Gravitational Re-allocation of Halftone Dots for Moire-Free Color Proofing

Abstract

The Remote color printing, where printing plate images are sent to remote printing factories by digital communication and printed there, necessitates the remote color proofing. High quality color proofs should be output at the printing sites. However, moire phenomenon occurs, when the printing plate image is output using a proof printer whose printing resolution is different from its original printing resolution and resized halftone images are printed. This work analyzes the moire phenomenon, and shows that the resizing does not cause the moire phenomenon if the image has gray levels, but binarization causes halftone dot size shift and the dot size shift leads to the moiré phenomenon. Based on this understanding, a new algorithm (the gravitational re-allocation algorithm) to re-allocate halftone dots is proposed. In the algorithm, fractions of halftone dots are pulled against each other to form concentrated halftone dots, and no halftone dot parameters detection or image region classification are necessary. © 2005, The Institute of Image Electronics Engineers of Japan. All rights reserved.