Resolution Independent NPR-Style 3D Line Textures

IEEE Transactions on Visualization and Computer Graphics, 2000

Rendering large numbers of dense line bundles in three dimensions is a common need for many visualization techniques, including streamlines and fiber tractography. Unfortunately, depiction of spatial relations inside these line bundles is often difficult but critical for understanding the represented structures. Many approaches evolved for solving this problem by providing special illumination models or tube-like renderings. Although these methods improve spatial perception of individual lines or related sets of lines, they do not solve the problem for complex spatial relations between dense bundles of lines. In this paper, we present a novel approach that improves spatial and structural perception of line renderings by providing a novel ambient occlusion approach suited for line rendering in real time.

This paper revisits the problem of wireframe rendering, which, at first, appears to be an easily solved problem. However, the conventional solution is inefficient and does not result in high-quality images. Recently, graphics hardware programming has been employed to achieve high-quality solid line rendering. In this paper, we present a simpler and faster technique for wireframe rendering based on texture mapping. Our technique does not require (but can benefit from) graphics hardware programming and thus can be easily integrated into existing rendering engines, while resulting in fast, accurate, high-quality, anti-aliased, and still versatile, wireframe drawing. For topologically structured meshes, our approach allows the rendering of wireframe decoupled from the underlying mesh, making possible the rendering of original wireframes on top of decimated meshes.

1999

Most of the work in NPR has been static 2D images or image sequences generated by a batch process. In this part of the course notes we explore interactive NPR through the example of interactive technical illustration [4]. Work that has been done on computer generated technical illustrations has focused on static images and has not included all of the techniques used to hand draw technical illustrations. We present a paradigm for the display of technical illustrations in a dynamic environment. This display environment includes all of the benefits of computer generated technical illustrations such as a clearer picture of shape, structure, and material composition than traditional computer graphics methods. It also takes advantage of the threedimensional interactive strength of modern display systems. This is accomplished by using new algorithms for real time drawing of silhouette curves, algorithms which solve a number of the problems inherent in previous methods. We incorporate current non-photorealistic lighting methods, and augment them with new shadowing algorithms based on accepted techniques used by artists and studies carried out in human perception. An interactive NPR system needs the capability to interactively display a custom shading model and edge lines. In addition, this interaction must be possible for complex geometric models. In this part of the course notes we describe a variety of techniques for achieving these goals, and describe the tradeoffs involved in choosing a particular technique. 10.2 Making it Interactive There are several new issues to address when creating 3D illustrations. Three-dimensional technical illustrations involve an interactive display of the model while preserving the characteristics of technical illustrations. By allowing the user to move the objects in space, more shape information may be available than can be conveyed by 2D images. Interaction provides the user with motion cues to help deal with visual complexity, cues that are missing in 2D images. Also, removing the distracting wireframe lines and displaying just silhouettes, boundaries, and discontinuities will provide shape information without cluttering the screen, as discussed previously in Section 8. The question remains, "How do the 2D illustration rules change for a 3D interactive technical illustration?" Adapting the shading and line conventions presented previously in the course notes is fairly straightforward as long as the line width conventions have frame-to-frame coherence. The more interesting issues depend upon changing the viewer's position versus moving the object. Since there are no protocols in traditional illustration, it may be best to model these 3D illustration conventions based on how you would move real object. This has an effect on how the light changes with respect to the object. The light position can be relative to the object or to the viewer. When looking at a small object in your hand, you turn the object and do not move your head, so the light stays in the same position relative to your eye. However when you move an object in an modeling program or when you look at a large part, the view Non-Photorealistic Rendering 10-1

2014

Draping 2D vectorial information over a 3D terrain elevation model is usually performed by real-time rendering to texture. In the case of linear feature representation, there are several specific problems using the texturing approach, specially when using multi-resolution textures. These problems are related to visual quality, aliasing artifacts and rendering performance. In this paper, we address the problems of 2D line rasterization on a multi-resolution texturing engine from a pragmatical point of view; some alternative solutions are presented, compared and evaluated. For each solution we have analyzed the visual quality, the impact on the rendering performance and the memory consumption. The study performed in this work is based on an OpenGL implementation of a clipmap-based multi-resolution texturing system, and is oriented towards the use of inexpensive consumer graphics hardware.

2012

Figure 1: Stylized animation of a galloping horse. From left to right: line samples are extracted from a 3D model; active strokes track the samples; brush paths are attched to the strokes and stylized as circular arcs; two more frames of animation exhibit temporal coherence.

Proceedings of the 3rd international symposium on Non-photorealistic animation and rendering, 2004

at Twin Cities * Figure 1: Stylized rendering of 3D scanned real world environments using representative sketchy styles for feature illustration (from left to right: stippling (point sprites), textured strokes + stippling, and textured strokes + hatching (short line segments)).

2001

Our work in the area of non-photo-realistic rendering (NPR) focuses on visualising 3D models in a cartoon rendering style: the geometrical objects are internally coloured using two or three colours, while simultaneously using an explicit outline. Many NPR techniques are timeconsuming processes, whereas we aim at real-time rendering performance on mainstream graphics PC hardware without losing a high image quality. Particular emphasis is also put on getting smooth transition borders between the bi-tonal cartoon-colours by applying an object precision triangle subdivision technique. Rapidly finding these transition borders as well as silhouette edges is a topic of a new algorithm. As silhouette lines and light effects are useful indicators for computer vision, this algorithm also looks interesting for applications in that field.

This project discusses interactive non-photorealistic rendering techniques. It is split up into two sections – outlining merhods and shading methods. Three outlining methods were implemented – stencilling, front-face culling and ink-sketching. Sten- cilling uses the stencil buffer to create a mask to draw the outline. Front-face culling uses edge localisation methods to draw the silhouette as well as the outline. Ink- sketching builds on front-face culling to make the edges look like they have been sketched with an ink pen. The second section discusses three shading methods – cellshading, ‘simple’ crosshatching and ‘fine’ crosshatching. The cellshading method uses 1D textures to make the shading of the model discrete. ‘Simple’ crosshatch- ing uses textures to shade shade the polygons. ‘Fine’ crosshatching moves beyond current research and refines the ‘simple’ crosshatching to make it more accurate on models with low polygon counts. All of the work presented in this paper is designed to work in real-time with speeds ranging from 24 to 60 frames per second.

Lecture Notes in Computer Science, 2006

2006

This report presents a novel vector rendering pipeline that allows us to easily break the pixel barrier and create high-quality illustrations. Recently, most graphic research has been directed towards rendering pixel images that appear realistic. In contrast, we investigate the generation of vector graphic illustrations using non-photorealistic techniques such as line rendering and Gooch shading. By combining vector output from both shading and line rendering of 3D models we create high-quality illustrations that can directly be used in ...

Smart Graphics, 2007

Abstract. NPR Lenses is an interactive technique for producing ex-pressive non-photorealistic renderings. It provides an intuitive visual in-teraction tool for illustrators, allowing them to seamlessly apply a large variety of emphasis techniques. Advantages of 3D scene manipulation are ...

Computer Graphics Forum, 2008

In this paper we present a pipeline for rendering dynamic 2D/3D line drawings efficiently. Our main goal is to create efficient static renditions and coherent animations of line drawings in a setting where lines can be added, deleted and arbitrarily transformed on-the-fly. Such a dynamic setting enables us to handle interactively sketched 2D line data, as well as arbitrarily transformed 3D line data in a unified manner. We evaluate the proximity of screen projected strokes to simplify them while preserving their continuity. We achieve this by using a special data structure that facilitates efficient proximity calculations in a dynamic setting. This on-the-fly proximity evaluation also facilitates generation of appropriate visibility cues to mitigate depth ambiguities and visual clutter for 3D line data. As we perform all these operations using only line data, we can create line drawings from 3D models without any surface information. We demonstrate the effectiveness and applicability of our approach by showing several examples with initial line representations obtained from a variety of sources: 2D and 3D hand-drawn sketches and 3D salient geometry lines obtained from 3D surface representations.

Computer-Aided Design …, 2011

While many approaches have been developed to visualize 3D city scenes, most of them exhibit the visualization results in a uniform rendering style. This paper presents an expressive rendering approach for visualizing large-scale 3D city scenes with various rendering styles integrated in a seamless way. Each view is actually a combination of the photorealistic rendering, the nonphotorealistic rendering, and the line drawing, so as to highlight the information that is interesting for the users and de-emphasize the other that is less important. At run-time, the users are allowed to specify their interested locations with pre-determined 3D landmarks. Our system automatically computes the salience of each location and visualize the entire scene with emphasis in the area of interests. The GPU-based implementation enables real-time performance, and demonstrates outstanding practicality.

Computer Graphics Forum, 2013

Producing traditional animation is a laborious task where the key drawings are first drawn by artists and thereafter inbetween drawings are created, whether it is by hand or computer-assisted. Auto-inbetweening of these 2D key drawings by computer is a non-trivial task as 3D depths are missing. An alternate approach is to generate all the drawings by extracting lines directly from animated 3D models frame by frame, concatenating and rendering them together into an animation. However, animation quality generated using this straightforward method bears two problems. Firstly, the animation contains unsatisfactory visual artifacts such as line flickering and popping. This is especially pronounced when the lines are extracted using high-order derivatives, such as ridges and valleys, from 3D models represented in triangle meshes. Secondly, there is a lack of temporal continuity as each drawing is generated without taking its neighboring drawings into consideration. In this paper, we propose an improved approach over the straightforward method by transferring extracted 3D line drawings of each frame into individual 3D lines and processing them along the time domain. Our objective is to minimize the visual artifacts and incorporate temporal relationship of individual lines throughout the entire animation sequence. This is achieved by creating correspondent trajectory of each line from each frame and applying global optimization on each trajectory. To realize this target, we present a fully automatic novel approach, which consists of (1) a line matching algorithm, (2) an optimizing algorithm, taking into account both the variations of numbers and lengths of 3D lines in each frame, and (3) a robust tracing method for transferring collections of line segments extracted from the 3D models into individual lines. We evaluate our approach on several animated model sequences to demonstrate its effectiveness in producing line drawing animations with temporal coherence.

1997

Nonphotorealistic rendering (NPR) can help make comprehensible but simple pictures of complicated objects by employing an economy of line. But current nonphotorealistic rendering is primarily a batch process. This paper presents a real-time nonphotorealistic renderer that deliberately trades accuracy and detail for speed. Our renderer uses a method for determining visible lines and surfaces which is a modification of Appel's hidden-line algorithm, with improvements which are based on the topology of singular maps of a surface into the plane. The method we describe for determining visibility has the potential to be used in any NPR system that requires a description of visible lines or surfaces in the scene. The major contribution of this paper is thus to describe a tool which can significantly improve the performance of these systems. We demonstrate the system with several nonphotorealistic rendering styles, all of which operate on complex models at interactive frame rates.