CN102110281A - Method for embedding and extracting watermarks by adopting difference expansion aiming at shape point map layer data - Google Patents
Method for embedding and extracting watermarks by adopting difference expansion aiming at shape point map layer data Download PDFInfo
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Abstract
The invention discloses a digital watermark method for embedding and extracting watermarks by adopting a difference expansion technology aiming at shape point map layer data. The watermark embedding method comprises the following processes of: analyzing all points in shape carrier data to determine a projection axis; sequencing all the points according to the projection axis to form a continuous point sequence with unique value; sequentially pairing every two data of the point sequence, judging whether the watermarks are suitable to be embedded into the points of the group by adopting the difference expansion technology by using the corresponding data precision requirements of geographic information system (GIS) vector data as judgment conditions, if so, modifying the coordinate difference of the related points to embed watermark information, otherwise, embedding the watermark information by using a least significant bit (LSB) displacement method; and simultaneously recording the embedded information in the process. According to the method, the difference expansion technology can be applied in reversible watermark embedment and extraction of the GIS point map layer data and applied in interpolation identification of the GIS vector point map layer data, copyright protection, GIS vector point map layer data-based concealed communication and the like.
Description
Technical field
The invention belongs to geography information copyright protection field, be specifically related to a kind of digital watermark method that adopts embedding of difference expansion technique and extraction watermark at shape point diagram layer data; But the present invention is a kind of inverse approach, extracts in the watermark process, can recover raw data in conjunction with key.
Background technology
At present, digital watermark technology is just becoming the major technique means that solve Geographic Information System (GIS) vector data product safety problem.Chinese scholars is directed to the GIS vector data, has proposed multiple digital watermarking algorithm.Because the embedding of watermark data can bring disturbance to raw data inevitably, has reduced the quality of GIS vector data to a certain extent, therefore, the reversible water mark technology is introduced into into.The reversible water mark technology, i.e. lossless data hiding, be meant can complete recovery initial carrier data watermarking algorithm.At present the main method of reversible water mark technology comprises and utilizes difference expansion, lossless compress, invertible module to add and changes the reversibility that histogram comes implementation algorithm, and only receives small part scholar's concern at reversible algorithm research of GIS vector data.
The basic thought of difference expansion technique is by the coordinate difference that satisfies the consecutive point that embed precision conditions in the carrier data being carried out shifting function, provide extra storage space for watermark data under the situation of not losing raw information.Wherein, Shao Chengyong etc. (" Chinese image graphics journal ", Vol.12, No.2,206-211 page or leaf, 2007) have proposed a kind of lossless data hiding algorithm that is applied to map vector based on the thought that difference enlarges.Its essence is to have utilized map neighbouring vertices coordinate data to have the characteristics of strong correlation, thereby this algorithm only is applicable to polygon curve and two kinds of data types of polygon in the GIS vector data, can not the process points data, this propagation of giving this technology has undoubtedly brought certain obstacle with promoting.
Summary of the invention
The objective of the invention is to: the reversible water mark that can not be applied to GIS point diagram layer data at present difference dilation technique embeds and the extraction problem, propose a kind of watermark embedding and extracting method, thereby the difference dilation technique can be applied in the digital watermarking algorithm of each data type of GIS vector data at shape point diagram layer data.
To achieve these goals, the technical solution used in the present invention mainly comprises following process:
(1) watermark embed process:
Step 1: read GIS point diagram layer data, configuration embeds the parameter of algorithm, mainly contains trueness error tolerance limit, coordinate expansion multiple and key file and deposits the path, checks the legitimacy of input data and configuration parameter then;
Step 2: analyze above-mentioned point data, determine the axis of projection that telescopiny adopts according to following formula:
Y＝Ymax-(Ymax-Ymin)×1/2
Wherein Y represents the transverse projection axle, and Ymax is a maximum ordinate in the data point, and Ymin is a minimum ordinate in the data point; Sort from small to large according to the coordinate figure of data point on this axis of projection again,, then choose the point that the nearest point of this axis of projection of vertical range embeds as watermark before the projection for the identical overlapping point of coordinate; Thus, a point sequence that coordinate is unique and continuous on the formation axis of projection direction;
Step 3: the carrier that above-mentioned point sequence is embedded as watermark utilizes the difference expansion technique to embed reversible water mark, specifically adopts difference to expand twice mode and carries out, and promptly the coordinate difference of binary mode moves to left one;
(a) at first with the data in step 2 pairing in twos successively, will be the coordinate x of decimal originally
0iBecome integer x
i, formula is as follows:
Wherein,
Expression rounds downwards, and K is that the coordinate in the step 1 enlarges multiple;
(b) calculate the difference d and the integer mean value m of per two match point coordinate figures then;
(c) requiring with the corresponding data precision of GIS vector data is criterion again, and the following formula of d substitution is judged whether this group point is suitable for adopting difference extended mode embed watermark:
-2×R+1≤d≤2×R-2
Wherein, R is the trueness error tolerance limit, x
FrontAnd x
BackBe that this point is to x
iAnd x
I+1The front and back point coordinate; If d does not satisfy in above-mentioned three any one, then, adopt the mode embed watermark of replacing least significant bit (LSB) in order to increase the embedding capacity; Otherwise, adopt difference extended mode embed watermark, and in telescopiny recording-related information so that recover raw data;
Step 4: preserve embed watermark point data afterwards, the relevant information that produces in the telescopiny is saved as key file;
(2) extract watermark and raw data rejuvenation:
Step 1: read the GIS point diagram layer data of watermark to be extracted, from key file, read the embedding correlation parameter, check the legitimacy of parameter;
Step 2: determine the axis of projection that watermark extraction process adopts according to the parameter that reads, sort from small to large according to the coordinate figure of point on this axis of projection again, for the identical overlapping point of coordinate, then choose the nearest point of this axis of projection of vertical range before the projection as the point that extracts watermark; Thus, form a point sequence that coordinate is unique and continuous on the axis of projection direction, be the carrier that extracts watermark;
Step 3: utilize the method in the above-mentioned watermark embed process step 3, point sequence is matched grouping earlier in twos, coordinate is through calculating the difference and the integer mean value of per two match point coordinate figures respectively after enlarging; Extract the lowest bit position of each point then successively, promptly obtain the watermark that embeds the coordinate difference; Respectively each is put calculating original difference again: recover coordinate data afterwards according to coordinate difference and integer mean value computation at last;
Step 4: the raw data after the saving/restoring, the watermark that output extracts.
Wherein the step 2 in the telescopiny why select carrier data intermediate value as axis of projection, mainly be in order to weaken the influence of embed watermark to the data quality.In addition, for ordinate, embed with mode such as extraction and said method just the same.
The present invention has proposed a kind of method at shape point diagram layer data employing difference dilation technique embedding reversible water mark according to the strict demand of GIS vector data for data precision, when extracting watermark, can can't harm and recover the original point data.This method is equally applicable to the GIS vector point data of other non-shape forms.Application prospect of the present invention comprise GIS vector point diagram layer data distort discriminating, copyright protection and based on hiding communication of GIS vector point diagram layer data etc.
Description of drawings
Fig. 1 is that watermark embeds process flow diagram in the inventive method.
Fig. 2 is watermark extracting and a restore data process flow diagram in the inventive method.
Fig. 3 is administrative village, the Jiangsu Province point diagram layer vector data that the embodiment of the invention is chosen.
Fig. 4 amplifies data afterwards for Fig. 3 carries out part.
Embodiment
Be described in further details below in conjunction with drawings and Examples.
This example is selected a kind of typical shape point data, and the whole process at the reading of data, processing, watermark embedding, preservation as a result, watermark extracting, data are recovered further describes the present invention.Present embodiment selects Jiangsu Province's administrative village point level vector data (as Fig. 3) as experimental data, and the data recording number is 17521.The watermark content is " Nanjing Normal University " text message, and corresponding scale-of-two watermark sequence W is " 11000100110011111 ... 100111 ", and length is 96.
1, expands watermark embedding method at the difference of shape point diagram layer data.
As Fig. 1, be the embedding process flow diagram of difference expansion watermark embedding method at shape point diagram layer data proposed by the invention.Whole flow process is divided into following components:
Step 1: the reading and handling of data.
1) utilize the increase income function reading of plug-in unit of MapWinGIS to read corresponding point diagram layer data, and be List＜Point with data organization structure, be designated as S0;
2) input copyright mark watermark information W is provided with trueness error tolerance limit R=500m, and coordinate enlarges multiple K=10000;
3) data processing comprise with W be converted into algorithm inside watermark W2 to be embedded, check the legitimacy of all input data and configuration parameters.
Step 2: calculate and definite transverse projection axle.
Point among the traversal S0 obtains maximum ordinate Ymax=35.116 and minimum ordinate Ymin=30.769, then according to formula:
Y＝Ymax-(Ymax-Ymin)×1/2 (1)
Determine axis of projection Y=32.9425.
Step 3: the point sequence of choosing embed watermark.
Point among the S0 is sorted from small to large according to horizontal ordinate, obtain S1 as a result; Check S1, calculate its fore-and-aft distance to the transverse projection axle for the point that wherein horizontal ordinate is identical, keep the point with minor increment, reject remaining point, obtain S2 as a result, be the point sequence of watermark to be embedded, length is designated as N.If
Less than the length of watermark W2, then this point sequence can not embed once complete watermark, and this flow process finishes; Otherwise enter next step.Present embodiment length N=17489, then
Greater than the length 96 of watermark W2, carry out next step.
Step 4: utilize difference expansion technique embed watermark to above-mentioned point sequence.
At first with the data S2 in step 3 pairing in twos successively, below with prepare first to x
01, x
02Be example, the coordinate that originally is decimal is become integer, formula is as follows:
Wherein,
Expression rounds downwards, and K is that the coordinate of importing in the step 1 enlarges multiple.
Calculate the difference d and the integer mean value m of per two match point coordinate figures then:
d＝x
1-x
2 (4)
To judge according to following formula whether this group point is suitable for adopting difference extended mode embed watermark by the d that formula (4) calculate:
-2×R+1≤d≤2×R-2 (6)
Wherein, R is the trueness error tolerance limit, x
FrontAnd x
BackBe that this point is to x
01, x
02The front and back point coordinate.Formula (6) is in order to guarantee the trueness error tolerance limit of the caused disturbance of data of embed watermark less than map datum, and formula (7), formula (8) are to be constrained to before and after it between coordinate containing the watermark coordinate data, prevents the change of factor certificate and causes the entanglement of point sequence order.If d does not satisfy in above-mentioned three any one, then adopt the mode embed watermark of replacing least significant bit (LSB); Otherwise, adopt difference extended mode embed watermark.In this process, generate a two-value flag sequence
Wherein, f
iIt is right to be that the representative of 0 position is not suitable for the point that the difference expansion embeds, and f
iBe that then corresponding to be fit to carry out the point that the difference expansion embeds right for 1 position.This flag sequence is preserved as the part of key.
Adopt the difference expansion at each some centering embed watermark according to each sign (being designated as f) among the flag sequence flag, formula is as follows:
f＝1，d′＝2×d+w (9)
Inverse transformation formula calculating according to formula (4), formula (5) obtains to contain the watermark point to x
01, x
02The horizontal ordinate data, formula is as follows:
In the process of above-mentioned expansion difference with embed watermark, flag is 0 point to being to adopt the mode of directly replacing least significant bit (LSB) (LSB) to store watermark information.,, use when these original LSB data that are replaced must be preserved for the recovery raw data for this reason, be designated as lsb for guaranteeing the reversibility of algorithm.The same with flag, will preserve as the part of key.
Step 5: preserve embed watermark data and key file afterwards.Detailed process is as follows:
The least significant bit (LSB) lsb information of axis of projection data, two-value flag sequence flag and raw data that the embedding parameter that 1) will import in telescopiny (enlarging multiple as coordinate), calculating obtain saves as key file with certain form.
2) the point sequence S2 with embed watermark information is integrated among the total data S0;
3) data S0 is saved to hard disk.
2, expand watermark extracting and data reconstruction method at the difference of shape point diagram layer data.
Fig. 2 is the workflow diagram that extracts watermark and restore data method.Concrete steps are as follows:
Step 1: the point data that reads watermark to be extracted.
Utilize the increase income function reading of plug-in unit of MapWinGIS to read corresponding point diagram layer data, and be List＜Point with data organization structure, be designated as S0.
Step 2: read key file and parsing.
In this step, obtain coordinate and enlarge multiple K, axis of projection Y, two-value identifier flag, original least significant bit (LSB) data sequence lsb.
Step 3: the point sequence of determining to extract watermark.
With the axis of projection is reference orientation, and the point among the S0 is sorted from small to large according to coordinate data, obtains S1 as a result; Check S1, calculate its vertical range to axis of projection for the point that wherein coordinate is identical, keep the point with minor increment, reject remaining point, obtain S2 as a result, be the point sequence of watermark to be extracted, length is designated as N.
Step 4: the difference extended method extracts watermark and restore data.
With method same in the telescopiny point sequence is matched grouping in twos, to each point to coordinate through enlarging (formula (2), (3)) calculated difference d ' and average m (formula (4), (5)) respectively afterwards, extract each point then successively and the lowest bit position of difference d ' promptly obtained the watermark w ' that embeds.Respectively each point is calculated original difference to foundation following formula (13), formula (14) then:
Wherein, f is the mark among the corresponding flag, and l is data corresponding among the lsb.
Calculate the coordinate data after recovering according to formula (11), formula (12) then.
Step 5: the data behind output watermark and the saving/restoring.
1) according to rule parsing watermark w ', draws original watermark w (11000100110011111 ... 100111); After the reduction is original copyright information " Nanjing Normal University ".
2) will recover point sequence S2 afterwards is integrated among the total data S0;
3) recovered data S0 is saved to hard disk.
In the leaching process of watermark, preserve the embedding information and the original LSB data of getting off during according to embed watermark and not only can obtain watermark information, and can nondestructively recover the initial carrier data.Point is intensive more, and the correlativity of coordinate figure is strong more, and the error of introducing also will be more little.
In addition, for ordinate, embed with mode such as extraction and said method just the same.
3, test analysis.
Target of the present invention is to solve the problem that difference expansion reversible water mark technology can not be applied to GIS vector point data, and therefore test also mainly launches based on the reversible recovery of data aspect.Through the step that above-mentioned watermark extracting data are recovered, the data after being restored.Utilize the topological analysis of ArcGIS software that recovered data and raw data are carried out analytical review, the result shows entirely true, so this method has the ability of recovering raw data fully.In addition, the disturbance of data that algorithm is introduced is born jointly by two points, so the error that each point is born significantly reduces, and does not influence the availability of data.
To sum up analyze, the method applied in the present invention is expanded the reversible water mark technology with difference and is successfully applied to shape point diagram layer data, and simultaneously, this method is equally applicable to the GIS vector point data of other non-shape forms.
Claims (1)
1. the difference at shape point diagram layer data is expanded watermark embedding and extracting method, mainly comprises following process:
(1) watermark embed process:
Step 1: read GIS point diagram layer data, configuration embeds the parameter of algorithm, mainly contains trueness error tolerance limit, coordinate expansion multiple and key file and deposits the path, checks the legitimacy of input data and configuration parameter then;
Step 2: analyze above-mentioned point data, determine the axis of projection that telescopiny adopts according to following formula:
Y＝Ymax-(Ymax-Ymin)×1/2
Wherein Y represents the transverse projection axle, and Ymax is a maximum ordinate in the data point, and Ymin is a minimum ordinate in the data point; Sort from small to large according to the coordinate figure of data point on this axis of projection again,, then choose the point that the nearest point of this axis of projection of vertical range embeds as watermark before the projection for the identical overlapping point of coordinate; Thus, a point sequence that coordinate is unique and continuous on the formation axis of projection direction;
Step 3: the carrier that above-mentioned point sequence is embedded as watermark utilizes the difference expansion technique to embed reversible water mark, specifically adopts difference to expand twice mode and carries out, and promptly the coordinate difference of binary mode moves to left one; (a) at first with the data in step 2 pairing in twos successively, will be the coordinate x of decimal originally
0iBecome integer x
i, formula is as follows:
Wherein,
Expression rounds downwards, and K is that the coordinate in the step 1 enlarges multiple, and N is the number of watermark data point to be embedded;
(b) calculate the difference d and the integer mean value m of per two match point coordinate figures then;
(c) requiring with the corresponding data precision of GIS vector data is criterion again, and the following formula of d substitution is judged whether this group point is suitable for adopting difference extended mode embed watermark:
-2×R+1≤d≤2×R-2
Wherein, R is the trueness error tolerance limit, x
FrontAnd x
BackBe that this point is to x
iAnd x
I+1The front and back point coordinate; If d does not satisfy in above-mentioned three any one, then, adopt the mode embed watermark of replacing least significant bit (LSB) in order to increase the embedding capacity; Otherwise, adopt difference extended mode embed watermark; Simultaneously in telescopiny recording-related information so that recover raw data;
Step 4: preserve embed watermark point data afterwards, the relevant information that produces in the telescopiny is saved as key file;
(2) extract watermark and raw data rejuvenation:
Step 1: read the GIS point diagram layer data of watermark to be extracted, from key file, read the embedding correlation parameter, check the legitimacy of parameter;
Step 2: determine the axis of projection that watermark extraction process adopts according to the parameter that reads, sort from small to large according to the coordinate figure of point on this axis of projection again, for the identical overlapping point of coordinate, then choose the nearest point of this axis of projection of vertical range before the projection as the point that extracts watermark; Thus, form a point sequence that coordinate is unique and continuous on the axis of projection direction, be the carrier that extracts watermark;
Step 3: utilize the method in the above-mentioned watermark embed process step 3, point sequence is matched grouping earlier in twos, coordinate is through calculating the difference and the integer mean value of per two match point coordinate figures respectively after enlarging; Extract the lowest bit position of each point then successively, promptly obtain the watermark that embeds the coordinate difference; Respectively each is put calculating original difference again: recover coordinate data afterwards according to coordinate difference and integer mean value computation at last;
Step 4: the raw data after the saving/restoring, the watermark that output extracts.
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| CN105574803A (en) * | 2015-09-16 | 2016-05-11 | 湖南大学 | Reversible watermark method and watermark embedment and watermark extraction method of two-dimensional CAD engineering drawing |
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