Color Halftoning Based on Neugebauer Primary Area Coverage and Novel Color Halftoning Algorithm for INK Savings

Wanling Jiang, Purdue University

Abstract

This dissertation primarily studies the problem related to image quality and ink savings in printing devices. It consists of three parts: color halftoning based on Neugebauer Primary area coverage, PARAWACS screen design and optimization and a novel color halftoning algorithm for ink savings. We will first illustrate a halftoning method with Neugebauer Primary Area Coverage (NPAC) direct binary search (DBS). To represent a continuous-tone color image in limited amount of ink, we need the assistance of the human visual system (HVS) model, by comparing the filtered original and halftoned images, we are able to obtain a homogeneous and smooth halftone colored image. The halftoning is based on separating the colored image represented in Neugebauer Primary space in three channels based on human visual system. The optimization is obtained by swapping the halftoned image pixels and bringing the error metric to its minimum (swap only DBS). The separation of chrominance HVS filters between red-green and blue-yellow channels allows us to represent the HVS more accurately. Color halftone images generated using this method and the method of using traditional screening methods are compared, and our method significantly reduces moire effect. Then, we discuss how to achieve faster halftoning speed using PARAWACS screen. PARAWACS screen in this document refer to a screen designed using DBS to generate halftone images mimicking the effect of DBS monochrome as well as colored halftone, this screen is created level by level.With PARAWACS screen, we can create halftone using simple pixel by pixel comparison to create halftone with the merit of DBS, an iterative method to create homogeneous, visually pleasing halftone. Although PARAWACS screen is a monochrome screen, we can use it to create color halftone with good results. Next, we will discuss a novel halftoning method that we call Ink-Saving, SingleFrequency, Single-Angle, Multi-Drop (IS-SF-SA-MD) halftoning. The application target for our algorithm is high-volume production ink-jet printing in which the user will value a reduction in ink usage. Unlike commercial offset printing in which fourcolorant printing is achieved by rotating a single screen to four different angles, our method uses a single frequency screen at a single angle, and depends on accurate registration between colorant planes to minimize dot-overlap especially between the black (K) colorant and the other colorants (C, M, and Y). To increase the number of graylevels for each colorant, we exploit the multidrop capabilities of the target writing system. We also use the hybrid screening method to yield improved halftone texture in the highlights and shadows.

Degree

Ph.D.

Advisors

Allebach, Purdue University.

Subject Area

Design

COinS