surface also zoom in/out. This result(too large or too small brush strokes) can not represent hand-crafted brush strokes. To remove this problem, we suggest stroke generation algorithm that dynamically maintains the number of brush stroke and its size during camera zoom in/out.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.3
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• pp.147-156
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• 2006

Physically-based simulation modeling is to simulate the real world by using physical laws such as Newton's second law of motion, while other modelings use only geometric Properties. In this paper, we present a real time simulation of stone skipping by using the physically-based modeling. We also describe interaction of a stone on the surface of water, and focus on calculating the path of the stone and the natural phenomena of water The path is decided by velocity of the stone and drag force from the water The motion is recalculated until the stone is immersing into the water surface. Our simulation provides a natural motion of stone skippings in real time. And the motion of stone skippings are generated by give interactive displays on the PC platforms. The techniques presented can easily be extended to simulate other interactive dynamics systems.

• Archives of design research
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• v.15 no.4
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• pp.77-86
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• 2002

3D computer applications provide various functions such as modeling, rendering, animation, lighting and so on. Lighting is the core element in that light visualizes shape and develops characteristics of surface. In spatial design, light is the most important factor in deciding color, texture and illumination level which are the basic factors of spatial design. The purpose of this study is to define the characteristics of lighting in digital space provided by the computer, based on the fact that physical space cannot be separated from digital space, and to show how light in the physical realm relates to computer graphics technologies. This study shows there are following characteristics of light in digital space; iconic light, modifiable surface, shadowless light, 2-dimensional perception, and the particulate aspect of light but not the wave aspect of light. Light in physical or digital space is capable of producing a visual sensation. The experimental space can be realized due to the lack of physics. Further study in new illumination procedures are required as computer media expands.

• Journal of Korea Multimedia Society
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• v.14 no.1
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• pp.133-143
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• 2011

This paper proposes a mobile navigation system which haptically presents the way to go to visually impaired persons. In order to convey the tactile information to the visually impaired persons, we develop a new tactile module with a solenoid, a permanent magnet and an elastic spring. Furthermore, we suggest 2D vibration flow which originates from one point and gradually propagates to other points on a surface of the haptic navigation system. The tactile module and the vibration flow method are incorporated into the proposed haptic navigation system and they stimulate the user's finger pad and palm, respectively. We conduct experiments to investigate that the proposed navigation system haptically provides the direction to the users. From the experimental results, we verify that the proposed system can generate enough tactile sensation to guide the direction to go in real-time.

• Journal of Korea Multimedia Society
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• v.10 no.7
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• pp.846-855
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• 2007

Significant feature extraction in cancer cell image analysis is an important process for grading cell carcinoma. In this study, we propose a method for 3D quantitative analysis of cell nuclei based upon digital image cytometry. First, we acquired volumetric renal cell carcinoma data for each grade using confocal laser scanning microscopy and segmented cell nuclei employing color features based upon a supervised teaming scheme. For 3D visualization, we used a contour-based method for surface rendering and a 3D texture mapping method for volume rendering. We then defined and extracted the 3D morphological features of cell nuclei. To evaluate what quantitative features of 3D analysis could contribute to diagnostic information, we analyzed the statistical significance of the extracted 3D features in each grade using an analysis of variance (ANOVA). Finally, we compared the 2D with the 3D features of cell nuclei and analyzed the correlations between them. We found statistically significant correlations between nuclear grade and 3D morphological features. The proposed method has potential for use as fundamental research in developing a new nuclear grading system for accurate diagnosis and prediction of prognosis.

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.3
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• pp.184-193
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• 2010

This paper proposes a biological iridescence BRDF(Bidirectional Reflectance Distribution Function) compression and rendering method. In the graphics technology, iridescence sometimes is named structure colors. The main features of these symptoms are shown transform of color and brightness by varying viewpoint. Graphics technology to render this is the BRDF technology. The BRDF methods enable realistic representation of varying view direction, but it requires a lot of computing power because of large data. In this paper, we obtain reflection map from iridescence BRDF, analyze color of reflection map and propose representation method by several colorfully concentric circle. The one concentric circle represents beam width of reflection ray by one normal vector. In this paper, we synthesize rough concentric by using several virtually optical normal vectors. And we obtain spectrum information from concentric circles passing through the center point. The proposed method enables IBR(image based rendering) technique which results is realistic illuminance and spectrum distribution by one texture from reduced BRDF data within spectrum.

• Journal of Korea Multimedia Society
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• v.12 no.9
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• pp.1262-1272
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• 2009

In computer graphics, there exist many studies about illumination and radiance for a realistic description of the 3D modeling and rendering. When we see a scene, the scene is lit by a source of light and the radiance of the points by a source in the scene. The radiance has direct light and glight component. The direct light gets lights directly from light source, but the global light gets lights indirectly by interreflections among complicated geometrical components. In this paper, we studied a method for increasing the accuracy of separating direct light and global light components from a scene by using high frequency illumination pattern. For experiments, we applied the separating method of Nayar's and found the best configurations for the separation through the experiments. We improved the separation accuracy of direct and global light by measuring the value of unilluminated area, which depends on the characteristics of object. Furthermore, we enhanced invisible scene of the global light by applying the image filtering technique.