CN105404817A - (k,n) threshold based user-friendly visual secret sharing method - Google Patents
(k,n) threshold based user-friendly visual secret sharing method Download PDFInfo
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Abstract
The invention discloses a (k,n) threshold based user-friendly visual secret sharing method and mainly solves the problems of low security and contrast in the prior art. The method is implemented by the steps of 1, performing (k,n) random grid processing on a binary secret image S to obtain n basic shared images of random grids; 2, performing block segmentation on an input gray cover image by using histogram equalization to obtain a gray level equivalent to the gray level of each small image block; 3, performing halftone processing on the cover image subjected to the block segmentation, and according to a generated dithering matrix, obtaining a shared cover image after the halftone processing; and 4, performing block segmentation on the generated basic shared images and cover image, performing combination according to a stacking ratio of a constant value delta, and performing block segmentation and combination to generate a meaningful final shared image. According to the method, the attack of attackers can be prevented, the meaningful final shared image can be generated, and the application range of visual secret sharing can be extended.
Description
Technical field
The present invention relates to field of information security technology, is a kind of visual secret sharing scheme method of Information hiding, is called the user-friendly visual secret sharing scheme method of (k, n) thresholding, can be used for protect image, Image Sharing, Image Real-time Transmission etc.
Background technology
1979, Blakley and Shamir proposed the concept of privacy share respectively.Privacy share method is that secret is divided into different shares, and the share being wherein more than or equal to specific quantity arbitrarily can recover secret, otherwise then can not.Because image uses widely in life, nineteen ninety-five, Naor and Shamir is incorporated into image processing field privacy share method, and proposes first visual secret image share method.Secret Image is divided into different shares by visual secret sharing scheme method, and the share being wherein more than or equal to arbitrarily specific quantity can recover Secret Image, otherwise then can not.Secret image share method is that the security of Secret Image in transmission or storing process provides a kind of effective method, especially in military affairs, and business, the fields such as finance.Secret image share method is divided into two kinds now.The first is visual secret sharing scheme, and the share by some is superimposed just can find out Secret Image by vision.The second is computable Secret Image Sharing, namely just can recover Secret Image by the share of computer disposal some.Because computable Secret Image Sharing needs very complicated algorithm and operation, and rejuvenation is very complicated, so visual secret sharing scheme obtains large quantifier elimination.In the visual secret sharing scheme in early stage, share Secret Image converted to has pixel expansion, and the size of the image after conversion is more much bigger than original image.Due to the existence of pixel expansion, make Secret Image can not by undistorted recovery.1987, Kafri and Keren proposes the visual secret sharing scheme method based on random grid, but do not cause enough attention at that time, after 2006, a lot of method brings into use the visual secret sharing scheme method based on random grid, and this method had not both had pixel expansion not need to make complicated code book yet.But this method is producing in the process sharing image, because produced shared image is insignificant random grid image, so easily cause the attention of assailant, and then destroy shared image or the image that betrays the pot to the roses, the Secret Image contrast after simultaneously recovering is not high yet.Simultaneously a lot of people propose based on the visual secret sharing scheme method of threshold schemes and the visual secret sharing scheme method of general access structure, this method is extended from security and the scope of application, but because the image of the random grid produced is meaningless, security is defectiveness still.After 2011, formally proposed based on user-friendly visual secret sharing scheme method first time, random grid image Secret Image produced embeds in surface plot picture, thus forms significant share, becomes user-friendly method.Compared with single random grid image, the same with shared image in user-friendly shared image visual effect after recovery, therefore it can prevent the attention and the destruction that cause malicious attacker.But the method is only applicable to the threshold schemes of (n, n), and after superposition, picture contrast is low especially, and color of image is black especially.In user-friendly visual secret sharing scheme method, contrast is an important indicator weighing performance quality, generally there are contrast two coefficients of shared picture contrast and the rear Secret Image of recovery, generally share image more, Secret Image contrast after recovery is lower, and black picture element is also more.
Document " Thresholdvisualsecretsharingbyrandomgrids.TheJournalofSy stemsandSoftware; 2011; 84 (2011) 1197 – 1208. " proposes (a k, n) the visual secret sharing scheme method based on random grid of thresholding, visual secret sharing scheme method is got a promotion in the safety and anti-fraud of transmission, wherein k represents threshold value and namely deciphers required minimum participant's number, picture number and participant's number, wherein k≤n are shared in n representative.The key step of the method is: the first, with reference to the visual secret sharing scheme method of tradition based on random grid, and operates the pixel of Secret Image; The second, according to the random grid method adopted, the pixel of Secret Image is operated, produce the pixel required by k; The pixel of the 3rd, remaining n-k determines its pixel value according to toss a coin method; 4th, calculated n position pixel is randomly assigned to n width image, and every locus selected by width figure must be consistent; 5th, continue aforesaid operations, until the pixel of all Secret Image is all removed, finally obtain n width random grid image, and at least k width imaging importing just can draw Secret Image.But the method exists some defects: the first, the contrast of the method is very low.The method obtains n-k pixel at random owing to using, and the contrast after causing superimposed image is low especially.Second, the method security is low especially, the random grid of random generation is all insignificant, be inconvenient to manage, this is easy to the attention causing malicious attacker in transmission and storing process, thus destroys the integrality of image, causes recovering Secret Image, sometimes even can be stolen shared share, causes Secret Image to leak.
Summary of the invention
The object of the invention is for above-mentioned the deficiencies in the prior art, propose a kind of based on (k, n) the user-friendly visual secret sharing scheme method of threshold schemes, the method is applied in gray-scale map, to strengthen the range of application of visual Secret Image, improve the transmission of image and the security of storage.
The main technical principle realizing the object of the invention is:
First utilize histogram equalization to reach and improve final significant shared image and recover the object of rear Secret Image contrast.Concrete grammar is to fragmental image processing, carries out equivalence similar, obtain the gray shade scale of every fritter gray equivalent with image to the mean gradation of each block of the image after piecemeal, improves the contrast of the surface plot picture after sharing.Adopt shaking way to carry out the halftone process of gray level image, produce dither matrix, the method speed is fast, can expand the method and be applied in gray-scale map.Combine with (k, n) gate method simultaneously, and in conjunction with above-mentioned two kinds of mode process surface plot pictures and Secret Image, obtain last significant shared image, reach the object that shared Graphical User contrast that is friendly and Secret Image after recovering improves.
According to above principle, the method performing step comprises as follows:
(1) the two-value Secret Image S that will protect carries out (k, n) random grid encryption, obtain k width basis and share random grid image, then generate remaining n-k width basis according to toss a coin method and share random grid image, altogether obtain n width basis and share random grid image, wherein k is threshold value, and n is the quantity of participant;
(2) n width gray scale surface plot picture is inputted, first every width gray level image is divided into the identical fritter of size, utilize histogram equalization process image fritter, then it is similar to carry out equivalence to the mean gradation of each image fritter, obtains the gray shade scale with each image fritter equivalence;
(3) as fritter, shake halftone process is carried out to the surface plot after step (2) histogram equalization process, first produce dither matrix, according to dither matrix, obtain the front cover after halftone process and share image;
(4) stacking ratio δ is set, wherein 0≤δ≤1, the basis that step (1) produces is shared the front cover that random grid image and step (3) produce and share the first piecemeal process of image, image after piecemeal process is carried out stacking process, generates user-friendly final shared image.
(5) the n width generated in step (4) is finally shared image to take out and be more than or equal to arbitrarily k width and finally share image they are superposed, the Secret Image after being restored.
Utilize histogram equalization process front cover image method described in step of the present invention (2), carry out as follows:
2a) by surface plot as C
1, C
2..., C
nall change and be decomposed into the pixel fritter that size is h × w, and h × w is minimum can not be less than 2;
2b) establish D
i,jfor surface plot is as C
ia jth data block, ask for the β simultaneously meeting formula (1) and (2), make D
i,jprogression equal β,
β≤d≤β+1(1)
Wherein, D
i,jrepresentative is at original covers image C
ia jth data block, D
i,javerage gray level be d, in formula
what represent is at original image C
imiddle gray level is the number of pixels of k, β ∈ 0,1 ..., h × w-1} is the value of all progression, and its value is determined by the size of piecemeal, wherein 1≤i≤n, 1≤j≤(r × c)/(h × w);
2c) when the progression of all piecemeals is by step 2b) in after formula obtains, label matrix L
1, L
2..., L
nrespectively by the surface plot of correspondence as C
1, C
2..., C
nobtain, L
isize is (r × c)/(h × w), store all at surface plot as C
ithe progression of piecemeal, to fragmental image processing, equivalence is carried out to the mean gradation of each block similar, obtains the gray shade scale of every fritter h × w gray equivalent with image, wherein i=1,2 ..., n.
Utilize dither matrix to carry out halftoning method in step of the present invention (3) to obtain as follows:
3a) utilize original gradation surface plot as C
1, C
2..., C
nrebuild n dither matrix M
1, M
2..., M
n, be of a size of h × w, dither matrix M
tin pixel be M
t i,j, wherein t=1,2 ..., n, 1≤i≤h, 1≤j≤w;
If label matrix L 3b) required by step (2)
tpixel value L
i,j≤ M
i,j, at P
i,jcoordinate (i, j) position get black picture element, otherwise at P
i,j(i, j) position extracting waste pixel, wherein t=1,2 ..., n, 1≤i≤h, 1≤j≤w;
3c) in conjunction with all halftone pattern P
i,jproduce final required half tone image, 1≤i≤r, 1≤j≤c and then obtain all piecemeal front covers and share image P
t, wherein t=1,2 ..., n;
3d) partitioned matrix is converted to original matrix P
i, being converted to final size is successively that n the matrix of r × c shares image as required front cover, wherein i=1,2 ..., n.
The present invention compared with the conventional method tool has the following advantages:
1. because the present invention uses shake halftone technique, therefore (k, n) scheme can be applied in gray scale surface plot picture, improve the image applications scope of scheme;
2. owing to present invention uses histogram equalization, obtain the image outline of gray-scale map more clearly, improve the final contrast sharing image and the Secret Image after recovering, improve the visual effect that front cover shares image, thus the usable range of the program;
3. because the present invention utilizes basis surface plot picture being embedded into Secret Image to share in random grid image, shared image is made to become meaningful, improve the security of (k, n) scheme, simultaneously significant shared image is also convenient to user and is managed numerous shared image.
Accompanying drawing explanation
Fig. 1 of the present inventionly realizes general flow chart;
Fig. 2 be four of use of the present invention large little be 512 × 512 gray scale surface plot picture, in figure, (a)-(d) is respectively four surface plot pictures;
Fig. 3 is use two-value Secret Image S of the present invention;
Fig. 4 is four (a)-(d) finally sharing image and correspond to respectively that the present invention produces;
Fig. 5 is that four emulation stack result images of the present invention correspond to (a)-(d) respectively;
Fig. 6 is that four final images of sharing that tradition (k, n) scheme produces correspond to (a)-(d) respectively;
Fig. 7 is that four emulation stack result images of tradition (k, n) scheme correspond to (a)-(d) respectively.
Embodiment
Below in conjunction with the description that accompanying drawing carries out the specific embodiment of the present invention.
With reference to Fig. 1, performing step of the present invention is as follows:
Step 1, input needs a width Secret Image S of protection, and n width surface plot is as C.
Secret Image S is the image needing protection, and surface plot is used for hiding Secret Image S as C, and surface plot picture is necessary equal with secret dimension of picture, and be set to r × c here, r represents the height of Secret Image and surface plot picture, and c represents the width of Secret Image and surface plot picture.
Step 2, utilize tradition to produce shared image based on the method for random grid, what Secret Image S adopted is bianry image, for traditional visual secret sharing scheme method based on random grid, first to the pixel S of Secret Image S
i,jencode, first traditional random grid is introduced below.
2a) produce random grid G according to toss a coin mode
1;
2b) as the pixel S of Secret Image S
i,jduring for white, then second random grid G
2in pixel G
2 i,jwith random grid G
1in pixel G
1 i,jbe worth identical, otherwise value is contrary, wherein 1≤i≤r, 1≤j≤c, wherein r and c is respectively the wide and high of Secret Image S.
Step 3, random grid image B is shared on the basis producing (k, n) gate method
t:
3a) according to above-mentioned steps 2 couples of S
i,jall pixels are encoded successively, to each the pixel S in Secret Image S
i,jencode successively, obtain pixel bit value g1
i,jand g2 '
i,j; In the same manner to g2 '
i,jencode, obtain bit value g2
i,jand g3 '
i,j, more in the same manner to g3 '
i,jencode, obtain bit value g3
i,jand g4 '
i,j, repeat this computing, obtain g1
i,j, g2
i,j..., gk
i,j, wherein gk
i,jwith gk '
i,jwhat represent is same bit, and wherein i, j are respectively pixel horizontal ordinate and the ordinate of Secret Image S, 1≤i≤r, 1≤j≤c;
3b) random selecting k random grid, by step 3a) calculated by k bit value put into the pixel at the same spatial location place of this k random grid, form k sub-set B
* 1 i,j, B
* 2 i,j..., B
* k i,j, wherein 1≤i≤r, 1≤j≤c;
3c) by the n-k of remainder random grid image { B
1, B
2..., B
n}-{ B
* 1, B
* 2..., B
* kpixel randomly draw pixel value according to toss a coin mode, these obtain pixel value and B at random
* 1 i,j, B
* 2 i,j..., B
* k i,jthe locus got is consistent, wherein 1≤i≤r, 1≤j≤c;
3d) repeat step 3a)-3b), until all pixel coders complete in Secret Image S, thus produce all bases and share random grid image B
i, wherein i=1,2 ..., n.
Step 4, carries out histogram equalization to each surface plot as C, and surface plot picture is decomposed into the fritter that pixel is h × w size, and h represents the height of piecemeal, and w represents the width of piecemeal.
Surface plot picture is all gray level image, to fragmental image processing, equivalence is carried out to the mean gradation of each block similar, obtain the gray shade scale of every fritter gray equivalent with image, in order to improve share after the contrast of surface plot picture, histogram equalization can obtain the image outline of gray-scale map more clearly, and the contrast of Secret Image is after recovery also very high, map the block of block to its shared image of Secret Image, this method uses the concrete steps of histogram equalization as follows:
4a) by surface plot as C
1, C
2..., C
nall change and be decomposed into the pixel fritter that size is h × w.For the image of different size, h × w is not identical yet, and generally h × w is less, and h × w is minimum can be 2, after front cover share visual quality better;
4b) establish D
i,jfor surface plot is as C
ia jth data block, ask for the β simultaneously meeting formula (1) and (2), make D
i,jprogression equal β,
β≤d≤β+1(1)
Wherein, D
i,jrepresentative is at original covers image C
ia jth data block, D
i,javerage gray level be d, in formula
what represent is at original image C
imiddle gray level is the number of pixels of k, β ∈ 0,1 ..., h × w-1} is the value of all progression, and its value is determined by the size of piecemeal, wherein 1≤i≤n, 1≤j≤(r × c)/(h × w);
4c) when the progression by all piecemeals is by step 4b) in formula determine after, label matrix L
1, L
2..., L
nrespectively by the C of correspondence
1, C
2..., C
nobtain.Label matrix L
i, size is (r × c)/(h × w), its store all at surface plot as C
ithe progression of piecemeal, to fragmental image processing, equivalence is carried out to the mean gradation of each block similar, obtains the gray shade scale of every fritter h × w gray equivalent with image, facilitate the halftone process of ensuing gray-scale map, wherein i=1,2 ..., n.
Step 5, all blocks obtained are carried out the halftone process of jitter mode:
5a) utilize original gradation surface plot as C
1, C
2..., C
nrebuild n dither matrix M
1, M
2..., M
n, be of a size of h × w, dither matrix M
tin pixel be M
t i,j, wherein t=1,2 ..., n, 1≤i≤h, 1≤j≤w;
If if label matrix L 5b) required by step 4
tpixel value L
i,j≤ M
i,j, at P
i,jcoordinate (i, j) position get black picture element, otherwise at P
i,j(i, j) position extracting waste pixel 1, wherein t=1,2 ..., n, 1≤i≤h, 1≤j≤w;
5c) in conjunction with all halftone pattern P
i,jproduce final required half-tone, and then obtain all piecemeal front covers and share image P
t, wherein t=1,2 ..., n, 1≤i≤h, 1≤j≤w;
5d) partitioned matrix is converted to original matrix P
i, being converted to final size is successively that n the matrix of r × c shares image as required front cover, wherein i=1,2 ..., n.
Step 6, produces final privacy share:
Random grid image is shared on basis described in above-mentioned steps and front cover shares picture size and former Secret Image S-phase is same, is r × c by the size Expressing of all images, the P that correspondence is obtained
iand B
i, from P
iin randomly draw δ × r × c pixel, wherein δ is stacking ratio, and uses B
iin same coordinate position pixel replace, finally shared image F
i, wherein i=1,2 ..., n, the final security producing the user-friendly visual secret sharing scheme method based on random grid is determined by correspondence (k, n) threshold schemes, and the shared image obtained is all significant.
Step 7, Restore Secret image:
The n width generated through step 6 is finally shared in image therefrom to take out and is more than or equal to arbitrarily k width and finally shares image and they superposed, the Secret Image after just can being restored.
Effect of the present invention can be further illustrated by emulation:
1. simulated conditions
This example, under Intel (R) Core (i5) CPU3.20GHZWindows7 system, on Matlab2014a operation platform, completes emulation experiment of the present invention.
2. emulation experiment content
Choose 4 image sizes be 512 × 512 gray-scale map as surface plot picture as Fig. 2, choose 1 large little be 512 × 512 bianry image as Secret Image S as Fig. 3.
For based on (k, n) the user-friendly visual secret sharing scheme method of thresholding, with (2,4) threshold schemes are example, finally (a)-(d) shared in image is respectively 4 user-friendly shared images finally generating with original cover sheet to Fig. 4 is that size is identical with Secret Image S, and from 4 shared images, also can not get information secret arbitrarily separately, so Secret Image S is safe, shared image is no longer insignificant random grid image, they are significant images, thus facilitate the numerous shared image of user management.Wherein the shared imaging importing of any 2 or more can obtain required Secret Image, and these four images are distributed to the shared share that 4 participants have as everyone respectively afterwards.
Fig. 5 represents imaging importing result, wherein (a)-(d) is respectively (a)+(b) in Fig. 4, (a)+(d), the stack result of (b)+(c) and (a)+(b)+(c)+(d), wherein '+' represents overlap-add operation, (a)-(d) of Fig. 5 clearly can find out that the superposition of any two images obtains Secret Image, in order to prove this method superiority, also simulate traditional (k, n) thresholding visual cryptography scheme contrasts, same with (2, 4) scheme is example, Fig. 6 is 4 traditional shared images, they are all insignificant random grid, and with the naked eye cannot find out the difference of 4 images, so sometimes easily cause assailant to note, also management is difficult to for supvr, Fig. 7 is then for representing traditional (k, n) threshold image stack result, (a)-(d) of Fig. 7 is respectively (a)+(b) in Fig. 6, (a)+(d), the stack result of (b)+(c) and (a)+(b)+(c)+(d), Fig. 7 tradition (k, n) stack result of threshold image stack result and this method Fig. 5 is basically identical.
Through simulation results show, the shared image that the method provides is no longer insignificant random grid, but significant shared image, namely user friendly, easily distinguish image, and after the significant shared superposition that generates of the method contrast comparatively before scheme also do not alter a great deal, be in this way feasible be also better than before scheme.
Explanation of nouns
S: Secret Image;
C
i: surface plot picture, wherein i=1,2 ..., n;
G
i: random grid matrix, wherein i=1,2 ..., k;
K: threshold value, the required minimum participant's number of deciphering;
N: shared picture number and participant's number;
B
i: random grid image is shared on the basis having Secret Image to produce, wherein i=1, and 2 ..., n;
D
i,j: the fritter after front cover picture breakdown, wherein 1≤i≤n, 1≤j≤(r × c)/(h × w);
The average gray level of d:D;
β: the gray shade scale of the every fritter gray equivalent of image;
L
i: label matrix, wherein i=1,2 ..., n;
M
i: dither matrix, wherein i=1,2 ..., n;
R: the line number of Secret Image and surface plot picture;
C: the columns of Secret Image and surface plot picture;
H: the line number of the fritter produced;
W: the columns of the fritter produced;
G
1, g
2..., g
k: k the bit number produced through random grid conversion;
δ: the shared random grid image in adjustment basis and front cover share the coefficient of pixel ratio, 0≤δ≤1;
P
i: the front cover after shadow tone computing shares image, wherein i=1, and 2 ..., n;
F
i: finally share image, wherein i=1,2 ..., n.
Claims (6)
1., based on the user-friendly visual secret sharing scheme method of (k, n) thresholding, comprise the steps:
(1) the Secret Image S that will protect carries out (k, n) the encrypting based on random grid of thresholding, obtain k width basis and share random grid image, then remaining n-k width random grid image is generated according to toss a coin mode, altogether obtain n width basis and share random grid image, wherein k is threshold value, and n is the quantity of participant;
(2) n width gray scale surface plot picture is inputted, first every width gray level image is divided into the identical fritter of size, utilize histogram equalization process image fritter, then it is similar to carry out equivalence to the mean gradation of each image fritter, obtains the gray shade scale of each image fritter equivalence;
(3) as fritter, shake halftone process is carried out to the surface plot after step (2) histogram equalization process, first produce dither matrix, after utilizing dither matrix halftone process, obtain front cover and share image;
(4) stacking ratio δ is set, wherein 0≤δ≤1, the front cover that the shared random grid image in n width basis step (1) produced and step (3) produce shares the first piecemeal process of image, image after piecemeal process is carried out stacking process, generates user-friendly final shared image;
(5) the n width generated in step (4) is finally shared image to take out and be more than or equal to arbitrarily k width and finally share image they are superposed, the Secret Image after being restored.
2. according to claim 1 based on (k, n) the user-friendly visual secret sharing scheme method of thresholding, it is characterized in that: described in step (1), random grid encryption is carried out to Secret Image S, the step generating the shared random grid of (k, n) thresholding is as follows:
2a) produce random grid G according to toss a coin mode
1;
2b) as the pixel S of Secret Image S
i,jduring for white, then second random grid G
2in pixel G
2 i,jwith random grid G
1in pixel G
1 i,jbe worth identical, on the contrary then with pixel G
1 i,jvalue is contrary, and wherein 1≤i≤r, 1≤j≤c, r and c is respectively the wide and high of Secret Image S;
2c) according to above-mentioned steps 2a) and 2b) to each the pixel S in Secret Image S
i,jencode successively, obtain pixel bit value g1
i,jand g2 '
i,j; In the same manner to g2 '
i,jencode, obtain bit value g2
i,jand g3 '
i,j, more in the same manner to g3 '
i,jencode, obtain bit value g3
i,jand g4 '
i,j, repeat this encoding operation, obtain g1
i,j, g2
i,j..., gk
i,j, wherein gk
i,jwith gk '
i,jwhat represent is same bit, and wherein i, j are respectively pixel horizontal ordinate and the ordinate of Secret Image S, 1≤i≤r, 1≤j≤c;
2d) random selecting k random grid, by step 2c) calculated by k bit value put into the pixel at the same spatial location place of a selected k random grid, form k sub-set B
* 1 i,j, B
* 2 i,j..., B
* k i,j, wherein 1≤i≤r, 1≤j≤c;
2e) by the n-k of remainder random grid image { B
1, B
2..., B
n}-{ B
* 1, B
* 2..., B
* kpixel randomly draw pixel value according to toss a coin mode, these obtain pixel value and B at random
* 1 i,j, B
* 2 i,j..., B
* k i,jthe locus got is consistent, wherein 1≤i≤r, 1≤j≤c;
2f) repeat step 2c) – 2e), until all pixel coders complete in Secret Image S, thus produce all bases and share random grid image B
i, wherein i=1,2 ..., n.
3. the user-friendly visual secret sharing scheme method based on (k, n) thresholding according to claim 1, is characterized in that: utilize histogram equalization process front cover image method described in step (2), carries out as follows:
3a) by surface plot as C
1, C
2..., C
nall change and be decomposed into the pixel fritter that size is h × w, and h × w is minimum can not be less than 2;
3b) establish D
i,jfor surface plot is as C
ia jth data block, ask for the β simultaneously meeting formula (1) and (2), make D
i,jprogression equal β,
β≤d≤β+1(1)
Wherein, D
i,jrepresentative is at original covers image C
ia jth data block, D
i,javerage gray level be d, n in formula
i kwhat represent is at original image C
imiddle gray level is the number of pixels of k, β ∈ 0,1 ..., h × w-1} is the value of all progression, and its value is determined by the size of piecemeal, wherein 1≤i≤n, 1≤j≤(r × c)/(h × w);
3c) when the progression of all piecemeals is by step 3b) in after formula obtains, label matrix L
1, L
2..., L
nrespectively by the surface plot of correspondence as C
1, C
2..., C
nobtain, L
isize is (r × c)/(h × w), store all at surface plot as C
ithe progression of piecemeal, to fragmental image processing, equivalence is carried out to the mean gradation of each block similar, obtains the gray shade scale of every fritter h × w gray equivalent with image, wherein i=1,2 ..., n.
4. the user-friendly visual secret sharing scheme method based on (k, n) thresholding according to claim 1, is characterized in that: utilize dither matrix to carry out halftoning method in step (3) and obtain as follows:
4a) utilize original gradation surface plot as C
1, C
2..., C
nrebuild n dither matrix M
1, M
2..., M
n, be of a size of h × w, dither matrix M
tin pixel be M
t i,j, wherein t=1,2 ..., n, 1≤i≤h, 1≤j≤w;
If label matrix L 4b) required by step (2)
tpixel value L
i,j≤ M
i,j, at P
i,jcoordinate (i, j) position get black picture element, otherwise at P
i,j(i, j) position extracting waste pixel, wherein t=1,2 ..., n, 1≤i≤h, 1≤j≤w;
4c) in conjunction with all halftone pattern P
i,jproduce final required half tone image, 1≤i≤r, 1≤j≤c and then obtain all piecemeal front covers and share image P
t, wherein t=1,2 ..., n;
4d) partitioned matrix is converted to original matrix P
i, being converted to final size is successively that n the matrix of r × c shares image as required front cover, wherein i=1,2 ..., n.
5. according to claim 1 based on (k, n) the user-friendly visual secret sharing scheme method of thresholding, it is characterized in that: random grid image is shared on step (2) and the basis described in step (4) and front cover shares picture size and former Secret Image S-phase is same, be r × c by the size Expressing of all images, the P that correspondence is obtained
iand B
i, from P
iin randomly draw δ × r × c pixel, wherein δ is stacking ratio, and uses B
iin same coordinate position pixel replace, finally shared image F
i, wherein i=1,2 ..., n.
6. according to claim 1 based on (k, n) the user-friendly visual secret sharing scheme method of thresholding, it is characterized in that: step (5) utilizes the final process sharing Postprocessing technique Secret Image generated, as long as from generate n width finally share image take out be more than or equal to arbitrarily k width finally share image they are superposed, the Secret Image after being just restored.
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