A new method for evaluating the perceptual resolution of the actual image has been developed. The characteristic of this
new evaluation method is that the square sum of the cross correlation coefficients becomes the index of the evaluation.
Because the RIT Contrast-Resolution Test Target was a very systematic analysis pattern that contains spatial resolution
and contrast, it was used for this study. The cross correlation coefficient is calculated between the reference image and
the printed image read by a scanner. To provide the precision of the new evaluation method, subjective evaluation was
performed with the actual image. As a result of having confirmed correlation of the evaluation value from subjective
evaluation and the new evaluation method, the correlation was much higher than other evaluation method using a similar
analysis pattern. Furthermore, the sharpness evaluation of the actual image was enabled by applying the evaluation value
of this new method to evaluate the perceptual resolution, that correlation with the subjectivity was high.
Printing processes of electrophotography basically involve some unstableness of analog nature. The unstableness causes stochastic reproduction of small dots and degrades image quality. To overcome the analog unstableness, this paper presents a new dispersed-dot halftoning technique for high resolution electrophotography. We combine a Gaussian filter with a sigmoid nonlinear function to compute the probability of toner transfer in print using the characteristic of electrophotography. We can predict an image to be printed out using this nonlinear printer model. Using this model we can produce halftoned images of good image quality with small perceptive error against an original gray scale image. To achieve this, we rely on iterative improvement to remove as many unstable pixels as possible whose transfer probabilities lie within a band in our nonlinear printer model. Experimental results show great improvement of the perceptive error compared to the conventional cluster-dot halftoning.
All printing processes basically involve some instabilities of analog nature. To overcome such instabilities, in this paper, we have developed a unique halftoning technique for stable printing. Based on the charateristics of xerography, a combination of Gaussian filter with a sigmoid nonlinear function was used to calculate the probability of toner transfer in print. We can obtain a simulated i mage in print for xerography using this nonlinear printer model. Halftone images are formed to have a good image quality under this model in a way so that the perceptive error with respect to an original gray scale image is small. To achieve this, ambiguous pixels that have their transfer probabilities within a band in our nonlinear printer model as eliminated as much as possible by an iterative improvement method. As a result, we can obtain an ideal halftone screen without anisotropy for xergraphic printer.