Volume 27 (2008)

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https://diglib.eg.org/handle/10.2312/133

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Modeling a Generic Tone-mapping Operator
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Mantiuk, Rafal; Seidel, Hans-Peter
Although several new tone-mapping operators are proposed each year, there is no reliable method to validate their performance or to tell how different they are from one another. In order to analyze and understand the behavior of tone-mapping operators, we model their mechanisms by fitting a generic operator to an HDR image and its tone-mapped LDR rendering. We demonstrate that the majority of both global and local tone-mapping operators can be well approximated by computationally inexpensive image processing operations, such as a per-pixel tone curve, a modulation transfer function and color saturation adjustment. The results produced by such a generic tone-mapping algorithm are often visually indistinguishable from much more expensive algorithms, such as the bilateral filter. We show the usefulness of our generic tone-mapper in backward-compatible HDR image compression, the black-box analysis of existing tone mapping algorithms and the synthesis of new algorithms that are combination of existing operators.
A Hidden-picture Puzzles Generator
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Yoon, Jong-Chul; Lee, In-Kwon; Kang, Henry
A hidden-picture puzzle contains objects hidden in a background image, in such a way that each object fits closely into a local region of the background. Our system converts image of the background and objects into line drawing, and then finds places in which to hide transformed versions of the objects using rotation-invariant shape context matching. During the hiding process, each object is subjected to a slight deformation to enhance its similarity to the background. The results were assessed by a panel of puzzle-solvers.
Reconstructing head models from photographs for individualized 3D-audio processing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Dellepiane, M.; Pietroni, N.; Tsingos, N.; Asselot, M.; Scopigno, R.
Visual fidelity and interactivity are the main goals in Computer Graphics research, but recently also audio is assuming an important role. Binaural rendering can provide extremely pleasing and realistic three-dimensional sound, but to achieve best results it s necessary either to measure or to estimate individual Head Related Transfer Function (HRTF). This function is strictly related to the peculiar features of ears and face of the listener. Recent sound scattering simulation techniques can calculate HRTF starting from an accurate 3D model of a human head. Hence, the use of binaural rendering on large scale (i.e. video games, entertainment) could depend on the possibility to produce a sufficiently accurate 3D model of a human head, starting from the smallest possible input. In this paper we present a completely automatic system, which produces a 3D model of a head starting from simple input data (five photos and some key-points indicated by user). The geometry is generated by extracting information from images and accordingly deforming a 3D dummy to reproduce user head features. The system proves to be fast, automatic, robust and reliable: geometric validation and preliminary assessments show that it can be accurate enough for HRTF calculation.
Real-Time Indirect Illumination and Soft Shadows in Dynamic Scenes Using Spherical Lights
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Guerrero, P.; Jeschke, S.; Wimmer, M.
We present a method for rendering approximate soft shadows and diffuse indirect illumination in dynamic scenes. The proposed method approximates the original scene geometry with a set of tightly fitting spheres. In previous work, such spheres have been used to dynamically evaluate the visibility function to render soft shadows. In this paper, each sphere also acts as a low-frequency secondary light source, thereby providing diffuse one-bounce indirect illumination. The method is completely dynamic and proceeds in two passes: In a first pass, the light intensity distribution on each sphere is updated based on sample points on the corresponding object surface and converted into the spherical harmonics basis. In a second pass, this radiance information and the visibility are accumulated to shade final image pixels. The sphere approximation allows us to compute visibility and diffuse reflections of an object at interactive frame rates of over 20 fps for moderately complex scenes.
G2 Tensor Product Splines over Extraordinary Vertices
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Loop, Charles; Schaefer, Scott
We present a second order smooth filling of an n-valent Catmull-Clark spline ring with n biseptic patches. While an underdetermined biseptic solution to this problem has appeared previously, we make several advances in this paper. Most notably, we cast the problem as a constrained minimization and introduce a novel quadratic energy functional whose absolute minimum of zero is achieved for bicubic polynomials. This means that for the regular 4-valent case, we reproduce the bicubic B-splines. In other cases, the resulting surfaces are aesthetically well behaved. We extend our constrained minimization framework to handle the case of input mesh with boundary.
The Shadow Meets the Mask: Pyramid-Based Shadow Removal
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Shor, Yael; Lischinski, Dani
In this paper we propose a novel method for detecting and removing shadows from a single image thereby obtaining a high-quality shadow-free image. With minimal user assistance, we first identify shadowed and lit areas on the same surface in the scene using an illumination-invariant distance measure. These areas are used to estimate the parameters of an affine shadow formation model. A novel pyramid-based restoration process is then applied to produce a shadow-free image, while avoiding loss of texture contrast and introduction of noise. Unlike previous approaches, we account for varying shadow intensity inside the shadowed region by processing it from the interior towards the boundaries. Finally, to ensure a seamless transition between the original and the recovered regions we apply image inpainting along a thin border. We demonstrate that our approach produces results that are in most cases superior in quality to those of previous shadow removal methods. We also show that it is possible to easily composite the extracted shadow onto a new background or modify its size and direction in the original image.
New EUROGRAPHICS Fellows
(The Eurographics Association and Blackwell Publishing Ltd, 2008)
Image-Based Surface Compression
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ochotta, Tilo; Saupe, Dietmar
We present a generic framework for compression of densely sampled three-dimensional (3D) surfaces in order to satisfy the increasing demand for storing large amounts of 3D content. We decompose a given surface into patches that are parameterized as elevation maps over planar domains and resampled on regular grids. The resulting shaped images are encoded using a state-of-the-art wavelet image coder. We show that our method is not only applicable to mesh- and point-based geometry, but also outperforms current surface encoders for both primitives.
Adaptive Surface Texture Synthesis Using Round-Shaped Neighbourhoods
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Chen, D.; Dong, F.
This paper presents a novel surface texture synthesis method, which is capable of producing high-quality results by performing the synthesis within an effective multi-resolution scheme using an adaptive texture similarity metric. Compared with related works, our method allows us to directly carry out multi-resolution synthesis without involving complicated operations such as mesh hierarchy and partitioning on the target surface. Also, the adaptive similarity metric focuses on measuring texture properties at different scales ranging from local to global, allowing for consistency within differently-sized texture structures. Further, with the introduced round shaped neighbourhoods, we can save considerable amount of computation for the surface texture synthesis over variable texture directions. Experimental results are provided and comparisons are made against other latest works.
Ray Casting Algebraic Surfaces using the Frustum Form
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Reimers, Martin; Seland, Johan
We propose an algorithm for interactive ray-casting of algebraic surfaces of high degree. A key point of our approach is a polynomial form adapted to the view frustum. This so called frustum form yields simple expressions for the Bernstein form of the ray equations, which can be computed efficiently using matrix products and pre-computed quantities. Numerical root-finding is performed using B-spline and Bezier techniques, and we compare the performances of recent and classical algorithms. Furthermore, we propose a simple and fairly efficient anti-aliasing scheme, based on a combination of screen space and object space techniques. We show how our algorithms can be implemented on streaming architectures with single precision, and demonstrate interactive frame-rates for degrees up to 16.
Image-based Aging Using Evolutionary Computing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Hubball, Daniel; Chen, Min; Grant, Phil W.
Aging has considerable visual effects on the human face and is difficult to simulate using a universally-applicable global model. In this paper, we focus on the hypothesis that the patterns of age progression (and regression) are related to the face concerned, as the latter implicitly captures the characteristics of gender, ethnic origin, and age group, as well as possibly the person-specific development patterns of the individual. We use a data-driven framework for automatic image-based facial transformation in conjunction with a database of facial images. We build a novel parameterized model for encoding age-transformation in addition with the traditional model for face description. We utilize evolutionary computing to learn the relationship between the two models. To support this work, we also developed a new image warping algorithm based on non-uniform radial basis functions (NURBFs). Evolutionary computing was also used to handle the large parameter space associated with NURBFs. In comparison with several different methods, it consistently provides the best results against the ground truth.
GPU-Based Spherical Light Field Rendering with Per-Fragment Depth Correction
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Todt, S.; Rezk-Salama, C.; Kolb, A.; Kuhnert, K.-D.
Image-based rendering techniques are a powerful alternative to traditional polygon-based computer graphics. This paper presents a novel light field rendering technique which performs per-pixel depth correction of rays for high-quality reconstruction. Our technique stores combined RGB and depth values in a parabolic 2D texture for every light field sample acquired at discrete positions on a uniform spherical setup. Image synthesis is implemented on the GPU as a fragment program which extracts the correct image information from adjacent cameras for each fragment by applying per-pixel depth correction of rays.We show that the presented image-based rendering technique provides a significant improvement compared to previous approaches. We explain two different rendering implementations which make use of a uniform parametrisation to minimise disparity problems and ensure full six degrees of freedom for virtual view synthesis. While one rendering algorithm implements an iterative refinement approach for rendering light fields with per pixel depth correction, the other approach employs a raycaster, which provides superior rendering quality at moderate frame rates.GPU based per-fragment depth correction of rays, used in both implementations, helps reducing ghosting artifacts to a non-noticeable amount and provides a rendering technique that performs without exhaustive pre-processing for 3D object reconstruction and without real-time ray-object intersection calculations at rendering time.
Deep Opacity Maps
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Yuksel, Cem; Keyser, John
We present a new method for rapidly computing shadows from semi-transparent objects like hair. Our deep opacity maps method extends the concept of opacity shadow maps by using a depth map to obtain a per pixel distribution of opacity layers. This approach eliminates the layering artifacts of opacity shadow maps and requires far fewer layers to achieve high quality shadow computation. Furthermore, it is faster than the density clustering technique, and produces less noise with comparable shadow quality. We provide qualitative comparisons to these previous methods and give performance results. Our algorithm is easy to implement, faster, and more memory efficient, enabling us to generate high quality hair shadows in real-time using graphics hardware on a standard PC.
A smart stochastic approach for manifolds smoothing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) El Ouafdi, A.F.; Ziou, D.; Krim, H.
In this paper, we present a probabilistic approach for 3D object s smoothing. The core idea behind the proposed method is to relate the problem of smoothing objects to that of tracking the transition probability density functions of an underlying random process. We show that such an approach allows for additional insight and sufficient flexibility compared with existing standard smoothing techniques. In particular, we are able to propose a newer, faster, and simpler smoothing approach that retains and enhances important manifold features. Furthermore, it is demonstrated to improve performance over existing smoothing techniques.
Gradient-based Interpolation and Sampling for Real-time Rendering of Inhomogeneous, Single-scattering Media
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ren, Zhong; Zhou, Kun; Lin, Stephen; Guo, Baining
We present a real-time rendering algorithm for inhomogeneous, single scattering media, where all-frequency shading effects such as glows, light shafts, and volumetric shadows can all be captured. The algorithm first computes source radiance at a small number of sample points in the medium, then interpolates these values at other points in the volume using a gradient-based scheme that is efficiently applied by sample splatting. The sample points are dynamically determined based on a recursive sample splitting procedure that adapts the number and locations of sample points for accurate and efficient reproduction of shading variations in the medium. The entire pipeline can be easily implemented on the GPU to achieve real-time performance for dynamic lighting and scenes. Rendering results of our method are shown to be comparable to those from ray tracing.
Video Relighting Using Infrared Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Wang, Oliver; Davis, James; Chuang, Erika; Rickard, Ian; De Mesa, Krystle; Dave, Chirag
Inappropriate lighting is often responsible for poor quality video. In most offices and homes, lighting is not designed for video conferencing. This can result in unevenly lit faces, distracting shadows, and unnatural colors. We present a method for relighting faces that reduces the effects of uneven lighting and color. Our setup consists of a compact lighting rig and a camera that is both inexpensive and inconspicuous to the user. We use unperceivable infrared (IR) lights to obtain an illumination bases of the scene. Our algorithm computes an optimally weighted combination of IR bases to minimize lighting inconsistencies in foreground areas and reduce the effects of colored monitor light. However, IR relighting alone results in images with an unnatural ghostly appearance, thus a retargeting technique is presented which removes the unnatural IR effects and produces videos that have substantially more balanced intensity and color than the original video.
Table of Contents and Cover
(The Eurographics Association and Blackwell Publishing Ltd, 2008)
The Visual Computing of Projector-Camera Systems
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Bimber, Oliver; Iwai, Daisuke; Wetzstein, Gordon; Grundhoefer, Anselm
This article focuses on real-time image correction techniques that enable projector-camera systems to display images onto screens that are not optimized for projections, such as geometrically complex, coloured and textured surfaces. It reviews hardware-accelerated methods like pixel-precise geometric warping, radiometric compensation, multi-focal projection and the correction of general light modulation effects. Online and offline calibration as well as invisible coding methods are explained. Novel attempts in super-resolution, high-dynamic range and high-speed projection are discussed. These techniques open a variety of new applications for projection displays. Some of them will also be presented in this report.
CHC++: Coherent Hierarchical Culling Revisited
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Mattausch, Oliver; Bittner, Jiri; Wimmer, Michael
We present a new algorithm for efficient occlusion culling using hardware occlusion queries. The algorithm significantly improves on previous techniques by making better use of temporal and spatial coherence of visibility. This is achieved by using adaptive visibility prediction and query batching. As a result of the new optimizations the number of issued occlusion queries and the number of rendering state changes are significantly reduced. We also propose a simple method for determining tighter bounding volumes for occlusion queries and a method which further reduces the pipeline stalls. The proposed method provides up to an order of magnitude speedup over the previous state of the art. The new technique is simple to implement, does not rely on hardware calibration and integrates well with modern game engines.
Ptex: Per-Face Texture Mapping for Production Rendering
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Burley, Brent; Lacewell, Dylan
Explicit parameterization of subdivision surfaces for texture mapping adds significant cost and complexity to film production. Most parameterization methods currently in use require setup effort, and none are completely general. We propose a new texture mapping method for Catmull-Clark subdivision surfaces that requires no explicit parameterization. Our method, Ptex, stores a separate texture per quad face of the subdivision control mesh, along with a novel per-face adjacency map, in a single texture file per surface. Ptex uses the adjacency data to perform seamless anisotropic filtering of multi-resolution textures across surfaces of arbitrary topology. Just as importantly, Ptex requires no manual setup and scales to models of arbitrary mesh complexity and texture detail. Ptex has been successfully used to texture all of the models in an animated theatrical short and is currently being applied to an entire animated feature. Ptex has eliminated UV assignment from our studio and significantly increased the efficiency of our pipeline.

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