Showing papers by "Nagaaki Ohyama published in 2009"

Piecewise Wiener estimation for reconstruction of spectral reflectance image by multipoint spectral measurements

Abstract: This study proposes a piecewise Wiener estimation method to reconstruct a spectral reflectance image from a three-band image by multipoint spectral information collected simultaneously with image acquisition. A three-band image is divided into several blocks and the spectral estimation is carried out using the Wiener estimation matrix assigned to each block. Each Wiener estimation matrix is constructed on the basis of spectral measurement data. The experimental results show that the proposed method reduces the average estimation error monotonically as the number of spectral measurements increases. In addition, the computational time of the piecewise Wiener estimation costs only severalfold of the computational time of the conventional single-matrix method.

A subjective evaluation of high chroma color with wide color gamut display

Abstract: Displays tends to expand its color gamut, such as multi-primary color display, Adobe RGB and so on. Therefore displays got possible to display high chroma colors. However sometimes, we feel unnatural some for the image which only expanded chroma. Appropriate gamut mapping method to expand color gamut is not proposed very much. We are attempting preferred expanded color reproduction on wide color gamut display utilizing high chroma colors effectively. As a first step, we have conducted an experiment to investigate the psychological effect of color schemes including highly saturated colors. We used the six-primary-color projector that we have developed for the presentation of test colors. The six-primary-color projector's gamut volume in CIELAB space is about 1.8 times larger than the normal RGB projector. We conducted a subjective evaluation experiment using the SD (Semantic Differential) technique to find the quantitative psychological effect of high chroma colors.

Feasibility study of near-infrared fluorescence tomography using a positron emission tomograph equipped with depth-of-interaction PET detectors

Abstract: We are currently developing an imaging system that combines simultaneous positron emission tomography (PET) with near-infrared (NIR) optical tomography, thus supporting two different types of molecular imaging. For this system, we are considering whether to use depth of interaction (DOI) PET detectors as simultaneous detectors of gamma rays and NIR light by changing the original upper reflectors to dichroic mirrors. The DOI-PET detector has very low spatial resolution for NIR light compared to the charge-coupled device cameras that are normally used. However, it is possible to reconstruct images of comparable value from the data acquired by low-resolution devices because the light is scattered by biological tissues and high-resolution devices are not necessarily effective at improving image quality. In this study, we demonstrate the feasibility of 3D NIR fluorescence tomography imaging by employing DOI-PET detectors in computer simulations. In the simulations, we used a 40 mm × 40 mm × 40 mm cubic phantom, a square detector geometry, and an optical diffusion equation to approximate the light propagation. We then evaluated imaging systems for 3D fluorescence tomography with different detector resolutions and excitation light arrangements using singular-value analysis and imaging simulation. We confirmed that the reconstructed images from low-resolution detectors (8 × 8 pixels for an area of 40 mm × 40 mm) are the same as those from high-resolution detectors (16 × 16 pixels for the same area).