JP2007010862A - Image distribution information generation device, and image distribution information compositing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image distribution information generation device which disables making automatic decision that an image has been reproduced normally, and which can control the quality of the reproduced image by the number of pieces of partial information to be combined, and to provide a device for combining the same. <P>SOLUTION: The image decentralization information generation device includes a hierarchical encoding means 31 which collects bit planes of image information (a) contributing, to a similar degree to the improvement of quantization error, and divides them into a plurality of hierarchies and encodes them; and compositable number variable partial data generation means 32(1)-32(L) which generate, so that the original code data can be reproduced from at least k (an integer of 1≤k≤N) partial data, N (integer N≥1) different partial data from code data in a hierarchy, by varying the k value for each hierarchy by using a secret sharing scheme and in such a manner that the higher the bit planes is, the smaller number of partial data can be generated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

   The present invention belongs to the field of digital image processing, and particularly relates to an image distributed information generation device and a composition device thereof that can realize high security at the content level against loss of image content and theft.

  The content business has been developed through the development of broadband networks. When storing high-value content information, in order to prevent data loss due to disasters or physical server failures, a method of storing duplicates in another location is used. In this case, due to the presence of a plurality of data, there is an increased risk of information leaking due to a server crack or the like and the value of the content being reduced.

  Therefore, a method for distributing and storing information using a method called secret sharing scheme has been proposed. As shown in FIG. 8 (a), the image information is distributed and stored in a plurality of pieces of shared information, and as shown in FIG. It is to be obtained.

  By distributing and accumulating information by this method, the reproducibility of the original image information can be compensated even if part of the distributed information is lost as shown in FIG. As shown in FIG. 4, even at the time when a part of the distributed information is leaked, the security at the strong content level is realized in which the original information is kept secret.

Here, the (k, n) threshold secret sharing method, which is the most famous of the secret sharing methods, will be described below. In this system, secret information is distributed and encoded using a (k-1) degree polynomial called a dispersion function, and the general form of the dispersion function is the secret information S and the random term r _i (1 ≦ i ≦ k−). 1) and the prime number p are expressed as follows.

f (x) = S + a ₁ x + Λ + a _k−1 x ^k−1 (mod p) (1)

The distribution information W _i is calculated as W _i = f (i) by substituting arbitrary i (i <p) into the above dispersion function. Since the distribution function f (x) is a (k−1) degree polynomial, the distribution function itself can be restored by collecting k pieces of dispersion information, and thus the secret information S can be restored. 10 and dispersion function f (x) shows a conceptual diagram of the relationship between the distributed information W _i. In general, the secret information S is restored by solving simultaneous equations representing k pieces of shared information. However, in the threshold secret sharing method, the following Lagrange interpolation formula is often used.

  In the threshold secret sharing method, there are only two ways to restore the secret information S. Such a secret sharing method is called a complete secret sharing method.

In addition, there exist some which are described in the following patent documents 1 and 2 as a prior art relevant to this invention.
Japanese Patent Laid-Open No. 2002-358013 JP 2002-135247 A

  Problem 1: In the above secret sharing scheme, it is possible to construct a higher-strength system by not disclosing the value of k. That is, the third party does not know how many pieces of shared information can be combined to reproduce the original image. However, if the secret sharing scheme is applied as it is to the compressed image file, the shared information becomes an almost random bit string, and the original file format is completely lost. Therefore, if the original image was compressed by a general image compression format such as JPEG or JPEG 2000, it could be synthesized even if the information on how many more to synthesize was unknown on the synthesizer side Data is first input to these image decoders, and if normal processing can be performed, it can be automatically determined that the image has been reproduced normally. Therefore, a technique is desired in which the fact that the original image can be reproduced cannot be automatically determined by an image decoder or other software.

  Problem 2: Also, in the shared information created by the general secret sharing scheme, there is a problem in convenience because the contents of the original information cannot be confirmed unless a certain number of shared information is collected. That is, when a large value of k is used to increase the security level, even the administrator cannot confirm the original information without collecting a large number of distributed information. It is possible to reproduce only the summary of the original information with a smaller number of distributed information in order to confirm what kind of information is included without collecting a certain number of distributed information and reproducing the original information completely. By doing so, it is considered that convenience is improved.

  The object of the present invention has been made in view of the above-described problems of the prior art, and it is impossible to automatically determine that an image has been normally reproduced, and the image to be reproduced depends on the number of pieces of partial information to be synthesized. An object of the present invention is to provide an image dispersion information generation device and a synthesis device thereof capable of controlling quality. It is another object of the present invention to provide an image distribution information generation device and its composition device that realize high security at the content level against loss and theft of image content.

  In order to achieve the above-described object, the present invention provides a hierarchical code that collects bit planes of image information that contributes to the same extent in improving quantization error in an image dispersion information generation apparatus, and divides the encoded information into a plurality of hierarchies. And N (N ≧ 1 integer) different partial data so that the original encoded data can be reproduced from the encoding means and at least k (1 ≦ k ≦ N) partial data. Can be generated by changing the value of k for each layer so that it can be combined from a smaller number of partial data using the secret sharing scheme and the upper bit plane, and created in each layer Select one of the N partial data, collect the partial data for all layers into one shared information file, and create N shared information files using all the N partial data of each layer That there is a first feature in that comprising a dispersion information file creation means.

  Further, the present invention provides an apparatus for synthesizing an image distribution information file, a partial data extraction unit for extracting partial data of each layer from N image distribution information files created by the image distribution information generation apparatus, and the extracted partial data The second feature is that it comprises a composite number variable distributed information combining means for combining and using the secret sharing scheme to reproduce the encoded data, and a hierarchical decoding means for decoding the reproduced encoded data. is there.

  The third feature of the present invention resides in that the image distribution information generating apparatus includes means for adding information indicating which number of partial data can be synthesized from which partial data to the image distribution information file. is there.

  Furthermore, the present invention extracts the number of the image dispersion information files used for composition and the information added to the image dispersion information file in the image dispersion information file composition device, and can synthesize any level of encoded data. There is a fourth feature in that there is provided a means for specifying the above and a partial data extraction means for extracting only partial data of a layer that can be combined in order from the layer including the upper bit plane.

  According to the present invention, in image distribution information generation / synthesis in which bit planes that contribute to the same degree of improvement in quantization error are collected and controlled hierarchically, pixels (or conversions) are maintained while maintaining the hierarchical structure in the image compression format. By performing the secret sharing process only on the code information of the coefficient, even the data synthesized from the k or less shared information files can be made to conform to the compression format of the original image. For this reason, the correctness / incorrectness determination of the reproduced image must be performed with the human eye, and it can be difficult to determine whether or not the original image has been automatically reproduced. Thus, even if a malicious third party can automatically collect the distributed information image by a program or the like, the reproduction of the image needs to be visually confirmed one by one.

  In addition, according to the present invention, since an outline of an image can be understood only by collecting a smaller number of shares than the number of shares necessary for completely reproducing image information, convenience is improved. For example, it is effective when an administrator of a system having a secret sharing function manages image contents.

  Further, according to the present invention, the quality of an image reproduced by the bit plane of the partial information file to be combined can be controlled. In other words, when combining image distribution information files, if the number of files to be combined is small, only the upper bit plane is reproduced to obtain an image with low quantization accuracy, and the lower bit is increased as the number of files increases. An image including a plane and having a high quantization accuracy (an image with a small quantization error) is reproduced. If necessary, it is possible to reproduce a low-quality image from only a part of information of the upper bit plane, and it is possible to provide a means for the user to know the outline of the image hierarchically.

  Further, according to the present invention, it is possible to realize high security at the content level against loss and theft of image content and to provide high convenience such as hierarchical half-disclosure.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention uses a secret sharing scheme and a hierarchical image coding technique. The outline of the secret sharing scheme is the same as described above (described in the background art section), and thus the description thereof will be omitted. Hereinafter, the hierarchical encoding technique will be described.

  Hierarchical encoding techniques include wavelet transform encoding, bit plane encoding, or a combination of these. The present invention also includes a scheme that combines ROI encoding that preferentially encodes a region of interest (ROI) and a secret sharing method.

  As shown in FIG. 1A, the hierarchical encoder encodes image information in a hierarchical encoding unit 1 in a hierarchical manner. Thereafter, the file creation unit 2 adds information q necessary for extracting and decoding the encoded data p of each layer on the decoder side, and outputs it as one encoded file. On the other hand, in the decoder, as shown in FIG. 5B, the encoded data extraction unit 3 extracts the encoded data p of each layer based on the information q added as described above. Thereafter, the decoder 4 decodes the encoded data p of each layer using the additional information q.

  Various methods have been proposed for hierarchization. Here, frequency subband coding by bitlet transform, bit plane coding and ROI coding will be described. By subjecting the frequency-decomposed transform coefficient to bit-plane coding, the above-described two codings, frequency subband coding and bit-plane coding, can be performed simultaneously.

(Frequency subband coding)
By performing wavelet transform, it is decomposed into subbands indicating frequencies as shown in FIG. The spatial position information of the original image information remains inside each subband. Here, two divisions are used for each of the vertical direction and the horizontal direction, and the low frequency component is repeatedly divided. FIG. 2 shows the result of two repetitions. Since subbands with a higher number of decompositions contain lower frequency components, subbands are hierarchized according to the number of decompositions, and each layer is encoded. By transmitting and decoding only the low-frequency subband hierarchy, an image including only the low-frequency component, that is, an image representing an outline of the original image information can be reproduced.

(Bitplane coding)
As shown in FIG. 3, when encoding the transform coefficient in the pixel or subband of the image information, each pixel (coefficient) is viewed as a sequence of bits, and only the bit at a specific position is scanned in the spatial direction. As a result, the bit plane is extracted, and the bit plane is encoded as a hierarchical unit.

  In JPEG 2000 or the like, a plurality of encoding passes are generated from each bit plane in a smaller rectangular area in the subband. A collection of paths having almost the same degree of contribution to the coding error of the reproduced image is collected from each rectangular area to form one layer (layer). Here, coding methods using the concept of the bit plane in this way are collectively referred to as bit plane coding.

  In bit plane coding, the quantization error of a reproduced image becomes smaller as the number of layers to be reproduced increases.

(ROI encoding)
Since ROI encoding that preferentially encodes a specific area is also performed by classifying the portion of interest and the portion that is not, encoding will be discussed below. In JPEG 2000 ROI encoding, a region of interest is preferentially encoded by shifting up a wavelet transform coefficient before encoding corresponding to the region of interest and performing bit-plane encoding. This kind of ROI coding is also included in the hierarchical coding here.

  Next, a distributed storage device and a synthesis device (distribution device) according to the present invention that combine the secret sharing scheme and the hierarchical encoding technique will be described.

  First, an embodiment of a distributed storage device that creates and stores image distribution information using the secret sharing scheme will be described.

  FIG. 4 is a block diagram illustrating a configuration of the image dispersion information generation apparatus. The shared image information generation apparatus includes a hierarchical encoding unit 11, partial data creation units 12 (1) to 12 (L), shared information file creation units 13 (1) to 13 (N), and a control unit 14.

  In the hierarchical encoding unit 11, the image information a is hierarchically encoded into the L hierarchy (from the viewpoint of frequency, quantization accuracy, a specific region in an image having a specific meaning, etc.) and encoded. Details of this hierarchical encoding are as described above. The hierarchical encoding unit 11 sends only code data of pixels and coefficients not including information necessary for determining the encoding file format to the partial data creation units 12 (1) to 12 (L). On the other hand, information necessary to determine the encoding file format is sent to the shared information file creation units 13 (1) to 13 (N) as “additional information q necessary for decoding”. The “additional information q necessary for decryption” is commonly used in all the shared information files when the shared information file is created.

  The control unit 14 gives different IDs 15 to the N pieces (N ≧ 1) of shared information to be created. The partial data creation units 12 (1) to 12 (L) use each of these N IDs 15 as x in the equation (1), so that N different partial data 16 can be obtained from the encoded data of a certain layer. create. At this time, the secret code sharing method is used so that the original code data can be reproduced from at least k (1 ≦ k ≦ N) partial data. Here, k is the same for all layers.

  The shared information file creation units 13 (1) to 13 (N) collect one partial data among N partial data created in each layer from all layers, and create one shared information file. . Since N partial data are created from each layer, N shared information files are created.

  At this time, the shared information file creation units 13 (1) to 13 (N) add the value of the ID 15 to the header of each shared information file as “additional information 17 necessary for synthesis”. When the encoded file format is a general standard format, it is written in an area in the header where private information can be written.

  The distributed information files 1 to N created as described above are stored in a storage device (image distributed storage device) not shown.

  Next, synthesis of image sharing information using the secret sharing scheme will be described. FIG. 5 is a block diagram showing the configuration of the image sharing information file composition apparatus.

  The synthesizing apparatus includes partial data extraction units 21 (1) to 21 (n), encoded data synthesis units 22 (1) to 22 (L), and a decoding unit 23.

  Images are reproduced from n (1 ≦ n ≦ N) image dispersion information files among the N image dispersion information files created by the image dispersion information generation device of FIG. In the partial data extraction units 21 (1) to 21 (n), L-level partial data and information (ID of the partial information file) 24 required for synthesis are extracted from each shared information file. The n pieces of partial data for the respective layers are combined by the encoded data combining units 22 (1) to 22 (L) to generate encoded data of the respective layers.

  The encoded data of all layers are collectively decoded by the decoding unit 23, and a decoded image is generated. Here, the original encoded data is reproduced only when n ≧ k.

  According to this embodiment, only the code information of pixels (or conversion coefficients) is distributed while maintaining the hierarchical structure in the image compression format. Complies with the compression format of the original image. For this reason, the correctness / incorrectness determination of the reproduced image must be performed with human eyes, and it can be difficult to determine whether or not the original image has been automatically reproduced. For this reason, the said subject 1 can be solved.

  Next, a second embodiment of the present invention, a shared information generation apparatus and a hierarchical synthesis apparatus that can hierarchically control the quality of a reproduced image according to the number of shared information files to be synthesized, will be described. .

  FIG. 6 is a block diagram showing a configuration of an image dispersion information generation apparatus having the above-described features. The image shared information generation apparatus includes a hierarchical encoding unit 31, partial data creation units 32 (1) to 32 (L), shared information file creation units 33 (1) to 33 (N), a control unit 34, and a k value determination. Part 35.

  The hierarchical encoding unit 31 hierarchically encodes the image information a into the L hierarchy (from the viewpoint of frequency, quantization accuracy, a specific region in the image having a specific meaning, etc.), and determines an encoding file format. Only the code data of the pixels and coefficients not including the information necessary for the transmission are sent to the partial data creation units 32 (1) to 32 (L). Information necessary for determining the encoding file format is commonly used in all the shared information files when the shared information file is created as “additional information q necessary for decoding”.

  The control unit 34 gives one different ID 36 to each of the N pieces (N ≧ 1) of distributed information to be created.

  The k value determination unit 35 determines a total of L k values 35a, one for each layer, so that a lower k value is assigned to a higher priority layer.

  The partial data creation units 32 (1) to 32 (L) create N different partial data 37 from the encoded data of a certain layer by using each of the N IDs as x in Expression (1). At this time, the value of k determined by the k value determination unit 35 according to which hierarchy is processed is used. That is, the partial data 37 is created by changing the value of k for each layer so that encoded data can be reproduced from a different number of partial data for each layer. The k value determined for each layer, that is, the k value 35b for all layers is sent to the distributed information file creation units 33 (1) to 33 (N) via the control unit 34 and is necessary for synthesis. The additional information 38 is added to all the distributed information files 1 to N.

  The shared information file creation unit 33 (1) to 33 (N) collects one partial data among N partial data 37 created in each layer from all layers, and creates one shared information file. To do. Since N partial data are created from each layer, N shared information files are created. The shared information file creation units 33 (1) to 33 (N) also add the ID value to the header of each shared information file as “additional information 38 necessary for synthesis”. When the encoded file format is a general standard format, the “additional information 38 necessary for synthesis” can be written in an area in a header where private information can be written.

  For example, in the k value determination unit 35, it is assumed that k = 2 is set for the hierarchy 1 (the highest hierarchy), k = 3 is set for the hierarchy 2, and k = 4 is set for the hierarchy lower than the hierarchy 3. Then, in the synthesizing apparatus of FIG. 5, by collecting any two distributed information files (when n = 2), the hierarchy 1 is correctly reproduced. Also, by collecting any three shared information files (when n = 3), layer 1 and layer 2 are correctly reproduced, and by collecting any four shared information files (when n = 4) ), All hierarchies will be played correctly. Since the lower layer that has not been correctly reproduced in the composition processing of FIG. 5 is sent to the decoding unit 23 with a value different from the data of the original layer, it becomes a noise component of the reproduced image.

  Furthermore, in addition to the ID value as “additional information 38 necessary for synthesis”, a table (k value table) indicating the value of k used when processing all the hierarchies is included, which will be described later with reference to FIG. This synthesizer uses this table, so that a layer that has not been reproduced correctly can not be used for image decoding, and a reproduced image can be obtained only from an upper layer that does not contain noise components. Become.

  FIG. 7 is a block diagram showing a configuration of an image dispersion information file composition apparatus that can hierarchically control the reproduction image quality without including noise components in accordance with the number of pieces of dispersion information to be synthesized. The synthesizing apparatus includes a reproduction hierarchy determining unit 41, partial data extracting units 42 (1) to 42 (n), encoded data synthesizing units 43 (1) to 43 (m), a hierarchy selecting unit 44, and a decoding unit 45. .

  Images are reproduced from n (1 ≦ n ≦ N) image dispersion information files among the N image dispersion information files created by the image dispersion information generation device of FIG. The k value table d is extracted from the partial data extraction units 42 (1) to 42 (n). The k value table d describes the value of k used when distributedly processing each layer, and the playback layer determination unit 41 reproduces how many layers from the upper layer according to the value of n and the k value table d. You can see if it is possible. Here, as an example, it is assumed that m layers can be reproduced.

  Further, in the partial data extraction units 42 (1) to 42 (n), partial data of L layers and information necessary for synthesis (ID of the partial information file) are extracted from each distributed information file.

  The n partial data for a certain layer are collected and combined in a code data combining unit corresponding to the layer to generate encoded data. Since the encoded data in the lower hierarchy than the upper m hierarchy is not correctly reproduced, the hierarchy selection unit 44 discards the remaining m hierarchy from the upper. The m layers from the top are collectively decoded by the decoding unit 45 to generate a decoded image. At this time, an image closer to the original is reproduced as the number m is closer to L.

As more specific examples, the following three types of shared information generating / synthesizing apparatuses can be cited.
(a) Image dispersion information generator / synthesizer that hierarchically controls frequency components
(b) Image dispersion information generator / synthesizer that hierarchically controls quantization error
(c) Image dispersion information generator / synthesizer that hierarchically controls ROI playback

The shared information generating / synthesizing apparatuses (a) to (c) will be described below.
(a) Image dispersion information generating / synthesizing device for hierarchically controlling frequency components In FIG. 6, the hierarchical encoding unit 31 in the image dispersion information generating device capable of hierarchically controlling the reproduction image quality in accordance with the number of pieces of shared information to be combined. The frequency information to be reproduced can be controlled in accordance with the number of distributed information files to be synthesized by performing frequency conversion such as wavelet conversion on the image information and performing layering and encoding according to the frequency component.
When the number of images to be combined is small, an image with only low frequency components (an overview of the entire image) is obtained, and an image including a high frequency component (detailed portion) is reproduced as the number increases.

(b) Image dispersion information generating / synthesizing device for hierarchically controlling quantization error Hierarchical encoding unit in image dispersion information generating device of FIG. In 31, bit-plane encoding is performed, and hierarchization is performed so that the quantization error of the reproduced image becomes smaller as the number of hierarchies to be reproduced increases. Thereby, the reproduction | regeneration quantization precision can be controlled according to the number of the distributed information files to synthesize | combine.
When synthesizing the image sharing information file generated by the image sharing information generating device, if the number of files to be combined is small, only the upper bit plane is reproduced and an image with low quantization accuracy is obtained. As the number increases, an image with high quantization accuracy (an image with little quantization error) including a lower bit plane is reproduced.

(c) Image shared information generating / combining apparatus that hierarchically controls ROI reproduction Hierarchical encoding unit 31 in the image distributed information generating apparatus shown in FIG. 6 that can hierarchically control the reproduction image quality in accordance with the number of distributed information to be combined. In FIG. 7, ROI encoding is performed so that the specific region of interest and the background region are in different layers. As a result, ROI playback can be hierarchically controlled according to the number of distributed information files to be combined.
When the number of files to be combined at the time of combining is small, only a specific area to be noticed is reproduced, and all images including the background are reproduced as the number of files increases.

(d) Image dispersion information generation capable of semi-disclosure of information with only single image dispersion information As still another embodiment, a normal decoding device (see FIG. In the case of decoding in 1 (b)), an image shared information generating apparatus that creates a file in which an image is reproduced (semi-disclosed) with low quality is shown.
In the image dispersion information generating apparatus capable of hierarchically controlling the reproduction image quality according to the number of pieces of the shared information to be combined, the encoded data of the highest importance layer (the lowest frequency component, the highest bit plane, or the specific image region) With respect to the above, the distributed processing using the secret sharing scheme is not performed, but the replica is simply used, and partial data is created for the remaining layers by the distributed processing using the secret sharing scheme.

  Thus, the image shared information file can be decoded not only by the synthesizing device corresponding to the shared information generating device but also by a normal decoding device. The decoded image is reproduced as it is with respect to the component of the higher importance layer that has not been subjected to distributed processing, but the remaining partial data of the layer subjected to distributed processing is also decoded in the same manner as that which is not subjected to distributed processing. This component is added to the reproduced image as noise, and a low-quality image is reproduced, or a semi-disclosure image is reproduced.

It is a block diagram which shows the outline | summary of a structure of this invention. It is explanatory drawing of the frequency subband decomposition | disassembly by wavelet transformation. It is explanatory drawing of a bit plane. It is a block diagram which shows the structure of the image dispersion | distribution information generation apparatus of one Embodiment of this invention. It is a block diagram which shows the structure of the synthetic | combination apparatus of the image dispersion | distribution information file of one Embodiment of this invention. It is a block diagram which shows the structure of the image dispersion | distribution information generation apparatus of 2nd Embodiment of this invention. It is a block diagram which shows the structure of the synthetic | combination apparatus of the image dispersion | distribution information file of 2nd Embodiment of this invention. It is explanatory drawing of the outline of the conventional dispersion | distribution storage system using the secret sharing method. It is a figure explaining that original image information can be reproduced even if some shared information is lost, and that image information is not reproduced even if some shared information leaks to a third party. It is a diagram showing the relationship between the dispersion function f (x) shared information W _i.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Hierarchical encoding part, 2 ... File preparation part, 3 ... Encoded data extraction part, 4 ... Decoder, 11, 31 ... Hierarchical encoding part, 12 (1)- 12 (L), 32 (1) to 32 (L) ... partial data creation unit, 13 (1) to 13 (N), 33 (1) to 33 (N) ... shared information file creation unit, 14, 34 ... control unit, 15, 36 ... ID, 16, 37 ... partial data, 17, 38 ... additional information necessary for composition, 21 (1) to 21 (n), 42 (1) to 42 (n) ... partial data extraction unit, 22 (1) to 22 (L), 43 (1) to 43 (m) ... encoded data synthesis unit, 23, 45 ... Decoding unit, 35... K value determining unit, 41... Playback layer determining unit, 44.

Claims (5)

Hierarchical encoding means that collects bit planes of image information that contributes to the improvement of quantization error to the same extent, divides and encodes into a plurality of hierarchies,
Secret sharing is performed on N (N ≧ 1 integer) different partial data from code data of a certain layer so that the original encoded data can be reproduced from at least k (integer of 1 ≦ k ≦ N). A variable number of partial data creation means that can be synthesized by changing the value of k for each layer so that the upper bit plane can be synthesized from a smaller number of partial data using a sharing method,
Select one of N partial data created in each hierarchy, collect partial data for all hierarchies into one shared information file, and use all N partial data in each hierarchy for N shared information An image shared information generating apparatus comprising: a shared information file creating means for creating a file. Partial data extracting means for extracting partial data of each layer from N image shared information files created by the image shared information generating apparatus according to claim 1;
A number-of-synthesis variable-distribution information synthesis unit that synthesizes the extracted partial data using a secret sharing scheme and reproduces encoded data;
An image dispersion information synthesizing apparatus comprising: hierarchical decoding means for decoding the reproduced encoded data. The image dispersion information generating apparatus according to claim 1,
An image distribution information generating apparatus, further comprising means for adding information indicating which level of encoded data can be combined from how many partial data to an image distribution information file. The number of image dispersion information files used for composition and information added to the image dispersion information file are extracted from N image dispersion information files created by the image dispersion information generation apparatus according to claim 3, Means for identifying whether the encoded data of the hierarchy can be combined;
Partial data extraction means for extracting only the partial data of the layer that can be combined from the N image distribution information files in order from the layer including the upper bit plane;
A number-of-synthesis variable-distribution information synthesis unit that synthesizes the extracted partial data using a secret sharing scheme and reproduces encoded data;
An image dispersion information synthesizing apparatus comprising: hierarchical decoding means for decoding the reproduced encoded data. In the image dispersion information generating device according to claim 1 or 3,
In the synthesizable number variable partial data creating means, the encoded data of the most important layer (the most significant bit plane) is not subjected to distributed processing using the secret sharing scheme, and is simply used for duplication and is used for the remaining layers. On the other hand, an image shared information generating apparatus characterized in that partial data is created by distributed processing using a secret sharing scheme.

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