Showing papers by "Wolfgang Heidrich published in 2011"
25 Jul 2011
TL;DR: The visibility metric is shown to provide much improved predictions as compared to the original HDR-VDP and VDP metrics, especially for low luminance conditions, and is comparable to or better than for the MS-SSIM, which is considered one of the most successful quality metrics.
Abstract: Visual metrics can play an important role in the evaluation of novel lighting, rendering, and imaging algorithms. Unfortunately, current metrics only work well for narrow intensity ranges, and do not correlate well with experimental data outside these ranges. To address these issues, we propose a visual metric for predicting visibility (discrimination) and quality (mean-opinion-score). The metric is based on a new visual model for all luminance conditions, which has been derived from new contrast sensitivity measurements. The model is calibrated and validated against several contrast discrimination data sets, and image quality databases (LIVE and TID2008). The visibility metric is shown to provide much improved predictions as compared to the original HDR-VDP and VDP metrics, especially for low luminance conditions. The image quality predictions are comparable to or better than for the MS-SSIM, which is considered one of the most successful quality metrics. The code of the proposed metric is available on-line.
691 citations
12 Dec 2011
TL;DR: The use of displacement interpolation is developed for this class of problem, which provides a generic method for interpolating between distributions or functions based on advection instead of blending.
Abstract: Interpolation between pairs of values, typically vectors, is a fundamental operation in many computer graphics applications. In some cases simple linear interpolation yields meaningful results without requiring domain knowledge. However, interpolation between pairs of distributions or pairs of functions often demands more care because features may exhibit translational motion between exemplars. This property is not captured by linear interpolation. This paper develops the use of displacement interpolation for this class of problem, which provides a generic method for interpolating between distributions or functions based on advection instead of blending. The functions can be non-uniformly sampled, high-dimensional, and defined on non-Euclidean manifolds, e.g., spheres and tori. Our method decomposes distributions or functions into sums of radial basis functions (RBFs). We solve a mass transport problem to pair the RBFs and apply partial transport to obtain the interpolated function. We describe practical methods for computing the RBF decomposition and solving the transport problem. We demonstrate the interpolation approach on synthetic examples, BRDFs, color distributions, environment maps, stipple patterns, and value functions.
239 citations
25 Jul 2011
TL;DR: Optimization of tomographic techniques for image synthesis on displays composed of compact volumes of light-attenuating material allows optimal construction of high dynamic range displays, confirming existing heuristics and providing the first extension to multiple, disjoint layers.
Abstract: We develop tomographic techniques for image synthesis on displays composed of compact volumes of light-attenuating material. Such volumetric attenuators recreate a 4D light field or high-contrast 2D image when illuminated by a uniform backlight. Since arbitrary oblique views may be inconsistent with any single attenuator, iterative tomographic reconstruction minimizes the difference between the emitted and target light fields, subject to physical constraints on attenuation. As multi-layer generalizations of conventional parallax barriers, such displays are shown, both by theory and experiment, to exceed the performance of existing dual-layer architectures. For 3D display, spatial resolution, depth of field, and brightness are increased, compared to parallax barriers. For a plane at a fixed depth, our optimization also allows optimal construction of high dynamic range displays, confirming existing heuristics and providing the first extension to multiple, disjoint layers. We conclude by demonstrating the benefits and limitations of attenuation-based light field displays using an inexpensive fabrication method: separating multiple printed transparencies with acrylic sheets.
228 citations
TL;DR: It is shown that the appropriate choice of a tone-mapping operator (TMO) can significantly improve the reconstructed HDR quality and a statistical model is developed that approximates the distortion resulting from the combined processes of tone- mapping and compression.
Abstract: For backward compatible high dynamic range (HDR) video compression, the HDR sequence is reconstructed by inverse tone-mapping a compressed low dynamic range (LDR) version of the original HDR content. In this paper, we show that the appropriate choice of a tone-mapping operator (TMO) can significantly improve the reconstructed HDR quality. We develop a statistical model that approximates the distortion resulting from the combined processes of tone-mapping and compression. Using this model, we formulate a numerical optimization problem to find the tone-curve that minimizes the expected mean square error (MSE) in the reconstructed HDR sequence. We also develop a simplified model that reduces the computational complexity of the optimization problem to a closed-form solution. Performance evaluations show that the proposed methods provide superior performance in terms of HDR MSE and SSIM compared to existing tone-mapping schemes. It is also shown that the LDR image quality resulting from the proposed methods matches that produced by perceptually-based TMOs.
196 citations
01 Dec 2011
TL;DR: This state‐of‐the‐art report reviews approaches that optically encode the dimensions of the plenoptic function transcending those captured by traditional photography and reconstruct the recorded information computationally.
Abstract: The plenoptic function is a ray-based model for light that includes the colour spectrum as well as spatial, temporal and directional variation. Although digital light sensors have greatly evolved in the last years, one fundamental limitation remains: all standard CCD and CMOS sensors integrate over the dimensions of the plenoptic function as they convert photons into electrons; in the process, all visual information is irreversibly lost, except for a two-dimensional, spatially varying subset—the common photograph. In this state-of-the-art report, we review approaches that optically encode the dimensions of the plenoptic function transcending those captured by traditional photography and reconstruct the recorded information computationally.
170 citations
12 Dec 2011
TL;DR: P polarization field displays are introduced as an optically-efficient design for dynamic light field display using multi-layered LCDs and achieve increased brightness, higher resolution, and extended depth of field, as compared to existing automultiscopic display methods for dual-layer and multi-layer LCDs.
Abstract: We introduce polarization field displays as an optically-efficient design for dynamic light field display using multi-layered LCDs. Such displays consist of a stacked set of liquid crystal panels with a single pair of crossed linear polarizers. Each layer is modeled as a spatially-controllable polarization rotator, as opposed to a conventional spatial light modulator that directly attenuates light. Color display is achieved using field sequential color illumination with monochromatic LCDs, mitigating severe attenuation and moire occurring with layered color filter arrays. We demonstrate such displays can be controlled, at interactive refresh rates, by adopting the SART algorithm to tomographically solve for the optimal spatially-varying polarization state rotations applied by each layer. We validate our design by constructing a prototype using modified off-the-shelf panels. We demonstrate interactive display using a GPU-based SART implementation supporting both polarization-based and attenuation-based architectures. Experiments characterize the accuracy of our image formation model, verifying polarization field displays achieve increased brightness, higher resolution, and extended depth of field, as compared to existing automultiscopic display methods for dual-layer and multi-layer LCDs.
123 citations
06 Nov 2011
TL;DR: A new, single image approach to reconstructing thin transparent surfaces, such as thin solids or surfaces of fluids, based on observing the distortion of light field background illumination, which shows that the additional information can be used to reconstruct refractive surface normals and a sparse set of control points from a single photograph.
Abstract: Acquiring transparent, refractive objects is challenging as these kinds of objects can only be observed by analyzing the distortion of reference background patterns. We present a new, single image approach to reconstructing thin transparent surfaces, such as thin solids or surfaces of fluids. Our method is based on observing the distortion of light field background illumination. Light field probes have the potential to encode up to four dimensions in varying colors and intensities: spatial and angular variation on the probe surface; commonly employed reference patterns are only two-dimensional by coding either position or angle on the probe. We show that the additional information can be used to reconstruct refractive surface normals and a sparse set of control points from a single photograph.
74 citations
01 Nov 2011
TL;DR: In this article, a single image approach is presented to reconstructing thin transparent surfaces, such as thin solids or surfaces of fluids, based on observing the distortion of light field background illumination.
Abstract: Acquiring transparent, refractive objects is challenging as these kinds of objects can only be observed by analyzing the distortion of reference background patterns. We present a new, single image approach to reconstructing thin transparent surfaces, such as thin solids or surfaces of fluids. Our method is based on observing the distortion of light field background illumination. Light field probes have the potential to encode up to four dimensions in varying colors and intensities: spatial and angular variation on the probe surface; commonly employed reference patterns are only two-dimensional by coding either position or angle on the probe. We show that the additional information can be used to reconstruct refractive surface normals and a sparse set of control points from a single photograph.
73 citations
01 Apr 2011
TL;DR: In this paper, the locations and directions of light rays emerging from a light field probe are encoded using color and intensity variations of a 4D probe instead of a diffuse 2D background.
Abstract: We introduce a new approach to capturing refraction in transparent media, which we call Light Field Background Oriented Schlieren Photography (LFBOS). By optically coding the locations and directions of light rays emerging from a light field probe, we can capture changes of the refractive index field between the probe and a camera or an observer. Rather than using complicated and expensive optical setups as in traditional Schlieren photography we employ commodity hardware; our prototype consists of a camera and a lenslet array. By carefully encoding the color and intensity variations of a 4D probe instead of a diffuse 2D background, we avoid expensive computational processing of the captured data, which is necessary for Background Oriented Schlieren imaging (BOS). We analyze the benefits and limitations of our approach and discuss application scenarios.
55 citations
06 Nov 2011
TL;DR: This work proposes a cluster-based approach for optimizing the transformation for individual images in a way that preserves as much of the information as possible from the source space while staying as faithful as possible to the natural mapping.
Abstract: Transformations between different color spaces and gamuts are ubiquitous operations performed on images. Often, these transformations involve information loss, for example when mapping from color to grayscale for printing, from multispectral or multiprimary data to tristimulus spaces, or from one color gamut to another. In all these applications, there exists a straightforward “natural” mapping from the source space to the target space, but the mapping is not bijective, resulting in information loss due to metamerism and similar effects. We propose a cluster-based approach for optimizing the transformation for individual images in a way that preserves as much of the information as possible from the source space while staying as faithful as possible to the natural mapping. Our approach can be applied to a host of color transformation problems including color to gray, gamut mapping, conversion of multispectral and multiprimary data to tristimulus colors, and image optimization for color deficient viewers.
54 citations
08 Apr 2011
TL;DR: A new approach to capturing refraction in transparent media, which is called Light Field Background Oriented Schlieren Photography (LFBOS), by optically coding the locations and directions of light rays emerging from a light field probe to avoid expensive computational processing of the captured data.
Abstract: We introduce a new approach to capturing refraction in transparent media, which we call Light Field Background Oriented Schlieren Photography (LFBOS) By optically coding the locations and directions of light rays emerging from a light field probe, we can capture changes of the refractive index field between the probe and a camera or an observer Rather than using complicated and expensive optical setups as in traditional Schlieren photography we employ commodity hardware; our prototype consists of a camera and a lenslet array By carefully encoding the color and intensity variations of a 4D probe instead of a diffuse 2D background, we avoid expensive computational processing of the captured data, which is necessary for Background Oriented Schlieren imaging (BOS) We analyze the benefits and limitations of our approach and discuss application scenarios
20 Jun 2011
TL;DR: A novel view of HDR capture is taken, which is based on a computational photography approach, that proposes to first optically encode both the low dynamic range portion of the scene and highlight information into a low dynamicrange image that can be captured with a conventional image sensor.
Abstract: Without specialized sensor technology or custom, multi-chip cameras, high dynamic range imaging typically involves time-sequential capture of multiple photographs. The obvious downside to this approach is that it cannot easily be applied to images with moving objects, especially if the motions are complex. In this paper, we take a novel view of HDR capture, which is based on a computational photography approach. We propose to first optically encode both the low dynamic range portion of the scene and highlight information into a low dynamic range image that can be captured with a conventional image sensor. This step is achieved using a cross-screen, or star filter. Second, we decode, in software, both the low dynamic range image and the highlight information. Lastly, these two portions can be combined to form an image of a higher dynamic range than the regular sensor dynamic range.
TL;DR: A complex, but mostly image‐independent relationship between matching blur levels in images at different resolutions is found and a new appearance‐preserving downsampling algorithm is incorporated, which alters blur magnitude locally to create a smaller image that gives the best reproduction of the original image appearance.
Abstract: Resizing to a lower resolution can alter the appearance of an image. In particular, downsampling an image causes blurred regions to appear sharper. It is useful at times to create a downsampled version of the image that gives the same impression as the original, such as for digital camera viewfinders. To understand the effect of blur on image appearance at different image sizes, we conduct a perceptual study examining how much blur must be present in a downsampled image to be perceived the same as the original. We find a complex, but mostly image-independent relationship between matching blur levels in images at different resolutions. The relationship can be explained by a model of the blur magnitude analyzed as a function of spatial frequency. We incorporate this model in a new appearance-preserving downsampling algorithm, which alters blur magnitude locally to create a smaller image that gives the best reproduction of the original image appearance.
01 Jan 2011
TL;DR: This work applies a method of reconstructing the region of origin and trajectories for particles given impact directions and positions to the case of forensic blood pattern reconstruction, by automatically estimating impact velocities directly form the blood patterns.
Abstract: We present a method of reconstructing the region of origin and trajectories for particles given impact directions and positions. This method works for nonlinear trajectories, such as parabolic motion or motion with drag if given drag parameters. Our method works if given the impact speeds as well, or they can be estimated using a similar total initial energy prior. We apply our algorithm to the case of forensic blood pattern reconstruction, by automatically estimating impact velocities directly form the blood patterns. We validate our method in physically accurate simulated experiments, a feasibility study varying the impact angle and speed to estimate the impact speed from blood drop densities, as well as a forensic experiment using blood to reconstruct the region of origin.
27 Aug 2011
TL;DR: There are many visual cues that provide sensations of depth or distance in the authors' observations of real-world 3D scenes as well as 2D images that are monocular in that the images appear the same to both retinae and do not have binocular disparity that can be used to form depth judgments.
Abstract: There are many visual cues that provide sensations of depth or distance in our observations of real-world 3D scenes as well as 2D images. In the latter case, these cues are monocular in that the images appear the same to both retinae and do not have binocular disparity that can be used to form depth judgments. Examples include perspective, relative sizes of objects, familiarity with sizes of objects, occlusion, contrast, brightness, color saturation, and haze. Contrast and brightness are of particular interest to us since they can be manipulated through a much greater range on high dynamic range displays than is possible on conventional displays.
Proceedings Article•
01 Jan 2011TL;DR: An experiment is conducted in which it is shown that negative polarity produces better performance in a legibility task than does positive polarity (dark text on a bright background).
Abstract: Most displays viewed in dark environments can easily cause dazzling glare and affect a viewer’s dark adaptation state (night vision). In previous work we showed that legibility could be improved and dark adaptation preserved in low-light environments by using a display design with a specially selected spectral light emission. We used long-wavelength light (red) that is easily visible to daylight vision photoreceptors (cones) but almost invisible to night vision photoreceptors (rods). In this paper we conduct an experiment in which we show that negative polarity (bright text on a dark background) produces better performance in a legibility task than does positive polarity (dark text on a bright background). Our results can serve as a guidelines for designing displays that change their color scheme at low ambient light levels.