JP2011211411A - Encoding device, encoding method, and encoding program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve probability to decode correct information from an image.SOLUTION: An encoding device divides image data into a plurality of blocks, and extracts a coincidence pair block being the pair block coinciding with prescribed determination reference among the pair blocks being the pairs of two adjacent blocks in the divided image data. The encoding device corrects small image data which are data forming a part of the image formed by the divided image data and forming an image different from an image forming a background, and extracts the coincidence pair block from the image data after the correction of the small image data. The encoding device performs comparison concerning the number of the coincidence pair blocks so as to select the image data with the smaller number of extracted coincidence pair blocks after comparison with the other data. The encoding device embeds information in the selected image data based on a magnitude relation of a feature quantity between the two blocks of the pair block.

Description

  The present invention relates to an encoding apparatus, an encoding method, and an encoding program.

  There is a steganography technique for embedding information in image data and reading out the information embedded in the image data. The image data in which the information is embedded is printed. The user reads information from the printed image using a camera-equipped mobile phone or the like. Embedding information in image data is also called “encoding”, and reading information embedded in image data is also called “decoding”.

  For example, an encoding apparatus that performs encoding divides image data into a plurality of blocks, and adjusts the magnitude relationship between the feature amounts of paired blocks that are pairs of two adjacent blocks, thereby obtaining “0” or “1”. Embed the information. To explain with a more detailed example, the encoding apparatus, when embedding “1”, makes the feature quantity of the block on the right side larger than the feature quantity of the block on the left side of the pair block. Adjust the feature amount. In addition, when embedding “0”, the encoding apparatus adjusts the feature amount of the pair block so that the feature amount of the block on the left side of the pair block is equal to or less than the feature amount of the block on the right side. The encoding device uses, for example, an average density or saturation of a specific color of a pixel in a block as a feature amount.

  In addition, for example, the encoding device does not match the magnitude relationship between the feature amounts of the pair blocks and the feature relationship indicating the information to be embedded, and the difference in the feature amounts between the two blocks of the pair block is greater than or equal to a predetermined value. In this case, the magnitude relationship between the feature values of the pair blocks is not adjusted. In other words, the encoding apparatus does not embed information when the information is embedded so that the feature amount is adjusted to change by a predetermined value or more. For example, when embedding “0”, the encoding device does not match the magnitude relationship between the feature quantities of the pair block and does not match the magnitude relationship indicating “0”, and the feature quantity difference is equal to or greater than a predetermined value. Do not adjust the amount. In this case, the feature amount of the pair block that should be embedded with “0” remains as it is, and “1” is read out when encoded.

  There is a decoding device that executes majority processing and error correction processing at the time of decoding. A majority decision process will be described as an example. For example, the encoding device executes the process of embedding the same information at each of a plurality of locations. In addition, the decoding apparatus decodes each of the plurality of locations, and sets the information obtained most from the information obtained from each of the plurality of locations as a decoding result. An example will be described in which the encoding apparatus executes the process of embedding “0” “10” times. In addition, in 3 out of 10 times, the encoding apparatus does not match the magnitude relationship of the feature quantity of the pair block in which “0” is embedded with the magnitude relation indicating “0”, and the feature quantity difference is equal to or larger than a predetermined value. A case where “0” is not embedded will be described as an example. In this case, the decoding apparatus reads “0” from 7 places and reads “1” from 3 places. Then, the decoding device takes a majority vote and uses “0” obtained from seven locations as a decoding result.

JP 2004-349879 A

  However, in the above-described apparatus, when the number of pair blocks in which information is not embedded increases, there is a problem that correct information may not be decoded even if the majority processing or error correction processing described above is executed. For example, in an image including symbols such as characters and codes, there are many pair blocks in which information is not embedded, and correct information may not be decoded.

  A description will be given of the fact that image data including symbols such as characters and codes increases the number of pair blocks in which information is not embedded. It is considered that the average density of blocks where symbols are present and the average density of blocks where symbols are not often different. For example, image data in which black characters are described on a map will be described as an example. Further, a case where black is used as the specific color will be described as an example. In this case, it is considered that the average density of blocks in which black characters are present is higher than a predetermined value compared to the average density of blocks in which black characters are not present. In addition, it is considered that the average density of blocks in which black characters do not exist is lower than a predetermined value compared to the average density of blocks in which black characters exist. As a result, the encoding apparatus does not embed information for a pair block including a block in which black characters exist unless the magnitude relationship of the feature amount indicating the information embedded by the encoding apparatus matches. As described above, it is considered that as the image data includes more symbols, the number of pair blocks in which information is not embedded increases.

  The disclosed technique has been made in view of the above, and an object thereof is to provide an encoding apparatus, an encoding method, and an encoding program capable of improving the probability that correct information is decoded from image data.

  In one aspect, the disclosed encoding apparatus includes a dividing unit that divides image data into a plurality of blocks. In addition, the encoding apparatus extracts a matched pair block that is a pair block that matches a predetermined determination criterion from a pair block that is a pair of two adjacent blocks of the image data divided by the dividing unit. An extraction unit is provided. The encoding device corrects small image data that forms a part of an image formed by the image data divided by the dividing unit and forms an image different from an image forming a background. A correction unit is provided. The encoding device further includes a second extraction unit that extracts the matched pair block from the image data after the small image data is corrected by the correction unit. The encoding apparatus compares the number of matched pair blocks extracted by the first extracting unit with the number of matched pair blocks extracted by the second extracting unit, and compares the number with the other. A selection unit for selecting image data having a small number of matched pair blocks. In addition, the encoding apparatus includes an encoding unit that embeds information in the image data selected by the selection unit based on the magnitude relationship between the feature quantities between the two blocks of the pair block.

  According to one aspect of the disclosed encoding device, there is an effect that the probability that correct information is decoded from image data can be improved.

FIG. 1 is a block diagram illustrating an example of the configuration of the encoding apparatus according to the first embodiment. FIG. 2 is a block diagram illustrating an example of the configuration of the encoding apparatus according to the second embodiment. FIG. 3 is a diagram illustrating an example of an image formed by image data received by the input unit according to the second embodiment. FIG. 4 is a diagram illustrating an example of a block of image data according to the second embodiment. FIG. 5 is a diagram illustrating pair block extraction processing from image data by the selection processing unit according to the second embodiment. FIG. 6 is a diagram illustrating pair block extraction processing from image data by the selection processing unit according to the second embodiment. FIG. 7 is a diagram illustrating pair block extraction processing from image data by the selection processing unit according to the second embodiment. FIG. 8 is a diagram illustrating an example of correction contents by the selection processing unit according to the second embodiment. FIG. 9 is a diagram illustrating processing for extracting a matched pair block from image data including small image data after correction. FIG. 10 is a diagram illustrating processing for extracting a matched pair block from image data including small image data after correction. FIG. 11 is a flowchart illustrating an example of a process flow performed by the encoding apparatus according to the second embodiment. FIG. 12 is a flowchart illustrating an example of a processing flow by the selection processing unit according to the second embodiment. FIG. 13 is a diagram illustrating an example of a computer that executes an encoding program according to the second embodiment.

  Hereinafter, embodiments of the disclosed encoding apparatus, encoding method, and encoding program will be described in detail with reference to the drawings. Note that the invention disclosed by this embodiment is not limited. Each embodiment can be appropriately combined within a range in which processing contents do not contradict each other.

  An example of the configuration of the encoding apparatus 100 according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating an example of the configuration of the encoding apparatus according to the first embodiment. In the example illustrated in FIG. 1, the encoding apparatus 100 includes a dividing unit 101, a first extracting unit 102, a correcting unit 103, a second extracting unit 104, a selecting unit 105, and an encoding unit 106.

  The dividing unit 101 divides the image data into a plurality of blocks. The first extraction unit 102 extracts a matched pair block that is a pair block that matches a predetermined determination criterion from among a pair block that is a pair of two adjacent blocks of the image data divided by the dividing unit 101.

  The correcting unit 103 corrects small image data that forms part of an image formed by the image data divided by the dividing unit 101 and forms an image different from the image forming the background. The second extraction unit 104 extracts a matched pair block from the image data after the small image data is corrected by the correction unit 103.

  The selection unit 105 compares the number of matched pair blocks extracted by the first extraction unit 102 with the number of matched pair blocks extracted by the second extraction unit 104, and compares the number with the other. Image data with a small number of matched pair blocks is selected. The encoding unit 106 embeds information in the image data selected by the selection unit 105 based on the magnitude relationship between the two adjacent blocks of the pair block.

  That is, the encoding apparatus 100 corrects small image data, compares the number of matched pair blocks before and after the correction, and selects image data with a small number of matched pair blocks, so that a pair block that does not embed information at the time of encoding can be obtained. Select less image data. Then, the encoding apparatus 100 embeds information in the selected image data. As a result, according to the encoding apparatus 100, the number of encoded pair blocks can be increased, and the probability that correct information is decoded from the image data can be improved.

[Configuration of encoding device]
An encoding apparatus 200 according to the second embodiment will be described. An example of the configuration of the encoding apparatus 200 according to the second embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating an example of the configuration of the encoding apparatus according to the second embodiment. In the example illustrated in FIG. 2, the encoding device 200 includes an input unit 201, an output unit 202, and a control unit 210.

  The encoding apparatus 200 according to the second embodiment divides the image data into a plurality of blocks, and adjusts the magnitude relationship between the feature amounts of the paired blocks that are pairs of two adjacent blocks, whereby “0” or “1”. Embed the information. Hereinafter, the encoding apparatus 200 will be described using a case where “1” is embedded so that the feature amount of the block on the right side is larger than the feature amount of the block on the left side of the pair block. Further, the encoding apparatus 200 will be described using a case where, when embedding “0”, the feature amount of the block on the left side of the pair block is adjusted to be equal to or less than the feature amount of the block on the right side. However, the present invention is not limited to this. For example, the magnitude relationship may be reversed. The encoding apparatus 200 will be described using a case where, for example, an average density of a specific color of a pixel in a block is used as the feature amount. However, the present invention is not limited to this, and arbitrary information may be used as the feature amount. For example, saturation may be used.

  In addition, the encoding apparatus 200 does not match the magnitude relationship between the feature amounts of the pair blocks and the feature amount relationship indicating the embedded information, and the pair whose feature amount difference between two blocks of the pair block is equal to or greater than a predetermined value. A case where information is not embedded in a block will be described. That is, the encoding apparatus 200 does not embed information in the pair block when the information amount is adjusted so that the feature amount of the block changes by a predetermined value or more.

  Returning to the description of FIG. The input unit 201 is connected to the control unit 210. The input unit 201 receives image data in which information is embedded and information to be embedded in the image data from a user, and inputs the received image data and information to the control unit 210. The information to be embedded in the image data corresponds to a character string, for example. The input unit 201 corresponds to, for example, a keyboard, various input terminals, a scanner, or the like. The output unit 202 is connected to the control unit 210. The output unit 202 receives image data in which information is embedded from the control unit 210, and outputs the received image data. The output unit 202 corresponds to, for example, a monitor or a printer.

  Hereinafter, a case where the encoding apparatus 200 embeds information in the image data received by the input unit 201 will be described as an example, but the present invention is not limited to this. For example, the encoding apparatus 200 may embed information in an image stored in advance in the storage unit of the encoding apparatus 200. Embedding information in an image is also called “encoding”, and reading information embedded in an image from an image is also called “decoding”.

  An example of an image formed from image data received by the input unit 201 will be described with reference to FIG. FIG. 3 is a diagram illustrating an example of an image formed by image data received by the input unit according to the second embodiment. The image data includes background image data that forms a background and small image data that forms a small image that is an image different from the background image that forms the background. In the example shown in FIG. 3, the image data forming the background indicates image data forming the map. For example, the small image data corresponds to a symbol or a geometric pattern written in the background image. In the example shown in FIG. 3, the small image data corresponds to characters such as “X Building”, “□ △ × Corporation”, and “▽ ○ △ Hospital”.

  Hereinafter, the image data will be described using a case where the image data includes background image data, small image data, and position information indicating where the small image data is located on the background image. Further, the background image data will be described by taking as an example a case where the background image data includes data indicating the background image under the position superimposed with the small image. In other words, a case where the background image is not lost even if the small images are overlaid will be described as an example.

  The control unit 210 is connected to the input unit 201 and the output unit 202. The control unit 210 has an internal memory that stores a program that defines various processing procedures and the like, and controls various processes. The control unit 210 is an electronic circuit such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a central processing unit (CPU), or a micro processing unit (MPU). In the example illustrated in FIG. 2, the control unit 210 includes a code bit string generation unit 211, a division unit 212, a small image identification unit 213, a selection processing unit 214, an image format change unit 215, and an encoding unit 216. .

  The code bit string generation unit 211 converts information embedded in the image data input from the input unit 201 into a code bit string that is a code string expressed in bits. That is, the code bit string generation unit 211 generates a code bit string indicating the character string received by the input unit 201. For example, the code bit string generation unit 211 generates a 16-bit code bit string “1010110101001010”. However, the present invention is not limited to this, and the code bit string generation unit 211 may generate a code bit string of 15 bits or less or a code bit string of 17 bits or more. The code bit string generation unit 211 may generate a code bit string including bits for error correction.

  The dividing unit 212 divides the image data received by the input unit 201 into a plurality of blocks. Specifically, the dividing unit 212 divides the image data into “N rows × M columns” blocks. Here, N and M are natural numbers.

  An example of a block of image data in the second embodiment will be described with reference to FIG. FIG. 4 is a diagram illustrating an example of a block of image data according to the second embodiment. In the example illustrated in FIG. 4, the case where the size of the image data received by the input unit 201 is “1024 × 1024” will be described as an example. An example in which the size of one block is “64 × 64” will be described. In this case, as illustrated in FIG. 4, the dividing unit 212 divides the image data into “16 rows × 16 columns” blocks.

  As shown by 301 to 308 in FIG. 4, the dividing unit 212 associates two adjacent block pairs. Hereinafter, a pair of two adjacent blocks of the image data divided by the dividing unit 212 is referred to as a “pair block”. In the example illustrated in FIG. 4, the image data is divided into “16 rows × 16 columns” blocks, and there are “8 × 16” pair blocks.

  Here, the relationship between each pair block shown in FIG. 4 and the embedded bits will be described. When the code bit string “1010110101001010” embedded by the encoding apparatus 200 is “16 bits” and there are “8 × 16” pair blocks, the encoding apparatus 200 repeatedly embeds the code bit string “8 times”. Specifically, the encoding apparatus 200 executes a process of embedding “1”, which is the first bit of the code bit string, in 301 of FIG. The process of embedding “0”, which is the bit of, is executed. Similarly, the encoding apparatus 200 executes a process of embedding the bits of the code bit string one by one in the pair block.

  In addition, the encoding apparatus 200 does not match the magnitude relationship between the feature amounts of the pair blocks and the feature amount relationship indicating the embedded information, and the pair whose feature amount difference between two blocks of the pair block is equal to or greater than a predetermined value. Do not embed information in the block. For this reason, for example, in 301 of FIG. 4 in which the bit “1” is embedded, the magnitude relationship between the two pair blocks does not match the magnitude relationship corresponding to “1”, and the difference between the feature amounts of the two pair blocks is predetermined. If the value is greater than or equal to the value, the encoding apparatus 200 does not embed “1”. The case where the magnitude relationship between the two pair blocks does not match the magnitude relationship corresponding to “1” is a case where the magnitude relationship corresponding to “0” is indicated. Then, the encoding apparatus 200 executes a process of embedding “0”, which is the second bit of the code bit string, regardless of whether information is embedded in 301 of FIG. That is, in this case, if “0” is actually embedded in 302 of FIG. 4, “01” is decoded from 301 and 302 of FIG. 4 by decoding. In other words, when the encoding apparatus 200 embeds the code bit string for the first time, the first bit is not embedded. However, the same code bit string is repeatedly embedded in the image data a plurality of times, and majority processing and correction processing using error correction bits are executed at the time of decoding, so that the first bit is also read appropriately. .

  The small image identification unit 213 identifies small image data from the image data. Specifically, the small image identification unit 213 identifies the position of the small image in the image data. For example, taking the image data shown in FIG. 3 as an example, the small image “Ox Bill” is identified from the image formed by the image data, and the position of the small image “Ox Bill” is identified. For example, the small image identification unit 213 identifies the position of the small image by acquiring the position information of the small image from the image data.

  As will be described below, the selection processing unit 214 extracts a matched pair block that is a pair block that matches a predetermined determination criterion from the image data received by the input unit 201. In addition, the selection processing unit 214 corrects the small image data, and extracts a matched pair block from the image data including the corrected small image data. The selection processing unit 214 selects image data. Below, each process is demonstrated in order. An example of the flow of processing by the selection processing unit 214 will be described later with reference to FIG.

  Processing for extracting a matched pair block from image data received by the input unit 201 will be described. The matched pair block corresponds to a pair block in which information is not embedded at the time of encoding or a pair block in which information is not likely to be embedded at the time of encoding. In the second embodiment, a case where the selection processing unit 214 extracts a pair block in which information is not embedded during encoding as a matched pair block will be described. As described above, in the encoding apparatus 200 according to the second embodiment, the encoding apparatus 200 does not match the magnitude relationship between the pair blocks in which the feature amount difference between the two blocks of the pair block is equal to or greater than a predetermined value. Do not embed. As a result, the selection processing unit 214 according to the second embodiment extracts a pair block whose magnitude relationship does not match and a difference in feature amount between two blocks of the pair block is equal to or greater than a predetermined value as a matched pair block.

  The selection processing unit 214 extracts matching pair blocks and counts the number of extracted pair blocks. Specifically, the selection processing unit 214 uses each of the pair blocks as a predetermined criterion using whether or not the magnitude relationship between the two features of the pair block matches the magnitude relationship indicating information to be embedded. judge. In addition, the selection processing unit 214 determines each pair block using whether or not the difference in feature amount between the two blocks of the pair block exceeds the upper limit threshold value. Here, the selection processing unit 214 determines each pair block of image data. Then, the selection processing unit 214 extracts a pair block that is determined not to match the magnitude relationship and is determined to exceed the upper limit threshold as a matched pair block, and counts the number of extracted matched pair blocks.

  An example of embedding in a pair block in which “1” is embedded will be described. Further, the case where “20” is used as the upper limit threshold will be described as an example. “20” indicates that when the average density of the specific color is represented by a value from “0” to “255”, the upper limit threshold value of the average density of the specific color of the two blocks is “20”. “0” indicates that there is no pixel of a specific color in the block, and “255” indicates that all the pixels in the block have a specific color. However, the present invention is not limited to this. For example, the selection processing unit 214 may use a value of “19” or less as the upper limit threshold value, or a value of “21” or more.

  In this case, the selection processing unit 214 determines whether the magnitude relationship between the two blocks of the pair block matches the magnitude relationship indicating “1”. To explain with a specific example, the selection processing unit 214 determines whether the feature amount of the block on the right side is larger than the feature amount of the block on the left side of the pair block. In addition, the selection processing unit 214 determines whether or not the difference in feature amount between the two blocks of the pair block exceeds “20”. Then, the selection processing unit 214 determines that the magnitude relationship between the two blocks of the pair block does not match the magnitude relationship indicating “1”, and determines that the difference in the feature amount between the two blocks exceeds “20”. If so, it is extracted as a matched pair block. Then, the selection processing unit 214 counts the number of matched pair blocks, for example, “49”.

  The pair block extraction processing from the image data by the selection processing unit 214 in the second embodiment will be further described with reference to FIGS. 5 to 7 are diagrams illustrating pair block extraction processing from image data by the selection processing unit according to the second embodiment. 5 to 7, image data including “Fuji” will be described as an example. FIG. 5 is an example of image data divided into a plurality of blocks by the dividing unit 212 and shows image data including “Fuji”. FIG. 6 shows a pair block in which characters exist among the pair blocks. FIG. 7 shows pair blocks extracted by the selection processing unit 214.

  In the example shown in FIG. 7, for convenience of explanation, the size relationship of the feature amount between two blocks of the pair block does not match the size relationship indicating the information to be embedded for all the pair blocks in which characters exist. The case where the difference in feature amount exceeds the upper threshold is shown. In this case, the selection processing unit 214 extracts “49” pair blocks.

  Processing for correcting the small image data will be described. The selection processing unit 214 corrects one or more of the position of the symbol formed by the small image data, the interval with other symbols, the type of font, and the size of the symbol. In addition, the selection processing unit 214 creates small image data with different correction contents. For example, the selection processing unit 214 creates small image data having different position adjustment amounts, font types, symbol size adjustment amounts, and the like.

  An example of processing by the selection processing unit 214 when correcting the symbol position will be briefly described. The initial value of the position of the small image data in the image data is described as “X, Y”, and the movement amount in the X direction and the movement amount in the Y direction are described as “ix, iy”, respectively. Further, a case where the position of the small image data is corrected in the range of “X, Y” to “± 10” pixels will be described as an example. In this case, the selection processing unit 214 selects one combination of “ix” and “iy” that satisfies “−10 ≦ ix ≦ 10” and “−10 ≦ iy ≦ 10”, and corresponds to the selected combination. Create small image data that has been corrected. Similarly, the selection processing unit 214 selects other combinations and creates small image data.

  In the example shown in FIG. 8, the selection processing unit 214 changes the character spacing between “wealth” and “shi” to become narrower as shown in (1) of FIG. As shown, the position of “Shi” is changed. FIG. 8 is a diagram illustrating an example of correction contents by the selection processing unit according to the second embodiment.

  Here, for example, as shown in FIG. 3, even if the small image data in the image data in which the map or sketch is used as the background image and the character is the small image data is corrected, the character position and the character spacing If the change is within a predetermined range, it will not look bad. Similarly, the location on the map indicated by characters and symbols does not change. Based on this, the correction processing unit 214 corrects the small image data.

  A process for extracting a matched pair block from image data including small image data after correction will be described. The selection processing unit 214 extracts a matched pair block from the image data after the small image data is corrected. Specifically, the selection processing unit 214 extracts a matched pair block for each of the image data corresponding to each of the small image data having different correction contents. Then, the selection processing unit 214 counts the number of extracted matched pair blocks. The matching pair block extraction method is the same as that described above.

  The process of extracting the matched pair block from the image data including the corrected small image data will be further described with reference to FIGS. 9 and 10 are diagrams illustrating processing for extracting a matched pair block from image data including the corrected small image data. FIG. 9 shows a pair block in which characters exist in the image data including the corrected small image data. FIG. 10 shows a matched pair block extracted by the selection processing unit 214.

  In the example shown in FIG. 9, as in FIG. 6, for all pair blocks where characters exist, the magnitude relationship between the two features of the pair block does not match the magnitude relationship indicating the embedded information. The case where the difference of the feature quantity of the block exceeded the upper threshold was shown. In this case, the selection processing unit 214 extracts “39” matched pair blocks.

  A process for selecting image data will be described. The selection processing unit 214 compares the number of matched pair blocks extracted from the image data received by the input unit 201 with the number of matched pair blocks extracted from the image data after the small image data is corrected. Then, the selection processing unit 214 selects image data with a smaller number of matched pair blocks extracted compared to the other.

  Specifically, the selection processing unit 214 selects image data having the smallest matching pair block among the image data received by the input unit 201 and each of the image data corresponding to each of the small image data having different correction contents. . For example, description will be made using the image data shown in FIG. 7 and the image data shown in FIG. In this case, “49” matched pair blocks are extracted from the image data shown in FIG. 7, and “39” matched pair blocks are extracted from the image data shown in FIG. The image data shown in FIG. 10 is selected. In other words, the selection processing unit 214 selects image data with the smallest number of matched pair blocks.

  The image format changing unit 215 changes the format of the image data to an image format that can be encoded. For example, the image format changing unit 215 converts the format of the image data into a bitmap format. However, the present invention is not limited to this, and the image format changing unit 215 may change the image format to any format as long as the encoding unit 216 can encode the image data.

  The encoding unit 216 embeds information in the image data selected by the selection processing unit 214 based on the feature size relationship between two adjacent blocks of the pair block. That is, the encoding unit 216 creates image data in which the code bit string is embedded based on the magnitude relationship between the feature amounts between the two blocks of the pair block. Note that the encoding process by the encoding unit 216 is the same as the encoding process in the prior art document.

  Specifically, the encoding unit 216 embeds information of “0” or “1” by adjusting the magnitude relationship between the feature amounts of the pair blocks that are pairs of two adjacent blocks. For example, when “1” is embedded, the encoding unit 216 adjusts the feature amount of the block on the right side to be larger than the feature amount of the block on the left side of the pair block. Also, when embedding “0”, the encoding unit 216 performs adjustment so that the feature amount of the block on the left side of the pair block is equal to or less than the feature amount of the block on the right side. The encoding unit 216 uses, for example, the average density and saturation of a specific color of pixels in the block as the feature amount.

  The encoding unit 216 determines whether or not the magnitude relationship between the feature amounts in the pair block matches the code to be embedded, and maintains the feature magnitude relationship when it is determined that they match. For example, the encoding unit 216 maintains the magnitude relationship between the feature amounts by adjusting no feature amounts. In addition, for example, the encoding unit 216 matches the code to which the magnitude relationship between the feature amounts in the pair block matches the code to be embedded, and if the difference in the feature amount between the blocks in the pair block is less than the lower limit threshold, the difference is the lower limit threshold. The feature amount in the pair block is changed so as to be equal to or greater than the value.

  In addition, the encoding unit 216 does not match the magnitude relationship between the feature amounts of the pair blocks and the feature relationship between the feature amounts indicating the information to be embedded, and a pair in which the difference in feature amounts between the two blocks of the pair block is equal to or greater than a predetermined value. Do not embed information in the block. That is, the encoding apparatus 200 does not embed information in the pair block when the information is adjusted so that the feature amount of the block changes by a predetermined value or more by embedding the information.

  In addition, the encoding unit 216 does not match the magnitude relationship between the feature amounts of the pair blocks and the feature amount indicating the information to be embedded, and the pair in which the difference in the feature amounts between the two blocks of the pair block does not exceed a predetermined value. For the block, the feature amount is adjusted so that the magnitude relationship matches.

  The encoding device 200 may be realized by using an information processing device such as a known personal computer, mobile phone, PHS (Personal Handyphone System) terminal, mobile communication terminal, or PDA (Personal Digital Assistant). For example, an information processing apparatus such as a PDA includes a code bit string generation unit 211, a division unit 212, a small image identification unit 213, a selection processing unit 214, an image format change unit 215, and an encoding unit 216 shown in FIG. It may be realized by installing each function.

[Processing by encoding device]
Next, an example of the flow of processing by the encoding apparatus 200 according to the second embodiment will be described with reference to FIG. FIG. 11 is a flowchart illustrating an example of a process flow performed by the encoding apparatus according to the second embodiment.

  As shown in FIG. 11, when the input unit 201 receives information to be embedded in image data and the image data (Yes in step S101), the code bit string generation unit 211 generates a code bit string (step S102). For example, the code bit string generation unit 211 generates a 16-bit code bit string “1010110101001010” by converting information embedded in the image data into a code bit string.

  Then, the dividing unit 212 divides the image data into a plurality of blocks (step S103), and associates a pair of two adjacent blocks into a pair block (step S104). For example, the division unit 212 will be described as an example in which the size of the image data is “1024 × 1024” and the size of one block is “64 × 64”. In this case, the dividing unit 212 divides the image data into “16 rows × 16 columns” blocks, and associates two adjacent blocks to make the image data “8 × 16” pair blocks.

  Then, the small image identification unit 213 identifies small image data in the image formed by the image data (step S105). In the example illustrated in FIG. 3, the small image identifying unit 213 identifies the small image “○ × Bill” from the image formed by the image data, and identifies the position of the small image “○ × Bill”.

  The selection processing unit 214 corrects the small image data and selects image data with a small number of matched pair blocks (step S106). Details of the processing for selecting image data will be described with reference to FIG.

  Then, the image format changing unit 215 converts the format of the image data selected by the selection processing unit 214 into an image format that can be encoded (step S107). For example, the image format changing unit 215 changes the bitmap format. Then, the encoding unit 216 encodes the image data selected by the selection processing unit 214 (step S108). That is, the encoding unit 216 embeds information based on the magnitude relationship between the feature amounts between two adjacent blocks of the pair block. In other words, the encoding unit 216 creates image data in which the code bit string is embedded based on the magnitude relationship between the feature amounts between the two blocks of the pair block.

  In addition, said process procedure is not limited to said order, You may change suitably in the range which does not contradict a process content. For example, after executing the process for identifying small image data in step S105, the process for dividing the image data in steps S103 to S104 may be executed.

[Processing by selection processing unit]
Next, an example of a processing flow by the selection processing unit 214 in the second embodiment will be described with reference to FIG. FIG. 12 is a flowchart illustrating an example of a processing flow by the selection processing unit according to the second embodiment. A series of processes described with reference to FIG. 12 corresponds to step S106 in FIG.

  As shown in FIG. 12, the selection processing unit 214 extracts a matched pair block from the image data received by the input unit 201 (step S201). Here, an example in which “1” is embedded in a pair block embedded will be described. Further, the case where “20” is used as the upper limit threshold will be described as an example. In this case, the selection processing unit 214 determines whether the magnitude relationship between the two blocks of the pair block matches the magnitude relationship indicating “1”, and the difference in feature amount between the two blocks of the pair block is “20”. ] Is exceeded. Here, the selection processing unit 214 determines each pair block of image data. When it is determined that the magnitude relationship between the two blocks of the pair block does not match the magnitude relationship indicating “1”, and the difference between the feature amounts of the two blocks exceeds “20”, the matched pair block Extract as

  Then, the selection processing unit 214 counts the number of matched pair blocks (step S202). In the example illustrated in FIG. 6, the selection processing unit 214 counts “49”.

  Then, the selection processing unit 214 selects one correction content (step S203), and corrects the small image data using the selected correction content (step S204). For example, the selection processing unit 214 selects one combination of “ix” and “ii” that satisfies “−10 ≦ ix ≦ 10” and “−10 ≦ iy ≦ 10”, and the correction corresponding to the selected combination. Create small image data that has been executed.

  Then, the selection processing unit 214 extracts a matched pair block from the image data including the corrected small image data (step S205). The selection processing unit 214 extracts a matched pair block by executing the same process as in step S201 described above. Then, the selection processing unit 214 counts the number of matched pair blocks extracted from the image data including the corrected small image data (step S206). In the example illustrated in FIG. 9, the selection processing unit 214 counts “39”.

  Then, the selection processing unit 214 compares the number of matched pair blocks (step S207). For example, the selection processing unit 214 sets the number of matched pair blocks “49” extracted from the image data received by the input unit 201 and the matched pair blocks extracted from the image data after the small image data is corrected. The number “39” is compared.

  Then, the selection processing unit 214 selects image data with a smaller number of matched pair blocks extracted compared to the other (step S208). For example, the selection processing unit 214 selects the image data created in step S203 from which “39” pair blocks, which are smaller than “49”, are extracted.

  Then, the selection processing unit 214 determines whether all correction contents have been selected (step S209). If the selection processing unit 214 determines that all have been selected (Yes at step S209), the process ends. On the other hand, if it is determined that not all have been selected (No at Step S209), the process returns to Step S203 described above, and the processes from Step S203 to S209 are repeated. Here, when step S207 is executed again, the number of matched pair blocks for the image data selected when step S207 was executed last time, the number of matched pair blocks newly extracted in step S205, and Will be compared. As a result, when it is determined that all the correction contents have been selected (Yes at step S209), the selection processing unit 214 selects image data with the smallest number of matched pair blocks among the image data on which different correction contents are executed. Will do.

  In addition, said process procedure is not limited to said order, You may change suitably in the range which does not contradict a process content. For example, in the processing flow shown in FIG. 12, every time the matched pair block extracted from the image data including the corrected small image data is counted, image data having fewer matched pair blocks than the other is selected. However, the present invention is not limited to this. For example, a plurality of image data corresponding to each correction content may be created, and after counting the number of matched pair blocks for the plurality of image data, the image data with the least number of matched pair blocks may be selected.

[Effect of Example 2]
As described above, according to the second embodiment, the encoding apparatus 200 divides image data into a plurality of blocks. Then, the encoding apparatus 200 extracts a matched pair block from the divided image data. Then, the encoding apparatus 200 corrects the small image data and extracts a matched pair block from the corrected image data. Then, the encoding apparatus 200 compares the number of extracted matched pair blocks, and selects image data with a smaller number of extracted matched pair blocks compared to the other. Then, the encoding apparatus 200 embeds information in the selected image data based on the size relationship between the two adjacent blocks of the pair block. As a result, according to the encoding apparatus 200, the number of encoded pair blocks can be increased, and the probability that correct information is decoded from image data can be improved.

  For example, when small image data forming a symbol such as a character or a code is included in the image data, the number of pair blocks in which no information is embedded increases. This is because the average density of blocks in which symbols are present and the average density of blocks in which symbols are not present are often very different. For example, image data in which black characters are described on a map will be described as an example. Further, a case where black is used as the specific color will be described as an example. In this case, the average density of blocks where black characters are present is higher than a predetermined value compared to the average density of blocks where black characters are not present. In addition, the average density of blocks in which black characters do not exist is lower than a predetermined value compared to the average density of blocks in which black characters exist. As a result, the encoding apparatus does not embed information for a pair block including a block in which black characters exist unless the magnitude relationship of the feature amount indicating the information embedded by the encoding apparatus matches. As described above, it is considered that as the image data includes more symbols, the number of pair blocks in which information is not embedded increases. On the other hand, the encoding apparatus 200 corrects the small image data and embeds information in the image data with a small number of matched pair blocks, so that the number of pair blocks to be encoded can be increased, and correct information can be obtained from the image data. Can improve the probability of decoding.

  Further, according to the second embodiment, the encoding apparatus 200 uses a pair of blocks as a predetermined determination criterion based on whether or not the magnitude relationship between the two blocks of the pair block matches the magnitude relationship indicating the embedded information. Each block is determined. In addition, the encoding apparatus 200 determines each pair block using whether or not the difference in feature amount between the two blocks of the pair block exceeds the upper limit threshold value. Then, the encoding device 200 determines that the magnitude relationship does not match and extracts the pair block determined to exceed the upper limit threshold. As a result, according to the encoding apparatus 200, the number of pair blocks in which no information is embedded at the time of encoding can be compared before and after correction, and image data with the largest number of pair blocks to be encoded can be selected reliably.

  Although the embodiments of the present invention have been described so far, the present invention may be implemented in other embodiments besides the above-described embodiments. Therefore, other embodiments will be described below.

[Image data format]
For example, in the above-described embodiment, the case where the image data separately includes the background image data and the small image data has been described, but the present invention is not limited to this. For example, unlike bitmap image data, background image data and small image data are not separated, and only one of the pixels forming the background image or the pixels forming the small image is formed in each image area. There may be some image data. In this case, the encoding apparatus 200 recognizes symbols such as characters and codes included in the image data using a known image recognition process. Then, the recognized character or code is corrected. At that time, if the symbol position is shifted and a region without pixels is generated by executing the correction, the encoding apparatus 200 corresponds to the region without pixels based on the background image around the region without pixels. A new pixel is generated, and the generated pixel is used to complement a region without a pixel. A known image correction technique may be used for processing for newly generating a pixel corresponding to a region without a pixel based on a background image around a region without a pixel.

[Upper threshold]
Further, for example, in the above-described embodiment, for the pair block in which the magnitude relationship between the two blocks of the pair block does not coincide with the magnitude relationship indicating the information to be embedded, and the difference between the feature amounts of the two blocks exceeds the upper limit threshold, The case of extracting as a matched pair block has been described as an example. However, the present invention is not limited to this. For example, a pair block that does not match the magnitude relationship indicating the information in which the magnitude relationship between the two blocks of the pair block is embedded may be extracted as a matched pair block. In other words, a matched pair block may be extracted without determining the upper limit threshold.

[Extract from paired blocks with small image data]
Further, for example, in the above-described embodiment, the case where a matched pair block is extracted using a predetermined determination criterion for the entire area of the image data has been described as an example, but the present invention is not limited to this. For example, the encoding apparatus 200 extracts a matching pair block using a predetermined determination criterion for a pair block in which small image data exists, while using a predetermined determination criterion for a pair block in which small image data does not exist. It is not necessary to extract the matched pair block. That is, in a pair block in which small image data exists, the processing is executed only for the pair block in which small image data exists in consideration of the fact that the difference between the feature amounts of the two blocks is often large. As a result, it is possible to shorten the processing time as compared with a method of executing processing on the entire image data.

[Extract pair blocks with small image data]
In addition, for example, the selection processing unit 214 may determine each pair block using whether or not small image data exists as a predetermined determination criterion, and may extract a pair block determined to have small image data. . In other words, in a pair block in which small image data exists, whether or not there is small image data may be used as a predetermined determination criterion in consideration of the fact that the difference between the feature amounts of two blocks is often large. In this case, it is possible to shorten the processing time as compared with the case where the magnitude relation or the difference in the feature amount is used as the predetermined reference.

[System configuration]
In addition, among the processes described in the present embodiment, all or part of the processes described as being automatically performed can be manually performed. For example, the user may manually execute processing for identifying small image data. In addition, the processing procedures, control procedures, specific names, and information including various data and parameters shown in the above-mentioned document and drawings (FIGS. 1 to 12) are arbitrarily changed unless otherwise specified. be able to.

  Further, each component of each illustrated apparatus is functionally conceptual, and does not necessarily need to be physically configured as illustrated. That is, the specific form of distribution / integration of each device is not limited to the one shown in the figure, and all or a part of the distribution / integration is functionally or physically distributed in arbitrary units according to various loads and usage conditions. Can be integrated and configured. For example, using the example shown in FIG. 2, the encoding unit 216 of the control unit 210 may be connected as an external device of the encoding device 200 via a network.

[Computer]
The various processes described in the above embodiments can be realized by executing a program prepared in advance on a computer such as a personal computer or a workstation. Therefore, in the following, an example of a computer that executes an encoding program having the same function as that of the above-described embodiment will be described with reference to FIG. FIG. 13 is a diagram illustrating an example of a computer that executes an encoding program according to the second embodiment.

  As illustrated in FIG. 13, the computer 3000 according to the second embodiment includes an operation unit 3001, a microphone 3002, a display 3003, a printer 3004, a communication unit 3006, a CPU 3010, a ROM 3011, and the like. The computer 3000 includes an HDD (Hard Disk Drive) 3012 and a RAM 3013. Further, the computer 3000 is connected to each other by a bus 3009.

  The ROM 3011 exhibits the same functions as the code bit string generation unit 211, the division unit 212, the small image identification unit 213, the selection processing unit 214, the image format change unit 215, and the encoding unit 216 shown in FIG. The control program to be stored is stored. That is, as shown in FIG. 13, the ROM 3011 stores a code bit string generation program 3011a, a division program 3011b, and a small image identification program 3011c. The ROM 3011 stores a selection processing program 3011d, an image format change program 3011e, and an encoding program 3011f. Note that these programs 3011a to 3011f may be appropriately integrated or separated in the same manner as each component of the encoding apparatus 200 shown in FIG.

  Then, the CPU 3010 reads these programs 3011a to 3011f from the ROM 3011 and executes them. As a result, as shown in FIG. 13, each program functions as a code bit string generation process 3010a, a division process 3010b, a small image identification process 3010c, and a selection processing process 3010d. Each program functions as an image format change process 3010e and an encode process 3010f. Each of the processes 3010a to 3010f includes the code bit string generation unit 211, the division unit 212, the small image identification unit 213, the selection processing unit 214, the image format change unit 215, and the encoding unit 216 shown in FIG. And correspond respectively.

  The CPU 3010 executes the encoding program using the image data 3013a, the code bit data string data 3013b, and the upper threshold data 3013c stored in the RAM 3013.

  However, in the above description, the case where all the processes 3010a to 3010f are always virtually realized on the CPU 3010 is shown. However, the present invention is not limited to this. For example, some processes required for processing among the processes 3010a to 3010f may be virtually realized on the CPU 3010. In other words, not all processes always operate on the CPU 3010, but processes necessary for processing may selectively operate.

[Others]
Note that the encoding program described in the present embodiment may be distributed via a network such as the Internet. The encoding program may be recorded on a computer-readable recording medium such as a hard disk, a flexible disk (FD), a CD-ROM, an MO, and a DVD, and may be executed by being read from the recording medium by the computer.

DESCRIPTION OF SYMBOLS 100 Encoding apparatus 101 Dividing part 102 Extracting part 103 Correction part 104 Extracting part 105 Selecting part 106 Encoding part 200 Encoding apparatus 201 Input part 202 Output part 210 Control part 211 Code bit stream generation part 212 Dividing part 213 Small image identification part 214 Selection processing part 215 Image format changing unit 216 Encoding unit

Claims (7)

A dividing unit for dividing the image data into a plurality of blocks;
A first extraction unit that extracts a matched pair block that is a pair block that matches a predetermined determination criterion among a pair block that is a pair of two adjacent blocks of image data divided by the dividing unit;
A correction unit that corrects small image data that forms part of an image formed by the image data divided by the dividing unit and forms an image different from an image that forms a background;
A second extraction unit for extracting the matched pair block from the image data after the small image data is corrected by the correction unit;
The number of matched pair blocks extracted by comparing the number of matched pair blocks extracted by the first extracting unit with the number of matched pair blocks extracted by the second extracting unit A selection unit that selects image data with less
An encoding apparatus comprising: an encoding unit that embeds information in the image data selected by the selection unit based on a magnitude relationship between feature quantities between two blocks of the pair block.   The first extraction unit and the second extraction unit determine the pair block using whether or not the small image data exists as the predetermined determination criterion, and determine that the small image data exists. 2. The encoding apparatus according to claim 1, wherein the pair block is extracted.   The first extraction unit and the second extraction unit are configured to determine whether or not the size relationship between the two blocks of the pair block matches a size relationship indicating information to be embedded. To determine the pair block, to determine whether the difference in feature quantity between the two blocks of the pair block exceeds an upper limit threshold as the predetermined criterion, and to determine the size of the pair block The encoding apparatus according to claim 1, wherein a pair block that is determined not to match and determined to exceed the upper threshold is extracted. The image formed by the small image is a symbol,
The correction unit corrects at least one of a position of a symbol formed by the small image, an interval with another symbol, a font type, and a symbol size. The encoding device according to any one of claims 1 to 3. A dividing step in which the computer divides the image data into a plurality of blocks;
A first extraction step of extracting a matched pair block that is a pair block that matches a predetermined determination criterion from a pair block that is a pair of two adjacent blocks of the image data divided by the dividing step;
A correction step for correcting small image data that forms part of an image formed by the image data divided by the dividing step and forms an image different from an image forming a background;
A second extraction step of extracting the matched pair block from the image data after the small image data is corrected by the correction step;
The number of matched pair blocks extracted by comparing the number of matched pair blocks extracted by the first extracting step with the number of matched pair blocks extracted by the second extracting step A selection step to select image data with less
An encoding method comprising: performing an encoding step of embedding information on the image data selected in the selection step based on a magnitude relationship between feature quantities between two blocks of the pair block. A division procedure for dividing the image data into a plurality of blocks;
A first extraction procedure for extracting a matched pair block that is a pair block that matches a predetermined determination criterion from a pair block that is a pair of two adjacent blocks of image data divided by the division procedure;
A correction procedure for correcting small image data that forms part of an image formed by the image data divided by the division procedure and forms an image different from an image that forms a background;
A second extraction procedure for extracting the matched pair block from the image data after the small image data is corrected by the correction procedure;
The number of matched pair blocks extracted by comparing the number of matched pair blocks extracted by the first extracting procedure with the number of matched pair blocks extracted by the second extracting procedure A selection procedure to select image data with less
An encoding program for causing a computer to execute an encoding procedure for embedding information on the image data selected by the selection procedure on the basis of a magnitude relationship between feature quantities between two blocks of the pair block. A dividing unit for dividing the image data into a plurality of blocks;
A first extraction unit that extracts a matched pair block that is a pair block that matches a predetermined determination criterion among a pair block that is a pair of two adjacent blocks of image data divided by the dividing unit;
A correction unit that corrects small image data that forms part of an image formed by the image data divided by the dividing unit and forms an image different from an image that forms a background;
A second extraction unit for extracting the matched pair block from the image data after the small image data is corrected by the correction unit;
The number of matched pair blocks extracted by comparing the number of matched pair blocks extracted by the first extracting unit with the number of matched pair blocks extracted by the second extracting unit A selection unit that selects image data with less
An image data output device comprising: an output unit that outputs the image data selected by the selection unit.

Images