Overview of digital watermarking in China Printing

The basic idea of digital watermarking technology is to embed specific information (such as copyright information, serial number, company logo, meaningful text, etc.) into various digital media in China Printing, such as image, voice, video, etc., in order to achieve the purpose of information hiding. This process does not affect the normal use of the original data, does not change the size of the original data, does not change the appearance of the original information.


1. The anti-counterfeiting characteristics of digital watermarking

The invisibility of digital watermarking determines that it can be combined with other anti-counterfeiting technologies. The printing anti-counterfeiting technology of digital watermark is different from the traditional printing anti-counterfeiting technology. It completely updates the traditional concept of printing anti-counterfeiting, and has unique properties in the anti-counterfeiting of printed matter.


① Technology exclusivity. The embedding and content of digital watermarking are random. The digital watermark hidden in each printed matter can be different, and the position of watermark is also random, which makes it difficult for forgers to counterfeit.


② Anti-counterfeiting investment is small and the cost is low. Digital watermarking users can embed the anti-counterfeiting information directly into the printed matter through the special software processing of digital watermarking. There is no need to change the production or printing process, add special materials, increase china printing quality and printing costs and change the original design appearance.


③ Technology upgrading is fast. According to the characteristics of the products, different and easy to update the special software, so that the corresponding printing anti-counterfeiting technology can also be constantly updated.


④ High confidentiality. In addition to the individuation and unidirectionality, as well as the concealment hidden in the media, digital watermarking technology can also be combined with private key and public key control detection, which is more secure than other technologies.


⑤ Product value added. Using the internationally recognized high-end anti-counterfeiting technology digital watermarking technology will make counterfeiters have nothing to do, so as to enhance customers' trust in digital watermarking users and their products, enhance and maintain the brand image of users, and improve the value-added value of products.


2. The core technology of digital watermarking

① Digital watermarking generation and hiding algorithm based on wavelet algorithm.

In this paper, wavelet algorithm is used to transform the spatial domain data of digital image into corresponding wavelet domain coefficients through discrete wavelet transform (DWT). According to the type of information to be hidden, it is encoded and deformed appropriately. Then, according to the size of hidden information and the corresponding security target, the square frequency domain coefficient sequence is selected. Finally, the frequency domain coefficients of digital image are transformed into spatial domain data by inverse transformation.


② Watermark anti duplication technology.

When the counterfeiter gets the printing package containing the digital watermark, he will try to copy it (such as using a high-precision digital scanner). In order to prevent the digital watermark information from being copied, the digital watermark embedding software adopts the algorithm of the given chromatographic equivalent when hiding the watermark information. This method can ensure that the counterfeiter cannot avoid changing the chromatogram when meeting the technical requirements of adjusting the color of the original image in this way, the watermark will not be copied.


③ Anti attenuation technology in China Printing.

From digital image to printed matter, it has to go through many processes, such as plate making and printing. The characteristics of digital watermark must be attenuated in each process. In order to ensure that the digital watermark has sufficient signal strength on the final printed matter, the digital watermark embedding software takes into account the sufficient signal strength when generating the watermark information to ensure that the signal strength (robustness) can still be reliable after multiple processes Machine readable.


④ Digital watermark testing machine-readable.

Digital watermark inspection machine-readable can eliminate the uncertainty of human factors, improve the inspection speed, enhance the security of hidden information (watermark) recognition, and can form a multi-dimensional anti-counterfeiting system with RFID, UV, magnetic stripe and other mature anti-counterfeiting inspection equipment to improve the comprehensive security level.


3、 Framework of digital watermarking

A typical digital watermarking model consists of two main processes: one is the watermark embedding process, the other is the watermark extraction or detection process. Each owner has a unique watermark, or an owner can embed different watermarks into different objects. Embedding watermark information into the carrier after preprocessing is called embedding. Watermark embedding can be understood as transmitting a wideband signal (watermark) on a wideband channel (original image) by spread spectrum communication technology. The design of embedding stage mainly solves two problems: the generation of digital watermark and the embedding algorithm. Extracting watermark information from watermarked data or detecting the existence of watermark information is called watermark extraction and detection. At present, most watermarking schemes use the key when adding and extracting. Only those who master the key can read the watermark.


The principle of digital watermarking technology used for bill anti-counterfeiting is roughly the same as that of audio and video, except that screening should be considered in the embedding process of watermark, and the graphic information of printed matter should be scanned in the process of watermark extraction and detection. In this process, there is an analog-to-digital (A / D) conversion process. This requires that the algorithm based on halftone digital watermarking technology must consider these factors in the corresponding embedding and detection process. The process of embedding and extracting is shown in Fig. 1 and Fig. 2.


4、 Application of digital watermarking in ticket security at China Printing and abroad printing

With the development of digital watermarking technology, the application field of digital watermarking has been expanded, from the early use of audio, video and other anti-counterfeiting to the anti-counterfeiting of various certificates, bills and other high-value commodities such as famous cigarettes, wine, precious drugs and so on. At present, digital watermarking has been widely used in the anti-counterfeiting printing of various tickets.


In Germany, digital watermarking is used to prevent forgery of electronic photos, and the imperceptible information is processed on the photos. This method can quickly and accurately determine the authenticity of the documents. The Media Laboratory of Massachusetts Institute of Technology (MIT) has studied how to add a unique and invisible digital watermark to each image output by color printer and copier. By judging whether the watermark exists or not from the scanned bill in real time, the authenticity can be quickly identified. Japan adds watermarks to insurance bills and proposes data hiding as a solution to identify the integrity of digital photos, judge whether the photos have been tampered with and locate the tampered places.


Digital watermarking technology is a hot topic at home and abroad. It is in a stage of rapid and continuous development, and its application field is also expanding rapidly. It plays a more and more important role in the field of anti-counterfeiting printing and has become the highlight of anti-counterfeiting packaging. Commercial paper has an important value in social life, and the anti-counterfeiting work of commercial paper is particularly necessary. The trend of counterfeit tickets has been banned for many times. Ticket companies have adopted seven anti-counterfeiting measures on a ticket, but they still cannot stop the spread of fake tickets. Therefore, it is the development direction to choose the advanced digital watermarking technology to replace the traditional anti-counterfeiting technology. With the constant innovation of digital watermarking anti-counterfeiting technology, it is bound to provide greater security for bill packaging anti-counterfeiting, and will bring considerable economic and social benefits.