Image filtering, edge detection, and edge tracing using fuzzyreasoning

We characterize the problem of detecting edges in images as a fuzzy reasoning problem. The edge detection problem is divided into three stages: filtering, detection, and tracing. Images are filtered by applying fuzzy reasoning based on local pixel characteristics to control the degree of Gaussian smoothing. Filtered images are then subjected to a simple edge detection algorithm which evaluates the edge fuzzy membership value for each pixel, based on local image characteristics. Finally, pixels having high edge membership are traced and assembled into structures, again using fuzzy reasoning to guide the tracing process. The filtering, detection, and tracing algorithms are tested on several test images. Comparison is made with a standard edge detection technique     

Efficient,complete radiosity ray tracing using a shadow-coherence method

Most two-pass rendering methods calculate a radiosity shading for each patch or element in a scene in the first pass. This shading contains two components: one for the light received directly from the main light sources and one representing the intensity of the light received indirectly by means of diffuse and specular interreflection between patches. However, it is very difficult to achieve accurate representation of the distribution of this radiosity shading over the patch, particularly where clearly visible shadow boundaries exist. A better approach is to store only the indirect reflection component in the form of radiosity shading, and to calculate the direct reflection component during the second pass by casting shadow rays. This approach normally requires that many shadow rays must be cast. However, the number of rays for shadow testing can be kept low by selecting only those light sources that substantially contribute to the shading of a patch and applying an adaptive image refinement technique in combination with a shadow coherence method.     

Efficient shadow computations in ray tracing

Two techniques to speed up shadow computations in ray tracing are examined. The first, atomic adaptive sampling, is intended for any light type, such as directional, spot, point, linear, and area lights, in antialiasing, while the second, plane-vertex checking, specifically accelerates shadow computation of linear and area lights. The basic ideas can be extended to other ray types and, for the plane-vertex check, to radiosity applications as well. Existing surveys explain the fundamentals and provide references to intersection culler and shadow algorithms     

Efficient data management for incoherent ray tracing

To obtain good performance on the GPU hardware, it is necessary to design algorithms to manage data, access memory under GPU memory hierarchy, and schedule more efficient threads. In this paper, we propose an efficient data management and task management designed for GPU based ray tracing. Due to the dynamic and uncertainty in ray tracing, we design data-management layer and task-management layer combined with fuzzy spatial analysis, use the two-level ray sorting and a ray bucket structure to reorganize ray data, then a warp's threads can be scheduled to access coherent geometry and nodes data, reduce memory bandwidth, and dispatch the data locally. We schedule tasks in data-driven execution according to coherent data, propose an adaptive ray compaction to eliminate inactive threads, maintain task efficiency of threads in a warp, and design two heuristics to decrease the compaction cost. On the basis of it, we also introduce a memory-optimized dynamic traversal management to reduce incoherent memory access, and avoid frequent sorting computation and compaction operations. Our experiments demonstrate all of these work combined can achieve good performance.     

Faster ray tracing using adaptive grids

A new hybrid approach is presented which outperforms the regular grid technique in scenes with highly irregular object distributions by a factor of hundreds, and combined with an area interpolator, by a factor of thousands. Much has been said about scene independence of different acceleration techniques and the alleged superiority of one approach over another. Several theoretical and practical studies conducted in the past have led to the same conclusion: a space partitioning method that allows the fastest rendering of one scene often fails with another. Specialization may be the answer. This has always been pursued, consciously or not, in developing various ray-tracing systems. Despite our new algorithm's impressive efficiency, we don't interpret the new method as the fastest ray-tracing scene decomposition possible. This is because our recent groundwork experiments with a derivative method produced in some of the test scenes presented in this article produced timings that were better by approximately 50%     

Heuristics for ray tracing using space subdivision

Ray tracing requires testing of many rays to determine intersections with objects. A way of reducing the computation is to organize objects into hierarchical data structures. We examine two heuristics for space subdivisions using bintrees, one based on the intuition that surface area is a good estimate of intersection probability, one based on the fact that the optimal splitting plane lies between the spatial median and the object median planes of a volume. Traversal algorithms using cross links between nodes are presented as generalizations of ropes in octrees. Simulations of the surface area heuristic and the cross link scheme are presented. These results generalize to other hierarchical data structures.     

Rendering large scenes using parallel ray tracing

Ray tracing is a powerful technique to generate realistic images of 3D scenes. However, rendering complex scenes may easily exceed the processing and memory capabilities of a single workstation. Distributed processing offers a solution if the algorithm can be parallelized in an efficient way. In this paper a hybrid scheduling approach is presented that combines demand driven and data parallel techniques. Which tasks to process demand driven and which data parallel, is decided by the data intensity of the task and the amount of data locality (coherence) that will be present in the task. By combining demand driven and data driven tasks, a better load balance may be achieved, while at the same time the communication is spread evenly across the network. This leads to a scalable and efficient parallel implementation of the ray tracing algorithm with little restriction on the size of the model data base to be rendered.     

Faster isosurface ray tracing using implicit KD-trees

The visualization of high-quality isosurfaces at interactive rates is an important tool in many simulation and visualization applications. Today, isosurfaces are most often visualized by extracting a polygonal approximation that is then rendered via graphics hardware or by using a special variant of preintegrated volume rendering. However, these approaches have a number of limitations in terms of the quality of the isosurface, lack of performance for complex data sets, or supported shading models. An alternative isosurface rendering method that does not suffer from these limitations is to directly ray trace the isosurface. However, this approach has been much too slow for interactive applications unless massively parallel shared-memory supercomputers have been used. In this paper, we implement interactive isosurface ray tracing on commodity desktop PCs by building on recent advances in real-time ray tracing of polygonal scenes and using those to improve isosurface ray tracing performance as well. The high performance and scalability of our approach will be demonstrated with several practical examples, including the visualization of highly complex isosurface data sets, the interactive rendering of hybrid polygonal/isosurface scenes, including high-quality ray traced shading effects, and even interactive global illumination on isosurfaces.     

Efficient parallel spatial subdivision algorithm for object-based parallel ray tracing

Parallel ray tracing of complex scenes on multicomputers requires the distribution of both computation and scene data to the processors. This is carried out during preprocessing and usually consumes too much time and memory. The paper presents an efficient parallel subdivision algorithm that decomposes a given scene into rectangular regions adaptively and maps the resultant regions to the node processors of a multicomputer. The proposed algorithm uses efficient data structures to identify the splitting planes quickly. Furthermore the mapping of the regions and the objects to the node processors is performed while parallel spatial subdivision proceeds. The proposed algorithm is implemented on an Intel iPSC/2 hypercube multicomputer and promising results have been obtained.     

Accelerated ray tracing using an nCUBE2 multicomputer

Acceleration techniques for rendering a dynamic sequence of frames (animations) and static scenes using ray tracing are presented. The first technique discusses temporal acceleration for dynamic scenes which takes advantage of ray coherence, while the second technique discusses acceleration for complex static scenes based on parallelism. Several practical aspects of the parallel implementation on an nCUBE2 hypercube computer are included.     

Efficient facet edge detection and quantitative performance evaluation

In this paper, we first introduce a recursive procedure for efficiently computing cubic facet parameters for edge detection. The procedure allows to compute facet parameters in a fixed number of operations independent of kernel size. We then introduce an image independent quantitative criterion for analytically evaluating different edge detectors (both gradient and zero-crossing based methods) without the need of ground-truth information. Our criterion is based on our observation that all edge detectors make a decision of whether a pixel is an edgel or not based on the result of convolution of the image with a kernel. The variance of the convolution output therefore directly affects the performance of an edge detector. We propose to analytically compute the variance of the convolution output and use it as a measure to characterize the performance of four well-known edge detectors.     

Efficient construction of bounding volume hierarchies into a complete octree for ray tracing

This paper proposes an efficient construction scheme for bounding volume hierarchies based on a complete tree. This construction offers up to 4× faster construction times than binned‐surface area heuristic and offers competitive ray traversal performance. The construction is fully parallelized on x86 CPU architectures; it takes advantage of the eight‐wide vector units and exploits the advance vector extensions available for current x86 CPU architectures. Additionally, this work presents a clustering algorithm for grouping primitives, which can be computed in linear time O(n). Furthermore, this construction uses the graphics processing unit to perform intensive operations efficiently. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation of starburst phenomenon using ray tracing for touch screen panels

We investigate the effect of the metal pattern shape (i.e., square, hexagonal, and random grids) on the starburst phenomenon of touch screen panels (TSPs) based on opaque metallic grids. It is demonstrated that a standalone random metal grid can suppress the starburst phenomenon to a great extent. By way of ray tracing simulation, we have found that specular reflection of light on the gentle slope of the patterned edges of metallic grids contributes to the generation of starburst patterns. It is also addressed that employing a light-absorbing material and increasing metal grid spacing can reduce the intensity of starburst patterns.     

Shape estimation of transparent objects by using inverse polarization ray tracing

Few methods have been proposed to measure three-dimensional shapes of transparent objects such as those made of glass and acrylic. In this paper, we propose a novel method for estimating the surface shapes of transparent objects by analyzing the polarization state of the light. Existing methods do not fully consider the reflection, refraction, and transmission of the light occurring inside a transparent object. We employ a polarization raytracing method to compute both the path of the light and its polarization state. Polarization raytracing is a combination of conventional raytracing, which calculates the trajectory of light rays, and Mueller calculus, which calculates the polarization state of the light. First, we set an initial value of the shape of the transparent object. Then, by changing the shape, the method minimizes the difference between the input polarization data and the rendered polarization data calculated by polarization raytracing. Finally, after the iterative computation is converged, the shape of the object is obtained. We also evaluate the method by measuring some real transparent objects.     

Iris detection using intensity and edge information

In this paper we propose a new algorithm to detect the irises of both eyes from a face image. The algorithm first detects the face region in the image and then extracts intensity valleys from the face region. Next, the algorithm extracts iris candidates from the valleys using the feature template of Lin and Wu (IEEE Trans. Image Process. 8 (6) (1999) 834) and the separability filter of Fukui and Yamaguchi (Trans. IEICE Japan J80-D-II (8) (1997) 2170). Finally, using the costs for pairs of iris candidates proposed in this paper, the algorithm selects a pair of iris candidates corresponding to the irises. The costs are computed by using Hough transform, separability filter and template matching. As the results of the experiments, the iris detection rate of the proposed algorithm was 95.3% for 150 face images of 15 persons without spectacles in the database of University of Bern and 96.8% for 63 images of 21 persons without spectacles in the AR database.     

Scale-space and edge detection using anisotropic diffusion

A new definition of scale-space is suggested, and a class of algorithms used to realize a diffusion process is introduced. The diffusion coefficient is chosen to vary spatially in such a way as to encourage intraregion smoothing rather than interregion smoothing. It is shown that the `no new maxima should be generated at coarse scales' property of conventional scale space is preserved. As the region boundaries in the approach remain sharp, a high-quality edge detector which successfully exploits global information is obtained. Experimental results are shown on a number of images. Parallel hardware implementations are made feasible because the algorithm involves elementary, local operations replicated over the image     

River detection algorithm in SAR images based on edge extraction and ridge tracing techniques

This article presents a novel river detection algorithm in synthetic aperture radar (SAR) images. It is based on edge extraction in the wavelet domain followed by ridge tracing to merge the water region. The edge detection is approached by direct spatial correlation of wavelet transform data at several adjacent scales. For the ridge tracing algorithm, the concept used in fingerprint identification is introduced to complete riverbank linking and connecting based on a greyscale image. This improvement avoids the disadvantages of the widely used snake model in coastline connection. As indicated by the river detection results from the real SAR images, our river detection algorithm is efficient and robust in detecting the river in complicated suburb and nature water areas.     

Parallel processing of an object space for image synthesis using ray tracing

This paper presents a novel parallel processing system for image synthesis using ray tracing. An object space is divided into parts (subspaces), each of which is allocated to a processor. The processor detects, simultaneously the intersections of the surfaces of each object and a fixed number of rays over the whole space, and calculates the local intensity on an object in each subspace. The global intensities of pixels on a screen are calculated by the other kind of processors simultaneously. We also present the optimal data structure, based on an adaptive division algorithm, for parallel processing of the object space.     

Analysis of an algorithm for fast ray tracing using uniform space subdivision

Ray tracing is becoming popular as the best method of rendering high quality images from three dimensional models. Unfortunately, the computational cost is high. Recently, a number of authors have reported on ways to speed up this process by means of space subdivision which is used to minimize the number of intersection calculations. We describe such an algorithm together with an analysis of the factors which affect its performance. The critical operation of skipping an empty space subdivision can be done very quickly, using only integer addition and comparison. A theoretical analysis of the algorithm is developed. It shows how the space and time requirements vary with the number of objects in the scene.