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Item Virtual Passepartouts(The Eurographics Association, 2012) Ritschel, Tobias; Templin, Krzysztof; Myszkowski, Karol; Seidel, Hans-Peter; Paul Asente and Cindy GrimmIn traditional media, such as photography and painting, a cardboard sheet with a cutout (called passepartout) is frequently placed on top of an image. One of its functions is to increase the depth impression via the ''looking-through-a-window'' metaphor. This paper shows how an improved 3D effect can be achieved by using a virtual passepartout: a 2D framing that selectively masks the 3D shape and leads to additional occlusion events between the virtual world and the frame. We introduce a pipeline to design virtual passepartouts interactively as a simple post-process on RGB images augmented with depth information. Additionally, an automated approach finds the optimal virtual passepartout for a given scene. Virtual passepartouts can be used to enhance depth depiction in images and videos with depth information, renderings, stereo images and the fabrication of physical passepartoutsItem Mapping Images to Target Devices: Spatial, Temporal, Stereo, Tone, and Color(The Eurographics Association, 2012) Banterle, Francesco; Artusi, Alessandro; Aydin, Tunc O.; Didyk, Piotr; Eisemann, Elmar; Gutierrez, Diego; Mantiuk, Rafael; Myszkowski, Karol; Ritschel, Tobias; Renato Pajarola and Michela SpagnuoloRetargeting is a process through which an image or a video is adapted from the display device for which it was meant (target display) to another one (retarget display). The retarget display can have different features from the target one such as: dynamic range, discretization levels, color gamut, multi-view (3D), refresh rate, spatial resolution, etc. This tutorial presents the latest solutions and techniques for retargeting images along various dimensions (such as dynamic range, colors, temporal and spatial resolutions) and offers for the first time a much-needed holistic view of the field. This includes how to measure and analyze the changes applied to an image/video in terms of quality using both (subjective) psychophysical experiments and (objective) computational metrics.Item Homunculus Warping: Conveying Importance Using Self-intersection-free Non-homogeneous Mesh Deformation(The Eurographics Association and Blackwell Publishing Ltd., 2012) Reinert, Bernhard; Ritschel, Tobias; Seidel, Hans-Peter; C. Bregler, P. Sander, and M. WimmerSize matters. Human perception most naturally relates relative extent, area or volume to importance, nearness and weight. Reversely, conveying importance of something by depicting it at a different size is a classic artistic principle, in particular when importance varies across a domain. One striking example is the neuronal homunculus; a human figure where the size of each body part is proportional to the neural density on that part. In this work we propose an approach which changes local size of a 2D image or 3D surface and, at the same time, minimizes distortion, prevails smoothness, and, most importantly, avoids fold-overs (collisions). We employ a parallel, two-stage optimization process, that scales the shape non-uniformly according to an interactively-defined importance map and then solves for a nearby, self-intersection-free configuration. The results include an interactive 3D-rendered version of the classic sensorical homunculus but also a range of images and surfaces with different importance maps.Item The State of the Art in Interactive Global Illumination(The Eurographics Association and Blackwell Publishing Ltd., 2012) Ritschel, Tobias; Dachsbacher, Carsten; Grosch, Thorsten; Kautz, Jan; Holly Rushmeier and Oliver DeussenThe interaction of light and matter in the world surrounding us is of striking complexity and beauty. Since the very beginning of computer graphics, adequate modelling of these processes and efficient computation is an intensively studied research topic and still not a solved problem. The inherent complexity stems from the underlying physical processes as well as the global nature of the interactions that let light travel within a scene. This paper reviews the state of the art in interactive global illumination (GI) computation, i.e., methods that generate an image of a virtual scene in less than 1 s with an as exact as possible, or plausible, solution to the light transport. Additionally, the theoretical background and attempts to classify the broad field of methods are described. The strengths and weaknesses of different approaches, when applied to the different visual phenomena, arising from light interaction are compared and discussed. Finally, the paper concludes by highlighting design patterns for interactive GI and a list of open problems.Item Exploring Shape Variations by 3D-Model Decomposition and Part-based Recombination(The Eurographics Association and John Wiley and Sons Ltd., 2012) Jain, Arjun; Thormählen, Thorsten; Ritschel, Tobias; Seidel, Hans-Peter; P. Cignoni and T. ErtlWe present a system that allows new shapes to be created by blending between shapes taken from a database. We treat the shape as a composition of parts; blending is performed by recombining parts from different shapes according to constraints deduced by shape analysis. The analysis involves shape segmentation, contact analysis, and symmetry detection. The system can be used to rapidly instantiate new models that have similar symmetry and adjacency structure to the database shapes, yet vary in appearance.Item A Computational Model of Afterimages(The Eurographics Association and John Wiley and Sons Ltd., 2012) Ritschel, Tobias; Eisemann, Elmar; P. Cignoni and T. ErtlAfterimages are optical illusions, particularly well perceived when fixating an image for an extended period of time and then looking at a neutral background, where an inverted copy of the original stimulus appears. The full mechanism that produces the perceived specific colors and shapes is complex and not entirely understood, but most of the important attributes can be well explained by bleaching of retinal photoreceptors (retinal kinetics). We propose a model to compute afterimages that allows us to simulate their temporal, color and time-frequency behavior. Using this model, high dynamic range (HDR) content can be processed to add realistic afterimages to low dynamic range (LDR) media. Hereby, our approach helps in conveying the original source's luminance and contrast. It can be applied in real-time on full-HD HDR content using standard graphics hardware. Finally, our approach is validated in a perceptual study.Item 3D Material Style Transfer(The Eurographics Association and John Wiley and Sons Ltd., 2012) Nguyen, Chuong H.; Ritschel, Tobias; Myszkowski, Karol; Eisemann, Elmar; Seidel, Hans-Peter; P. Cignoni and T. ErtlThis work proposes a technique to transfer the material style or mood from a guide source such as an image or video onto a target 3D scene. It formulates the problem as a combinatorial optimization of assigning discrete materials extracted from the guide source to discrete objects in the target 3D scene. The assignment is optimized to fulfill multiple goals: overall image mood based on several image statistics; spatial material organization and grouping as well as geometric similarity between objects that were assigned to similar materials. To be able to use common uncalibrated images and videos with unknown geometry and lighting as guides, a material estimation derives perceptually plausible reflectance, specularity, glossiness, and texture. Finally, results produced by our method are compared to manual material assignments in a perceptual study.Item Pre-convolved Radiance Caching(The Eurographics Association and Blackwell Publishing Ltd., 2012) Scherzer, Daniel; Nguyen, Chuong; Ritschel, Tobias; Seidel, Hans-Peter; Fredo Durand and Diego GutierrezThe incident indirect light over a range of image pixels is often coherent. Two common approaches to exploit this inter-pixel coherence to improve rendering performance are Irradiance Caching and Radiance Caching. Both compute incident indirect light only for a small subset of pixels (the cache), and later interpolate between pixels. Irradiance Caching uses scalar values that can be interpolated efficiently, but cannot account for shading variations caused by normal and reflectance variation between cache items. Radiance Caching maintains directional information, e. g., to allow highlights between cache items, but at the cost of storing and evaluating a Spherical Harmonics (SH) function per pixel. The arithmetic and bandwidth cost for this evaluation is linear in the number of coefficients and can be substantial. In this paper, we propose a method to replace it by an efficient per-cache item pre-filtering based on MIP maps - such as previously done for environment maps - leading to a single constant-time lookup per pixel. Additionally, per-cache item geometry statistics stored in distance-MIP maps are used to improve the quality of each pixel's lookup. Our approximate interactive global illumination approach is an order of magnitude faster than Radiance Caching with Phong BRDFs and can be combined with Monte Carlo-raytracing, Point-based Global Illumination or Instant Radiosity.