Grid DEM (digital elevation model) blind watermark method resistant to elevation translation and clipping attack

A blind watermark and grid technology, applied in the field of cartography and geographic information science, can solve the problems of poor robustness and achieve the effect of advanced methods, good use value and guaranteed accuracy

Active Publication Date: 2015-07-22

LANZHOU JIAOTONG UNIV

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Problems solved by technology

In the research of DEM data watermarking technology, elevation translation and cropping are the most common attack methods against...

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Abstract

Elevation translation and clipping are common attacking manners specific to DEM data watermark, and the invention provides a grid DEM (digital elevation model) blind watermark method resistant to elevation translation and clipping attack effectively. The method takes account of the characteristics of DEM data, carries out spread spectrum processing to an original watermark, makes the original watermark and an elevation difference value form a mapping relation, utilizes the feature that the elevation difference value of adjacent grids does not change in an elevation translation attack, embeds the bitwise of the watermark subjected to spread spectrum into the elevation difference value in a quantification manner, and apportions the expansive difference value to back single bit of the adjacent elevations. The watermark method has good invisibility, has a relatively small influence on the DEM data accuracy and application accuracy, and has good robustness in resisting the elevation translation and the clipping attack.

Application Domain

Image data processing details

Technology Topic

Digital elevation modelInvisibility +4

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[0019] In order to describe in detail the technical content, structural features, achieved objectives and achieved effects of the present invention, the following detailed descriptions are combined with specific embodiments.

[0020] The implementation steps of the present invention can be summarized into two parts: watermark information embedding and watermark information extraction. The implementation steps are further elaborated below.

[0021] Step 1: Read the original DEM data to get the elevation value matrix z ( i , j ), 0i ≤ M , 0j ≤ N , M × N Is the total number of grids of DEM. If the original elevation value is a floating point number, in order to facilitate processing, it is expanded to an integer value. After the watermark is embedded, it can be restored to a floating point number.

[0022] Step 2: Spread spectrum processing for the watermark information added to DEM data, the spread spectrum method is the overall repetition increase, forming multiple repetitions of the original single watermark, and obtain w ’( i , j )={0,1}, i =(1,2,……, a × K ), j =(1,2,……, b × L ),among them a = M / K , b =( N -1)/ L.

[0023] Step 3: The watermark information after spreading corresponds to the adjacent elevation difference matrix one-to-one, and the watermark information bits are extracted according to the matrix row and column order w ’( i , j ) To extract, judge and modify the corresponding adjacent elevation differences one by one d = z ( i , j +1)- z ( i , j ), modify the last bit of the adjacent elevation in a quantitative manner to realize the embedding of the watermark, and deal with the following two situations:

[0024] (a) if w ’( i , j )=0 and mod( z ( i , j +1)- z ( i , j ),2) = 1

[0025] z ( i , j +1) = z ( i , j +1)-1

[0026] (b) if w ’( i , j )=1 and mod( z ( i , j +1)- z ( i , j ),2) = 0

[0027] z ( i , j +1)= z ( i , j +1)+1

[0028] Step 4: After the above operations, a new elevation value matrix can be obtained z ( i , j ) To replace the original elevation value with the new elevation value matrix;

[0029] Step 5: Save the DEM data to obtain the watermarked DEM data.

[0030] Watermark information extraction refers to the extraction of watermark information content from DEM data to be detected. The specific steps are as follows:

[0031] Step 1: Read the elevation data of the DEM to be detected to obtain the elevation value matrix z ’(I,j), 0≤ i ≤ M , 0≤ j ≤ N }. If it is a floating point number, expand to an integer value;

[0032] Step 2: Define a null value matrix with one column less than the elevation value matrix of the DEM data to be detected w ’’(I,j), 0≤ i ≤ M , 0≤ j ≤ N -1, where M ×N is the size of the DEM elevation value matrix to be detected;

[0033] Step 3: Judge and extract adjacent elevation differences one by one (without considering inter-row adjacent elevation differences), and the quantization range takes the value at the time of embedding R =2, as shown in formula 1:

[0034] (1)

[0035] Step 4: Convert the extracted binary spread spectrum watermark information into a visual watermark image, and extract the best quality single watermark image from it.

[0036] To sum up, the present invention effectively solves the effective extraction of watermark information in grid DEM data, ensures the accuracy of the data as much as possible, and has strong robustness against elevation translation and data cropping attacks. The blind watermarking method has good use value.

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Grid DEM (digital elevation model) blind watermark method resistant to elevation translation and clipping attack

A blind watermark and grid technology, applied in the field of cartography and geographic information science, can solve the problems of poor robustness and achieve the effect of advanced methods, good use value and guaranteed accuracy

AI-Extracted Technical Summary

Problems solved by technology

Abstract

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Description & Claims & Application Information

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