Byeong-Seok Shin

Fast 3D solid model reconstruction from orthographic views

As the number of applications that use 3D solid models increases, there is a need to devise an efficient method of constructing a solid model. One approach is reconstruction from orthographic projections. With this method input of geometric information is easy. However, it requires combinatorial searches and complicated geometric operations because of the loss of semantic information during projection. In this paper, we propose an efficient algorithm for reconstructing solid models using geometric properties and the topology of geometric primitives. The experimental results show that the algorithm can reconstruct 3D models much faster than previous algorithms.

Obstacle detection and avoidance system for visually impaired people

In this paper, we implemented a wearable system for visually impaired users which allows them to detect and avoid obstacles. This is based on ultrasound sensors which can acquire range data from objects in the environment by estimating the time-of-flight of the ultrasound signal. Using a hemispherical sensor array, we can detect obstacles and determine which directions should be avoided. However, the ultrasound sensors are only used to detect whether obstacles are present in front of users. We determine unimpeded directions by analyzing patterns of the range values from consecutive frames. Feedback is presented to users in the form of voice commands and vibration patterns. Our system is composed of an ARM9-based embedded system, an ultrasonic sensor array, an orientation tracker and a set of vibration motors with controller.

Adaptive power control of obstacle avoidance system using via motion context for visually impaired person

We propose adaptive power control of obstacle avoidance system for visually impaired person. It utilizes multiple ultrasonic sensors to avoid obstacles lying in the path. We evaluate complex structure in front of the user with predefined patterns and determine avoidance direction by analysing those patterns. It controls the number of active ultrasonic sensors by evaluating motion context using built-in accelerometer sensor. Our system safely guides visually impaired person as well as adaptively control power consumption of mobile devices.

Interactive classification for pre-integrated volume rendering of high-precision volume data

The pre-integrated volume rendering technique is widely used for creating high quality images. It produces good images even though the transfer function is nonlinear. Because the size of the pre-integration lookup table is proportional to the square of data precision, the required storage and computation load steeply increase for rendering of high-precision volume data. In this paper, we propose a method that approximates the pre-integration function proportional to the data precision. Using the arithmetic mean instead of the geometric mean and storing opacity instead of extinction density, this technique reduces the size and the update time of the pre-integration lookup table so that it classifies high-precision volume data interactively. We demonstrate performance gains for typical renderings of volume datasets.

Efficient volumetric ray casting for isosurface rendering

Abstract While volume rendering is becoming more widely used in medical applications, it is still difficult to generate a good-quality image interactively without expensive hardware when the size of the dataset is quite large. For interactive rendering of a large dataset, we present an acceleration method, image–space bounding surface. Using an image–space bounding surface, the isosurface ray casting is accelerated by avoiding unnecessary volume traversals. Image–space bounding surface can be interactively handled by polygon-rendering hardware even in a conventional personal computer. Two optimization techniques, LF-minmax map and memory bricking, are also employed to efficiently render isosurfaces. This paper also shows that the algorithm can be extended to multiple isosurfaces rendering. The experimental results show that the algorithm generates a good-quality image of a large dataset interactively on a standard PC platform.

Reducing redundancy in wireless capsule endoscopy videos

We eliminate similar frames from a wireless capsule endoscopy video of the human intestines to maximize spatial coverage and minimize the redundancy in images. We combine an intensity correction method with a method based an optical flow and features to detect and reduce near-duplicate images acquired during the repetitive backward and forward egomotions due to peristalsis. In experiments, this technique reduced duplicate image of 52.3% from images of the small intestine.

Laparoscopic and endoscopic exploration of the ascending colon wall based on a cadaver sectioned images

For realistic virtual dissection, the sectioned images of a cadaver are a desirable material because of their high resolution and real body color. After a volume model is made of the sectioned images, it can be piled or peeled at the intended thickness as if a structure’s surface is expanded and shrunken. The purpose of our study was to confirm whether laparoscopic and endoscopic exploration of the processed volume model plays a part in anatomy investigation. The ascending colon was outlined in serially sectioned images and accumulated to build a volume model. While the volume model was being piled or peeled, the ascending colon was observed laparoscopically and endoscopically in comparison with the original sectioned image. The trial efficiently demonstrated layers of the colon wall and surrounding tissues which could not be visualized by conventional macroscopic or microscopic techniques. The availability and contribution of this new method will be confirmed by application to other various organs.

GPU-accelerated 3D mipmap for real-time visualization of ultrasound volume data

Ultrasound volume rendering is an efficient method for visualizing the shape of fetuses in obstetrics and gynecology. However, in order to obtain high-quality ultrasound volume rendering, noise removal and coordinates conversion are essential prerequisites. Ultrasound data needs to undergo a noise filtering process; otherwise, artifacts and speckle noise cause quality degradation in the final images. Several two-dimensional (2D) noise filtering methods have been used to reduce this noise. However, these 2D filtering methods ignore relevant information in-between adjacent 2D-scanned images. Although three-dimensional (3D) noise filtering methods are used, they require more processing time than 2D-based methods. In addition, the sampling position in the ultrasonic volume rendering process has to be transformed between conical ultrasound coordinates and Cartesian coordinates. We propose a 3D-mipmap-based noise reduction method that uses graphics hardware, as a typical 3D mipmap requires less time to be generated and less storage capacity. In our method, we compare the density values of the corresponding points on consecutive mipmap levels and find the noise area using the difference in the density values. We also provide a noise detector for adaptively selecting the mipmap level using the difference of two mipmap levels. Our method can visualize 3D ultrasound data in real time with 3D noise filtering.

A distance template for octree traversal in CPU-based volume ray casting

Several optimization techniques have been proposed to improve the speed of direct volume rendering. A hierarchical representation formed by an octree is a data structure to skip over transparent regions while requiring little preprocessing and data storage. However, in order to skip over an octant estimated to be transparent (a transparent octant), the distance from a boundary to another boundary of the octant should be calculated. Because the distance computation is expensive, we propose a precomputed data structure, the distance template, which stores direction and distance values from one boundary voxel on a face to all the boundary voxels on the remaining five faces. In the rendering step, if a ray reaches a transparent octant, it leaps over the octant by referring to the stored distance value.

Wearable Computer System Reflecting Spatial Context

We have a lot of interests to wearable computer as an IT technology has been advanced. Although aids for disabled persons are also developed variously, those for visually impaired persons were limited. In this study, we proposed a wearable system that can do walk safely to the destination for the visually impaired persons. Our system guides a user to arrive at destination using marker information detected by camera. Also it uses multiple ultrasonic sensors array to detect and avoid obstacles. After recognizing position and orientation of markers attached on the indoor ceiling, we can estimate relative direction to destination. At the same time, we simplify a complex spatial structure in front of user into some patterns by means of ultrasonic sensors and determine an avoidance direction by estimating the patterns. Our system helps users to arrive to destination safely without others help.