Shinji Sasahara

Disc Covering Problem with Application to Digital Halftoning

One of the popular geometric optimization problems is that of finding the maximum radius r n of n equal and non-overlapping discs to be packed in a unit square. It has been widely explored with a number of surprising results (see e.g. [2]).

A Generalization of Magic Squares with Applications to Digital Halftoning

Abstract A semimagic square of order n is an n×n matrix containing the integers 0,…,n2−1 arranged in such a way that each row and column add up to the same value. We generalize this notion to that of a zero k×k-discrepancy matrix by replacing the requirement that the sum of each row and each column be the same by that of requiring that the sum of the entries in each k×k square contiguous submatrix be the same. We show that such matrices exist if k and n are both even, and do not if k and n are relatively prime. Further, the existence is also guaranteed whenever n=km, for some integers k,m≥2. We present a space-efficient algorithm for constructing such a matrix. Another class that we call constant-gap matrices arises in this construction. We give a characterization of such matrices. An application to digital halftoning is also mentioned.

Color image quality prediction models for color hard copy

Color image quality prediction models for two typical documents used as input for color copying machines have been developed to relate subjective image quality ratings to physical image quality metrics using stepwise multiple regression analysis. The typical documents consist of colored map and portrait images. The models were consistent with technical knowledge and achieved high correlation between predicted ratings and measured subjective image quality ratings. By utilizing the models, subjective color image quality can be measured by instrumental measurements, and also color imaging system of preferred image quality can be designed by physical image quality metrics, and this leads to effective image quality design.

A generalization of magic squares with applications to digital halftoning

A semimagic square of order n is an n × n matrix containing the integers 0, ..., n2–1 arranged in such a way that each row and column add up to the same value We generalize this notion to that of a zero k×k-discrepancy matrix by replacing the requirement that the sum of each row and each column be the same by that of requiring that the sum of the entries in each k × k square contiguous submatrix be the same We show that such matrices exist if k and n are both even, and do not if k and n are are relatively prime Further, the existence is also guaranteed whenever n = km, for some integers k,m ≥ 2 We present a space-efficient algorithm for constructing such a matrix. Another class that we call constant-gap matrices arises in this construction We give a characterization of such matrices. An application to digital halftoning is also mentioned.

New dispersed-dot halftoning technique by elimination of unstable pixels for electrophotography

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.