Kyungha Min

An Active Contour Approach to Extract Feature Regions from Triangular Meshes

We present a novel active contour-based two-pass approach to extract smooth feature regions from a triangular mesh. In the first pass, an active contour formulated in level-set surfaces is devised to extract feature regions with rough boundaries. In the second pass, the rough boundary curve is smoothed by minimizing internal energy, which is derived from its curvature. The separation of the extraction and smoothing process enables us to extract feature regions with smooth boundaries from a triangular mesh without users initial model. Furthermore, smooth feature curves can also be obtained by skeletonizing the smooth feature regions. We tested our algorithm on facial models and proved its excellence.

Feature-guided Convolution for Pencil Rendering

We re-render a photographic image as a simulated pencil drawing using two independent line integral convolution (LIC) algorithms that express tone and feature lines. The LIC for tone is then applied in the same direction across the image, while the LIC for features is applied in pixels close to each feature line in the direction of that line. Features are extracted using the coherent line scheme. Changing the direction and range of the LICs allows a wide range of pencil drawing style to be mimicked. We tested our algorithm on diverse images and obtained encouraging results.

A combustion-based technique for fire animation and visualization

In this paper, we present a new fire animation and visualization scheme. The most difficult problem in creating fire animation is how to simulate the mechanism of emitting the light and heat of fire. We attack the difficulty by presenting a simulation scheme for the combustion process in voxelized space where the numerical solution of the classical fluid equations is implemented. Therefore, the combustion process is simulated at each voxel and the amount of heat generated at the voxel is estimated. The generated heat will increase the temperature at the voxel, which results in the increase of the turbulent motion of fire. We also propose a visualization scheme that is based on a photon mapping algorithm in order to render fire and various lighting effects of fire to the environments.

VirtualPhonepad : a text input tool for virtual environments

This paper presents an effective text input tool for virtual environments. The key idea of this paper is that we make use of the text input mechanism of mobile phones. We present a 3 × 3 keypad widget whose user interface is similar to the keypad of mobile phones, where each key on the widget has several characters. We present indexing schemes by which users locate the key on the keypad they want and selection schemes by which users choose the desired character from the characters on the keys of the keypad using diverse input devices.

Technical Section: Pencil rendering on 3D meshes using convolution

We produce various styles of pencil drawings from a 3D triangular mesh using a new two-phase approach based on convolution. First, we generate the noise particles and integration directions required for convolution on the mesh and project them onto the image space. We then use the improved convolution algorithm to integrate the projected noise along the generated integration directions. This scheme produces pencil drawings in different styles, including feature-conveying, monochrome tone-depicting and smooth color-depicting styles, examples of which are provided in this study. This rendering process is temporally coherent. Therefore, it can be used to create drawing-styled animations.

Estimating principal properties on triangular meshes

In this paper, we estimate the principal curvatures of surfaces represented as triangular meshes using a generic model constructed from Euler Formula. Normal curvatures are sampled in the vertices on the direction of a 1- ring neighborhood of a target vertex. Our model is then fitted to a normal curvature graph that connects the pairs of sampled directions and normal curvatures. The principal properties of the surface at the target vertex are estimated from the parameters of the fitted model. We have tested our algorithm on triangular meshes generated from analytic surfaces and show that the errors in our technique are acceptable. We also apply the method to mesh models and discuss degenerate cases.

VirtualQWERTY : textual communication in virtual reality

This paper presents VirtualQWERTY, an effective and powerful textual communication toolkit for virtual reality. The first key idea of this paper is that we exploit the text input mechanism on mobile phones. We present a widget whose user interface is similar to that of the keypad on a mobile phone. Each keypad is composed of several buttons that have several characters. The second key idea of this paper is that the characters on the keypad are arranged by mimicking the character layout of the QWERTY keyboard. These key ideas present users an intuitive and easily learnable textual communication toolkit in virtual reality. In order to exploit VirtualQWERTY, we present an indexing scheme by which users locate the button they want and a selection scheme by which users choose the desired character from the characters on the button using various input devices. After testing this tool by many subjects, we draw an important conclusion about the performance of the textual communication toolkit in virtual environments.

Color Pencil Rendering of Photographs

We produce color pencil drawings from photographs using feature strokes to create the salient linear elements of the picture, and hatching strokes to fill areas. Both types of strokes are generated using line integral convolution (LIC). We improve previous LIC schemes by using feature lines to determine the integration direction, and by introducing grayscale noise into each CMY color channel. Our scheme can produce visually pleasing color pencil drawings in various styles.

Texture-Based Pencil Drawings from Pictures

We re-render a black-and-white picture as a pencil drawing by overlapping pencil textures along the flow of the picture. The pencil textures are generated by overlapping pencil stroke textures captured from real strokes. An input picture is segmented into iso-tonal regions, each of which is textured in a direction determined by an algorithm for detecting smooth and feature-sensitive flow on the picture. Finally, we add contours and feature lines to emphasize salient shapes in the scene. We present several images that show the degree of realism which can be achieved.

Texture-based Hatching for Color Image and Video

We present a texture-based hatching technique for color images and video. Whereas existing approaches produce monochrome hatching effects in considering of triangular mesh models by applying strokes of uniform size, our scheme produces color hatching effects from photographs and video using strokes with a range of sizes. We use a Delaunay triangulation to create a mesh of triangles with sizes that reflect the structure of an input image. At each vertex of this triangulation, the flow of the image is analyzed and a hatching texture is then created with the same alignment, based on real pencil strokes. This texture is given a modified version of a color sampled from the image, and then it is used to fill all the triangles adjoining the vertex. The three hatching textures that accumulate in each triangle are averaged and the result of this process across all the triangles forms the output image. We can also add a paper texture effect and enhance feature lines in the image. Our algorithm can also be applied to video. The results are visually pleasing hatching effects similar to those seen in color pencil drawings and oil paintings.