Illustrative volume visualization frequently employs non-photorealistic rendering techniques to enhance important features or to suppress unwanted details. However, it is difficult to integrate multiple non-photorealistic rendering approaches into a single framework due to great differences in the individual methods and their parameters. In this paper, we present the concept of style transfer functions. Our approach enables flexible data-driven illumination which goes beyond using the transfer function to just assign colors and opacities. An image-based lighting model uses sphere maps to represent non-photorealistic rendering styles. Style transfer functions allow us to combine a multitude of different shading styles in a single rendering. We extend this concept with a technique for curvaturecontrolled style contours and an illustrative transparency model. Our implementation of the presented methods allows interactive generation of high-quality volumetric illustrations. Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism

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Deep shadow maps unify the computation of volumetric and geometric shadows. For each pixel in the shadow map, a fractional visibility function is sampled, pre-filtered, and compressed as a piecewise linear function. However, the original implementation targets software-based off-line rendering. Similar previous algorithms on GPUs focus on geometric shadows and lose many important benefits of the original concept. We focus on shadows for interactive direct volume rendering, where shadow algorithms currently either compute additional per-voxel shadow data, or employ half-angle slicing to generate shadows during rendering. We adapt the original concept of deep shadow maps to volume ray-casting on GPUs, and show that it can provide anti-aliased high-quality shadows at interactive rates. Ray-casting is used for both generation of the shadow map data structure and actual rendering. High frequencies in the visibility function are captured by a pre-computed lookup table for piecewise linear segments. Direct volume rendering is performed with an additional deep shadow map lookup for each sample. Overall, we achieve interactive high-quality volume ray-casting with accurate shadows. To conclude, we briefly describe how semi-transparent geometry such as hair could be integrated as well, provided that rasterization can write to arbitrary locations in a texture. This would be a major step toward full deep shadow map functionality.

Surgical approaches tailored to an individual patient’s anatomy and pathology have become standard in neurosurgery. Precise preoperative planning of these procedures, however, is necessary to achieve an optimal therapeutic effect. Therefore, multiple radiological imaging modalities are used prior to surgery to delineate the patient’s anatomy, neurological function, and metabolic processes. Developing a three-dimensional perception of the surgical approach, however, is traditionally still done by mentally fusing multiple modalities. Concurrent 3D visualization of these datasets can, therefore, improve the planning process significantly. In this paper we introduce an application for planning of individual neurosurgical approaches with high-quality interactive multimodal volume rendering. The application consists of three main modules which allow to (1) plan the optimal skin incision and opening of the skull tailored to the underlying pathology; (2) visualize superficial brain anatomy, function and metabolism; and (3) plan the patient-specific approach for surgery of deep-seated lesions. The visualization is based on direct multi-volume raycasting on graphics hardware, where multiple volumes from different modalities can be displayed concurrently at interactive frame rates. Graphics memory limitations are avoided by performing raycasting on bricked volumes. For preprocessing tasks such as registration or segmentation, the visualization modules are integrated into a larger framework, thus supporting the entire workflow of preoperative planning.

This paper presents an extendable, simple, and efficient software framework that implements the GPU-based volume rendering pipeline. We use volume graphics for realistic image synthesis taking into account aspects of visual perception by means of real-time high dynamic range tone mapping. We propose a software architecture that embeds the volume rendering pipeline by using object-oriented design patterns, layers, and the concept of a shared application state. The pipeline is made flexible by representing stages as objects, loosely coupled via the shared state. We demonstrate the benefits of our architecture in a modern volume rendering application that incorporates state-of-the-art features such as pre-integration, pre-integrated lighting, and volumetric shadows. The full source code of our framework is made publicly available. 1

Existing techniques for rendering arbitrary-form implicit surfaces are limited, either in performance, correctness or flexibility. Ray tracing algorithms employing interval arithmetic (IA) or affine arithmetic (AA) for root-finding are robust and general in the class of surfaces they support, but traditionally slow. Nonetheless, implemented efficiently using a stack-driven iterative algorithm and SIMD vector instructions, these methods can achieve interactive performance for common algebraic surfaces on the CPU. A similar algorithm can also be implemented stacklessly, allowing for efficient ray tracing on the GPU. This paper presents these algorithms, as well as an inclusion-preserving reduced affine arithmetic (RAA) for faster ray-surface intersection. Shader metaprogramming allows for immediate and automatic generation of symbolic expressions and their interval or affine extensions. Moreover, we are able to render even complex forms robustly, in real-time at high resolution.

Abstract — This paper presents a scalable framework for real-time raycasting of large unstructured volumes that employs a hybrid bricking approach. It adaptively combines original unstructured bricks in important (focus) regions, with structured bricks that are resampled on demand in less important (context) regions. The basis of this focus+context approach is interactive specification of a scalar degree of interest (DOI) function. Thus, rendering always considers two volumes simultaneously: a scalar data volume, and the current DOI volume. The crucial problem of visibility sorting is solved by raycasting individual bricks and compositing in visibility order from front to back. In order to minimize visual errors at the grid boundary, it is always rendered accurately, even for resampled bricks. A variety of different rendering modes can be combined, including contour enhancement. A very important property of our approach is that it supports a variety of cell types natively, i.e., it is not constrained to tetrahedral grids, even when interpolation within cells is used. Moreover, our framework can handle multi-variate data, e.g., multiple scalar channels such as temperature or pressure, as well as time-dependent data. The combination of unstructured and structured bricks with different quality characteristics such as the type of interpolation or resampling resolution in conjunction with custom texture memory management yields a very scalable system. Index Terms—Volume Rendering of Unstructured Grids, Focus+Context Techniques, Hardware-Assisted Volume Rendering 1

This paper reviews the latest developments of displacement mapping algorithms implemented on the vertex, geometry, and fragment shaders of graphics cards. Displacement mapping algorithms are classified as per-vertex and per-pixel methods. Per-pixel approaches are further categorized as safe algorithms that aim at correct solutions in all cases, to unsafe techniques that may fail in extreme cases but are usually much faster than safe algorithms, and to combined methods that exploit the robustness of safe and the speed of unsafe techniques. We discuss the possible roles of vertex, geometry, and fragment shaders to implement these algorithms. Then the particular GPU based bump, parallax, relief, sphere, horizon mapping, cone stepping, local ray tracing, pyramidal and view-dependent displacement mapping methods, as well as their numerous variations are reviewed providing also implementation details of the shader programs. We present these methods using uniform notations and also point out when different authors called similar concepts differently. In addition to basic displacement mapping, self-shadowing and silhouette processing are also reviewed. Based on our experiences gained having re-implemented these methods, their performance and quality are compared, and the advantages and disadvantages are fairly presented.

Traditional volume rendering does not incorporate a number of optical properties that are typically observed for semi-transparent materials, such as glass or water, in the real world. Therefore, we have extended GPUbased raycasting to spectral volume rendering based on the Kubelka-Munk theory for light propagation in parallel colorant layers of a turbid medium. This allows us to demonstrate the effects of selective absorption and dispersion in refractive materials, by generating volume renderings using real physical optical properties. We show that this extended volume rendering technique can be easily incorporated into a flexible framework for GPU-based volume raycasting. Our implementation shows a promising performance for a number of real data sets. Particularly, we obtain up to 100 times the performance of a comparable CPU implementation.

Abstract. Smooth trivariate splines on uniform tetrahedral partitions are well suited for high-quality visualization of isosurfaces from scalar volumetric data. We propose a novel rendering approach based on spline patches with low total degree, for which ray-isosurface intersections are computed using efficient root finding algorithms. Smoothly varying surface normals are directly extracted from the underlying spline representation. Our approach is using a combined CUDA and graphics pipeline and yields two key advantages over previous work. First, we can interactively vary the isovalues since all required processing steps are performed on the GPU. Second, we employ instancing in order to reduce shader complexity and to minimize overall memory usage. In particular, this allows to compute the spline coefficients on-the-fly in real-time on the GPU. 1