Anti-Counterfeit Technology Based On Digital Screening

With the development of information technology, digital watermarking technology,which palys an important role in digital communication, ensures safe in image transmission.When the digital watermarking is applied into the printing, there are some problems. In thedigital screening process, a hafltone image is produced by digital screening algorithm from acontinuous digital image, which greatly affects and even destroys the hidden watermarkinformation. In the printing and storage section, paper and other print substrates may bedeformed and fuzzy. After printing and scanning process, the graphic geometry and tone ofimages on the substrates may be changed. Images lose much information by the secondaryscreening and different sampling frequency.Firstly, common digital screening methods were introduced in this paper, including theAM screening, FM screening and hybird screening, and the screening effects of the threemethods were simulated. Then, the commonly halftone security ways for printing imageswere classified. There were scanned extracting halftone watermarking, overlaid extractinghalftone watermarking, microstructure sceening anti-counterfeiting and hybird screeninganti-counterfeiting. The multi-resolution halftone watermarking and the noise balance errordiffusion were improved, and showed good security effect.From the perspective of digital printing, this study focused on researching theanti-counterfeit print technology of halftone images and directly detecting techniques whichwere not influenced by secondary screening adverse effects. In this paper, the anti-counterfeittechnology combined the grating film to achieve the halftone image security. Cylindrical lenshad converged effect on light in the corresponding direction, which made it compress andisolate images. According to this feature of grating, three halftone anti-counterfeitingtechnologies were proposed, including dot moving technology, variable frequency technologyand variable angle technology. The principles of these anti-counterfeiting technologies weredescribed in detail, and then the security effect was simulated. The experimental resultsshowed that these three anti-counterfeiting technologies had nice security effect, and could beused in practical application.Finally, the current halftone watermarking technologies were summarized, and someideas were proposed to the development of halftone anti-counterfeiting technology.