Bon-Ki Koo

Practical animation of turbulent splashing water

Despite recent advances in fluid animation, producing small-scale detail of turbulent water still remains challenging. In this paper, we extend the well-accepted particle level set method in an attempt to integrate the dynamic behavior of splashing water easily into a fluid animation system. Massless marker particles that still escape from the main body of water, in spite of the level set correction, are transformed into water particles to represent subcell-level features that are hard to capture with a limited grid resolution. These physical particles are then moved in the air through a particle simulation system that, combined with the level set, creates realistic turbulent splashing. In the rendering stage, the particles physical properties such as mass and velocity are exploited to generate a natural appearance of water droplets and spray. In order to visualize the hybrid water, represented in both level set and water particles, we also extend a Monte Carlo ray tracer so that the particle agglomerates are smoothed, thickened, if necessary, and rendered efficiently. The effectiveness of the presented technique is demonstrated with several examples of pictures and animations.

Convenient calibration method for unsynchronized camera networks using an inaccurate small reference object

In this paper, a new and convenient calibration algorithm is proposed for unsynchronized camera networks with a large capture volume. The proposed method provides a simple and accurate means of calibration using a small 3D reference object. Moreover, since the inaccuracy of the object is also compensated simultaneously, the manufacturing cost can be decreased. The extrinsic and intrinsic parameters are recovered simultaneously by capturing an object placed arbitrarily in different locations in the capture volume. The proposed method first resolves the problem linearly by factorizing projection matrices into the camera and the object pose parameters. Due to the multi-view constraints imposed on factorization, consistency of the rigid transformations among cameras and objects can be imposed. These consistent estimation results can be further refined using a non-linear optimization process. The proposed algorithm is evaluated via simulated and real experiments in order to verify that it is more efficient than previous methods.

Linear stratified approach using full geometric constraints for 3D scene reconstruction and camera calibration

This paper presents a new linear framework to obtain 3D scene reconstruction and camera calibration simultaneously from uncalibrated images using scene geometry. Our strategy uses the constraints of parallelism, coplanarity, colinearity, and orthogonality. These constraints can be obtained in general man-made scenes frequently. This approach can give more stable results with fewer images and allow us to gain the results with only linear operations. In this paper, it is shown that all the geometric constraints used in the previous works performed independently up to now can be implemented easily in the proposed linear method. The study on the situations that cannot be dealt with by the previous approaches is also presented and it is shown that the proposed method being able to handle the cases is more flexible in use. The proposed method uses a stratified approach, in which affine reconstruction is performed first and then metric reconstruction. In this procedure, the additional constraints newly extracted in this paper have an important role for affine reconstruction in practical situations.

Real-time video photomosaics with optimized image set and GPU

We propose a real-time approach to automatically generate photomosaic videos from a set of optimized images by taking advantage of CUDA GPU acceleration. Our approach divides an input image into smaller cells—usually rectangular cells—and replaces each cell with a small image of an appropriate color pattern. Photomosaics require a large set of tile images with a variety of patterns to create high-quality digital mosaic images. Because a large database of images requires longer processing time and larger storage space for searching patterns from the database, this requirement causes problems in developing a real-time system or mobile applications that have limited resources. This paper deals with a real-time video photomosaics using genetic feature selection method for building an optimized image set and taking advantage of CUDA to accelerate pattern searching that minimizes computation cost.

Calibration of multi-Kinect and multi-camera setup for full 3D reconstruction

In this paper, a new calibration method is presented for multi-Kinect and multi-camera setup. This method is developed by considering that the depth measurement principle of the Kinect is triangulation. The depth values obtained from the Kinect are sometimes inaccurate because the manufacturers calibration between IR projector and IR camera becomes invalid by the tolerances in manufacturing, temperature variation and vibration during transportation. To improve the results from the previous calibration methods, an analytic approach is presented. Experiments show that the induced depth correction model is reasonable and the results from the proposed approach are better than those of the previous approaches.

An intuitive system for 3D avatar with high-quality

According to advancements in computer technology, there are lots of needs for customized contents, which show up a user as a main character. These needs are implemented in computer games for the first time. In these games, a user can easily create a game character which resembles him/her and is called avatar. But for the limit of game itself, the game supports the avatar with low quality. When the user wants realistic his/her avatar and uses conventional computer graphics, the user might be amazed at the high level avatar as well as the production costs and periods. In this paper, we suggest an intuitive system to generate the 3D avatar easily from the users picture and users minimum interaction. The result 3D avatar has high quality and resembles the user. Our system will be helpful at 3D UCC.

Optimization of an image set by genetic feature selection for real-time photomosaics

We present a genetic feature selection method for the optimization of an image set for producing real-time photomosaics. A photomosaic is an image that is divided into grid cells, each of which is replaced with another image of an appropriate color pattern. Construction of a photomosaic requires a large set of tile images with different patterns. However, a large number of photo images requires expensive pattern searching and a large storage space. These requirements can cause problems in applications to real-time domains or mobile devices with limited resources. We present a genetic feature selection method for building an optimized image set to accelerate pattern searching and minimize the memory cost.

Painterly caricature maker

This study describes a fully automated system for generating caricature images by using a painterly rendering method. This system transforms photos into caricature images automatically. A few similar approaches have been proposed by other researchers including [Gooch et al. 2004] and [Liang et al. 2002]. These methods, however, did not produce satisfying results, as the caricatures produced did not resemble handiwork. By simulating the brush strokes used by painters [Park et al. 2006], we reproduced the brush painting technique and incorporated it into our caricature system.

Template based image mosaics

We propose an image mosaic method based on tile template. Compared with a conventional mosaic which is comprised of the circle or the square tiles, our approach uses the arbitrary shaped tiles. But an arbitrary shaped tile leaves the excessive gap between tiles in the mosaic construction. Then the gap makes it difficult to preserve the fine detail of an original image. Our approach controls overlap between tiles to minimize the gap by using the mask technique and adopts stackable technique to represent the fine detail of a source image automatically.

Layered-depth image using pixel grouping

Recent advance in computer hardware and Internet technology makes more realistic images affordable on our computer systems. However, the image creation by using conventional geometry modelling have limitations in terms of rendering time and image quality to be used in interactive rendering applications. Image-based rendering (IBR) technique is a good solution to reducing those limitations in such applications. As an improvement on the well-known layered-depth image (LDI) method, we propose a way of pixel grouping from depth images and making image generation efficient by utilizing the information obtained from the grouping.