CN110570345A - Blind watermarking method of spatial domain color digital image fused with discrete cosine transform - Google Patents

Abstract

The invention discloses a blind watermarking method of a spatial domain color digital image fused with discrete cosine transform by combining the advantages of high operation speed of a spatial domain digital watermarking algorithm and high robustness of the spatial domain digital watermarking algorithm. According to the unique characteristic of the discrete cosine transform direct current coefficient, the digital watermark embedding and blind extraction are completed in the airspace by utilizing the correlation principle of the direct current coefficients of adjacent pixel blocks, and the real discrete cosine transform is not needed. The invention embeds the color digital watermark image into the color carrier image, has stronger robustness and higher real-time property on the premise of better watermark invisibility, solves the problems of low running speed and weak robustness of a large-capacity color image digital watermark algorithm, and is suitable for the occasion of quickly and efficiently protecting the copyright of a digital media.

Description

blind watermarking method of spatial domain color digital image fused with discrete cosine transform

Technical Field

The invention belongs to the technical field of network space security, and relates to copyright protection of a color digital image as a digital watermark.

Background

With the rapid development of multimedia technology, it is possible to efficiently store and transmit digitized information, but at the same time, a series of serious problems such as piracy, infringement, falsification and the like are caused. Therefore, the copyright protection problem is more and more concerned by scholars at home and abroad. The digital watermarking technology is taken as an effective digital product copyright protection and data security maintenance technology, and the successful embedding and extraction of the watermark can effectively protect the digital copyright, thereby solving the difficult problem of copyright protection.

according to different processing modes of carrier images, a digital watermarking algorithm is divided into a spatial domain watermarking algorithm and a frequency domain watermarking algorithm, the spatial domain watermarking algorithm has the advantages of simple algorithm and high running speed, but the robustness is poor, and although the robustness is strong, the running time of the watermarking algorithm is long due to forward transformation and inverse transformation of a corresponding transformation domain. Therefore, how to combine the advantages of the two, and on the premise of ensuring good invisibility of the digital watermark, designing a digital watermark algorithm with strong robustness and high real-time performance becomes a problem to be solved urgently at present.

disclosure of Invention

the invention aims to provide a spatial domain color digital image blind watermarking method fused with discrete cosine transform, which comprises two specific watermark embedding processes and watermark extracting processes, wherein the watermark embedding process is described as follows:

The first step is as follows: one width is as large asM×MColor carrier image ofHDivided into three layered carrier images of red, green and blueH _i And laminating each of the layered carrier imagesH _i Is divided intom×mThe non-overlapping pixel block of (1), whereini=1, 2, 3 respectively represent red, green, blue three layers;

The second step is that: one width is as large asN×NColor watermark image ofWDividing the image into red, green and blue layered watermark images, and performing key-based encryption on each layered watermark image to improve the security of the watermarkKa _i The Arnold transformation obtains three layered watermark images after scramblingW _i (ii) a Watermarking images in layersW _i Each decimal pixel value in the decimal system is converted into 8-bit binary number and is connected into 8-bit binary number in sequenceN ² Watermark bit sequence ofSW _i Whereini=1, 2, 3 respectively represent red, green, blue three layers;

The third step:Sequentially from layered carrier images in longitudinal orderH _i In selecting adjacent pixel blockAandBWhereini=1, 2, 3 respectively represent red, green, blue three layers;

The fourth step: directly computing blocks of pixels in the spatial domain according to equation (1)AAndBDirect current coefficient ofdc _p ；

(1)

wherein the content of the first and second substances,p=1, 2 denotes a pixel block, respectivelyAAndB，mis the size of the row (column) of the pixel square,f _p (x, y) Is a pixel blockpFirst, thexGo to the firstyPixel values of the columns;

The fifth step: sequential order dependent hierarchical watermark sequenceSW _i in which the watermark bit to be embedded is selectedw(ii) a According to the correlation of DC coefficients of adjacent pixel blocks, embedding watermark information by using formulas (2) and (3)wobtaining a pixel blockpModified DC coefficientdc _p ^*，p=1, 2 denotes a pixel block, respectivelyAAndB；

(2)

(3)

wherein the content of the first and second substances,win order for the watermark bits to be embedded,avg=(dc ₁ +dc ₂ )/2，T _i Is as followsiThe quantization step size of a layer is,i=1, 2, 3 respectively represent red, green, blue three layers;

and a sixth step: using the modified pixel values according to equation (4)f _p ^* (x, y) Block for replacing original pixelpPixel value of corresponding positionf _p (x, y) Obtaining a pixel block containing a watermarkA ^* AndB ^*Whereinp=1, 2；

(4)

the seventh step: printing a block of pixels containing waterA ^*AndB ^*respectively updated to its layered carrier imageH _i In a corresponding position in (b), whereini=1, 2, 3, respectively representing three layers of red, green, blue;

Eighth step: repeating the third to seventh steps until all watermark information is embedded, thereby obtaining a layered carrier image containing watermarkH _i ^*(ii) a Finally, three layers of layered carrier images containing watermarks are combinedH _i ^*Obtaining a color carrier image containing a watermarkH ^*Whereini=1, 2, 3 respectively represent red, green, blue three layers;

The watermark extraction process is described as follows:

The first step is as follows: aqueous print bearing image by dimension reductionH ^*divided into three layered images of red, green and blueH _i ^*(ii) a Simultaneously, each containing a printed layered imageH _i ^*is divided into sizes ofm×mThe non-overlapping pixel block of (1), whereini=1, 2, 3 respectively represent red, green, blue three layers;

The second step is that: sequentially laminating images from aqueous media in a longitudinal orderH _i ^*In selecting adjacent blocks of water-containing print pixelsA ^*AndB ^*Whereini=1, 2, 3 respectively represent red, green, blue three layers;

The third step: directly calculating the block of pixels containing watermark in the spatial domain according to the formula (5)A ^*AndB ^*Direct current coefficient ofdc _p ^* ；

(5)

wherein the content of the first and second substances,mis the size of the row (column) of the pixel square,f _p ^* (x, y) For water-containing printing pixel blockspFirst, thexGo to the firstyThe pixel values of the columns are selected,p=1, 2 denotes each block of water-containing print pixelsA ^*AndB ^*；

the fourth step: on block of pixels containing waterA ^*AndB ^*Direct current coefficient ofdc _p ^* the size relationship between the blocks of pixels containing water print by using the formula (6)A ^*AndB ^*Extracting watermark bits from the imagew*Whereinp=1, 2；

(6)

the fifth step: repeating the second step to the fourth step of the process to obtain the extracted binary watermark sequenceSW _i ^*To watermark the binary sequenceSW _i ^*Dividing each 8-bit binary information into a group and converting into decimal pixel values to form a layered watermark image, whereini=1, 2, 3 respectively represent red, green, blue three layers;

And a sixth step: key-based watermarking of layered imagesKa _i Inverse Arnold transform to obtain watermark image of each layerW _i ^*(ii) a Combining layers of extracted watermark imagesW _i ^*Forming a final extracted watermark imageW ^*WhereiniAnd =1, 2 and 3 respectively represent red, green and blue three layers.

The method utilizes the correlation rule of direct current coefficients of adjacent image blocks to directly obtain the discrete cosine transform direct current coefficient in a space domain and finish the embedding and blind extraction of the color digital watermark without carrying out real discrete cosine transform; the method has the advantages of good watermark invisibility, strong watermark robustness and high algorithm instantaneity.

Drawings

Fig. 1 (a) and 1 (b) show two original color carrier images.

Fig. 2 (a) and 2 (b) show two original color watermark images.

fig. 3 (a) and 3 (b) show watermark images obtained by embedding the watermark shown in fig. 2 (a) into the carrier images such as fig. 1 (a) and 1 (b) in this order, wherein the structural similarity SSIM values are 0.9343 and 0.9351 in this order, and the peak signal-to-noise ratios PSNR values are 37.4377dB and 37.2156dB in this order.

fig. 4 (a) and 4 (b) show watermarks extracted from fig. 3 (a) and 3 (b) in this order, and normalized cross-correlation coefficients NC of the watermarks are 1.0000 and 1.0000, respectively.

Fig. 5 (a), 5 (b), 5 (c), 5 (d), and 5 (e) show watermarks extracted after the watermark-containing image shown in fig. 3 (a) is subjected to attacks such as JPEG2000 compression (4: 1), JPEG compression (70), salt-and-pepper noise (0.2%), median filtering (3 × 3), and scaling (75%) in this order, and normalized cross-correlation coefficients NC thereof are 0.9684, 0.9573, 0.9950, 0.9142, and 0.9626, respectively.

Fig. 6 (a) and 6 (b) show watermark images obtained by embedding the watermark shown in fig. 2 (b) into the carrier images such as fig. 1 (a) and 1 (b) in this order, wherein the structural similarity SSIM values are 0.9346 and 0.9297 in this order, and the peak signal-to-noise ratios PSNR values are 37.4091dB and 37.2863dB in this order.

Fig. 7 (a) and 7 (b) show watermarks extracted from fig. 6 (a) and 6 (b) in this order, and normalized cross-correlation coefficients NC of the watermarks are 1.0000 and 1.0000, respectively.

Fig. 8 (a), 8 (b), 8 (c), 8 (d), and 8 (e) show watermarks extracted after the watermark-containing image shown in fig. 6 (a) is subjected to attacks such as JPEG2000 compression (4: 1), JPEG compression (70), salt-and-pepper noise (0.2%), median filtering (3 × 3), and scaling (75%) in this order, and normalized cross-correlation coefficients NC thereof are 0.9676, 0.9526, 0.9956, 0.9018, and 0.9673, respectively.

Detailed Description

The invention aims to provide a spatial domain color digital image blind watermarking method fused with discrete cosine transform, which comprises two specific watermark embedding processes and watermark extracting processes, wherein the watermark embedding process is described as follows:

The first step is as follows: an image of a color carrier with a size of 512 x 512 is formedHdivided into three layered carrier images of red, green and blueH _i And laminating each of the layered carrier imagesH _i Divided into 2 x 2 non-overlapping blocks of pixels, in whichi=1, 2, 3 respectively represent red, green, blue three layers;

The second step is that: a color watermark image with the size of 32 multiplied by 32 is formedWDividing the image into red, green and blue layered watermark images, and performing key-based encryption on each layered watermark image to improve the security of the watermarkKa _i the Arnold transformation obtains three layered watermark images after scramblingW _i (ii) a Watermarking images in layersW _i Each decimal pixel value in (a) is converted into an 8-bit binary number (e.g., the decimal number 225 may be converted into the binary sequence '11100001'), concatenated into the watermark bit sequence in turnSW _i ，SW _i Is 8X 32 in length² =8192, whereini=1, 2, 3 respectively represent red, green, blue three layers;

the third step: sequentially from layered carrier images in longitudinal orderH _i In selecting adjacent pixel blockAAndBwhereini=1, 2, 3 respectively represent red, green, blue three layers; here, leti=1, square of pixels selected from red layerAis composed ofselected pixel blockBIs composed of；

the fourth step: directly calculating adjacent pixel blocks in the spatial domain according to equation (1)AandBdirect current coefficient ofdc _p ；

(1)

Wherein the content of the first and second substances,p=1, 2 denotes a pixel block, respectivelyAandB，mis the size of the row (column) of the pixel square,f _p (x, y) Is a pixel blockpFirst, thexgo to the firstypixel values of the columns; at this time, the size of the row (column) of the pixel blockm=2, calculated pixel squareADirect current coefficient ofdc ₁ =448.5000, square of pixelsBDirect current coefficient ofdc ₂ =448.5000；

the fifth step: sequential order dependent hierarchical watermark sequenceSW _i In which the watermark bit to be embedded is selectedw(ii) a According to the correlation of DC coefficients of adjacent pixel blocks, embedding watermark information by using formulas (2) and (3)wObtaining a pixel blockpModified DC coefficientdc _p ^*，p=1, 2 denotes a pixel block, respectivelyAAndB；

(2)

(3)

wherein the content of the first and second substances,wIn order for the watermark bits to be embedded,avg=(dc ₁ +dc ₂ )/2，T _i is as followsiThe quantization step size of a layer is,i=1, 2, 3 respectively represent red, green, blue three layers; at this time, the process of the present invention,i=1, from watermark sequencesSW ₁ In the selected watermark bit to be embeddedw=‘0’，T ₁ =24.18，avg=448.5000, then calculate the modified pixel square block according to the formulas (2) and (3)A ^*Direct current coefficient ofdc ₁ ^* =448.5000, square of pixelsB ^*Direct current coefficient ofdc ₂ ^* =448.5000；

And a sixth step: using the modified pixel values according to equation (4)f _p ^* (x, y) Block for replacing original pixelpPixel value of corresponding positionf _p (x, y) Obtaining a pixel block containing a watermarkA ^* andB ^*；

(4)

Whereinp=1, 2; at this time, the block of water-containing print pixels is obtainedA ^* Is composed ofContaining blocks of pixels printed with waterB ^*Is composed of；

The seventh step: printing a block of pixels containing waterA ^*AndB ^*Respectively updated to its layered carrier imageH _i In a corresponding position in (b), whereini=1, 2, 3, respectively representing three layers of red, green, blue; at this time, the process of the present invention,i=1, block of water-containing printed pixelsA ^*AndB ^*Are updated to their respective layered carrier imagesH ₁ The respective position in (a);

eighth step: repeating the third to seventh steps until all watermark information is embedded, thereby obtaining a layered carrier image containing watermarkH _i ^*(ii) a Finally, three layers of layered carrier images containing watermarks are combinedH _i ^*obtaining a color carrier image containing a watermarkH ^*Whereini=1, 2, 3 respectively represent red, green, blue three layers;

the watermark extraction process is described as follows:

the first step is as follows: aqueous print bearing image by dimension reductionH ^*Divided into three layered images of red, green and blueH _i ^*(ii) a Simultaneously, each containing a printed layered imageH _i ^*Divided into non-overlapping blocks of pixels of size 2 x 2, whereini=1, 2, 3 respectively represent red, green, blue three layers;

The second step is that: sequentially laminating images from aqueous media in a longitudinal orderH _i ^*In selecting adjacent blocks of water-containing print pixelsA ^*AndB ^*Whereini=1, 2, 3 respectively represent red, green, blue three layers; at this time, leti=1, block of water-containing printed pixels from red layerA ^* Is composed ofblocks of pixels containing watermarksB ^*is composed of；

the third step: direct computation of block of pixels containing watermark in spatial domain according to equation (5)A ^*AndB ^*Direct current coefficient ofdc _p ^* ；

(5)

Wherein the content of the first and second substances,mIs the size of the row (column) of the pixel square,f _p ^* (x, y) For water-containing printing pixel blockspFirst, thexgo to the firstythe pixel values of the columns are selected,p=1, 2 denotes each block of water-containing print pixelsA ^*AndB ^*(ii) a At this time, the size of the row (column) of the pixel blockm=2, calculated pixel squareA ^*direct current coefficient ofdc ₁ ^* =448.5000, square of pixelsB ^*Direct current coefficient ofdc ₂ ^* =448.5000；

The fourth step: on block of pixels containing waterA ^*AndB ^*direct current coefficient ofdc _p ^* the size relationship between the blocks of pixels containing water print by using the formula (6)A ^*andB ^*Extracting watermark bits from the imagew ^*whereinp=1, 2；

(6)

At this time, the process of the present invention,dc ₁ ^* -dc ₂ ^* If =0, the extracted watermark bit is obtained according to equation (6)w ^*=‘0’；

The fifth step: repeating the second step to the fourth step of the process to obtain the extracted binary watermark sequenceSW _i ^*To watermark the binary sequenceSW _i ^*Dividing each 8-bit binary information into a group and converting the group into decimal pixel values to form a layered watermark image, whereini=1, 2, 3 respectively represent red, green, blue three layers;

And a sixth step: key-based watermarking of layered imagesKa _i Inverse Arnold transform to obtain watermark image of each layerW _i ^*(ii) a At the same time, the extracted watermark images of the layers are combinedW _i ^*Forming a final extracted watermark imageW ^*Whereiniand =1, 2 and 3 respectively represent red, green and blue three layers.

The method has the advantages of good watermark invisibility, strong robustness and high algorithm real-time performance, and is suitable for copyright protection of the color digital image as the watermark.

Validation of the invention

In order to prove the effectiveness of the invention, two 24-bit standard color images with the size of 512 × 512 as shown in fig. 1 (a) and 1 (b) are selected as carrier images, and two 24-bit color images with the size of 32 × 32 as shown in fig. 2 (a) and 2 (b) are respectively used as digital watermarks for verification.

Fig. 3 (a) and 3 (b) show watermark images obtained by embedding the watermark shown in fig. 2 (a) into the carrier images such as fig. 1 (a) and 1 (b) in sequence, wherein the structural similarity SSIM values are 0.9343 and 0.9351 in sequence, and the peak signal-to-noise ratios PSNR values are 37.4377dB and 37.2156dB in sequence; fig. 4 (a) and 4 (b) show watermarks extracted from fig. 3 (a) and 3 (b) in sequence, and normalized cross-correlation coefficients NC of the watermarks are 1.0000 and 1.0000, respectively; fig. 5 (a), 5 (b), 5 (c), 5 (d), and 5 (e) show watermarks extracted after the watermark-containing image shown in fig. 3 (a) is subjected to attacks such as JPEG2000 compression (4: 1), JPEG compression (70), salt-and-pepper noise (0.2%), median filtering (3 × 3), and scaling (75%) in this order, and normalized cross-correlation coefficients NC thereof are 0.9684, 0.9573, 0.9950, 0.9142, and 0.9626, respectively.

Fig. 6 (a) and 6 (b) show watermark images obtained by embedding the watermark shown in fig. 2 (b) into the carrier images (fig. 1 (a) and 1 (b) in sequence, wherein the structural similarity SSIM values are 0.9346 and 0.9297 in sequence, and the peak signal-to-noise ratios PSNR values are 37.4091dB and 37.2863dB in sequence; fig. 7 (a) and 7 (b) show watermarks extracted from fig. 6 (a) and 6 (b) in sequence, and normalized cross-correlation coefficients NC of the watermarks are 1.0000 and 1.0000, respectively; fig. 8 (a), 8 (b), 8 (c), 8 (d), and 8 (e) show watermarks extracted after the watermark-containing image shown in fig. 6 (a) is subjected to attacks such as JPEG2000 compression (4: 1), JPEG compression (70), salt-and-pepper noise (0.2%), median filtering (3 × 3), and scaling (4: 1) in this order, and normalized cross-correlation coefficients NC values thereof are 0.9676, 0.9526, 0.9956, 0.9018, and 0.9673, respectively.

The algorithm is operated on platforms 2.60GHZ CPU, 4.00GB RAM, Win10 and MATLAB (R2017a) for nearly ten thousand times, the average embedding time of the digital watermark is 0.605655 seconds, the average extraction time is 0.255208 seconds, and the total time is 0.860863 seconds.

In conclusion, the embedded digital image watermark has higher invisibility, and the invisibility requirement of the watermark algorithm is met; meanwhile, digital image watermarks extracted from various attacked images have good identifiability and high NC values, which shows that the method has strong robustness; in addition, the average running total time of the algorithm is less than 1 second, and the requirement of the multimedia big data on quick copyright protection is met.

Claims (1)

1. A method for blind watermarking a spatial domain color digital image fused with discrete cosine transform is characterized in that: the method is realized through a specific watermark embedding process and a watermark extracting process, wherein the watermark embedding process is described as follows:

the first step is as follows: one width is as large asM×MColor carrier image ofHDivided into three layered carrier images of red, green and blueH _i And laminating each of the layered carrier imagesH _i Is divided intom×mthe non-overlapping pixel block of (1), whereini=1, 2, 3 respectively represent red, green, blue three layers;

The second step is that: one width is as large asN×NColor watermark image ofWDividing the image into red, green and blue layered watermark images, and performing key-based encryption on each layered watermark image to improve the security of the watermarkKa _i the Arnold transformation obtains three layered watermark images after scramblingW _i (ii) a Watermarking images in layersW _i each decimal pixel value in the decimal system is converted into 8-bit binary number and is connected into 8-bit binary number in sequenceN ² watermark bit sequence ofSW _i Whereini=1, 2, 3 respectively represent red, green, blue three layers;

the third step: sequentially from layered carrier images in longitudinal orderH _i In selecting adjacent pixel blockAAndBWhereini=1, 2, 3 respectively represent red, green, blue three layers;

The fourth step: directly computing blocks of pixels in the spatial domain according to equation (1)AAndBDirect current coefficient ofdc _p ；

(1)

wherein the content of the first and second substances,p=1, 2 denotes a pixel block, respectivelyAandB，mIs the size of the row (column) of the pixel square,f _p (x, y) Is a pixel blockpFirst, thexgo to the firstyPixel values of the columns;

the fifth step: sequential order dependent hierarchical watermark sequenceSW _i In which the watermark bit to be embedded is selectedw(ii) a According to the correlation of DC coefficients of adjacent pixel blocks, embedding watermark information by using formulas (2) and (3)wobtaining a pixel blockpModified DC coefficientdc _p ^*，p=1, 2 denotes a pixel block, respectivelyAandB；

(2)

(3)

Wherein the content of the first and second substances,wIn order for the watermark bits to be embedded,avg=(dc ₁ +dc ₂ )/2，T _i Is as followsiThe quantization step size of a layer is,i=1, 2, 3 respectively represent red, green, blue three layers;

And a sixth step: using the modified pixel values according to equation (4)f _p ^* (x, y) Block for replacing original pixelpPixel value of corresponding positionf _p (x, y) Obtaining a pixel block containing a watermarkA ^* andB ^*Whereinp=1, 2；

(4)

the seventh step: printing the water-bearing photoPlain squareA ^*andB ^*Respectively updated to its layered carrier imageH _i In a corresponding position in (b), whereini=1, 2, 3, respectively representing three layers of red, green, blue;

Eighth step: repeating the third to seventh steps until all watermark information is embedded, thereby obtaining a layered carrier image containing watermarkH _i ^*(ii) a Finally, three layers of layered carrier images containing watermarks are combinedH _i ^*Obtaining a color carrier image containing a watermarkH ^*Whereini=1, 2, 3 respectively represent red, green, blue three layers;

The watermark extraction process is described as follows:

The first step is as follows: aqueous print bearing image by dimension reductionH ^*Divided into three layered images of red, green and blueH _i ^*(ii) a Simultaneously, each containing a printed layered imageH _i ^*Is divided into sizes ofm×mThe non-overlapping pixel block of (1), whereini=1, 2, 3 respectively represent red, green, blue three layers;

The second step is that: sequentially laminating images from aqueous media in a longitudinal orderH _i ^*In selecting adjacent blocks of water-containing print pixelsA ^*AndB ^*whereini=1, 2, 3 respectively represent red, green, blue three layers;

The third step: directly calculating the block of pixels containing watermark in the spatial domain according to the formula (5)A ^*AndB ^*Direct current coefficient ofdc _p ^* ；

(5)

wherein the content of the first and second substances,mIs the size of the row (column) of the pixel square,f _p ^* (x, y) For water-containing printing pixel blockspFirst, thexGo to the firstyThe pixel values of the columns are selected,pEach of =1 and 2 represents a group containingwatermark pixel blockA ^*AndB ^*；

the fourth step: on block of pixels containing waterA ^*andB ^*Direct current coefficient ofdc _p ^* The size relationship between the blocks of pixels containing water print by using the formula (6)A ^*AndB ^*Extracting watermark bits from the imagew*Whereinp=1, 2；

(6)

The fifth step: repeating the second step to the fourth step of the process to obtain the extracted binary watermark sequenceSW _i ^*To watermark the binary sequenceSW _i ^*dividing each 8-bit binary information into a group and converting into decimal pixel values to form a layered watermark image, whereini=1, 2, 3 respectively represent red, green, blue three layers;

And a sixth step: key-based watermarking of layered imagesKa _i Inverse Arnold transform to obtain watermark image of each layerW _i ^*(ii) a Combining layers of extracted watermark imagesW _i ^*Forming a final extracted watermark imageW ^*WhereiniAnd =1, 2 and 3 respectively represent red, green and blue three layers.