CN113556440B - Line drawing map lossless data hiding and recovering method for dividing embedded area - Google Patents
Line drawing map lossless data hiding and recovering method for dividing embedded area Download PDFInfo
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Abstract
The invention discloses a line drawing map lossless data hiding and recovering method for dividing an embedded area, belongs to the technical field of information transmission, and can solve the problem that the whole embedded capacity of the existing line drawing map lossless data hiding method is limited. The method comprises the following steps: firstly, dividing geographic element units, calculating coordinate difference values through correlation of adjacent coordinates in the same unit, respectively counting frequency numbers of the coordinate difference values, and dividing a frequency distribution area into a combined area and a dispersed area by combining the characteristics of a line map. And then, determining the coordinate difference to be modified in the combined area by a method of selecting the frequency peak value, selecting the frequency peak value again in the scattered areas on the left side and the right side of the combined area, and hiding information by adopting a specific modification strategy. The extraction corresponds to the hiding process, and the line drawing map can be restored to the original state in a lossless manner after the extraction is finished. The invention is used for lossless data hiding and recovery.
Description
Technical Field
The invention relates to a line drawing map lossless data hiding and recovering method for dividing an embedded area, and belongs to the technical field of information transmission.
Background
The traditional data hiding is focused on the transmission of secret information, and the core aim is to send the secret information to a receiver in an invisible mode safely, so that the carrier is not focused after the secret information is transmitted successfully. And lossless data hiding is more focused on protecting a carrier, and secret information hidden in the carrier is mainly used for ownership certification, integrity authentication or hidden communication. For whatever application purpose, after the recipient has extracted the secret information, the carrier must be able to recover to the original state without loss, which means that not only the secret information is sent, but also a carrier with loss free recovery is available by means of a lossless data hiding technique. In the current research, most lossless data hiding belongs to the category of fragile watermarks, and the focus of the research is on how to restore an original carrier without distortion, so that the lossless property is a main concern of each algorithm, and not the robustness.
For a line drawing map which is widely applied to the fields of measurement, drawing and military and has extremely high requirements on data precision, not only the safety of embedded data needs to be ensured, but also the quality of the line drawing map itself needs to be ensured. In conventional data hiding techniques, however, the embedding of data inevitably causes disturbances to the carrier, and such changes to the carrier are permanent and unrecoverable even if the data has been successfully extracted. The lossless data hiding is an effective means for solving the bottleneck due to the technical characteristics, and has the core advantages that the disturbed carrier can be completely restored to the original state before embedding after data extraction on the premise of not being attacked, so that the purpose of no damage is achieved. In general, lossless data hiding is mainly applied to integrity authentication and covert communication, so invisibility, lossless, embedded capacity are main indicators for evaluating performance thereof.
The current line map lossless data hiding generally adopts lossless compression, difference expansion, iteration and quantization methods. However, some algorithms cause larger disturbance to the line map, and other algorithms need to store auxiliary information, so that the overall embedding capacity is limited.
Disclosure of Invention
The invention provides a line drawing map lossless data hiding and recovering method for dividing an embedded area, which can solve the problem that the whole embedded capacity of the existing line drawing map lossless data hiding method is limited.
In one aspect, the present invention provides a line map lossless data hiding method for dividing an embedded area, the method comprising:
step 11, dividing the line map into a plurality of non-overlapping geographic element units;
step 12, extracting the coordinates of all points in each geographic element unit, and separating the coordinates of all points into an integer part and a decimal part according to a preset numerical digit; subtracting the coordinates of integer parts of adjacent points in the same geographic element unit to form coordinate differences, counting the corresponding frequency of the coordinate differences, and dividing a combined area and a dispersed area according to frequency distribution;
step 13, obtaining the frequency sum of the coordinate differences in the combination area in a range of a preset modification level, and marking the coordinate difference with the largest frequency sum as the optimal point coordinate difference;
step 14, respectively obtaining a left frequency number maximum point and a left frequency number zero point closest to the left frequency number maximum point, and a right frequency number maximum point and a right frequency number zero point closest to the right frequency number maximum point in each dispersion area on the left side and the right side of the optimal point coordinate difference according to the frequency number of each coordinate difference;
step 15, updating each coordinate difference in the combined area according to the optimal point coordinate difference, the preset modification level and the data bit to be hidden and a first preset rule, and marking each updated coordinate difference as a first coordinate difference;
step 16, updating the first coordinate difference in the dispersion area according to a second preset rule according to the left frequency maximum point, the left frequency zero point, the right frequency maximum point, the right frequency zero point and the preset modification level, and recording each updated coordinate difference as a second coordinate difference;
and step 17, calculating the coordinates of each point in each geographic element unit in the line map according to the second coordinate difference.
Optionally, the first preset rule includes a first rule, a second rule and a third rule;
and updating each coordinate difference in the combined area according to the optimal point coordinate difference, the preset modification level and the data bit to be hidden and a first preset rule, wherein each updated coordinate difference is marked as a first coordinate difference, and the method specifically comprises the following steps of:
step 21, updating each coordinate difference in the combined area according to the first rule according to the optimal point coordinate difference and the preset modification level;
step 22, updating each coordinate difference in the combined area processed in step 21 according to the second rule according to the data bit to be hidden and the preset modification level;
step 23, repeatedly executing step 22, and subtracting 1 from the value of the preset modification level every time until the preset modification level is decremented to 0;
and step 24, updating each coordinate difference in the combined area processed in the step 21 according to a third rule and the data bit to be hidden and the optimal point coordinate difference, wherein each updated coordinate difference is recorded as a first coordinate difference.
Optionally, the first rule is:
will all be greater than a r The coordinate difference of +rank plus the integer rank+1;
will all be less than a r -the difference in coordinates of rank minus the integer rank;
all are positioned at a r +rank and a r The coordinate difference between the rank remains unchanged;
wherein a is r And as the optimal point coordinate difference, rank is the preset modification level.
Optionally, the second rule is:
if the coordinate difference is a r +rank, adding the value of the coordinate difference to an integer w+2×rank;
if the coordinate difference is a r -rank, then adding the value of the coordinate difference to an integer 1-w-2 x rank;
wherein a is r For the optimal point coordinate difference, rank is the preset modification level, and w is the data bit to be hidden.
Optionally, the third rule is:
if the coordinate difference is a r Then add it to w;
if the coordinate difference is not a r Its value remains unchanged;
wherein a is r For the optimal point coordinate difference, w is the data bit to be hidden.
Optionally, the second preset rule is:
if a is E (L) min -rank,L max -rank), its value is decremented by 1;
if a is E (R) max +rank+1,R min +rank+1), then add 1 to its value;
if a=l max -rank, then subtracting its value by w;
if a=r max +rank+1, then add w to its value;
if a does not meet the conditions, keeping the value unchanged;
wherein a is the first coordinate difference, L max L is the maximum point of the left frequency min For the left frequency zero point, R max R is the maximum point of the right frequency min And for the right frequency zero point, rank is the preset modification level, and w is the data bit to be hidden.
Optionally, the calculating coordinates of each point in each geographic element unit in the line map according to the second coordinate difference specifically includes:
calculating an integer part of each point coordinate after hiding the data according to the second coordinate difference;
and combining the integer part and the decimal part of each point coordinate to obtain the complete coordinates of each point in each geographic element unit in the line map.
Optionally, the calculating the integer part of the coordinates of each point after hiding the data according to the second coordinate difference specifically includes:
if the point is the first point in the geographic element unit, the value of the point coordinate is kept unchanged;
if the point is not the first point in the geographic element unit, subtracting a' from the value of the point coordinate;
wherein a' is the second coordinate difference.
Optionally, the step 11 specifically includes:
constructing a characteristic point of each geographic element unit;
the center point of the map data is marked by a whole line as a circle center, and the distance between the circle center and the farthest characteristic point is taken as a radius, so that a circular area is formed; dividing the circular area into different granularities from two dimensions of a central angle and a radius of the circular area;
the feature points in the same dividing region belong to the same geographic element unit, so that a plurality of geographic element units which are not overlapped with each other are formed.
In another aspect, the present invention provides a restoration method applied to any one of the above line map lossless data hiding methods for dividing an embedded area, the method including:
step 101, dividing a line drawing map to be detected into a plurality of non-overlapping geographic element units;
102, extracting coordinates of all points in each geographic element unit, and separating the coordinates of all points into an integer part and a decimal part according to a preset numerical digit; subtracting the coordinates of integer parts of adjacent points in the same geographic element unit to form a second coordinate difference a';
step 103, if a' e [ L ] min -rank,L max -rank-1]Then add 1 to its value;
if a' is E [ R ] max +rank+2,R min +rank+1]Then its value is decremented by 1;
if a' does not meet the condition, keeping the value unchanged;
the coordinate difference processed by the step 103 is recorded as a first coordinate difference a;
step 104, if a e (a) r +2×rank+1, ++ infinity a) of the above-mentioned components, then subtract (rank+1) from its value;
if a is E (- ≡a) r -2 x rank), then add rank to its value;
if a is E { a r +2u,a r +2u+1, then its value is replaced with u+a r Where u ε { rank, rank-1, …,0};
if a is E { a r -2u,a r -2u+1, then replace its value with a r -u, where u e { rank, rank-1, …,1};
step 105, if the point is the first point in the geographic element unit, the value of the point coordinate is kept unchanged;
if the point is not the first point in the geographic element unit, subtracting a first coordinate difference a from the value of the point coordinate; obtaining an integer part of each point coordinate;
step 106, combining the integer part and the decimal part of each point coordinate to obtain the complete coordinates of each point in each geographic element unit in the line drawing map;
step 107, if a' ∈ { a r +2×rank，a r -2 x rank+1, then the extracted data bit is 0;
if a' e { a r +2×rank+1，a r -2 x rank }, the extracted data bit is 1; extracting hidden data bits of the combined area step by step;
step 108, repeatedly executing step 107, and subtracting 1 from the value of the preset modification level every time until the preset modification level is decremented to 0;
step 109, if a' =a r The extracted data bit is 0;
if a' =a r +1, the extracted data bit is 1;
step 110, if a' e { L max -rank，R max +rank+1}, the extracted data bit is 0;
if a' is { L ∈ - max -rank-1，R max +rank+2}, the extracted data bit is 1; extracting hidden data bits of the scattered area;
step 111, performing steps 102 to 110 in each geographic element unit in a traversing manner, and sequentially connecting all the extracted data bits, so as to obtain the complete data hidden in the whole map and the line map after lossless recovery.
The invention has the beneficial effects that:
the line drawing map lossless data hiding method for dividing the embedded area provided by the invention can recover the carrier in a lossless manner after extracting the information to be hidden into the line drawing map, has higher embedding rate and good invisibility, and can be applied to multiple fields of line drawing map data security. Meanwhile, the disturbance of the invention to the carrier is obviously reduced; and the embedded capacity of lossless data hiding of the line map is improved as much as possible on the basis of keeping the data precision.
Drawings
FIG. 1 is a flowchart of a line map lossless data hiding method according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a construction of feature points of a geographic element according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a method for dividing geographic element units according to an embodiment of the present invention;
FIG. 4 is a schematic illustration of a scribe line provided by an embodiment of the present invention;
FIG. 5 is a diagram showing the experimental results of data accuracy provided by the embodiment of the invention;
fig. 6 is a diagram showing a relationship between modification level and embedding capacity according to an embodiment of the present invention.
Detailed Description
The present invention is described in detail below with reference to examples, but the present invention is not limited to these examples.
The embodiment of the invention provides a line map lossless data hiding method for dividing an embedded area, as shown in fig. 1, comprising the following steps:
and 11, dividing the line map into a plurality of non-overlapping geographic element units.
In order to effectively keep the integral characteristics of the line map data, firstly, dividing the geographic element units and dividing the whole line map into a plurality of geographic element units. To increase the hidden capacity, the data may be repeatedly embedded into different geographic element units. All the geographic element units together form the complete line map data, and the different geographic element units should not overlap each other. The data represents the complete line map data, and the unit represents the geographic element units, so that the relationship between the geographic element units is as follows:
s (s is more than or equal to 1) coordinate points are arranged on a certain geographic element unit, wherein the first coordinate point is (X) 1 ,Y 1 ) The last coordinate point is (X s ,Y s )，The minimum and maximum values of the X and y coordinates on the geographic element unit are respectively X min ,X max ,Y min ,Y max Let d=max (Y max -Y min ,X max -X min ) The geographic element unit division adopts the following method:
first, feature points (X f ,Y f ) To mark the approximate location of the geographic element, feature points (X f ,Y f ) The calculation formula of (2) depends on X min ,X max ,Y min ,Y max Referring to fig. 2:
if d=y max -Y min Then
If d=x max -X min Then
Secondly, grouping the characteristic points, namely taking a midpoint O of the map data of the whole line as a circle center, taking a distance R between the circle center and the farthest characteristic point as a radius to form a circular area, and dividing the circular area into different granularities from two dimensions of a central angle theta and a radius R according to different requirements of users as shown in fig. 3:
according to the formula (4), the central angle is divided into m parts averagely, and the radius is divided into n parts averagely:
the group to which each feature point belongs is a group to which the corresponding geographic element belongs, and each group is formed into an independent geographic element unit. Accordingly, the entire line map data can be divided into a plurality of non-overlapping geographic element units.
Step 12, extracting the coordinates of all points in each geographic element unit, and separating the coordinates of all points into an integer part and a decimal part according to a preset numerical digit; and subtracting the coordinates of the integral parts of adjacent points in the same geographic element unit to form coordinate differences, counting the corresponding frequency of the coordinate differences, and dividing a combined area and a dispersed area according to frequency distribution.
A map is composed of several geographic elements, each of which is composed of a series of coordinate points, and on a two-dimensional map, the coordinates of each coordinate point include x and y coordinates, so that the ith coordinate point can be expressed as V i (x i ,y i ). To facilitate calculation of the coordinate difference, the double-precision coordinates (x i ,y i ) Separating the integer and the decimal part, setting the t-th position after the separated integer part contains the original decimal point, and calculating according to a formula (5):
in the method, in the process of the invention,
to round down the function, the value of t should be located after the precision bit. The lossless data hiding algorithm provided herein is described by taking the x coordinate of the line map as an example, and the processing method of the y coordinate is the same as the lossless data hiding algorithm and is not repeated.
After the geographical element units are divided, the coordinates of adjacent points in the same unit have certain correlation, so that the coordinate differences are calculated by subtracting the adjacent coordinate points in the unit in sequence, and the frequency of the differences is counted respectively.
The level of iterative modification during data hiding is set as rank, rank is a positive integer, and the value of rank is related to hiding capacity and data precision of a line map. The larger the value is, the larger the hidden capacity is, but the larger the disturbance generated on the line map is; the smaller the value, the smaller the capacity that can be hidden, but the less disturbance to the line map. Dividing a distribution area of the frequency number into a combination area and a dispersion area according to the statistical result of the coordinate difference frequency number of the line map: for the coordinate difference with the frequency of h, if no frequency zero value appears in the range of the left and right rank, the region is a combined region; otherwise, if the frequency number zero value appears, the frequency number zero value is a scattered area.
And step 13, obtaining the frequency sum in the range of the preset modification level about each coordinate difference in the combination area, and recording the coordinate difference with the largest frequency sum as the optimal point coordinate difference.
Let us assume that the coordinate difference a in a certain combined area r Frequency of (2) is h r Calculating a r Sum of frequencies within left and right rank ranges:
Sum＝h r-rank +…+h r-1 +h r +h r+1 +…h r+rank (6)
sequentially calculating according to the above, selecting a combination region with the maximum Sum value from the combination regions, and obtaining a coordinate difference a in the region r The best point coordinate difference is obtained.
And 14, respectively acquiring a left frequency number maximum point and a left frequency number zero point closest to the left frequency number maximum point and a right frequency number zero point closest to the right frequency number maximum point in each dispersion area on the left side and the right side of the optimal point coordinate difference according to the frequency number of each coordinate difference.
Specifically, at the optimum point coordinate difference a r In each dispersing area on the left side, the frequency maximum point L is respectively selected according to the frequency of each coordinate difference value max And the frequency zero point L nearest to it min Similarly, the same operation is performed on the right side, and the two points selected correspondingly are designated as R max And R is min 。
And 15, updating each coordinate difference in the combined area according to the optimal point coordinate difference, a preset modification level and data bits to be hidden and a first preset rule, and marking each updated coordinate difference as a first coordinate difference. The first preset rule comprises a first rule, a second rule and a third rule;
step 15 specifically includes:
step 21, updating each coordinate difference in the combined area according to a first rule according to the optimal point coordinate difference and a preset modification level;
wherein, the first rule is:
will all be greater than a r The coordinate difference of +rank plus the integer rank+1;
will all be less than a r -the difference in coordinates of rank minus the integer rank;
all are positioned at a r +rank and a r The coordinate difference between the rank remains unchanged;
wherein a is r For the optimal point coordinate difference, rank is a preset modification level.
Step 22, updating each coordinate difference in the combined area processed in the step 21 according to a second rule according to the data bit to be hidden and a preset modification level;
wherein, the second rule is:
if the coordinate difference is a r +rank, the value of the coordinate difference is added with an integer w+2×rank;
if the coordinate difference is a r -rank, then the value of the coordinate difference is added to the integer 1-w-2 x rank;
wherein a is r For the optimal point coordinate difference, rank is a preset modification level, and w is a data bit to be hidden.
Step 23, repeatedly executing the step 22, and subtracting 1 from the value of the preset modification level every time until the preset modification level is decremented to 0;
step 24, updating each coordinate difference in the combined area processed in the step 21 according to a third rule and the data bit to be hidden and the optimal point coordinate difference, and marking each updated coordinate difference as a first coordinate difference a;
wherein, the third rule is:
if the coordinate difference is a r Then add it to w;
if the coordinate difference is not a r Its value remains unchanged;
wherein a is r For the optimal point coordinate difference, w is the data bit to be hidden.
And step 16, updating the first coordinate difference in the dispersion area according to a second preset rule according to the left frequency maximum point, the left frequency zero point, the right frequency maximum point, the right frequency zero point and the preset modification level, and marking each updated coordinate difference as a second coordinate difference a'.
The second preset rule is as follows:
if a is E (L) min -rank,L max -rank), its value is decremented by 1;
if a is E (R) max +rank+1,R min +rank+1), then add 1 to its value;
if a=l max -rank, then subtracting its value by w;
if a=r max +rank+1, then add w to its value;
if a does not meet the conditions, keeping the value unchanged;
wherein a is a first coordinate difference, L max Is the maximum point of left frequency, L min For the left frequency zero point, R max R is the maximum point of the right frequency min For the right frequency zero, rank is a preset modification level, and w is a data bit to be hidden.
And 17, calculating the coordinates of each point in each geographic element unit in the line map according to the second coordinate difference.
The method specifically comprises the following steps:
calculating an integer part of each point coordinate after hiding the data according to the second coordinate difference;
if the point is the first point in the geographic element unit, the value of the point coordinate is kept unchanged; if the point is not the first point in the geographic element unit, subtracting a' from the value of the point coordinate; a' is the second coordinate difference.
And combining the integer part and the decimal part of each point coordinate to obtain the complete coordinates of each point in each geographic element unit in the line map.
The point coordinates are x coordinates or y coordinates; and performing the same operation on the y coordinate and the x coordinate to finally obtain the complete coordinates of each point in each geographic element unit in the line map.
In summary, the general idea of the invention is as follows: firstly, dividing geographic element units, calculating coordinate difference values through correlation of adjacent coordinates in the same unit, respectively counting frequency numbers of the coordinate difference values, and dividing a frequency distribution area into a combined area and a dispersed area by combining the characteristics of a line map. And then, determining the coordinate difference to be modified in the combined area by a method of selecting the frequency peak value, selecting the frequency peak value again in the scattered areas on the left side and the right side of the combined area, and hiding information by adopting a specific modification strategy. The extraction corresponds to the hiding process, and the line drawing map can be restored to the original state in a lossless manner after the extraction is finished. According to the invention, the information to be hidden is embedded into the line drawing map, and the carrier can be recovered after extraction without damage, so that the line drawing map has high embedding rate and good invisibility, and can be applied to multiple fields of line drawing map data security. Meanwhile, the disturbance of the invention to the carrier is obviously reduced; and the embedded capacity of lossless data hiding of the line map is improved as much as possible on the basis of keeping the data precision.
Another embodiment of the present invention provides a restoration method applied to any one of the above line map lossless data hiding methods for dividing an embedded area, the method including:
step 101, dividing a line drawing map to be detected into a plurality of non-overlapping geographic element units;
102, extracting coordinates of all points in each geographic element unit, and separating the coordinates of all points into an integer part and a decimal part according to a preset numerical digit; subtracting the coordinates of integer parts of adjacent points in the same geographic element unit to form a second coordinate difference a';
step 103, recovering the value of a' by case-by-case processing;
if a' is E [ L ] min -rank,L max -rank-1]Then add 1 to its value;
if a' is E [ R ] max +rank+2,R min +rank+1]Then its value is decremented by 1;
if a' does not meet the condition, keeping the value unchanged;
the coordinate difference processed by the step 103 is recorded as a first coordinate difference a;
104, continuing to recover the first coordinate difference a;
if a is E (a) r +2×rank+1, ++ infinity a) of the above-mentioned components, then subtract (rank+1) from its value;
if a is E (- ≡a) r -2 x rank), then add rank to its value;
if a is E { a r +2u,a r +2u+1, then its value is replaced with u+a r Where u ε { rank, rank-1, …,0};
if a is E { a r -2u,a r -2u+1, then replace its value with a r -u, where u e { rank, rank-1, …,1};
the processed coordinate differences through this step have been restored to the original differences when the data was not hidden.
Step 105, calculating and recovering integer parts of coordinates of each point one by one;
if the point is the first point in the geographic element unit, the value of the point coordinate is kept unchanged;
if the point is not the first point in the geographic element unit, subtracting a first coordinate difference a from the value of the point coordinate; obtaining an integer part of each point coordinate;
step 106, combining the integer part and the decimal part of each point coordinate to obtain the complete coordinates of each point in each geographic element unit in the line map;
step 107, extracting hidden data bits of the combined area step by step according to conditions;
if a' e { a r +2×rank，a r -2 x rank+1, then the extracted data bit is 0;
if a' e { a r +2×rank+1，a r -2 x rank }, the extracted data bit is 1;
step 108, repeatedly executing step 107, and subtracting 1 from the value of the preset modification level rank every time until the preset modification level rank is decremented to 0;
step 109, when the rank value is 0;
if a' =a r The extracted data bit is 0;
if a' =a r +1, the extracted data bit is 1;
step 110, extracting hidden data bits of the scattered area in case of occurrence;
if a' is { L ∈ - max -rank，R max +rank+1}, the extracted data bit is 0;
if a' is { L ∈ - max -rank-1，R max +rank+2}, the extracted data bit is 1;
step 111, performing steps 102 to 110 in each geographic element unit in a traversing manner, and sequentially connecting all the extracted data bits, so as to obtain the complete data hidden in the whole map and the line map after lossless recovery.
In order to verify the performance of the designed lossless data hiding algorithm, a Matlab simulation platform is adopted on a Windows 10 operating system to carry out a series of experiments. The simulation experiment is carried out by adopting more than 100 line drawing maps with different scales and different element types, and the performance of the method is comprehensively evaluated from the aspects of data precision, lossless recovery, hidden capacity and the like. Two exemplary data are selected for the present invention and are shown in detail in fig. 4.
In the line map for experiments, the scale of road data is 1:100000, the error margin is 10 meters, the number of geographic elements is 632, and the total number of coordinate points is 19123; the scale of the residential data is 1:50000, the error margin is 5 meters, the number of geographic elements is 716, and the total number of coordinate points is 8109.
The line map lossless data hiding method must meet the requirement of data precision. The resident data is taken as a carrier to hide the data according to the proposed method, and the local enlarged areas of the map of the line drawing before and after hiding are compared, and the experimental result is shown in figure 5. Therefore, the difference of the contour map before and after embedding can not be perceived from subjective vision of human eyes, the existence of hidden data can not be perceived from the difference, and the method well keeps the data precision of the line map. Objectively analyzing, the maximum change of the carrier data by the proposed method is (rank+2) ×10 -t And errors caused to the carrier coordinates are all behind the precision bits, so that normal use of the line map data is not affected, and the algorithm maintains good data precision.
The lossless data hiding technology requires that the carrier can be recovered in a lossless manner after the extraction is finished, as long as the root mean square error of the recovered coordinates and the original coordinatesAt 10 -13 Hereinafter, both can be regarded as lossless recovery. In order to verify the lossless of the algorithm, the rounding bit t is set as a fixed value 6, different iteration modification levels rank are selected, the corresponding processed line map is subjected to lossless recovery, the root mean square error between the line map and the original data is calculated, and the experimental result is shown in fig. 6: as can be seen from fig. 6, the root mean square error of the recovered data and the original data is maintained at 10 -17 The magnitude of the magnitude is that the line drawing map after the hidden data is extracted can be restored to the original state, so that the proposed algorithm is completely lossless and can meet the high requirement of the line drawing map on data restoration.
The embedding capacity is the maximum data amount which can be hidden in the whole carrier line map, and is an important standard for evaluating the performance of a lossless hiding algorithm. The embedding capacity of the lossless data hiding method based on the coordinate difference modification is the sum of the embedding quantity of the combined area and the embedding quantity of the scattered area in all geographic element units. For a certain geographic element unit, let L thereof max Frequency of (2) is h L ，R max Frequency of (2) is h R From this, it can be deduced that in the geographic element unit, the embedding capacity Cap (bits) is:
Cap＝(h L +h R )+(h r-rank +…+h r-1 +h r +h r+1 +…h r+rank ) (7)
as can be seen from equation (7), the embedding capacity of the algorithm in a specific geographic element unit is determined by two aspects: the first is the level rank of iterative modification when the data is hidden; and secondly, the maximum value of the difference frequency of the coordinates of the scattered area. Which in turn depends on the correlation between adjacent coordinates in the same line map. Setting the number of divided geographic element units as 50, and testing the embedding capacity (bits) of the whole line map under different rank values by the 5 th bit after the integer part of the x and y coordinates after separation processing contains the original decimal point, wherein the experimental results are shown in table 1:
table 1 relationship between embedding capacity and iterative modification level
Therefore, the embedding capacity of the whole line map is positively correlated with the iterative modification level under the condition that the number of the geographic element units and the x and y coordinates are unchanged, namely the embedding capacity is increased along with the increase of the iterative modification level.
Setting the number of divided geographic element units as 50, the rank value as 3, testing the relation between the integer bit and the embedded capacity (bits) in the x and y coordinate separation processing, and the experimental results are shown in table 2:
TABLE 2 Embedded Capacity versus separation processing taking integer bits
It can be shown that the embedding capacity of the whole line map and the integer number of the x and y coordinates are inversely related under the condition that the number of the geographic element units and the iterative modification level are unchanged, namely the embedding capacity is reduced along with the increase of the integer number of the x and y coordinates after separation processing.
To test the relation between the embedding capacity of the whole line map and the number of the divided geographic element units, setting the 5 th bit after the integer part of the x and y coordinates after separation processing contains the original decimal point, wherein the rank value is 3, and the experimental result is shown in table 3:
TABLE 3 Embedded Capacity vs. number of geographic element units
It can be shown that the embedding capacity of the whole line map and the number of divided geographic element units show positive correlation under the condition that the iterative modification level and the integer number of x and y coordinates are unchanged, namely the embedding capacity is increased along with the increase of the number of divided geographic element units.
The foregoing description is only a few examples of the present application and is not intended to limit the present application in any way, and although the present application is disclosed in the preferred examples, it is not intended to limit the present application, and any person skilled in the art may make some changes or modifications to the disclosed technology without departing from the scope of the technical solution of the present application, and the technical solution is equivalent to the equivalent embodiments.
Claims (10)
1. A line map lossless data hiding method for dividing an embedded area, the method comprising:
step 11, dividing the line map into a plurality of non-overlapping geographic element units;
step 12, extracting the coordinates of all points in each geographic element unit, and separating the coordinates of all points into an integer part and a decimal part according to a preset numerical digit; subtracting the coordinates of integer parts of adjacent points in the same geographic element unit to form coordinate differences, counting the corresponding frequency of the coordinate differences, and dividing a combined area and a dispersed area according to frequency distribution;
step 13, obtaining the frequency sum of the coordinate differences in the combination area in a range of a preset modification level, and marking the coordinate difference with the largest frequency sum as the optimal point coordinate difference;
step 14, respectively obtaining a left frequency number maximum point and a left frequency number zero point closest to the left frequency number maximum point, and a right frequency number maximum point and a right frequency number zero point closest to the right frequency number maximum point in each dispersion area on the left side and the right side of the optimal point coordinate difference according to the frequency number of each coordinate difference;
step 15, updating each coordinate difference in the combined area according to the optimal point coordinate difference, the preset modification level and the data bit to be hidden and a first preset rule, and marking each updated coordinate difference as a first coordinate difference;
step 16, updating the first coordinate difference in the dispersion area according to a second preset rule according to the left frequency maximum point, the left frequency zero point, the right frequency maximum point, the right frequency zero point and the preset modification level, and recording each updated coordinate difference as a second coordinate difference;
and step 17, calculating the coordinates of each point in each geographic element unit in the line map according to the second coordinate difference.
2. The method of claim 1, wherein the first preset rule comprises a first rule, a second rule, and a third rule;
and updating each coordinate difference in the combined area according to the optimal point coordinate difference, the preset modification level and the data bit to be hidden and a first preset rule, wherein each updated coordinate difference is marked as a first coordinate difference, and the method specifically comprises the following steps of:
step 21, updating each coordinate difference in the combined area according to the first rule according to the optimal point coordinate difference and the preset modification level;
step 22, updating each coordinate difference in the combined area processed in step 21 according to the second rule according to the data bit to be hidden and the preset modification level;
step 23, repeatedly executing step 22, and subtracting 1 from the value of the preset modification level every time until the preset modification level is decremented to 0;
and step 24, updating each coordinate difference in the combined area processed in the step 21 according to a third rule and the data bit to be hidden and the optimal point coordinate difference, wherein each updated coordinate difference is recorded as a first coordinate difference.
3. The method of claim 2, wherein the first rule is:
will all be greater than a r The coordinate difference of +rank plus the integer rank+1;
will all be less than a r -the difference in coordinates of rank minus the integer rank;
all are positioned at a r +rank and a r The coordinate difference between the rank remains unchanged;
wherein a is r And as the optimal point coordinate difference, rank is the preset modification level.
4. A method according to claim 3, wherein the second rule is:
if the coordinate difference is a r +rank, adding the value of the coordinate difference to an integer w+2×rank;
if the coordinate difference is a r -rank, then adding the value of the coordinate difference to an integer 1-w-2 x rank;
wherein a is r For the optimal point coordinate difference, rank is the preset modification level, and w is the data bit to be hidden.
5. The method of claim 4, wherein the third rule is:
if the coordinate difference is a r Then add it to w;
if the coordinate difference is not a r Its value remains unchanged;
wherein a is r For the optimal point coordinate difference, w is the data bit to be hidden.
6. The method of claim 5, wherein the second preset rule is:
if a is E (L) min -rank,L max -rank), its value is decremented by 1;
if a is E (R) max +rank+1,R min +rank+1), then add 1 to its value;
if a=l max -rank, then subtracting its value by w;
if a=r max +rank+1, then add w to its value;
if a does not meet the conditions, keeping the value unchanged;
wherein a is the first coordinate difference, L max L is the maximum point of the left frequency min For the left frequency zero point, R max R is the maximum point of the right frequency min And for the right frequency zero point, rank is the preset modification level, and w is the data bit to be hidden.
7. The method according to claim 1 or 6, wherein calculating coordinates of each point in each geographic element unit in the scribe map according to the second coordinate difference specifically includes:
calculating an integer part of each point coordinate after hiding the data according to the second coordinate difference;
and combining the integer part and the decimal part of each point coordinate to obtain the complete coordinates of each point in each geographic element unit in the line map.
8. The method according to claim 7, wherein calculating the integer part of the coordinates of each point after hiding the data according to the second coordinate difference specifically includes:
if the point is the first point in the geographic element unit, the value of the point coordinate is kept unchanged;
if the point is not the first point in the geographic element unit, subtracting a' from the value of the point coordinate;
wherein a' is the second coordinate difference.
9. The method according to claim 1, wherein the step 11 specifically comprises:
constructing a characteristic point of each geographic element unit;
the center point of the map data is marked by a whole line as a circle center, and the distance between the circle center and the farthest characteristic point is taken as a radius, so that a circular area is formed; dividing the circular area into different granularities from two dimensions of a central angle and a radius of the circular area;
the feature points in the same dividing region belong to the same geographic element unit, so that a plurality of geographic element units which are not overlapped with each other are formed.
10. A restoration method applied to the line map lossless data hiding method dividing an embedded area as claimed in any one of claims 6 to 9, characterized by comprising:
step 101, dividing a line drawing map to be detected into a plurality of non-overlapping geographic element units;
102, extracting coordinates of all points in each geographic element unit, and separating the coordinates of all points into an integer part and a decimal part according to a preset numerical digit; subtracting the coordinates of integer parts of adjacent points in the same geographic element unit to form a second coordinate difference a';
step 103, if a' e [ L ] min -rank,L max -rank-1]Then add 1 to its value;
if a' is E [ R ] max +rank+2,R min +rank+1]Then its value is decremented by 1;
if a' does not meet the condition, keeping the value unchanged;
the coordinate difference processed by the step 103 is recorded as a first coordinate difference a;
step 104, if a e (a) r +2×rank+1, ++ infinity a) of the above-mentioned components, then subtract (rank+1) from its value;
if a is E (- ≡a) r -2 x rank), then add rank to its value;
if a is E { a r +2u,a r +2u+1, then its value is replaced with u+a r Where u ε { rank, rank-1, …,0};
if a is E { a r -2u,a r -2u+1, then replace its value with a r -u, where u e { rank, rank-1, …,1};
step 105, if the point is the first point in the geographic element unit, the value of the point coordinate is kept unchanged;
if the point is not the first point in the geographic element unit, subtracting a first coordinate difference a from the value of the point coordinate; obtaining an integer part of each point coordinate;
step 106, combining the integer part and the decimal part of each point coordinate to obtain the complete coordinates of each point in each geographic element unit in the line drawing map;
step 107, if a' ∈ { a r +2×rank，a r -2 x rank+1, then the extracted data bit is 0;
if a' e { a r +2×rank+1，a r -2 x rank }, the extracted data bit is 1;extracting hidden data bits of the combined area step by step;
step 108, repeatedly executing step 107, and subtracting 1 from the value of the preset modification level every time until the preset modification level is decremented to 0;
step 109, if a' =a r The extracted data bit is 0;
if a' =a r +1, the extracted data bit is 1;
step 110, if a' e { L max -rank，R max +rank+1}, the extracted data bit is 0;
if a' is { L ∈ - max -rank-1，R max +rank+2}, the extracted data bit is 1; extracting hidden data bits of the scattered area;
step 111, performing steps 102 to 110 in each geographic element unit in a traversing manner, and sequentially connecting all the extracted data bits, so as to obtain the complete data hidden in the whole map and the line map after lossless recovery.
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