The Experts below are selected from a list of 177828 Experts worldwide ranked by ideXlab platform
Katsushi Ikeuchi - One of the best experts on this subject based on the ideXlab platform.
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Wavelet-Texture Method: Appearance Compression by Polarization, Parametric Reflection Model, and Daubechies Wavelet
International Journal of Computer Vision, 2009Co-Authors: Daisuke Miyazaki, Takushi Shibata, Katsushi IkeuchiAbstract:In order to create a photorealistic Virtual Reality Model, we have to record the appearance of the object from different directions under different illuminations. In this paper, we propose a method that renders photorealistic images from a small amount of data. First, we separate the images of the object into a diffuse Reflection component and a specular Reflection component by using linear polarizers. Then, we estimate the parameters of the Reflection Model for each component. Finally, we compress the difference between the input images and the rendered images by using wavelet transform. At the rendering stage, we first calculate the diffuse and specular Reflection images from the Reflection parameters, then add the difference decompressed by inverse wavelet transform into the calculated Reflection images, and finally obtain the photorealistic image of the object.
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Wavelet-Texture Method: Appearance Compression by Daubechies Wavelet, Reflection Model, and Polarization
2007Co-Authors: Daisuke Miyazaki, Tadashi Shibata, Katsushi IkeuchiAbstract:In order to create a photorealistic Virtual Reality Model, we have to record the appearance of the object from different directions under different illuminations. In this paper, we propose a method that renders photorealistic images from a small amount of data. First, we separate the images of the object into a diffuse Reflection component and a specular Reflection component by using linear polarizers. Then, we estimate the parameters of the Reflection Model for each component. Finally, we compress the difference between the input images and the rendered images by using wavelet transform. At the rendering stage, we first calculate the diffuse and specular Reflection images from the Reflection parameters, then add the difference decompressed by inverse wavelet transform into the calculated Reflection images, and finally obtain the photorealistic image of the object.
Qian Liu - One of the best experts on this subject based on the ideXlab platform.
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intelligent reflecting surface enhanced wideband mimo ofdm communications from practical Model to Reflection optimization
arXiv: Signal Processing, 2020Co-Authors: Wenhao Cai, Yang Liu, Qian LiuAbstract:Intelligent reflecting surface (IRS) is envisioned as a revolutionary technology for future wireless communication systems since it can intelligently change radio environment and integrate it into wireless communication optimization. However, most recent investigation utilized an ideal IRS Reflection Model, which is impractical and can cause significant performance degradation in realistic wideband systems. In this work, we first study the amplitude-frequency-phase relationship of reflected signals and present a simplified practical IRS Reflection Model for wideband signals. Then, an IRS enhanced wideband multiuser multi-input single-output orthogonal frequency division multiplexing (MU-MISO-OFDM) system is investigated. We aim to jointly design the transmit beamformer and IRS Reflection to maximize the average sum-rate over all subcarriers. With the aid of the relationship between sum-rate maximization and mean square error (MSE) minimization, the original problem is equivalently transformed into a multi-block/variable problem, which can be solved by classic block coordinate descent (BCD) method. Complexity and convergence for both cases are analyzed or illustrated. Simulation results demonstrate that the proposed algorithm can offer significant average sum-rate enhancement compared to that achieved using the ideal Reflection Model, which confirms the importance of the use of the practical Model for the design of wideband systems.
Shoji Tominaga - One of the best experts on this subject based on the ideXlab platform.
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Invariant representation for spectral reflectance images and its application
EURASIP Journal on Image and Video Processing, 2011Co-Authors: Abdelhameed Ibrahim, Shoji Tominaga, Takahiko HoriuchiAbstract:Spectral images as well as color images observed from object surfaces are much influenced by various illumination conditions such as shading and specular highlight. Several invariant representations were proposed for these conditions using the standard dichromatic Reflection Model of dielectric materials. However, these representations are inadequate for other materials like metal. This article proposes an invariant representation that is derived from the standard dichromatic Reflection Model for dielectric and the extended dichromatic Reflection Model for metal. We show that a normalized surface-spectral reflectance by the minimum reflectance is invariant to highlights, shading, surface geometry, and illumination intensity. Here the illumination spectrum and the spectral sensitivity functions of the imaging system are measured in a separate way. As an application of the proposed invariant representation, a segmentation algorithm based on the proposed representation is presented for effectively segmenting spectral images of natural scenes and bare circuit boards.
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Estimation of a 3D spectral Reflection Model for color image rendering
9th Congress of the International Colour Association, 2002Co-Authors: Norihiro Tanaka, Shoji TominagaAbstract:This paper describes a method for estimating a Reflection Model from a color image of an object taken by a multi-band CCD camera. The Torrance-Sparrow Model is used for Modeling light Reflection on an object surface. We propose algorithms for estimating Model parameters from a single image by the multi-band CCD camera. To estimate the surface roughness, we propose the use of the brightness image and the reflectance map in the neighborhood of a highlight peak point. An algorithm is presented for finding a particular solution of the surface orientation. The feasibility of the method is demonstrated in an experiment using a painted object. The estimation accuracy of the whole Model is confirmed based on computer graphics images.
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Dichromatic Reflection Models for a variety of materials
Color Research & Application, 1994Co-Authors: Shoji TominagaAbstract:This article proposes dichromatic Reflection Models adequate for describing surface-spectral reflectances of a variety of materials. the standard dichromatic Reflection Model for inhomogeneous materials assumes that light reflected from an object's surface is decomposed into two additive components: the body Reflection and the interface Reflection, which is independent of wavelength. First, we present a method for testing the adequacy of this standard Model based on the observations of surface-spectral reflectances. the standard dichromatic Reflection Model is adequate for many materials. However, the test results point out that there are some cloths for which the standard Model is inadequate, and metals that have only the interface Reflection. Next, we extend the standard Model to have an interface Reflection component that depends on wavelength. an algorithm is presented for estimating two reflectance functions in the generalized Model. Moreover, a dichromatic Reflection Model specialized for only the specular Reflection is defined for approximating metal's Reflection. the Reflection characteristics are analyzed using a chromaticity diagram. It is concluded that surfacespectral reflectances of most materials are described by three types of the dichromatic Reflection Model. © 1994 John Wiley & Sons, Inc.
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Surface identification using the dichromatic Reflection Model
IEEE Transactions on Pattern Analysis and Machine Intelligence, 1991Co-Authors: Shoji TominagaAbstract:The author describes a method based on the dichromatic Reflection Model for identifying object surfaces. The surface spectral reflectance function of an inhomogeneous object is described as the sum of a constant interface (specular) reflectance and a body (diffuse) reflectance under all illumination geometries. The interface component is used to estimate the spectral power distribution of the illuminant without using a reference white standard, whereas the body component is used as the principal indication of the surface identity. The body reflectance function of each surface is recovered. A method to classify the observed reflectances is developed, and an algorithm to estimate a body reflectance function, unique to each surface, from the classified reflectances is proposed. The author shows the reliability of the surface classification method and the accuracy of estimated body reflectance function. >
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Parameter estimation of a Reflection Model from a multi-band image
Proceedings Workshop on Photometric Modeling for Computer Vision and Graphics (Cat. No.PR00271), 1Co-Authors: Shoji Tominaga, E. Takahashi, Norihiro TanakaAbstract:The present paper proposes a method for estimating various parameters of a Reflection Model from a single image of an object taken by a multi-band CCD camera. It is assumed that the object's surface is composed of an inhomogeneous dielectric material and has the shape of a cylinder. The Phong Model is used as the three-dimensional Reflection Model, and a six-color camera is used as the multi-band CCD camera. We show some features of the Reflection Model and the image histogram. The Model parameters to be estimated are such parameters as (1) surface-spectral reflectance, (2) illuminant spectral distribution, (3) illumination direction, (4) specular Reflection exponent, and (5) ratio of body to interface intensity. The Reflection parameters are estimated by analyzing the histogram on the color signal plane and making a relationship between the histogram features and the spatial points. The feasibility of the proposed method is demonstrated in an experiment using a plastic object. Computer graphics images are produced on the estimated Model.
Daisuke Miyazaki - One of the best experts on this subject based on the ideXlab platform.
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Wavelet-Texture Method: Appearance Compression by Polarization, Parametric Reflection Model, and Daubechies Wavelet
International Journal of Computer Vision, 2009Co-Authors: Daisuke Miyazaki, Takushi Shibata, Katsushi IkeuchiAbstract:In order to create a photorealistic Virtual Reality Model, we have to record the appearance of the object from different directions under different illuminations. In this paper, we propose a method that renders photorealistic images from a small amount of data. First, we separate the images of the object into a diffuse Reflection component and a specular Reflection component by using linear polarizers. Then, we estimate the parameters of the Reflection Model for each component. Finally, we compress the difference between the input images and the rendered images by using wavelet transform. At the rendering stage, we first calculate the diffuse and specular Reflection images from the Reflection parameters, then add the difference decompressed by inverse wavelet transform into the calculated Reflection images, and finally obtain the photorealistic image of the object.
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Wavelet-Texture Method: Appearance Compression by Daubechies Wavelet, Reflection Model, and Polarization
2007Co-Authors: Daisuke Miyazaki, Tadashi Shibata, Katsushi IkeuchiAbstract:In order to create a photorealistic Virtual Reality Model, we have to record the appearance of the object from different directions under different illuminations. In this paper, we propose a method that renders photorealistic images from a small amount of data. First, we separate the images of the object into a diffuse Reflection component and a specular Reflection component by using linear polarizers. Then, we estimate the parameters of the Reflection Model for each component. Finally, we compress the difference between the input images and the rendered images by using wavelet transform. At the rendering stage, we first calculate the diffuse and specular Reflection images from the Reflection parameters, then add the difference decompressed by inverse wavelet transform into the calculated Reflection images, and finally obtain the photorealistic image of the object.
Wenhao Cai - One of the best experts on this subject based on the ideXlab platform.
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intelligent reflecting surface enhanced wideband mimo ofdm communications from practical Model to Reflection optimization
arXiv: Signal Processing, 2020Co-Authors: Wenhao Cai, Yang Liu, Qian LiuAbstract:Intelligent reflecting surface (IRS) is envisioned as a revolutionary technology for future wireless communication systems since it can intelligently change radio environment and integrate it into wireless communication optimization. However, most recent investigation utilized an ideal IRS Reflection Model, which is impractical and can cause significant performance degradation in realistic wideband systems. In this work, we first study the amplitude-frequency-phase relationship of reflected signals and present a simplified practical IRS Reflection Model for wideband signals. Then, an IRS enhanced wideband multiuser multi-input single-output orthogonal frequency division multiplexing (MU-MISO-OFDM) system is investigated. We aim to jointly design the transmit beamformer and IRS Reflection to maximize the average sum-rate over all subcarriers. With the aid of the relationship between sum-rate maximization and mean square error (MSE) minimization, the original problem is equivalently transformed into a multi-block/variable problem, which can be solved by classic block coordinate descent (BCD) method. Complexity and convergence for both cases are analyzed or illustrated. Simulation results demonstrate that the proposed algorithm can offer significant average sum-rate enhancement compared to that achieved using the ideal Reflection Model, which confirms the importance of the use of the practical Model for the design of wideband systems.
