Volume rendering is a technique for visualizing 3D arrays of sampled data. It has applications in areas such as medical imaging and scientific visualization, but its use has been limited by its high computational expense. Early implementations of volume rendering used brute-force techniques that require on the order of 100 seconds to render typical data sets on a workstation. Algorithms with optimizations that exploit coherence in the data have reduced rendering times to the range of ten seconds but are still not fast enough for interactive visualization applications. In this thesis we present a family of volume rendering algorithms that reduces rendering times to one second. First we present a scanline-order volume rendering algorithm that exploits coherence in both the volume data and the image. We show that scanline-order algorithms are fundamentally more efficient than commonly-used ray casting algorithms because the latter must perform analytic geometry calculations (e.g. intersecting rays with axis-aligned boxes). The new scanline-order algorithm simply streams through the volume and the image in storage order. We describe variants of the algorithm for both parallel and perspective projections and

This paper describes a method for synthesizing images that match the texture appearanceof a given digitized sample. This synthesis is completely automatic and requires only the "target" texture as input. It allows generation of as much texture as desired so that any object can be covered. It can be used to produce solid textures for creating textured 3-d objects without the distortions inherent in texture mapping. It can also be used to synthesize texture mixtures, images that look a bit like each of several digitized samples. The approach is based on a model of human texture perception, and has potential to be a practically useful tool for graphics applications. 1 Introduction Computer renderings of objects with surface texture are more interesting and realistic than those without texture. Texture mapping [15] is a technique for adding the appearance of surface detail by wrapping or projecting a digitized texture image ontoa surface. Digitized textures can be obtained from a variety ...

We present a method that uses measured scene radiance and global illumination in order to add new objects to light-based models with correct lighting. The methodusesahighdynamicrangeimagebasedmodelofthescene, ratherthansyntheticlightsources,toilluminatethe new objects. Tocomputetheillumination,thesceneis consideredasthreecomponents:thedistantscene, the localscene, andthesyntheticobjects. The distant scene is assumed tobephotometricallyunaffectedbytheobjects, obviatingtheneedforreflectancemodelinformation. Thelocalsceneisendowedwithestimatedreflectancemodel informationsothatitcancatchshadows andreceivereflectedlightfromthenewobjects. Renderings are createdwithastandardglobalilluminationmethodby simulating theinteractionoflightamongstthethreecomponents. A differentialrenderingtechniqueallowsforgoodresults to be obtained when only an estimate ofthelocalscenereflectancepropertiesisknown. Weapplythegeneralmethodtotheproblemofrendering syntheticobjectsintorealscenes. The light-based model is constructed from an approximategeometricmodelofthesceneandbyusinga lightprobetomeasuretheincidentilluminationatthe locationof thesyntheticobjects. Theglobalilluminationsolutionisthen compositedintoaphotographofthesceneusing thedifferentialrenderingtechnique. Weconcludebydiscussingtherelevance of the technique to recovering surface reflectance properties in uncontrolled lighting situations. Applications of the method include visual effects, interior design, and architectural visualization.

Abstract not found

The applications of texture mapping in computer graphics and image distortion (warping) in image processing share a core of fundamental techniques. We explore two of these techniques, the twodimensional geometric mappings that arise in the parameterization and projection of textures onto surfaces, and the filters necessary to eliminate aliasing when an image is resampled during texture mapping or warping. With respect to mappings, this work presents a tutorial on three common classes of mapping: the affine, bilinear, and projective. For resampling, this work develops a new theory describing the ideal, space variant antialiasing filter for signals warped and resampled according to an arbitrary mapping. Efficient implementations of the mapping and filtering techniques are discussed and demonstrated.

Leonard McMillan Jr. An Image-Based Approach to Three-Dimensional Computer Graphics (Under the direction of Gary Bishop) The conventional approach to three-dimensional computer graphics produces images from geometric scene descriptions by simulating the interaction of light with matter. My research explores an alternative approach that replaces the geometric scene description with perspective images and replaces the simulation process with data interpolation. I derive an image-warping equation that maps the visible points in a reference image to their correct positions in any desired view. This mapping from reference image to desired image is determined by the center-of-projection and pinhole-camera model of the two images and by a generalized disparity value associated with each point in the reference image. This generalized disparity value, which represents the structure of the scene, can be determined from point correspondences between multiple reference images. The image-warpi...

Figure 1: (Left) Uniform 512x512 shadow map and resulting image. (Right) The same with a perspective shadow map of the same size. Shadow maps are probably the most widely used means for the generation of shadows, despite their well known aliasing problems. In this paper we introduce perspective shadow maps, which are generated in normalized device coordinate space, i.e., after perspective transformation. This results in important reduction of shadow map aliasing with almost no overhead. We correctly treat light source transformations and show how to include all objects which cast shadows in the transformed space. Perspective shadow maps can directly replace standard shadow maps for interactive hardware accelerated rendering as well as in high-quality, offline renderers. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation—Bitmap and framebuffer operations; I.3.7 [Computer

Three dimensional scenes are typically modeled using a single, fixed resolution model of each geometric object. Renderings of such a model are often either slow or crude, however: slow for distant objects, where the chosen detail level is excessive, and crude for nearby objects, where the detail level is insufficient. What is needed is a multiresolution model that represents objects at multiple levels of detail. With a multiresolution model, a rendering program can choose the level of detail appropriate for the object's screen size so that less time is wasted drawing insignificant detail. The principal challenge is the development of algorithms that take a detailed model as input and automatically simplify it, while preserving appearance. Multiresolution techniques can be used to speed many applications, including real time rendering for architectural and terrain simulators, and slower, higher quality rendering for entertainment and radiosity. This paper surveys existing multiresolutio...

A reflection and refraction model for anisotropic surfaces is introduced. The anisotropy is simulated by small cylinders (added or subtracted) distributed on the anisotropic surface. Different levels of anisotropy are achieved by varying the distance between each cylinder and/or rising the cylinders more or less from the surface. Multidirectional anisotropy is modelled by orienting groups of cylinders in different direction. The intensity of the reflected light is computed by determining the visible and illuminated portion of the cylinders, taking self-blocking into account. We present two techniques to compute this in practice. In one the intensity is computed by sampling the surface of the cylinders. The other is an analytic solution. In the case of the diffuse component, the solution is exact. In the case of the specular component, an approximation is developed using a Chebyshev polynomial approximation of the specular term, and integrating the polynomial. This model can be implemented easily within most rendering system, given a suitable mechanism to define and alter surface tangents. The effectiveness of the model and the visual importance of anisotropy are illustrated with some pictures.

Creating realistic images has been a major focus in the study of computer graphics for much of its history. This e ort has led to mathematical models and algorithms that can compute predictive, or physically realistic, images from known camera positions and scene descriptions that include the geometry of objects, the re ectance of surfaces, and the lighting used to illuminate the scene. These images accurately describe the physical quantities that would be measured from a real scene. Because these algorithms can predict real images, they can also be used in inverse problems to work backward from photographs to attributes of the scene. Work on three such inverse rendering problems is described. The rst, inverse lighting, assumes knowledge of geometry, re ectance, and the recorded photograph and solves for the lighting in the scene. A technique using a linear least-squares system is proposed and demonstrated. Also demonstrated is an application of inverse lighting, called re-lighting, which modi es lighting in photographs. The second two inverse rendering problems solve for unknown re ectance, given images with known geometry, lighting, and camera positions. Photographic texture measurement