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Now showing 1 - 7 of 7
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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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    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.
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    Analysis of Coded Apertures for Defocus Deblurring of HDR Images
    (The Eurographics Association, 2012) Garcia, Luis; Presa, Lara; Gutierrez, Diego; Masia, Belen; Isabel Navazo and Gustavo Patow
    In recent years, research on computational photography has reached important advances in the field of coded apertures for defocus deblurring. These advances are known to perform well for low dynamic range images (LDR), but nothing is written about the extension of these techniques to high dynamic range imaging (HDR). In this paper, we focus on the analysis of how existing coded apertures techniques perform in defocus deblurring of HDR images. We present and analyse three different methods for recovering focused HDR radiances from an input of blurred LDR exposures and from a single blurred HDR radiance, and compare them in terms of the quality of their results, given by the perceptual metric HDR-VDP2. Our research includes the analysis of the employment of different statistical deconvolution priors, made both from HDR and LDR images, performing synthetic experiments as well as real ones.
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    Where are the Lights? Measuring the Accuracy of Human Vision
    (The Eurographics Association, 2009) Lopez-Moreno, Jorge; Sangorrin, Francisco; Latorre, Pedro; Gutierrez, Diego; Carlos Andujar and Javier Lluch
    In real life, light sources are frequently not present in our view field. However human vision is able to infer the illumination just by observing its effect on visible objects (serving as lightprobes) or, inverting the idea, it is able to spot an object which is incoherently lit in a composition. These lightprobes have been used by computer algorithms in the same manner to detect lights, mimicking the human visual system (HVS). It has been proved that the presence of shadows or highlights in the lightprobe affects the accuracy of HVS, although its degree of influence remains unbeknownst until now. The present work performs a psychophysical analysis which aims to provide accurate data for light detection, perception-oriented rendering, image compositing and augmented reality.
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    Light Source Detection in Photographs
    (The Eurographics Association, 2009) Lopez-Moreno, Jorge; Hadap, Sunil; Reinhard, Erik; Gutierrez, Diego; Carlos Andujar and Javier Lluch
    Common tasks related to image processing or augmented reality include rendering new objects into existing images, or matching objects with unknown illumination. To facilitate such algorithms, it is often necessary to infer from which directions a scene was illuminated, even if only a photograph is available. For this purpose, we present a novel light source detection algorithm that, contrary to the current state-of-the-art, is able to detect multiple light sources with sufficient accuracy. 3D measures are not required, only the input image and a very small amount of unskilled user interaction.
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    Faster Rendering of Human Skin
    (The Eurographics Association, 2008) Jimenez, Jorge; Gutierrez, Diego; Luis Matey and Juan Carlos Torres
    Rendering realistic human skin is not a trivial task. It means dealing with light diffusion in a multi-layered material, where multiple subsurface scattering events take place. Great care must be taken when simulating its appearance, to avoid an unnatural, waxy look. Recent works in the field of computer graphics have provided us with the ability to accurately render human skin, both off-line and in real time. The latter takes advantage of modern graphics hardware, defining light diffusion in texture space. In this paper we leverage this framework and optimize the irradiance map calculations, which simulate light diffusion in skin. We present three simple yet effective improvements implemented on top of the state-of-the-art, real-time rendering algorithm published by d'Eon et al. We achieve maximum speed-ups in excess of 2:7x using the same hardware configuration. Our implementation scales well, and is particularly efficient in multiple-character scenarios. This should be specially useful for real-time realistic human skin rendering for crowds.