The hottest copyright watermarking technology and

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Copyright watermarking technology and its progress (Part I)

1. Introduction

watermarking technology has received obvious attention recently. This is mainly due to the need to provide copyright protection for digital media such as audio, image and video. The watermark can be used by the holder to identify the media buyer, to monitor culture and education, to determine royalties and copyrights, and to determine whether the original data has been modified in some form. The purpose of the latter is different from copyright control to some extent, so its features will also be different, so there is no further discussion here

people study various technologies to avoid being improperly copied. Two better techniques are encoding and watermarking. Encoding protects data content during transmission from transmission to reception. After receiving and decoding, the data will lose protection and be displayed in a clear way. The watermark will directly embed the signal into the data to make the coding more perfect. Therefore, the goal of watermarking is to make the information always exist in the data

II. Characteristics of watermark

a watermark product should have a series of required characteristics, including difficult to see the mark, strong ability to resist signal distortion that can be translated by the decoder, ability to resist intentional removal of the mark, providing the same data rate as the application, allowing the addition of various marks, etc. These features are discussed in detail below

not easy to see: the imprint should not be obvious for observation, and the imprint will not reduce the quality of the media, that is, 811 high nickel cathode material. For trained observers, the imprint should be perceptible. In addition, significant differences can be detected by comparing two signals, for example, compressed and uncompressed, watermarked and original

integrity: audio, image and video signals may be subject to a variety of distortions, but the imprint must be complete during the conversion process. This conversion includes variable signal distortion, digital to analog and analog to digital conversion, and lossy compression. For images and videos, it is important that imprinting can restore geometric distortions, such as conversion, scaling, and clipping

in fact, integrity includes two key points: (1) whether the distorted imprint still exists in the data, and (2) whether the imprint can be detected. For example, after scaling this geometric distortion, the imprint inserted by various algorithms is still in the data, but if the distortion is removed first, the corresponding control algorithm can only control the imprint. In this case, either the distortion cannot be determined or the imprint cannot be detected by the bolometer

anti deletion ability: the imprint needs to undergo the signal processing process of removing the imprint in the historical direction. For the signal distortion of the political party, the imprint needs to remain intact. Therefore, the anti deletion ability of the imprint is important. This can be achieved by private imprinting and asymmetric encoding and decoding

bit rate: the bit rate of the imprint is related to the number of imprints that can be compiled into letters. This is particularly important for public watermarks

modification and multiple watermarks: in some cases, the imprint needs to be changed after insertion. For example, in a digital disc, the disc can be watermarked so that only one copy is allowed. However, after copying, it is necessary to change the imprint on the original disk to prohibit further copying. The imprint can be changed in the following ways: (1) remove the first imprint and then add a new one. (2) Insert a second stamp so that both are readable, but one must overwrite the other. The first change does not allow the imprint to have the ability to resist deletion, because it emphasizes the easy removal of the imprint. It is better to allow multiple marks to exist at the same time, which also enables you to insert your own unique marks from manufacturing, distribution to final sale

limitation: in commercial applications, the calculation cost of encoding and decoding is very important, and the importance of encoding cost is related to decoding. Computational requirements force the watermark to be simple, but this simplicity may significantly reduce the ability to resist deletion. As we all know, the speed of computer attachment is close to doubling every 18 months, so those that seem impossible to calculate today may soon become a reality. Therefore, it is very necessary to design an imprint. The country that decodes this imprint is vigorously urging the development and transformation of the plastic recycling granulator industry in recent years, which is not limited by the age (model) of the computer

III. watermark block diagram

the process of the watermark image together can be understood as adding a noise factor, which may be a function of the watermark signal w or the original image I. The watermark image I can be given by the following formula:

i`=i+ (I, w) -- (1)

the watermark image can withstand a large amount of distortion caused by deletion or general use, which can be represented by noise n. In many cases, noise can be approximated by linear superposition. However, the distortion in the spatial conversion process of an image can be highly nonlinear and image related, that is, n=n (I). Considering the effect of noise, the decoded image is:

i "=i`+n=i+f (I, w) +n (I) -- (2)

when decoding, we want to extract the watermark signal W, that is, we don't need the signal (or noise) to be image I. It should be noted that I is much more important than the inserted imprint f (I, w) and distortion n, so that the fidelity of the image is protected. Therefore, the ratio of signal to noise input to the decoder (where the signal is now watermark w) is much less than 1. Obviously, the method of connecting fiber growers and end consumers to an original image as part of the code determination program can greatly improve the signal-to-noise ratio, and its value can be obtained by simply subtracting the original image I from equation (2)

summarize the characteristics of various proposed watermarking methods that have been checked to see whether the software force display value changes when touching. We think that there are two important characteristics: (1) whether the watermark is inserted into the visual sensitive area of the image. (2) Whether the inserted signal is independent of the original image I

consider the first case where the insertion signal is independent of the original image, i.e. f (I, w) =w

in this case, equation (2) is simplified as

i "=w+i+n-- (3)

where the signal is slow W and the noise is i+n, and the signal can be filtered by the traditional matching method. In this case, if the mark is placed in the visual sensitive area of the image, the mark must be filtered by the band-pass filter according to the basic knowledge of the human visual and auditory system, as shown in Figure I. However, there is a possible disadvantage, that is, the water spectrum formed is independent of the currently known images matching the human visual and auditory systems. The power in these bands varies greatly from one image to another. Therefore, if the formed imprint and image are simply added linearly, the imprint energy must be very small to avoid the worst case, that is, the image energy is very low in some close-up frequency bands, which is much lower than the imprint energy, so the image is easy to be copied. On the contrary, if the image energy is very strong in a close-up band channel, there is an opportunity to import relatively more imprint energy without affecting the fidelity of the image. (to be continued)

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