Computational Aesthetics: EG Workshop on Computational Aesthetics in Graphics, Visualization and Imaging

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Sketch Based Construction and Rendering of Implicit Models
(The Eurographics Association, 2005) Wyvill, Brian; Foster, Kevin; Jepp, Pauline; Schmidt, Ryan; Sousa, Mario Costa; Jorge, Joaquim A.; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
We present an implicit modeling system as a tool for creating a wide range of aesthetic models. Because of their ability to form blends and produce both organic shapes as well as man-made objects, implicit surfaces are a good medium for artists seeking new ways to experiment with 3D modeling. Implicit models can be created using our sketch-based modeling tool Shapeshop and also by using a procedural interface. Further, we exploit the differential properties of implicit surfaces to explore new techniques for rendering hierarchical, skeletal implicit models in several pen and ink styles. Our method extracts and stylizes silhouette strokes, lines following local shape features, such as those caused by CSG junctions and abrupt blends, and short interior marks to reveal basic form. In this approach we use a particle system as a basis for the stroke extraction method.
Fast Techniques for Mosaic Rendering
(The Eurographics Association, 2005) DiBlasi, G.; Gallo, G.; Petralia, M.; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
Art often provides valuable hints for technological innovations especially in the field of Image Processing and Computer Graphics. In this paper we survey in an unified framework three methods to transform a raster input image into good quality mosaics: artificial mosaic, photomosaic and puz zle image mosaic. The common and different ideas among these methods are reported. The main goal of all the methods is to produce good results in an acceptable time and without user intervention. Examples reported in the paper show how the right mixture of mathematical tools may lead to impressive results.
Global Contrast Factor - a New Approach to Image Contrast
(The Eurographics Association, 2005) Matkovic, Kresimir; Neumann, László; Neumann, Attila; Psik, Thomas; Purgathofer, Werner; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
Contrast in image processing is usually defined as a ratio between the darkest and the brightest spots of an image. In this paper we introduce a different contrast definition. The newly introduced Global Contrast Factor (GCF) corresponds closer to the human perception of contrast. GCF uses contrasts at various resolution levels in order to compute overall contrast. Experiments were conducted in order to find weight factors needed to calculate GCF. GCF measures richness of detail as perceived by a human observer, and as such can be used in various application areas like rendering, tone mapping, volume visualization, and lighting design.
An Information-Theoretic Framework for Image Complexity
(The Eurographics Association, 2005) Rigau, Jaume; Feixas, Miquel; Sbert, Mateu; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
In this paper, we introduce a new information-theoretic approach to study the complexity of an image. The new framework we present here is based on considering the information channel that goes from the histogram to the regions of the partitioned image, maximizing the mutual information. Image complexity has been related to the entropy of the image intensity histogram. This disregards the spatial distribution of pixels, as well as the fact that a complexity measure must take into account at what level one wants to describe an object. We define the complexity by using two measures which take into account the level at which the image is considered. One is the number of partitioning regions needed to extract a given ratio of information from the image. The other is the compositional complexity given by the Jensen-Shannon divergence of the partitioned image.
Benford's Law for Natural and Synthetic Images
(The Eurographics Association, 2005) Acebo, Esteve Del; Sbert, Mateu; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
Benford's Law (also known as the First Digit Law) is well known in statistics of natural phenomena. It states that, when dealing with quantities obtained from Nature, the frequency of appearance of each digit in the first significant place is logarithmic. This law has been observed over a broad range of statistical phenomena. In this paper, we will explore its application to image analysis. We will show how light intensities in natural images, under certain constraints, obey this law closely. We will also show how light intensities in synthetic images follow this law whenever they are generated using physically realistic methods, and fail otherwise. Finally, we will study how transformations on the images affect the adjustment to the Law and how the fitting to the law is related to the fitting of the distribution of the raw intensities of the image to a power law.
Designing Metrics for the Purpose of Aesthetically Evaluating
(The Eurographics Association, 2005) Greenfield, Gary R.; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
The algorithmic and evolutionary art movements within computer-generated art have helped spur interest in evaluating images on the basis of their aesthetic merit. When attempting to use non-interactive techniques to address this issue, two problems arise: (1) designing metrics that have explicit computational representations, and (2) establishing that such metrics actually fulfill their intended purpose. We survey our experiences in designing metrics for non-interactively guiding image evolution to obtain aesthetic images and we propose a taxonomy for metric frameworks. We also discuss some issues relevant to validating such metrics.
Viewpoint Quality: Measures and Applications
(The Eurographics Association, 2005) Sbert, Mateu; Plemenos, Dimitri; Feixas, Miquel; González, Francisco; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
Several methods that use the notion of viewpoint quality have been recently introduced in different areas of computer graphics, such as scene understanding, exploration of virtual worlds, radiosity and global illumination, image-based rendering and modelling. In this paper, we analyze the behavior of three different viewpoint quality measures. The first one is a heuristic measure, the second one is the viewpoint entropy, and the third one is a new measure based on the Kullback-Leibler distance between the projected and actual distributions of the areas of the polygons in the scene. In addition, this paper reviews different applications and introduces a new algorithm using the Kullback-Leibler distance for the selection of a representative set of n views. Our method is based in selecting the view that minimizes the Kullback-Leibler distance between the mixture of the distributions of all selected views and the actual area distribution.
Breaking the Pixel Barrier
(The Eurographics Association, 2005) Isenberg, Tobias; Carpendale, M. Sheelagh T.; Sousa, Mario Costa; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
The majority of the current advances in computer graphic rendering strive for fast and realistic creation of pixel images, e. g., for the film and gaming industry. This development, unfortunately, leads to various problems due to limitations of pixel images, in particular, when they are not used for screen viewing. Thus, in this paper we argue for the placement of greater emphasis on the generation of vector graphics. Vector graphics offer the best approach for achieving effectiveness for both media simulation and illustration techniques. We discuss advantages of using vector graphics, pose a number of questions in this context, and evaluate directions of further research.
Abstraction and Depiction of Sparsely Scanned Outdoor Environments
(The Eurographics Association, 2005) Xu, Hui; Gossett, Nathan; Chen, Baoquan; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
This paper describes various techniques and applications of rendering three-dimensionally digitized outdoor en- vironments in non-photorealistic rendering styles. The difficulty in rendering outdoor environments is accommodating their inaccuracy, incompleteness, and large size to deliver a smooth animation without suggesting the underlying data deficiency. Standard rendering approaches often expose and inadvertently emphasize missing and noisy data, producing unpleasant images. Our use of non-photorealistic rendering allows us to de-emphasize these problems and produce aesthetically pleasing images. The key approach discussed in this paper employs artistic drawing techniques to illustrate features of varying importance and accuracy. We use point-based representations of the scanned environments and operate directly on the point-based models for abstraction and rendering. We de- velop a unified framework for producing sketchy, profile, painterly, cartoon, and intermingled styles. We describe a level-of-detail data structure, the continuous resolution queue, to promise coherent and consistent animation. We also leverage modern graphics hardware to achieve interactive rendering of large scenes.
On Nonlinear Perspectives in Science, Art and Nature
(The Eurographics Association, 2005) Glaeser, Georg; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
Classic perspectives, i.e., central projections onto a plane, are extremely common in our days. Photos, movies, computer generated animations almost exclusively use this technique. They are linear since straight lines in space appear as straight lines in the image. Nevertheless, humans and animals of all kind have a more complicated method to develop images in their brains. They measure angles, not lengths. Together with nonlinear projections onto curved surfaces, impressions are transformed into spatial imagination. When it comes to 2D-reproduction of such processes, we need nonlinear perspectives in 2-space. They usually look like fisheye-images, i.e., projections of space onto a plane via a not symmetric, extremely refracting spherical lens. Similar distortions occur when we look out of still water or into reflecting spheres. In fine Arts, the angle measuring was intuitively applied by artists. In geometry, the inversion at a circle (sphere), several models of non-Euclidean geometries and the stereographic projection onto the plane or mappings of the sphere respectively lead to comparable results. We call the latter transformations secondary nonlinear perspectives. Finally, realtime algorithms are presented that transform primary nonlinear perspectives like special refractions into classic perspectives. Therefore, we work with Taylor series (or, if possible, with accurate formulas) and for speed reasons with precalculated tables.
Color Search and Replace
(The Eurographics Association, 2005) Grundland, Mark; Dodgson, Neil A.; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
We present an interactive image enhancement technique to adjust the global color composition of an image by finding and replacing color gradients. We show how color gradient transformations can perform the basic operations of color editing. To recolor an image, the user designates a mapping of source color gradients to corresponding target color gradients. Each color gradient can be represented by a spherical parameterization, consisting of its midpoint color, contrast radius, as well as hue and luminance angles, in order to give the user separate and independent control over color shift, contrast adjustment, and color variation. Color gradients provide not only a flexible way of selecting color features but also a powerful way of manipulating image colors, as each mapping between a source and a target color gradient defines an affine color transformation. To determine the region of influence of each color mapping, perceptual similarity between colors is evaluated by applying Shepard s law of generalization to color differences. Through a feature-based warping approach, our color warping algorithm applies a continuous, nonlinear, volumetric deformation to the color space in order to approximate the requested color mappings. By making interactive color correction easier to control, our technique may prove useful in a variety of color image enhancement tasks in digital photography, video processing, and information visualization.
Defining Computational Aesthetics
(The Eurographics Association, 2005) Hoenig, Florian; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
This paper attempts to define the discipline of Computational Aesthetics in the context of computer science, partly reflecting the contributions and comprehensive discussions of the first EG Workshop on Computational Aesthetics in Graphics, Visualization and Imaging. It points out the current problem of "aesthetic pollution" as a side effect of computer aided design and gives motivation to improve current computational methods by adding aesthetic awareness. An introduction on how this could be achieved is given, listing significant results of previous research. It turned out that there are factors of aesthetics such as complexity and order, that could add up to a working measure. For building a pragmatic view on such measures, very restrictive scenarios of application are given. To conclude, the major aspects of this new discipline are stressed. They are (1) developing computational methods for aesthetic decisions, (2) taking human perception into account and (3) focusing on aesthetics in form and particularly objects of design, in order to guarantee immediate application.
Straight away on Curved Spaces
(The Eurographics Association, 2005) Marty, Alain; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
Two points of a Euclidean space can always be connected by the simplest of the curves, the straight line. This curve is unique (it s required), with a constant direction and a minimal length between the two points. The straight line is known to be fundamental in the building of the Euclidean geometry, for the production of all imaginable figures, from the simple triangle to the most complex curved shapes. And when the figures have to be immersed in curved shapes, out of a Euclidean space and without its useful straight line tool, it seems natural to search for a similar fundamental curve possessing its basic properties : uniqueness of the curve, constant direction, minimal length. This curve, known to be a geodesic line, is defined by a differential system whose solutions cannot generally be expressed in a simple way, (let s say as a finite degree polynomial expression), and so leads to a great complexity in the definition of figures belonging to curved spaces. But other approachs exist... The present contribution, based on a conceptual tool for creating and managing curved shapes, the Pascalian Forms, or pForms, (published in Editions de l Esperou / Montpellier / 2004), an attempt to generalize the de Casteljau algorithm, focuses on three cases of "straight lines" drawn on curved shapes : 1) the first case shows how a geodesic can be the solution to a very practical problem : applying a long thin plank on a toroidal roof upon a swimming pool ; 2) the second case shows how an apparently complex spatial curve (the Threefoil Knot Curve) followed by a staircase in the MC Escher style can be simplified by using immersed pSegments ; 3) the third case shows how the natural/organic shapes in the Sagrada Familia Temple dreamed by the catalan architect A. Gaudi have been mastered using ruled surfaces (pSurfaces).
Form Follows Function: Aesthetic Interactive Labels
(The Eurographics Association, 2005) Götzelmann, Timo; Ali, Kamran; Hartmann, Knut; Strothotte, Thomas; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
Labels effectively convey co-referential relations between textual and visual elements and are a powerful tool to support learning tasks. Therefore, almost all illustrations in scientific or technical documents employ a large number of labels. This paper introduces a novel approach to integrate internal and external labels into projections of complex 3D models in the fashion of hand-made illustrations. The real-time label layout algorithms proposed in the paper balance a number of conflicting requirements such as unambiguity, readability, aesthetic considerations and frame-coherency.
Color Style Transfer Techniques using Hue, Lightness and Saturation Histogram Matching
(The Eurographics Association, 2005) Neumann, Attila; Neumann, László; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
We present new methods which transfer the color style of a source image into an arbitrary given target image having a different 3D color distribution. The color transfer has a high importance ensuring a wide area of applications from artistic transformation of the color atmosphere of images until different scientific visualizations using special gamut mappings. Our technique use a permissive, or optionally strict, 3D histogram matching, similarly to the sampling of multivariable functions applying a sequential chain of conditional probability density functions. We work by order of hue, hue dependent lightness and from both dependent saturation histograms of source and target images, respectively. We apply different histogram transformations, like smoothing or contrast limitation, in order to avoid some unexpected high gradients and other artifacts. Furthermore, we use dominance suppression optionally, by applying sub-linear functions for the histograms in order to get well balanced color distributions, or an overall appearance reflecting the memory color distribution better. Forward and inverse operations on the corresponding cumulative histograms ensure a continuous mapping of perceptual attributes correlating to limited derivatives. Sampling an appropriate fraction of the pixels and using perceptually accurate and continuous histograms with minimal size as well as other gems make this method robust and fast.
Smart Visibility in Visualization
(The Eurographics Association, 2005) Viola, Ivan; Gröller, Eduard; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
In this paper we discuss expressive visualization techniques that smartly uncover the most important information in order to maximize the visual information in the resulting images. This is achieved through dynamic changes in visual representations, through deformations, or through spatial modifications of parts of the data. Such techniques originate from technical illustration and are called cut-away views, ghosted views, and exploded views. These illustrative techniques unveil the most important visual information by employing high levels of abstraction. The change in visual representation or spatial position is done easily perceivable and the overall visual harmony is preserved.
Illustrative Scientific Visualization Framework
(The Eurographics Association, 2005) Sousa, Mario Costa; Gooch, Amy Ashurst; Gooch, Bruce; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
Current scientific visualization techniques create complex images that may be difficult to interpret and do not have the expressiveness of illustrations. Incorporating traditional scientific illustration techniques into a visualization system enables artists and non-artists to harnesses the power of traditional illustration techniques when visually representing scientific data. In this paper we present an illustrative scientific visualization framework incorporating general illustration principles, as well as techniques and aesthetics of various styles. Such a framework provides a basic foundation for categorizing and communicating research and may stimulate future illustrative visualization systems.
On the Origins of the Term Computational Aesthetics
(The Eurographics Association, 2005) Greenfield, Gary; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
To provide some background, as well as a historical context, for the Eurographics 2005 Workshop on Graphics, Visualization and Imaging we provide a chronology, complete with references, covering various research activities that invoke the term aesthetics in a computational setting. Much of the research cited focuses on the problem of making numerical assessments of the aesthetic content of works of art.
Computational Automotive Color Appearance
(The Eurographics Association, 2005) Meyer, Gary W.; Shimizu, Clement; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
A computer graphic system has been developed that permits the interactive design of new automotive finishes. The software makes use of a reflection model for car paint that is based on industry standards for measuring the appearance characteristics of the paint. These measurements include gloss for the clearcoat and three aspecular measurements for the metallic basecoat. The program interface provides a means for altering the reflectance properties of the paint and for visualizing the effect of those changes on the color appearance of the car. The desired aspecular measurements for the new paint can be input to a paint formulation system so that the paint can be manufactured. A test of the system shows good correspondence between the designed and the fabricated paint.
Illustrative Visualization for Medical Training
(The Eurographics Association, 2005) Sousa, Mario Costa; Ebert, David S.; Stredney, Don; Svakhine, Nikolai A.; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
A system is presented that produces images that simulate pictorial representations for both scientific and biomedical visualization. It combines traditional and novel volume illustration techniques. We present examples to distill representational techniques for both creative exploration and emphatic presentation for clarity. More specifically, we present adaptations of these techniques for interactive simulation sessions being developed in a concurrent project for resident training in temporal bone dissection simulation. The goal of this effort is to evaluate the use of emphatic rendering to guide the user in an interactive session and to facilitate the learning of complex biomedical information, including structural, functional, and procedural information.

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