CN111242825B

CN111242825B - Water depth feature-based ENC electronic nautical chart zero-watermarking method

Info

Publication number: CN111242825B
Application number: CN201911299047.1A
Authority: CN
Inventors: 彭认灿; 董箭; 陈阳; 贾帅东; 李彬彬
Original assignee: PLA Dalian Naval Academy
Current assignee: PLA Dalian Naval Academy
Priority date: 2019-12-17
Filing date: 2019-12-17
Publication date: 2022-09-23
Anticipated expiration: 2039-12-17
Also published as: CN111242825A

Abstract

The ENC electronic nautical chart zero-watermarking method based on the water depth features comprises a zero-watermarking structure and a zero-watermarking extraction inspection method, not only is certain data (space) disturbance caused to electronic nautical chart data by a reversible watermarking algorithm of space features overcome, but also the resistance of nondestructive watermarking algorithm precision reduction of attribute features is improved.

Description

Water depth feature-based ENC electronic nautical chart zero-watermarking method

Technical Field

The invention relates to the technical field of ocean mapping.

Background

The ENC electronic nautical chart zero-watermarking technology belongs to a digital watermarking technology in a special application range, and is widely applied to the fields of ENC electronic nautical chart copyright protection or content authentication and the like.

Currently, researches on a two-dimensional electronic chart digital watermarking algorithm mainly include a reversible watermarking algorithm based on spatial characteristics, a lossless watermarking algorithm based on attribute characteristics and a digital watermarking algorithm based on semantics. The reversible watermark algorithm based on the spatial characteristics is characterized in that an electronic chart is essentially evolved from discrete vector nodes through continuous change, embedding nodes of watermarks can be obtained through analyzing the evolution process of the chart, then embedding of the reversible watermark algorithm is achieved, the embedding process of the watermarks needs to be kept within a certain disturbance range in order to avoid causing overlarge data disturbance to the electronic chart, and similarity calculation is carried out on digital watermark information after the watermark information is successfully extracted. The lossless watermark algorithm based on the attribute characteristics adopts a zero-bit dynamic lossless watermark implementation method based on a gradient algorithm, uses a zero-bit expansion technology for watermark processing, is combined with an embedding point selection technology of a digital watermark gradient algorithm, and has better watermark invisibility and robustness. The digital watermarking algorithm based on the semantics, the use target of the semantic watermark is limited in a legal user, the propagation environment is controlled, on the basis, the authority of each user is limited, before map data is opened, the user can not launch direct attack on the semantic watermark, meanwhile, the semantic watermark adopts a redundant embedding mode, before a map is distributed, some redundant vertexes are embedded into the map, before the user uses the map, the authority watermark is extracted, the redundant vertexes are synchronously removed, and the normal use of the map is not interfered.

The three algorithms described above still have many disadvantages: a reversible watermark algorithm based on spatial characteristics causes a certain data (spatial) disturbance range to the electronic chart data; the lossless watermarking algorithm based on the attribute characteristics is difficult to add zero-bit watermarks into the ENC electronic nautical chart, because the unit used by the position in the S57 specification is latitude and longitude coordinates and is converted into an integer value through a multiplier factor COMF, and meanwhile, the precision reduction resistance, the format conversion resistance and the interpretation attack resistance are poor. The digital watermarking algorithm based on the semantics emphasizes the adoption of an image matching technology, the digital watermarking of wider semantic information needs to be researched, meanwhile, the chart updating ER is the most common operation, and the correctability of ENC chart data is insufficient. In terms of experimental environment, the three algorithms all use MapInfo software, and the main forming form of the electronic chart is an SHP file.

Disclosure of Invention

In order to overcome the defects of the three methods, the invention provides an ENC electronic nautical chart zero-watermark technology based on water depth characteristics.

The technical scheme adopted by the invention for realizing the purpose is as follows: a water depth feature-based ENC electronic nautical chart zero watermark method comprises a zero watermark construction method and comprises the following steps:

the method comprises the following steps: preprocessing the ENC electronic chart to obtain water depth data;

step two: constructing a Delaunay triangulation network for the water depth data constructing the zero watermark, extracting a slope characteristic line by utilizing water depth interpolation, and judging the slope characteristic between point pairs on the line according to the extracted characteristic line as a skeleton line so as to extract characteristic points;

step three: selecting a proper threshold value for the extracted feature points to carry out point constraint blocking, and then sequencing the water depth points in each block through ZigZag to further obtain a longitude and latitude coordinate binary sequence of the water depth points, and ensuring that the length of the coordinate binary sequence in each block is greater than that of the watermark sequence;

step four: performing Arnold scrambling on an original watermark image to obtain an encrypted watermark image, and performing grouping conversion to obtain a watermark sequence;

step five: carrying out bit-filling XOR operation on the longitude and latitude coordinate binary sequence and the watermark sequence to obtain a zero watermark image, namely a zero watermark; step six: storing the zero watermark image generated by each block and the original watermark image;

the zero watermark extracting and checking method comprises the following steps:

the method comprises the following steps: preprocessing an ENC electronic chart to be detected to obtain water depth data;

step two: constructing a Delaunay triangulation network for the water depth data, and further judging and extracting water depth feature points by extracting a slope characteristic line through water depth interpolation;

step three: performing point constraint blocking on the extracted feature points, and sequencing water depth points in each block through ZigZag to obtain a binary sequence of longitude and latitude coordinate of the water depth points;

step four: grouping and converting the watermark images to obtain a watermark sequence, performing complementary XOR operation on the longitude and latitude coordinate binary sequence and the watermark sequence, extracting a plurality of encrypted watermark images according to the size of the original watermark, and performing Arnold reverse scrambling to obtain a watermark image of data to be detected;

step five: comparing and verifying the extracted watermark images with the original watermark image, and measuring the similarity of the two images by using the normalized correlation coefficient NC value so as to judge the copyright ownership of the data to be detected.

In the third step of the zero watermark construction, the unit used by the position in the ENC electronic nautical chart is the decimal degree converted into an integer, the integer value of the converted coordinate is encoded by using a binary system, and the integer value before the precision effective bit is converted into the binary system.

In the fourth and fifth zero watermark construction steps, the watermark is encrypted by adopting an Arnold conversion mode, picture data Arnold with equal length and width are scrambled, and the Arnold conversion formula is as follows:

and N is the length and width of the picture, X and Y are the horizontal and vertical coordinates of one point on the original image, another point coordinate X 'and Y' is formed through transformation, the transformed image is subjected to binarization processing, and the binary sequence of the coordinates after the transformation and the binary sequence of the coordinates after the block division are subjected to complementary exclusive OR operation to obtain a zero watermark image.

In the fourth step of zero watermark extraction and inspection, when the extracted scrambled image is subjected to reduction processing, the inverse matrix of the forward substitution formula is obtained to obtain the inverse transformation formula of Arnold substitution, and the original image is formed directly through the inverse transformation formula, wherein the inverse transformation formula of Arnold transformation is as follows:

in the step five of zero watermark extraction and inspection, whether the watermark data has copyright authentication is judged by comparing the similarity value with a set threshold value, and the calculation formula of the similarity (NC) is as follows:

wherein W (i, j) represents the pixel value at (i, j) in the original watermark data, W' (i, j) represents the pixel value at (i, j) in the watermark data extracted from the vector chart, m, n represents the values of the row and column of the watermark picture data,

when NC is 1, the extracted watermark picture data is completely the same as the original watermark picture data, and the picture is not changed after being attacked; when the NC value is between 0 and 1, the closer to 1, the higher the data similarity is, and the watermark robustness is strong; conversely, the lower the similarity is, the less the watermark robustness is, wherein the NC value takes 0.7 as the threshold for identifying the watermark.

In the step five of zero watermark extraction and inspection, the comparison and verification are measured by the structural similarity SSIM, and the SSIM is as follows:

SSIM(W,W')＝l(W,W')c(W,W')s(W,W')#(4)

where W is the watermark image, W' is the extracted watermark image,

the closer the value of SSIM is to 1, the more similar the two images and the better the quality of the images can be said to be.

The ENC electronic nautical chart zero-watermarking method based on the water depth characteristics overcomes certain data (space) disturbance of a reversible watermarking algorithm of the space characteristics on electronic nautical chart data, and improves the resistance of approximately reducing the precision of a lossless watermarking algorithm of the attribute characteristics.

Drawings

FIG. 1 is a flow chart of the ENC electronic nautical chart zero watermark construction of the present invention.

FIG. 2 is a flow chart of ENC electronic nautical chart zero watermark extraction and inspection.

Fig. 3 is a schematic diagram of the operation platform of the SuperMap software.

Fig. 4(a) is a diagram of an original watermark.

Fig. 4(b) is a schematic diagram of the watermark after the watermark image Arnold is scrambled for 1 time.

Fig. 4(c) is a schematic diagram of the watermark after 2 times of Arnold scrambling of the watermark image.

Fig. 4(d) is a schematic diagram of the watermark after the watermark image Arnold is scrambled 10 times.

Fig. 4(e) is a schematic diagram of the watermark after the watermark image Arnold is scrambled for 20 times.

Fig. 4(f) is a schematic diagram of the watermark after the watermark image Arnold is scrambled for 30 times.

Detailed Description

The invention relates to a water depth feature-based ENC electronic nautical chart zero-watermark method, which comprises a zero-watermark structure and zero-watermark extraction inspection, wherein the zero-watermark structure is shown in figure 1 and comprises the following steps:

the method comprises the following steps: preprocessing the ENC electronic nautical chart through Supermap hyper-map software to obtain water depth data;

step two: the method comprises the steps of constructing a Delaunay triangulation network for water depth data with zero watermarks, extracting a slope characteristic line by utilizing water depth interpolation, judging slope characteristics between point pairs on the line according to the extracted characteristic line serving as a skeleton line, further extracting characteristic points, wherein the slope characteristic line is a concept line used for describing a water depth point slope relation tree and is a transition virtual connection line for providing judgment basis for characteristic shallow point extraction, and limiting conditions are that a threshold interval is selected for depth values of set water depth data, namely water depth data in a closed equal-depth area on a graph are taken as a class, so that influence of data outside the interval on data in the interval is avoided. After a triangulation network is constructed and a characteristic line is extracted, the characteristic line is used as a skeleton line of the submarine topography, and slope direction characteristics between point pairs on the line are judged, namely, a shallowest point and a relatively shallow point in water depth data are regarded as 'characteristic shallow points' to be extracted;

step three: selecting a proper threshold value for the extracted characteristic points to carry out point constraint blocking, sequencing the water depth points in each block by ZigZag to further obtain a longitude and latitude coordinate binary system sequence of the water depth points, ensuring that the length of the coordinate binary system sequence in each block is greater than that of a watermark sequence, converting the unit used by the position in the ENC electronic nautical chart into an integer decimal degree, coding the converted coordinate integer value by using the binary system, converting the integer value before the precision effective bit (after two bits are abandoned) into the binary system for resisting the reduction of precision, sequencing by ZigZag and recording the longitude and latitude binary system sequence in each block, ensuring that the length of the coordinate sequence in each block is greater than that of the watermark sequence, and enabling the longitude and latitude of a single water depth point to pass through a multiplier factor COMF (10) ⁷ ) Converting into integer, discarding last (two) bits and using binary coding within the precision allowable range;

step four: performing Arnold scrambling on an original watermark image to obtain an encrypted watermark image, performing grouping conversion to obtain a watermark sequence, and encrypting the watermark by using an Arnold conversion mode, as shown in FIG. 4;

step five: and carrying out bit-complementing XOR operation on the longitude and latitude coordinate binary sequence and the watermark sequence to obtain a zero watermark image, namely a zero watermark, and carrying out Arnold scrambling on picture data with the same length and width to simplify calculation. The Arnold transformation formula is:

n is the size of the length and the width of a picture, X and Y are the horizontal and vertical coordinates of one point on an original image, another point coordinate X 'and Y' is formed through transformation, the transformed image is subjected to binarization processing, and the binary sequence of the transformed image and a partitioned coordinate binary sequence are subjected to complementary exclusive-or operation to obtain a zero watermark image, wherein the larger N is, the larger the represented watermark information quantity is, the longer the cycle period T is, and the more users of the chart are mapped through scrambling times (secret keys);

step six: and storing the zero watermark image generated by each block and the original watermark image to a copyright protection center (IPR), and adding a time stamp with legal effectiveness to resist interpretation attack.

The zero watermark extraction test is shown in fig. 2 and comprises the following steps:

step four: grouping and converting watermark images to obtain a watermark sequence, performing complementary XOR operation on a longitude and latitude coordinate binary sequence and the watermark sequence, extracting a plurality of encrypted watermark images according to the size of an original watermark, performing Arnold inverse scrambling to obtain a watermark image of data to be detected, and recovering the original image by performing T-n iterations if the extracted scrambled image is subjected to n times of replacement, wherein obviously, the operation amount of the original image is too large by only depending on one forward formula, so that an inverse matrix is solved for the forward replacement formula to obtain an Arnold replacement inverse transformation formula, and the original image can be formed by directly performing n times of transformation through the inverse transformation formula, and the Arnold transformation inverse transformation formula is as follows:

step five: comparing and verifying a plurality of extracted watermark images with an original watermark image, measuring the similarity of the two images by using a Normalized correlation coefficient (NC) (Normalized correlation) value, further judging the copyright attribution of the data to be detected, detecting to test the robustness of the embedded digital watermark, calculating the Normalized correlation coefficient (NC) of the extracted watermark data and the original watermark data after performing geometric transformation (translation, rotation and scaling), map cutting, data deletion and addition on a vector chart, and comparing and judging whether the watermark data has copyright certification or not through the similarity value and a set threshold value. The calculation formula of the similarity (NC) is as follows:

when NC is 1, the extracted watermark picture data is completely the same as the original watermark picture data, and the picture is not changed after being attacked; when the NC value is between 0 and 1, the closer to 1, the higher the data similarity is, and the watermark robustness is strong; the lower the similarity, the less robust the watermark is. Where the NC value typically takes 0.7 as the threshold for identifying the watermark.

The comparison verification can also be measured by Structural Similarity (SSIM), which is defined as:

SSIM(W,W')＝l(W,W')c(W,W')s(W,W')#(4)

where W is the watermark image, W' is the extracted watermark image,

the closer the value of SSIM is to 1, the more similar the two images are and the better the quality of the images, generally speaking, the SSIM value is greater than 0.5, and one can accept the quality of the images.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A water depth feature-based ENC electronic nautical chart zero watermarking method is characterized by comprising the following steps: the method comprises a zero watermark construction method, and comprises the following steps:

step two: constructing a Delaunay triangulation network for the water depth data with the zero watermark, extracting a slope characteristic line by utilizing water depth interpolation, and judging the slope characteristic between point pairs on the line according to the extracted characteristic line as a skeleton line so as to extract characteristic points;

step five: carrying out bit-filling XOR operation on the longitude and latitude coordinate binary sequence and the watermark sequence to obtain a zero watermark image, namely a zero watermark;

step six: and storing the zero watermark image generated by each block and the original watermark image.

2. The ENC electronic nautical chart zero-watermarking method based on water depth features as claimed in claim 1, wherein: the zero watermark extracting and checking method comprises the following steps:

step four: performing grouping conversion on the watermark images to obtain a watermark sequence, performing complementary exclusive or operation on the longitude and latitude coordinate binary sequence and the watermark sequence, extracting a plurality of encrypted watermark images according to the size of the original watermark, and performing Arnold reverse scrambling to obtain a watermark image of the data to be detected;

step five: comparing and verifying the extracted watermark images with the original watermark image, measuring the similarity of the two images by using the normalized correlation coefficient NC value, and further judging the copyright attribution of the data to be detected.

3. The ENC electronic nautical chart zero-watermarking method based on water depth features as claimed in claim 1, wherein: in the third step of the zero watermark construction, the unit used by the position in the ENC electronic nautical chart is the decimal degree converted into an integer, the integer value of the converted coordinate is encoded by using a binary system, and the integer value before the precision effective bit is converted into the binary system.

4. The ENC electronic nautical chart zero-watermarking method based on water depth features as claimed in claim 1, characterized in that: in the fourth and fifth zero watermark construction steps, the watermark is encrypted by adopting an Arnold conversion mode, picture data Arnold with equal length and width are scrambled, and the Arnold conversion formula is as follows:

5. The ENC electronic nautical chart zero-watermarking method based on water depth features as claimed in claim 2, wherein: in the fourth step of zero watermark extraction and inspection, when the extracted scrambled image is subjected to reduction processing, the inverse matrix of the forward substitution formula is obtained to obtain the inverse transformation formula of Arnold substitution, and the original image is formed directly through the inverse transformation formula, wherein the inverse transformation formula of Arnold transformation is as follows:

6. the ENC electronic nautical chart zero-watermarking method based on water depth features as claimed in claim 2, wherein: in the step five of zero watermark extraction and inspection, whether the watermark data has copyright authentication is judged by comparing the similarity value with a set threshold value, and the calculation formula of the similarity (NC) is as follows:

when NC is 1, the extracted watermark picture data is completely the same as the original watermark picture data, and the picture is not changed after being attacked; when the NC value is between 0 and 1, the closer to 1, the higher the data similarity is, and the watermark robustness is strong; and conversely, the lower the similarity is, the lower the watermark robustness is, wherein the NC value is 0.7 as the threshold value for identifying the watermark.

7. The ENC electronic nautical chart zero-watermarking method based on water depth features as claimed in claim 2, wherein: in the step five of zero watermark extraction and inspection, the comparison and verification are measured by the structural similarity SSIM, and the SSIM is as follows:

SSIM(W,W')＝l(W,W')c(W,W')s(W,W')#(4)

where W is the watermark image, W' is the extracted watermark image,