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ComputerGenerated PenandInk Illustration
, 1996
"... This dissertation describes the principles of penandink illustration, and shows how a great number of them can be implemented as part of an automated rendering system. Illustration techniques in general, and penandink rendering in particular, offer great potential for creating effective images f ..."
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Cited by 218 (11 self)
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This dissertation describes the principles of penandink illustration, and shows how a great number of them can be implemented as part of an automated rendering system. Illustration techniques in general, and penandink rendering in particular, offer great potential for creating effective images from CAD models. And with the computer's ability to manipulate increasingly large models, communicating complex information in an effective and comprehensible manner is becoming an important problem. However, this potential remains relatively untapped in the field of computer graphics. After discussing principles of traditional penandink rendering, this dissertation shows how the traditional graphics pipeline must be modified to support penandink rendering. Then, it introduces the new concept of prioritized stroke textures. Prioritized stroke textures form the central mechanism by which strokes are generated so as to both convey a certain texture, such as "bricks", and achieve a target tone simultaneously. Prioritized stroke textures also have the advantages of being resolution dependent
A survey of visibility for walkthrough applications
 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER
, 2003
"... Visibility algorithms for walkthrough and related applications have grown into a significant area, spurred by the growth in the complexity of models and the need for highly interactive ways of navigating them. In this survey, we review the fundamental issues in visibility and conduct an overview of ..."
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Cited by 184 (9 self)
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Visibility algorithms for walkthrough and related applications have grown into a significant area, spurred by the growth in the complexity of models and the need for highly interactive ways of navigating them. In this survey, we review the fundamental issues in visibility and conduct an overview of the visibility culling techniques developed in the last decade. The taxonomy we use distinguishes between pointbased and fromregion methods. Pointbased methods are further subdivided into object and imageprecision techniques, while fromregion approaches can take advantage of the cellandportal structure of architectural environments or handle generic scenes.
A survey of shadow algorithms
 IEEE Computer Graphics and Applications
, 1990
"... Essential to realistic and visually appealing images, shadows are difficult ta compute in most display environments. This survey characterizes the various types of shadows. It also describes most existing shadow algorithms and discusses their complexities, advantages, and shommings. We examine herd ..."
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Cited by 150 (3 self)
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Essential to realistic and visually appealing images, shadows are difficult ta compute in most display environments. This survey characterizes the various types of shadows. It also describes most existing shadow algorithms and discusses their complexities, advantages, and shommings. We examine herd shadows, soft shadbws, shadows of transparent objects, and shadows for complex modeling primitives. For each type, we examine shadow algorithms within various rendswing techniques. This survey attempts to provide readem with enough background and insight on the various rmthods to dow them to choose the algorithm best wpuited to their W. We also hope that our analysis will h&p identify the a m that need more research and point bo possible sotutkms. A shadowa region of relative darkness within an not necessarily attenuate the light it occludes. In fact, illuminated regionoccurs when an object totally or it can concentrate light. However, as is traditional in partially occludes the light. A transparent object does image synthesis, lve will consider a region to be in
Fast Calculation of Soft Shadow Textures Using Convolution
, 1998
"... The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some ..."
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Cited by 130 (9 self)
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The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative "ideal" configuration. We analyze the various sources of approximation in the process and derive a hierarchical, errordriven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamic environments.
Discontinuity Meshing for Radiosity
 Third Eurographics Workshop on Rendering
, 1992
"... The radiosity method is the most popular algorithm for simulating interreflection of light between diffuse surfaces. Most existing radiosity algorithms employ simple meshes and piecewise constant approximations, thereby constraining the radiosity function to be constant across each polygonal element ..."
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Cited by 96 (2 self)
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The radiosity method is the most popular algorithm for simulating interreflection of light between diffuse surfaces. Most existing radiosity algorithms employ simple meshes and piecewise constant approximations, thereby constraining the radiosity function to be constant across each polygonal element. Much more accurate simulations are possible if linear, quadratic, or higher degree approximations are used. In order to realize the potential accuracy of higherdegree approximations, however, it is necessary for the radiosity mesh to resolve discontinuities such as shadow edges in the radiosity function. A discontinuity meshing algorithm is presented that places mesh boundaries directly along discontinuities. Such algorithms offer the potential of faster, more accurate simulations. Results are shown for threedimensional scenes. Keywords: global illumination, diffuse interreflection, adaptive mesh, shadow. 1 Introduction One of the most challenging tasks of image synthesis in computer ...
Rendering Parametric Surfaces in Pen and Ink
, 1996
"... This paper presents new algorithms and techniques for rendering parametric freeform surfaces in pen and ink. In particular, we introduce the idea of “controlleddensity hatching ” for conveying tone, texture, and shape. The fine control over tone this method provides allows the use of traditional t ..."
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Cited by 83 (4 self)
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This paper presents new algorithms and techniques for rendering parametric freeform surfaces in pen and ink. In particular, we introduce the idea of “controlleddensity hatching ” for conveying tone, texture, and shape. The fine control over tone this method provides allows the use of traditional texture mapping techniques for specifying the tone of penandink illustrations. We also show how a planar map, a data structure central to our rendering algorithm, can be constructed from parametric surfaces, and used for clipping strokes and generating outlines. Finally, we show how curved shadows can be cast onto curved objects for this style of illustration.
Fast Computation of Shadow Boundaries Using Spatial Coherence and Backprojections
, 1994
"... This paper describes a fast, practical algorithm to compute the shadow boundariesin a polyhedral scene illuminated by a polygonal light source. The shadow boundaries divide the faces of the scene into regions such that the structure or "aspect" of the visible area of the light source is co ..."
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Cited by 76 (5 self)
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This paper describes a fast, practical algorithm to compute the shadow boundariesin a polyhedral scene illuminated by a polygonal light source. The shadow boundaries divide the faces of the scene into regions such that the structure or "aspect" of the visible area of the light source is constant within each region. The paper also describes a fast, practical algorithm to compute the structure of the visible light source in each region. Both algorithms exploit spatial coherence and are the most efficient yet developed. Given the structure of the visible light source in a region, queries of the form "What specific areas of the light source are visible?" can be answered almost instantly from any point in the region. This speeds up by several orders of magnitude the accurate computation of first level diffuse reflections due to an area light source. Furthermore, the shadow boundaries form a good initial decomposition of the scene for global illumination computations. CR category: I.3.7 [Co...
Balanced Aspect Ratio Trees: Combining the Advantages of kd Trees and Octrees
"... Given a set S of n points in R^d, we show, for fixed d, how to construct in O(n log n) time a data structure we call the Balanced Aspect Ratio (BAR) tree. A BAR tree is a binary space partition tree on S that has O(logn) depth and in which every region is convex and “fat ” (that is, has a bounded as ..."
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Cited by 61 (7 self)
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Given a set S of n points in R^d, we show, for fixed d, how to construct in O(n log n) time a data structure we call the Balanced Aspect Ratio (BAR) tree. A BAR tree is a binary space partition tree on S that has O(logn) depth and in which every region is convex and “fat ” (that is, has a bounded aspect ratio). While previous hierarchical data structures, such as kd trees, quadtrees, octrees, fairsplit trees, and balanced box decompositions can guarantee some of these properties, we know of no previous data structure that combines alI of these properties simultaneously. The BAR tree data structure has numerous applications ranging from solving several geometric searching problems in fixed dimensional space to aiding in the visualization of graphs and threedimensional worlds.
Progressive radiance evaluation using directional coherence maps
 In SIGGRAPH 98
, 1998
"... We develop a progressive refinement algorithm that generates an approximate image quickly, then gradually refines it towards the final result. Our algorithm can reconstruct a highquality image after evaluating only a small percentage of the pixels. For a typical scene, evaluating only 6 % of the pi ..."
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Cited by 53 (2 self)
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We develop a progressive refinement algorithm that generates an approximate image quickly, then gradually refines it towards the final result. Our algorithm can reconstruct a highquality image after evaluating only a small percentage of the pixels. For a typical scene, evaluating only 6 % of the pixels yields an approximate image that is visually hard to distinguish from an image with all the pixels evaluated. At this low sampling rate, previous techniques such as adaptive stochastic sampling suffer from artifacts including heavily jagged edges, missing object parts, and missing highfrequency details. A key ingredient of our algorithm is the directional coherence map (DCM), a new technique for handling general radiance discontinuities in a progressive ray tracing framework. Essentially an encoding of the directional coherence in image space, the DCM performs well on discontinuities that are usually considered extremely difficult, e.g. those involving nonpolygonal geometry or caused by secondary light sources. Incorporating the DCM into a ray tracing system incurs only a negligible amount of additional computation. More importantly, the DCM uses little memory and thus it preserves the strengths of ray tracing systems in dealing with complex scenes. We have implemented our algorithm on top of RADIANCE. Our enhanced system can produce highquality images significantly faster than RADIANCE – sometimes by orders of magnitude. Moreover, when the baseline system becomes less effective as its Monte Carlo components are challenged by difficult lighting configurations, our system will still produce high quality images by redistributing computation to the small percentage of pixels as dictated by the DCM.
Partitioning Tree Image Representation and Generation from 3D Geometric Models
, 1996
"... While almost all research on image representation has assumed an underlying discrete space, the most common sources of images have the structure of the continuum. Although employing discrete space representations leads to simple algorithms, among its costs are quantization errors, significant verbos ..."
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Cited by 50 (1 self)
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While almost all research on image representation has assumed an underlying discrete space, the most common sources of images have the structure of the continuum. Although employing discrete space representations leads to simple algorithms, among its costs are quantization errors, significant verbosity and lack of structural information. A neglected alternative is the use of continuous space representations. In this paper we discuss one such representation and algorithms for its generation from views of 3D continuous space geometric models. For this we use binary, space partitioning trees for representing both the model and the image. Our approach falls under the general rubric of visible surface algorithms, providing an objectspace algorithm which under certain conditions requires only sublinear time for a partitioning tree represented model, and in general exploits occlusion so that the computational cost converges toward the complexity of the image as the depth complexity increases. Visible edges can also be generated as a step following visible surface determination. However, an important contextual difference is that the resulting image trees are used in subsequent continuous space operations. These include affine transformations, set operations, and metric calculations, which can be used to provide image compositing, incremental image modification in a sequence of frames, and facilitating matching for computer vision/robotics. Image trees can also be used with the hemicube and light buffer illumination methods as a replacement for regular grids, thereby providing exact rather than approximate visibility.