M. Sramek - Academia.edu (original) (raw)

Papers by M. Sramek

Fourth International Workshop on Volume Graphics, 2005., 2005

We present a new approach for voxelization of implicit solids which contain sharp details. If suc... more We present a new approach for voxelization of implicit solids which contain sharp details. If such objects are processed by common techniques, voxelization artifacts may appear, resulting, among others, in jaggy edges in rendered images. To cope with this problem we proposed a technique called Sharp Details Correction. The main idea is to modify objects during the process of voxelization according to the representability criterion. This means that sharp edges end vertices are rounded to a curvature, which depends on the grid resolution. Thus, we obtain artifact-free voxelized solids which produce alias-free images.

IEEE Visualization, 2002. VIS 2002.

IEEE Visualization 2004

Figure 1: Cross-section view of a vessel (a) and the best fitted model (b) from an initial model (c)

Radiology, 2007

The study was approved by the institutional review board, and informed consent was obtained. The ... more The study was approved by the institutional review board, and informed consent was obtained. The purpose of the study was to prospectively quantify the angular visibility range, determine the existence of orthogonal viewing pairs, and characterize the conditions that cause artifacts in multipath curved planar reformations (MPCPRs) of the peripheral arterial tree in 10 patients (eight men and two women; mean age, 69 years; range, 54-80 years) with peripheral arterial occlusive disease. Percentage of segments with the maximal possible visibility score of 1 was significantly greater (odds ratio, 1.42; P Ͻ .001) for MPCPRs than for maximum intensity projections. One or more orthogonal viewing pairs were identified for all above-knee arterial segments, and artifactual vessel distortion was observed when the vessel axis approached a horizontal course in MPCPRs.

IEEE Transactions on Visualization and Computer Graphics, 2000

ÐThis paper discusses and experimentally compares distance-based acceleration algorithms for ray-... more ÐThis paper discusses and experimentally compares distance-based acceleration algorithms for ray-tracing of volumetric data with an emphasis on the Chessboard Distance (CD) voxel traversal. The acceleration of this class of algorithms is achieved by skipping empty macro regions, which are defined for each background voxel of the volume. Background voxels are labeled in a preprocessing phase by a value, defining the macro region size, which is equal to the voxel distance to the nearest foreground voxel. The CD algorithm exploits the chessboard distance and defines the ray as a nonuniform sequence of samples positioned at voxel faces. This feature assures that no foreground voxels are missed during the scene traversal. Further, due to parallelepipedal shape of the macro region, it supports accelerated visualization of cubic, regular, and rectilinear grids. The CD algorithm is suitable for all modifications of the ray tracing/ray casting techniques being used in volume visualization and volume graphics. However, when used for rendering based on local surface interpolation, it also enables fast search of intersections between rays and the interpolated surface, further improving speed of the process.

Computers & Graphics, 2010

IEEE Transactions on Visualization and Computer Graphics, 1999

ÐWe introduce a new concept for alias-free voxelization of geometric objects based on a Voxelizat... more ÐWe introduce a new concept for alias-free voxelization of geometric objects based on a Voxelization model (V-model). The V-model of an object is its representation in three-dimensional continuous space by a trivariate density function. This function is sampled during the voxelization and the resulting values are stored in a volume buffer. This concept enables us to study general issues of sampling and rendering separately from object specific design issues. It provides us with a possibility to design such V-models, which are correct from the point of view of both the sampling and rendering, thus leading to both alias-free volumetric representation and alias-free rendered images. We performed numerous experiments with different combinations of V-models and reconstruction techniques. We have shown that the V-model with a Gaussian surface density profile combined with tricubic interpolation and Gabor derivative reconstruction outperforms the previously published technique with a linear density profile. This enables higher fidelity of images rendered from volume data due to increased sharpness of edges and thinner surface patches.

IEEE Transactions on Visualization and Computer Graphics, 2006

Journal of Applied Mathematics and Mechanics, 1998

Computer Assisted Radiology / Computergestützte Radiologie, 1993

Proceedings. 2nd International Symposium on 3D Data Processing, Visualization and Transmission, 2004. 3DPVT 2004., 2004

ABSTRACT Structured grids and some of their applications in natural sciences are discussed. The p... more ABSTRACT Structured grids and some of their applications in natural sciences are discussed. The problem of their visualization and quantitative evaluation is considered and possible ways for its solution sketched. Resampling a structured grid onto a regular one is such a possible solution offering the additional benefit of enabling quantitative evaluations, too. This resampling is achieved by a preliminary tetrahedronization of the structured grid(s) and a subsequent digitalization of the constituent tetrahedrons using an adaptation of the 3D-Bresenham algorithm. Advantages and disadvantages of this approach as compared to other possible schemes are discussed. An implementation based on our open source f3d-file format for storage and transmission of volumetric data is presented, and results from applying it to real-world data shown.

IEEE Visualization 2004, 2004

Accurate and reliable visualization of blood vessels is still a challenging problem, notably in t... more Accurate and reliable visualization of blood vessels is still a challenging problem, notably in the presence of morphologic changes resulting from atherosclerotic diseases. In this paper we take advantage of partially segmented data with approximately identified vessel centerlines to comprehensively visualize the diseased peripheral arterial tree. We introduce the VesselGlyph as an abstract notation for novel focus & context visualization techniques of tubular structures such as contrast-medium enhanced arteries in CT-Angiography (CTA). The proposed techniques combine direct volume rendering (DVR) and curved planar reformation (CPR) within a single image. The VesselGlyph consists of several regions where different rendering methods are used. The region type, the used visualization method and the region parameters depend on the distance from the vessel centerline and on viewing parameters as well. By selecting proper rendering techniques for different regions, vessels are depicted in a naturally looking and undistorted anatomic context. This may facilitate the diagnosis and treatment planning of patients with peripheral arterial occlusive disease. In this paper we furthermore present a way how to implement the proposed techniques in software and by means of modern 3D graphics accelerators.

Proceedings Visualization '94, 1994

... The 500x500 image in Figure 8 was rendered by the CD voxel traversal algorithm using trilinea... more ... The 500x500 image in Figure 8 was rendered by the CD voxel traversal algorithm using trilinear interpolation with recursion depth 4 in 128 ... To obtain information about the behavior of the CD algorithm over scenes with various complexities, a com-puter experiment ...

Proceedings Computer Graphics International, 2004., 2004

We present a new technique for CSG operations with voxelized geometric objects, which are represe... more We present a new technique for CSG operations with voxelized geometric objects, which are represented by truncated discrete distance fields supplemented by additional information about the surface normal. The technique removes artifacts of straightforward volumetric CSG operations by taking into account conditions for object representability, according to which sharp details are not correctly representable in discrete distance fields. The proposed technique solves this shortcoming by rounding edges and other sharp details. It works at the voxel level without the necessity for reconstruction of continuous object models.

Proceedings Spring Conference on Computer Graphics, 2001

Abstract: Volume graphics represents a set of techniques aimed at modeling, manipulation and rend... more Abstract: Volume graphics represents a set of techniques aimed at modeling, manipulation and rendering of objects represented by means of a 3D raster of elementary volume primitives - voxels. It represents a viable alternative for the standard surface graphics, and as such, it provides us with a possibility to overcome some of its bottlenecks and to extend its capabilities even further. Namely, by means of voxelization, it decouples object specific issues from rendering and enables uniform representation of all objects by a single primitive, the voxel. Thus, instead of dealing with a number of different objects with specific features, a renderer processes only one primitive object, which simplifies its architecture and leads to a more effective implementation. Moreover, rendering is independent on the original number of objects and hence a complete independence on object and scene complexity is achieved. Voxelization, i.e. a conversion of object representation by means of analytic formulas to the discrete 3D raster stands in the core of volume graphics techniques. In the paper we present and critically analyze distance oriented techniques as a tool for alias-free volumetric representation of geometric objects.

Sixth International Workshop on Digital Image Processing and Computer Graphics: Applications in Humanities and Natural Sciences, 1998

ABSTRACT

Proceedings of the 1998 IEEE symposium on Volume visualization - VVS '98, 1998

We analyze different filters used for the voxelization of analytically described objects. We show... more We analyze different filters used for the voxelization of analytically described objects. We show that, when the voxel model is used for visualization, the filter design is related to the subsequent rendering phase, namely the gradient estimation technique. Our theoretical and experimental analyses show that, in order to avoid a systematic error in normal estimation, the density profile near the surface should be linearly proportional to the distance from the surface. Optimal thickness of this transient region has been estimated to be about 3 voxel units. Based on these results, we propose a technique for voxelization of arbitrary parametric surfaces, using a hierarchical subdivision of the 2D surface domain.