Dr. Shiying Li Profile

Dr. Shiying Li

at Tohoku Univ

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Publications (3)

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Proceedings Article | 28 January 2008 Paper

An improved method to estimate reflectance parameters for high dynamic range imaging

Shiying Li, Koichiro Deguchi, Renfa Li, Yoshitsugu Manabe, Kunihiro Chihara

Proceedings Volume 6807, 680706 (2008) https://doi.org/10.1117/12.766524

KEYWORDS: Reflection, Reflectivity, Specular reflections, Diffuse reflectance spectroscopy, Surface roughness, Image segmentation, RGB color model, High dynamic range imaging, Data modeling, Cameras

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Two methods are described to accurately estimate diffuse and specular reflectance parameters for colors, gloss intensity and surface roughness, over the dynamic range of the camera used to capture input images. Neither method needs to segment color areas on an image, or to reconstruct a high dynamic range (HDR) image. The second method improves on the first, bypassing the requirement for specific separation of diffuse and specular reflection components. For the latter method, diffuse and specular reflectance parameters are estimated separately, using the least squares method. Reflection values are initially assumed to be diffuse-only reflection components, and are subjected to the least squares method to estimate diffuse reflectance parameters. Specular reflection components, obtained by subtracting the computed diffuse reflection components from reflection values, are then subjected to a logarithmically transformed equation of the Torrance-Sparrow reflection model, and specular reflectance parameters for gloss intensity and surface roughness are finally estimated using the least squares method. Experiments were carried out using both methods, with simulation data at different saturation levels, generated according to the Lambert and Torrance-Sparrow reflection models, and the second method, with spectral images captured by an imaging spectrograph and a moving light source. Our results show that the second method can estimate the diffuse and specular reflectance parameters for colors, gloss intensity and surface roughness more accurately and faster than the first one, so that colors and gloss can be reproduced more efficiently for HDR imaging.

Proceedings Article | 17 January 2006 Paper

Estimating reflectance parameters from saturated spectral images

Shi Ying Li, Yoshitsugu Manabe, Kunihiro Chihara

Proceedings Volume 6062, 606208 (2006) https://doi.org/10.1117/12.642331

KEYWORDS: Reflectivity, Reflection, Refractive index, Specular reflections, Data modeling, Visual process modeling, Dielectrics, Cameras, Error analysis, Diffuse reflectance spectroscopy

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Since commercial image detectors, such as charge-coupled device (CCD) cameras, have a limited dynamic range, it is difficult to obtain images that really are unsaturated, as a result of which the reflectance parameters may be inaccurately estimated. To solve this problem, we describe a method to estimate reflectance parameters from saturated spectral images. We separate reflection data into diffuse and specular components at 5-nm intervals between 380nm and 780nm for each pixel of the spectral images, which are captured at different incident angles, and estimate the diffuse reflectance parameters by applying the Lambertian model to the diffuse components. To estimate the specular reflectance parameters from the specular components, we transform the Torrance-Sparrow equation to a linear form, assuming Fresnel reflectance is constant. We then estimate specular parameters for intensity of the specular reflection and standard deviation of the Gaussian distribution, using the least squares method from unsaturated values of the specular components. Since Fresnel reflectance contributes to the physically based Torrance-Sparrow model in computer graphics and vision, we estimate both the Fresnel reflectance in terms of the Fresnel equation for the incident angle and the refractive index of the surface for dielectric materials, which varies with wavelength. We carried out experiments with measured data, and with simulated specular components at different saturation levels, generated according to the Torrance-Sparrow model. Our experimental results reveal that the diffuse and specular reflectance parameters are estimated with high quality.

Proceedings Article | 17 January 2005 Paper

Color and gloss reproduction from multispectral images

Shi-Ying Li, Yoshitsugu Manabe, Kunihiro Chihara

Proceedings Volume 5667, (2005) https://doi.org/10.1117/12.586951

KEYWORDS: Reflection, Specular reflections, Multispectral imaging, Light sources, CCD cameras, RGB color model, Spectrographs, Data modeling, Dielectrics, Reflectivity

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We propose a new technique to reproduce faithfully both the color and the gloss of an object on a computer, using multispectral images. An imaging spectrograph equipped with a monochrome charge-coupled device (CCD) camera is fixed in front of the target object. Multispectral images of a linear portion of the object's surface are captured at suitable intervals by a measuring system which comprises a light source orbiting the target object. To obtain spectral images for the whole surface, the target object is also rotated. The reflection is separated into diffuse and specular components, according to the dichromatic reflection model, and the diffuse parameters are estimated at 5-nm intervals between 380nm and 780nm for each pixel. Since the CCD camera used to capture images has a limited dynamic range, we suppose that the specular reflection is independent of wavelength for the dielectrics, and that the specular reflections are saturated, although some of them can be non-saturated. We adopt the Torrance-Sparrow reflectance model for the specular reflection, and estimate the specular parameters using the least squares method for each pixel. Our experimental results reveal that the diffuse parameters for the color and the specular parameters for the gloss of the target object are satisfactorily estimated.

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