Anti-counterfeiting company introduces the anti-counterfeiting technology of halftone images_Anti-counterfeiting company-Shanghai Nuobiao Anti-counterfeiting Technology Development Co., Ltd.
Digital watermarking technology plays an extremely important role in the copyright protection of digital information, communication security and other fields. Academic institutions and enterprises that study information hiding have carried out very in-depth research on this technology. However, in the field of digital printing, these computer talents have not done enough research on realizing the watermarking technology of printed images. Since the advent of the printing press, halftone images have always been an important way of information dissemination, and are widely used in advertising, newspapers, magazines, packaging, currency and bills and other aspects. Especially in the issuance of negotiable securities such as currency and bills, its value is huge and the circulation is large. In addition to using anti-counterfeiting materials, halftone image anti-counterfeiting is a low-cost and effective anti-counterfeiting method. Anti-counterfeiting companies introduce anti-counterfeiting technology for halftone images. 1. The quality of extracted information The information to be hidden, such as images, text or characters, etc., is hidden in the printed image through the watermark embedding algorithm, and the visual effect of the overall printed image is not changed. In the process of watermark extraction and detection, there are different watermark extraction methods or algorithms according to different embedded watermarks. At various stages after printing, substrates such as paper, cloth and plastic may be deformed, and the printed image will be blurred. Therefore, after the printing and scanning process, the geometric shape and tone of the printed image may be distorted, which greatly affects the quality of extracting hidden information. 2. The image information anti-counterfeiting company claims that the original digital image has undergone CMYK color separation or multi-channel color separation, and the image formed by the digital screening process is a halftone image, that is, a halftone image. The advantage of halftone digital watermarking is that, after the process of color separation and digital screening, compared with the original digital image processing, the loss of hidden information caused by color separation and digital screening will be reduced. However, the halftone image is a binary image, so the significant bit algorithm (LSB) in the space domain is not suitable for the halftone image to a certain extent. In the transform domain, based on methods such as DFT, DCT and DWT transforms, in essence, it is also the image gray value modified by the transform domain coefficients of the image, and then the transform domain coefficients are modified to hide the information, and the watermark image is obtained according to its inverse transform. . For printed images, after the image is inversely transformed from the frequency domain back to the spatial domain, it should also be binarized. However, the anti-counterfeiting company claims that the binarization process weakens or enhances the energy in the frequency domain of the watermark, so that the embedded watermark is usually greatly affected or even cannot be extracted. Therefore, for halftone images, the effect of embedding watermark in transform domain is not obvious. The disadvantage of halftone digital watermarking is that embedding the watermark from the space domain will easily affect the visual effect of the image, so the amount of hidden information is small; embedding the watermark from the transform domain, the hidden information is easily destroyed, and it will also affect the visual effect of the image, which is also halftone. The technical difficulties of watermarking technology.