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IS&T BOARD OF DIRECTORS President Eric G. Hanson Department Manager Hewlett Packard Company Immediate Past President James R. Milch Jim Director Research & Innovation Labs. Carestream Health, Inc. Executive Vice President Rita Hofmann Chemist, R&D Manager Ilford Imaging Switzerland GmbH Conference Vice President Robert R. Buckley Rob Research Fellow Xerox Corporation Publication Vice President Franziska Frey Assist. Prof., School of Print Media Rochester Institute of Technology Secretary Ramon Borrell R & D Director Xaar Plc Treasurer Peter D. Burns Principal Scientist Carestream Health, Inc. Vice Presidents Choon-Woo Kim Inha University Laura Kitzmann Marketing Dev. & Comm. Manager Sensient Imaging Technologies, Inc. Michael A. Kriss MAK Consultants continued from previous page Special Section: Digital Fabrication, including papers presented at IS&T DigiFab2006 452 Hybrid Stacked RFID Antenna Coil Fabricated by Ink Jet Printing of Catalyst with Self-assembled Polyelectrolytes and Electroless Plating Chung-Wei Wang, Ming-Huan Yang, Yuh-Zheng Lee, and Kevin Cheng 456 Top Contact Organic Thin Film Transistors with Ink Jet Printed Metal Electrodes Kuo-Tong Lin, Chia-Hsun Chen, Ming-Huan Yang, Yuh-Zheng Lee, and Kevin Cheng 461 Ring Edge in Film Morphology: Benefit or Obstacle for Ink Jet Fabrication of Organic Thin Film Transistors Jhih-Ping Lu, Ying-pin Chen, Yuh-Zheng Lee, Kevin Cheng, and Fang-Chung Chen 465 Digital Fabrication Using High-resolution Liquid Toner Electrophotography Atsuko Iida, Koichi Ishii, Yasushi Shinjo, Hitoshi Yagi, and Masahiro Hosoya IS&T Conference Calendar For details and a complete listing of conferences, visit www.imaging.org IS&T/SID’s Fifteenth Color Imaging Conference cosponsored by SID November 5–November 9, 2007 Albuquerque, New Mexico General chairs: Jan Morovic and Charles Poynton Electronic Imaging IS&T/SPIE 20th Annual Symposium January 27–January 31, 2008 San Jose, California General chair: Nitin Sampat CGIV 2008: The Fourth European Conference on Color in Graphics, Image and Vision June 9–June 13, 2008 Terrassa, Spain General chair: Jaume Pujol Archiving 2008 June 24–June 27, 2008 Bern, Switzerland General chair: Rudolf Gschwind Ross N. Mills CTO & Chairman Imaging Technology International Jin Mizuguchi Professor, Yokohama National Univ. David Weiss Scientist Fellow, Eastman Kodak Company Chapter Director Franziska Frey – Rochester Patrick Herzog – Europe Takashi Kitamura – Japan Executive Director Suzanne E. Grinnan IS&T Executive Director ii J. Imaging Sci. Technol. 515/Sep.-Oct. 2007
Journal of Imaging Science and Technology® 51(5): 391–401, 2007. © Society for Imaging Science and Technology 2007 Digital Color Image Halftone: Hybrid Error Diffusion Using the Mask Perturbation and Quality Verification JunHak Lee, Takahiko Horiuchi, Ryoichi Saito and Hiroaki Kotera Graduate School of Science and Technology, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-Shi, Chiba, 263-8522, Japan E-mail: leejunhak@graduate.chiba-u.jp Abstract. Error diffusion is widely used in digital image halftones. The algorithm is very simple to implement and very fast to calculate. However, it is known that standard error diffusion algorithms, such as the Floyd Steinberg error diffusion, produce undesirable artifacts in the form of structure artifacts, such as worms, checkerboard patterns, diagonal stripes, and other repetitive structures. The boundaries between structural artifacts break the visual continuity in regions of low intensity gradients and therefore may be responsible for false contours. In this paper, we propose a new halftone method to reduce the structural artifacts and to improve the gray expression, called hybrid error diffusion, by using the concept of “error diffusion by perturbing the error coefficient with a mask.” The proposed algorithm consists of two steps in each pixel position. In the first step, a perturbation is calculated using the internal pseudorandom number and a selected 44 mask, similar to a dither mask. In the second step, error diffusion weights are calculated with the criterion for each pixel value. The proposed hybrid method can reduce the structural artifacts while keeping the advantage of the error diffusion. This paper discusses the performance of the proposed algorithm with experimental results for natural test images. Then, objective assessment results are given using statistical tools and the structural similarity measure for color images. © 2007 Society for Imaging Science and Technology. DOI: 10.2352/J.ImagingSci.Technol.200751:5391 INTRODUCTION Halftoning is a method of producing the pseudocontinuous tone images using only a finite number of gray levels. Because of the inherent characteristic of the human visual system with regard to observing average gray level over an area, the human observer perceives intermediate tones. Generally, halftoning is considered as a simple “on” and “off” modulation technique, where the sensation of intermediate tones is created by the presence and absence of a pixel. The digital halftone technology plays an important role in transforming a continuous tone (gray or color) image to an image with a reduced number of gray levels for display devices. For halftone technologies, each pixel value is determined to be white or black when compared to the threshold value, and the quantization error is then fed back and added to adjacent pixels. 1,2 The conventional error diffusion algorithm has the advantages of simple implementation and fast calculation speed. It uses the concept of overflow and diffusion of the quantized error, and then resets the diffusion. Received Oct. 28, 2006; accepted for publication Jun. 5, 2007. 1062-3701/2007/515/391/11/$20.00. However, the conventional error diffusion algorithm introduces distortion, reducing the visibility, worms, and false textures or additive noise. In order to solve these problems, many digital halftone algorithms have been proposed. Examples include using variable thresholds, 3 and variable filter weights 4–6 with input data. There were also approaches that considered the color channel correlation 6–8 for improving the color halftone visibility in color images. However, these methods require a complex process and long calculation time or many lookup tables. In this paper, we propose a well-organized halftone algorithm, hybrid error diffusion (HED) to improve the conventional halftone artifacts and enhance the visibility of color. The proposed algorithm is very simple, easy to implement, and can reduce the structural artifacts, keeping with the advantage of the error diffusion algorithms. We use the concept of a perturbing error filter weight by using the mask value, which is perturbed with a pseudorandom number. The proposed algorithm is basically the same as using the four-tap style error filter similar to that of the Floyd– Steinberg error diffusion. The basic procedure of the proposed algorithm is as follows: 1. Determine the mask value for each color plane and added to pseudorandom number. 2. Calculate the error filter weights for each color plane. The mask that is used is similar to the ordered dither mask. The mask value is selected by pixel, line, and each color plane. We also use the different error filter weights for each color plane to enhance the color visibility. The error filter weights were calculated by using a different mask for each color plane. The results of the proposed algorithm show good performance for reducing artifacts, worms, and false textures. The paper is organized as follows. In the next section, we review the conventional error diffusion algorithm and investigate its general problem. In the Hybrid Error Diffusion Algorithm section, we explain the proposed HED algorithm in detail. In Experimental Results, we introduce the conventional halftone evaluation tools, pair correlation, and radially averaged power spectrum density. As another method of halftone evaluation, a structural similarity mea- 391
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