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18 June 1993 Highly sensitive register mark based on moire patterns
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Proceedings Volume 1912, Color Hard Copy and Graphic Arts II; (1993) https://doi.org/10.1117/12.146280
Event: IS&T/SPIE's Symposium on Electronic Imaging: Science and Technology, 1993, San Jose, CA, United States
Abstract
A highly sensitive register mark is formed by the moire pattern resulting from the overprinting of two screened patches. The two screened patches have slightly different screen frequencies so that when the two planes are in exact register a bright spot appears in the center of the register mark. When the two planes are misregistered, the bright spot is displaced by a gain factor times the misregister, where the gain factor is approximately equal to the size of the patch times the screen frequency (typically 10 to 20). The register mark indicates both the direction and degree of misregister. If the screen frequency were uniform throughout the patch, the mark could falsely indicate register when in fact the misregister was a multiple of exactly one dot. We warp the frequency of the screen pattern, with the center of the patch having a finer screen than the perimeter. A misregister of one dot or more does not produce a symmetrical bright spot in the center of the mark. Thus, the mark provides a positive indication of exact register. The range of sensitivity is nominally plus or minus half of a screen dot in both X and Y directions. It may, however, be extended by recognition of the frequency warped patterns resulting from larger misregistrations.
© (1993) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Raphael L. Levien "Highly sensitive register mark based on moire patterns", Proc. SPIE 1912, Color Hard Copy and Graphic Arts II, (18 June 1993); https://doi.org/10.1117/12.146280
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