Periodic screen design

For electrophotographic printers, periodic clustered screens are preferable due to their homogeneous halftone texture, robustness to dot gain, and increased dot stability. In traditional periodic clustered-dot color halftoning, to avoid the complete dot-on-dot printing, each color plane is independently rendered with a different screen at a different angle. However, depending on the screen angle and frequency, the final halftone may have strong visible moire due to the interaction of the periodic structure. Additionally, the slight displacement between each color plane may cause significant color shifts in the final halftone. This thesis addresses issues on finding optimal color screen sets which produce the minimal visible moire and are also robust to registration errors. To achieve these goals, this thesis proposes new techniques including common periodicity, halftone microtexture spectrum, and registration sensitivity analysis. The common periodicity of two different periodic screens characterizes the structural patterns of the mixed colors. In particular, large common periodic patterns are found to inherently produce dot-on-dot patterns with good robustness against registration errors. The halftone microtexture spectrum method is shown to predict the visible moire more accurately than the conventional moire-free conditions. In our registration sensitivity analysis, three propositions are established using the periodicity of periodic screens. From the established propositions, we derive the conditions for registration insensitivity. Our results demonstrate significant improvements of clustered-dot screens in terms of the resilience against registration errors and minimizing the visible moire over the conventional periodic screens