Showing papers by "Nagaaki Ohyama published in 1997"

Natural color reproduction in the television system for telemedicime

Abstract: In the telemedicine application through visual communication systems, the reproduction of color is quite important. The purpose of this work is to develop a method for the reproduction of the natural color of the object in the TV system for telemedicine. When the illumination of observation environment is different form the object illumination, the change in color perception is caused by the color adaptation of human vision. In the method presented in this paper, the difference of illumination condition is corrected by using multispectral information captured by a multispectral camera. This paper shows the methods and the basic results for the reproduction of two types of color; the reproduction of color image as if the object is directly observed, and the reproduction of color appeared when the object is placed under the observation condition.

Optical implementation of the stream cipher based on the irreversible cellular automata algorithm

Abstract: A hybrid optical scheme for efficient hardware implementation of the one-dimensional, three-neighborhood binary cellular automata rule ai′=ai-1 XOR ai OR ai+1–based stream cipher is proposed. The system makes full use of the parallel, space-invariant, cascadable, and modular structure of the algorithm and is simple, robust, and compact. The number of cellular automata arrays can be as large as the number of pixels on the spatial light modulator, which results in an increase in speed (number of bits operated in parallel) and security (key length). The system can be made fully optical with the use of an optically addressable spatial light modulator for the input plane and for the nonlinear threshold element.

Color measurement of the mucous membrane using sequential endoscopic images

Abstract: In order to give medical doctors objective information of the internal surface of the organs, which will lead to an improvement of the quality of the endoscopic diagnosis, it is necessary to develop a method to quantitatively measure colors from the digital images of CCD endoscope. However, when the internal surface of the human digestive organs is illuminated by the light of the endoscope, images captured by the endoscope become reddish compared to the original object due to the reflections by the surrounding red mucosal surface. This phenomenon makes it difficult to measure the object color correctly. We propose a method to compensate the color shift of illumination and to estimate the color of the mucous internal surface from CCD endoscopic images. In this method, the spectral reflectance of the internal surface and the spectral distribution of the illumination are represented by a weighted sum of some functions given by the statistical analysis of the surface reflectances. Each weighting factor is estimated from sequential images captured by the CCD endoscope. The effectiveness of the proposed method is confirmed by a basic experiment using a CCD endoscope and color charts.

Correction method for shift-variant characteristics of the SPECT measurement system

Abstract: SPECT imaging system has shift-variant characteristics due to nonuniform attenuation of gamma-ray, collimator design, scattered photons, etc. In order to provide quantitatively accurate SPECT images, these shift-variant characteristics should be compensated in reconstruction. This paper presents a method to correct the shift-variant characteristics based on a continuous-discrete mapping model. In the proposed method, the projection data are modified using sensitivity functions so that filtered backprojection (FBP) method can be applied. Since the projection data are assumed to be acquired by narrow ray sum beams in the FBP method, narrow ray sum beams are approximated by a weighted sum of sensitivity functions of the measurement system, then the actual projection data are corrected by the weighting factors. Finally, FBP method is applied to the corrected projection data and a SPECT image is reconstructed. Since the proposed method requires the inversion of smaller matrices than the conventional algebraic methods, the amounts of calculation and memory space become smaller, and the stability of the calculation is greatly improved as well. The results of the numerical simulations are also demonstrated.

Optical Interpolation of Volume Data Using Pseudo Color and an Electro-Optical-Hybrid-System

Abstract: Volume data is interpolated using pseudo color and an electro-optical-hybrid-system. The method proposed in this paper is called optical interpolation. The visualization of a volumetric array of computed tomography data is achieved using the optical interpolation technique in combination with the optical model and the electro-optical-hybrid-system. To show the advantages of optical interpolation, the results are compared with those obtained by the traditional technique.