Showing papers by "Nagaaki Ohyama published in 2001"

Color image reproduction based on multispectral and multiprimary imaging: experimental evaluation

Abstract: Multispectral imaging is significant technology for the acquisition and display of accurate color information. Natural color reproduction under arbitrary illumination becomes possible using spectral information of both image and illumination light. In addition, multiprimary color display, i.e., using more than three primary colors, has been also developed for the reproduction of expanded color gamut, and for discounting observer metamerism. In this paper, we present the concept for the multispectral data interchange for natural color reproduction, and the experimental results using 16-band multispectral camera and 6-primary color display. In the experiment, the accuracy of color reproduction is evaluated in CIE (Delta) Ea*b* for both image capture and display systems. The average and maximum (Delta) Ea*b* = 1.0 and 2.1 in 16-band mutispectral camera system, using Macbeth 24 color patches. In the six-primary color projection display, average and maximum (Delta) Ea*b* = 1.3 and 2.7 with 30 test colors inside the display gamut. Moreover, the color reproduction results with different spectral distributions but same CIE tristimulus value are visually compared, and it is confirmed that the 6-primary display gives improved agreement between the original and reproduced colors.

Multispectral image retrieval using vector quantization

Abstract: A novel method for multispectral image retrieval is presented. This method uses a representation of image features based on vector quantization. Feature representation is important for image retrieval, but there are difficulties in applying conventional histogram-based representations to multispectral images. We developed an efficient feature representation and a novel method for the retrieval of images by quantizing each image adaptively.

High-Fidelity Image Reproduction Using Angular Distribution of Reflected Spectral Intensity

Abstract: A method to reproduce images of an object under various observation conditions is presented In this method, a series of multispectral images is captured by rotating the object under a point light source of which spectral power distribution and the position are known The captured images are decomposed into diffuse and specular reflection component images based on the dichromatic reflection and the Lambertian models Next, the incident angle of the illumination light and the angle between viewing direction and regular reflection are calculated based on observation geometry Finally, the image under observation geometry is synthesized using the light-ray rearrangement technique The experiments are carried out using two-dimensional objects, leather and fabric Most of the synthesized images are shown to be the same as the images actually captured under the assumed illumination geometry, even if the object has complex reflection like fabric for which it is difficult to apply the reflection model used in computer graphics

Depth-of-Interaction情報を用いた代数的な2次元PET画像再構成

Abstract: Recently a high-performance PET scanner, which measures depth-of-interaction (DOI) information, is being developed for molecular imaging. DOI measurement of multi-layered thin crystals can improve spatial resolution and scanner sensitivity simultaneously. In this paper, we apply an algebraic image reconstruction method to 2-dimensional (2D) DOI-PET scanners using accurate system modeling, in order to evaluate the effects of using DOI information on PET image quality. Algebraic image reconstruction methods have been successfully used to improve PET image quality, compared with the conventional filtered backprojection method. The proposed method is applied to simulated data for a small 2D DOI-PET scanner. The results show that accurate system modeling improves spatial resolution without noise emphasis, and that DOI information improves uniformity of spatial resolution.