JP5030141B2 - Structured document image processing apparatus, structured document image encryption processing method, program, and information recording medium - Google Patents

Description

The present invention relates to a technique for performing encryption processing on a structured document image for concealing its contents or making it difficult to read.

  Here, the structured document image targeted by the present invention is “a raster image of a page of a document is synthesized as a background layer (1), n foreground layers (i) and mask layers ( i) pairs (where n is an integer greater than or equal to 1; i = 1, 2,..., n), and one of the foreground layer (i) and the background layer (i) according to the mask layer (i) A method of selecting a value for each pixel or a method of synthesizing the background layer (i + 1) by a method of taking a weighted average of the values of the foreground layer (i) and the background layer (i) for each pixel according to the mask layer (i) , I = 1 to i = n, and the raster image of the page of the document is restored as the finally synthesized background layer (n + 1).

  In the following description, the background layer, foreground layer, and mask layer may be referred to as the background, foreground, and mask, respectively.

  Specific examples of such structured document images include MRC and JPM structured document images described below. In JPM, a layer is called an object, a background is called a base page object, and a foreground is called an image object. Thus, the name of each layer (background, foreground, mask) itself is not important, and it is not important whether it is called a layer or an object. Any structured document image that substantially conforms to the above definition is included in the structured document image of the present invention.

  In general, a document is a mixture of characters / line drawings and images. In recent years, in order to efficiently encode the raster image of such a mixed document page, the raster image of the document page is decomposed into a background and one or more pairs of foregrounds and masks, and each layer is separated separately. An encoding method has been proposed.

  For example, in a technique called an MRC (Mixed Raster Content) model, as schematically illustrated in FIG. 1, a raster image of a document page is converted to a foreground that is character color information, a mask that is character area information, an image The information is decomposed into a background, and the background, foreground, and mask are encoded separately. When restoring a raster image of a document page, the background, foreground, and mask codes are decoded, and then the foreground or background value is selected for each pixel in accordance with the mask to synthesize the restored image. It is also possible to decompose the raster image of the document page into a background and two or more sets of foregrounds and masks, and encode the background, foreground, and mask. Also, the mask may have a foreground transmittance (a foreground / background mixture ratio). The background, mask, and foreground resolution may be arbitrarily selected.

  With regard to this MRC, for example, Japanese Patent Application Laid-Open No. H10-228867 discloses a multi-valued picture image (background) representing a picture part of a raster image of a document page, and a multi-valued picture representing color information of a character / line drawing part of a raster image of a document page. Imports the character color image (foreground), the binary selection data (mask) representing the character / line image shape of the raster image of the document page, and the codes encoded by JPEG, Lempel-Ziv, and MMR, respectively, and decompresses each code Then, an invention of an image processing apparatus is described in which a raster image of a page of a document is synthesized and restored by selecting expanded picture image data or character color image data for each pixel in accordance with the expanded selection data. According to the description of paragraphs (0003) to (0005) of the patent document, the prior invention is mainly intended to prevent deterioration of characters and line drawings at a high compression rate.

  An example of the file structure of the structured document image by MRC is shown in FIG. As shown, an MRC file typically consists of an overall header, a background code and its header, one or more foreground and mask code pairs, and a header for each pair. is there.

  In recent years, with the advent of a new encoding method JPEG2000, a method called JPM (JPEG2000 Multi Layer) has been proposed that enables the use of JPEG2000 as a foreground, mask, and background compression method of the MRC model.

  FIG. 3 is a schematic diagram for explaining the outline of JPM. The raster image Page of each page of the document is decomposed into one or more sets of layout objects (Layout Objects) and a background (Base Page). In the case of JPM, the background (Base Page) is defined as a single color or transparent, and is specified by a parameter. The layout object (Layout Object) includes a foreground (Image) and a mask (Mask). Normal image data is stored in the foreground. The mask represents the opacity of the foreground. A layout object is usually a pair of a mask and a foreground, but can be only one of them. If the layout object consists of only the foreground, the mask is treated as 1 (all overwritten). When the layout object consists only of a mask, the foreground is a specified value. The foreground and mask are usually encoded. In JPM, the background, foreground, and mask layers are called objects, and the foreground is called an image object.

  FIG. 4 is a diagram for explaining an example of page image reproduction of a structured document image by JPM. An arithmetic expression for image composition (reproduction) is shown in the lower part of FIG. Prior to page image reproduction, the encoded foreground and mask are decoded.

  First, Base Page (background) is set to PageImage_0 (background 0), and PageImage_1 (background 1) is synthesized from image_0 (foreground 0) and Mask_0 (mask 0) of the first layout object. That is, the opacity is 1 at the black pixel position of Mask_0, and Image_0 is overwritten on PageImage_0. At the white pixel position of Mask_0, the transparency is 1, and PageImage_0 is displayed. Similarly, PageImage_2 (background 2) is created from PageImage_1 (background 1) and the second layout object Image_1 (foreground 1) and Mask_1 (mask 1). That is, Image_1 is overwritten on PageImage_1 at the black pixel position of Mask_1, and PageImage_1 is displayed at the white pixel position of Mask_1. In this example, PageImage_2 is a reproduced image PageImage that is finally displayed.

  The second expression shown at the bottom of FIG. 4 is an arithmetic expression for combining the background and the foreground. Mm and Im represent the pixel value of the mask and the pixel value of the background in the mth layout object. c represents a component. The mask is a single component. [X, y] represents the coordinates of the pixel, Sm represents the maximum value of Mm (power of 2−1), and n represents the number of layout objects.

The explanation for the second equation will be supplemented. In the example of FIG. 4, since the mask is binary (1 bit per pixel) and Sm = 1,
When the mask value is 1, composite image value = foreground value,
When the mask value is 0, the composite image value = background value. That is, either the foreground value or the background value is selected according to the mask value.

However, the mask can be multi-valued. For example, when each pixel of the mask takes an 8-bit positive value (including 0), Sm = 255, so that the composite image value = (255 −mask value) / 255) × background value + (mask value / 255) × foreground value is a value obtained by taking a weighted average of the foreground value and the background value as a composite image value. In this way, the mask can have foreground transmittance (foreground / background mixture ratio).

  Another example of a structured document by JPM is shown in FIG. In this example, the original image (the same as in the example of FIG. 1) is decomposed into one background and two layout objects, and the foreground and mask of each layout object are tiled at the same dividing boundary and encoded by JPEG2000. ing. In this example, the mask 1 is a single color (“1” at all pixel positions), and represents only the area of the layout object or the area information, and does not have information such as the character shape. Another mask 2 represents the shape (area) of the character.

  FIG. 6 shows the file structure of the structured document image by JPM described above. Since the dotted line portion in the figure is an option, it will be briefly described centering on the solid line portion. “JPEG2000 Signature box” is an entire header indicating that the file belongs to the JPEG2000 family. “File Type box” is an entire header indicating that the file is in JPM format. The “Compound Image Header box” is an entire header including general information on the contents of the file. The “Page Collection box” is a table of contents indicating the order of each page in the case of multi-pages. “Page box” is an overall header indicating the resolution of the page. Here, the page is a canvas for sequentially superimposing (combining) images, and has the same size as the image after the composition is finished. In the case of JPM, layout objects composed of foreground and mask pairs are sequentially drawn on the page. “Layout Object box” is a header for the foreground and the mask indicating the size and position of the foreground and the mask. The “Media Data box” and “Contiguous Codestream box” are portions including foreground and mask codes. In JPM, as can be seen from the example in FIG. 4, the background (BasePage) is handled as an initial page before the layout object is drawn. Further, as described above, there are a synthesis method for selecting one of the foreground and the background according to the mask, and a synthesis method for taking a weighted average of the foreground and the background according to the mask. Each pair of masks (layout object) can be specified in each pair header.

  The MRC and JPM have been described above as specific examples of the structured document image that is the subject of the present invention. The present invention performs processing for concealing the contents of the structured document image or making it difficult to read.

Patent Document 2 discloses an invention for concealing a portion that should restrict the browsing of a document, which is not a structured document image as described above, but an electronic document created by a computer. ing. Specifically, as described in paragraph [0028], FIG. 3, FIG. 4 and the like of Patent Document 2 , the electronic document handled in the prior invention is a text layer including text data and other than text data. Image graphics layers including computer graphics or raster images. And in this prior invention, the concealment process which replaces a text layer with an unreadable image, encrypts it, masks an image layer, or makes it scramble is performed about the area | region to conceal.

Japanese Patent Laid-Open No. 11-177777 JP 2004-289456 A

  With the recent increase in security needs, there is an increasing need to encrypt structured document images targeted by the present invention in order to conceal their contents or make them difficult to read. However, encryption (and its decryption) is difficult because it requires a large amount of processing. In particular, since the structured document image targeted by the present invention has a multi-layer structure, the amount of processing for encryption (and decryption) is extremely large when trying to conceal it by simply encrypting all layers. There is a problem that it gets bigger.

Therefore, an object of the present invention is to provide an apparatus or method , a program, a program for concealing or making a structured document image defined previously difficult by encryption, while suppressing an increase in processing amount for encryption (and decryption) , It is to provide an information recording medium .

  Here, as described above, the structured document image of the present invention includes a “raster image of a document page, a background layer (1) for synthesizing and restoring it, and n foreground layers. (i) and mask layer (i) pairs (where n is an integer greater than or equal to 1; i = 1, 2,..., n), and foreground layer (i) and background according to mask layer (i) The background layer (by selecting one value of the layer (i) for each pixel, or by taking a weighted average of the values of the foreground layer (i) and the background layer (i) for each pixel according to the mask layer (i) The procedure for synthesizing i + 1) is repeated in order from i = 1 to i = n, and the raster image of the document page is restored as the finally synthesized background layer (n + 1) ”. However, the name of each layer (background, foreground, mask) itself is not important, and it is not important to call it a layer or an object. If it is a structured document image that substantially conforms to the above definition, As described above, it is included in the structured document image of the present invention.

The invention according to claim 1 is a structured document image processing apparatus for encrypting a structured document image composed of a background layer and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers, for layer group of the structured document image, and means for setting a code amount of the background layer to a predetermined value, the layer group of the structured document image, means for obtaining the code amount of each layer, the background layer code Means for comparing the obtained code amount of each layer with the set predetermined value, selecting a layer with a large code amount as a layer to be encrypted, and encrypting the selected layer, And means for replacing the code of the layer in the structured document image with the code after encryption.

The invention according to claim 2 is a structured document image processing apparatus for encrypting a structured document image comprising a background layer and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers, Means for acquiring a resolution of a background layer from the layer group of the structured document image; means for setting the resolution of the background layer to a predetermined value when the resolution of the background layer cannot be acquired; For a group of document images, a means for calculating the resolution of the foreground layer or mask layer using the resolution of the background layer, and encrypting a high resolution layer based on the calculated resolution of the foreground layer or mask layer Means for selecting as a layer to be encrypted, and means for encrypting the selected layer and replacing the code of the layer in the structured document image with the code after encryption Characterized in that it has a.

According to a third aspect of the invention, the structured document image processing apparatus according to claim 2, wherein the means for selecting, including the background layer resolution with the resolution of the foreground layer or mask layer that the calculated, high-resolution It is characterized by selecting a layer.

The invention according to claim 4 is a structured document image processing apparatus for encrypting a structured document image comprising a background layer and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers, Means for acquiring a resolution of a background layer from the layer group of the structured document image; means for setting the resolution of the background layer to a predetermined value when the resolution of the background layer cannot be acquired; Means for detecting a mask layer from a layer group of document images; means for calculating the resolution of the detected mask layer using the resolution of the background layer; and the resolution of the calculated mask layer is a predetermined value or more. Means for selecting a mask layer as an encryption target layer, encrypting the selected mask layer, and encrypting the code of the mask layer in the structured document image And having a means for replacing at issue.

The invention according to claim 5 is a structured document image processing apparatus for encrypting a structured document image comprising a background layer and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers, With respect to the layer group of the structured document image, a means for detecting the number of colors of each layer and whether the detected number of colors of each layer is 1 or plural are determined, and the layer having a plurality of colors is encrypted. Means for selecting as a layer to be encrypted, and means for encrypting the selected layer and replacing the code of the layer in the structured document image with the code after encryption.

The invention according to claim 6 is a storage unit that stores a structured document image including a background layer, n sets (n is an integer of 1 or more) of foreground layers and / or mask layers, and is stored in the storage unit. In a structured document image processing apparatus comprising a processing unit for encrypting a structured document image , a step of setting a code amount of a background layer to a predetermined value for a layer group of the structured document image, the processing unit includes: A step of acquiring the code amount of each layer for the layer group of the structured document image, comparing the acquired code amount of each layer with the code amount of the background layer as the set predetermined value , Selecting a layer having a large amount as an encryption target layer, encrypting the selected layer, and replacing the code of the layer in the structured document image with the code after encryption It is a structured document image encryption processing method, characterized by executing.

The invention according to claim 7 is a storage unit that stores a structured document image including a background layer, and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers, and is stored in the storage unit A structured document image processing apparatus comprising: a processing unit that encrypts a structured document image; wherein the processing unit obtains a resolution of a background layer from a layer group of the structured document image; The step of setting the resolution of the background layer to a predetermined value when the resolution cannot be obtained, and calculating the resolution of the foreground layer or the mask layer for the group of layers of the structured document image using the resolution of the background layer Selecting a high-resolution layer as an encryption target layer based on the calculated foreground layer or mask layer resolution, Encrypt-option and Layer, a structured document image encryption processing method the sign of the layers in the structured document image and executes a step of replacing the sign of the encrypted.

The invention according to claim 8 is a storage unit that stores a structured document image including a background layer, and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers, and is stored in the storage unit. A structured document image processing apparatus comprising: a processing unit that encrypts a structured document image; wherein the processing unit obtains a resolution of a background layer from a layer group of the structured document image; If the resolution cannot be obtained, setting the resolution of the background layer to a predetermined value; detecting the mask layer from the group of layers of the structured document image; and determining the resolution of the detected mask layer as the background layer The step of calculating using the resolution of the mask layer, and the step of selecting the mask layer whose resolution of the calculated mask layer is equal to or greater than a predetermined value as the layer to be encrypted. Flop, encrypting the selected mask layer, a structured document image encryption processing method the sign of the mask layer in the structured document image and executes a step of replacing the sign of the encrypted.

The invention according to claim 9 is a storage unit that stores a structured document image including a background layer, n sets (n is an integer of 1 or more) foreground layer and / or mask layer, and is stored in the storage unit. In the structured document image processing apparatus including a processing unit that encrypts a structured document image, the processing unit detects the number of colors of each layer for the layer group of the structured document image, the detected Determining whether the number of colors of each layer is 1 or more, selecting a layer having a plurality of colors as a layer to be encrypted, encrypting the selected layer, and The structured document image encryption processing method is characterized by executing a step of replacing the code of the layer with the code after encryption.

According to a tenth aspect of the present invention, there is provided a program for causing a computer to function as each unit of the structured document image processing apparatus according to any one of the first to fifth aspects.

An information recording medium according to an eleventh aspect of the present invention is a computer-readable recording medium storing a program that causes the computer to function as each means of the structured document image processing apparatus according to any one of the first to fifth aspects. Information recording medium.

According to the present invention, by encrypting only a part of the layer of the structured document image, an increase in the processing amount for encryption (and decryption) is suppressed, and the structured document image is effectively concealed or It can be difficult to read.

  FIG. 7 is a block diagram for explaining an embodiment of the structured document image processing apparatus of the present invention.

  The structured document image processing apparatus of the present invention includes an input unit 100 for inputting a structured document image to be processed from a local storage device or a network device, and concealing or interpreting the input structured document image. A processing unit 101 that performs difficult processing, and an output unit 104 that outputs a structured document image processed by the processing unit 101 to a local storage device or a device on a network. The processing unit 101 selects an encryption target selection that selects a part of layers to be encrypted from a group of layers (background, one or more foreground and mask pairs) constituting the input structured document image. Means 102 and encryption means 103 for performing encryption of the layer selected as the encryption target by the encryption target selection means 102.

Such a structured document image processing apparatus is realized on a general computer in which a CPU 201, a main memory 202, a hard disk device 203 and the like as shown in FIG. A program for that purpose, that is, a program that causes the computer to function as the input unit 100, the processing unit 101, and the output unit 104 shown in FIG. 7 is loaded from the hard disk device 203 to the main computer 202 and executed by the CPU 201. Such a program and a computer-readable information recording (storage) medium such as a magnetic disk, an optical disk, a magneto-optical disk, and a semiconductor storage element on which the program is recorded are also included in the present invention .

The flow of processing when the structured document image processing apparatus of the present invention is realized on a computer as shown in FIG. 8 is as follows.
(1) A structured document image stored in the hard disk device 203 is read into the main memory 202 by an instruction (from a program) from the CPU 201.
(2) The CPU 201 (program) selects a layer to be encrypted of the structured document image on the main memory 202 and executes a process of encrypting the selected layer.
(3) A structured document image after processing on the main memory 202 is written out to the hard disk device 203 by an instruction from the CPU 201 (program).

  Although any encryption method can be basically used for encryption, in this embodiment, the same encryption key is secretly shared between the encryption side and the decryption side, and each block having an appropriate length is shared. It is assumed that a common key encryption method that performs encryption with the same key is used. This encryption method is a known method such as DES (Data Encryption Standard) or AES (Advanced Encryption Standard).

  There are two basic operations of DES: (1) dividing data into 64-bit blocks, and (2) encrypting each block with a 56-bit key. There are four modes, ECB, CB, CFB, and OFB.

  ECB (Electronic Code Block) is a mode that can be said to be a basic type of DES, and the basic operation described above is performed as it is. That is, after the data is divided into blocks, each block is encrypted with a secret key, and the encrypted blocks are connected in the original order.

  CBC (Cipher Block Chaining) takes an XOR (exclusive OR) of an encrypted previous block and an unencrypted current block and encrypts it with a secret key. As the term “Chaining” is used, the encryption of each block proceeds in a chain.

  CFB (Cipher Feedback) is a mode in which a part (m bits) of the encryption result of the previous block is fed back as a value that XORs with the m bits of the next block.

  OFB (Output Feedback) generates a ciphertext using a certain initial value as the first block, uses that ciphertext (part) as input for the next ciphertext, and simultaneously uses part (m bits) as a random number. In this mode, the corresponding m-bit data is XORed. By appropriately selecting m bits, it is possible to realize encryption for each arbitrary bit length.

  Next, some examples of the structured document image processing apparatus according to this embodiment will be described. In each embodiment, the structured document image to be processed is input as a JPM file having a configuration as shown in FIG.

  Here, the description of the Box information in the JPM file will be supplemented to the extent necessary for understanding each embodiment.

  The number of pages in the file (= number of page boxes) can be known from the Compound Image Header box.

  The Page box of each page includes a Page Header box, a Resoltion box, and a Base Color box. The number of layout objects in the page (= number of foreground / mask pairs = number of masks) can be known from the Page Header box. The bit depth of the page background can be found from the Base Color box. The resolution of the page background can be found from the Page Resolution box. However, the Page Resolution box is an optional box. If this box does not exist, it is assumed that the background resolution = 1 in this embodiment.

  The Layout Object box of each layout object includes a Layout Object Header box and an Object box, and the Object box includes an Object Header box, a Base Color box, and an Object Scale box. The layout object ID number (layout order of layout objects) can be known from the Layout Object Header box. Whether an object (layer) in the layout object is a foreground or a mask can be known from the Object Header box. The code length (= code amount) of each object (foreground or mask) in the layout object can be known from the Object Header box. The bit depth of each object (foreground or mask) can be known from the Base Color box. Note that although the bit depth for each component is described in the Base Color box, in the present embodiment, it is assumed that the bit depth of all components is the same.

The ratio of the resolution of each object (foreground or mask) to the background can be known from the Object Scale box. More specifically, the Object Scale box describes values (HRN, HRD) indicating the horizontal resolution magnification with respect to the background and values (VRN, VRD) indicating the vertical resolution magnification with respect to the background. (HRN / HRD) is the horizontal resolution magnification with respect to the background, and (VRN / VRD) is the vertical resolution magnification with respect to the background. In this embodiment, a magnification in a large direction is adopted,
Object resolution = max (VRD / VRD, HRN / HRD) × background resolution Formula (1)
The resolution of the object is calculated by However, when there is no Resolution box as described above, the background resolution is set to 1 for convenience.

  When the code amount of an object (foreground or mask) in the layout object changes due to encryption, it is necessary to correct the LEN field in the Object Header box. However, in this embodiment, since the code amount before encoding is aligned to 8 bytes by padding and DES is used as an encryption method, it is not necessary to modify the LEN field accompanying encryption. .

  A processing flow in this embodiment is shown in FIG. In this embodiment, it is assumed that the number of pages = 1 and the number of layout objects = 1.

  First, a JPM file is input by the input unit 100 (step 1).

  The processing unit 101 detects the page box of the input JPM file (step 2).

  Next, the processing unit 101 detects the resolution box and acquires the background resolution (step 3). However, as described above, when the Resolution box cannot be detected, the background resolution is set to 1.

Next, the processing unit 101 detects the layout object box (step 4), detects the first object box (step 5), detects the object header box, and detects the entity of the code of the object (foreground or mask). The position and code amount are acquired (step 6). Next, an Object Scale box in the Object box is detected, and the value of the VRN, VRD, HRN, and HRD described in the Object box and the background resolution acquired in Step 3 are used to calculate the object scale box according to the equation (1). The resolution is calculated (step 7).
The processing unit 101 detects the next object box (step 8), detects the object header box, and acquires the position and code amount of the code entity of the object (foreground or mask) (step 9). Next, an Object Scale box in the Object box is detected, and the value of the VRN, VRD, HRN, and HRD described in the Object box and the background resolution acquired in Step 3 are used to calculate the object scale box according to the equation (1). The resolution is calculated (step 10).

The processing unit 101 uses the encryption target selection unit 102 to compare the resolutions of the two objects (foreground and mask) calculated in step 7 and step 10, and sets the object with the higher resolution as the object (layer) to be encrypted. Select (step 11). In JPM, the background is defined as a single color or transparent, and is designated as a parameter and does not have a code itself. The processing unit 101 reads the code of the selected object, encrypts the code with the DES by the encryption unit 103, and performs a process of replacing the original code of the object with the code after the encryption (step 12).

  The processed JPM file is output by the output unit 104 (step 13), and the series of processing ends.

Thus, in the present embodiment, an object (layer) having a high resolution is preferentially selected as an encryption target in the foreground and the mask. In general, it can be said that the higher the resolution of a layer, the greater the amount of information in that layer. Therefore, it is estimated that the higher the resolution, the greater the concealment effect obtained by encryption. Therefore, the structured document image can be effectively concealed or difficult to read by preferentially selecting and encrypting a layer with high resolution.

(Modification of Example 1)
When there are a plurality of layout objects, it is possible to compare the resolution of the foreground and the mask for each layout object, and select the object with the higher resolution (foreground or mask) as an encryption target. Are also included in this embodiment .

  A processing flow in this embodiment is shown in FIG. In this embodiment, a JPM file with the number of pages = 1 and the number of layout objects = 1 is assumed.

  First, a JPM file is input by the input unit 100 (step 21).

  The processing unit 101 sets the background code amount = 0 (step 22). In the case of JPM, the background is defined as a single color or transparent, and is designated by a parameter, so the code amount is set to 0 for convenience.

  The processing unit 101 detects the page box of the input JPM file (step 23), detects the layout object box (step 24), detects the first object box (step 25), and detects the object header box. It detects and acquires the position and code amount of the code of the object (foreground or mask) (step 26).

  The processing unit 101 detects the next Object box (step 27), detects the Object Header box, and acquires the position and code amount of the code entity of the object (foreground or mask) (step 28).

  The processing unit 101 compares the code amounts of the three objects (background, foreground, and mask) acquired in step 22, step 26, and step 29 by the encryption target selection unit 102, and the object having the largest code amount (background code amount). = 0, foreground or mask) is selected as an object (layer) to be encrypted (step 30). The processing unit 101 reads the code of the selected object, encrypts the code with the DES by the encryption unit 103, and performs a process of replacing the original code of the object with the code after the encryption (step 12). The processed JPM file is output by the output unit 104 (step 13), and the series of processing ends.

In this embodiment, an object (layer) having a large code amount is preferentially selected as an encryption target. In general, even if the layers have the same resolution and bit depth, a large amount of code means that the amount of information is large. Therefore, it is estimated that the layer with a large amount of code has a greater concealment effect due to encryption. Is done. Therefore, the structured document image can be effectively concealed or difficult to read by preferentially selecting and encrypting a layer having a large code amount.

(Modification of Example 2)
In the case of JPM, since the background is monochromatic or transparent and the code itself does not exist, step 22 is omitted, and in step 29 the code amount is compared between the foreground and the mask to select the encryption target. Good.

On the other hand, in the MRC file described with reference to FIGS. 1 and 2, the background is often an image such as a photograph. Therefore, when handling an MRC file, it is preferable to obtain the amount of code of the background, compare the amount of code between the background, foreground, and mask layers, and select the layer with the largest code amount as the encryption target. . Such an embodiment is also included in the present embodiment .

  A processing flow in this embodiment is shown in FIG. Note that a JPM file with the number of pages = 1 and the number of layout objects = 1 is assumed.

  First, a JPM file is input by the input unit 100 (step 41).

  The processing unit 101 detects the page box of the input JPM file (step 42), and detects the layout object box (step 43). The first Object box is detected (step 44), the Object Header box is detected, and the position and code length of the code body of the object (foreground or mask) are acquired (step 45). Next, the Base Color box in the Object box is detected, and the bit depth of the object described therein is acquired (step 46).

  The processing unit 101 detects the next object box (step 47), detects the object header box, and acquires the position and code amount of the code entity of the object (foreground or mask) (step 48). Next, the Base Color box in the Object box is detected, and the bit depth of the object described therein is acquired (step 49).

  The processing unit 101 uses the encryption target selection unit 102 to check whether the two objects (foreground and mask) obtained in step 46 and step 49 have a bit depth of 1 bit, and encrypt the object having a bit depth of 1 bit. As an object (layer) to be converted, it is selected (step 50). An object having a bit depth of 1 bit, that is, a binary object is highly likely to represent the shape of a character, and it is estimated that the concealment effect by encryption is also high. In JPM, the background is defined as a single color or transparent, and is designated as a parameter and does not have a code itself.

  The processing unit 101 reads the code of the selected object, encrypts this code with the DES by the encryption unit 103, and performs a process of replacing the original code of the object with the code after the encryption (step 51). The processed JPM file is output by the output unit 104 (step 52), and the series of processing ends.

As described above, in this embodiment, an object (layer) having a bit depth of 1 bit is preferentially selected as an encryption target . That the bit depth of a layer is 1 bit means that the layer is expressed in binary, and it is highly likely that the layer represents a character image or a character shape. Such a layer generally has a high concealment effect by encryption. Therefore, the structured document image can be effectively concealed or difficult to read by preferentially selecting and encrypting a layer having a bit depth of 1 bit.

(Modification of Example 3)
The background of the MRC described with reference to FIGS. 1 and 2 is not limited as the background of the JPM. Accordingly, when handling an MRC file, the bit depth of the background is also obtained, and if it is 1 bit, it can be selected as an encryption target. Such an embodiment is also included in the present embodiment .

  A processing flow in this embodiment is shown in FIG. In this embodiment, a JPM file is assumed in which the number of pages is 1 or 2 or more and the number of layout objects is 2 or more.

  First, a JPM file is input by the input unit 100 (step 61).

  The processing unit 101 detects the Compound Image Header box of the input JPM file and acquires the number of pages described in the NP field (step 62).

  The processing unit 101 detects the page box of the first page (step 63), detects the page header box, and acquires the number of layout objects (= number of masks) described in the NLobj field (step 64). Next, the resolution box is detected and the background resolution is acquired (step 65). As described above, when the Resolution box cannot be detected, the background resolution = 1.

  Next, the processing unit 101 detects the layout object box (step 66), detects the first object box (step 67), detects the object header box, and determines the type of the object from the description of the ObjType field. (Foreground or mask) is identified (step 68). When it is determined that the object is not a mask, that is, a foreground (step 69, No), the process returns to step 67 to detect the next Object box.

  When it is determined in step 69 that the object is a mask (step 69, Yes), the position and code length of the code of the mask are acquired from the Objdect Header box (step 70). Next, an Object Scale box in the Object box is detected, and the value of the VRN, VRD, HRN, and HRD described in the Object box and the background resolution acquired in Step 65 are used to calculate the mask size of the mask according to the equation (1). The resolution is calculated (step 71).

  Next, the encryption target selection unit 102 of the processing unit 101 compares the resolution of the mask calculated in step 71 with a predetermined value (for example, 200 dpi) (step 72). If the mask resolution is equal to or higher than the predetermined value, the mask is encrypted. Is selected as a target to be converted (step 73). When the mask is selected as an encryption target by the encryption target selection unit 102, the processing unit 101 reads the code of the mask, encrypts it with DES by the encryption unit 103, and uses the code after the encryption to mask the mask. The process of replacing the original code of (step 74) is performed.

  The processing unit 101 compares the number of layout objects in the page (= number of masks) acquired in step 64 with the number of layout objects already processed in the page, and checks whether all masks in the page have been detected. (Step 75). If an undetected mask remains in the page (step 75, No), the process returns to step 66 to detect the layout object box of the next layout object.

  If it is determined that all the masks in the page have been detected (step 75, Yes), the processing unit 101 compares the number of pages processed so far with the number of pages in the file acquired in step 62, and determines all pages. It is checked whether the process of (1) has been completed (step 76). If an unprocessed page remains (step 76, No), the process returns to step 63 to detect the page box of the next page.

  If the processing unit 101 determines that all pages have been processed (step 76, Yes), the processed JPM file is output by the output unit 104 (step 77), and the series of processing ends.

As described above, in this embodiment, an object (layer) selected as an encryption target is limited to a mask, and a mask having a resolution higher than a predetermined resolution is selected as an encryption target . Since the mask layer often represents the shape of a character, a high concealment effect can be expected by the encryption. Therefore, the structured document image can be effectively concealed or difficult to read by preferentially selecting and encrypting the mask layer.

  A processing flow in this embodiment is shown in FIG. In this embodiment, a JPM file is assumed in which the number of pages is 1 or 2 or more and the number of layout objects (= number of masks) is 1 or 2 or more.

  First, a JPM file is input by the input unit 100 (step 81).

  The processing unit 101 detects the Compound Image Header box of the input JPM file and acquires the number of pages described in the NP field (step 82).

The processing unit 101 detects the page box of the first page (step 83), detects the page header box, and acquires the number of layout objects (= number of masks) described in the NLobj field (step 84). Next, the processing unit 101 detects the layout object box (step 85), detects the first object box (step 86), detects the object header box, and determines the object from the description of the ObjType field. The type (foreground or mask) is identified (step 87). Then, the encryption target selection unit 102 determines whether the type of the identified object is a mask (step 88), and if it is a mask, the object is selected as an encryption target (step 89).

  When the object to be encrypted is not selected by the encryption target selection unit 102, that is, when the object is the foreground (step 88, No), the processing unit 101 returns to step 86 and detects the next Object box.

  When the object is selected as an object to be encrypted, the processing unit 101 obtains the position and code length of the object, that is, the code of the mask, from the Objdect Header box, reads the code of the mask, and encrypts it by the encryption unit 103. A process of encrypting with DES and replacing the original code of the mask with the encrypted code is performed (step 90).

  The processing unit 101 compares the number of layout objects in the page (= number of masks) acquired in step 84 with the number of layout objects already processed in the page, and checks whether all masks in the page have been detected. (Step 91). If an undetected mask remains in the page (step 91, No), the process returns to step 85 to detect the layout object box of the next layout object.

  If it is determined that all the masks in the page have been detected (step 91, Yes), the processing unit 101 compares the number of pages processed so far with the number of pages in the file acquired in step 82, and determines all pages. It is checked whether the process of (1) has been completed (step 92). If an unprocessed page remains (step 92, No), the process returns to step 83 to detect the Page box of the next page.

  If the processing unit 101 determines that all pages have been processed (step 92, Yes), the processed JPM file is output by the output unit 104 (step 93), and the series of processing ends.

As described above, in the present embodiment, only the mask is selected as an encryption target as in the fourth embodiment .

(Modification of Example 5)
In JPM, the background is defined as a single color or transparent, and is specified as a parameter, and is excluded from the encryption target because there is no code itself. However, in the MRC described with reference to FIGS. 1 and 2, there is no such restriction on the background, and usually an image is stored in the background, while the foreground often represents a character color or the like.

Therefore, when handling an MRC file, the encryption target selection unit 102 is allowed to select an encryption target when the type of the layer is mask or background, that is, to select a layer other than the foreground as the encryption target. Is also possible. Such a mode is also included in this embodiment because the mask is given priority over the foreground.

  The processing flow in the present embodiment is shown in FIG. In the present embodiment, a JPM file having one page and one or more layout objects is assumed.

  First, a JPM file is input by the input unit 100 (step 101).

  The processing unit 101 detects the page box of the first page (step 102), detects the page header box, and acquires the number of layout objects described in the NLobj field (step 103). Next, the processing unit 101 detects the layout object box (step 104), detects the object box of the first object (step 105), detects the object header box, and detects the object (foreground or mask). The position and code length of the code entity are acquired (step 106), the code of the object is read and decoded, and the number of colors is detected (step 107). The processing unit 101 determines in the encryption target selection unit 102 whether the number of colors detected in step 107 is 1 or plural (step 108). If the number of colors is 2 or more (not a single color), the processing unit 101 The object is selected as an encryption target (step 109). That is, the monochrome mask and foreground are excluded from the encryption target. For example, the monochrome mask 1 in FIG. 5 is excluded from the encryption target. In JPM, since the background is a single color and there is no code itself, it is excluded from the encryption target from the beginning.

  When the object is selected as an object to be encrypted, the processing unit 101 encrypts the code of the object with DES by the encryption unit 103, and performs a process of replacing the code of the object with the code after the encryption (step 110). ). If there is an unprocessed object remaining in the layout object (step 111, No), the processing unit 101 returns to step 105 and detects the next object box. If all the objects of the layout object have been processed (step 111, Yes), it is determined whether all layout objects have been processed by comparing the number of layout objects acquired in step 103 with the number of layout objects already processed (step 111). step 112). If an unprocessed layout object remains (step 112, No), the process returns to step 104 to detect the layout object box of the next layout object.

  If it is determined that the processing of all object layouts has been completed by the processing unit 101 (step 112, Yes), the processed JPM file is output by the output unit 104 (step 113), and the series of processing ends.

As described above, in this embodiment, a monochrome object (layer) is excluded from the encryption target. For example, the mask 1 shown in FIG. 5 is a single color and does not have information such as the shape of characters, so the amount of information is extremely small. In addition, since the monochrome foreground layer and the background layer do not include textures (pictures), the amount of information is extremely small. Such a layer with a small amount of information has a low concealment effect by encryption. Therefore, for example, if the same number of layers are encrypted, the structured document image can be effectively concealed or difficult to read by excluding the monochrome layer from the encryption target.

  A processing flow in this embodiment is shown in FIG. In this embodiment, it is assumed that the number of pages is 1 and the layout object is a plurality of JPM files.

  First, a JPM file is input by the input unit 100 (step 121).

  The processing unit 101 detects the page box of the first page of the input JPM file (step 122), detects the resolution box, and acquires the background resolution (step 123). As described above, when the Resolution box cannot be detected, the background resolution = 1. Next, the Page Header box is detected, and the number of layout objects described in the NLobj field is acquired (step 124).

  Next, the processing unit 101 detects the layout object box (step 126), detects the first object box (step 126), detects the object header box, and detects the position and code of the object code. The length is acquired (step 127). Next, an Object Scale box in the Object box is detected, and the value of the VRN, VRD, HRN, and HRD described in the Object box and the background resolution acquired in Step 123 are used to calculate the object scale box by the equation (1). The resolution is calculated (step 128).

  The processing unit 101 checks whether all the objects in the layout object have been processed (step 129). If there is an unprocessed object, the processing unit 101 returns to step 126 and detects the object box of the next object.

If all the objects of the layout object have been processed (step 129, Yes), the processing unit 101 compares the number of layout objects acquired in step 124 with the number of layout objects already processed, and has processed all the layout objects? Determination is made (step 130). If an unprocessed layout object remains (step 130, No), the process returns to step 125 and the layout object of the next layout object.
Perform box detection.

  If it is determined that all layout objects have been processed (step 130, Yes), the encryption target selection unit 102 of the processing unit 101 ranks all layout object objects (foreground, mask) in descending order of resolution, A predetermined upper number of objects (for example, objects up to the top three) are selected as encryption targets (step 131). It should be noted that the background of JPM does not have a code itself and is excluded from the encryption target from the beginning.

  The processing unit 101 reads the code of the object (foreground or mask) selected as the encryption target by the encryption target selection unit 102, encrypts it with the DES by the encryption unit 103, and uses the encrypted code for the object. A process for replacing the original code is performed (step 132). Then, the processed JPM file is output by the output unit 104 (step 133), and the series of processing ends.

As described above, in this embodiment, similarly to the first embodiment, an object (mask or foreground) having a high resolution is preferentially selected as an encryption target.

(Modification of Example 7)
In the MRC described with reference to FIGS. 1 and 2, there is no restriction on the background as in JPM. Therefore, when processing the MRC file, the encryption target selection unit 102 may rank the layers including the background in descending order of resolution, and may select, for example, the top three layers as encryption targets. Is possible.

  A processing flow in this embodiment is shown in FIG. In this embodiment, a JPM file having a plurality of pages is assumed.

  First, a JPM file is input by the input unit 100 (step 141).

  The processing unit 101 detects the Compound Image Header box of the input JPM file and acquires the number of pages described in the NP field (step 142).

  The processing unit 101 detects the page box of the first page (step 143), detects the resolution box, and acquires the background resolution (step 144). As described above, when the Resolution box cannot be detected, the background resolution = 1. Next, the Page Header box is detected, and the number of layout objects described in the NLobj field is acquired (step 145).

  Next, the processing unit 101 detects the layout object box (step 146), detects the first object box (step 147), detects the object header box, and detects the position and code of the object code. The length is acquired (step 148). Next, an Object Scale box in the Object box is detected, and the value of the VRN, VRD, HRN, and HRD described in the Object box and the background resolution acquired in Step 144 are used to calculate the object scale box according to the equation (1). The resolution is calculated (step 149).

  The processing unit 101 checks whether all the objects of the layout object have been processed (step 150). If there are any unprocessed objects, the processing unit 101 returns to step 147 to detect the object box of the next object.

If all the objects of the layout object have been processed (step 150, Yes), the processing unit 101 compares the number of layout objects acquired in step 145 with the number of already processed layout objects, and has processed all the layout objects? Determination is made (step 151). If an unprocessed layout object remains (step 151, No), the process returns to step 146 to return to the layout object of the next layout object.
Perform box detection.

  If the processing unit 101 determines that all layout objects on the page have been processed (step 151, Yes), the processing unit 101 compares the number of pages processed so far with the number of pages in the file acquired in step 142, It is determined whether the page has been processed (step 152). If an unprocessed page remains (step 152, No), the process returns to step 143 to detect the page box of the next page.

  If all pages are processed (step 152, Yes), the encryption target selection unit 102 of the processing unit 101 ranks all objects (foreground, mask) of all layout objects on all pages in descending order of resolution. Are selected as objects to be encrypted (step 153). Note that the background of JPM is excluded from the encryption target from the beginning because there is no code itself.

  The processing unit 101 reads the code of the object (foreground or background) selected as the encryption target by the encryption target selection unit 102, encrypts the code using the DES by the encryption unit 103, and uses the code after the encryption to encrypt the object. Processing to replace the original code is performed (step 154). Then, the processed JPM file is output by the output unit 104 (step 155), and the series of processing ends.

As described above, in this embodiment, as in the first embodiment, an object with high resolution is preferentially selected as an encryption target.

Although the embodiment of the structured document image processing apparatus according to the present invention has been described above, it is obvious that the description is also the description of the embodiment of the structured document image encryption processing method according to the present invention . That is, the flowcharts of FIGS. 9 to 16 are also flowcharts for explaining an embodiment of the structured document image encryption processing method. Each process of the structured document image encryption processing method according to the present invention can be executed by a program using a computer as shown in FIG. The flowcharts of FIGS. 9 to 16 also show an embodiment of the program according to the present invention or the program recorded on the information recording medium .

It is a schematic diagram for description of the structured document image of MRC. It is a figure which shows the structural example of a MRC file. It is a schematic diagram for description of a structured document image of JPM. It is a schematic diagram for description of image reproduction in JPM. It is a schematic diagram which shows the example of the structured document image of JPM. It is a figure which shows the structural example of a JPM file. It is a block diagram for demonstrating embodiment of this invention. It is a block diagram for demonstrating the structure of a computer. 3 is a flowchart illustrating a processing flow in the first embodiment. 10 is a flowchart illustrating a processing flow in the second embodiment. 10 is a flowchart illustrating a processing flow in Embodiment 3. 10 is a flowchart illustrating a processing flow in Embodiment 4. 10 is a flowchart illustrating a processing flow in Embodiment 5. 10 is a flowchart showing a processing flow in Embodiment 6. 14 is a flowchart illustrating a processing flow in Embodiment 7. 10 is a flowchart illustrating a processing flow according to an eighth embodiment.

DESCRIPTION OF SYMBOLS 100 Input part 101 Processing part 102 Encryption object selection means 103 Encryption means 104 Output part

Claims (11)

A structured document image processing apparatus that encrypts a structured document image including a background layer, and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers,
Means for setting a code amount of a background layer to a predetermined value for the layer group of the structured document image;
Means for acquiring a code amount of each layer for the layer group of the structured document image;
Means for comparing the obtained code amount of each layer with the code amount of the background layer as the set predetermined value, and selecting a layer with a large code amount as a layer to be encrypted;
Means for encrypting the selected layer and replacing the code of the layer in the structured document image with the code after encryption;
A structured document image processing apparatus comprising: A structured document image processing apparatus that encrypts a structured document image including a background layer, and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers,
Means for obtaining a resolution of a background layer from the layer group of the structured document image;
Means for setting the resolution of the background layer to a predetermined value when the resolution of the background layer could not be obtained;
Means for calculating the resolution of the foreground layer or the mask layer for the layer group of the structured document image using the resolution of the background layer;
Means for selecting a high resolution layer as an encryption target layer based on the calculated foreground layer or mask layer resolution;
Means for encrypting the selected layer and replacing the code of the layer in the structured document image with the code after encryption;
A structured document image processing apparatus comprising: 3. The structured document image processing apparatus according to claim 2, wherein the selecting means selects a layer having a high resolution including a resolution of the background layer as well as the calculated resolution of the foreground layer or the mask layer. A structured document image processing apparatus that encrypts a structured document image including a background layer, and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers,
Means for obtaining a resolution of a background layer from the layer group of the structured document image;
Means for setting the resolution of the background layer to a predetermined value when the resolution of the background layer could not be obtained;
Means for detecting a mask layer from a layer group of the structured document image;
Means for calculating the resolution of the detected mask layer using the resolution of the background layer;
Means for selecting a mask layer having a resolution of the calculated mask layer equal to or higher than a predetermined value as a layer to be encrypted;
Means for encrypting the selected mask layer and replacing the code of the mask layer in the structured document image with a code after encryption;
A structured document image processing apparatus comprising: A structured document image processing apparatus that encrypts a structured document image including a background layer, and n sets (n is an integer of 1 or more) of foreground layers and / or mask layers,
Means for detecting the number of colors of each layer for the layer group of the structured document image;
Means for determining whether the number of colors of each detected layer is 1 or plural, and selecting a layer having a plurality of colors as a layer to be encrypted;
Means for encrypting the selected layer and replacing the code of the layer in the structured document image with the code after encryption;
A structured document image processing apparatus comprising: A storage unit for storing a structured document image including a background layer, n sets (n is an integer of 1 or more) foreground layer and / or mask layer, and a structured document image stored in the storage unit is encrypted. In a structured document image processing apparatus comprising a processing unit,
The processor is
For a layer group of the structured document image, setting a code amount of a background layer to a predetermined value;
Obtaining a code amount of each layer for the layer group of the structured document image;
A step of comparing a code amount of each acquired layer with a code amount of a background layer as the set predetermined value and selecting a layer with a large code amount as a layer to be encrypted;
Encrypting the selected layer and replacing the code of the layer in the structured document image with the encrypted code;
A structured document image encryption processing method characterized by executing: A storage unit for storing a structured document image including a background layer, n sets (n is an integer of 1 or more) foreground layer and / or mask layer, and a structured document image stored in the storage unit is encrypted. In a structured document image processing apparatus comprising a processing unit,
The processor is
Obtaining a resolution of a background layer from the layer group of the structured document image;
When the resolution of the background layer cannot be obtained, setting the resolution of the background layer to a predetermined value;
Calculating a resolution of a foreground layer or a mask layer for the layer group of the structured document image using a resolution of the background layer;
Selecting a high resolution layer as an encryption target layer based on the calculated foreground layer or mask layer resolution;
Encrypting the selected layer and replacing the code of the layer in the structured document image with the encrypted code;
A structured document image encryption processing method characterized by executing: A storage unit for storing a structured document image including a background layer, n sets (n is an integer of 1 or more) foreground layer and / or mask layer, and a structured document image stored in the storage unit is encrypted. In a structured document image processing apparatus comprising a processing unit,
The processor is
Obtaining a resolution of a background layer from the layer group of the structured document image;
When the resolution of the background layer cannot be obtained, setting the resolution of the background layer to a predetermined value;
Detecting a mask layer from a layer group of the structured document image;
Calculating the resolution of the detected mask layer using the resolution of the background layer;
Selecting a mask layer whose resolution of the calculated mask layer is a predetermined value or more as a layer to be encrypted;
Encrypting the selected mask layer and replacing the code of the mask layer in the structured document image with the code after encryption;
A structured document image encryption processing method characterized by executing: A storage unit for storing a structured document image including a background layer, n sets (n is an integer of 1 or more) foreground layer and / or mask layer, and a structured document image stored in the storage unit is encrypted. In a structured document image processing apparatus comprising a processing unit,
The processor is
Detecting the number of colors of each layer for the layer group of the structured document image;
Determining whether the number of colors of each detected layer is 1 or plural, and selecting a layer having a plurality of colors as a layer to be encrypted;
Encrypting the selected layer and replacing the code of the layer in the structured document image with the encrypted code;
A structured document image encryption processing method characterized by executing: A program that causes a computer to function as each unit of the structured document image processing apparatus according to claim 1. 6. A computer-readable information recording medium in which a program for causing a computer to function as each unit of the structured document image processing apparatus according to claim 1 is recorded.

Images