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Item Interactive Motion Mapping for Real-time Character Control(The Eurographics Association and John Wiley and Sons Ltd., 2014) Rhodin, Helge; Tompkin, James; Kim, Kwang In; Varanasi, Kiran; Seidel, Hans-Peter; Theobalt, Christian; B. Levy and J. KautzAbstract It is now possible to capture the 3D motion of the human body on consumer hardware and to puppet in real time skeleton-based virtual characters. However, many characters do not have humanoid skeletons. Characters such as spiders and caterpillars do not have boned skeletons at all, and these characters have very different shapes and motions. In general, character control under arbitrary shape and motion transformations is unsolved - how might these motions be mapped? We control characters with a method which avoids the rigging-skinning pipeline - source and target characters do not have skeletons or rigs. We use interactively-defined sparse pose correspondences to learn a mapping between arbitrary 3D point source sequences and mesh target sequences. Then, we puppet the target character in real time. We demonstrate the versatility of our method through results on diverse virtual characters with different input motion controllers. Our method provides a fast, flexible, and intuitive interface for arbitrary motion mapping which provides new ways to control characters for real-time animation.Item Dynamic Display of BRDFs(The Eurographics Association and Blackwell Publishing Ltd., 2011) Hullin, Matthias B.; Lensch, Hendrik P. A.; Raskar, Ramesh; Seidel, Hans-Peter; Ihrke, Ivo; M. Chen and O. DeussenThis paper deals with the challenge of physically displaying reflectance, i.e., the appearance of a surface and its variation with the observer position and the illuminating environment. This is commonly described by the bidirectional reflectance distribution function (BRDF). We provide a catalogue of criteria for the display of BRDFs, and sketch a few orthogonal approaches to solving the problem in an optically passive way. Our specific implementation is based on a liquid surface, on which we excite waves in order to achieve a varying degree of anisotropic roughness. The resulting probability density function of the surface normal is shown to follow a Gaussian distribution similar to most established BRDF models.Item Manipulating Refractive and Reflective Binocular Disparity(The Eurographics Association and John Wiley and Sons Ltd., 2014) Dabala, Lukasz; Kellnhofer, Petr; Ritschel, Tobias; Didyk, Piotr; Templin, Krzysztof; Myszkowski, Karol; Rokita, P.; Seidel, Hans-Peter; B. Levy and J. KautzPresenting stereoscopic content on 3D displays is a challenging task, usually requiring manual adjustments. A number of techniques have been developed to aid this process, but they account for binocular disparity of surfaces that are diffuse and opaque only. However, combinations of transparent as well as specular materials are common in the real and virtual worlds, and pose a significant problem. For example, excessive disparities can be created which cannot be fused by the observer. Also, multiple stereo interpretations become possible, e. g., for glass, that both reflects and refracts, which may confuse the observer and result in poor 3D experience. In this work, we propose an efficient method for analyzing and controlling disparities in computer-generated images of such scenes where surface positions and a layer decomposition are available. Instead of assuming a single per-pixel disparity value, we estimate all possibly perceived disparities at each image location. Based on this representation, we define an optimization to find the best per-pixel camera parameters, assuring that all disparities can be easily fused by a human. A preliminary perceptual study indicates, that our approach combines comfortable viewing with realistic depiction of typical specular scenes.Item NoRM: No-Reference Image Quality Metric for Realistic Image Synthesis(The Eurographics Association and John Wiley and Sons Ltd., 2012) Herzog, Robert; CadÃk, Martin; Aydin, Tunç O.; Kim, Kwang In; Myszkowski, Karol; Seidel, Hans-Peter; P. Cignoni and T. ErtlSynthetically generating images and video frames of complex 3D scenes using some photo-realistic rendering software is often prone to artifacts and requires expert knowledge to tune the parameters. The manual work required for detecting and preventing artifacts can be automated through objective quality evaluation of synthetic images. Most practical objective quality assessment methods of natural images rely on a ground-truth reference, which is often not available in rendering applications. While general purpose no-reference image quality assessment is a difficult problem, we show in a subjective study that the performance of a dedicated no-reference metric as presented in this paper can match the state-of-the-art metrics that do require a reference. This level of predictive power is achieved exploiting information about the underlying synthetic scene (e.g., 3D surfaces, textures) instead of merely considering color, and training our learning framework with typical rendering artifacts. We show that our method successfully detects various non-trivial types of artifacts such as noise and clamping bias due to insufficient virtual point light sources, and shadow map discretization artifacts. We also briefly discuss an inpainting method for automatic correction of detected artifacts.Item Perceptually-motivated Real-time Temporal Upsampling of 3D Content for High-refresh-rate Displays(The Eurographics Association and Blackwell Publishing Ltd, 2010) Didyk, Piotr; Eisemann, Elmar; Ritschel, Tobias; Myszkowski, Karol; Seidel, Hans-PeterHigh-refresh-rate displays (e. g., 120 Hz) have recently become available on the consumer market and quickly gain on popularity. One of their aims is to reduce the perceived blur created by moving objects that are tracked by the human eye. However, an improvement is only achieved if the video stream is produced at the same high refresh rate (i. e. 120 Hz). Some devices, such as LCD TVs, solve this problem by converting low-refresh-rate content (i. e. 50 Hz PAL) into a higher temporal resolution (i. e. 200 Hz) based on two-dimensional optical flow.In our approach, we will show how rendered three-dimensional images produced by recent graphics hardware can be up-sampled more efficiently resulting in higher quality at the same time. Our algorithm relies on several perceptual findings and preserves the naturalness of the original sequence. A psychophysical study validates our approach and illustrates that temporally up-sampled video streams are preferred over the standard low-rate input by the majority of users. We show that our solution improves task performance on high-refresh-rate displays.Item Scalable Remote Rendering with Depth and Motion-flow Augmented Streaming(The Eurographics Association and Blackwell Publishing Ltd., 2011) Paja, Dawid; Herzog, Robert; Eisemann, Elmar; Myszkowski, Karol; Seidel, Hans-Peter; M. Chen and O. DeussenIn this paper, we focus on efficient compression and streaming of frames rendered from a dynamic 3D model. Remote rendering and on-the-fly streaming become increasingly attractive for interactive applications. Data is kept confidential and only images are sent to the client. Even if the client's hardware resources are modest, the user can interact with state-of-the-art rendering applications executed on the server. Our solution focuses on augmented video information, e.g., by depth, which is key to increase robustness with respect to data loss, image reconstruction, and is an important feature for stereo vision and other client-side applications. Two major challenges arise in such a setup. First, the server workload has to be controlled to support many clients, second the data transfer needs to be efficient. Consequently, our contributions are twofold. First, we reduce the server-based computations by making use of sparse sampling and temporal consistency to avoid expensive pixel evaluations. Second, our data-transfer solution takes limited bandwidths into account, is robust to information loss, and compression and decompression are efficient enough to support real-time interaction. Our key insight is to tailor our method explicitly for rendered 3D content and shift some computations on client GPUs, to better balance the server/client workload. Our framework is progressive, scalable, and allows us to stream augmented high-resolution (e.g., HDready) frames with small bandwidth on standard hardware.Item Mutable Elastic Models for Sculpting Structured Shapes(The Eurographics Association and Blackwell Publishing Ltd., 2013) Milliez, Antoine; Wand, Michael; Cani, Marie-Paule; Seidel, Hans-Peter; I. Navazo, P. PoulinIn this paper, we propose a new paradigm for free-form shape deformation. Standard deformable models minimize an energy measuring the distance to a single target shape. We propose a new, ''mutable'' elastic model. It represents complex geometry by a collection of parts and measures the distance of each part measures to a larger set of alternative rest configurations. By detecting and reacting to local switches between best-matching rest states, we build a 3D sculpting system: It takes a structured shape consisting of parts and replacement rules as input. The shape can subsequently be elongated, compressed, bent, cut, and merged within a constraints-based free-form editing interface, where alternative rest-states model to such changes. In practical experiments, we show that the approach yields a surprisingly intuitive and easy to implement interface for interactively designing objects described by such discrete shape grammars, for which direct shape control mechanisms were typically lacking.Item Material Editing in Complex Scenes by Surface Light Field Manipulation and Reflectance Optimization(The Eurographics Association and Blackwell Publishing Ltd., 2013) Nguyen, Chuong H.; Scherzer, Daniel; Ritschel, Tobias; Seidel, Hans-Peter; I. Navazo, P. PoulinThis work addresses the challenge of intuitive appearance editing in scenes with complex geometric layout and complex, spatially-varying indirect lighting. In contrast to previous work, that aimed to edit surface reflectance, our system allows a user to freely manipulate the surface light field. It then finds the best surface reflectance that ''explains'' the surface light field manipulation. Instead of classic L2 fitting of reflectance to a combination of incoming and exitant illumination, our system infers a sparse L0 change of shading parameters instead. Consequently, our system does not require ''diffuse'' or ''glossiness'' brushes or any such understanding of the underlying reflectance parametrization. Instead, it infers reflectance changes from scribbles made by a single simple color brush tool alone: Drawing a highlight will increase Phong specular; blurring a mirror reflection will decrease glossiness; etc. A sparse-solver framework operating on a novel point-based, pre-convolved lighting representation in combination with screen-space edit upsampling allows to perform editing interactively on a GPU.Item Shape Analysis with Subspace Symmetries(The Eurographics Association and Blackwell Publishing Ltd., 2011) Berner, Alexander; Wand, Michael; Mitra, Niloy J.; Mewes, Daniel; Seidel, Hans-Peter; M. Chen and O. DeussenWe address the problem of partial symmetry detection, i.e., the identification of building blocks a complex shape is composed of. Previous techniques identify parts that relate to each other by simple rigid mappings, similarity transforms, or, more recently, intrinsic isometries. Our approach generalizes the notion of partial symmetries to more general deformations. We introduce subspace symmetries whereby we characterize similarity by requiring the set of symmetric parts to form a low dimensional shape space. We present an algorithm to discover subspace symmetries based on detecting linearly correlated correspondences among graphs of invariant features. We evaluate our technique on various data sets. We show that for models with pronounced surface features, subspace symmetries can be found fully automatically. For complicated cases, a small amount of user input is used to resolve ambiguities. Our technique computes dense correspondences that can subsequently be used in various applications, such as model repair and denoising.Item Guiding Image Manipulations using Shape-appearance Subspaces from Co-alignment of Image Collections(The Eurographics Association and John Wiley & Sons Ltd., 2015) Nguyen, Chuong H.; Nalbach, Oliver; Ritschel, Tobias; Seidel, Hans-Peter; Olga Sorkine-Hornung and Michael WimmerWe propose a system to restrict the manipulation of shape and appearance in an image to a valid subspace which we learn from a collection of exemplar images. To this end, we automatically co-align a collection of images and learn a subspace model of shape and appearance using principal components. As finding perfect image correspondences for general images is not feasible, we build an approximate partial alignment and improve bad alignments leveraging other, more successful alignments. Our system allows the user to change appearance and shape in real-time and the result is ''projected'' onto the subspace of meaningful changes. The change in appearance and shape can either be locked or performed independently. Additional applications include suggestion of alternative shapes or appearance.