• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.691-693
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• 2005

가상 내시경 기법 중 하나 펼친 영상 가시화(unfold rendering) 기법은 장기 내부를 펼쳐서 본 영상을 제공함으로써 장기의 내부 구조와 병변의 유무를 쉽게 판단할 수 있도록 해준다. 가장 일반적으로 사용하는 원형 광선 투사법은 곡률이 급격하게 변하는 경우에 광선들이 교차하여 병변이 두 개로 나타나는 문제가 발생할 수 있다. 본 논문에서는 경로의 제어점을 따라 광선 템플릿을 적용하여 적은 비용으로 펼친 영상을 생성하는 방법을 제안한다. 우선 중심 경로의 제어점들에서 곡률을 계산하여 곡률에 해당하는 광선 템플릿을 적용하여 광선 원뿔(ray Cone)을 구한다. 그리고 생성된 광선 원뿔간의 교차 검사와 보정을 통해 이들이 서로 교차하지 않도록 조정한다. 제어점들 사이의 샘플점들은 앞서 구한 제어점에서의 광선 투사 위치로부터 다음 제어점에서의 투사 위치를 잇는 선분을 보간하여 광선 투사 방향을 결정하게 된다. 마지막으로 계산된 방향에 따라 광선을 투사하여 영상을 생성한다.

• Journal of Korea Game Society
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• v.12 no.2
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• pp.53-62
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• 2012

Visualizing a volume dataset with ray-casting which of visualization methods provides high quality image. However it spends too much time for rendering because the size of volume data are huge. Recently, various researches have been proposed to accelerate GPU-based volume rendering to solve these problems. In this paper, we propose an efficient GPU-based empty space skipping to accelerate volume ray-casting using octree traversal. This method creates min-max octree and searches empty space using vertex splitting. It minimizes the bounding polyhedron by eliminating empty space found in the octree traveral step. The rendering results of our method are identical to those of previous GPU-based volume ray-casting, with the advantage of faster run-time because of using minimized bounding polyhedron.

• Journal of Korea Game Society
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• v.9 no.4
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• pp.89-96
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• 2009

In general, the size of volume data is large since it has logical 3D structure so it takes long time to manipulate. Much work has been done to improve processing speed of volume data. In this paper, we propose a interlaced scanning volume rendering that reduce computation time by using temporal coherence with minimum loss of image quality. It renders a current frame by reusing information of previous frame. Conventional volume raycasting renders each frame by casting rays on every pixels. On the other hand, our methods divided an image into n-pixel blocks, then it casts a ray on a pixel of a block per each frames. Consequently, it generates an image by accumulating pixel values of previous n frames. The quality of rendered image of our method is better than that of simple screen space subsampling method since it uses afterimage effect of human cognitive system, and it is n-times faster that the previous one.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.3
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• pp.210-216
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• 2009

Several empty-space leaping methods have been proposed for CPU-based volume ray casting. When sample points are located in semi-transparent cells, however, previous leaping methods perform unnecessary resamplings even if the scalar values on those points are confined within transparent range. A semi-transparent cells leaping method for volume ray casting using the Marching Cubes algorithm is proposed to solve this problem in our previous work. When a ray reaches a semi-transparent cell, our method performs in-out test between current sample point and the bounding box enclosing the triangles generated by the Marching Cubes. If the sample point lies on outside of the bounding box, we estimate the point is regarded as transparent. In this case, the ray advances to the next sample point without performing a resampling operation. We can frequently refer the tables for neighboring voxels, however, when we exploit conventional data structures of the Marching Cubes. We propose modified Marching Cubes tables for solving this problem.

• Journal of the Korea Computer Graphics Society
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• v.10 no.1
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• pp.23-28
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• 2004

가상 내시경의 주된 목적은 체내 장기의 3차원적 구조를 가시화하여 광학 내시경을 모사하는데 있다. 가상 내시경 기법 중 펼친 영상 가시화 기법(unfold rendering)은 장기의 내부 구조와 병변의 유무를 쉽게 판단할 수 있도록 하는 장점이 있다. 가장 일반적으로 사용 하는 중심 경로 기반의 광선 투사법은 곡률이 급격하게 변하는 경우 광선들이 교차하여 병변이 두개로 나타나 문제가 발생할 수 있다. 이를 해결하기위해 광선들이 겹치지 않도록 보장하는 여러 기법들이 발표되었지만 계산량이 많은 단점을 가지고 있다. 본 논문에서는 경로의 제어점을 이용하여 적은 비용으로 펼친 영상을 재구성하는 방법을 제안한다. 우선 모든 중심 경로의 제어점에서 경로에 수직인 절단면을 찾는다. 이때 제어점으로부터 방사상으로 광션을 투사하여 절단면과 만나는 장기 내 벽의 위치를 파악한다. 절단면간의 교차 검사 및 보정을 통해 절단연들이 서로 교차하지 않도록 조정한다. 제어점들 사이의 샘플점들은 앞서 구한 임의의 제어점에서 광선이 투사된 위치로 부터 다음 제어점에서 투사된 위치를 잇는 선분을 보간하여 광선 투사 위치를 결정하게 된다. 마지막으로 계산된 방향 따라 광선을 투사하여 영상을 생성한다.

• Journal of the Korea Computer Graphics Society
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• v.17 no.3
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• pp.1-7
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• 2011

Recently, various researches have been proposed to accelerate GPU-based volume ray-casting. However, those researches may cause several problems such as bottleneck of data transmission between CPU and GPU, requirement of additional video memory for hierarchical structure and increase of processing time whenever opacity transfer function changes. In this paper, we propose an efficient GPU-based empty space skipping technique to solve these problems. We store maximum density in a brick of volume dataset on a vertex element. Then we delete vertices regarded as transparent one by opacity transfer function in geometry shader. Remaining vertices are used to generate bounding boxes of non-transparent area that helps the ray to traverse efficiently. Although these vertices are independent on viewing condition they need to be reproduced when opacity transfer function changes. Our technique provides fast generation of opaque vertices for interactive processing since the generation stage of the opaque vertices is running in GPU pipeline. The rendering results of our algorithm are identical to the that of general GPU ray-casting, but the performance can be up to more than 10 times faster.

• Journal of Biomedical Engineering Research
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• v.25 no.2
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• pp.103-109
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• 2004

A virtual arthroscopy is a simulation of optical arthroscopy that reconstructs anatomical structures from tomographic images in joint region such as a knee, a shoulder and a wrist. In this paper, we propose a virtual arthroscopy based on isosurface raycasting, which is a kind of volume rendering methods for generating 3D images within a short time. Our method exploits a spatial data structure called min-max map to produce high-quality images in near real-time. Also we devise a physically-based camera control model using potential field. So a virtual camera can fly through in articular cavity without restriction. Using the high-speed rendering method and realistic camera control model, we developed a virtual arthroscopy system.

• Journal of Korea Game Society
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• v.11 no.6
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• pp.71-80
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• 2011

Recent terrain rendering applications such as 3D games and virtual reality, use GPU-based ray-casting method for rendering high-quality scenes in realtime. As the size of terrain dataset grows bigger, the rendering speed will be decreased by the increase of the number of texture samplings. To accelerate the conventional ray-casting, we propose an efficient ray casting method with subdivided bounding boxes which are based-on GPU quadtree traversal. The subdivision of the terrain's bounding box can reduce the empty spaces effectively. By performing the ray-casting with this compact bounding box, we can efficiently reduce computation with empty space skipping. Unlike the recent quadtree-based empty space skipping techniques which perform the tree traversal at each ray, our method traverses the tree only once per frame. Therefore, we can save much computational time.

• Journal of the Korea Computer Graphics Society
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• v.19 no.2
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• pp.19-27
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• 2013

This paper presents a real-time GPU (Graphics Processing Unit) isosurface ray-caster that improves the performance by 4-7 folds from our previous method, while keeping the superior visual quality. Such an improvement is achieved by incorporating an efficient empty-space skipping scheme and an analytic normal computation. The empty-space skipping scheme is done by building an min/max octree computed from the BB(Bernslein-B$\acute{e}$zier)-form of spline pieces and the analytic normal Formula provides not only a nice visual quality but also an improved evaluation performance.

• Journal of Korea Multimedia Society
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• v.14 no.8
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• pp.981-991
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• 2011

MIP(Maximum Intensity Projection) is a volume rendering technique which is essential for the medical imaging system. MIP rendering based on the ray casting method produces high quality images but takes a long time. Our aim is improvement of the rendering speed using GPGPU(General-purpose computing on Graphic Process Unit) technique. In this paper, we present the ray casting algorithm based on CUDA(an acronym for Compute Unified Device Architecture) which is a programming language for GPGPU and we suggest new acceleration methods for CUDA. In detail, we propose the block based space leaping which skips unnecessary regions of volume data for CUDA, the bisection method which is a fast method to find a block edge, and the initial value estimation method which improves the probability of space leaping. Due to the proposed methods, we noticeably improve the rendering speed without image quality degradation.