Search Results

Now showing 1 - 10 of 17
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    NURBS-based Inverse Reflector Design
    (The Eurographics Association, 2008) Anson, Oscar; Seron, Francisco J.; Gutierrez, Diego; Luis Matey and Juan Carlos Torres
    Commonly used direct rendering techniques simulate light transport for a complete scene, specified in terms of light sources, geometry, materials, participating media, etc. On the other hand, inverse rendering problems take as input a desired light distribution and try to find the unknown parts of the scene needed to get such light field. The latter kind, where inverse reflector design is included, is traditionally solved by simulation optimization methods, due to the high complexity of the inverse problem. In this paper we present an inverse reflector design method which handles surfaces as NURBS and simulates accurately the light transport by means of a modified photon mapping algorithm. The proposed method is based on an optimization method, called pattern search, in order to compute the reflector needed to generate a target near light field. Some assumptions are determined in order to reduce the complexity of the problem, such as a rotationally symmetric reflector or its perfectly specular reflective behavior. The optimization method specifies the reflector shape by handling a NURBS curve as a generatrix, sequentially modifying the position and weights of its control points in order to obtain the reflector solution. Areas of applications of inverse reflector design span from architectural lighting design to car headlamps design
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    Bidirectional Clustering for Scalable VPL-based Global Illumination
    (The Eurographics Association, 2015) Jarabo, Adrian; Buisan, Raul; Gutierrez, Diego; Mateu Sbert and Jorge Lopez-Moreno
    Virtual Point Lights (VPL) methods approximate global illumination (GI) in a scene by using a large number of virtual lights modeling the reflected radiance of a surface. These methods are efficient, and allow computing noise-free images significantly faster that other methods. However, they scale linearly with the number of virtual lights and with the number of pixels to be rendered. Previous approaches improve the scalability of the method by hierarchically evaluating the virtual lights, allowing sublinear performance with respect the lights being evaluated. In this work, we introduce a novel bidirectional clustering approach, by hierarchically evaluating both the virtual lights and the shading points. This allows reusing radiance evaluation between pixels, and obtaining sublinear costs with respect to both lights and camera samples. We demonstrate significantly better performance than state-of-the-art VPL clustering methods with several examples, including high-resolution images, distributed effects, and rendering of light fields.
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    Structure-preserving Style Transfer
    (The Eurographics Association, 2019) Calvo, Santiago; Serrano, Ana; Gutierrez, Diego; Masia, Belen; Casas, Dan and Jarabo, Adrián
    Transferring different artistic styles to images while preserving their content is a difficult image processing task. Since the seminal deep learning approach of Gatys et al. [GEB16], many recent works have proposed different approaches for performing this task. However, most of them share one major limitation: a trade-off between how much the target style is transferred, and how much the content of the original source image is preserved [GEB16, GEB*17, HB17, LPSB17]. In this work, we present a structure-preserving approach for style transfer that builds on top of the approach proposed by Gatys et al. Our approach allows to preserve regions of fine detail by lowering the intensity of the style transfer for such regions, while still conveying the desired style in the overall appearance of the image. We propose to use a quad-tree image subdivision, and then apply the style transfer operation differently for different subdivision levels. Effectively, this leads to a more intense style transfer in large flat regions, while the content is better preserved in areas with fine structure and details. Our approach can be easily applied to different style transfer approaches as a post-processing step.
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    Bidirectional Rendering of Polarized Light Transport
    (The Eurographics Association, 2016) Jarabo, Adrian; Gutierrez, Diego; Alejandro Garcia-Alonso and Belen Masia
    On the foundations of many rendering algorithm is the symmetry between the path traversed by light and its adjoint from the camera. However, several effects, including polarization or fluorescence, break that symmetry and are defined only on the direction of light. This complicates the applicability of bidirectional methods, that exploit the symmetry for effective rendering light transport. In this work we focus on how to include polarization within a bidirectional rendering algorithm. For that, we generalize the path integral to support the constraints imposed by non-symmetric light transport. Based on this theoretical framework, we propose modifications on two bidirectional methods, namely bidirectional path tracing and photon mapping, extending them to support polarization.
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    Low Cost Decomposition of Direct and Global Illumination in Real Scenes
    (The Eurographics Association, 2015) Garces, Elena; Martin, Fernando; Gutierrez, Diego; Mateu Sbert and Jorge Lopez-Moreno
    Recent advances in the field of computational light transport have made it possible to solve previously unsolvable problems thanks to incorporating new devices and techniques. One of these problems is the decomposition of the illumination into its local and global components in real scenes. Previous work has managed to perform such a decomposition by projecting several light patterns on a target scene and processing its captures. In this work we build on that approach and propose two novel contributions: first, a new interpolation method, which allows the decomposition of the light components from a single capture of the projected scene into the native resolution, without requiring down-sampling; second, we propose an implementation of the algorithm for a mobile platform.
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    Transient Photon Beams
    (The Eurographics Association, 2017) Marco, Julio; Jarosz, Wojciech; Gutierrez, Diego; Jarabo, Adrian; Fco. Javier Melero and Nuria Pelechano
    Recent advances on transient imaging and their applications have opened the necessity of forward models that allow precise generation and analysis of time-resolved light transport data. However, traditional steady-state rendering techniques are not suitable for computing transient light transport due to the aggravation of the inherent Monte Carlo variance over time. These issues are specially problematic in participating media, which demand high number of samples to achieve noise-free solutions. We address this problem by presenting the first photon-based method for transient rendering of participating media that performs density estimations on time-resolved precomputed photon maps. We first introduce the transient integral form of the radiative transfer equation into the computer graphics community, including transient delays on the scattering events. Based on this formulation we leverage the high density and parameterized continuity provided by photon beams algorithms to present a new transient method that allows to significantly mitigate variance and efficiently render participating media effects in transient state.
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    Compressive High Speed Video Acquisition
    (The Eurographics Association, 2015) Serrano, Ana; Gutierrez, Diego; Masia, Belen; Mateu Sbert and Jorge Lopez-Moreno
    Traditional video capture is limited by the trade-off between spatial and temporal resolution. When capturing videos of high temporal resolution, the spatial resolutions decreases due to bandwidth limitations in the capture system. Achieving both high spatial and temporal resolution is only possible with highly specialized and very expensive hardware; although the bandwidth is higher, the same basic trade-off remains. In this paper, we make use of a single-shot, high-speed video capture system, in order to overcome this limitation. It is based on compressive sensing, and relies on dictionary learning for sparse video representation. This allows capturing a video sequence by coding the temporal information in a single frame, and then reconstructing the full video sequence from this single coded image. We perform an in-depth analysis of the parameters of influence in the system, providing insights for future developments of similar systems.
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    A Physically-Based Spatio-Temporal Sky Model
    (The Eurographics Association, 2018) Guimera, David; Gutierrez, Diego; Jarabo, Adrián; García-Fernández, Ignacio and Ureña, Carlos
    In this work we present a physically-based optical model of the atmosphere, that takes into account the seasonal and geographic variation of its composition. Based on data from the atmospheric science literature, we build a highly detailed the composition of the atmosphere, and how it varies depending on the position of the observer, or the time of the year. Then, based on precise measurements of the optical properties of the components of the atmosphere, we map our model into a radiative model, which can be rendered in any existing volumetric renderer. We demonstrate our model in multispectral renders of daylight sky-domes, showing the changes in the appearance occurring when varying the season or location of the observer.
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    Understanding Exposure for Reverse Tone Mapping
    (The Eurographics Association, 2008) Martin, Miguel; Fleming, Roland; Sorkine, Olga; Gutierrez, Diego; Luis Matey and Juan Carlos Torres
    High dynamic range (HDR) displays are capable of providing a rich visual experience by boosting both luminance and contrast beyond what conventional displays can offer.We envision that HDR capture and display hardware will soon reach the mass market and become mainstream in most fields, from entertainment to scientific visualization. This will necessarily lead to an extensive redesign of the imaging pipeline. However, a vast amount of legacy content is available, captured and stored using the traditional, low dynamic range (LDR) pipeline. The immediate question that arises is: will our current LDR digital material be properly visualized on an HDR display? The answer to this question involves the process known as reverse tone mapping (the expansion of luminance and contrast to match those of the HDR display) for which no definite solution exists. This paper studies the specific problem of reverse tone mapping for imperfect legacy still images, where some regions are under- or overexposed. First, we show the results of a psychophysical study compared with first-order image statistics, in an attempt to gain some understanding in what makes an image be perceived as incorrectly exposed; second, we propose a methodology to evaluate existing reverse tone mapping algorithms in the case of imperfect legacy content.
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    Image-based Participating Media
    (The Eurographics Association, 2008) Lopez-Moreno, Jorge; Cabanes, Angel; Gutierrez, Diego; Luis Matey and Juan Carlos Torres
    Light transport inside participating media, like fog or water, involves complex interaction phenomena, which make traditional 3D rendering approaches challenging and computationally expensive. To circumvent this, we propose an image-based method which adds perceptually plausible participating media effects to a single, clean high dynamic range image. We impose no prior requirements on the input image, and show that the underconstrained nature of the problem (where variables like depth or reflectance properties of the objects are obviously unknown) can be overcome with relatively little unskilled user input, similar to other image-editing techniques. We additionally validate the visual correctness of the results by means of psychophysical tests.