Sea chart image watermark embedding method and system based on contourlet transformation

Abstract

The invention relates to a nautical chart image watermark embedding method and system based on contourlet transformation, and the method considers the complex content of a nautical chart image, the region usually comprises symbols or lines, and the nautical chart image has a large direction coefficient after contourlet transformation. Firstly, a proper watermark embedding area is selected based on direction coefficient energy of contourlet transformation, a to-be-embedded sea chart image is segmented into a plurality of sub-blocks, and whether watermark embedding is suitable is determined through content complexity. And then, for the selected embedding area, watermark embedding is realized by adopting a splicing embedding strategy based on a direction mask, and blind extraction of the watermark is ensured. According to the method, a splicing implementation mode is determined according to the direction of the maximum coefficient energy of the current to-be-embedded sub-block, so that the splicing implementation mode conforms to the direction of the maximum energy, and watermark embedding is inconspicuous as far as possible and has better robustness.

Description

Technical Field

[0001] The present invention relates to the technical field of image watermarking, and in particular to a method and system for embedding watermarks in nautical chart images based on contourlet transform. Background Art

[0002] Digital image watermarking technology helps identify the ownership of images and prevent unauthorized use of images by embedding invisible information in them. However, most current watermarking methods are mainly designed for natural images, and are usually based on the processing of image texture and color to achieve the concealment and robustness of watermarks. However, since nautical chart images are usually composed of highly abstract graphic features such as symbols, lines, and regions, which are significantly different from natural images (such as landscapes, figures, etc.), such watermarking methods are difficult to adapt to their specific structures, often resulting in visible visual loss of watermark information embedding, or becoming less robust under common processing such as image compression. Therefore, it is urgent to develop watermarking technology specifically for nautical chart images to enhance their security and protect the legitimacy of nautical chart information.

[0003] In recent years, the copyright protection of nautical charts has gradually received attention. The existing electronic nautical chart watermarking technologies mainly include: 1. Considering the high quality of electronic nautical charts, Chen Yang et al. proposed to use a zero watermark method to protect the copyright of electronic nautical charts, which is robust to common distortions. For details, see the paper "A Study on Zero Watermark of Electronic Navigation Charts Supporting Tampering Positioning", Bulletin of Surveying and Mapping, Issue 10, 2020 and the paper "Zero Watermark Algorithm for Angle Construction of Feature Points of Electronic Navigation Charts", Surveying and Mapping Science, Issue 11, 2021; 2. In the study of modified electronic chart watermarks, Peng Rencan et al. proposed a dual watermarking method for vector charts, which has strong robustness. For details, see the paper "Research on a Dual Watermarking Technology for Vector Charts", Marine Surveying and Mapping, Issue 06, 2019.

[0004] However, the above-mentioned electronic chart watermarking method is mainly designed based on the high precision and vector characteristics of electronic chart files, and is also not applicable to digital chart images.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The present invention proposes a method and system for embedding watermarks in nautical chart images based on contourlet transform, which improves the watermark embedding and extraction performance of nautical chart images through the superior feature extraction capability of contourlet transform, significantly improves the concealment of watermarks in nautical chart images and has good robustness.

[0007] In a first aspect, the present invention proposes a method for embedding watermarks in a nautical chart image based on contourlet transform, comprising: S101. A color chart image is preset as a carrier image I0, the carrier image I0 is converted from an RGB format to a YCbCr format, and the Y channel in the YCbCr format is used as a grayscale component Y0 of the carrier image I0, and the grayscale component Y0 of the carrier image I0 is divided into N non-overlapping sub-blocks B; S102. Preset watermark information M, which is a 0, 1 bit sequence with a length of L, where M = {M1, M2, ..., M i , ..., M L}; S103. Perform non-subsampled contourlet transform on each of the N non-overlapping sub-blocks B, set the decomposition parameter to n, and obtain a coefficient set C of the N non-overlapping sub-blocks B, wherein the coefficient set C of the N non-overlapping sub-blocks B consists of a low-frequency coefficient C0 and 2^n directional coefficients Composition, where j = 1, 2, ..., 2^n; S104. Calculate the directional subband of the maximum energy of each sub-block in the N non-overlapping sub-blocks B in, S105. Traverse the N non-overlapping sub-blocks B, and select the sub-block B with the largest directional sub-band energy among the N non-overlapping sub-blocks B. i As the embedding carrier of the watermark information M, the sub-block B1={B1, B2, . . . , B i , ..., B L}; S106. For the carrier sub-block B i Implement non-subsampled contourlet transform to obtain the carrier sub-block B i The maximum energy direction subband and other sub-bands C else , where the carrier sub-block B i Other sub-bands of C else Including low frequency coefficient C 0,i and the directivity j=1,2,……,2^n and j≠Max; S107. Calculate the carrier sub-block B i The direction of the maximum energy subband The mask matrix Mask, wherein the mask matrix Mask is a subband with the same size as the maximum energy direction The same, and along the maximum energy direction subband The corresponding direction is divided into two regions of the matrix, one side is 0 and the other side is 1; S108. Calculate the maximum energy direction subband divided by the mask matrix Mask The energy P1, P0, and the difference D between P1 and P0 on the patchwork area are specifically: D=P1-P0 Wherein, P1 represents the energy of the area where one side of the mask matrix Mask is 1, and P0 represents the energy of the area where one side of the mask matrix Mask is 0; S109. Based on the watermark embedding strength parameter s and the watermark information M, the i-th watermark bit M i , for the carrier sub-block B i The maximum energy direction subband Modify to obtain the carrier sub-block B i Directional subband after watermarking Specifically include: a. When M i =1 and D<s or when M i =0 and D>-s, △=(sD) / 2 P′1=P1+Δ P′0=P0-Δ Where △ is the i-th watermark bit Mi of the watermark information M 的 The watermark modification amount, P'1 is the energy modification amount of the area where one side of the mask matrix Mask is 1, and P'0 is the energy modification amount of the area where one side of the mask matrix Mask is 0. and is the i-th watermark bit M of the watermark information M i Embed the carrier sub-block B i The posterior directional subband; b. In other cases, no Modify and directly make the directional subband after embedding the watermark S110. By i Directional subband after watermarking and the carrier sub-block B i Other sub-bands of C else Implement the non-subsampled contourlet inverse transform to obtain the carrier sub-block B i Watermark sub-block S111. Repeat S109-S110, and convert the L watermark bits M in the watermark information M into i Embedded into L of the carrier sub-blocks B i In the above example, L carrier sub-blocks B are obtained. i Watermark sub-block remember S112. The L carrier sub-blocks B in the grayscale component Y0 of the carrier image I0 are i Replaced by L watermark sub-blocks Get the grayscale component Y of the carrier image I0 after embedding the watermark W ; S113. embedding the grayscale component Y of the carrier image I0 into the watermark W Combined with the CbCr format of the carrier image I0 and converted back to RGB format, the watermarked chart image I of the carrier image I0 is obtained. W .

[0008] In a second aspect, the present invention proposes a nautical chart image watermark embedding system based on contourlet transform, which adopts the nautical chart image watermark embedding method based on contourlet transform as described in the first aspect, comprising: Carrier image processing module D21: presets a color chart image as a carrier image I0, converts the carrier image I0 from an RGB format to a YCbCr format, uses the Y channel in the YCbCr format as the grayscale component Y0 of the carrier image I0, and divides the grayscale component Y0 of the carrier image I0 into N non-overlapping sub-blocks B; Watermark information processing module D22: preset watermark information M, the watermark information M is a string of 0, 1 bit sequence with a length of L, denoted by M = {M1, M2, ..., M i , ..., M L}; The maximum energy directional sub-calculation module D23: performs non-subsampled contourlet transform on each of the N non-overlapping sub-blocks B, sets the decomposition parameter to n, and obtains a coefficient set C of the N non-overlapping sub-blocks B, wherein the coefficient set C of the N non-overlapping sub-blocks B consists of a low-frequency coefficient C0 and 2^n directional coefficients , wherein j = 1, 2, ..., 2^n; calculating the directional subband of the maximum energy of each sub-block in the N non-overlapping sub-blocks B in, Watermark information embedding carrier selection module D24: traverse the N non-overlapping sub-blocks B, and select the sub-block B with the largest directional sub-band energy among the N non-overlapping sub-blocks B. i As the embedding carrier of the watermark information M, the sub-block B1={B1, B2, . . . , B i , ..., B L}; Watermark information embedding module D25: embeds the carrier sub-block B iImplement non-subsampled contourlet transform to obtain the carrier sub-block B i The maximum energy direction subband and other sub-bands C else ; Calculate the carrier sub-block B i The direction of the maximum energy subband The mask matrix Mask, wherein the mask matrix Mask is a subband with the same size as the maximum energy direction The same, and along the maximum energy direction subband The corresponding direction is divided into a matrix with one side being 0 and the other side being 1 in two regions; Calculate the maximum energy direction subband divided by the mask matrix Mask The energy P1, P0 on the patchwork area, and the difference D between P1 and P0; according to the watermark embedding strength parameter s and the i-th watermark bit M of the watermark information M i , for the carrier sub-block B i The maximum energy direction subband Modify to obtain the carrier sub-block B i Directional subband after watermarking By the carrier sub-block B i Directional subband after watermarking and the carrier sub-block B i Other sub-bands of C else Implement the non-subsampled contourlet inverse transform to obtain the carrier sub-block B i Watermark sub-block Repeat the above steps to convert the L watermark bits M in the watermark information M into i Embedded into L of the carrier sub-blocks B i In the above example, L carrier sub-blocks B are obtained. i Watermark sub-block remember The watermarked chart image acquisition module D26: the L carrier sub-blocks B in the grayscale component Y0 of the carrier image I0 are i Replaced by L watermark sub-blocks Get the grayscale component Y of the carrier image I0 after embedding the watermark W ; Embed the gray component Y of the carrier image I0 after the watermark W Combined with the CbCr format of the carrier image I0 and converted back to RGB format, the watermarked chart image I of the carrier image I0 is obtained. W .

[0009] In a third aspect, the present invention proposes a method for extracting watermarks from a nautical chart image based on contourlet transform, which adopts the method for embedding watermarks from a nautical chart image based on contourlet transform as described in the first aspect, comprising: S201. The color chart image is preset as a carrier image I0, and the carrier image I0 contains watermark information M, wherein the watermark information M is composed of L embedded watermark sub-blocks. Composition, where i = {1, 2, ..., L}; S202. For the L watermarked sub-blocks Each watermark sub-block Implement non-subsampled contourlet transform to obtain the watermark sub-block The direction of the maximum energy subband S203. Based on the watermark sub-block The direction of the maximum energy subband By formula Get L watermark bits M in the watermark information M i ; S204. Combine the L watermark bits M in the watermark information M. i , for the L watermark bits M i The watermark information M is obtained by decoding.

[0010] In a fourth aspect, the present invention provides a system for extracting watermarks from nautical chart images based on contourlet transform, which uses a method for extracting watermarks from nautical chart images based on contourlet transform as described in the third aspect, comprising: Carrier image acquisition module D31: Assume that the color chart image is carrier image I0, and the carrier image I0 contains watermark information M, wherein the watermark information M is composed of L embedded watermark sub-blocks. composition; Maximum energy direction sub-calculation module D32: for the L watermarked sub-blocks Each watermark sub-block Implement non-subsampled contourlet transform to obtain the watermark sub-block The direction of the maximum energy subband Watermark bit extraction module D33: according to the watermark embedded sub-block The direction of the maximum energy subband Calculate and obtain L watermark bits M in the watermark information M i ; Watermark information embedding acquisition module D34: combining L watermark bits M in the watermark information M i , for the L watermark bits M i The watermark information M is obtained by decoding.

[0011] In a fifth aspect, the present invention proposes a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for embedding watermarks in nautical chart images based on contourlet transform as described above.

[0012] In a sixth aspect, the present invention proposes an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method for embedding watermarks in nautical chart images based on contourlet transform as described above when executing the program.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The embedding area selection strategy based on directional coefficient energy priority proposed in the present invention can more accurately select the watermark embedding area in the chart image and improve the concealment of the watermark after embedding; 2. The patchwork embedding strategy based on directional mask proposed in this invention can realize blind extraction of watermarks; 3. Compared with other traditional digital image watermarking methods, the watermarking method proposed in the present invention has better visual quality and robustness on digital nautical chart images. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings herein are incorporated into and constitute a part of the specification, illustrate embodiments consistent with the present invention, and together with the specification are used to explain the principles of the present invention. Obviously, the accompanying drawings described below are only some embodiments of the present invention, and for those of ordinary skill in the art, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0015] Figure 1 A schematic flow chart of a method for embedding watermarks in nautical chart images based on contourlet transform proposed in the present invention.

[0016] Figure 2 Schematic diagram of the patchwork embedding process based on directional mask proposed in the present invention.

[0017] Figure 3 Visual illustration of the proposed watermarking method.

[0018] Figure 4 Visual quality indicators of the present invention and the comparative method.

[0019] Figure 5 The extraction accuracy (%) of the present invention and the comparative method under JPEG compression distortion.

[0020] Figure 6 The extraction accuracy (%) of the present invention and the comparative method under Gaussian noise.

[0021] Figure 7The extraction accuracy (%) of the present invention and the comparative method under sharpening distortion.

[0022] Figure 8 The extraction accuracy (%) of the present invention and the comparative method under Gaussian blur. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0025] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0026] As used herein, the words "if" and "if" may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0027] It should also be noted that the term "includes", "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, so that a commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the commodity or device including the elements.

[0028] The optional embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0029] First, as Figure 1 , Figure 2 As shown, the present invention proposes a method for embedding watermarks in nautical chart images based on contourlet transform, comprising: S101. A color chart image is preset as a carrier image I0, the carrier image I0 is converted from an RGB format to a YCbCr format, and the Y channel in the YCbCr format is used as a grayscale component Y0 of the carrier image I0, and the grayscale component Y0 of the carrier image I0 is divided into N non-overlapping sub-blocks B; S102. Preset watermark information M, which is a 0, 1 bit sequence with a length of L, where M = {M1, M2, ..., M i , ..., M L}; S103. Perform non-subsampled contourlet transform on each of the N non-overlapping sub-blocks B, set the decomposition parameter to n, and obtain a coefficient set C of the N non-overlapping sub-blocks B, wherein the coefficient set C of the N non-overlapping sub-blocks B consists of a low-frequency coefficient C0 and 2^n directional coefficients Composition, where j = 1, 2, ..., 2^n; S104. Calculate the directional subband of the maximum energy of each sub-block in the N non-overlapping sub-blocks B in, S105. Traverse the N non-overlapping sub-blocks B, and select the sub-block B with the largest directional sub-band energy among the N non-overlapping sub-blocks B. i As the embedding carrier of the watermark information M, the sub-block B1={B1, B2, . . . , B i , ..., B L}; S106. For the carrier sub-block B i Implement non-subsampled contourlet transform to obtain the carrier sub-block B i The maximum energy direction subband and other sub-bands C else , where the carrier sub-block B i Other sub-bands of C else Including low frequency coefficient C 0,i and the directivity j=1,2,……,2^n and j≠Max; S107. Calculate the carrier sub-block B i The direction of the maximum energy subband The mask matrix Mask, wherein the mask matrix Mask is a subband with the same size as the maximum energy direction The same, and along the maximum energy direction subband The corresponding direction is divided into two regions of the matrix, one side is 0 and the other side is 1; S108. Calculate the maximum energy direction subband divided by the mask matrix Mask The energy P1, P0, and the difference D between P1 and P0 on the patchwork area are specifically: D=P1-P0 Wherein, P1 represents the energy of the area where one side of the mask matrix Mask is 1, and P0 represents the energy of the area where one side of the mask matrix Mask is 0; S109. Based on the watermark embedding strength parameter s and the watermark information M, the i-th watermark bit M i , for the carrier sub-block B i The maximum energy direction subband Modify to obtain the carrier sub-block B i Directional subband after watermarking Specifically include: a. When M i =1 and D<s or when M i =0 and D>-s, △=(sD) / 2 P′1=P1+Δ P′0=P0-Δ Wherein, △ is the i-th watermark bit M of the watermark information M i The watermark modification amount, P'1 is the energy modification amount of the area where one side of the mask matrix Mask is 1, and P'0 is the energy modification amount of the area where one side of the mask matrix Mask is 0. and is the i-th watermark bit M of the watermark information M i Embed the carrier sub-block B i The posterior directional subband; b. In other cases, no Modify and directly make the directional subband after embedding the watermark S110. By i Directional subband after watermarking and the carrier sub-block B i Other sub-bands of C else Implement the non-subsampled contourlet inverse transform to obtain the carrier sub-block B i Watermark sub-block S111. Repeat S109-S110, and convert the L watermark bits M in the watermark information M intoi Embedded into L of the carrier sub-blocks B i In the above example, L carrier sub-blocks B are obtained. i Watermark sub-block remember S112. The L carrier sub-blocks B in the grayscale component Y0 of the carrier image I0 are i Replaced by L watermark sub-blocks Get the grayscale component Y of the carrier image I0 after embedding the watermark W ; S113. embedding the grayscale component Y of the carrier image I0 into the watermark W Combined with the CbCr format of the carrier image I0 and converted back to RGB format, the watermarked chart image I of the carrier image I0 is obtained. W .

[0030] Furthermore, the decomposition parameter set in S103 is 3, the spatial filter is 'pkva', and the directional filter is '9-7'. The decomposition parameter 3, the spatial filter 'pkva', and the directional filter '9-7' have been proven to have better contourlet reconstruction performance in some image processing and watermark embedding.

[0031] Among them, the decomposition parameters, spatial filters, and directional filters for implementing the non-subsampled contourlet inverse transform in S106 and S110 are the same as the decomposition parameters, spatial filters, and directional filters set in S103.

[0032] S107 Select along The corresponding direction is designed to piece together the embedded watermark so that the watermark embedding modification does not destroy the original pattern of the watermark sub-block.

[0033] From S111, we know that according to the embedded watermark bit M i Different, Shows the same or opposite energy relationship as Mask, but maintains the The corresponding direction and generate watermark sub-blocks with less visual disturbance

[0034] The present invention uses non-subsampled contourlet transform (NSCT) which is one of the improved versions and can avoid the distortion caused by the downsampling process. By introducing the non-subsampled structure, NSCT can analyze the image more freely in multiple scales and directions while maintaining the geometric information of the image. This transform has higher spatial and frequency localization performance, so that it has achieved superior performance in applications such as compression, denoising, and image fusion.

[0035] The watermark embedding method proposed in the present invention first selects a suitable watermark embedding area based on the directional coefficient energy of the contourlet transform to ensure the concealment and robustness of the watermark. Then, for the selected embedding area, a patchwork embedding strategy based on a directional mask is used to implement watermark embedding. This strategy determines the implementation method of patchwork according to the direction with the maximum energy of the current sub-block coefficient to be embedded, so that it conforms to the direction with the maximum energy, making the watermark embedding as inconspicuous as possible and having good robustness, which can ensure the blind extraction of the embedded watermark.

[0036] In the specific implementation, 8 nautical chart images are selected as experimental images and carrier images I0. The nautical chart images are crawled from the public data on the Internet, and the image size is 512×512. Figure 3 ,in Figure 3 The first row is the original image, the second row is the watermarked image, and the third row is the watermark residual magnified three times. In human vision, it is difficult to detect the watermark modification of the method in this paper.

[0037] The preset embedded watermark information sequence M is a randomly generated 0, 1 bit sequence with a length of L = 64. The sub-block size is set to n = 16, so there are a total of I = (512 / 16) × (512 / 16) = 1024 sub-blocks. Theoretically, the carrier image I0 can embed up to 1024 bits of information. We select the sub-blocks with the first L = 64 directional sub-band energy size among the 1024 sub-blocks as the watermark embedding area. The watermark embedding strength is set to s = 3.3.

[0038] The experimental results are compared with the performance of representative traditional digital image watermarking methods LGDR and DWT-DFT. In the experiment, Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index (SSIM) are used as indicators to evaluate the visual quality of the embedded image, and the watermark extraction accuracy (ACC) under different distortion conditions is used as an indicator to evaluate the robustness. The results are shown in Figure 4-Figure 8 .

[0039] like Figure 4 As shown, the average PSNR of the nautical chart watermarking method proposed by the watermarking algorithm of the present invention is 42.914dB, and the average SSIM is 0.9981, and the visual quality is the best among the comparison methods.

[0040] like Figure 5 As shown, the watermark algorithm proposed in the present invention exhibits excellent robustness under all tested JPEG compression distortion conditions and achieves the highest extraction accuracy among all compared methods.

[0041] like Figure 6 As shown in the figure, under different Gaussian noise variances, the watermark algorithm proposed in the present invention always maintains 100% watermark extraction accuracy, showing excellent robustness. In contrast, the accuracy of LGDR and DWT-DFT methods gradually decreases with the increase of noise variance.

[0042] like Figure 7 As shown in the figure, the watermark algorithm proposed in the present invention has 100% extraction accuracy when the standard deviation is 0.3 and 0.5, but the accuracy drops to 76.366% when the standard deviation is 1. The possible reason is that the watermark modification of the watermark algorithm proposed in the present invention is highly correlated with the contour information in the chart image. Blurred distortion seriously weakens the contour information in the image, making the watermark algorithm proposed in the present invention more vulnerable to blurry distortion.

[0043] like Figure 8 As shown in the figure, with the increase of sharpening intensity, the extraction accuracy of LGDR and DWT-DFT methods gradually decreases, while the watermark algorithm proposed in the present invention maintains relatively high robustness under various sharpening intensities, and the extraction accuracy remains above 97% when the intensity is 2, indicating its superior performance under sharpening distortion conditions.

[0044] In a second aspect, the present invention proposes a nautical chart image watermark embedding system based on contourlet transform, which adopts the nautical chart image watermark embedding method based on contourlet transform as described in the first aspect, comprising: Carrier image processing module D21: presets a color chart image as a carrier image I0, converts the carrier image I0 from an RGB format to a YCbCr format, uses the Y channel in the YCbCr format as the grayscale component Y0 of the carrier image I0, and divides the grayscale component Y0 of the carrier image I0 into N non-overlapping sub-blocks B; Watermark information processing module D22: preset watermark information M, the watermark information M is a string of 0, 1 bit sequence with a length of L, denoted by M = {M1, M2, ..., M i , ..., M L}; The maximum energy directional sub-calculation module D23: performs non-subsampled contourlet transform on each of the N non-overlapping sub-blocks B, sets the decomposition parameter to n, and obtains a coefficient set C of the N non-overlapping sub-blocks B, wherein the coefficient set C of the N non-overlapping sub-blocks B consists of a low-frequency coefficient C0 and 2^n directional coefficients , wherein j = 1, 2, ..., 2^n; calculating the directional subband of the maximum energy of each sub-block in the N non-overlapping sub-blocks B in, ; Watermark information embedding carrier selection module D24: traverse the N non-overlapping sub-blocks B, and select the sub-block B with the largest directional sub-band energy among the N non-overlapping sub-blocks B. i As the embedding carrier of the watermark information M, the sub-block B1={B1, B2, . . . , B i , ..., B L}; Watermark information embedding module D25: embeds the carrier sub-block B i Implement non-subsampled contourlet transform to obtain the carrier sub-block B i The maximum energy direction subband and other sub-bands C else ; Calculate the carrier sub-block B i The direction of the maximum energy subband The mask matrix Mask, wherein the mask matrix Mask is a subband with the same size as the maximum energy direction The same, and along the maximum energy direction subband The corresponding direction is divided into a matrix with one side being 0 and the other side being 1 in two regions; Calculate the maximum energy direction subband divided by the mask matrix Mask The energy P1, P0 on the patchwork area, and the difference D between P1 and P0; according to the watermark embedding strength s of the watermark information M as a whole and the i-th watermark bit M of the watermark information M i , for the carrier sub-block B i The maximum energy direction subband Modify to obtain the carrier sub-block B i Directional subband after watermarking By the carrier sub-block B i Directional subband after watermarking and the carrier sub-block B i Other sub-bands of C else Implement the non-subsampled contourlet inverse transform to obtain the carrier sub-block B i Watermark sub-block Repeat the above steps to convert the L watermark bits M in the watermark information M into i Embedded into L of the carrier sub-blocks B i In the above example, L carrier sub-blocks B are obtained. i Watermark sub-block remember The watermarked chart image acquisition module D26: the L carrier sub-blocks B in the grayscale component Y0 of the carrier image I0 are i Replaced by L watermark sub-blocks Get the grayscale component Y of the carrier image I0 W; The gray component Y of the carrier image I0 W Combined with the CbCr format of the carrier image I0 and converted back to RGB format, the watermarked chart image I of the carrier image I0 is obtained. W .

[0045] In a third aspect, the present invention proposes a method for extracting watermarks from a nautical chart image based on contourlet transform, which adopts the method for embedding watermarks from a nautical chart image based on contourlet transform as described in the first aspect, comprising: S201. The color chart image is preset as a carrier image I0, and the carrier image I0 contains watermark information M, wherein the watermark information M is composed of L embedded watermark sub-blocks. Composition, where i = {1, 2, ..., L}; S202. For the L watermarked sub-blocks Each watermark sub-block Implement non-subsampled contourlet transform to obtain the watermark sub-block The direction of the maximum energy subband S203. Based on the watermark sub-block The direction of the maximum energy subband By formula Get L watermark bits M in the watermark information M i ; S204. Combine the L watermark bits M in the watermark information M. i , for the L watermark bits M i The watermark information M is obtained by decoding.

[0046] The decomposition parameters, spatial filter, and directional filter used in implementing the non-subsampled contourlet transform in S202 are the same as the decomposition parameters, spatial filter, and directional filter set in S103.

[0047] In a fourth aspect, the present invention provides a system for extracting watermarks from nautical chart images based on contourlet transform, which uses a method for extracting watermarks from nautical chart images based on contourlet transform as described in the third aspect, comprising: Carrier image acquisition module D31: Assume that the color chart image is carrier image I0, and the carrier image I0 contains watermark information M, wherein the watermark information M is composed of L embedded watermark sub-blocks. composition; Maximum energy direction sub-calculation module D32: for the L watermarked sub-blocks Each watermark sub-block Implement non-subsampled contourlet transform to obtain the watermark sub-block The direction of the maximum energy subband Watermark bit extraction module D33: according to the watermark embedded sub-block The direction of the maximum energy subband Calculate and obtain L watermark bits M in the watermark information M i ; Watermark information embedding acquisition module D34: combining L watermark bits M in the watermark information M i , for the L watermark bits M i The watermark information M is obtained by decoding.

[0048] In a fifth aspect, the present invention proposes a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for embedding watermarks in nautical chart images based on contourlet transform as described above.

[0049] In a sixth aspect, the present invention proposes an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method for embedding watermarks in nautical chart images based on contourlet transform as described above when executing the program.

[0050] Specifically, a system or device equipped with a storage medium can be provided, on which software program code that implements the functions of any of the above-mentioned embodiments is stored, and a computer (or CPU or MPU) of the system or device can be enabled to read and execute the program code stored in the storage medium.

[0051] In this case, the program code itself read from the storage medium can realize the function of any one of the above-mentioned embodiments, and thus the program code and the storage medium storing the program code constitute a part of the present invention.

[0052] The storage medium embodiments for providing the program code include a floppy disk, a hard disk, a magneto-optical disk, an optical disk (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RYM, DVD-RW, DVD+RW), a magnetic tape, a non-volatile memory card, and a ROM. Alternatively, the program code can be downloaded from a server computer via a communication network.

[0053] In addition, it should be clear that the functions of any of the above embodiments can be implemented not only by executing the program code read by the computer, but also by enabling an operating system operating on the computer to complete part or all of the actual operations based on instructions from the program code.

[0054] In addition, it can be understood that the program code read from the storage medium is written to a memory provided in an expansion board inserted into the computer or written to a memory provided in an expansion unit connected to the computer, and then based on the instructions of the program code, a CPU installed on the expansion board or the expansion unit is enabled to perform part or all of the actual operations, thereby realizing the functions of any of the above-mentioned embodiments.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for embedding watermarks in nautical chart images based on contourlet transform, characterized in that: include: S101. A color chart image is preset as a carrier image I0, the carrier image I0 is converted from an RGB format to a YCbCr format, and the Y channel in the YCbCr format is used as a grayscale component Y0 of the carrier image I0, and the grayscale component Y0 of the carrier image I0 is divided into N non-overlapping sub-blocks B; S1 02. Preset watermark information M, which is a sequence of 0 and 1 bits with a length of L, where M = {M1, M2, ..., M i , ..., M L }; S103. Perform non-subsampled contourlet transform on each of the N non-overlapping sub-blocks B, set the decomposition parameter to n, and obtain a coefficient set C of the N non-overlapping sub-blocks B, wherein the coefficient set C of the N non-overlapping sub-blocks B consists of a low-frequency coefficient C0 and 2^n directional coefficients Composition, where j = 1, 2, ..., 2^n; S104. Calculate the directional subband of the maximum energy of each sub-block in the N non-overlapping sub-blocks B in, S105. Traverse the N non-overlapping sub-blocks B, and select the sub-block B with the largest directional sub-band energy among the N non-overlapping sub-blocks B. i As the embedding carrier of the watermark information M, the sub-block B1={B1, B2, . . . , B i , ..., B L }; S106. For the carrier sub-block B i Implement non-subsampled contourlet transform to obtain the carrier sub-block B i The maximum energy direction subband and other sub-bands C else , where the carrier sub-block B i Other sub-bands of C else Including low frequency coefficient C 0,i and the directivity And j≠Max; S107. Calculate the carrier sub-block B i The direction of the maximum energy subband The mask matrix Mask, wherein the mask matrix Mask is a subband with the same size as the maximum energy direction The same, and along the maximum energy direction subband The corresponding direction is divided into two regions of the matrix, one side is 0 and the other side is 1; S108. Calculate the maximum energy direction subband divided by the mask matrix Mask The energy P1, P0, and the difference D between P1 and P0 on the patchwork area are specifically: D=P1-P0 Wherein, P1 represents the energy of the area where one side of the mask matrix Mask is 1, and P0 represents the energy of the area where one side of the mask matrix Mask is 0; S109. Based on the watermark embedding strength parameter s and the watermark information M, the i-th watermark bit M i , for the carrier sub-block B i The maximum energy direction subband Modify to obtain the carrier sub-block B i Directional subband after watermarking Specifically include: a. When M i =1 and D<s or when M i =0 and D>-s, △=(sD) / 2 P′1=P1+Δ P′0=P0-Δ Wherein, △ is the i-th watermark bit M of the watermark information M i The watermark modification amount, P'1 is the energy modification amount of the area where one side of the mask matrix Mask is 1, and P'0 is the energy modification amount of the area where one side of the mask matrix Mask is 0. and is the i-th watermark bit M of the watermark information M i Embed the carrier sub-block B i The posterior directional subband; b. In other cases, there is no need to modify the carrier sub-block B i The maximum energy direction subband Modify and directly make the directional subband after embedding the watermark S110. By i Directional subband after watermarking and the carrier sub-block B i Other sub-bands of C else Implement the non-subsampled contourlet inverse transform to obtain the carrier sub-block B i Watermark sub-block S111. Repeat S109-S110, and convert the L watermark bits M in the watermark information M into i Embedded into L of the carrier sub-blocks B i In the above example, L carrier sub-blocks B are obtained. i Watermark sub-block remember S112. The L carrier sub-blocks B in the grayscale component Y0 of the carrier image I0 are i Replaced by L watermark sub-blocks Get the grayscale component Y of the carrier image I0 after embedding the watermark W ; S113. embedding the grayscale component Y of the carrier image I0 into the watermark W Combined with the CbCr format of the carrier image I0 and converted back to RGB format, the watermarked chart image I of the carrier image I0 is obtained. W .

2. According to the method for embedding watermark in nautical chart images based on contourlet transform in claim 1, it is characterized in that: The decomposition parameter set in S103 is 3, the spatial filter is 'pkva', and the directional filter is '9-7'.

3. A watermark embedding system for nautical chart images based on contourlet transform, characterized in that: The method for embedding watermarks in nautical chart images based on contourlet transform as claimed in claim 1 comprises: Carrier image processing module D21: presets a color chart image as a carrier image I0, converts the carrier image I0 from an RGB format to a YCbCr format, uses the Y channel in the YCbCr format as the grayscale component Y0 of the carrier image I0, and divides the grayscale component Y0 of the carrier image I0 into N non-overlapping sub-blocks B; Watermark information processing module D22: preset watermark information M, the watermark information M is a string of 0, 1 bit sequence with a length of L, denoted by M = {M1, M2, ..., M i , ..., M L }; The maximum energy directional sub-calculation module D23: performs non-subsampled contourlet transform on each of the N non-overlapping sub-blocks B, sets the decomposition parameter to n, and obtains a coefficient set C of the N non-overlapping sub-blocks B, wherein the coefficient set C of the N non-overlapping sub-blocks B consists of a low-frequency coefficient C0 and 2^n directional coefficients , wherein j = 1, 2, ..., 2^n; calculating the directional subband of the maximum energy of each sub-block in the N non-overlapping sub-blocks B in, Watermark information embedding carrier selection module D24: traverse the N non-overlapping sub-blocks B, and select the sub-block B with the largest directional sub-band energy among the N non-overlapping sub-blocks B. i As the embedding carrier of the watermark information M, the sub-block B1={B1, B2, . . . , B i , ..., B L }; Watermark information embedding module D25: embeds the carrier sub-block B i Implement non-subsampled contourlet transform to obtain the carrier sub-block B i The maximum energy direction subband and other sub-bands C else ; Calculate the carrier sub-block B i The direction of the maximum energy subband The mask matrix Mask, wherein the mask matrix Mask is a subband with the same size as the maximum energy direction The same, and along the maximum energy direction subband The corresponding direction is divided into a matrix with one side being 0 and the other side being 1 in two regions; Calculate the maximum energy direction subband divided by the mask matrix Mask The energy P1, P0 on the patchwork area, and the difference D between P1 and P0; according to the watermark embedding strength parameter s and the i-th watermark bit M of the watermark information M i , for the carrier sub-block B i The maximum energy direction subband Modify to obtain the carrier sub-block B i Directional subband after watermarking By the carrier sub-block B i Directional subband after watermarking and the carrier sub-block B i Other sub-bands of C else Implement the non-subsampled contourlet inverse transform to obtain the carrier sub-block B i Watermark sub-block Repeat the above steps to convert the L watermark bits M in the watermark information M into i Embedded into L of the carrier sub-blocks B i In the above example, L carrier sub-blocks B are obtained. i Watermark sub-block remember The watermarked chart image acquisition module D26: the L carrier sub-blocks B in the grayscale component Y0 of the carrier image I0 are i Replaced by L watermark sub-blocks Get the grayscale component Y of the carrier image I0 after embedding the watermark W ; Embed the gray component Y of the carrier image I0 after the watermark W Combined with the CbCr format of the carrier image I0 and converted back to RGB format, the watermarked chart image I of the carrier image I0 is obtained. W .

4. A method for extracting watermark from a nautical chart image based on contourlet transform, characterized in that: The method for embedding watermarks in nautical chart images based on contourlet transform as claimed in claim 1 comprises: S201. The color chart image is preset as a carrier image I0, and the carrier image I0 contains watermark information M, wherein the watermark information M is composed of L embedded watermark sub-blocks. Composition, where i = {1, 2, ..., L}; S202. For the L watermarked sub-blocks Each watermark sub-block Implement non-subsampled contourlet transform to obtain the watermark sub-block The direction of the maximum energy subband S203. Based on the watermark sub-block The direction of the maximum energy subband By formula Get L watermark bits M in the watermark information M i ; S204. Combine the L watermark bits M in the watermark information M. i , for the L watermark bits M i The watermark information M is obtained by decoding.

5. A nautical chart image watermark extraction system based on contourlet transform, characterized in that: A method for extracting watermark from a nautical chart image based on contourlet transform as described in claim 4 is adopted, comprising: Carrier image acquisition module D31: Assume that the color chart image is carrier image I0, and the carrier image I0 contains watermark information M, wherein the watermark information M is composed of L embedded watermark sub-blocks. composition; Maximum energy direction sub-calculation module D32: for the L watermarked sub-blocks Each watermark sub-block Implement non-subsampled contourlet transform to obtain the watermark sub-block The direction of the maximum energy subband Watermark bit extraction module D33: based on the watermark embedded sub-block The direction of the maximum energy subband Calculate and obtain L watermark bits M in the watermark information M i ; Watermark information embedding acquisition module D34: combining L watermark bits M in the watermark information M i , for the L watermark bits M i The watermark information M is obtained by decoding.

6. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed by a processor, the steps of the method for embedding watermarks in nautical chart images based on contourlet transform as claimed in claim 1 are implemented.

7. An electronic device, characterized in that: The method comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the method for embedding watermarks in nautical chart images based on contourlet transform as described in claim 1 are implemented.

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