JP4796150B2 - Image encryption / decryption device, method and program - Google Patents

Description

  The present invention relates to an image encryption and decryption technique for visually encrypting a part of an image such as an important part in an image printed on a printed matter or a digital image and preventing information leakage to a third party. It is about.

  With the progress of informatization in society, leakage of confidential information has become a serious problem, and development of technology for preventing information leakage is desired. For example, with regard to digital data, a technology for encrypting data so that the contents cannot be seen even when information is passed to a third party has been developed, and has already been used as a useful means for preventing information leakage.

  On the other hand, a technology for preventing information leakage of printed matter printed on a paper medium or the like has not yet been sufficiently developed, and there has been no practical example. In fact, it is said that about half of the information leakage is from the printed material, and it is an urgent need to develop a technology for preventing information leakage from the printed material as well as digital data.

  Specific examples of countermeasures against information leaks in printed materials include bills at the time of product purchase, specifications such as credit cards, hospital charts, school records, and rosters. It can be used as a technology to prevent information leakage by encryption.

  Conventionally, as a publicly known example dealing with encryption of printed matter, there is, for example, Japanese Patent Laid-Open Publication No. Hei 8-179689 (hereinafter referred to as Patent Document 1). In Patent Document 1, first, the entire image is divided into a plurality of blocks, the images of the divided blocks are rearranged based on the parameter obtained from the input password (encryption key), and the image of the block specified by the parameter is reversed in black and white. The image is encrypted by mirror inversion. When decrypting an encrypted image, a positioning frame is added to the outside of the image, a password (decryption key) is input, and then the original image is decrypted in the reverse procedure of encryption.

  As another conventional technique, for example, as disclosed in Japanese Patent No. 2938338 (hereinafter referred to as Patent Document 2), there is a technique in which binary data is imaged and embedded in a printed matter. Imaging in this prior art is realized by representing binary data in a black and white square of a specified size and arranging them in a matrix. Further, a positioning symbol is added to a designated position in the matrix so that the imaged position can be known at the time of decoding. By using this positioning symbol as a reference, it is possible to decode information embedded by photographing an image with a scanner or a camera.

However, the conventional techniques as described above have the following problems to be solved.
For example, a technique such as Patent Document 1 can apply encryption only to the entire image, and cannot perform efficient encryption when the area that needs to be encrypted is only a part of the entire image. There was a problem.

  Furthermore, since the technique such as Patent Document 1 needs to add a positioning frame to the outside of the encrypted image, the image information originally associated with the added portion of the frame is sacrificed at the time of encryption. There was a problem.

  Further, the technique as disclosed in Patent Document 1 has a problem in that a scramble block unit cannot be accurately extracted as an image becomes larger because distortion inside the image is not taken into consideration.

  In the present invention, it is possible to encrypt a part of the entire image, and the image corresponding to the “positioning frame” as in Patent Document 1 is generated by the pixel value conversion processing of the input image. Loss of information can be minimized. Furthermore, there is a feature that a scramble block unit can be easily detected.

  Further, the technique such as Patent Document 2 can embed data with a relatively small amount of information such as text information, but there is a large amount of information such as image and audio information, and there is no problem even if some decoding errors occur. Not suitable for storing data. Furthermore, there is a restriction that it is a certain size and a square, and there is a problem that it cannot be used for an application that hides a part of characters.

Furthermore, the technique such as Patent Document 2 is premised on black and white characters and drawings, and has a problem that it cannot be applied to an image having multiple gradations such as a photograph.
According to the present invention, it is possible to encrypt image data having a large amount of information that cannot be encrypted by the technique as described in Patent Document 2 so that a human cannot visually recognize it.

In the present invention, the following three means are used in order to encrypt a part of the input image and specify the encrypted area at the time of decryption.
The first means is a means for performing encryption by regularly converting pixel values in the encryption area and generating a unique pattern corresponding to the pixel value conversion.

The second means is a means for adding positioning markers for specifying the encryption position to at least two of the four corners of the encryption area.
The third means is a means for adding at least one check mark for verifying the validity of the decrypted image in the encryption area before the encryption processing.

  According to the present invention, even when a part of an input image is encrypted by these three means, the encrypted area can be correctly specified at the time of decryption, and the original image is restored so that a human can visually recognize it. It becomes possible.

  That is, according to one aspect of the present invention, the present invention is an image encryption executed in an image encryption apparatus that encrypts a digital image into an encrypted image, and a partial region to be encrypted from the digital image is Designating and converting the selected partial area into a processed image based on an encryption key, and regularly converting pixel values of the converted processed image in order to be able to specify the position of the partial area To generate a converted image.

  Further, the conversion to the processed image may be performed by dividing the partial area into a plurality of minute areas and rearranging the plurality of divided minute areas based on the encryption key, or by converting the partial area by an arbitrary compression method. It is desirable to convert into compressed data and arrange each bit of the converted compressed data as white or black pixels of any size.

  Further, the conversion to the converted image is performed by converting the pixel value at a constant cycle in the horizontal direction of the processed image and converting the pixel value at a constant cycle in the vertical direction, thereby forming a substantially striped pattern. It is desirable to generate such a converted image.

In addition, in order to specify the position of the partial region, it is preferable that the encrypted image is generated by adding a specific marker to the generated converted image.
In addition, the marker may be a solid circular shape or a polygonal shape, and may have a shape in which a plurality of lines intersecting the circumference of the circular shape or the polygon exist on the inside thereof, or the foreground is formed by pixel value conversion. Is desirable.

  According to another aspect of the present invention, the present invention provides image decryption executed in an image decryption device that decrypts an encrypted image into a digital image, and specifies the position of the encrypted partial region. Therefore, a specific marker added to the encrypted image is detected, an encrypted encrypted image region is detected based on the detected marker, and a pixel of the detected encrypted image region is detected. An encrypted position whose value is regularly converted is detected, and the encrypted image area is decrypted into the digital image based on the detected encrypted position and a decryption key.

  According to another aspect of the present invention, the present invention is an image decryption executed in an image decryption device for decrypting an encrypted image into a digital image, wherein the encrypted encrypted image region is detected. And detecting an encrypted position in which pixel values are regularly converted in the detected encrypted image area, and determining the encrypted image area based on the detected encrypted position and a decryption key. The digital image is decoded, and a specific check mark for verifying the validity of the decoding is detected from the decoded digital image.

  According to another aspect of the present invention, the present invention provides image decryption executed in an image decryption device that decrypts an encrypted image into a digital image, and specifies the position of the encrypted partial region. Therefore, a specific marker added to the encrypted image is detected, an encrypted encrypted image region is detected based on the detected marker, and a pixel of the detected encrypted image region is detected. An encrypted position whose value is regularly converted is detected, the encrypted image area is decrypted into the digital image based on the detected encrypted position and a decryption key, and the decrypted digital image In this case, a specific check mark for verifying the validity of the decoding is detected.

  In the present invention, the problem of loss of image information caused by adding a positioning frame to the outside of the encrypted image as in the technique of Patent Document 1, the pixel value of the encrypted area is regularly converted, and the pixel This is solved by means for generating a unique pattern corresponding to value conversion. If there is an image with edges such as characters in the encryption area, the pattern shape of the encrypted image obtained by the above processing will not be perfect, but it will be encrypted by using the statistical properties of the entire encrypted image The position can be detected correctly.

  Further, in the encryption processing according to the present invention, the regular pattern for detecting the encrypted position generated by converting the pixel value has a certain width, so that even if the encrypted image is read by a low-resolution camera, the encryption is performed. The correct position can be detected and decoded. If a method for compressing and encrypting an image is used in combination, a decrypted image having an image quality independent of the resolution of the scanner or camera can be realized.

It is a figure which shows the process outline | summary (the 1) of embodiment to which this invention is applied. It is a figure which shows the process outline | summary (the 2) of embodiment to which this invention is applied. It is a figure which shows the outline | summary of the encryption process in 1st Embodiment. It is a figure which shows the example which selects an encryption area | region. It is a figure which shows the example of input of an encryption key. It is a figure which shows an example of the scramble process in an image conversion part. It is a figure which shows the other example of the scramble process in an image conversion part. It is a figure which shows the modification of the shape of the micro area | region in a scramble process. It is a figure which shows the compression process in an image conversion part. It is a figure which shows the process which images conversion data. It is a figure which shows the example (the 1) of the pixel value conversion process in a pixel value conversion part. It is a figure which shows the example (the 2) of the pixel value conversion process in a pixel value conversion part. It is a figure which shows the example of the positioning marker used by an encryption process. It is a figure which shows the example of an encryption image. It is a figure which shows the example of encryption of a gray scale image. It is a figure which shows the outline | summary of the decoding process in 1st Embodiment. It is a figure which shows the process of detecting an encryption area | region from a positioning marker. It is a flowchart which shows the flow of an encryption area | region detection process. It is a figure which shows the example by which the encryption position was detected. It is a figure which shows the whole image of 2nd Embodiment. It is a figure which shows the outline | summary of the encryption process in 2nd Embodiment. It is a figure which shows the outline | summary of the decoding process in 2nd Embodiment. It is a figure for demonstrating the detection method of an encryption area | region. It is a figure for demonstrating the detection method of an encryption position (horizontal direction). It is a figure which shows the example which detected the detection of the encryption position incorrectly. It is a figure which shows the outline | summary of the encryption process in 3rd Embodiment. It is a figure which shows the outline | summary of the decoding process in 3rd Embodiment. It is a block diagram of the processing apparatus which performs the encryption process and decryption process in this invention. It is a figure for demonstrating loading to the computer of the encryption and the decoding program in this invention.

Hereinafter, embodiments to which the present invention is applied will be described with reference to the drawings.
First, an outline of encryption processing and decryption processing in the first to third embodiments to which the present invention is applied will be described with reference to FIGS. 1 and 2.

FIG. 1 is a diagram showing a processing outline (part 1) of an embodiment to which the present invention is applied.
In FIG. 1, an encryption unit 11 (referred to as encryption units 11A, 11B, and 11C in the first to third embodiments, respectively) includes an input digital image and an encryption key indicating an encryption method. Based on the above, an encrypted image obtained by encrypting a part of the digital image is output. The printer output unit 12 prints the digital image encrypted by the encryption unit 11 on a printable physical medium such as paper. The scanner (camera) reading unit 13 reads the print image output from the printer output unit 12 using a scanner or a camera.

  The decryption unit 14 (referred to as decryption units 14A, 14B, and 14C in each of the first to third embodiments, respectively) prints the print image output from the printer output unit 12 and the input decryption key. To obtain a decoded image. Only when the input decryption key is correct, the encrypted image can be appropriately decrypted, and the information hidden by the encryption by the encryption unit 11 can be viewed.

FIG. 2 is a diagram showing a processing outline (part 2) of the embodiment to which the present invention is applied.
As shown in FIG. 2, the encryption process and the decryption process in the first to third embodiments to which the present invention is applied are used to convert a digital image encrypted by the encryption unit 11 into a printer, It is also possible to obtain a decoded image by inputting the electronic document image as it is to the decoding unit 14 without using a scanner.

Next, first to third embodiments to which the present invention is applied will be described.
First, a first embodiment to which the present invention is applied will be described.
FIG. 3 is a diagram showing an outline of the encryption processing in the first embodiment.

In FIG. 3, the encryption unit 11 </ b> A includes an encryption area determination unit 31, an image conversion unit 32, a pixel value conversion unit 33, and a marker addition unit 34.
The encryption area designating unit 31 selects an area to be encrypted from the input image including the area to be encrypted.

FIG. 4 is a diagram illustrating an example of selecting an encryption area.
That is, as shown in FIG. 4A, the encryption area designating unit 31 selects an area 42 to be encrypted from a digital image (input image) 41 including an area to be encrypted. This area 42 is converted into a converted image 43 as shown in FIG. 4B by the processing of the image conversion unit 32 and the pixel value conversion unit 33 described later, and the digital image 41 is an encrypted image including the converted image 43. 44.

Returning to the description of FIG.
When the area 42 to be encrypted is selected by the encryption area designating unit 31, the area 42 to be encrypted and the encryption key are input in the image conversion unit 32, and the image of the area 42 to be encrypted by the conversion method corresponding to the encryption key Is visually transformed. The conversion parameter at that time is created from binary data obtained from the input encryption key.

FIG. 5 is a diagram illustrating an input example of the encryption key.
The example shown in FIG. 5 is an example of an encryption key and binary data generated by the encryption key. For example, a numerical value “1234” as an encryption key is input as binary data “100011010010”, and a character string “ango” as an encryption key is input as binary data “01100001011011100110011101101111”.

  As the image conversion method, in the first embodiment, there are two methods, a conversion method by dividing an image into minute regions and rearranging the minute regions (referred to as scramble processing), and a conversion method by compressing an image. Indicates one.

First, the scramble process will be described.
In the scramble process, first, the image of the selected area 42 is divided into small areas of a certain size, and then the small areas are rearranged by binary data obtained from the encryption key.

FIG. 6 is a diagram illustrating an example of the scramble process in the image conversion unit.
As shown in FIG. 6A, first, the area 42 selected by the encryption area designating unit 31 is divided in the vertical direction, and each bit of the binary string of the encryption key 61 is used as the boundary of the divided area 42. Corresponding in order from the left, when the bit is “1”, adjacent divided columns are exchanged, and when the bit is “0”, nothing is performed in order from the left. When the number of bits in the binary string is insufficient with respect to the number of division boundaries, the same binary string is repeated from the position where the binary string is insufficient, and the exchange processing is performed up to the right end of the region 42.

  Subsequently, as shown in FIG. 6B, the image area 62 subjected to the exchange process is divided in the horizontal direction, and each bit of the binary string of the encryption key 61 is moved up to the boundary of the divided image area 62. The same exchange processing as that performed in the vertical division is performed in order from the top in line units.

Then, as shown in FIG. 6C, as a result of performing the exchange process on each divided image, a scrambled image 63 that is a processed image obtained by scrambled the original area 42 is obtained.
As an expansion method of this scramble processing example, the horizontal direction and the vertical direction can be performed twice or more, and the size of the divided area can be changed in the second and subsequent replacements. Furthermore, another binary string can be used for exchanging the divided areas in the horizontal direction and the vertical direction. These extension methods are particularly effective as means for preventing the same processed image from being generated from different encryption keys when the size of the input image is small and the bit length of the encryption key is long.

FIG. 7 is a diagram illustrating another example of the scramble process in the image conversion unit.
As a scramble processing method different from the scramble processing described with reference to FIG. 6, a method of exchanging pixels in units of minute regions as shown in FIG. 7 is also possible. That is, the input image is divided into rectangular minute areas, and the divided minute areas are exchanged. As a result, the number of scrambles is increased and the encryption strength can be increased as compared with the above-described method using the exchange between the horizontal direction and the vertical direction (row and column).

FIG. 8 is a diagram illustrating a modified example of the shape of the minute region in the scramble process.
Further, as the shape of the micro area in the scramble processing, for example, a triangle as shown in FIG. 8A can be used in addition to the quadrangle shown in FIG. Further, as shown in FIG. 8B, minute regions having different shapes and sizes can coexist.

Next, a conversion method by compressing an image will be described.
FIG. 9 is a diagram illustrating compression processing in the image conversion unit.
When the input image 41 is a binary image, the image of the area 42 selected by the encryption area designating unit 31 is first compressed as shown in FIG. 9A, and shown in FIG. A binary string 71 is created. The compression methods here include all kinds of compression, such as run-length compression used when transferring binary image data in a facsimile machine, and JBIG (Joint Bi-level Image experts Group) compression, which is a standard compression method for binary images. The method is applicable.

FIG. 10 is a diagram illustrating a process for imaging the converted data.
Subsequent to the compression of the area 42 as shown in FIG. 9, each bit of the binary string 71 which is the converted compressed data is converted to “white” if the bit is “0” as shown in FIG. If the bit is “1”, the rectangular image (processed image) 81 is created by enlarging the rectangle to a specified size of “black”, and arranged as a monochrome rectangular image 81 in the area 42 of the image to be encrypted.

  When it is desired to arrange the converted compressed data (binary string 71) so as to fit within the image of the selected area 42, the size of the rectangular image 81 depends on the compression ratio of the selected area 42. For example, when the compression ratio is 1/4 or less, the size of the square image 81 is 2 × 2 pixels at most, and when it is 1/16 or less, the size is 4 × 4 pixels at most.

  On the other hand, when the size of the square image 81 is designated in advance and it is desired to store the compressed data in the image of the selected area 42, it is necessary to achieve a compression ratio depending on the size of the square image 81 in the first image compression processing. There is. For example, when the square is 4 × 4 pixels in size, a compression ratio of 1/16 or more is required. In this case, a method of compressing the information in the selected area 42 in advance or a method using an irreversible compression method are effective.

  With the encryption processing for enlarging and compressing the compressed data, for example, the enlarged monochrome block can be recognized even when the encrypted image is read with a low-resolution camera, so that the encrypted image can be correctly decrypted.

Returning to the description of FIG.
The pixel value conversion unit 33 converts the pixels in the processed image 63 converted by the image conversion unit 32 at regular intervals so that the converted image 43 forms a substantially grid-like striped pattern.

FIG. 11 is a diagram illustrating an example (part 1) of the pixel value conversion processing in the pixel value conversion unit.
In the pixel value conversion unit 33, the pixels of the processed image 63 in which the area 42 is scrambled by the image conversion unit 32 are converted at regular intervals so that the encrypted image 44 forms a generally grid-like striped pattern as a whole. . For example, as shown in FIG. 11, the conversion is performed such that the scrambled image 63 shown in FIG. 11A is inverted at the colored portion of the checkered pattern (checkered) image 91 shown in FIG. As a result, as shown in (C), the converted image 92 in which the encrypted image 44 as a whole forms a substantially grid-like striped pattern is obtained. Thereby, the generated striped pattern is used to detect the detailed position of each pixel in the encryption area when the encrypted image 44 is decrypted.

It is also possible to carry out another conversion for these series of processes. For example, the process of inverting the pixel value may be a process of adding a specified value.
Further, the checkered pattern image 91 shown in FIG. 11B is substantially the same size as the scrambled image 63 shown in FIG. 11A, but by using a size smaller than the scrambled image 63, the periphery of the scrambled image 63 is displayed. Only the center part other than the above may be reversed.

FIG. 12 is a diagram illustrating an example (part 2) of the pixel value conversion process in the pixel value conversion unit.
Further, various shapes can be applied to the region 42 where the pixel value is converted, as shown in FIGS. Since the pixel value conversion is a process aimed at detecting the boundary position between the small regions with high accuracy, it is also conceivable to convert the pixel value only at the boundary part as shown in FIG. Also, by performing pixel value conversion while shifting little by little with respect to the minute area as shown in FIG. 12B, the boundary between conversion and non-conversion appears at a finer interval. Can be detected in more detail. In addition, if pixel value conversion is performed only on a portion where the boundaries of minute regions intersect as shown in FIG. 12C, image quality degradation when reading and decoding an image printed on paper with a scanner or camera is minimized. Can be suppressed.

In addition, pixel value conversion (for example, pixel value conversion in units of regions divided in a triangular shape) using a divided region different from the shape of the minute region as a unit is also applicable.
Furthermore, when the shape of the minute region is not a square having a uniform size, a triangle (FIG. 8A) or different sizes and shapes coexist as shown in FIG. 8 (FIG. 8B). The pixel value conversion (for example, a triangular pixel value conversion to a triangular minute region) may be performed by a method according to the shape, not limited to the above conversion example, or a pixel value conversion independent of the scramble shape (For example, a rectangular pixel value conversion may be performed on a triangular minute region).

  As described above, in the present invention, the regular pattern representing the encrypted position is not generated by overwriting the input image as in Patent Document 1, but is generated by converting the pixel value of the input image. is doing. Therefore, unlike the prior art, the image information at the end of the encrypted image is not sacrificed for position detection, and the original image information can be efficiently encrypted in the form of coexisting position detection information. The

  Note that if some image information is included in the part constituting the pattern, the regularity is somewhat lost, but by using the statistical properties of the entire encrypted image as described in the processing of the decryption unit 14 described later, The encrypted position can be detected.

Returning to the description of FIG.
The marker adding unit 34 adds the positioning markers to, for example, three places other than the lower right among the four corners of the converted image 92 converted by the pixel value converting unit 33 to create the encrypted image 44.

The marker adding unit 34 arranges positioning markers for specifying the position of the encrypted area 42 at, for example, three positions other than the lower right among the four corners of the converted image 92.
FIG. 13 is a diagram illustrating an example of a positioning marker used in the encryption process.

  The positioning marker used in the first embodiment is assumed to have a round cross shape as shown in FIG. If the shape of the positioning marker is more broadly described, it may be constituted by a solid circle or polygon and a plurality of lines intersecting with the circumference. As an example of this, three lines extending from the center toward the circumference, such as those in the shape of a Chinese character “field” like the positioning marker in FIG. Examples include those that appear in a radial pattern, and those in which the line is cut halfway like the positioning marker of (D).

  In addition, the color configuration of the positioning marker may be the simplest as long as the background is white and the foreground is black, but is not limited thereto, and may be appropriately changed according to the color (pixel value) distribution of the converted image 92. Absent. In addition, instead of designating a predetermined color for the background and the foreground, a method of forming a positioning marker by inverting the foreground pixel values while the background color remains the digital image 41 may be considered. In this way, it is possible to encrypt the image while retaining the input image information of the positioning marker portion.

FIG. 14 is a diagram illustrating an example of an encrypted image.
The encrypted image 44 as shown in FIG. 14 is finally generated by the above processing of the encryption unit 11A. The encrypted image 44 includes a converted image 92 and a positioning marker 121.

  Furthermore, in the encryption method according to the first embodiment, when “processing for rearranging micro regions (scramble processing)” is used in the image conversion unit 32, not only a binary image but also a grayscale or color image. Encryption processing can also be applied to.

FIG. 15 shows an example in which a grayscale image is encrypted.
In FIG. 15, the grayscale image 131 shown in FIG. 15A is processed by the encryption unit 11A to generate an encrypted image 132 including a converted image 133 and a positioning marker 134 as shown in FIG.

Next, the decoding unit 14A will be described.
FIG. 16 is a diagram showing an outline of the decryption processing in the first embodiment.
In FIG. 16, the decryption unit 14A includes a marker detection unit 141, an encryption area detection unit 142, an encryption position detection unit 143, and an image reverse conversion unit 144.

  The marker detection unit 141 detects the position of the positioning marker added by the marker adding unit 34 from the encrypted image using a general image recognition technique. As a detection method, pattern matching, analysis on graphic connectivity, or the like can be applied.

The encryption area detection unit 142 detects the area of the encrypted image based on the positional relationship between the three positioning markers detected by the marker detection unit 141.
FIG. 17 is a diagram illustrating a process of detecting the encryption area from the positioning marker.

  As shown in FIG. 17A, when at least three positioning markers 152 are detected from the encrypted image 151 by the marker detection unit 141, as shown in FIG. 17B, one encrypted area 153 is stored. Can be detected. That is, since the three positioning markers 152 are arranged at the four corners of the rectangular encryption area 153, the figure obtained by connecting these three points (positions of the positioning markers 152) with a line is approximately a right triangle. Therefore, when three or more positioning markers 152 are detected, the positional relationship of the three positioning markers 152 includes an area configured in a shape close to a right triangle, and the positions of the three positioning markers 152 are set to four corner portions. A rectangle having three corners is defined as an encryption area 153. If the number of detected positioning markers 152 is two or less, the corresponding encrypted area 153 cannot be specified, and therefore the decryption process is terminated because there is no encrypted image.

FIG. 18 is a flowchart showing the flow of the encrypted area detection process.
In the encryption area detection process executed by the encryption area detection unit 142, first, in step S1601, the number of positioning markers 152 detected by the marker detection unit 141 is substituted into a variable n, and in step S1602, the encryption area detection process is performed. 0 is substituted into the detection flag reg_detect 153.

  In step S1603, it is determined whether or not the variable n to which the number of positioning markers 152 is assigned is 3 or more. If the variable n is not 3 or more, that is, if the variable n is 2 or less (step S1603). : No), the decryption process including the present encrypted area detection process is terminated.

  On the other hand, if the variable n is 3 or more (step S1603: Yes), in step S1604, three positioning markers 152 among the positioning markers 152 detected by the marker detection unit 141 are selected, and the selection is performed in step S1605. It is determined whether or not the positional relationship between the three positioning markers 152 is a substantially right triangle.

  If the positional relationship between the three selected positioning markers 152 is not a substantially right triangle (step S1605: No), whether or not all three combinations of the positioning markers 152 detected by the marker detection unit 141 have been completed in step S1606. If not completed (step S1606: No), the process returns to step S1604 to select the other three points, and if completed (step S1606: Yes), the process proceeds to step S1608.

  On the other hand, if the positional relationship between the three selected positioning markers 152 is a substantially right triangle (step S1605: Yes), 1 is substituted into the detection flag reg_detect in step S1607.

  In step S1608, it is determined whether or not 1 is substituted for the detection flag reg_detect, that is, whether or not the three positioning markers 152 whose three-point positional relationship is a right triangle can be detected. If 1 is assigned (step S1608: Yes), the process proceeds to the encryption position detection unit 143. If 1 is not assigned to reg_detect (step S1608: No), decryption including the present encryption area detection process is performed. The process is terminated.

Returning to the description of FIG.
The encrypted position detecting unit 143 uses the fact that the end portion of the encrypted area 153 detected by the encrypted area detecting unit 142 forms a regular pixel distribution in order to correctly decrypt the encrypted image 151. Then, the detailed position of each pixel in the encryption area 153 is detected by frequency analysis or pattern matching. This detection uses the property that the entire encrypted image 151 forms a periodic pattern by the pixel value conversion (inversion) processing of the pixel value conversion unit 33.

  As one detection method, the pattern period (width) is first obtained by a frequency analysis method such as Fast Fourier Transform (FFT) in the horizontal and vertical directions of the image, and then the boundary position (offset) by template matching or the like. ) Can be considered.

  In addition, it is possible to detect the boundary position by Hough transform by using the property that the boundary portion becomes linear when an edge detection filter (Laplacian filter or the like) is applied to the encrypted image.

FIG. 19 is a diagram illustrating an example in which the encrypted position is detected.
When the encrypted digital image 41 is complicated, there is a possibility that a portion where the periodicity of the encrypted image 44 is significantly impaired appears. In such a case, it is effective to perform the encryption position detection by limiting the image area used for the calculation of the pattern period and the boundary position to a portion having a relatively strong periodicity.

Returning to the description of FIG.
The image reverse conversion unit 144 uses the encrypted position information detected by the encrypted position detection unit 143 and the decryption key input by the user to convert the encrypted image 44 into the image conversion unit 32 by a method corresponding to the decryption key. The inverse conversion process of the conversion process is performed to generate a decoded image. The decryption processing procedure is realized by the reverse procedure of the encryption processing, and thus description thereof is omitted.

The above is the description of the first embodiment to which the present invention is applied.
Next, a second embodiment to which the present invention is applied will be described.
FIG. 20 is a diagram showing an overall image of the second embodiment.

  In the second embodiment, before the encryption process, a specific check mark 182 for verifying the validity of the decryption of the encrypted image 183 is added to an arbitrary location in the area 181 to be encrypted. (FIG. 20 (A)) is encrypted (FIG. 20 (B)), and if the check mark 182 added in advance after the encrypted image 183 is decrypted is detected from the decrypted image 184, it is correct. Decoding processing is ended as being decoded ((C) of FIG. 20). When the check mark 182 is not detected ((D) in FIG. 20), the encryption position is corrected, and the decryption process is repeated until the check mark 182 is detected or until a specified criterion is satisfied.

FIG. 21 is a diagram illustrating an outline of the encryption processing according to the second embodiment.
21, the encryption unit 11B includes an encryption area determination unit 31, a check mark addition unit 192, an image conversion unit 32, and a pixel value conversion unit 33.

As in the first embodiment, the encryption area designating unit 31 selects an area to be encrypted from the input image including the area to be encrypted.
Then, the check mark adding unit 192 adds a specific check mark 182 for verifying the validity of the decryption of the encrypted image 183 to any place in the area 181 to be encrypted. It is desirable to add the check mark 182 to a flat region having a pixel distribution with as little image information as possible.

  After adding the check mark 182 to the designated position, the area 181 to be encrypted and the encryption key are input in the image conversion unit 32 and the area is encrypted by the conversion method corresponding to the encryption key, as in the first embodiment. The image 181 is visually converted, and the pixel value conversion unit 33 converts the pixels in the processed image converted by the image conversion unit 32 at regular intervals so that the converted image has a substantially grid-like striped pattern. Make it.

FIG. 22 is a diagram illustrating an outline of the decrypting process according to the second embodiment.
22, the decryption unit 14B includes an encryption area detection unit 201, an encryption position detection unit 143, an image reverse conversion unit 144, a check mark detection unit 204, and an encryption position correction unit 205.

  First, the encrypted area detection unit 201 detects a rough area of the encrypted image 183. Since the pixel distribution of the encrypted image 183 is approximately checkered by the encryption processing of the encryption unit 11B, performing frequency analysis such as FFT in the horizontal direction and the vertical direction respectively corresponds to the fringe period. The power of the frequency becomes remarkably strong.

FIG. 23 is a diagram for explaining a method of detecting an encryption area.
As shown in FIG. 23A, when the encrypted image 211 is subjected to frequency analysis, as shown in FIG. 23B, a region where the power of a certain frequency (a frequency that is an integer multiple of the frequency) protrudes is expressed as “periodicity”. It is expressed as “strong” 214. Since the periodicity of the pixel distribution tends to be strong in the encryption area, it is possible to detect the approximate encryption area and period of the striped pattern.

Returning to the description of FIG.
The encryption position detection unit 143 identifies a rough area for encryption by the encryption area detection unit 201, and then more accurately detects the encryption area, and at the same time, detects the detailed position of each pixel in the encryption area. To do. As an example of position detection, first, a boundary position (offset) of pixel value conversion is obtained from the period of the striped pattern obtained by the encryption area detection unit 201 and the distribution of pixel absolute value difference, and the pixel absolute value difference is further relative from there. A method of narrowing a large area can be considered. Further, as with the encrypted position detection unit 143 of the first embodiment, it is possible to use Hough transform for detecting the encrypted position.

FIG. 24 is a diagram for explaining a method of detecting an encryption position (horizontal direction).
When the encryption area detection process as described above is performed in the horizontal and vertical directions, the encrypted position 221 is detected as shown in FIG.

Returning to the description of FIG.
The image inverse transform unit 144 performs the same method as in the first embodiment using the encrypted position information and the decryption key, and generates a decrypted image.

  The check mark detection unit 204 attempts to detect a check mark from the decoded image decoded by the image inverse conversion unit 144. Since the detection method is the same as the marker detection process in the first embodiment, the description thereof is omitted. When a check mark is detected, a decoded image is output and the process is completed. When the check mark is not detected, the encryption position correction unit 205 corrects the encrypted position, and the decryption process (image reverse conversion process) is performed again until the check mark is detected or until the specified standard is satisfied.

FIG. 25 is a diagram illustrating an example in which the detection of the encrypted position is incorrect.
As shown in FIG. 25, a case where the end of the encrypted image is overlooked (missing line 231) can be considered. Therefore, when the detection of the check mark 221 fails, the lines indicating the encryption position are added or deleted at the left and right ends and the upper and lower ends, and image reverse conversion processing is performed to determine whether the check mark 221 can be detected. consider. If the check mark 221 cannot be detected no matter how the line is added or deleted, the process ends without outputting the decoded image.

The above is the description of the second embodiment to which the present invention is applied.
Next, a third embodiment to which the present invention is applied will be described.
In the third embodiment of the present invention, the positioning marker for specifying the encryption area shown in the first embodiment and the check mark for judging the validity of the decrypted image of the second embodiment are provided. Both are used to encrypt and decrypt images. By using these two types of positioning markers for position detection and check marks for confirming the decrypted image, it is possible to reduce image decryption errors when a correct decryption key is input.

FIG. 26 is a diagram illustrating an outline of the encryption processing according to the third embodiment.
In FIG. 26, the encryption unit 11C includes an encryption area determination unit 31, a check mark addition unit 192, an image conversion unit 32, a pixel value conversion unit 33, and a marker addition unit 34.

  First, an image area to be encrypted is selected by the encryption area designating unit 31, and a check mark for decryption verification is added by the check mark adding unit 192 in the same manner as in the second embodiment. After adding the check mark, the image conversion unit 32 and the pixel value conversion unit 33 perform image processing in the same manner as in the first and second embodiments, and the image is encrypted. The marker addition unit 34 encrypts the image. A positioning marker for area detection is added by the same method as in the first embodiment. Since the contents of these processes are the same as those in the first embodiment or the second embodiment, description thereof will be omitted.

FIG. 27 is a diagram illustrating an outline of the decrypting process according to the third embodiment.
In FIG. 27, the decryption unit 14C includes a marker detection unit 141, an encryption area detection unit 142, an encryption position detection unit 143, an image reverse conversion unit 144, a check mark detection unit 204, and an encryption position correction unit 205. ing.

  First, the marker detection unit 141 detects the positioning marker by the same method as in the first embodiment, and the subsequent encryption region detection unit 142 detects the encryption region by the same method as in the first embodiment. Further, the encrypted position detection unit 143 detects the detailed position of each pixel in the encryption area by the same method as in the first embodiment. The processing procedures executed by the image reverse conversion unit 144, the check mark detection unit 204, and the encrypted position correction unit 205 are the same as those in the second embodiment, and thus the description thereof is omitted.

The above is the description of the third embodiment to which the present invention is applied.
As described above, the embodiments of the present invention have been described with reference to the drawings. However, the functions of the processing apparatus that executes the encryption process and the decryption process to which the present invention is applied are executed. If there is, the present invention is not limited to the above-described embodiment, and processing is performed via a network such as a LAN or WAN, whether it is a single device, a system composed of a plurality of devices, or an integrated device. Needless to say, it may be a system.

  As shown in FIG. 28, a CPU 2601 connected to a bus 2608, a ROM or RAM memory 2602, an input device 2603, an output device 2604, an external recording device 2605, a medium driving device 2606, a portable recording medium 2609, a network connection It can also be realized by a system constituted by the device 2607. That is, a ROM or RAM memory 2602, an external recording device 2605, and a portable recording medium 2609 that record software program codes for realizing the system of the above-described embodiment are supplied to the processing device, and the computer of the processing device Needless to say, this can also be achieved by reading and executing the program code.

  In this case, the program code read from the portable recording medium 2609 or the like realizes the novel function of the present invention, and the portable recording medium 2609 or the like on which the program code is recorded constitutes the present invention. become.

  As a portable recording medium 2609 for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a DVD-ROM, a DVD-RAM, a magnetic tape, a non-volatile Various recording media recorded via a network connection device 2607 (in other words, a communication line) such as a memory card, a ROM card, electronic mail or personal computer communication can be used.

  Further, as shown in FIG. 29, the function of the above-described embodiment is realized by executing the program code read out on the memory 2602 by the computer, and is operated on the computer based on the instruction of the program code. The operating system or the like performs part or all of the actual processing, and the functions of the above-described embodiments are also realized by the processing.

  Further, the program code read from the portable recording medium 2609 and the program (data) provided by the program (data) provider are provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. After being written in the memory 2602, the CPU 2601 provided in the function expansion board or function expansion unit performs part or all of the actual processing based on the instruction of the program code. A function can be realized.

  That is, the present invention is not limited to the embodiment described above, and can take various configurations or shapes without departing from the gist of the present invention.

Claims (24)

In an image encryption apparatus that encrypts a digital image into an encrypted image,
An encryption area specifying means for specifying a partial area to be encrypted from the digital image;
Image conversion means for converting the partial area selected by the encryption area specifying means into a processed image based on an encryption key;
Pixel value conversion means for generating a converted image by regularly converting pixel values of the processed image converted by the image conversion means in order to be able to specify the position of the partial region;
An image encryption apparatus comprising:   The image encryption apparatus according to claim 1, wherein the image conversion unit divides the partial region into a plurality of minute regions, and rearranges the divided plurality of minute regions based on the encryption key.   The image conversion means converts the partial area into compressed data by an arbitrary compression method, and arranges each bit of the converted compressed data as white pixels or black pixels of an arbitrary size. Item 2. The image encryption device according to Item 1.   The pixel value conversion means converts the pixel value at a constant cycle with respect to the horizontal direction of the processed image, and converts the pixel value at a constant cycle with respect to the vertical direction, thereby forming a generally striped pattern. The image encryption apparatus according to claim 1, wherein a converted image is generated. Marker adding means for generating the encrypted image by adding a specific marker to the converted image generated by the pixel value converting means in order to specify the position of the partial region;
The image encryption apparatus according to claim 1, further comprising:   6. The image encryption apparatus according to claim 5, wherein the marker has a solid circular shape or a polygonal shape, and a plurality of lines that intersect with the circumference of the circular shape or the polygon exist on the inside thereof.   The image encryption apparatus according to claim 5 or 6, wherein the marker has a foreground formed by pixel value conversion. Check mark adding means for adding a specific check mark for verifying the validity of decryption of the encrypted image to the digital image before the designation of the partial area by the encrypted area specifying means;
The image encryption apparatus according to claim 1, further comprising: In an image decryption apparatus that decrypts an encrypted image into a digital image,
Marker detection means for detecting a specific marker added to the encrypted image in order to specify the position of the encrypted partial area;
An encrypted area detecting means for detecting an encrypted image area encrypted based on the marker detected by the marker detecting means;
An encrypted position detecting means for detecting an encrypted position in which pixel values are regularly converted in the encrypted image area detected by the encrypted area detecting means;
Decrypting means for decrypting the encrypted image area into the digital image based on the encrypted position and the decryption key detected by the encrypted position detecting means;
An image decoding apparatus comprising: In an image decryption apparatus that decrypts an encrypted image into a digital image,
Encrypted area detecting means for detecting an encrypted image area encrypted;
An encrypted position detecting means for detecting an encrypted position in which pixel values are regularly converted in the encrypted image area detected by the encrypted area detecting means;
Decrypting means for decrypting the encrypted image area into the digital image based on the encrypted position and the decryption key detected by the encrypted position detecting means;
A check mark detection means for detecting a specific check mark for verifying the validity of decoding from the digital image decoded by the decoding means;
An image decoding apparatus comprising: In an image decryption apparatus that decrypts an encrypted image into a digital image,
Marker detection means for detecting a specific marker added to the encrypted image in order to specify the position of the encrypted partial area;
An encrypted area detecting means for detecting an encrypted image area encrypted based on the marker detected by the marker detecting means;
An encrypted position detecting means for detecting an encrypted position in which pixel values are regularly converted in the encrypted image area detected by the encrypted area detecting means;
Decrypting means for decrypting the encrypted image area into the digital image based on the encrypted position and the decryption key detected by the encrypted position detecting means;
A check mark detection means for detecting a specific check mark for verifying the validity of decoding from the digital image decoded by the decoding means;
An image decoding apparatus comprising: An encrypted position correcting means for correcting an encrypted position detected by the encrypted position detecting means when a check mark is not detected by the check mark detecting means;
The image decoding apparatus according to claim 10, further comprising:   The image according to any one of claims 9 to 12, wherein the encrypted image is an image encrypted by the image encryption device according to any one of claims 1 to 8. Decryption device.   The encrypted image is an image obtained by printing an image encrypted by the image encryption apparatus according to any one of claims 1 to 8, and reading the printed image. The image decoding device according to any one of 9 to 12. An image encryption method executed in an image encryption apparatus for encrypting a digital image into an encrypted image,
Specify a partial area to be encrypted from the digital image,
Converting the selected partial region into a processed image based on an encryption key;
In order to be able to specify the position of the partial area, a converted image is generated by regularly converting pixel values of the converted processed image.
An image encryption method characterized by the above. Generating the encrypted image by adding a specific marker to the generated converted image to identify the position of the partial region;
The image encryption method according to claim 15. An image decryption method executed in an image decryption apparatus for decrypting an encrypted image into a digital image,
In order to identify the position of the encrypted partial area, a specific marker added to the encrypted image is detected,
Based on the detected marker, an encrypted encrypted image area is detected,
Detecting an encrypted position in which pixel values are regularly converted in the detected encrypted image region;
Decrypting the encrypted image region into the digital image based on the detected encryption position and decryption key;
An image decoding method characterized by the above. An image decryption method executed in an image decryption apparatus for decrypting an encrypted image into a digital image,
Detect the encrypted image area encrypted,
Detecting an encrypted position in which pixel values are regularly converted in the detected encrypted image region;
Decrypting the encrypted image region into the digital image based on the detected encryption position and decryption key;
Detecting a specific check mark for verifying the validity of decoding from the decoded digital image;
An image decoding method characterized by the above. An image decryption method executed in an image decryption apparatus for decrypting an encrypted image into a digital image,
In order to identify the position of the encrypted partial area, a specific marker added to the encrypted image is detected,
Based on the detected marker, an encrypted encrypted image area is detected,
Detecting an encrypted position in which pixel values are regularly converted in the detected encrypted image region;
Decrypting the encrypted image region into the digital image based on the detected encryption position and decryption key;
Detecting a specific check mark for verifying the validity of decoding from the decoded digital image;
An image decoding method characterized by the above. A computer of an image encryption device that encrypts a digital image into an encrypted image,
An encryption area specifying means for specifying a partial area to be encrypted from the digital image;
Image conversion means for converting the partial area selected by the encryption area designating means into a processed image based on an encryption key;
Pixel value conversion means for generating a converted image by regularly converting the pixel values of the processed image converted by the image conversion means in order to be able to specify the position of the partial region;
Image encryption program to function as Marker adding means for generating the encrypted image by adding a specific marker to the converted image generated by the pixel value converting means in order to specify the position of the partial region;
The image encryption program according to claim 20, further comprising: A computer of an image decryption apparatus that decrypts an encrypted image into a digital image,
Marker detection means for detecting a specific marker added to the encrypted image in order to specify the position of the encrypted partial area;
An encrypted area detecting means for detecting an encrypted image area encrypted based on the marker detected by the marker detecting means;
An encrypted position detecting means for detecting an encrypted position in which pixel values are regularly converted in the encrypted image area detected by the encrypted area detecting means;
Decrypting means for decrypting the encrypted image area into the digital image based on the encrypted position and the decryption key detected by the encrypted position detecting means;
Decoding program for functioning as. A computer of an image decryption apparatus that decrypts an encrypted image into a digital image,
Encrypted area detecting means for detecting an encrypted image area encrypted;
An encrypted position detecting means for detecting an encrypted position in which pixel values are regularly converted in the encrypted image area detected by the encrypted area detecting means;
Decrypting means for decrypting the encrypted image area into the digital image based on the encrypted position and the decryption key detected by the encrypted position detecting means;
A check mark detection means for detecting a specific check mark for verifying the validity of decoding from the digital image decoded by the decoding means;
Decoding program for functioning as. A computer of an image decryption apparatus that decrypts an encrypted image into a digital image,
Marker detection means for detecting a specific marker added to the encrypted image in order to specify the position of the encrypted partial area;
An encrypted area detecting means for detecting an encrypted image area encrypted based on the marker detected by the marker detecting means;
An encrypted position detecting means for detecting an encrypted position in which pixel values are regularly converted in the encrypted image area detected by the encrypted area detecting means;
Decrypting means for decrypting the encrypted image area into the digital image based on the encrypted position and the decryption key detected by the encrypted position detecting means;
A check mark detection means for detecting a specific check mark for verifying the validity of decoding from the digital image decoded by the decoding means;
Decoding program for functioning as.

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