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Method for Generating Threshold Arrays for Clustered-Dot Halftone Screening

IP.com Disclosure Number: IPCOM000010883D
Publication Date: 2003-Jan-29

Publishing Venue

The IP.com Prior Art Database

Abstract

This report describes a method for generating threshold arrays for clustered-dot halftone screening. Clustered-dot ordered dithering is the conventional method of halftoning that has been widely used throughout the printing industry in one form or another since the mid 19th century [1]. Despite the introduction of more exotic forms of halftoning made possible by electronic and computing advances, it remains the most durable and flexible option available for the industry, particularly where high-volume output is a priority. Recent years have seen stiff competition everywhere, and the ever-increasing demand for quality and productivity together with the ubiquitous availability of computing power, has taken clustered-dot halftoning well into the realms of mathematics and computing. In this report, it will be shown how this form of halftoning involving the use of a threshold array, now part of a standard paradigm, can be controlled, measured and optimised before being used with ink and paper. The method of constructing a threshold array in two or three principal stages is presented here. First the basic array is written using a spot function, then a second, optional stage performs histogram equalisation and organises the array data spatially to ensure minimal processing in the third stage. Finally, the third stage is a multi-pass process that successively reorganises the numerical order of the spots for optimal spatial frequency properties.