Research On The Grating Anti-Counterfeit Technology Based On The Phase Modulation Method

Combined with the digital screen technology and human visual system, grating anti-counterfeit technology consists of embedding and extraction these two parts: During the embedding process, the host images are chosen from the pre-printing halftone image and the master plate is chosen from the four layers on them, then the hidden information will be designed and embedded into the master plate; During the extraction process, the grating with corresponding period will be designed to extract the hidden information. The anti-counterfeit technology based on the phase modulation has the advantages of the high detection accuracy and clarity. Moreover, the key of this technology lies in the embed of the anti-fake information, which each parameter setting directly influences the final anti-counterfeiting effect.This paper studied the grating anti-counterfeiting technology which based on phase modulation, analyzed the factors that affect the anti-counterfeit effect, and put forward the improved method. This paper mainly includes the following parts:The choice of anti-fake master plate is put forward by analyzing its effect on anti-counterfeiting. The anti-fake master plate is chosen from the C,M,Y and K layer on the halftone host images. Then the corresponding grating will be covered on rotated the host image to finish the extraction. The results showed that K layer has the worst concealment of the latent image which is not suitable for master plate while the M and C layers proves the best concealment and intelligibility.The concept of the hidden information capacity is put forward by analyzing its effect on anti-counterfeit. Based on the Weber's Law and image significance, the relationship model between the visual perception and hidden information capacity is established to study the its influence on the embedding and extracting performance. During the whole process, four host images with different brightness and structure are chosen to imbedded with different information capacity, then analyzing the relationship between the hidden information capacity and the embedding and extraction performance. The results show that the greater the capacity of information hiding, the worse the concealment, the better the performance of the extraction. Moreover, after many experiments, the texture complex image is more suitable as the carrier of the hidden information.An improved method based on phase modulation screening is proposed for increasing concealment performance of the grating anti-counterfeit technology. The operation is performed in three steps. First, we analyze the factors that how the variation of the dots during embedding process effect the concealment performance, combining with the Weber law. Second, the dots on the upper and lower boundary of the anti-counterfeit image area will be displaced and supplemented respectively. Finally, the dot percentage of the dots disposed in last step will be changed through rigorous theoretical derivation. The experimental results show that the improved method can significantly increase the concealment performance of embedding, and also guarantee the conspicuousness performance of detection.