CompAesth 10: Workshop on Computational Aesthetics

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https://diglib.eg.org/handle/10.2312/317

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Interactive Volume Illustration Using Intensity Filtering
(The Eurographics Association, 2010) Ruiz, Marc; Boada, Imma; Feixas, Miquel; Sbert, Mateu; Pauline Jepp and Oliver Deussen
We propose a simple and interactive technique for volume illustration by using the difference between the original intensity values and a low-pass filtered copy. This difference, known as unsharped mask, provides us with a spatial importance map that captures salient and separability information about regions in the volume. We integrate this map in the visualization pipeline and use it to modulate the color and the opacity assigned by the transfer function to produce different illustrative effects. We also apply stipple rendering modulating the density of the dots with the spatial importance map. The core of our approach is the computation of a 3D Gaussian filter, which is equivalent to three consecutive 1D filters. This separability feature allows us to obtain interactive rates with a CUDA implementation. We show results of our approach for different data sets.
Procedural Generation of Surface Detail for Science Fiction Spaceships
(The Eurographics Association, 2010) Kinnear, Kate; Kaplan, Craig S.; Pauline Jepp and Oliver Deussen
Procedural modelling can be used to generate digital content such as 3D digital models programmatically. In computer graphics, Procedural modelling has focused primarily on natural scenery and cityscapes. This paper considers the use of procedural modelling in a new domain: science fiction spaceships. We examine aesthetic principles as they relate to the beauty and visual interest of spaceships, especially surface details, and determine how these principles can be applied in a practical procedural modelling algorithm.We describe a prototype system that synthesizes and distributes surface details on large-scale spaceships. Given a surface representing the frame of a spaceship, we distribute geometry automatically in a coherent manner to achieve a characteristic science fiction aesthetic.
Brush Stroke Ordering Techniques for Painterly Rendering
(The Eurographics Association, 2010) Northam, Lesley; Istead, Joe; Kaplan, Craig S.; Pauline Jepp and Oliver Deussen
Painterly rendering algorithms often mimic classical hand-painting techniques to automatically generate stylized paintings from input images. These algorithms use a combination of techniques to express a variety of styles and artistic properties (e.g., contrast, mood), but often restrict the user from controlling the rendering order of overlapping brush strokes. This paper illustrates the importance of brush stroke ordering in creating stylistic effects and presents a layer-based painterly rendering algorithm that allows the user to specify a brush stroke ordering. Several of the presented orderings enable the renderer to reduce detail obstruction, simulate handpainting techniques and enhance artistic styles.
Pannini: A New Projection for RenderingWide Angle Perspective Images
(The Eurographics Association, 2010) Sharpless, Thomas K.; Postle, Bruno; German, Daniel M.; Pauline Jepp and Oliver Deussen
The widely used rectilinear perspective projection cannot render realistic looking flat views with fields of view much wider than 70°. Yet 18th century artists known as 'view painters' depicted wider architectural scenes without visible perspective distortion.We have found no written records of how they did that, however, quantitative analysis of several works suggests that the key is a system for compressing horizontal angles while preserving certain straight lines important for the perspective illusion. We show that a simple double projection of the sphere to the plane, that we call the Pannini projection, can render images 150° or more wide with a natural appearance, reminiscent of vedutismo perspective. We give the mathematical formulas for realizing it numerically, in a general form that can be adjusted to suit a wide range of subject matter and field widths, and briefly compare it to other proposed alternatives to the rectilinear projection.
Suggestive Hatching
(The Eurographics Association, 2010) Singh, Mayank; Schaefer, Scott; Pauline Jepp and Oliver Deussen
We present a method for drawing lines on an object that depict both the shape and shading of the object. To do so, we construct a gradient field of the diffuse intensity of the surface to guide a set of adaptively spaced lines. The shape of these lines reflect the lighting under which the object is being viewed and its shape. When the light source is placed at the viewer's location, these lines emanate from silhouettes and naturally extend Suggestive Contours. By using a hierarchical proximity grid, we can also improve the quality of these lines as well as control their density over the image. We also provide a method for detecting and removing ridge lines in the intensity field, which lead to artifacts in the line drawings.
Toward Auvers Period: Evolution of van Gogh's Style
(The Eurographics Association, 2010) Rigau, Jaume; Feixas, Miquel; Sbert, Mateu; Wallraven, Christian; Pauline Jepp and Oliver Deussen
In this paper, we analyze the evolution of van Gogh's style toward the Auvers final period using informational measures. We will try to answer the following questions: Was van Gogh exploring new ways toward changing his style? Can informational measures support the claim of critics on the evolution of his palette and composition? How "far" was van Gogh's last period from the previous ones, can we find out an evolutionary trend? We will extend here the measures defined in our previous work with novel measures taking into account spatial information and will present a visual tool to examine the palette. Our results confirm the usefulness of an approach rooted in information theory for the aesthetic study of the work of a painter.
Line Drawings vs. Curvature Shading:Scientific Illustration of Range Scanned Artefacts
(The Eurographics Association, 2010) Hörr, Christian; Brunnett, Guido; Vix, Christian; Pauline Jepp and Oliver Deussen
For scientific archaeological illustrations, pen-and-ink drawings are traditionally the most prevalent type. Over the years, drawing styles have substantially changed several times and even today there is basically no general agreement about how to illustrate objects best. Without doubt, this is one major reason why most computergenerated line drawings are still recognized as such, although non-photorealistic rendering has made significant advances during the past decade. With a special focus on cultural heritage objects and the theoretical and practical restrictions of current NPR techniques on scanned range data, we discuss the question if line drawings could generally be replaced by a detail-shaded view, which highlights relevant features, but still conveys an objective plastic impression as well.
Recursive Scene Graphs for Art and Design
(The Eurographics Association, 2010) Wyvill, Brian; Dodgson, Neil A.; Pauline Jepp and Oliver Deussen
Conventional scene graphs use directed acyclic graphs; conventional iterated function systems use infinitely recursive definitions. We investigate scene graphs with recursive cycles for defining graphical scenes. This permits both conventional scene graphs and iterated function systems within the same framework and opens the way for other definitions not possible with either. We explore several mechanisms for limiting the implied recursion in cyclic graphs, including both global and local limits. This approach permits a range of possibilities, including scenes with carefully controlled and locally varying recursive depth. It has applications in art and design.
Subdivision Beyond Smoothness
(The Eurographics Association, 2010) Hansmeyer, Michael; Pauline Jepp and Oliver Deussen
This paper examines the role that subdivision processes can have in the production of form. It explores how subdivision processes can generate complex geometries from very simple input meshes. In a first step, this paper presents modifications to the established subdivision processes' weighting schemes. In a second step, this paper considers formalized and extended methods for applying these schemes. Finally the paper presents forms generated with these modified processes.
Realtime Aesthetic Image Retargeting
(The Eurographics Association, 2010) Liu, Ligang; Jin, Yong; Wu, Qingbiao; Pauline Jepp and Oliver Deussen
Humans have always sought to achieve aesthetics in art. In this paper, we present a novel approach for retargeting images to different aspect ratios while improving the composition aesthetics of the results. A simpler computational aesthetic energy is proposed and used to drive the salient objects and prominent lines to move towards their corresponding optimal positions. A mesh-based warping scheme is presented to transform the images while protecting the visual appearance of salient objects. The objective function is quadratic and thus it can be quickly minimized by solving a sparse linear system. The retargeting results are generated in realtime while the user changes the aspect ratios of the target images. A variety of experiments have shown the applicability and effectiveness of our algorithm.
Learning about Shadows from Artists
(The Eurographics Association, 2010) Fourquet, Elodie; Pauline Jepp and Oliver Deussen
Renaissance artists discovered methods for imaging realistic depth on a two dimensional surface by re-inventing linear perspective. In solving the problem of depth depiction, they observed how shadows project and volumes flatten in nature. They investigated how controlled illumination projects volumes onto walls, exploring the phenomena long before physical optics, such as the camera, existed. This paper specifically examines artists' constructions for depicting shadows, a 3D double projection problem that artists solved completely within two dimensions. The larger goal is to develop new computational methods for creating 3D perceptions without having to leave the 2D canvas. Those methods have potential application in constructing user interfaces, in 2D image compositing and in simultaneous 2D/3D composition. This paper develops geometric constructions for casting shadows onto planar surfaces, adapted from artists' methods. Their algebraization for integration into imaging software is demonstrated, and their optically accuracy is shown. Finally, resulting images are included, along with a discussion of limitations.
Discretization of 3D Models Using Voxel Elements of Different Shapes
(The Eurographics Association, 2010) Cavagnino, Davide; Gribaudo, Marco; Pauline Jepp and Oliver Deussen
This paper presents a voxelization algorithm that uses elements of various shapes that are not larger than a single voxel. Elements are chosen from a palette in order to minimize the deviation from the actual object according to a given metric. An analytical framework is presented and then an implementation based on a statistical sampling on the object is proposed. The result obtained is used to guide the recreation of the original model using small components that resemble the palette elements but emphasize the artistic nature of the reconstruction. Several examples where the proposed technique has been used to create some models with artistic and advertising purposes are presented to show the effectiveness of the technique.
A Robust and Universal Gradient Domain Imaging Solver Using Gradient Variables and Locally Varying Metrics
(The Eurographics Association, 2010) Neumann, László; Hegedüs, Ramón; Pauline Jepp and Oliver Deussen
Gradient Domain Imaging (GDI) has gained a high importance and provoked numerous powerful applications over the last decade. It employs a workflow of creating an inconsistent gradient field (GF) from one or more images using different non-linear operations and finally it determines an image with a consistent, integrable GF that falls near to the prescribed inconsistent one. However, the result is not really predictable, often suffers from halo-effects and other local distortions at higher frequencies as well as from uncontrollable far-effects arising from local gradient-contradictions. The unfolding of these artifacts culminates in an undesired overall image appearance. None of the common GDI solvers can overcome these side-effects as they utilize the same local isotropic 'coefficient-pattern' in a sparse matrix description and they differ only in the numerical solution techniques. We present a powerful GDI method solving the problem completely in the gradient domain with gradient-variables and using spatially varying metrics that depends only on the starting inconsistent gradient field. After obtaining the nearest consistent gradient field with the pre-defined metrics we return into the image space by double integration that yields the wanted pixel intensity values. Our method delivers a great aesthetic enhancement by eliminating halo effects and saving small details, furthermore providing a realistic and pleasant overall light distribution at lower frequencies. By significantly extending the range of allowed inconsistency in the prescribed gradient field, it also allows for solving a large class of problems that proved hopeless beforehand.
Stroke Matching for Paint Dances
(The Eurographics Association, 2010) Colton, Simon; Pauline Jepp and Oliver Deussen
We have implemented a non-photorealistic rendering system which simulates the placement of paint/pencil/pastel strokes to produce representational artworks from digital images. The system is able to record an image of each paint stroke independent of the overall picture, in addition to some details about each stroke. Working with sets of paint strokes from paintings of different images, we investigate how to determine which stroke from one picture most closely resembles a given stroke from another picture. This enables the paint strokes from one picture to be used to paint a different painting. This further enables the animation of one picture morphing into another, as the paint strokes move and rotate into new positions and orientations. Using a K-means clustering approach, we can extract a set of representative strokes from a series of paintings/drawings, and animate the same set of strokes moving around a picture in order to represent different scenes at different times. We call such animations paint dances .We apply this technique to sets of portraits and we present the resulting paint dances in an artistic context as video art. We describe here the various methods we experimented with in order to determine an optimal stroke matching and extraction approach.

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