CN102368328A - Digital watermarking method applied to counterfeit prevention for print documents - Google Patents
Digital watermarking method applied to counterfeit prevention for print documents Download PDFInfo
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- CN102368328A CN102368328A CN2011102767654A CN201110276765A CN102368328A CN 102368328 A CN102368328 A CN 102368328A CN 2011102767654 A CN2011102767654 A CN 2011102767654A CN 201110276765 A CN201110276765 A CN 201110276765A CN 102368328 A CN102368328 A CN 102368328A
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Abstract
The invention discloses a digital watermarking method applied to counterfeit prevention for print documents, wherein a multilayer watermark is used for preventing counterfeit of the print documents so as to protect the print documents. The method comprises two aspects of constructing the multi-layer watermark and constructing an anti-scanning/copying watermark layer, wherein the multi-layer watermark is constructed by firstly utilizing factors which mainly comprise contrast ratio and chromatic aberration and influence human vision on identifying objects, providing a concept of watermark contrast ratio by combining with a used scene in the method, further judging factors influencing an watermark extraction effect according to the watermark contrast ratio, finally comprehensively analyzing results and designing parameters; and the anti-scanning/copying watermark layer which is weak to scanning/copying is designed by firstly analyzing a scanning process and summing the features of scanning, therefore the purpose of preventing counterfeit due to scanning/copying can be achieved. The final multi-layer watermark is finallyformed by combining the multi-layer watermark with the anti-scanning/copying watermark layer.
Description
Technical field
The present invention relates to multimedia digital watermark structure, embedding and detection method, the false proof digital watermark method of particularly a kind of document printing.
Background technology
At present; Document printing such as various certificates, bill, trade mark have been brought into play irreplaceable vital role in people's life, however along with digital technology constantly popularize the fast development with technique of internet, forge; Problems such as piracy grow in intensity; How to protect these and our closely bound up product, i.e. copyright protection, information security, data authentication and access control or the like becomes the problem that presses for solution now.
Document printing anti-counterfeiting technology commonly used has that paper false proof, specialty inks are false proof, adhesive sticker micro text antiforge, the extraordinary anti-counterfeit printing of bill, safety line, encryption technology, laser hologram transfer techniques, locating thermoprint, telephone code is false proof, the two cards of atomic nucleus are false proof, anti-counterfeiting mark and hand engraving intaglio printing etc.But there is weakness separately in these technology, such as, material that the false proof needs of paper false proof and specialty inks are special or manufacture craft.And traditional anti-counterfeiting technology is grasped by the fake producer easily, thereby loses its antiforge function.On the other hand, the traditional document printing anti-counterfeiting technology and the equipment and the material of use are closely related, and can't accomplish versatility, and range of application is narrow.
The appearance of digital watermarking provides a kind of new solution for document printing is false proof.Compare with traditional approach, digital watermark technology has that hiding property is good, cost is low, good confidentiality, be difficult to advantages such as forgery, has higher utility.Be applied to the false proof digital watermarking of document printing and mainly comprise two kinds of anti printing and scanning watermark and vision watermarks, wherein, the vision watermark is a kind of visual watermark technology that grew up in recent years, has characteristics such as efficient, applied range.The United States Patent (USP) of Adi Shamir application has used a kind of visual watermark that is used for print image; Adopted an image with the monochrome pixels of fine structures substitute realize false proof; This method is relatively responsive to scanning device, and along with the development of scanning device, its effect also worse and worse.Another United States Patent (USP) of William H.Mowry application has used a kind of method of controlling pixel printing back size to realize false proof; Because the meeting that big pixel remains is more; And the error that small pixel has after printing owing to printer disappears; This kind method generally is that specific resolution is carried out to specific printer, and the lifting of effect depends on the machine that micro is printed.The multilayer optical watermark based on dot matrix that Huang and Wu proposed in 2007, this method use phase modulating method to realize on the basis of principles of modulation and demodulation; Then Lu YiFeng has proposed in 2008 based on the optical watermark of phenomenon how not; Compare with the optical watermark based on dot matrix, how phenomenon is not to be interfered by black and white strip to form, so bigger noise is arranged itself; The watermark that realizes multilayer is relatively more difficult, and capacity is less.
Summary of the invention
The technical matters that the present invention will solve is: the deficiency that overcomes prior art; Provide a kind of document printing false proof digital watermark method; This method is at first passed through the factor of analyzing influence watermark extracting effect; The standard that has proposed the watermark contrast is weighed the effect of multilayer watermark, on based on this basis, the parameter of structure multilayer watermark is analyzed then, and has been made a concrete analysis of the relation of cycle and live width; Analyzed the angle problem of multilayer watermark then, constructed the multilayer watermark according to analysis result.Last this paper has proposed the anti-counterfei waterprint layer after the characteristics of analysis scan appearance work, in conjunction with the multilayer watermark, finally obtain the scanning anti-counterfei waterprint of multilayer.
The technical solution adopted for the present invention to solve the technical problems: the digital watermark method that a kind of document printing is false proof comprises the analysis of watermark contrast, anti-scanning/duplicating watermark layer, watermark embedding and watermark extracting four major parts.The analysis of watermark contrast is to utilize contrast and these two human eyes of colour-difference to distinguish that the object key factor uses the watermark contrast to come the quantisation watermarking extraction effect; Anti-scanning/duplicating watermark layer is through scanning process being analyzed, being constructed anti-scanning/duplicating watermark layer according to scan characteristic; It is the basis of analyzing in the watermark contrast that watermark embeds, and selects suitable embedding cycle and angle according to analysis result, and combines the watermark of anti-scanning/duplicating watermark layer structure Multi-layer anti-counterfeit;
Analytic process to the watermark contrast is following:
A1. the analyzing influence human vision is recognized the factor of object;
A2., the watermark contrast is proposed;
A3. the watermark extracting effect is carried out mathematical analysis;
A4. select suitable embedding cycle and angle according to analysis result;
The building process of anti-scanning/duplicating watermark layer is following:
B1. the analysis scan process is to the influence of image
B2. make up anti-scanning/duplicating watermark layer based on scan characteristic
The telescopiny of watermark is following:
C1. according to embedding cycle and the angle basis of formation layer selected;
C2. select certain one deck as anti-scanning/duplicating watermark layer;
C3. watermark is embedded in the basal layer;
C4. make up the multilayer watermark;
C5. generate respective decoder;
The leaching process of watermark is following:
D1. use corresponding demoder to carry out watermark extracting;
The advantage that the present invention is compared with prior art had is:
(1) a kind of standard---watermark contrast of new measurement watermark extracting effect has been proposed, the extraction effect that this standard can more efficiently quantisation watermarking.
(2) the embedding cycle that influences the watermark extracting effect is carried out mathematical analysis, and used a large amount of repeated experiments that analysis result is verified, experimental result has shown according to the bigger lifting of the embedding cycle of analysis result selection the watermark extracting effect.
(3) the embedding angle that influences the watermark extracting effect is carried out mathematical analysis; And used a large amount of repeated experiments that analysis result is verified, experimental result shows that the embedding angle of selecting according to analysis result has prevented that effectively same demoder from extracting several watermarks and a plurality of demoder can only extract the abnormal conditions of same watermark.
(4) scanning process is analyzed, and constructed anti-scanning/duplicating watermark layer according to scan characteristic, this layer watermark is relatively more fragile to scanning/duplicating, can disappear in scanning or after duplicating, and can effectively protect document printing.
Description of drawings
Fig. 1 is the false proof digital watermark method overall flow figure of a kind of document printing of the present invention;
Fig. 2 is the watermark contrast synoptic diagram among the present invention;
Fig. 3 increases along with the cycle for D=1 among the present invention, and the watermark contrast is at the decline synoptic diagram;
Fig. 4 is the 2k+1 synoptic diagram for D＞1m=2 optimal period among the present invention;
Fig. 5 is the 3k+1 synoptic diagram for D＞1m=3 optimal period among the present invention;
Fig. 6 is for changing synoptic diagram before and after the image scanning among the present invention;
Fig. 7 is original watermark synoptic diagram among the present invention;
Fig. 8 is numeral replacement back watermark synoptic diagram among the present invention;
Fig. 9 is basal layer synoptic diagram among the present invention;
Figure 10 for embed watermark among the present invention after the image synoptic diagram;
Figure 11 is demoder synoptic diagram among the present invention;
Figure 12 is not for adding the watermark extracting synoptic diagram of anti-scanning/duplicating watermark layer among the present invention;
Figure 13 is the watermark extracting synoptic diagram of anti-scanning/duplicating watermark layer among the present invention.
Embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is done further to describe in detail.
The overall flow figure of the digital watermark method that a kind of document printing of the present invention is false proof is as shown in Figure 1.Overall flow comprises the analysis of watermark contrast, anti-scanning/duplicating watermark layer, watermark embedding and watermark extracting four major parts.
One, watermark contrast is analyzed
The study route of this part comprises four step: a1 steps, influences the factor of human vision identification object; The a2 step, the notion of proposition watermark contrast; In the a3 step, analyze the watermark extracting effect; In the a4 step, select suitable embedding cycle and angle.Specific as follows:
Step a1: the factor that influences human vision identification object
Because the extraction effect of watermark is apparent in view for human eye, but can't weigh on the computing machine, so before carrying out mathematical analysis, need to seek the standard of a suitable measurement watermark extracting effect.According to the experimental result of Hrishikesh, mark PSNR and cycle that tradition is weighed the watermark extracting effect do not have rule basically, so PSNR has been not suitable for being used for carrying out mathematical analysis in this case, so need a kind of new standard of weighing the watermark extracting effect.According to the analysis to human eye of Peter G.J.Barten and Oracle related data, the factor that influence is differentiated object mainly contains two: the contrast of background and prospect, and the color of background and prospect.
Step a2: watermark contrast
Because the watermarking images of this paper is a bianry image, so do not relate to the problem of color, the best means of therefore weighing the watermark extracting effect are exactly to weigh the contrast that extracts watermark.Based on above analysis, this paper has proposed a kind of measurement new standard of watermark extracting effect in such cases---watermark contrast, and it defines shown in formula (1):
contrast＝(A-B)/M×N (1)
Wherein A represents the number of black color dots, and B represents the number of white point, and the size of M * N presentation video is a M * N pixel, and its span is [1,1] ,-1 expression pure white, 1 expression ater.
The watermark contrast has been arranged, just can weigh the extraction effect of a width of cloth watermark picture, according to formula (1), this paper is divided into two parts to the watermark contrast: watermark part and watermark exterior portions.So whole watermark contrast can use formula (2) to calculate.
contrast＝abs(((A
1-B
1)/M
1×N
1)-((A
2-B
2)/M
2×N
2)) (2)
A wherein
1The stain of expression watermark part, B
1The white point of expression watermark part, M
1* N
1The size of expression watermark part; A
2The stain of expression watermark periphery, B
2The white point of expression watermark periphery, M
2* N
2The size of expression watermark periphery.The value of contrast is between [0,2], and it is big more to be worth big more expression contrast, and promptly effect is good, as shown in Figure 2 more.
Step a3: analyze the watermark extracting effect
A. use the watermark contrast that the embedding cycle is analyzed
The value of live width D can exert an influence to the extraction effect of watermark in the process of embed watermark; If the live width D that uses in the construction process accounts for the 1/m of cycle T; And because D is a positive integer;
arranged so so the conclusion of formula (3) is arranged
N＜m wherein, k=1,2,3...
When T when m * k changes to m * k+1, live width D has been increased to k+1 from k, so the increase of live width at this moment is more violent with respect to the increase in cycle.Because the increase of live width ratio, the reservation degree of watermark integral body is better, so the watermark contrast also has corresponding increase, therefore watermark this moment contrast is best.
Fig. 3 is we and the curve map of watermark contrast in calculate cycle when D=1, and this figure shows that when D=1 along with the increase of T, the watermark contrast is a monotone decreasing; Fig. 4 works as m=2, the curve map of D＞1 o'clock cycle and watermark contrast, and this chart open fire seal contrast is got peak value when getting 2 * k+1; Fig. 5 works as m=3, the curve map of D＞1 o'clock cycle and watermark contrast, and this chart open fire seal contrast is got peak value when getting 3 * k+1.
According to top analysis and result of calculation, T
kThe extraction effect of watermark is reasonable during=m * k+1, and contrast (T is arranged
1)＞contrast (T
2)＞...＞contrast (T
k).
In addition, as 2≤T
kDuring＜m, might exist effect to compare T
kThough the cycle that=m * k+1 is good is because T
kThe increase of live width has promoted extraction effect during=m * k+1, yet extraction effect is the decline that is increased in along with T, so 2≤T
k＜m need consider separately as particular point.
B. use the watermark contrast to analyze to embedding angle
The embedding angle does not exert an influence to the extraction of single-layer watermark.For the multilayer watermark, if select inappropriate words, and when the cycle of two-layer watermark is identical, i.e. T
X1=T
X2Perhaps T
Y1=T
Y2The time, two kinds of special circumstances can appear after carrying out the watermark stack:
A. use a plurality of demoders can only extract same watermark, perhaps can't successfully extract at all.
Can see simultaneously the situation of a plurality of watermarks when b. using a demoder.
More than the generation of two kinds of situation, all be because embedding angle chooses improperly, cause rotating too for a short time causing of distance between two points of back mapping.
Be located in the rectangular coordinate system in the original watermark layer a bit (x y) rotates θ respectively for P arbitrarily
1And θ
2After obtain corresponding point in the two-layer watermark:
P
1(xcosθ
1+ysinθ
1，ycosθ
1-xsinθ
1) (4)
P
2(xcosθ
2+ysinθ
2，ycosθ
2-xsinθ
2) (5)
The distance that calculates between this two-layer watermark according to the Euclidean distance formula is:
Can find out, in the formula (6)
Can't change the differential seat angle item that has only the back that can control | θ
1-θ
2|, and have | θ
1-θ
2|≤90 ° is the suitable distance of may command so calculate suitable angle difference, and then avoids the generation of the two kinds of special circumstances in front.
Through a large amount of experiments repeatedly, angle difference is got | θ
1-θ
2| can prevent the generation of two kinds of fortuitous events in the time of>=60 °, and the big more effect of value is good more, and because θ is the angle with the longitudinal axis, thereby angle difference is 90 ° to the maximum, promptly 90 ° of effects of value are best.
Step a4: select suitable embedding cycle and angle
According to analysis in the step 3 and experimental result, just like drawing a conclusion: the cycle is got T
kDuring=m * k+1 and | θ
1-θ
2| the watermark extracting effect is relatively good in the time of>=60 °.In this patent experiment, the concrete parameter of selecting is m=3, so the watermark extracting effect is relatively good when the cycle is selected T=3k+1, and owing to have particular point, so the final parameter of selecting is T
X1=2, T
Y1=2, θ
1=60 °, T
X2=4, T
Y2=4, θ
2=120 °.
Two, anti-scanning/duplicating watermark layer
In order to make up the anti-counterfei waterprint layer, which influence is the process of analysis scan produced to image is very necessary.The course of work of scanner is following: at first hard copies such as the image of papery, text are placed on the glass plate of scanner; Light source throws a branch of pure light on reverberator; CCD (Charged Coupled Device; Charge-coupled image sensor) inductor is converted into electronic signal with the optical signalling of sensing; The electronic signal that optics obtains is fed to ADC (Analog to Digital Converter, analogue-to-digital converters) system, and ADC generates the electronic signal of sending here digital picture and is sent to main frame.
The optics of scanner has determined the resolution of scanner, so optical MTF (Modulation Transfer Function, modulation transfer function) has been played the part of important role in scanning process.The optical modulation transition function MTF of scanner has roughly following character:
Wherein, dscan is meant the resolution (pixel/millimeter) of scanner, and MTF (f) is a modulation transfer function, and f is a spatial frequency.The optical modulation transition function can come modeling with a gaussian filtering, is equal to original image has been carried out Gauss's LPF attack.To a certain degree fuzzy, as shown in Figure 6 can appear in the periphery of original image after overscanning:
According to this characteristic, this paper has made up an anti-counterfei waterprint layer based on numeric structure, is divided into 3 * 5 piece to watermarking images, according to the number of black color dots in the image, replaces with the corresponding digital piece then then, finally obtains watermark picture to be embedded.
The number of black color dots is p in the note watermark block, 1≤p≤15, and corresponding relation is (8):
When numblock=1, represent, select digital block 1; When 5≤p≤9, selection 2,4,7 digital blocks at random.The digital block table is following:
Before the replacement be Fig. 7, and replacement back be Fig. 8, obtain the watermarking images after digital the replacement after, carry out the watermark embedding to it as one in the watermarking images, so just can construct the anti-counterfei waterprint layer.Based on the diffusion property of scanning, this watermark layer can the pixel value of periphery be close together after scanning, and then can't differentiate, and reaches the purpose that can't discern scanning and printing spare, just can't extract watermark in scanning/duplicating back like this.
Three, watermark embeds
The embedding step of watermark is following:
C1. according to embedding cycle and the angle basis of formation layer selected;
C2. select certain one deck as anti-scanning/duplicating watermark layer;
C3. watermark is embedded in the basal layer;
C4. make up the multilayer watermark;
C5. generate respective decoder;
Basal layer is shown in Fig. 9-a, and Fig. 9-b is the basal layer after amplifying, wherein T
x, T
yBe respectively the embedding cycle of the direction of x axle, y axle, D
x, D
yBe respectively x axle, the axial live width of y, shown in figure 10 behind the embed watermark, demoder is shown in figure 11.
Four, watermark extracting
Watermark extracting is to use respective decoder to extract watermark; Figure 12 is four layers of watermark extracting design sketch that do not add anti-scanning/duplicating watermark layer; Figure a is the extraction effect of embed watermark information " watermark ", and figure b is the extraction effect of embed watermark information " Beijing Institute of Aeronautics ", and figure c is the extraction effect of embed watermark information " original paper "; Figure d is the extraction effect of embed watermark information " false proof "; Figure 13 revises the original watermark layer for anti-scanning/duplicating watermark layer, scans respectively then and duplicates, and uses demoder to cover the synoptic diagram that watermark layer carries out watermark extracting.
In sum; The present invention is through the factor of analyzing influence watermark extracting effect; The standard that has proposed the watermark contrast is weighed the effect of multilayer watermark, on based on this basis, the parameter of structure multilayer watermark is analyzed then, and has been made a concrete analysis of the relation of cycle and live width; Analyzed the angle problem of multilayer watermark then, constructed the multilayer watermark according to analysis result.Last this paper has proposed the anti-counterfei waterprint layer after the characteristics of analysis scan appearance work, in conjunction with the multilayer watermark, finally obtain the scanning anti-counterfei waterprint of multilayer.Experimental result shows, mathematical analysis provides more rational cycle and angle selective: reasonably the cycle of embedding can reach and embed effect preferably, reasonably embeds the generation that angle can effectively be avoided two kinds of fortuitous events.So the operational analysis result can more obviously promote the extraction effect of watermark.
The part that the present invention does not set forth in detail belongs to techniques well known.
Claims (5)
1. digital watermark method that document printing is false proof is characterized in that: this method overall flow comprises the analysis of watermark contrast, anti-scanning/duplicating watermark layer, watermark embedding and watermark extracting four major parts; The analysis of watermark contrast is to utilize contrast and these two human eyes of colour-difference to distinguish that the object key factor uses the watermark contrast to come the quantisation watermarking extraction effect; Anti-scanning/duplicating watermark layer is through scanning process being analyzed, being constructed anti-scanning/duplicating watermark layer according to scan characteristic; It is the basis of analyzing in the watermark contrast that watermark embeds, and selects suitable embedding cycle and angle according to analysis result, and combines the watermark of anti-scanning/duplicating watermark layer structure Multi-layer anti-counterfeit; Be watermark extraction process at last; Specific as follows:
The analytic process of watermark contrast is following:
A1. the analyzing influence human vision is recognized the factor of object;
A2., the watermark contrast is proposed;
A3. the watermark extracting effect is carried out mathematical analysis;
A4. select suitable embedding cycle and angle according to analysis result;
The building process of anti-scanning/duplicating watermark layer is following:
B1. the analysis scan process is to the influence of image
B2. make up anti-scanning/duplicating watermark layer based on scan characteristic
The telescopiny of watermark is following:
C1. according to embedding cycle and the angle basis of formation layer selected;
C2. select certain one deck as anti-scanning/duplicating watermark layer;
C3. watermark is embedded in the basal layer;
C4. make up the multilayer watermark;
C5. generate respective decoder;
The leaching process of watermark is following:
D1. use corresponding demoder to carry out watermark extracting;
Wherein, described watermark contrast is the standard of quantisation watermarking extraction effect, and it is defined as: contrast=(A-B)/M * N wherein A represents the number of black color dots; B represents the number of white point; The size of M * N presentation video is a M * N pixel, and its span is [1,1];-1 expression pure white, 1 expression ater.
2. the false proof digital watermark method of a kind of document printing according to claim 1; It is characterized in that: the described embedding cycle is relevant with live width to the influence of watermark contrast, and when T=m * k+1, the watermark contrast is got maximal value; Wherein m is the ratio that live width accounts for the cycle, and k is a natural number.
3. the false proof digital watermark method of a kind of document printing according to claim 1 is characterized in that: described embedding angle is when embedding multilayer, to influence each other to the influence of watermark contrast, and each layer distance was good more far more when multilayer embedded, and its distance does
Therefore controlling its angle difference gets final product.
4. the false proof digital watermark method of a kind of document printing according to claim 1 is characterized in that: when making up the multilayer watermark, added anti-scanning/duplicating watermark layer.
5. the false proof digital watermark method of a kind of document printing according to claim 4 is characterized in that: because scanning process is equivalent to LPF one time, so make up the watermark that anti-scanning/duplicating watermark layer uses a kind of numeric structure.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103679624A (en) * | 2013-10-30 | 2014-03-26 | 北京航空航天大学 | Scanning and copying prevention method based on gray scale image light watermarking |
| CN107644391A (en) * | 2017-09-18 | 2018-01-30 | 北京邮电大学 | A kind of digital watermark treatment method and device traced to the source for printed document |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1512438A (en) * | 2002-12-30 | 2004-07-14 | 北京邮电大学 | File anti-fake method and its device based on digital water print |
| CN1828666A (en) * | 2006-04-12 | 2006-09-06 | 上海理工大学 | Fake proof method for printing optical holographic watermark certificate |
-
2011
- 2011-09-19 CN CN 201110276765 patent/CN102368328B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1512438A (en) * | 2002-12-30 | 2004-07-14 | 北京邮电大学 | File anti-fake method and its device based on digital water print |
| CN1828666A (en) * | 2006-04-12 | 2006-09-06 | 上海理工大学 | Fake proof method for printing optical holographic watermark certificate |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103679624A (en) * | 2013-10-30 | 2014-03-26 | 北京航空航天大学 | Scanning and copying prevention method based on gray scale image light watermarking |
| CN103679624B (en) * | 2013-10-30 | 2017-01-04 | 北京航空航天大学 | A kind of anti-scan and copy method based on gray level image optical watermark |
| CN107644391A (en) * | 2017-09-18 | 2018-01-30 | 北京邮电大学 | A kind of digital watermark treatment method and device traced to the source for printed document |
| CN107644391B (en) * | 2017-09-18 | 2019-11-26 | 北京邮电大学 | It is a kind of for printing the digital watermark treatment method and device that document is traced to the source |
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