Tetsuya Itoh

Evaluation of spectral color reproduction by vector error diffusion method

The vector error diffusion method was applied to spectral color reproduction of hardcopy. Reflection spectra of the object and primary colors used in the printer were estimated by low dimensional linear model. The accuracy of spectral color reproduction was evaluated and analyzed by computer simulation. It was shown that the spectral color reproduction can be improved by the proposed method.

Evaluation of digital halftones image by vector error diffusion

The vector error diffusion (VED) method is applied to proudce the digital halftone images by an electrophotographic printer with 600 dpi. Objective image quality of those obtained images is evaluated and analyzed. As a result, in the color reproduction of halftone image by the VED method, it was clear that there are large color difference between target color and printed color typically in the mid-tone colors. We consider it is due to the printer properties including dot-gain. It was also clear that the color noise of the VED method is larger compared with that of the conventional scalar error diffusion method in some patches. It was remarkable that ununiform patterns are generated by the VED method.

Effect of gloss on perceived lightness

In this paper, we propose a calculation model that gives a unique metric-lightness for object-colors, which is independent of different kinds of colorimeters and also matches the actually perceived lightness. Each colorimetric result with different types of measuring geometry, for example, 0/45, d/8(SCI), and d/8(SCE), can be considerably different from others, because of the influence f the component reflected normally from the sample surface. In order to investigate the difference between the actual sensation and each output of measuring geometry, we have made a subjective experiment for many achromatic samples that are composed of various levels of reflectance and those of gloss. As a result, the measured results with d/8(SCE) are shown to be closest to human perception. However, by relating the correlation of gloss to the metric-lightness for any measuring geometry, these differences for the same sample can be decreased.

Color noise of various printer outputs

A new graininess metrics, differing from the traditional ones in taking into consideration the effects of lightness, chroma and hue angle, and applicable to digital prints, is posed. Print samples from electrophotography, offset print, ink jet, thermal dye transfer, thermofusible ink transfer, and silver halide are evaluated with this new metrics, and the results are compared. The graininess index calculated from this metrics is used to classify the graininess rating based on subjective observations.