watermark


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watermark:

see paperpaper,
thin, flat sheet or tissue made usually from plant fiber but also from rags and other fibrous materials. It is used principally for printing and writing on but has many other applications. The term also includes various types of paperboard, such as cardboard and wallboard.
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Watermark

 

a picture in a piece of paper, visible when the paper is held up to the light; it is formed during the process of making the paper.

Watermarks began to appear in Europe in the 13th century, and in Russia in the second half of the 17th century. The study of watermarks and the determination of the exact place and time of the making of a piece of paper are very important for the correct interpretation of a source.

Since 1723, Russia, following the example of other European countries, impressed watermarks on stamped paper (a depiction of the state coat of arms and the words“stamped paper”) in order to avoid counterfeiting of official documents and currency. Watermarks are usually made on paper at precise intervals, or they cover the whole field of the paper in the form of a repeated drawing or pattern. They can be used to distinguish genuine money, valuable papers and documents, and stamps from counterfeit items. Watermarks are also used as a means of ornamenting paper. The imprinting of watermarks is usually done with a dandy roll or with cylinders of a cylinder paper-making machine on a wet web of the paper.

N. M. BOKAREVA

watermark

[′wȯd·ər‚märk]
(graphic arts)
A localized modification of the structure and opacity of a sheet of paper so that a pattern or design can be seen when the sheet is held to the light.
References in periodicals archive ?
where the watermark detection threshold [tau] can be expressed as
To find the optimal value of the watermark embedding strength factor, a multi-objective optimization method is designed to determine an appropriate value for [lambda] that ensures invisibility with acceptable robustness by using the image quality evaluation measure and the watermark error probability.
In [21, 22] it is shown that blocking in the cover image increases the robustness of the watermark.
If the watermark is hidden on S coefficients then we have
Caption: Figure 2: Schematic for watermark extraction.
Caption: Figure 3: (a) Original MRI image; (b) chaotic watermark; (c) watermarked image.
(10) Again, arrange the pixels of RONI in the vector form as in step 4 and embed the watermark [W.sub.c] based on the chaotic key computed in step 3 by replacing the four LSBs of RONI with every 4 bits of the watermark [W.sub.c].
This sequence is an outcome of chaotic key which will give locations for extracting the concatenated watermark [W.sub.c] from RONI.
It should be noted that since the characteristic digest value is generated through taking a bit plane from the blocks of watermark W which originates from low-frequency part with compressive sensing, the characteristic digest value can only detect whether the watermark or low-frequency part is tampered and then find out the tampered blocks.
For the unimportant part, that is, high-frequency parts HL, LH, and HH, different compressive sensing operation will be employed to ensure the reasonability of watermark embedding and the invariance of image size before and after encryption.
The DWT is also shift variance which may cause a problem in the extraction of watermark information.
Since [[delta].sub.rn], [[delta].sub.gn] and [[delta].sub.bn] are un-correlated representations of the three-color channels, and therefore, modifying any one of them for watermark embedding will not cause any other channel to suffer.