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| Authors | A. Hertzmann, D. Zorin |
| Language | English |
| Type | public |
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We present a new set of algorithms for line-art rendering of
smooth surfaces. We introduce an efficient, deterministic
algorithm for finding silhouettes based on geometric duality, and
an algorithm for segmenting the silhouette curves into smooth
parts with con-stant visibility. These methods can be used to
find all silhouettes in real time in software. We present an
automatic method for generat-ing hatch marks in order to convey
surface shape. We demonstrate these algorithms with a drawing
style inspired by A Topological Picturebook by G. Francis.
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| Authors | G. Winkenbach, D.H. Salesin |
| Language | English |
| Type | public |
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This paper describes the principles of tradional pen-and-ink
illustration, and shows how a great number of them can be
implemented as part of an automated rendering system. It
introduces "stroke textures", which can be used for achieving both
thexture and tone with line drawing. Stroke textures also allow
resolution-dependant rendering, in which the choice of strokes
used in an illustration is appropriatly tied to the resolution of
the target medium. We demonstrate these techniques using complex
architectural models, including Frank Lloyd Wright's "Robie House".
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| Authors | A. Lake, C. Marshall, M. Harrist. M. Blackstein |
| Language | English |
| Type | public |
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| Summary |
Researchers in nonphotorealistic rendering (NPR) have investigated
a variety of techniques to simulate the styles of artists. Recent
work has resulted in methods for pen-and-ink illustration, pencil
sketching, watercolor, engraving, and silhouette edge
rendering. This paper presents real-time methods to emulate
cartoon styles. We also present variations on a texture mapping
technique to achieve real-time pencil sketching. We demonstrate
our method of inking silhouettes, material and mesh boundaries,
and crease edges. In addition, we present techniques for
emphasizing motion of cartoon objects by introducing geometry into
the cartoon scene. The rendering system is integrated with an
animation system and a runtime multi-resolution mesh (MRM) system
to achieve scalability, ensuring real-time performance on any
platform. Such solutions allow us to take advantage of evolving
hardware in order to make nonphotorealistic animation and
rendering achievable on low- and high-end consumer platforms. All
of the techniques described can be applied to models created with
standard modeling tools and require no additional mark-up information from the modeler.
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| Authors | Nick Halper, Stefan Schlechtweg, Thomas Strothotte |
| Language | English |
| Type | public |
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| Summary |
We present a novel way for quickly and easily designing
non-photorealistic images based on elementary operations which are
linked together to create a variety of visual effects. Rather than
mimicking a visual effect that an artist has already produced, we
instead mimick the process undergone for the artist to produce
that image. Compared to traditional approaches, this opens the
possibil-ity to have the images created by users with no
programming skills. We describe a modular system that makes these
elementary opera-tios available to the user. A specially designed
user interface allows for an easy and intuitive combination of
these operations to create an image. Visual feedback is provided
to the user at any time and for any stage in the process.
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| Authors | David Ebert, Penny Rheingans |
| Language | English |
| Type | public |
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| Summary |
Accurately and automatically conveying the structure of a volume
model is a problem not fully solved by existing volume rendering
approaches. Physics-based volume rendering approaches create
images which may match the appearance of translucent materials in
nature, but may not embody important structural details. Transfer
function approaches allow flexible design of the volume
appearance, but generally require substantial hand tuning for each
new data set in order to be effective. We introduce the volume
illustration approach, combining the familiarity of a
physics-based illumination model with the ability to enhance
important features using non-photorealistic rendering
techniques. Since features to be enhanced are defined on the basis
of local volume characteristics rather than volume sample value,
the application of volume illustration techniques requires less
manual tuning than the design of a good transfer function. Volume
illustration provides a flexible unified framework for enhancing
structural perception of volume models through the amplification
of features and the addition of illumination effects.
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| Authors | Ahna Girshick, Victoria Interrante, Steven Haker, Todd Lemoine |
| Language | English |
| Type | public |
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| Summary |
While many factors contribute to shape perception, psychological
research indicates that the direction of lines on the surface may
have an important influence. This is especially the case when
other techniques (shading, silhouetting) do not present sufficient
shape information. The psychology literature suggests that lines
in the principal directions of curvature may communicate surface
shape better than lines in other directions. Moreover, principal
directions have the quality of geometric invariance so line
directions are based on the surface geometry and are viewpoint and
light source independent, and the lines do not move above over the
surface during animation unless desired. In this work we describe
principal direction line drawings which show the flow of curvature
over the surface. The technique is presented for arbitrary
surfaces represented by either 3D volume data or a polygonal
surface mesh. The latter format is common in the field of computer
graphics yet thus far has not been widely used for principal
direction estimation. The methods offered in this paper can be
used alone or in conjunction with other NPR techniques to improve
artistic 3D renderings of arbitrary surfaces.
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| Authors | Aaron Hertzmann |
| Language | English |
| Type | public |
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| Summary |
We describe new algorithms and tools for generating paintings,
illustrations, and anima-tion on a computer. These algorithms are
designed to produce visually appealing and expressive images that
look hand-painted or hand-drawn. In many contexts, painting and
illustration have many advantages over photorealistic computer
graphics, in aspects such as aesthetics, expression, and
computational requirements. We explore three gen-eral strategies
for non-photorealistic rendering: First, we describe explicit
procedures for placing brush strokes. We begin with a painterly
image processing algorithm inspired by painting with real physical
media. This method produces images with a much greater subjective
impression of looking hand-made than do earlier methods. By
adjusting algorithm parameters, a variety of styles can be
generated, such as styles inspired by the Impressionists and the
Expres-sionists. This method is then extended to processing video,
as demonstrated by painterly animations and an interactive
installation. We then present a new style of line art
illus-tration for smooth 3D surfaces. This style is designed to
clearly convey surface shape, even for surfaces without predefined
material properties or hatching directions. Next, we describe a
new relaxation-based algorithm, in which we search for the
painting that minimizes some energy function. In contrast to the
first approach, we ide-ally only need to specify what we want, not
how to directly compute it. The system allows as fine user control
as desired: the user may interactively change the painting style,
specify variations of style over an image, and/or add specific
strokes to the paint-ing.
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| Authors | Lee Markosian, Michael A. Kowalski, Samuel J. Trychin,
Lubomir D. Bourdev, Daniel Goldstein, John F. Hughes |
| Language | English |
| Type | public |
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| Summary |
Nonphotorealistic rendering (NPR) can help make comprehensible but
simple pictures of complicated objects by employing an econ-omy 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 im-provements 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 re-quires 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 demon-strate the system with several
nonphotorealistic rendering styles, all of which operate on
complex models at interactive frame rates.
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| Authors | Christian Rư ossl, Leif Kobbelt |
| Language | English |
| Type | public |
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| Summary |
We present an interactive system for computer aided generation of line
art drawings to illustrate 3D mod- els that are given as
triangulated surfaces. In a pre- processing step an enhanced 2D
view of the scene is computed by sampling for every pixel the
shading, the normal vectors and the principal directions obtained
from discrete curvature analysis. Then streamlines are traced in
the 2D direction elds and are used to de- ne line strokes. In
order to reduce noise artifacts the user may interactively select
sparse reference lines and the system will automatically ll in
additional strokes. By exploiting the special structure of the
streamlines an intuitive and simple tone mapping algorithm can be
derived to generate the nal rendering.
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| Authors | Amy Ashurst Gooch and Bruce Gooch |
| Language | English |
| Type | public |
| Url | |
| Summary |
The advent of photography and computer graphics has not replaced
artists. Imagery generated by artists provides information about
objects that may not be readily apparent in photographs or real
life. The same goal should apply to computer-generated
images. This is the driving force behind non-photorealistic
rendering. The term non-photorealistic rendering (NPR) is applied
to imagery that looks as though it was made by artists, such as
pen-and-ink or watercolor. Many computer graphics researchers are
exploring NPR techniques as an alternative to photorealistic
rendering. More importantly, non-photorealistic rendering is now
being acknowledged for its ability to communicate the shape and
structure of complex models. Techniques which have long been used
by artists can emphasize specific features, expose subtle shape
attributes, omit extraneous information, and convey material
properties. These artistic techniques are the result of an
evolutionary process, refined over centuries. Therefore, imitating
some of these artistic methods and exploring the perceptual
psychology behind the techniques of artists are good first steps
in going beyond photorealistic rendering. In these notes, we have
gathered the ideas and methods from our previous work [11, 12, 13]
to demonstrate how non-photorealistic rendering methods can be
used to convey a more accurate representation of the shape and
material properties of objects than traditional computer graphics
methods. In order to demonstrate how non-photorealistic rendering
can be used to communicate shape, we have explored
computer-generated technical illustrations.
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| Authors | Derek Cornish, Andrea Rowan, David Luebke |
| Language | English |
| Type | public |
| Url | |
| Summary |
We present a novel framework for non-photorealistic rendering
(NPR) based on view-dependent geometric simplification
techniques. Following a common thread in NPR research, we
represent the model as a system of particles, which will be
rendered as strokes in the final image and which may optionally
overlay a polygonal surface. Our primary contribution is the use
of a hierarchical view-dependent clustering algorithm to regulate
the number and placement of these particles. This algorithm
unifies several tasks common in artistic rendering, such as
placing strokes, regulating the screen-space density of strokes,
and ensuring inter-frame coherence in animated or interactive
rendering. View-dependent callback functions determine which
particles are rendered and how to render the associated
strokes. The resulting framework is interactive and extremely
flexible, letting users easily produce and experiment with many
different art-based rendering styles.
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