CN113206926B - Method for balancing privacy and usability of image based on three-pixel-point encryption - Google Patents

Method for balancing privacy and usability of image based on three-pixel-point encryption Download PDF

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CN113206926B
CN113206926B CN202110471730.XA CN202110471730A CN113206926B CN 113206926 B CN113206926 B CN 113206926B CN 202110471730 A CN202110471730 A CN 202110471730A CN 113206926 B CN113206926 B CN 113206926B
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value
group
pixel group
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CN113206926A (en
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赵若宇
张玉书
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Nanjing University of Aeronautics and Astronautics
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/44—Secrecy systems
    • H04N1/448—Rendering the image unintelligible, e.g. scrambling
    • H04N1/4486—Rendering the image unintelligible, e.g. scrambling using digital data encryption
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
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Abstract

The invention discloses a method for balancing image privacy and usability based on three-pixel-point encryption, which comprises the steps of dividing an image into a plurality of pixel blocks, grouping pixels in each pixel block, and grouping every three pixels into one group; after the sum s of the pixel values in the pixel group is obtained, the domain is generated by using s, all the pixel groups in the domain are numbered by using ranksThe function calculates the number SN of the original pixel group; a random number is generated by using the secret key, and the random number is added with the SN to be complemented, namely the encrypted SN, namely the SN is generateden(ii) a By using
Figure DDA0003045615470000011
Function solving SNenA corresponding group of pixels in the domain; all pixels in a block of pixels are scrambled and encrypted. The method and the device can keep the accurate thumbnail of the original image in the ciphertext image, so that an image owner can obtain the usability by using the visual information of the ciphertext image.

Description

Method for balancing privacy and usability of image based on three-pixel-point encryption
Technical Field
The invention belongs to the field of privacy protection and image encryption, and particularly relates to a method for balancing image privacy and usability based on three-pixel-point encryption.
Background
With the continuous maturation of digital imaging technology, people have become accustomed to using electronic devices instead of traditional film cameras to capture images. This brings about a number of advantages such as low cost of taking images and what you see is what you get, so that ordinary people can easily take images at hand any time than ever before. These images record our daily lives, and although they enable us to recall at any time when it has happened, they undoubtedly record people's privacy, such as location, religious beliefs, interpersonal relationships. The illegal third party may further use the privacy information to perform privacy reasoning on the owner of the image, or directly use the image to perform AI model training, make a malicious image, and the like.
Meanwhile, the maturity of network infrastructure greatly promotes the development of cloud services. There is an increasing preference to upload pictures of local devices into the cloud due to the low cost, flexible scalability, and high availability of cloud services. This trend brings many benefits to cloud users, however, once the image is uploaded into the cloud, the privacy security of the image can only depend on the reliability of the cloud service provider, which undoubtedly greatly aggravates the privacy concern.
Generally, in order to solve the concern of image privacy, people often adopt a traditional image encryption algorithm to encrypt images. These encryption algorithms encrypt the image into a snowflake-like ciphertext image that does not reveal visual information, thus protecting privacy in the image. However, this is extremely unfriendly to the user. The user selects the cloud service not only because it relieves the pressure of insufficient storage of the local device, but also more importantly because of its ease of use feature. These techniques produce ciphertext images that do not reveal any useful visual information, so that the user must continually download, decrypt the image until the desired one is found, which is extremely time consuming, labor intensive, and time costly for the user. In other words, these techniques force the user to make choices in usability as well as privacy security. For ordinary users, although they know that a lot of privacy exists in the image, they still select the availability of the cloud. This is why there are a number of conventional image encryption algorithms that have been proven to be secure in theory, but have not been applied by the average user on a large scale to protect image privacy on cloud storage to date. Therefore, the method of protecting image privacy cannot be at the expense of the usability of the image.
Several methods to balance image privacy and usability have been proposed in large numbers. These methods can be broadly divided into three categories: image editing and image encryption. Image editing is one of the most common methods to balance privacy and usability. They hide or eliminate possible private information by modifying privacy sensitive areas in the image, but retain most of the visual information in the image. The methods mainly include image filtering, face de-identity recognition, object removal and object replacement. Such methods have been widely used in social networks and have achieved satisfactory results. However, they are not suitable for use on cloud storage, where the main purpose is to preserve the image, since most of these methods are irreversible damage to the image. While this damage can be mitigated by cropping only a small area in the image, the unprocessed background can expose too much complete semantic information. Image encryption refers to encoding image data in some way based on a key in order to make the image unintelligible, which is currently one of the most common means of ensuring image privacy during storage and transmission. The security of this method depends on the key used, in particular, a third party without the key can only see the encoded image, only the legitimate user with the correct key can see the original image. Although generally, the conventional image encryption method only considers the privacy security of the image and does not consider the usability brought by the image understandability, some more novel research works also consider the usability after the image encryption, such as ciphertext image retrieval and region-of-interest encryption. However, they have some common problems. If only a part of the area of the image is encrypted, how to distinguish the areas that should be encrypted, even if this problem is assumed to be solved, the unencrypted areas carry a lot of semantic information. The method of encrypting the whole image and obtaining the information of the image through the characteristics or the labels seems feasible, but the method of browsing the textual information to distinguish the image is difficult. Therefore, the existing method for balancing the privacy and the usability of the image in the cloud has some problems.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems in the prior art, the invention provides a method for balancing the image privacy and the usability based on three-pixel encryption, which can ensure the image privacy, enable an image owner to obtain the usability through the visual content of the image and is compatible with the existing cloud service.
The technical scheme is as follows: the invention relates to a method for balancing image privacy and usability based on three-pixel encryption, which comprises the following steps:
(1) original block segmentation: dividing a pre-acquired image into R, G, B three channels, wherein each channel is divided into a plurality of pixel blocks with b × b size according to a preset block dimension b;
(2) block-based encryption: dividing pixels in each block into a pixel group according to a preset rule, solving the sum s of pixel values in the pixel group, performing replacement encryption on the pixel group, and performing scrambling encryption on all pixels;
(3) ciphertext block integration: after the pixel blocks are encrypted, assembling the corresponding encrypted pixel blocks into ciphertext channels according to the sequence of block division, and then integrating the ciphertext channels together to form a ciphertext image;
(4) and (3) ciphertext block segmentation: acquiring parameters of a ciphertext image, dividing the ciphertext image into R, G, B three channels, wherein each channel is divided into a plurality of ciphertext pixel blocks with b × b sizes according to a preset block dimension b;
(5) block-based decryption: scrambling and decrypting all pixels and replacing and decrypting pixel groups;
(6) original block integration: after all pixel groups in the pixel block are decrypted, the original block is recovered; and assembling the corresponding decrypted pixel blocks into original channels according to the segmentation sequence of the blocks, and then integrating the original channels together to form an original image.
Further, the step (2) comprises the steps of:
(21) dividing the pixels in each block into a pixel group every three according to a preset rule, then solving the sum s of pixel values in the pixel group, generating a corresponding domain based on s, and simultaneously calculating the number of the pixel groups in the corresponding domain and numbering;
(22) by using ranksThe function determines the number SN of the original pixel group and uses the key1Generating a secret random number, and adding the secret random number to the SN; simultaneously, the number of pixel groups in the domain is solved, and the sum of the pixel groups and the pixel groups is subjected to complementation, namely the encrypted SN, namely the SNen(ii) a By using
Figure BDA0003045615450000031
Function solving SNenThe pixel group corresponding to the domain is a ciphertext pixel group, and the step is replacement encryption of the pixel group;
(23) substitutional encryption of all pixel groups in a pixel blockAfter operation, the key is utilized2All pixels in the pixel block are scrambled and encrypted.
Further, the step (5) includes the steps of:
(51) using key keys2Scrambling and decrypting all pixels in the pixel block; dividing every three pixel points into a pixel group according to a preset rule, then solving the sum s of pixel values in the pixel group, generating a corresponding domain based on s, and numbering the pixel groups in the domain;
(52) by using ranksFunction determination of ciphertext pixel group number SNenUsing key of key1Generating a secret random number, associated with the SNenSubtracting; simultaneously, the number of pixel groups in the domain is solved, and the sum of the pixel groups is subjected to complementation to obtain the original pixel group number, namely SN; by using
Figure BDA0003045615450000032
The function finds the pixel group corresponding to SN in the domain, i.e. the original pixel group, and this step is substitution decryption of the pixel group.
Further, the number of corresponding pixel groups in the domain in step (21):
Figure BDA0003045615450000041
wherein d represents the value range of the pixel value, s is the sum of the pixel values in the three-pixel group, and sum (x, y, z) is as follows:
Figure BDA0003045615450000042
where (x, y, z) represents the values of the first, second, and third pixels of the pixel group, respectively.
Further, the domain corresponding to the sum s of the pixel groups in the step (21) is:
Figure BDA0003045615450000043
wherein each one
Figure BDA0003045615450000044
Representing a group of pixels having the same pixel and s.
Further, the step (21) of calculating and numbering the number of pixel groups in the corresponding domain is as follows:
1) calculating the sum s of pixel values in the pixel group (i, j, c), giving SN to each pixel group (i, j, c) in the domain, and setting the initial value x of the SN equal to 0;
2) calculating the starting value a of the first pixel i in the pixel groupbeginBegin (s,3), wherein begin (s, n) is defined as follows:
Figure BDA0003045615450000045
wherein n is the number of pixel points in the pixel group, and d represents the value range of the pixel value;
3) calculating the end value a of the first pixel in the pixel groupendEnd(s), wherein end(s) is defined as follows:
Figure BDA0003045615450000046
wherein d is the value range of the pixel value;
4) the second and third pixels may form a two-pixel group (j, c) having a sum of pixels s2Starting value b of s-i, jbegin＝begin(s22), end value nend＝end(s2)；
5) The value c of the third pixel is s2-j；
6) SN of the three-pixel group (i, j, c) in the domain is x, and x is increased by 1, that is, x is x + 1;
7) j is increased by 1 if j is not greater than bendThen go to jumpGo to step 5);
8) i is increased by 1 if i is not greater than aendJumping to step 4);
9) SN assignment and numbering is done for all pixel groups in the domain.
Further, said utilizing rank of step (22)sThe function determines the number SN of the original pixel group as follows:
s1) adopt ranksThe function calculation value is the sum s of the pixels of the three-pixel group (i, j, c) of a, b and z, the value of the number of the pixel groups in the domain of the three pixels corresponding to the current value a is set as r, and the initial value of the r is 0;
s2) calculating the domain number r of the two-pixel group (b, z) in the two-pixel2＝rank2s(b, z) wherein rank2s(b, z) is defined as follows:
Figure BDA0003045615450000051
wherein d is the value range of the pixel value;
s3) calculates the start value a of the first pixel i in the pixel groupbegin＝begin(s,3)；
S4) the sum of two pixel groups (b, z) is S2＝s-i；
S5)r＝r+domain2(s2) Therein domain2(s2) Is defined as follows:
Figure BDA0003045615450000052
s6) i ═ i +1, and if i is not greater than a-1, then go to step S4);
s7) value a, b, z, the SN of a group of three pixels (i, j, c) is equal to r + r2。
Further, the step (52) utilizes
Figure BDA0003045615450000053
Function solving of pixel group realization corresponding to SN in domainThe process is as follows:
calculating the pixel value of the first pixel of the group of pixels: let r be 0 and the start value of the first pixel be abeginBegin (s,3), where s is the sum of the pixel values in the pixel group; current abeginSetting r as the number of pixel groups in the corresponding domainenWherein r isenIs 0; if SN is greater than ren+domain2(s-abegin) Then r isen＝ren+domain2(s-abegin) While a isbegin＝abegin+ 1; otherwise, the pixel value a of the first pixelSN＝abegin；
The sum of the pixel values of the second and third pixels is s2＝s-aSN(ii) a Calculating the pixel value b of the second pixelSNThe formula of (a) is as follows:
Figure BDA0003045615450000061
wherein d represents the value range of the pixel value; pixel value c of the third pixelSN＝s2-bSN(ii) a That is, SN corresponds to a pixel group of (a)SN,bSN,cSN)。
Further, the replacement encryption of the pixel group in the step (2) is implemented by the following formula:
Figure BDA0003045615450000062
wherein, SNenIs the encrypted SN, m is the key of the key1The generated random number is controlled, mod being the remainder symbol.
Further, the replacing decryption of the pixel group in the step (5) is implemented by the following formula:
Figure BDA0003045615450000063
wherein the content of the first and second substances,SN is the number after decryption, m is the key of the key1The generated random number is controlled, mod being the remainder symbol.
Has the advantages that: compared with the prior art, the invention has the beneficial effects that: the invention realizes the replacement encryption of the three-pixel group, enhances the connectivity of the Markov chain system modeled by the encryption scheme, maintains the accurate thumbnail of the original image, can perfectly recover the original image, and solves the problem of incompatibility of the privacy and the usability of the ciphertext image on the existing cloud service.
Drawings
FIG. 1 is a flow chart of an image encryption process of the present invention;
fig. 2 is a flow chart of pixel block based encryption of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The invention provides a method for balancing image privacy and usability based on three-pixel encryption, which comprises an encryption step and a decryption step, and specifically comprises the following steps:
step 1: as shown in fig. 1, the encryption process is as follows:
(1.1) original block segmentation:
the method comprises the steps of obtaining parameters of an input image, dividing the image into R, G, B three channels, and dividing each channel into a plurality of pixel blocks with b x b size according to a preset block dimension b.
(1.2) pixel block based encryption, as shown in fig. 2:
the pixels in each block are divided into three pixel groups according to a preset rule, then the sum s of pixel values in the pixel groups is obtained, a corresponding domain is generated based on s, and the number of the pixel groups in the corresponding domain is calculated and numbered.
And (3) calculating the number of pixel groups in the generation domain under the condition of s, wherein the calculation formula is as follows:
Figure BDA0003045615450000071
where d is a value range of a pixel value, generally d is 255, s is a sum of pixel values in the three-pixel group, and sum (x, y, z) is as follows:
Figure BDA0003045615450000072
where (x, y, z) represents the values of the first, second, and third pixels of the pixel group, respectively.
And generating a domain corresponding to the s, wherein the formula is as follows:
Figure BDA0003045615450000073
wherein each one
Figure BDA0003045615450000074
Representing a group of pixels having the same pixel and s.
Calculating the number of pixel groups in the corresponding domain and numbering, i.e. assigning SN to each pixel group (i, j, c) in the domain, the steps are as follows:
1) the sum s of pixel values in the pixel group (i, j, c) is calculated, SN is given to each pixel group (i, j, c) in the domain, and the initial value x of SN is set to 0.
2) Calculating the starting value a of the first pixel i in the pixel groupbeginBegin (s,3), wherein begin (s, n) is defined as follows:
Figure BDA0003045615450000075
wherein n is the number of pixel points in the pixel group, and d represents the value range of the pixel value.
3) Calculating the end value a of the first pixel in the pixel groupendEnd(s), wherein end(s) is defined as follows:
Figure BDA0003045615450000076
4) the second and third pixels may form a two-pixel group (j, c) having a sum of pixels s2Starting value b of s-i, jbegin＝begin(s22), end value b)end＝end(s2)。
5) The value c of the third pixel is s2-j。
6) SN of the three-pixel group (i, j, c) in the domain is x, and x is increased by 1, that is, x + 1.
7) j is increased by 1 if j is not greater than bendJump to step 5).
8) i is increased by 1 if i is not greater than aendJump to step 4).
9) SN assignment and numbering is done for all pixel groups in the domain.
By using ranksThe function determines the number SN of the original pixel group and uses the key1Generating a secret random number, and adding the secret random number to the SN; simultaneously, the number of pixel groups in the domain is solved, and the sum of the pixel groups and the pixel groups is subjected to complementation, namely the encrypted SN, namely the SNen(ii) a By using
Figure BDA0003045615450000081
Function solving SNenThe corresponding pixel group in the domain is the ciphertext pixel group, and the step is replacement encryption of the pixel group.
The replacement encryption of the pixel group is realized by the following formula:
Figure BDA0003045615450000082
wherein, SNenIs the encrypted SN, m is the key of the key1The generated random number is controlled, mod being the remainder symbol.
ranksThe procedure for calculating SN for a three-pixel group (i, j, c) with a calculated value of a, b, z is as follows:
1) firstly, calculating the sum s of pixels of a pixel group, recording the value of the number of pixel groups in a three-pixel domain corresponding to the current value a, and setting r, wherein the initial value of r is 0.
2) Calculating the sequence number r of the two-pixel group (b, z) in the domain of the two pixels2＝rank2s(b, z) wherein rank2s(b, z) is defined as follows:
Figure BDA0003045615450000083
3) calculating the starting value a of the first pixel i in the pixel groupbegin＝begin(s，3)。
4) The sum of the two pixel groups (b, z) is s2＝s-i。
5)r＝r+domain2(s2) Therein domain2(s2) Is defined as follows:
Figure BDA0003045615450000084
6) i +1, if i is not greater than a-1, go to step 4).
7) The SN of a three-pixel group (i, j, c) of values a, b, z is equal to r + r2
Figure BDA0003045615450000085
After performing the replacement encryption operation on all pixel groups in the pixel block, using the key2All pixels in the pixel block are scrambled and encrypted.
(1.3) ciphertext block integration:
after the pixel blocks are encrypted, the corresponding encrypted pixel blocks are assembled into ciphertext channels according to the sequence of block division, and then the ciphertext channels are integrated together to form a ciphertext image.
Step 2: the decryption process includes the following:
(2.1) ciphertext block partitioning:
acquiring parameters of a ciphertext image, dividing the ciphertext image into R, G, B three channels, wherein each channel is divided into a plurality of ciphertext pixel blocks with b × b sizes according to a preset block dimension b;
(2.2) pixel block based decryption:
using key keys2Scrambling and decrypting all pixels in the pixel block; dividing every three pixel points into a pixel group according to a preset rule, then solving the sum s of pixel values in the pixel group, generating a corresponding domain based on s, and numbering the pixel groups in the domain;
by using ranksFunction determination of ciphertext pixel group number SNenUsing key of key1Generating a secret random number, associated with the SNenSubtracting; simultaneously, the number of pixel groups in the domain is solved, and the sum of the pixel groups is subjected to complementation to obtain the original pixel group number, namely SN; by using
Figure BDA0003045615450000091
The function finds the pixel group corresponding to SN in the domain, i.e. the original pixel group, and this step is substitution decryption of the pixel group.
Calculating the pixel value of the first pixel of the pixel group to be the starting value of the first pixelbeginBegin (s,3), where s is the sum of the pixel values in the pixel group; record the current abeginSetting r as the number of pixel groups in the corresponding domainenWherein r isenIs 0; if SN is greater than ren+domain2(s-abegin) Then r isen＝ren+domain2(s-abegin) While a isbegin＝abegin+ 1; otherwise, the pixel value a of the first pixelSN＝anegin；
The sum of the pixel values of the second and third pixels is s2＝s-aSN(ii) a Calculating the pixel value b of the second pixelSNThe formula of (a) is as follows:
Figure BDA0003045615450000092
wherein d represents the value range of the pixel value; pixel value c of the third pixelSN＝s2-bSN(ii) a That is, SN corresponds to a pixel group of (a)SN,bSN,cSN)。
The replacement decryption of the pixel group is realized by the following formula:
Figure BDA0003045615450000093
wherein SN is the number after decryption, m is the key of the key1The generated random number is controlled, mod being the remainder symbol.
(2.3) original Block integration
After all pixel groups in the pixel block are decrypted, the original block is recovered; and assembling the corresponding decrypted pixel blocks into original channels according to the segmentation sequence of the blocks, and then integrating the original channels together to form an original image.
And circulating the operation until all pixel groups in the pixel block finish the operation, and utilizing the key2And carrying out scrambling encryption on pixels in the pixel block, namely completing encryption based on the pixel block.
After each pixel block in the image is subjected to the operation, the image thumbnail is kept, namely, the ciphertext image capable of balancing the privacy and the usability of the image is obtained. The sum of pixels in the pixel blocks is not changed in the whole encryption process, so that the scheme can generate accurate thumbnails. The decryption process of the scheme is the reverse process of the encryption process.

Claims (7)

1. A method for balancing image privacy and usability based on three-pixel encryption is characterized by comprising the following steps;
(1) original block segmentation: dividing a pre-acquired image into R, G, B three channels, wherein each channel is divided into a plurality of pixel blocks with b × b size according to a preset block dimension b;
(2) block-based encryption: dividing pixels in each block into a pixel group according to a preset rule, solving the sum s of pixel values in the pixel group, performing replacement encryption on the pixel group, and performing scrambling encryption on all pixels;
(3) ciphertext block integration: after the pixel blocks are encrypted, assembling the corresponding encrypted pixel blocks into ciphertext channels according to the sequence of block division, and then integrating the ciphertext channels together to form a ciphertext image;
(4) and (3) ciphertext block segmentation: acquiring parameters of a ciphertext image, dividing the ciphertext image into R, G, B three channels, wherein each channel is divided into a plurality of ciphertext pixel blocks with b × b sizes according to a preset block dimension b;
(5) block-based decryption: scrambling and decrypting all pixels and replacing and decrypting pixel groups;
(6) original block integration: after all pixel groups in the pixel block are decrypted, the original block is recovered; assembling the corresponding decrypted pixel blocks into original channels according to the segmentation sequence of the blocks, and then integrating the original channels together to form an original image;
the step (5) comprises the following steps:
(51) using key keys2Scrambling and decrypting all pixels in the pixel block; dividing every three pixel points into a pixel group according to a preset rule, then solving the sum s of pixel values in the pixel group, generating a corresponding domain based on s, and numbering the pixel groups in the domain;
(52) by using ranksFunction determination of ciphertext pixel group number SNenUsing key of key1Generating a secret random number, associated with the SNenSubtracting; simultaneously, the number of pixel groups in the domain is solved, and the sum of the pixel groups is subjected to complementation to obtain the original pixel group number, namely SN; by using
Figure FDA0003414179630000011
The function calculates the pixel group corresponding to the SN in the domain, namely the pixel group is the original pixel group, and the step is the replacement decryption of the pixel group;
the advantages of step (52)By using
Figure FDA0003414179630000012
The implementation process of the function for solving the pixel group corresponding to the SN in the domain is as follows:
calculating the pixel value of the first pixel of the group of pixels: let r be 0 and the start value of the first pixel be abeginBegin (s,3), where s is the sum of the pixel values in the pixel group; current abeginSetting r as the number of pixel groups in the corresponding domainenWherein r isenIs 0; if SN is greater than ren+domain2(s-abegin) Then r isen＝ren+domain2(s-abegin) While a isbegin＝abegin+ 1; otherwise, the pixel value a of the first pixelSN＝abegin；
The sum of the pixel values of the second and third pixels is s2＝s-aSN(ii) a Calculating the pixel value b of the second pixelSNThe formula of (a) is as follows:
Figure FDA0003414179630000021
wherein d represents the value range of the pixel value; pixel value c of the third pixelSN＝s2-bSN(ii) a That is, SN corresponds to a pixel group of (a)SN,bSN,cSN)。
2. The method for balancing privacy and usability of images based on triple pixel point encryption according to claim 1, wherein the step (2) comprises the steps of:
(21) dividing the pixels in each block into a pixel group every three according to a preset rule, then solving the sum s of pixel values in the pixel group, generating a corresponding domain based on s, and simultaneously calculating the number of the pixel groups in the corresponding domain and numbering;
(22) by using ranksThe function determines the number SN of the original pixel group and uses the key1Generating a secret random number, and adding the secret random number to the SN; simultaneously, the number of pixel groups in the domain is solved, and the sum of the pixel groups and the pixel groups is subjected to complementation, namely the encrypted SN, namely the SNen(ii) a By using
Figure FDA0003414179630000024
Function solving SNenThe pixel group corresponding to the domain is a ciphertext pixel group, and the step is replacement encryption of the pixel group;
(23) after performing the replacement encryption operation on all pixel groups in the pixel block, using the key2All pixels in the pixel block are scrambled and encrypted.
3. The method for balancing image privacy and usability based on triple-pixel encryption according to claim 2, wherein the sum s of the pixel groups in step (21) corresponds to a domain:
Figure FDA0003414179630000022
wherein each one
Figure FDA0003414179630000023
Representing a group of pixels having the same pixel and s.
4. The method for balancing image privacy and usability based on triple-pixel point encryption according to claim 2, wherein the step (21) of calculating and numbering the number of pixel groups in the corresponding domain is as follows:
1) calculating the sum s of pixel values in the pixel group (i, j, c), giving SN to each pixel group (i, j, c) in the domain, and setting the initial value x of the SN equal to 0;
2) calculating the starting value a of the first pixel i in the pixel groupbeginBegin (s,3), wherein begin (s, n) is defined as follows:
Figure FDA0003414179630000031
wherein n is the number of pixel points in the pixel group, and d represents the value range of the pixel value;
3) calculating the end value a of the first pixel in the pixel groupendEnd(s), wherein end(s) is defined as follows:
Figure FDA0003414179630000032
wherein d is the value range of the pixel value;
4) the second and third pixels may form a two-pixel group (j, c) having a sum of pixels s2Starting value b of s-i, jbegin＝begin(s22), end value b)end＝end(s2)；
5) The value c of the third pixel is s2-j；
6) SN of the three-pixel group (i, j, c) in the domain is x, and x is increased by 1, that is, x is x + 1;
7) j is increased by 1 if j is not greater than bendJumping to step 5);
8) i is increased by 1 if i is not greater than aendJumping to step 4);
9) SN assignment and numbering is done for all pixel groups in the domain.
5. The method of claim 2, wherein said step (22) of utilizing rank is based on triple-pixel encryption to balance image privacy and usabilitysThe function determines the number SN of the original pixel group as follows:
s1) adopt ranksThe function calculation value is the sum s of the pixels of the three-pixel group (i, j, c) of a, b and z, the value of the number of the pixel groups in the domain of the three pixels corresponding to the current value a is set as r, and the initial value of the r is 0;
s2) calculating the domain number of the two-pixel group (b, z) in the two-pixelr2＝rank2s(b, z) wherein rank2s(b, z) is defined as follows:
Figure FDA0003414179630000033
wherein d is the value range of the pixel value;
s3) calculates the start value a of the first pixel i in the pixel groupbegin＝begin(s,3)；
S4) the sum of two pixel groups (b, z) is S2＝s-i；
S5)r＝r+domain2(s2) Therein domain2(s2) Is defined as follows:
Figure FDA0003414179630000041
s6) i ═ i +1, and if i is not greater than a-1, then go to step S4);
s7) value a, b, z, the SN of a group of three pixels (i, j, c) is equal to r + r2。
6. The method for balancing image privacy and usability based on triple pixel point encryption according to claim 1, wherein the replacing encryption of the pixel group in the step (2) is implemented by the following formula:
Figure FDA0003414179630000042
wherein, SNenIs the encrypted SN, m is the key of the key1The generated random number is controlled, mod being the remainder symbol.
7. The method for balancing image privacy and usability based on triple-pixel point encryption according to claim 1, wherein the replacing decryption of the pixel group in the step (5) is implemented by the following formula:
Figure FDA0003414179630000043
wherein SN is the number after decryption, m is the key of the key1The generated random number is controlled, mod being the remainder symbol.
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