CN103295184B - The half water transfer impression method that a kind of frequency domain and spatial domain combine - Google Patents

The half water transfer impression method that a kind of frequency domain and spatial domain combine Download PDF

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CN103295184B
CN103295184B CN201310192123.5A CN201310192123A CN103295184B CN 103295184 B CN103295184 B CN 103295184B CN 201310192123 A CN201310192123 A CN 201310192123A CN 103295184 B CN103295184 B CN 103295184B
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piecemeal
watermark
image
value
watermarking images
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CN103295184A (en
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郑海红
王泉
李建平
潘蓉
王义峰
罗雪梅
谢琨
万波
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Xidian University
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Abstract

The invention discloses the half water transfer impression method that a kind of frequency domain and spatial domain combine, concrete steps comprise: (1) characteristic image extracts; (2) watermarking images pre-service; (3) watermark embedment preprocessing process; (4) eigenmatrix of water mark inlaying is obtained; (5) piecemeal halftone image is obtained; (6) embed watermark; (7) search element and obtain optimum halftone image; (8) image flame detection; (9) obtain containing watermark discrete cosine transform coefficient; (10) watermark is extracted.The invention solves spatial domain half water transfer impression method needs image binaryzation process when extracting watermark, the poor visual effect of image after water mark inlaying, the problem that watermark opposing printing-scanning attack is indifferent.Present invention utilizes the advantage of spatial domain and frequency domain water mark algorithm, not only attack print and scan, random correction and cutting etc. and have very strong robustness, and the visual effect of image is good, watermark embedment capacity increases substantially.

Description

The half water transfer impression method that a kind of frequency domain and spatial domain combine
Technical field
The invention belongs to technical field of image processing, further relate to the half water transfer impression method that a kind of frequency domain in Information Hiding Techniques field and spatial domain combine.While the present invention is used in printing/the output for printing image, by watermark information embedded images, and by the watermark information that the image zooming-out after scanning and printing embeds, realize the copyright protection to printing, printed matter.
Background technology
In recent years, in many printings and publication application, the fake and forged behavior be becoming increasingly rampant brought new challenge to the false proof of printing/the output for printing product.Digital watermark technology is widely used both at home and abroad as the technical measures of copyright protection of digital product.Watermark for printed matters such as printout, books, magazines is halftone image watermark.Half water transfer impression method of robust is mainly divided into two classes: the method that spatial domain method, frequency domain and spatial domain combine.
The patent " the half water transfer impression method based on block of pixels parity check sum block error diffusion " (application number: 201210434246.0, application publication number: CN102930497A) of Xian Electronics Science and Technology University's application discloses a kind of half water transfer impression method based on block of pixels parity check sum block error diffusion.This method propose a kind of using block of pixels as processing unit, and introduce the local binary patterns of reaction partial structurtes feature, embed watermark while adjusting image half, has stronger robustness.But the method still has the following disadvantages, because the method is that visual effect is bad at spatial domain embed watermark.In addition, the air space algorithm that the method adopts is poor to synchronous resistivity, and when synchronous correction is undesirable, watermark extracting can failure.
The people such as Jing-Ming G are at " Watermarking in halftone images with parity-matched errordiffusion " (" Signal Processing " 2011, 91:126-135) a kind of embedding inlay technique is indirectly proposed, the method is based on the statistical property in region, embed watermark is carried out by adding noise while half tune is carried out to image, improve the robustness of watermark to a certain extent, but, the method still has the following disadvantages, due to the method statistical property based on region when extracting watermark, depend on pixel value and quantization threshold, pixel value is unstable before and after print and scan, and work as printer, when scanner models is different, Threshold selection difficulty, therefore have impact on the robustness extracting watermark.
The people such as S.C.Pei are at " Joint halftoning and watermarking " (IEEE Transaction on SignalProcess.51, (4) (2003) 1054-1068) in half method being in harmonious proportion water mark inlaying propose a kind of while, spread spectrum is introduced half water transfer print field by the method, the water mark inlaying image visual effect obtained is good, and has stronger robustness to common image attack, print and scan.But still having the following disadvantages of the method, searches for the method for partly the changing the line map complexity of initial water mark inlaying and operand is very large; Watermark requires known original continuous tone images; Watermark is the sequence of obeying standardized normal distribution, and what can only represent watermark has or nothing, only embedded in 1 watermark in essence, and therefore, the watermark capacity of the method is low.
Summary of the invention
The object of this invention is to provide the half water transfer impression method that a kind of frequency domain and spatial domain combine, mainly while printing/printing to embed watermark in printing/printed works, for copyright protection provides foundation.The subject matter that the present invention will solve be the existing half water transfer impression method parameter combined based on frequency domain and spatial domain more, realize complicated, watermark capacity is low, especially needs the non-blind watermatking problem of continuous-tone image when extracting watermark.
The present invention includes watermark embedment and watermark extracting two processes;
The concrete steps of watermark embed process of the present invention are:
(1) characteristic image is extracted:
1a) carrier image is got from left to right, from top to bottom respectively to 8 pixels and carry out piecemeal, obtain block image;
1b) each piecemeal average is formed according to order from left to right, from top to bottom the eigenmatrix of size, wherein P, Q represent width and the height value of carrier image respectively.
(2) watermarking images pre-service:
Arnold scramble is carried out to binary bitmap matrix, obtains the watermarking images matrix after scramble.
(3) watermark embedment preprocessing process:
3a) 8 × 8 Block DCTs are carried out to the eigenmatrix that step (1) is extracted, obtain the long-lost cosine code matrix of coefficients of eigenmatrix;
3b) to the watermarking images matrix by rows arrangement after step (2) scramble, obtain one dimension watermark sequence;
3c) to one dimension watermark sequence piecemeal, obtain watermark segmentation sequences.
(4) eigenmatrix of water mark inlaying is obtained:
4a) to long-lost cosine code matrix of coefficients according to getting a piecemeal from left to right, from top to bottom, this piecemeal from last element according to "the" shape sequence, obtain long-lost cosine code coefficient sequence;
4b) to watermark segmentation sequences according to getting a piecemeal from front to back, successively all elements is got to piecemeal, if get element value be 1, then the element value of discrete cosine transform coefficient sequence is revised as 20, otherwise be revised as-20, obtain the discrete cosine transform coefficient sequence of embed watermark;
4c) judge whether all piecemeals taking dct coefficient matrix, if do not taken, then perform step 4a), until take all piecemeals of dct coefficient matrix, obtain the dct coefficient matrix of water mark inlaying;
4d) 8 × 8 piecemeal inverse discrete cosine transforms are carried out to the dct coefficient matrix of water mark inlaying, obtain the eigenmatrix of water mark inlaying.
(5) piecemeal halftone image is obtained:
5a) to the carrier image of step (1), adopt image partly to adjust method, partly mediate reason, obtain halftone image;
5b) halftone image is got from left to right, from top to bottom respectively to 8 pixels and carry out piecemeal, obtain piecemeal halftone image.
(6) embed watermark:
6a) piecemeal is got from left to right, from top to bottom to piecemeal halftone image, calculate piecemeal average, obtain piecemeal average;
6b) element is got from left to right, from top to bottom as comparison element to the eigenmatrix of water mark inlaying, the relatively value of this comparison element and the size of piecemeal average, if this comparison element value is greater than piecemeal average, then the value of the black picture element of in piecemeal is revised as 255; Otherwise, in piecemeal one white pixel value is revised as 0, recalculates piecemeal average, until when the absolute value of the difference of the value of this comparison element and piecemeal average is less than 2, no longer go to revise the pixel value in piecemeal, obtain a piecemeal in water mark inlaying piecemeal halftone image;
6c) judge whether all piecemeals taking piecemeal halftone image, if do not taken, then perform step 6a), until take all piecemeals of piecemeal halftone image, obtain water mark inlaying piecemeal halftone image.
(7) search obtains optimum water mark inlaying halftone image:
To water mark inlaying piecemeal halftone image according to from left to right, order from top to bottom performs the direct two-value search DBS method only exchanging and do not overturn to each piecemeal, until obtain optimum water mark inlaying halftone image, complete watermark embed process; Optimum water mark inlaying halftone image is printed, scans, obtain the image scanning rear embed watermark.
The concrete steps of described watermark extraction process are as follows:
(8) image flame detection:
Utilize Photoshop software to carry out cutting and scaling to the image after scanning, obtain the image containing watermark.
(9) obtain containing watermark dct coefficient matrix:
9a) 8 pixels are got from left to right, from top to bottom respectively to the image containing watermark and carry out piecemeal, obtain piecemeal containing watermarking images;
9b) ask each piecemeal containing the mean value of all pixels in watermarking images, then according to order composition from left to right, from top to bottom size containing watermarking images eigenmatrix, wherein P, Q represent width and the height value of carrier image respectively;
9c) carry out 8 × 8 Block DCTs to containing watermarking images eigenmatrix, obtain containing watermark dct coefficient matrix.
(10) watermark is extracted:
10a) get 8 × 8 piecemeals to containing watermark dct coefficient matrix order from left to right, from top to bottom, this piecemeal is sorted according to "the" shape from last element, obtain containing watermark discrete cosine transform coefficient sequence;
10b) get successively containing before watermark discrete cosine transform coefficient sequence each element of individual element judges, if element value is greater than 0, then watermark bit is set to 1, otherwise watermark bit is set to 0, obtain a piecemeal of watermark sequence, wherein U, V represent width and the height value of watermarking images respectively, and N represents the piecemeal number of Block DCT matrix of coefficients;
10c) judge whether to take all piecemeals containing watermark dct coefficient matrix, if do not taken, then perform step 10a), until take all piecemeals containing watermark dct coefficient matrix, obtain watermark sequence;
10d) watermark sequence of acquisition is become the two-dimensional matrix of U × V according to vertical sequential transformations, obtain original watermark image, wherein U, V represent width and the height value of watermarking images respectively;
10e) inverse Arnold scramble is carried out to original watermark image, obtain the watermarking images extracted.
Compared with prior art, the present invention has the following advantages:
First, the present invention selects at frequency domain embed watermark, and is tie with characteristic image, instructs generation spatial domain water mark inlaying partly to change the line map, overcome the anti-printing-scanning attack of spatial domain method this shortcoming indifferent in prior art, make the present invention have strong robustness and the good advantage of water mark inlaying picture quality.
Second, the present invention does not need to carry out binary conversion treatment to partly changing the line map of scanning before extracting watermark, the pixel value overcoming prior art is unstable before and after print and scan, and when printer, scanner models difference, the shortcoming of Threshold selection difficulty, makes the present invention have the advantage more easily extracting watermarking images.
3rd, the watermark embedding method of the present invention's structure, not only increases watermark capacity, and overcomes watermark extracting in existing similar technique and need the shortcoming of original continuous figure, make the present invention have watermark capacity high, can the advantage of Blind extracting.
Accompanying drawing illustrates:
Fig. 1 is process flow diagram of the present invention;
Fig. 2 is the schematic diagram that the present invention emulates 1;
Fig. 3 is the schematic diagram that the present invention emulates 2;
Fig. 4 is the schematic diagram that the present invention emulates 3;
Fig. 5 is the schematic diagram that the present invention emulates 4.
Embodiment:
Below in conjunction with accompanying drawing, the present invention is described in detail.
Concrete steps with reference to accompanying drawing 1 the inventive method are as follows.
Step 1, extracts characteristic image.
Carrier image is got from left to right, from top to bottom respectively to 8 pixels and carry out piecemeal, obtain block image.The mean value of the pixel value of all pixels that the piecemeal calculating block image comprises, then forms mean value according to order from left to right, from top to bottom the eigenmatrix of size, wherein P, Q represent width and the height value of carrier image respectively, and the carrier image size used in the embodiment of the present invention is 2048 × 2048, so the eigenmatrix size obtained is 256 × 256.
Step 2, watermarking images pre-service.
Carry out Arnold disorder processing to binary bitmap, obtain the watermarking images after scramble, scramble can strengthen the robustness that various attack is resisted in watermark.First the Arnold shuffling cycle of watermarking images is determined, scramble parameter can be selected to be greater than zero and the arbitrary integer being less than shuffling cycle, the watermarking images size used in the embodiment of the present invention is 64 × 64, and its Arnold shuffling cycle is 48, selects scramble parameter to be 20.
Step 3, watermark embedment preprocessing process.
8 × 8 Block DCTs are carried out to the eigenmatrix extracted, obtains the dct coefficient matrix of eigenmatrix, by discrete cosine transform, eigenmatrix is changed to frequency domain, the robustness of watermark can be increased at frequency domain water mark inlaying.
To the watermarking images matrix by rows arrangement after scramble, obtain one dimension watermark sequence.To one dimension watermark sequence according to vertical order, get at every turn get element as a piecemeal, until take all elements of one dimension watermark sequence, wherein U, V represent width and the height value of watermarking images respectively, N represents the piecemeal number of Block DCT matrix of coefficients, obtain watermark segmentation sequences, the watermarking images size used in the embodiment of the present invention is 64 × 64, so U=64, V=64.
Step 4, obtains the eigenmatrix of water mark inlaying.
The first step, to long-lost cosine code matrix of coefficients according to getting a piecemeal from left to right, from top to bottom, this piecemeal sorts according to "the" shape from last element, obtain long-lost cosine code coefficient sequence, the coefficient of the discrete cosine sequence that the method obtains, according to the order arrangement from high frequency to low frequency, is conducive to the embedding of watermark in step below.
Second step, to watermark segmentation sequences according to getting a piecemeal from front to back, successively all elements is got to piecemeal, if get element value be 1, then the element value of long-lost cosine code coefficient sequence is revised as 20, otherwise be revised as-20, obtain the long-lost cosine code coefficient sequence of embed watermark, drawn by a large amount of experimental results, when the embedment strength value of watermark is 20, the extraction effect of watermark is relatively good on the one hand, and after embed watermark, the visual effect of image is relatively good on the other hand, and these two aspects achieve a well compromise.
3rd step, judges whether all piecemeals taking long-lost cosine code matrix of coefficients, if do not taken, then forwards step 4 to and continues to perform, finally obtain the long-lost cosine code matrix of coefficients of water mark inlaying.
4th step, carries out 8 × 8 piecemeal inverse discrete cosine transforms to the dct coefficient matrix of water mark inlaying, obtains the eigenmatrix of water mark inlaying.
Step 5, obtains piecemeal halftone image.
Partly reason is mediated to carrier image, obtain halftone image, half tune method of image has three classes, one is dithering, two is error-diffusion methods, three is direct two-value search procedures, the processing speed of dither method is fast, but visual effect is poor, direct two-value searching method visual effect is best, but time complexity is the highest, and the visual effect of error-diffusion method and time complexity are between first two method, so the present invention adopts the Floyd half tune method of the classics in error-diffusion method partly to mediate reason to image.Halftone image is got from left to right, from top to bottom respectively to 8 pixels and carry out piecemeal, obtain piecemeal halftone image.
Step 6, embed watermark.
The first step, gets a piecemeal from left to right, from top to bottom to piecemeal halftone image, and calculate piecemeal average, obtain piecemeal average, piecemeal average here refers to the mean value of the pixel value of all pixels that this piecemeal comprises.
Second step, an element is got from left to right, from top to bottom to the eigenmatrix of water mark inlaying, as comparison element, the relatively value of this comparison element and the size of piecemeal average, if this comparison element value is greater than piecemeal average, then the value of the black picture element of in piecemeal is revised as 255, otherwise, the value of the white pixel of in piecemeal is revised as 0, recalculate piecemeal average, until the absolute value of the difference of the value of this element and piecemeal average is less than 2, no longer goes to revise the pixel value in piecemeal, obtain a piecemeal in water mark inlaying piecemeal halftone image.Here black picture element refers to the pixel that pixel value is 0, and white pixel here refers to the pixel that pixel value is 255.
3rd step, judges whether all piecemeals taking piecemeal half tone image, if do not taken, then performs the first step, until obtain water mark inlaying piecemeal halftone image.
Step 7, search obtains optimum water mark inlaying halftone image.
To water mark inlaying piecemeal halftone image according to from left to right, order from top to bottom performs the direct two-value search DBS method only exchanging and do not overturn to each piecemeal, until obtain optimum water mark inlaying halftone image, complete watermark embed process; Print optimum water mark inlaying halftone image, scan, obtain the image after scanning, only exchange the direct two-value search DBS method do not overturn and refer to that central element exchanges with the element of 8 neighborhoods, self does not overturn.
Step 8, image flame detection.
Utilize the automatic cutting function of Photoshop software to carry out cutting to the image after scanning, cut off the white edge scanned above the image that obtains, and by the scaling function of this software by image zooming to starting vector image size, obtain the image containing watermark.
Step 9, obtains containing watermark long-lost cosine code matrix of coefficients.
8 pixels are got from left to right, from top to bottom respectively to the image containing watermark and carries out piecemeal, obtain piecemeal containing watermarking images.Ask the mean value of all pixels in each block image, then according to order composition from left to right, from top to bottom size containing watermark eigenmatrix, wherein P, Q represent width and the height value of carrier image respectively, and the carrier image size used in the embodiment of the present invention is 2048 × 2048, so P=2048, Q=2048.Carry out 8 × 8 piecemeal long-lost cosine code to containing watermark eigenmatrix, obtain containing watermark long-lost cosine code matrix of coefficients.
Step 10, extracts watermark.
The first step, gets 8 × 8 piecemeals to containing watermark long-lost cosine code matrix of coefficients order from left to right, from top to bottom, sorts from last element to this piecemeal according to "the" shape, obtains containing watermark long-lost cosine code coefficient sequence.
Second step, gets successively containing before watermark long-lost cosine code coefficient sequence each element of individual element judges, if element value is greater than 0, then watermark bit is set to 1, otherwise watermark bit is set to 0, obtain a piecemeal of watermark sequence, wherein U, V represent width and the height value of watermarking images respectively, and N represents the piecemeal number of piecemeal long-lost cosine code matrix of coefficients.
3rd step, judges whether to take all piecemeals containing watermark long-lost cosine code matrix of coefficients, if do not taken, then performs the first step, until obtain watermark sequence.
4th step, the watermark sequence obtained is become to the two-dimensional matrix of U × V according to vertical sequential transformations, obtain original watermark image, wherein U, V represent width and the height value of watermarking images respectively, the watermarking images size used in the embodiment of the present invention is 64 × 64, so U=64, V=64.
5th step, carries out the watermarking images that inverse Arnold scramble obtains extracting.The watermarking images size used in the embodiment of the present invention is 64 × 64, and its Arnold shuffling cycle is 48, selects scramble parameter to be 20 in the embodiment of the present invention, so inverse Arnold scramble parameter is 28.
Below in conjunction with analogous diagram, effect of the present invention is further described.
The printer model selected in the present invention's emulation is HP Color LaserJet CP2025, and scanner models is EPSON Perfection1200U, and the resolution printing and scan is all 300dpi.Evaluate the quality containing watermarking images with Y-PSNR HPSNR, evaluate the quality extracting watermarking images with CDR (correct extraction ratio).Use the inventive method as follows to the watermark embedment of gray level image, extraction and attack emulation:
With reference to accompanying drawing 2, use in emulation 1 of the present invention model for HP Color LaserJet CP2025 printer and model be EPSON Perfection1200U scanner.Fig. 2 (a) is image-carrier image, and size is 2048 × 2048, Fig. 2 (b) is watermarking images, and size is 64 × 64.Use the inventive method, what obtain contains watermarking images as Fig. 2 (c), HPSNR=33.4602, the image after print scanned rectification is as Fig. 2 (d), and the watermarking images of extraction is as Fig. 2 (e), CDR=93.72%;
The interpretation of result of emulation 1, as can be seen from Fig. 2 (c), in carrier image after embed watermark, the quality of image does not almost decline.As can be seen from Fig. 2 (e), still can extract watermark clearly containing watermarking images through printing, scanning, illustrate that the inventive method has very strong robustness to attacks of print_scan.
Emulation 2, with reference to accompanying drawing 3 emulate in use model for HP Color LaserJet CP2025 printer and model be EPSON Perfection1200U scanner, Fig. 3 (a) is carrier image, size is 2048 × 2048, Fig. 3 (b) is watermarking images, and size is 64 × 64.Fig. 3 (c) is for containing watermarking images.To carrying out shearing attack containing watermarking images, cutting size is the white blocks of 1024 × 1024, as shown in Fig. 3 (d), the watermarking images of extraction as shown in Fig. 3 (e), CDR=92.7%.From the result of emulation 2, the inventive method has very strong robustness to shearing attack.
Emulation 3, with reference to accompanying drawing 4, use in emulation model for HP Color LaserJet CP2025 printer and model be EPSON Perfection1200U scanner, Fig. 4 (a) is carrier image, size is 2048 × 2048, Fig. 4 (b) is watermarking images, and size is 64 × 64.Fig. 4 (c) is for containing watermarking images.Attack adding salt-pepper noise containing watermarking images, plus noise parameter is 0.05, as shown in Fig. 4 (d), the watermarking images extracted, as shown in Fig. 4 (e), CDR=100%, from the result of emulation 3, method of the present invention is attacked salt-pepper noise also has very strong robustness.
Emulation 4, with reference to accompanying drawing 5.Use in emulation model for HP Color LaserJet CP2025 printer and model be EPSON Perfection1200U scanner, Fig. 5 (a) is carrier image, size is 2048 × 2048, Fig. 5 (b) is watermarking images, and size is 64 × 64.Fig. 5 (c) is for containing watermarking images.To altering attack at random containing watermarking images, as shown in Fig. 5 (d), the watermarking images of extraction as shown in Fig. 5 (e), CDR=99.07%.From the result of emulation 4, the inventive method is attacked random correction has very strong robustness equally.
Can be drawn by the result of emulation, use the inventive method obtain containing watermarking images through print scanned, alter, add salt-pepper noise and shearing attack after, watermark can be extracted clearly.Illustrate that method of the present invention can resist print scanned, correction, cutting, add the attacks such as salt-pepper noise thus, watermark has very strong robustness.

Claims (5)

1. the half water transfer impression method that combines of frequency domain and spatial domain, comprises watermark embedment and watermark extracting two processes;
The concrete steps of described watermark embed process are:
(1) characteristic image is extracted:
1a) carrier image is got from left to right, from top to bottom respectively to 8 pixels and carry out piecemeal, obtain block image;
1b) each piecemeal average is formed according to order from left to right, from top to bottom the eigenmatrix of size, wherein P, Q represent width and the height value of carrier image respectively;
(2) watermarking images pre-service:
Arnold scramble is carried out to binary bitmap matrix, obtains the watermarking images matrix after scramble;
(3) watermark embedment preprocessing process:
3a) carry out 8 × 8 Block DCTs to the eigenmatrix that step (1) is extracted, the discrete cosine obtaining eigenmatrix becomes changematrix of coefficients;
3b) to the watermarking images matrix by rows arrangement after step (2) scramble, obtain one dimension watermark sequence;
3c) to one dimension watermark sequence piecemeal, obtain watermark segmentation sequences;
(4) eigenmatrix of water mark inlaying is obtained:
4a) discrete cosine is become changematrix of coefficients is according to getting a piecemeal from left to right, from top to bottom, and this piecemeal according to "the" shape sequence, obtains discrete cosine and becomes from last element changecoefficient sequence;
4b) to watermark segmentation sequences according to getting a piecemeal from front to back, successively all elements is got to piecemeal, if get element value be 1, then the element value of discrete cosine transform coefficient sequence is revised as 20, otherwise be revised as-20, obtain the discrete cosine transform coefficient sequence of embed watermark;
4c) judge whether all piecemeals taking dct coefficient matrix, if do not taken, then perform step 4a), until take all piecemeals of dct coefficient matrix, obtain the dct coefficient matrix of water mark inlaying;
4d) 8 × 8 piecemeal inverse discrete cosine transforms are carried out to the dct coefficient matrix of water mark inlaying, obtain the eigenmatrix of water mark inlaying;
(5) piecemeal halftone image is obtained:
5a) to the carrier image of step (1), adopt image partly to adjust method, partly mediate reason, obtain halftone image;
5b) halftone image is got from left to right, from top to bottom respectively to 8 pixels and carry out piecemeal, obtain piecemeal halftone image;
(6) embed watermark:
6a) piecemeal is got from left to right, from top to bottom to piecemeal halftone image, calculate piecemeal average, obtain piecemeal average;
6b) element is got from left to right, from top to bottom as comparison element to the eigenmatrix of water mark inlaying, the relatively value of this comparison element and the size of piecemeal average, if this comparison element value is greater than piecemeal average, then the value of the black picture element of in piecemeal is revised as 255; Otherwise, in piecemeal one white pixel value is revised as 0, recalculates piecemeal average, until when the absolute value of the difference of the value of this comparison element and piecemeal average is less than 2, no longer go to revise the pixel value in piecemeal, obtain a piecemeal in water mark inlaying piecemeal halftone image;
6c) judge whether all piecemeals taking piecemeal halftone image, if do not taken, then perform step 6a), until take all piecemeals of piecemeal halftone image, obtain water mark inlaying piecemeal halftone image;
(7) search obtains optimum water mark inlaying halftone image:
To water mark inlaying piecemeal halftone image according to from left to right, order from top to bottom performs the direct two-value search DBS method only exchanging and do not overturn to each piecemeal, until obtain optimum water mark inlaying halftone image, complete watermark embed process; Optimum water mark inlaying halftone image is printed, scans, obtain the image scanning rear embed watermark;
The concrete steps of described watermark extraction process are as follows:
(8) image flame detection:
Utilize Photoshop software to carry out cutting and scaling to the image after scanning, obtain the image containing watermark;
(9) obtain containing watermark dct coefficient matrix:
9a) 8 pixels are got from left to right, from top to bottom respectively to the image containing watermark and carry out piecemeal, obtain piecemeal containing watermarking images;
9b) ask each piecemeal containing the mean value of all pixels in watermarking images, then according to order composition from left to right, from top to bottom size containing watermarking images eigenmatrix, wherein P, Q represent width and the height value of carrier image respectively;
9c) carry out 8 × 8 Block DCTs to containing watermarking images eigenmatrix, obtain containing watermark dct coefficient matrix;
(10) watermark is extracted:
10a) get 8 × 8 piecemeals to containing watermark dct coefficient matrix order from left to right, from top to bottom, this piecemeal is sorted according to "the" shape from last element, obtain containing watermark discrete cosine transform coefficient sequence;
10b) get successively containing before watermark discrete cosine transform coefficient sequence each element of individual element judges, if element value is greater than 0, then watermark bit is set to 1, otherwise watermark bit is set to 0, obtain a piecemeal of watermark sequence, wherein U, V represent width and the height value of watermarking images respectively, and N represents the piecemeal number of Block DCT matrix of coefficients;
10c) judge whether to take all piecemeals containing watermark dct coefficient matrix, if do not taken, then perform step 10a), until take all piecemeals containing watermark dct coefficient matrix, obtain watermark sequence;
10d) watermark sequence of acquisition is become the two-dimensional matrix of U × V according to vertical sequential transformations, obtain original watermark image, wherein U, V represent width and the height value of watermarking images respectively;
10e) inverse Arnold scramble is carried out to original watermark image, obtain the watermarking images extracted.
2. the half water transfer impression method that combines of a kind of frequency domain according to claim 1 and spatial domain, is characterized in that: step 3c) described in the method for one dimension watermark sequence piecemeal be, to the vertical order of one dimension watermark sequence, get at every turn get element as a piecemeal, until take all elements of one dimension watermark sequence, wherein U, V represent width and the height value of watermarking images respectively, and N represents that piecemeal discrete cosine becomes changethe piecemeal number of matrix of coefficients.
3. the half water transfer impression method that combines of a kind of frequency domain according to claim 1 and spatial domain, is characterized in that: step 6b) described in black picture element refer to, pixel value is the pixel of 0.
4. the half water transfer impression method that combines of a kind of frequency domain according to claim 1 and spatial domain, is characterized in that: step 6b) described in white pixel refer to, pixel value is the pixel of 255.
5. the half water transfer impression method that combines of a kind of frequency domain according to claim 1 and spatial domain, it is characterized in that: the method for the direct two-value search DBS that only exchanging described in step (7) does not overturn refers to, central element only exchanges with the element of 8 neighborhoods, and self does not overturn.
CN201310192123.5A 2013-05-13 2013-05-13 The half water transfer impression method that a kind of frequency domain and spatial domain combine Active CN103295184B (en)

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