Alex Veis

Multilevel halftone screen design: Keeping texture or keeping smoothness?

Multilevel halftoning algorithms are becoming increasingly important as the capabilities of image output devices improve. The traditional approach to multilevel halftoning is hampered by the appearance of contouring in the vicinity of native tones of the output device. To overcome this limitation, we propose a novel framework based on maintaining a consistent periodic, clustered-dot halftone texture across the tone scale. We develop metrics for granularity and structure dissimilarity, and show how these can be used to guide the manner in which the halftone texture evolves from native tone to native tone, across the tone scale. Experimental results confirm the benefits of our new approach.

Binary text image file preprocessing to account for printer dot gain

Dot gain is a classic problem in digital printing that causes printed halftones and text to appear darker than desired. For printing of text, we propose a method to preprocess the image sent to the printer in order to compensate for dot gain. It is based on an accurate model that predicts the printed absorptance for given local neighborhood in the digital image, a cost function to penalize lack of fidelity to the desired target text image, and the use of direct binary search (DBS) to minimize the cost.

Irregular clustered-dot periodic halftone screen design

With digital printing systems, the achievable screen angles and frequencies are limited by the finite address- ability of the marking engine. In order for such screens to generate dot clusters in which each cluster is identical, the elements of the periodicity matrix must be integer-valued, when expressed in units of printer-addressable pixels. To achieve a better approximation to the screen sets used for commercial offset printing, irregular screens can be used. With an irregular screen, the elements of the periodicity matrix are rational numbers. In this paper, we describe a procedure for design of high-quality irregular screens. We start with the design of the midtone halftone pattern. We then propose an algorithm to determine how to add dots from midtone to shadow and how to remove dots from mid-tone to highlight. We present experimental results illustrating the quality of the halftones resulting from our design procedure by comparing images halftoned with irregular screens using our approach and a template-based approach. Publisher’s Note: The first printing of this volume was completed prior to the SPIE Digital Library publication and this paper has since been replaced with a corrected/revised version.