| In the 21st century, along with the development of information technology and the advances of high-quality image input and output equipment, such as digital camera, VCR, scanner, printer equipment and powerful software, especially the high-precision color inkjet, laser printers and scanners are popularized and bring a lot of facilities to people's working and living. But at the same time they also make the packaging of the product, documents, checks, securities and files are counterfeited very easily. Therefore, the copyright protection of the printed pictures, files has been a problem that need be urgently solved and it makes the printing security technologies are important.But most of the existing security printing technologies have many deficiencies such as costly, complicated and narrowly applied, but with the development of piracy technology, security printing technologies must break through in material, design and the specialized technical limitations and use the high-tech to meet business needs. In such demand, the digital watermarking technology can effectively solve these problems, which will have a very good security result and effectively reduce cost. Digital watermarking describes methods and technologies that allow hiding of information, the embedding takes place by manipulating the content of the digital data, which means the information is not embedded in the frame around the data. The hiding process has to be such that that modification of the media is imperceptible. Furthermore, the watermark has to be robust or fragile, depending on the application and can be used as identification and prosecution of illegal infringement of evidence and ensure the integrity and reliability of the product. Compared with the traditional anti-counterfeit technology, the digital watermarking technology is speed, high security, low cost, and will have s a great prospect.This paper does a comprehensive summary of research and development of the digital watermarking technology for Digital Image Print-Scan Process. This paper based on the research of watermarking algorithm for Digital Image Print-Scan Process; first, it did a detailed analysis of Print-Scan systems; second, after the analysis of the advantages and disadvantages of the existing algorithms, itmade the new watermarking algorithms for Digital Image Print-Scan Process with the technologies and theories of signal processing areas. The paper's major achievements are as follow:1. This paper analyzed all kinds of impacts of Print-Scan Process to image and pointed out the correction methods. Made the comprehensive and detailed presentations of the characteristics of printers and scanners, and analyzed the factors of Print-Scan Process for image quality, including the objective factors of machine and human operational factors, at the same time gave the methods how to reduce the impact of various factors. Meanwhile, classed the distortion factors, and gave a simple mathematical model of the distortion, which pointed out the direction for the future design of the algorithm.2. Wavelet translation not only matches the characteristic of HVS (Human Visual System) preferably, but also is compatible with the JPEG2000 and MPEG-4 compression standard. Watermarking algorithm based on DWT has good visual effect and good robustness. In view of the current situation that the algorithm based on DWT algorithm for Digital Image Print-Scan Process is small, and the existing digital watermarking technology used the watermark which are most images, words and random sequences or noise and so on, this paper proposed a algorithm based on DWT for Digital Image Print-Scan Process, in which the watermark was based on the image future -- "approximate invariant" watermark algorithm. "Approximate invariant"in Print-Scan Process can retain most of the value of it and using it to be the original image signal can improve the robustness and visibility. Through the embedding methods to enhance it robustness to all kinds of attacks in Print-Scan Process to achieve the purpose of identification of Digital Image Print-Scan Process.3. In view of the actual demand to security matters, now the embedded information capacity is small (<500bit) in most of the existing Watermarking Algorithm for Digital Image Print-Scan Process. After did a comprehensive research of Digital Image Print-Scan Process, and calculated all the aspects of watermarking algorithm, in this paper a new method based on Walsh orthogonal transform sequence modulating watermark and DWT Transform is proposed. The embedded information capacity reaches 4096-bit under the NVF which combines HVS and the characteristic of the image to control the watermark embeddingintensity. The algorithm has proved to be robust against the various attacks during the print-scan process, such as image halftone, D/A conversion, A/D conversion, scaling, rotation, cropping, skew, and all kinds of random noise signal, and so on. And successfully solve the problem that the embedded information capacity is small in the Watermarking Algorithm for Digital Image Print-Scan Process.4. This paper made a research on how to improve the robustness of the digital watermarking algorithm for Digital Color Image Print-Scan Process. After various main color spaces, which have been presented by now, are classified and analyzed, and in the process of printing and scanning, the different color space transform of the display, printer and scanner are analyzed on image quality, summed up the precondition of the digital watermarking algorithm for Digital Color Image Print-Scan Process: color space's conversion. After a detailed comparison, it got a suitable color space's conversion for Digital Color Image Print-Scan Process: RGBâ†'CIEL~*a~*b~*â†'RGB, and embedded the watermarking in the brightness L~*of the color space. This method can be effective to reduce the color distortions by color space conversion, and improve the watermark extraction rate. Watermarking algorithms for Digital Color Image Print-Scan Process will improve the robustness and enhance the validity and reliability. |
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