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18 January 2010 Halftone moiré due to imager distortion
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Proceedings Volume 7528, Color Imaging XV: Displaying, Processing, Hardcopy, and Applications; 752811 (2010)
Event: IS&T/SPIE Electronic Imaging, 2010, San Jose, California, United States
Individual halftone color separations must possess a low degree of distortion to avoid undesirable moiré in the overlays that produce the process colors. Achieving low relative distortion requires precise registration between the exposure devices used to write the halftone separations. However, optical and mechanical errors within the multiple Raster Output Scanners (ROS's) or image bars of a printer result in differences in the trajectory and placement of the exposure spots among color planes. In this paper, color halftone moiré due to ROS errors is analyzed using a frequency vector representation of color halftones. We analyze three forms of process-direction distortion: skew, shear, and bow. Each distortion is inspired from a practical printing system (i.e. while shear and bow are observed in ROS systems, skew is observed in image bar imaging systems). The frequency vector formalism is used to derive bounds on distortion for a classical halftone screen configuration (square cell equal frequency halftones at 15°, 45°, and 75°). The bounds are examined for distortion of one halftone screen and the analysis can be readily applied to distortion of multiple screens. The bounds can be used to develop specifications for imaging components in the design of a ROS or image bar imaging system.
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Orhan Bulan, Robert Loce, and Beilei Xu "Halftone moiré due to imager distortion", Proc. SPIE 7528, Color Imaging XV: Displaying, Processing, Hardcopy, and Applications, 752811 (18 January 2010);

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