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

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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.
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.
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.
Enhancing Perceived Depth in Images Via Artistic Matting
(The Eurographics Association, 2005) Gooch, Amy A.; Gooch, Bruce; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
We present an algorithm for the addition of artistic mattes to digital images for the purpose of enhancing the sense of depth in the image. We provide examples exploring color and double mattes as well as report the results from a perception study which may indicate an increase in perceived depth in matted imagery.
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.
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.
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.
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.
A Generative Model For Dynamic Canvas Motion
(The Eurographics Association, 2005) Kaplan, Matthew; Cohen, Elaine; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
We present techniques for constructing realistic canvas and paper models and for enabling interactive dynamic canvas motion. Dynamic canvas motion means that there is a correspondence between the motion of canvas features and the motion of the models in the scene. Our artificial paper is created by simulating the physical process of creating paper with many individual fibers. To enable canvas motion, fibers are associated with each of the models in the scene. At runtime, the fibers associated with visible portions of the models and background fibers are used to construct a 2D canvas. Because fibers are "tied" to the models, the motion of canvas features corresponds to the motion of each model. This allows us to match the motion field of our dynamic 2D canvas to that of the the 3D scene exactly.
Computational Color Harmony based on Coloroid System
(The Eurographics Association, 2005) Neumann, László; Nemcsics, Antal; Neumann, Attila; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
This paper presents experimentally based rules and methods for the creation of harmonic color sets. First, dichromatic rules are presented which concern the harmony relationships of two hues. For an arbitrarily given hue pair, we define the just harmonic saturation values, resulting in minimally harmonic color pairs. These values express the fuzzy border between harmony and disharmony regions using a single scalar. Second, the value of harmony is defined corresponding to the contrast of lightness, i.e. the difference of perceptual lightness values. Third, we formulate the harmony value of the saturation contrast, depending on hue and lightness. The results of these investigations form a basis for a unified, coherent dichromatic harmony formula as well as for analysis of polychromatic color harmony. Introduced color harmony rules are based on Coloroid, which is one of the 5 - 6 main color-order systems and furthermore it is an aesthetically uniform continuous color space. Coloroid has simple closed forward and backward transformation formulas with the color space of CIE XYZ. It relies on a huge number of observations and experiments, and it is a very suitable tool of color dynamics for describing aesthetical relationships. It has been used in numerous architectural projects. The experimental data that may be retrieved from them are only partly processed and published so far. Our article utilizes a 'slice' of this database, together with additional complementary observations. This paper is the first of a planned series of articles, dealing with rules and coherences of color harmony based on the Coloroid system.
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.
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.
Aesthetics in Covariant Image Reconstruction
(The Eurographics Association, 2005) Georgiev, Todor; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
This paper describes a method of seamless cloning based on aesthetic theory of lightness perception. Judgment of lightness and color harmony is treated as low level aesthetic judgment made by the human visual system. The equation written based on this consideration is an improvement to Poisson image editing, and produces results that are better than the current state of the art in the area of scratch/object removal. The reason our result is aesthetically pleasing is that it is fundamentally based on aesthetic theory, and it proves the usefulness of our theoretical approach.
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.
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.
Computer Generated Stereoscopic Artwork
(The Eurographics Association, 2005) Stavrakis, Stathis; Gelautz, Margrit; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
The focus of this work is to investigate and simulate artistic techniques in stereoscopy that go beyond stereo photography, such as stereoscopic painting. We briefly discuss the topic from a stereo artist s perspective and map some of our observations from traditional stereo techniques to the scientific domain, where we use them to tackle technical tasks involved in the generation of stereo artwork. We describe a framework that we use in our stereoscopic image-based non-photorealistic rendering algorithms, but it can be adopted by other single-view artistic image synthesis techniques in order to generate stereoscopic output.
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.
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).
Spectral Colour Order Systems and Appearance Metrics for Fluorescent Solid Colours
(The Eurographics Association, 2005) Wilkie, Alexander; Larboulette, Caroline; Purgathofer, Werner; Laszlo Neumann and Mateu Sbert and Bruce Gooch and Werner Purgathofer
One aspect of Computational Aesthetics is the finding of harmonic colours for the objects in a scene. Although the obtained degree of colour harmony is a subjective criterion, experience shows that on average human observers tend to have quite similar responses to individual colour stimuli and their combinations. This observation is the basis for what is commonly referred to as Colour Order Systems (COS), which aim to arrange colours in a fashion such that users can intuitively select individual colours or even whole sets of them according to some criterion. However, when dealing with a spectral rendering system, the use of traditional colour space COS to obtain pleasant associations of colours becomes impossible, principally due to metamerism. An interesting problem would be the derivation of a COS for spectral data which includes the ability to deal with fluorescent colours, the indirect goal of such a metric system being the selection of aesthetically pleasing colour values for a spectral renderer.
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.

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