Yoshinobu Shiraiwa

Laser recording and image-quality evaluation

Various kinds of printers electrophotographic printers ink jet printers thermal printers etc. have been commercialized especially for DTP. The authors however have been unsatisfied with the image-quality of these printers. A laser recording apparatus was made for our study which is composed of a laser diode a polygonal mirror and a F-theta optical system. The recording apparatus selectively provides high density pixel (600 900 or 1 200 dpi). The gradation of each pixel is obtained by modulating the pulse width of the laser diode oscillation. We used the silver halide paper (PD-100WP Fuji Photo Film Co. Ltd. ) with the good spectrum sensitivity for the laser diode of 780 nm wavelength. The recorded image samples with three kinds of pixel densities and with gradation levels ranging from 16 to 166 were used for being evaluated by sixteen persons. As a result of analysis on the evaluated data we found out some relations between pixel densities and gradation levels for the satisfactory image-quality. 2.

Color appearance matching in hard-copy and soft-copy images in different office environments

This paper describes a method for matching the color appearances of hard copies and soft copies in ordinary office environments where lighting conditions usually vary. To develop this method, we studied ways of easily calculating the colorimetric values of hard copies under an arbitrary illuminant. In this report, we converted the colorimetric values of hard copies taken under a reference illuminant to the colorimetric values taken under a viewing illuminant by using a 3-by-3 matrix. The conversion matrix CR under an arbitrary illuminant is calculated by using the following equation: CR equals IH X CRh + (1-IH) X CRl. Here, CRh represents a conversion matrix for a high color-rendering illuminant, and CRl represents a conversion matrix for a low color-rendering illuminant. IH is the coefficient that represents the mixture ratio of high and low color-rendering illuminants. We calculated the colorimetric values of a hard copy under an arbitrary illuminant by using the above method, performed a color adaptation correction, and displayed the soft copy on a monitor. The color appearance of the soft copy matched that of the hard copy well under various illuminants.

High-quality image recorder and evaluation

As the desk-top publishing market has been rapidly expanding, high-quality image output technologies have been increasingly required; especially as to restoration for images with gradation like photographs. To meet this requirement, the authors developed a new high quality image recorder and tried some experiments of simulation image recording. In the high quality image recorder, the laser scanning optical system is used, including an anamorphic optical system. The laser spot diameter in the deflection plane is small as 30 micrometers in the image plane, and the scan length is large as 300 mm. A polygonal mirror is used as the beam deflector and the scanning optical system corrects the tilt error of the polygon facets. By using this image recorder, the authors obtained simulation image samples, which is based on the bi- level pixel of 1200 dpi density. The simulation image samples mean halftone images with some screen rulings. The simulation procedure and the result of the examination are reported.