T. Saito and T. Takahashi. Comprehensible rendering of 3-D shapes. Computer Graphics, 24(4):197--206, 1990.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....rendering [Lak00a] Image based algorithms represent one of the most important categories in NPR. As one of the most important approaches, geometric buffers, known as G buffers, preserve geometric properties of scene objects in image space such as normals, depth, or object identifiers [Sai90a]. They are evaluated and combined in a post processing step using image processing. Finally, derived image space information such as contour lines, is combined with the results of scene rendering to enhance scene elements that are important for visual perception. The derived information is not ....

....The remainder of this paper is structured as follows. Section 2 discusses related work. Section 3 gives a classification of edges. Section 4 describes the implementation of the algorithm. Section 5 presents applications. Section 6 draws conclusions. 2. RELATED WORK Saito and Takahashi [Sai90a] introduced the G buffer as a two dimensional data structure that stores geometric properties of 3D shapes. Important Gbuffers are the normal buffer, z buffer, and Id buffer. Furthermore, they describe image processing operations used to analyze G buffer contents to produce comprehensible ....

Saito, T. and Takahashi, T. Comprehensible Rendering of 3-D Shapes. In Computer Graphics (Proceedings of SIGGRAPH'90), 24(4), pp.197206, August 1990.

....maps visible points in the scene to point primitives in the image. Willats calls this optical denotation. In the line drawing primitive system, 1D lines in the picture denote silhouettes of the scene. Silhouette extraction is the main primitive issue in NPR, e.g. EC90, Goo98, MKT 97, ZH00, ST90, RC99, Cur98, BS00] There are also non trivial primitive systems, for example ball andstick drawing, where an elongated volumetric cylindrical shape such as an arm is mapped to a line primitive (Fig. 7) Wil97, HOT98] Figure 7: Ball and stick drawing of a man. Attribute system: The attribute ....

....the highlight) interacts with the attribute system (shininess of the material) Shadows raise similar issues, since they can depend on the primitive, attribute and spatial systems. We distinguish three approaches to silhouette extraction 3D 2D [EC90, Goo98, MKT 97, SGG 00, ZH00] 2D [ST90, RC99, Cur98, BS00] or 2D [Can86, PHM90] An important issue of future work is the design of edge selection algorithms. Artists have the ability to draw only the relevant edges to depict an object. This can be addressed by devising selection rules, or interactive selection tools. Elder et ....

[Article contains additional citation context not shown here]

T. Saito and T. Takahashi. Comprehensible Rendering of 3-D Shapes. In Computer Graphics (Proc. SIGGRAPH), 1990.

....or programmer must have control over how strokes are oriented as well as where they are placed. Salisbury et al. used a user specified vector field defined on an image to guide the orientation of pen and ink strokes [9] while others rasterize normal and curvature information from a 3 D model [6][8]. This use of orientation fields to guide stroke drawing is another common thread running through multiple NPR approaches. Screen space density: Careful attention to screen space density of strokes is yet another common theme. For example, concentrating strokes most densely on the silhouette of ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes. In SIGGRAPH 90 Conference Proceedings, pp. 197-206. ACM SIGGRAPH, August 1990.

....speeding up the process while at the same time improving the quality of the images. To find and render the silhouette edges in a polygonal model, two solution categories have been proposed. The first encompasses image space algorithms using several rendering stages, while either modifying depths [13] or scaling polygons [12] The main advantage of image space based methods is that they also work on unconnected polygon meshes without the need for pre processing, so they keep working well when the polygons are dynamically recreated or deformed for each individual animation frame. Drawbacks are ....

T. Saito and T. Takahashi. Comprehensible rendering of 3D shapes. Proceedings of SIGGRAPH '90, pages 197--206, 1990.

.... (NPR) has found methods to simulate the effects of various traditional media like pen and ink [4, 27, 28, 34, 35, 19] pencil sketches [1] water color [3] and engraving [21, 30] There has been work on rendering different styles like impressionism [8, 10, 15, 18] and technical illustrations [6, 26, 25]. There has also been work on non photorealistic rendering of specific objects like fur and grass [13, 14] To the best of our knowledge, except for an interactive 2D system developed in 1988 [2] we have not seen any work specifically on computer generated 3D charcoal rendering. However, there ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes. In Computer Graphics (SIGGRAPH '90 Proceedings), volume 24, pages 197--206, August 1990.

.... in painting, Gooch et al. developed a tone based illumination model that determined hue, as well as intensity, from the orientation of a surface element to a light source [Gooch98] The extraction and rendering of silhouettes and other expressive lines has been addressed by several researchers [including Saito90, Salisbury94, Gooch99, Interrante95, Girshik00]. Expressive textures have also been applied to surfaces to convey surface shape [including Levoy90b, Rheingans96, Salisbury97, Interrante97] A few researchers have applied NPR techniques to the display of data. Laidlaw used concepts from painting to create visualizations of 2D data, using ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes, Computer Graphics (Proceedings of SIGGRAPH 90), 24 (4), pp. 197-206 (August 1990, Dallas, Texas).

....denotation system maps a visible point in the scene to a point primitive in the image. Willats calls this optical denotation. In line drawing, 1D lines in the picture denote silhouettes of the scene. Silhouette extraction is the main denotation issue in NPR, e.g. EC90, Goo98, MKT 97, ZH00, ST90, RC99, Cur98, BS00] Denotation has long been neglected because the classical denotation systems may appear trivial at first sight. We mainly follow Willats s classification, but introduce the distinction between continuous and discrete point primitives. A discrete point primitive is e.g. the ....

....of specular highlights. The latter is a case where the denotation system (line drawing of the highlight) interacts with the attribute system (shininess of the material) We distinguish three approaches to silhouette extraction 3D # 2D [EC90, Goo98, MKT 97, SGG 00, ZH00] 2. 5D # 2D [ST90, RC99, Cur98, BS00] or 2D # 2D [Can86, PHM90] An important issue of future work is the design of edge selection algorithms. Artists have the ability to draw only the relevant edges to depict an object. This can be addressed by devising selection rules, or interactive selection tools. Elder ....

[Article contains additional citation context not shown here]

T. Saito and T. Takahashi. Comprehensible Rendering of 3-D Shapes. In Computer Graphics (Proc. SIGGRAPH), 1990.

....who has used a map with height contours will know. A disadvantage here is that in areas with a low magnitude of the gradient, i.e. more or less flat areas, large gaps lie between contours, and hence no information on local structure is shown. Saito and Takahashi have introduced dense contours [5]. Contours are generated such that the distance between contours is constant in the space of the domain of the function. A related topic is the generation of streamlines for 2D flow fields. How can we generate streamlines such that the area is uniformly covered Turk and Banks [7] use a complex ....

....weights w 0 and w 1 w 0 =#p# p,w 1 = p #p#. The graphical representation is constructed as a linear combination of graphical elements at the levels L 0 and L 1 , the weights denote the strengthtobeusedperlevel. Figure 7 shows a result. The function f is sampled pixel by pixel (similar to [5, 8]) and for each pixel is determined whether or not it lies on a contour. Here we used b = 2, i.e. between two diverging contours a single new contour starts. The width and the intensity of the contours are modulated by the weights, leading to tapered ends of contours. Note that the contours of L ....

T. Saito and T. Takahashi. Comprehensible rendering of 3-d shapes. Computer Graphics, 24(4):197--206, 1990.

....be drawn in a computer generated image to maximize the amount of shape information conveyed while minimizing the number of lines drawn. Interrante et al. 17] chose to use only view independent ridge and valley lines. Elber et al. 6] Gooch et al. 10, 11] Markosian et al. 20] and Saito et al. [21] included ridge and valley lines, as well as edge lines, consisting of surface boundaries, silhouettes, and discontinuities, to separate individual parts and to emphasize important features in the shape of each object. These edge lines lend definition to the image and give it form. However in the ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3D Shapes. In SIGGRAPH 90 Conference Proceedings, August 1990.

.... generate imagery in various traditional media like pen and ink [4, 25, 26, 28, 29, 17] pencil sketches [1] water color [3] and engraving [19, 27] There has been work on rendering different styles like impressionism [8, 10, 14, 16] rendering of fur and grass [12, 13] and technical illustrations [6, 24, 23]. However, to the best of our knowledge, except for an interactive 2D system developed in 1988 [2] we have not seen any work on computer generated 3D charcoal rendering. In this paper, we present a rendering algorithm that automatically generates charcoal drawings of a given 3D model at ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes. In Computer Graphics (SIGGRAPH '90 Proceedings), volume 24, pages 197--206, August 1990.

....by either performance limitations or attempts to achieve photorealism. A movement within the community to display images in non photorealistic, artistic styles began to gain momentum with Haeberli s impressionist painting programs [6] and Saito and Takahashi s Comprehensible Renderering paper [16]. These were soon followed by commercial tools such as Fractal Painter [3] Since then, there has been an explosion of new styles presented at SIGGRAPH and other venues. Just a few examples include impressionist painting [12] technical illustration [5] pen and ink [17] engraving [14] ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible rendering of 3-d shapes. Computer Graphics (Proceedings of SIGGRAPH 90), 24(4).

.... system for shading 3D models of arbitrary topology (6) 2 Previous work Much of the work in non photorealistic rendering has focused on tools to help artists (or non artists) generate imagery in various traditional media or styles such as impressionism [5, 12, 14] technical illustration [4, 19, 20], pen and ink [1, 21, 22, 26, 27] and engraving [16] Our work is applicable over a range of styles in which individual strokes are visible. One way to categorize NPR methods would be to consider the form of input used. One branch of stroke based NPR work uses a reference image for color, tone, ....

....and Perlin [6] addressed the challenge of frame toframe coherence by applying optical flow methods to approximate object space coherence for strokes. Our work follows a branch of research that relies on 3D models for input. Much of the work in 3D has focused on creating still images of 3D scenes [1, 2, 20, 24, 25, 26, 27]. Several systems have also addressed off line animation [1, 14] wherein object space stroke coherence is considerably easier to address than it is for processing of video. A number of researchers have introduced schemes for interactive non photorealistic rendering of 3D scenes, including ....

SAITO,T.,AND TAKAHASHI, T. Comprehensible rendering of 3D shapes. Proceedings of SIGGRAPH 90, 197--206.

....the first to consider illustration related issues rigorously, and to introduce the idea of using high level control, such as importance tags, to influence the rendering. 4 Saito and Takahashi also proposed a system that enhances a shaded image with features borrowed from the realm of illustration [34]. In their approach, they produce both an image and a G buffer using a modified ray tracer. The G buffer contains information such as z depth, surface normal, and object ID for each pixel in the image. They then use image processing techniques that operate on both the image and the G buffer to ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible rendering of 3D shapes. Computer Graphics 24, 4 (August 1990), 197--206. 70

.... shape and tone for surfaces of arbitrary topology (6) 2 Previous work Much of the work in non photorealistic rendering has focused on tools to help artists (or non artists) generate imagery in various traditional media or styles such as impressionism [8, 9, 16, 18] technical illustration [6, 23, 24], watercolor [2] engraving [20] and pen and ink [3, 26, 27, 31, 32] Our work is applicable over a range of artistic styles in which individual hatching strokes are visible, for example pencil, charcoal, or crayon. One way to categorize NPR methods would be to consider the form of input used. A ....

....and Perlin [10] addressed the challenge of frame toframe coherence by applying optical flow methods to approximate object space coherence for strokes. Our work follows a branch of research that relies on 3D models for input. Much of the work in 3D has focused on creating still images of 3D scenes [3, 4, 10, 24, 30, 29, 31, 32]. However, several systems have addressed off line animation [1, 3, 18] wherein object space stroke coherence is considerably easier to address than it is for processing of video. A number of researchers have introduced technologies for interactive NPR for 3D scenes, for example, shading for ....

SAITO,T.,AND TAKAHASHI, T. Comprehensible rendering of 3D shapes. Proceedings of SIGGRAPH 90, 197--206.

....of abstraction. Table 2.1. Summary of non photorealistic and other computer graphics papers. Author Line Drawing Shading Automatic (Not userdriven) 3D Interactive Applicable to Technical Illustration Additional Illustration Rules Markosian [24] p p p p Dooley [11] p p p p Saito [29] p p p p Driskill [12] p p Elber [13] p p p Seligmann [34] p p p p Land [22] p p p Gooch [15] p p p p Zeleznik [42] p p p Salisbury [32, 31] p p Salisbury [30] p p p Winkenbach [38] p p p Winkenbach [39] p p p Meier [27] p p Haeberli [17] p Litwinowicz [23] Curtis [10] ....

....by permission. Figure 2.2. Computer generated pen and ink illustrations. 8 2.2 One Shot Images Conveying Shape The research reviewed in the previous section concentrated on generating aesthetically pleasing images. The work done by Seligmann and Feiner [34] Winkenbach et al. 39] Saito et al. [29], Land et al. 22] Elber [13] and Dooley et al. 11] generated images in which the primary goal is to convey shape information. However, these techniques generate single images and do not allow user interaction. Seligmann and Feiner [34] created a system based on the idea that an illustration ....

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Saito, T., and Takahashi, T. Comprehensible rendering of 3D shapes. In SIGGRAPH 90 Conference Proceedings (Aug. 1990).

....Work done in computer graphics by Seligmann and Feiner [25] and Dooley and Cohen [7] concentrate on additional aspects of technical illustration like layout, object transparency, and line style. We have also drawn on the work of Markosian et al. 19] Elber [9] and Saito and Takahashi [24]. Markosian et al. 19] developed a real time 3D interactive system for illustrating silhouettes and creases of non self intersecting polygon mesh based models. Elber [9] provides algorithms for determining NURBS surface information by finding four types of curves: the surface boundary curves, ....

....non self intersecting polygon mesh based models. Elber [9] provides algorithms for determining NURBS surface information by finding four types of curves: the surface boundary curves, curves along C 1 discontinuities in the surface, isoparametric curves, and silhouette curves. Saito and Takahashi [24] offer convincing pictures to show how 3D models enhanced with discontinuity lines, contour lines, and curved hatching can generate images which convey shape and structure. In Section 8.3, we will discuss the rules, properties, and types of lines needed to convey shape information as accomplished ....

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Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3D Shapes. In SIGGRAPH 90 Conference Proceedings, August 1990.

....color, size, and orientation, from synthetically rendered or photographic reference pictures. Several commercial systems, such as [3] and [8] have incorporated the idea of reference pictures, and Saito andTakahashiusea similar concept, the G buffer, to create simplified illustration type images [11]. Our system also uses reference pictures to obtain brush stroke attributes. In Haeberli s system brush stroke positions are randomly distributed, so successive frames of an animation would change randomly. Alternatively, the positions and sizes of brush strokes could remain constant over the ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible rendering of 3-D shapes. In Computer Graphics (SIGGRAPH '90 Proceedings), volume 24, pages 197--206, August 1990.

....smooth, continuous silhouette curves on the actual model. As described in Section 4, our method generates this kind of output, and solves the problem of bifurcation along the silhouette edge by rendering the 3 D model colored with texture coordinates into a frame buffer. Saito and Takahashi [21] employed a similar technique for highlighting edges in technical illustrations, and Wallach et al. 29] used this idea for finding frame to frame coherence in 3 D animations. This project shares much in spirit with the recent progress of the computer graphics community toward non photorealistic ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes. In Forest Baskett, editor, SIGGRAPH 90 Conference Proceedings, Annual Conference Series, pages 197--206. ACM SIGGRAPH, Addison Wesley, August 1990.

....to the medical imaging application field. Using MIP some internal features can be hidden by higher density regions and using Fourier volume rendering, which is equivalent to density accumulation, similar problems arise. The application of well known non photorealistic rendering (NPR) techniques [9][11] 16] is a new direction in volume rendering research. Previously, these NPR methods have been proposed for polygonal surface models, therefore their application to iso surfaces extracted from volume data seems to be obvious. Interrante [13] uses principal direction driven 3D line integral ....

T. Saito and T. Takahashi. Comprehensible Rendering of 3-D Shapes. Computer Graphics (SIGGRAPH '90 Proceedings), pages 197--206, 1990.

....is a bump or a cavity or how much the surface is changing in an area. The level lines are generated from the depth image. Firstly, the gradient of the depth image is calculated using a rst derivative of the Gauss lter. The level lines are drawn based on the technique described by Saito et al. [10]. To draw a level line we de ne a value p i which corresponds to the depth of each level. p i is de ned discretely p i = p 0 iq, i is an integer and q is the depth interval between levels. d is de ned as the value of the depth image in the current pixel and g is its gradient. The level line ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible rendering of 3-D shapes. In Forest Baskett, editor, SIGGRAPH'90 Conference Proceedings, Annual Conference

....fields: For the full range of expressive effect, an artist or programmer must have control over how strokes are oriented as well as where they are placed. 9] used a user specified vector field defined on an image to guide the orientation of pen and ink strokes, while techniques such as [6] and [8] rasterize normal and curvature information from a 3 D model. This use of orientation fields to guide stroke drawing is another common thread running through multiple NPR approaches. Screen space density: Careful attention to screen space density of strokes is yet another common theme. For ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes. In SIGGRAPH 90 Conference Proceedings, pp. 197-206. ACM SIGGRAPH, August 1990.

....used in nonphotorealistic rendering can be separated into two groups: image space and object space. The image based approach is general and simple; however, it is not particularly suitable for generating concise line drawings of untextured smooth surfaces. Image based techniques are presented in [5, 30, 7, 18, 6, 28]; these algorithms exploit graphics hardware to produce image precision silhouette images. Our technique is an object space method; it directly uses the 3D representation of objects, rather than their images. Winkenbach and Salesin [36] describe a method for producing appealing pen and ink ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes. In Forest Baskett, editor, Computer Graphics (SIGGRAPH '90 Proceedings) , volume 24, pages 197--206, August 1990.

....either in model space or in camera space. In some situations there is no need to project the object normals into camera space so the test should be done in object space. Image space algorithms The use of silhouette edges has been discussed by several people, in particular Saito and Takahashi [6] showed how silhouette edges can be used to enhance the display of images. The silhouette edges can be rendered by highlighting the discontinuities in the z buffer derivative. In a similar fashion creases or folds in the image can be rendered by highlighting discontinuities in the second ....

....objects is that back facing polygons need not be submitted to the rendering pipeline. Unfortunately if the object is an open polyhedral object all of its polygons need to be submitted to the rendering pipeline, this is illustrated in Figure 3. After processing the polygons P[1,2,3,4] and P[3,7,6,4] the edges ##; ##,##; ## will have their front facing flags set. Similarly after polygons P[1,2,8,5] and P[8,7,6,5] have been processed the edges ##; ## and ##; ## will have their back facing flags set. After all the polygons in this open box have been processed the edges ##; ##; ##; ##; ##; ....

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T. Saito and T. Takahashi. Comprehensible rendering of 3d shapes. In Proc. of SIGGRAPH '90, pages 197--206, August 1990.

....is combined with hatches from the filtered principal directions. The previously mentioned approaches that respect the geometry of an object are all able to produce real stokes, e.g. in Postscript. Besides, there is another class of techniques that are pixel based and produce discrete images. [14] introduce the concept of G bu#ers that provide additional information per pixel such as depth value, normal vector or the parameter value of a parametric surface. Non photorealistic images that resemble line drawings can then be generated by applying well known image processing operators. In ....

....The other images show the color coded attribute fields, one for the normal vectors and one for each principal direction. We call the collection of all these images (with identical resolution) the enhanced frame bu#er with many di#erent values stored for each pixel. We prefer this term to G bu#er [14] because we interprete pixels as discrete samples that are used to (re )construct continous strokes. Once the given 3D object is rendered, the enhanced frame bu#er contains all the necessary information for the subsequent steps of the algorithm. Hence, phases two and three entirely work in 2D ....

Takafumi Saito, Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes. Computer Graphics (SIGGRAPH '90 Proceedings), 1990, pp. 197--206

....textures of parametric and implicit surfaces [6] Principal directions have been suggested [11,26] and approached [2,6] in line drawings. In [26,6] lines were traced along the parametric lines of parametric surfaces, which sometimes coincided with the principal directions. Saito and Takahashi [20] rendered line drawings lines of parametric surfaces along geodesic lines. Interrante et al. 11] used 3D principal direction textures to illustrate surface shape in volume data. However, none of these works addressed the challenge of estimating the principal directions from arbitrary surfaces ....

T.Saito and T.Takahashi, Comprehensible Rendering of 3D Shapes. Computer Graphics (Proceedings of SIGGRAPH 90), pp.197-206, 1990.

....of hand drawn images in children s picture books, for example, it appears that simple, brightly colored images that omit subtle detail but clearly delineate important objects appeal better to children than do photographs. The point about communication is also made in a number of recent papers [3, 7, 8, 9, 10, 12, 13, 15, 17, 16]. In our original method, the scene geometry itself does not contain any detail elements such as leaves, blades of grass, etc. which we call graftals. Instead, these are generated each frame just as needed. One benefit of this approach is that no work is expended on processing graftals that are ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3D Shapes. Computer Graphics (Proceedings of SIGGRAPH 90), 24(4):197--206, August 1990. ISBN 0201 -50933-4. Held in Dallas, Texas.

....of algorithms addresses the problems inherent to working with silhouette edges by ignoring them altogether. Image based silhouette rendering algorithms avoid explicitly finding the 3D silhouette edges and instead opt to use 2D image processing techniques. Notably, the work of Saito and Takahashi [16] renders the outlines of 3D objects by applying edge detection filters to specially prepared depth and normal maps, and compositing the results with the rest of the scene. However, such approaches suffer from aliasing as the silhouette positions jump from pixel to pixel in the image, because the ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3D Shapes. Computer Graphics (Proceedings of SIGGRAPH 90), 24(4):197--206, August 1990. ISBN 0-201-50933-4. Held in Dallas, Texas .

....along the length of their extent, and the texture definition is inherently tied to a specific surface definition and would have to be completely reiterated in order to be applied to multiple level surfaces from the same 3D distribution. In terms of more general inspiration, Saito and Takahashi [27] showed how the comprehensibility of 3D shaded surface renderings could be improved via highlighting the first and second order depth discontinuities in an image, and they suggested defining a hatching pattern, based on the latitude and longitude lines of a sphere, or on the parametric ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes, Computer Graphics (SIGGRAPH 90 Conference Proceedings), 24(4): 197-206, August 1990.

....images from a single viewpoint presented on a non stereo medium such as pen on paper. In this section we discuss the components of such illustrations that we use in a computer graphics context: line character, shading, and shadowing. 3. 1 Lines in Technical Illustration Several researchers [5, 6, 14, 23] examined which lines should be drawn in a computer generated image to maximize the amount of information conveyed while minimizing the number of lines drawn. They observed that illustrators use edge lines, consisting of surface boundaries, silhouettes, discontinuities, and creases to separate ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3D Shapes. In SIGGRAPH 90 Conference Proceedings, August 1990.

....Pearson and Robinson [13] show how images resembling artists line drawings can be computed from two dimensional digital photographs and they describe how the use of such representations can enable improved bandwidth for visual communication across low speed data lines. Saito and Takahashi [15] propose enhancing shaded renderings of polygonal models with lines representing the locus of first and second order depth discontinuities, and they describe how these lines can be calculated by applying standard gradient operators to a two dimensional depth map of the scene. Miller [12] ....

Saito, S., and Takahashi, T. Comprehensible Rendering of 3-D Shapes. Computer Graphics 24, 4 (August 1990), 197--206.

....to use motion, accommodation, or parallax cues to help deal with visual complexity. Using abstraction to simplify images helps the user overcome the loss of these spatial cues in a 2D image. In computer graphics, there has been little work related to technical illustration. Saito and Takahashi [19] use a variety of techniques to show geometric properties of objects, but their images do not follow many of the technical illustration conventions. Seligmann and Feiner present a system that automatically generates explanationbased drawings [21] Their system focuses primarily on what to draw, ....

....graphics libraries. Edge lines for highly complex objects can be generated interactively using Markosian et al. s technique [14] This only works for polygonal objects, so higher order geometric models must be tessellated to apply that technique. On high end systems, imageprocessing techniques [19] could be made interactive. For metals on a conventional API, we cannot just use a light source. However, either environment maps or texture maps can be used to produce alternating light and dark stripes. 5 Future Work and Conclusion The shading algorithm presented here is exploratory, and we ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3D Shapes. In SIGGRAPH 90 Conference Proceedings, August 1990.

....giving their clients a false impression of completeness. In general, the question of whether to use photorealistic imagery depends on the visual effect intended by the designer. A growing body of research in computer graphics has recognized the power and usefulness of nonphotorealistic imagery [21, 20, 13, 22, 10, 17, 11, 7, 16, 3]. Until now, though, nonphotorealistic rendering (NPR) methods have primarily been batch oriented rather than interactive. An exception is Zeleznik s SKETCH system [22] which makes crude nonphotorealistic renderings using tricks in the standard polygon rendering pipeline) One obstacle to ....

T. Saito and T. Takahashi. Comprehensible rendering of 3d shapes. In Proceedings of SIGGRAPH '90, pp. 197--206, aug 1990.

.... to our knowledge, the first to use orientable textures for image based pen and ink illustration (in which the strokes must convey not only orientation, but texture and tone) the idea of orienting strokes for illustration dates back at least as far as the seminal papers by Saito and Takahashi [11] and Haeberli [6] in SIGGRAPH 90. Winkenbach and Salesin [17] and Meier [9] also make use of oriented strokes for geometry based illustration. Supporting orientable textures for image based pen and ink illustration requires solutions to several new subproblems, which we discuss in this paper. ....

Takafumi Saito and Tokiichiro Takahashi. Comprehensible rendering of 3-D shapes. Computer Graphics, 24(4):197--206, August 1990.

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T. Saito and T. Takahashi. Comprehensible rendering of 3-D shapes. Computer Graphics, 24(4):197--206, 1990.

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Takafumi Saito and Tokiichiro Takahashi. Comprehensible Rendering of 3-D Shapes. In Computer Graphics (SIGGRAPH '90 Proceedings), volume 24, pages 197--206, August 1990.

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Takafumi Saito and Tokiichiro Takahashi. Comprehensible rendering of 3-D shapes. Computer Graphics, 24(4):197--206, 1990.

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T. Saito and T. Takahashi. Comprehensible rendering of 3D shapes. In SIGGRAPH 90 Conference Proceedings, pages 197--206. ACM SIGGRAPH, Addison Wesley, 1990.

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Takafumi Saito and Tokiichiro Takahashi. Comprehensible rendering of 3D shapes. Computer Graphics, 24(4):197--206, Aug 1990.

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T. Saito and T. Takahashi. Comprehensible rendering of 3-d shapes. In Proceedings of the 17th annual conference on Computer graphics and interactive techniques, pages 197--206. ACM Press, 1990.

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T. Saito and T. Takahashi. Comprehensible rendering of 3-d shapes. In SIGGRAPH 90 Conference Proceedings, pages 197 206. ACM, 1990. 4

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Saito, T., Takahashi, T. Comprehensible rendering of 3-D shapes. SIGGRAPH 90 Conference Proceedings, 197--206, 1990. 2

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Takafumi Saito and Toldichiro Takahashi. Comprehensible Rendering of 3-D Shapes. In Forest Baskerr, editor, Proceedings of SIGGRAPH 90 (Dallas, Texas, August 6-10 1990), Computer Graphics Proceedings, Annual Conference Series, pages 197 206, New York, 1990. ACM SIGGRAPH, ACM Press.

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T. Saito and T. Takahashi. Comprehensible Rendering of 3-D Shapes. Computer Graphics (SIGGRAPH '90 Proceedings), pages 197--206, 1990.

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ST90. T. Saito and T. Takahashi. Comprehensible rendering of 3-D shapes. In Proc. of SIGGRAPH, 1990.

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