JP5459481B2 - Image processing apparatus and image processing program - Google Patents

Description

  The present invention relates to an image processing apparatus and an image processing program.

  Conventionally, information is embedded so as not to stand out in an image, and information embedded in the image is extracted and used. For example, in Patent Document 1, color conversion processing is separately performed on an image and embedding information, and the embedding information is combined with an image by performing processing for adding a dot pattern to a yellow component, and is printed. In addition, as a technique for processing an image in which information is embedded in yellow as described above, for example, in Patent Document 2, whether or not an image has information embedded by detecting an isolated region of yellow surrounded by a white background. Judging. In Patent Document 3, the presence / absence of information is obtained by binarizing a specific signal color-separated by a blue filter based on a local average value and performing pattern matching on the binarized signal. Is judged.

  On the other hand, a limited color processing for reducing the number of colors used in an image has been conventionally performed. This limited color processing is performed for the purpose of removing noise and improving the compression rate. For example, in Patent Document 4, a color frequency distribution is generated, peak colors in the frequency distribution are integrated, and a representative color is selected to perform a limited color process. Also, for example, in Patent Document 5, a color space frequency distribution is generated from a color image, the color space is equally divided into cells, and adjacent cells on the color space are fused with cells having a higher frequency than others. This process is repeated. Further, for example, in Patent Document 6, a process of generating a color space frequency distribution from a color image and adding a color farthest on the color space from the representative color selected so far as a new representative color is preset. Repeat until the number of colors is reached.

  As for embedding information in a limited color image, for example, in Patent Document 7, the image is reduced in gradation, and the embedded image is reduced in gradation based on the reduced gradation image. It is described that the color is reduced and synthesized in accordance with the above.

JP 2001-045268 A JP-A-10-145623 JP-A-10-243221 JP 2008-0665803 A JP 09-127924 A JP 05-159050 A JP 2005-269039 A

  It is an object of the present invention to provide an image processing apparatus and an image processing program that can accurately extract embedded information from a color image in which information is embedded.

  According to the first aspect of the present invention, a color of a color image in which information is embedded is obtained from the color image by changing the color in the background image in accordance with a predetermined embedding method using a predetermined embedding color. Replacement means for replacing the representative colors, color set candidate extraction means for extracting a set of representative colors as color set candidates, and information embedded from the image replaced by the replacement means according to the color set candidates. Information acquisition means for acquiring, wherein the color set candidate extraction means sets a set of each representative color and a representative color corresponding to a color obtained when the representative color is changed according to the embedding method as a color set. An image processing apparatus is characterized in that it is extracted as a candidate.

  In the invention described in claim 2 of the present application, the embedding method in the invention described in claim 1 of the present application changes the color of the background image by mixing the embedded color and the color of the background image. The information is embedded, and the color set candidate extracting means includes each representative color and a representative color in a predetermined color range including a color obtained by mixing the representative color and the embedded color. An image processing apparatus is characterized in that a set is extracted as a color set candidate.

  The invention according to claim 3 of the present application is the color obtained by the color set candidate extracting means in the invention of claim 2 further mixing each representative color and the representative color and the embedded color. A combination with a representative color obtained by replacing a color in a predetermined color range including the color by the replacement unit is extracted as a color set candidate.

  According to a fourth aspect of the present invention, the embedding method in the first aspect of the present invention changes the color of the background image by mixing the embedding color and the color of the background image. The information is embedded, and the color set candidate extracting means has a predetermined color range including each representative color and a color obtained when the embedded color is changed to the representative color according to the embedding method. An image processing apparatus is characterized in that a set with a representative color obtained by replacing a certain color by the replacement unit is extracted as a color set candidate.

  In the invention according to claim 5 of the present application, the color set candidate extracting means according to any one of claims 2 to 4 adjusts the color range according to the resolution of the color image. An image processing apparatus characterized by the above.

  In the invention described in claim 6 of the present application, when the color set candidate extracting means in the invention described in any one of claims 2 to 5 of the present application is an image in which the color image is compressed, An image processing apparatus that adjusts the color range according to a degree of compression.

  The invention described in claim 7 of the present application is an image processing program for causing a computer to execute the function of the image processing apparatus described in any one of claims 1 to 6.

  According to the first aspect of the present invention, the embedded information can be extracted from the color image in which the information is embedded more accurately than in the case where the present configuration is not provided.

  According to the second aspect of the present invention, information embedded by color mixing can be extracted more accurately than in the case where the present configuration is not provided.

  According to the third aspect of the present invention, embedded information can be extracted from a deteriorated image more accurately than in the case where the present configuration is not provided.

  According to the fourth aspect of the present invention, even from a deteriorated image, it is possible to extract embedded information more accurately than in the case where the present configuration is not provided.

  According to the fifth aspect of the present invention, information can be extracted according to the degree of deterioration of embedded information due to the difference in resolution of a given image.

  According to the sixth aspect of the present invention, information can be extracted according to the degree of deterioration of embedded information due to the difference in the degree of compression of a given image.

  According to the invention of claim 7 of the present application, the effect of the invention of any one of claims 1 to 6 can be obtained.

It is a block diagram which shows one Embodiment of this invention. It is explanatory drawing of the 1st specific example of the operation | movement in one Embodiment of this invention. It is explanatory drawing of an example of the extraction process of a color group candidate. It is explanatory drawing of an example of adjustment of a color range. It is explanatory drawing of the 2nd specific example of operation | movement in one Embodiment of this invention. It is explanatory drawing of another example of the extraction process of a color group candidate. FIG. 3 is an explanatory diagram of an example of a computer program, a storage medium storing the computer program, and a computer when the function described in the embodiment of the present invention is realized by a computer program.

  FIG. 1 is a configuration diagram showing an embodiment of the present invention. In the figure, 11 is a replacement unit, 12 is a color set candidate extraction unit, 13 is a first candidate extraction unit, 14 is a second candidate extraction unit, and 15 is an information acquisition unit. The color image to be processed is an image in which information is embedded by changing the color of the background image in accordance with an embedding method predetermined by the embedding color. A known method may be selected and used as the information embedding method. As an example, there is a method of embedding information by subtracting or adding a predetermined embedded color to a subtractive color or additive color. It is assumed that information on the embedding color or information indicating the embedding method is given.

  The replacement unit 11 performs a limited color process, extracts a representative color from the color image to be processed, and generates a limited color image by replacing the color in the color image with the representative color. The number of representative colors may be extracted in the range with a predetermined upper limit, or may be smaller than the number of colors used in the color image to be processed. In addition, a known method may be selected and used as the representative color extraction method and the representative color replacement method. The limited color image is passed to the information acquisition unit 15, and the representative color information is passed to the color set candidate extraction unit 12.

  The color set candidate extraction unit 12 is preliminarily given as information about the embedding method used when embedding information in the color image and the embedded color (embedding color) as embedding method information. For each extracted representative color, a set of a plurality of representative colors is extracted as a color set candidate according to the embedding method information. In this example, color set candidates are extracted by the first candidate extraction unit 13 and the second candidate extraction unit 14. Note that the first candidate extraction unit 13 may be omitted or the second candidate extraction unit 14 may not be provided.

  The first candidate extraction unit 13 sets another representative color to a predetermined color range including a color obtained when the certain representative color is changed according to the embedding method used when embedding information in the background image. When a representative color exists, a set of two representative colors having the relationship is extracted as a color set candidate. For example, when the embedding method is a method that subtractively mixes the embedded color, another representative color exists in a predetermined color range that includes a color obtained by subtracting the embedded color from a certain representative color. Then, the set of the two representative colors is extracted as a color set candidate. For example, when the embedding method is to add and embed an embedded color, another representative color exists in a predetermined color range including a color obtained by adding an embedded color to a representative color. In this case, the set of the two representative colors is extracted as a color set candidate. Here, the color range means a range in the color space, but here includes a case where it means one specific color.

  The color range may be adjusted according to the degree of color degradation in the color image. For example, when the location where information is embedded by the embedded color is deteriorated, the distance between the color range and the representative color is preferably shorter than when the distance is not deteriorated. Further, for example, when the portion other than the portion where the information is embedded by the embedded color is deteriorated, the size of the color range is preferably made smaller than the case where the size is not deteriorated. For example, since the degree of deterioration varies depending on the resolution of the color image, the position and size of the color range may be adjusted according to the resolution of the color image. Further, when the color image is expanded from a compressed state, the degree of deterioration of the color image differs depending on the degree of compression. Therefore, the position and size of the color range may be adjusted according to the degree of compression.

  The second candidate extraction unit 14 includes a predetermined color range including colors obtained when a certain first representative color is changed according to the embedding method used when embedding information in the background image with the embedding color. When the replacement unit 11 substitutes the second representative color with the second representative color, a pair of the first representative color and the second representative color having such a relationship is extracted as a color set candidate. For example, when the embedding method is to subtract the embedded color, there is a color in a predetermined color range including a representative color and a color obtained by subtracting the representative color and the embedded color. A pair with a representative color when replaced by the replacement unit 11 is extracted as a color set candidate. Further, for example, when the embedding method is an additive color mixing of the embedding color, it is in a predetermined color range including a certain representative color and a color obtained by additively mixing the representative color and the embedding color. A set with a representative color whose color is replaced by the replacement unit 11 is extracted as a color set candidate.

  The color in the color range may be a color obtained by changing the representative color according to the embedding method, or a color obtained by adjusting a color obtained by changing the representative color according to the embedding method. This adjustment may be performed according to the degree of color degradation in the color image. For example, it may be adjusted so as to be closer to the representative color as the deterioration is severe. As an example, adjustment may be performed according to the resolution of the color image, and adjustment may be performed so that the lower the resolution, the closer to the representative color. Alternatively, when the color image is expanded from a compressed state, the color image may be adjusted according to the degree of compression, and adjusted so that the higher the degree of compression, the closer to the representative color.

  The information acquisition unit 15 acquires information embedded with embedded colors from the limited color image replaced by the replacement unit 11 in accordance with the color set candidates extracted by the color set candidate extraction unit 12. For example, it is only necessary to extract the pattern of the other representative color existing in one representative color from the two representative colors in the set, and acquire information embedded from the pattern. The process of acquiring the embedded information is performed according to the information embedding method, but may be performed by a known technique.

  An example of the operation of the above configuration will be described using a specific example. As a first specific example, a case will be described in which the embedding method is a method of subtractively mixing a yellow embedding color with dots. FIG. 2 is an explanatory diagram of a first specific example of the operation according to the embodiment of the present invention. FIG. 2A shows an example of a color image to be processed. In the color image shown in FIG. 2A, red “H” and a pink rectangle are drawn as a background image on a white background, and dots representing embedding information are scattered. For convenience of illustration, the difference in color is indicated by the difference in diagonal lines. The embedded dot is a yellow dot in the white background, a reddish dot due to subtractive color mixing within the pink rectangle, and an orange dot due to subtractive color mixing within the red character. For convenience, both are indicated by black dots. The color image to be processed may be an image in which color unevenness, blur, or noise is mixed. In the example shown in FIG. 2A, a diagonal line protrudes around the pink rectangle, and the periphery blurs and the color oozes out. It shows how it is.

  The replacement unit 11 extracts a representative color from the color image to be processed shown in FIG. 2A and replaces the color in the color image with the representative color to generate a limited color image. In this example, the ground color “white”, the letter “H” color “red”, the rectangle “pink”, the dot color embedded in the ground color “yellow”, and the like are representative colors. It shall be extracted. In the color image shown in FIG. 2A, in addition to this, there is a whited pink color around the pink rectangle, and the color of the reddish dot embedded by subtractive color mixing in the pink rectangle. Various colors exist depending on the color of the orange dot embedded in the red character, noise and uneven color, and the above representative color is selected as the main color.

  A limited color in which the colors used as shown in FIG. 2B are integrated with the representative colors by replacing various colors existing in the color image shown in FIG. 2A with any of the representative colors. An image is obtained. As described above, even if noise, color unevenness, blur, or the like occurs, these will not appear in the limited color image by being replaced with the representative color. For example, a whitish color portion existing around a pink rectangle is replaced with the representative color white or pink. Further, the yellow dot that is the embedded color is unified with the representative color “yellow” even if color unevenness occurs. Note that the dots in the pink rectangle remain as dots in the figure, but are replaced with “red” which is one of the representative colors. The dots inside the letter “H” are replaced with the representative color “red” and integrated with the letter “red”.

  Information on the extracted representative colors, that is, information on “white”, “yellow”, “red”, and “pink”, which are representative colors in this example, is passed to the color set candidate extraction unit 12. The color set candidate extraction unit 12 extracts color set candidates from these representative colors. FIG. 3 is an explanatory diagram of an example of color set candidate extraction processing. The black circles in the figure are representative colors. In FIG. 3, for the sake of convenience, a certain two-dimensional plane in the color space is shown, but it may be a three-dimensional or higher color space.

  First, the first candidate extraction unit 13 examines whether or not each representative color is extracted as a representative color by changing the representative color according to the embedding method, and extracts the representative colors before and after the change as color set candidates. To do. In this example, it is assumed that the subtractive color mixture is used with yellow as the embedding color as the embedding method. Therefore, a color obtained by subtracting the embedding color yellow from each representative color is used in a certain color range. Asking. In FIG. 3A, a color range including a color obtained by subtracting yellow from the representative color indicated by a black circle is indicated by an ellipse. The first candidate extraction unit 13 checks whether another representative color is included in the color range indicated by the ellipse. In this example, “yellow” which is another representative color is included in the color range indicated by an ellipse corresponding to “white” which is one of the representative colors. Therefore, “white” and “yellow” are used as a color set candidate.

  Note that the size of the color range indicated by the ellipse may be adjusted to be narrower as the deterioration is more severe, for example, according to the degree of deterioration of the color in the color image. Alternatively, the position of the color range may be shifted according to the degree of color degradation in the color image, and for example, adjustment may be made so that the closer the color is, the closer to the representative color. Or both of them may be adjusted. When the deterioration is severe, there are many cases where a color that is not present in the original color image and is generated by the deterioration is extracted as a representative color. For this reason, the size and position of the color range may be controlled in accordance with the degree of deterioration so that the representative colors generated due to deterioration are not extracted as color set candidates.

  FIG. 4 is an explanatory diagram of an example of color range adjustment. For example, when the resolution of a color image is high, there are various color pixels in the range of color changes caused by noise and color unevenness, but when the resolution is low, there are few pixels in that range. The difference in color due to noise and uneven color is directly linked to the selection of the representative color. For example, when such a color difference occurs in a pixel in which the embedded color is mixed with the background image, the color of the pixel in which the embedded color is mixed is close to the color of the background image because it is affected by the color of the background image. Become. Therefore, by bringing the color range close to the representative color as shown in FIG. 4A, a color set candidate corresponding to a color change is extracted. In addition, when the resolution is low, compared to the case where the resolution is high, the degree of isolated point noise and color unevenness is suppressed, and the edge portion that is not the extraction target may be dull and may be erroneously extracted. As shown in FIG. 4B, the color range may be narrowed so that the representative color that appears due to the color change is not selected.

  For example, even when a color image is expanded from a compressed state, the color range may be adjusted according to the degree of compression. In the JPEG method, which is a typical compression method, the compression rate is changed depending on the quantization parameter used when the DCT coefficient is quantized, but the degree of deterioration such as mosquito noise also changes accordingly. More specifically, the deterioration becomes more severe as the DCT coefficient is roughly quantized by the quantization parameter. For example, when the pixel in which the embedded color is mixed with the background image has deteriorated, the color of the pixel in which the embedded color is mixed becomes close to the color of the background image due to the deterioration. Therefore, as shown in FIG. 4A, by bringing the color range close to the representative color, color set candidates corresponding to the case where deterioration due to compression occurs are extracted. Further, when the resolution is low, compared to the case where the resolution is high, the edge portion that is not the extraction target may be dull and erroneously extracted, so the color range is narrowed as shown in FIG. The representative color that appears due to the color change should not be selected. Of course, in the irreversible compression method other than the JPEG method, the above-described image degradation occurs, and a corresponding color range may be set.

  In either case, the adjustment of the size of the color range and the adjustment of the position may be used together, and the color range may be set according to the deterioration of the image.

  Next, the second candidate extraction unit 14 determines, for each representative color, which representative color the color obtained by changing the representative color according to the embedding method is replaced by the replacement unit 11, and the original representative color. A color set candidate is formed by combining the color and the replaced representative color. In this example, it is assumed that the subtractive color mixture is used with yellow as the embedding color as the embedding method. Therefore, a color obtained by subtracting the embedding color yellow from each representative color is obtained. In FIG. 3B, a color obtained by subtracting yellow from the representative color indicated by a black circle is indicated by a cross. In the second candidate extraction unit 14, it is checked which representative color the color indicated by the cross is replaced by the replacement unit 11.

  In FIG. 3B, the color range to be replaced with each representative color is shown divided by thin lines. According to this classification, it is examined which representative color is replaced by the color indicated by the x mark corresponding to each representative color. Red and yellow remain red and yellow, respectively, but × corresponding to pink The color indicated by the mark is included in the red area, and the color indicated by the x mark corresponding to white is included in the yellow area. Accordingly, a combination of pink and red, and white and yellow is extracted as a color set candidate. Note that the white and yellow pairs have already been extracted by the first candidate extraction unit 13, and therefore, the pink and red color set candidates are added here.

  The color obtained by changing the representative color according to the embedding method may be adjusted according to the degree of color deterioration in the color image, and the color range to be adjusted is indicated by an ellipse in FIG. Yes. When the deterioration is severe, the color of the pixel in which the embedded color is mixed with the background image tends to approach the color of the background image. Further, there are many cases where a color that is not present in the original background image but is caused by deterioration is extracted as a representative color. Therefore, the representative color is embedded according to the degree of deterioration so that it approximates the deteriorated color of the pixel mixed with the embedded color and does not extract the representative color extracted due to the deterioration as a color set candidate. What is necessary is just to control the color obtained by changing according to a method. For example, the adjustment may be made according to the resolution of the color image so that the lower the resolution is, the easier it is to deteriorate, and the closer to the representative color. Alternatively, when the color image is expanded from a compressed state, the color image may be adjusted according to the degree of compression, and adjusted so as to be closer to the representative color as the degree of compression is high and deterioration is likely to occur. When JPEG is used as the compression method, the deterioration becomes more severe as the DCT coefficient is roughly quantized by the quantization parameter. The adjustment amount is, for example, a constant multiple of a color difference between a certain representative color and the color obtained by changing the representative color according to the embedding method (constant ≦ 1.0), and this constant can be changed according to the degree of deterioration. That's fine. Further, this adjustment amount is associated with the adjustment amount of the color range and the position performed by the first candidate extraction unit 13, and the size of the color range is reduced by the first candidate extraction unit 13 due to deterioration, or the position is changed. When the adjustment is performed so as to approach the representative color, the second candidate extraction unit 14 may perform the adjustment close to the representative color according to the adjustment amount in the first candidate extraction unit 13.

  Here, the description has been given of adjusting the color obtained by changing the representative color according to the embedding method within the color range indicated by the ellipse in FIG. 3B, but it is indicated by the ellipse in FIG. The color range may be regarded as a range obtained by changing the representative color according to the embedding method, and the size and position of the color range may be controlled. For example, when the extracted representative color is affected by noise or when the accuracy at the time of extraction is poor, a range in consideration of these effects may be set. In such a case, the size and position of the color range may be adjusted in the same manner as in the case of FIG.

  The color set candidates may be obtained without extracting the color set candidates in the second candidate extracting unit 14 or without extracting the color set candidates in the first candidate extracting unit 13. Alternatively, the first candidate extraction unit 13 and the second candidate extraction unit 14 may be switched from the outside or switched according to the color image to be processed, and the color set candidates may be obtained.

  The color set candidates extracted by the color set candidate extraction unit 12 are passed to the information acquisition unit 15. If no color set candidate is extracted by the color set candidate extraction unit 12, the process ends without acquiring information by the information acquisition unit 15. In this case, for example, it may be notified by displaying or sending a message that the embedded information is not acquired.

  The information acquisition unit 15 acquires information embedded in the color image from the limited color image replaced with the representative color by the replacement unit 11 and the color set candidate extracted by the color set candidate extraction unit 12. In this example, the limited color image shown in FIG. 2B and two sets of white and yellow and pink and red are received as color set candidates. Then, in the limited color image, yellow dots on white and red dots on pink are extracted, the dot arrangement is decoded, and the embedded information is acquired. The process of acquiring information from the arrangement of dots corresponds to the process of embedding information. Although details are not described here, for example, there is a method of decoding by pattern matching or the like.

  Since the colors used in the limited color image are limited to the representative colors, the representative colors of the color set candidates are clearly separated, and dots due to noise, color unevenness, etc., compared to the case where the limited color image is not used. The number of false extractions is reduced, and the embedded information is accurately acquired. Further, there are cases where the dots disappear due to the replacement with the representative color by the replacement unit 11, or the replacement with the representative color that has not been extracted as the color set candidate may occur. In such a case, countermeasures are taken into consideration by various known methods such as repeatedly arranging dots a plurality of times when embedding information, or using error correction coding, and there is no practical problem. Conversely, since information is acquired accurately, the number of information to be embedded may be increased by reducing the number of repetitions.

  As a second specific example, a case will be described in which the embedding method is an additive color mixture of blue embedding colors using dots. FIG. 5 is an explanatory diagram of a second specific example of the operation according to the embodiment of the present invention. FIG. 5A shows an example of a color image to be processed. In the color image shown in FIG. 5A, pink “H” and red rectangles are drawn on a black background, and dots representing embedding information are scattered. For convenience of illustration, the difference in color is indicated by the difference in diagonal lines. The embedded dot is a blue dot in the black area, a pink dot due to additive color mixing within the red rectangle, and a purple dot due to additive color mixing within the pink character. For convenience, both are indicated by white circles. The color image to be processed may be an image in which color unevenness, blur, or noise is mixed, and in the example shown in FIG. 5A, the red color oozes out at a portion where the diagonal line is different around the red rectangle. It shows how it is.

  The replacement unit 11 extracts a representative color from the color image to be processed shown in FIG. 5A and replaces the color in the color image with the representative color to generate a limited color image. In this example, “black” as the representative color, “peach” as the color of the letter “H”, “red” within the rectangle, “blue” as the color of the dots embedded on the ground color, etc. It shall be extracted. In the color image shown in FIG. 5A, dark red is also present around the red rectangle, and the dots in the pink and pink characters embedded by additive color mixing in the red rectangle are also present. There are various colors depending on the purple color of the dots embedded in the image, noise and uneven color, etc., but the above representative color is selected as the main color.

  A limited color in which the colors used as shown in FIG. 5B are integrated into the representative colors by replacing various colors existing in the color image shown in FIG. 5A with any of the representative colors. An image is obtained. As described above, even if noise, color unevenness, blur, or the like occurs, these will not appear in the limited color image by being replaced with the representative color. For example, a dark color portion existing around a red rectangle is replaced with the representative color black or red. Also, the blue dot that is the embedded color is unified to the representative color “blue” even if color unevenness occurs. Note that the dots in the red rectangle remain as dots in the figure, but are replaced with “pink” which is one of the representative colors. The dots inside the letter “H” are replaced with the representative color “pink” and integrated with the letter “pink”.

  Information on the extracted representative colors, that is, information on the representative colors “black”, “blue”, “red”, and “pink” in this example is passed to the color set candidate extraction unit 12. The color set candidate extraction unit 12 extracts color set candidates from these representative colors. FIG. 6 is an explanatory diagram of another example of color group candidate extraction processing. The black circles in the figure are representative colors. For convenience, FIG. 6 shows a certain two-dimensional plane in the color space, but it may be a three-dimensional or higher color space.

  First, the first candidate extraction unit 13 examines whether or not each representative color is extracted as a representative color by changing the representative color according to the embedding method, and extracts the representative colors before and after the change as color set candidates. To do. In this example, as an embedding method, it is assumed that additive color mixture is used with blue as an embedding color. Therefore, a color obtained by adding blue as the embedding color to each representative color is added to a certain color range. Asking. In FIG. 6A, a color range including a color obtained by additively mixing blue with the representative color indicated by a black circle is indicated by an ellipse. The first candidate extraction unit 13 checks whether another representative color is included in the color range indicated by the ellipse. In this example, “blue” that is another representative color is included in the color range indicated by an ellipse corresponding to “black” that is one of the representative colors. Therefore, “black” and “blue” are used as a set of color candidates.

  Note that the size and position of the color range indicated by the ellipse may be adjusted according to the degree of color degradation in the color image, as described in the case of performing subtractive color mixing as the embedding method. For example, the color range may be narrowed as the resolution of the color image is lower, or the color range may be adjusted closer to the representative color, or both may be adjusted. For example, when a color image is expanded from a compressed state, the color range may be adjusted according to the degree of compression. In JPEG or the like, the more the DCT coefficient is roughly quantized by a quantization parameter, the more the color range is Adjustment may be made by narrowing the range, bringing the color range closer to the representative color, or both.

  Next, the second candidate extraction unit 14 determines, for each representative color, which representative color the color obtained by changing the representative color according to the embedding method is replaced by the replacement unit 11, and the original representative color. A color set candidate is formed by combining the color and the replaced representative color. In this example, it is assumed that an additive color mixture is used with blue as an embedded color as an embedding method. Therefore, a color obtained by additively mixing an embedded color blue with each representative color is obtained. In FIG. 6B, a color obtained by additively mixing blue with the representative color indicated by a black circle is indicated by a cross. In the second candidate extraction unit 14, it is checked which representative color the color indicated by the cross is replaced by the replacement unit 11.

  In FIG. 6B, the color range to be replaced with each representative color is shown divided by thin lines. According to this division, it is examined which representative color is replaced by the color indicated by the x mark corresponding to each representative color. For pink and blue, the colors remain pink and blue, respectively. The color indicated by the mark is included in the pink area, and the color indicated by the x mark corresponding to black is included in the blue area. Therefore, a combination of red and pink, and black and blue is extracted as a color set candidate. Since the black and blue pairs have already been extracted by the first candidate extraction unit 13, red and pink color set candidates are added here.

  The color obtained by changing the representative color according to the embedding method may be adjusted according to the degree of color deterioration in the color image, and the color range to be adjusted is indicated by an ellipse in FIG. Yes. Alternatively, assuming that an error has occurred in the representative color, the color range including the error in the color obtained by changing the representative color according to the embedding method may be regarded as an ellipse. This adjustment of the color range is as described in the case of performing subtractive color mixing as an embedding method.

  Also in this specific example, the color set candidates may be obtained without extracting the color set candidates in the second candidate extracting unit 14 or without extracting the color set candidates in the first candidate extracting unit 13. Alternatively, the first candidate extraction unit 13 and the second candidate extraction unit 14 may be switched from the outside or switched according to the color image to be processed, and the color set candidates may be obtained.

  The color set candidates extracted by the color set candidate extraction unit 12 are passed to the information acquisition unit 15. If no color set candidate is extracted by the color set candidate extraction unit 12, the process ends without acquiring information by the information acquisition unit 15. In this case, for example, it may be notified by displaying or sending a message that the embedded information is not acquired.

  The information acquisition unit 15 acquires information embedded in the color image from the limited color image replaced with the representative color by the replacement unit 11 and the color set candidate extracted by the color set candidate extraction unit 12. In this example, the limited color image shown in FIG. 5B and two sets of black and blue and red and pink are received as color set candidates. Then, blue dots in black and pink dots in red are extracted from the limited color image, the dot arrangement is decoded, and the embedded information is acquired. The process of acquiring information from the arrangement of dots corresponds to the process of embedding information. Although details are not described here, for example, there is a method of decoding by pattern matching or the like.

  Since the colors used in the limited color image are limited to the representative colors, the representative colors of the color set candidates are clearly separated, and the influence of noise, color unevenness, and the like is eliminated. Further, there are cases where the dots disappear due to the replacement with the representative color by the replacement unit 11, or the replacement with the representative color that has not been extracted as the color set candidate may occur. In such a case, countermeasures are taken into consideration by various known methods such as repeatedly arranging dots a plurality of times when embedding information, or using error correction coding, and there is no practical problem. Conversely, since information is acquired accurately, the number of information to be embedded may be increased by reducing the number of repetitions.

  In the above specific example, the case of subtractive color mixing and the case of additive color mixing have been described as the embedding method. Of course, in the case of using these in combination and switching between subtractive and additive color mixing depending on the color used in the color image, the color set candidate and subtractive color mixture in the case of the above additive color mixing according to the switching condition, etc. In this case, color set candidates may be extracted and information embedded from the limited color image may be acquired. In addition to this, it goes without saying that color set candidates corresponding to various embedding methods may be extracted to obtain information embedded from the limited color image.

  FIG. 7 is an explanatory diagram of an example of a computer program, a storage medium storing the computer program, and a computer when the functions described in the embodiment of the present invention are realized by a computer program. In the figure, 21 is a program, 22 is a computer, 31 is a magneto-optical disk, 32 is an optical disk, 33 is a magnetic disk, 34 is a memory, 41 is a CPU, 42 is an internal memory, 43 is a reading unit, 44 is a hard disk, 45 is An interface 46 is a communication unit.

  The functions of the units described in the embodiment of the present invention described above may be realized in whole or in part by a program 21 that can be executed by a computer. In that case, the program 21 and the data used by the program may be stored in a computer-readable storage medium. The storage medium refers to the reading unit 43 provided in the hardware resource of the computer, causing a change state of energy such as magnetism, light, electricity, etc. according to the description content of the program, and corresponding signals. In this format, the description content of the program is transmitted to the reading unit 43. For example, there are a magneto-optical disk 31, an optical disk 32 (including a CD and a DVD), a magnetic disk 33, a memory 34 (including an IC card, a memory card, a flash memory, and the like). Of course, these storage media are not limited to portable types.

  The program 21 is stored in these storage media, and the program 21 is read from the computer by, for example, mounting these storage media on the reading unit 43 or the interface 45 of the computer 22, and the internal memory 42 or the hard disk 44 (magnetic disk) And the program 21 is executed by the CPU 41, the functions described in the above-described embodiment of the present invention are realized in whole or in part. Alternatively, the program 21 is transferred to the computer 22 via the communication path, and the computer 22 receives the program 21 by the communication unit 46 and stores it in the internal memory 42 or the hard disk 44, and the CPU 21 executes the program 21. May be.

  In addition, the computer 22 may be connected to various devices via an interface 45. For example, display means for displaying information, reception means for receiving information from the user, and the like may be connected. Further, for example, an image reading apparatus may be connected via the interface 45, and information may be acquired by using an image read by the image reading apparatus or an image obtained by processing the image as a color image to be processed. Further, an image forming apparatus as an output device may be connected via the interface 45.

  Of course, it may be partially configured by hardware, or all may be configured by hardware. Or you may comprise as a program which included all or one part of the function demonstrated by one Embodiment of this invention with the other structure. For example, you may comprise as one program with the program which utilizes the information embedded in the image. Of course, when applied to other purposes, it may be integrated with the program for that purpose.

  DESCRIPTION OF SYMBOLS 11 ... Replacement part, 12 ... Color set candidate extraction part, 13 ... 1st candidate extraction part, 14 ... 2nd candidate extraction part, 15 ... Information acquisition part, 21 ... Program, 22 ... Computer, 31 ... Magneto-optical disk, 32 DESCRIPTION OF SYMBOLS ... Optical disk, 33 ... Magnetic disk, 34 ... Memory, 41 ... CPU, 42 ... Internal memory, 43 ... Reading part, 44 ... Hard disk, 45 ... Interface, 46 ... Communication part.

Claims (7)

  A replacement means for changing the color in the background image according to a predetermined embedding method with a predetermined embedding color and replacing the color of the color image in which the information is embedded with a representative color obtained from the color image; A color set candidate extraction unit that extracts a set of a plurality of representative colors as a color set candidate; and an information acquisition unit that acquires information embedded from an image replaced by the replacement unit according to the color set candidate, The color set candidate extracting means extracts a set of each representative color and a set of representative colors corresponding to colors obtained when the representative color is changed according to the embedding method as an image set candidate. Processing equipment.   The embedding method is to embed information by changing the color of the background image by mixing the embedding color and the color of the background image, and the color set candidate extracting means includes each representative color and 2. A set of representative colors in a predetermined color range including a color obtained by mixing the representative color and the embedded color is extracted as a color set candidate. Image processing apparatus.   The color set candidate extraction unit further includes a representative in which the replacement unit replaces each representative color and a color in a predetermined color range including a color obtained by mixing the representative color and the embedded color. The image processing apparatus according to claim 2, wherein a set with a color is extracted as a color set candidate.   The embedding method is to embed information by changing the color of the background image by mixing the embedding color and the color of the background image, and the color set candidate extracting means includes each representative color and A set of representative colors in which the replacement means replaces a color in a predetermined color range including a color obtained when the embedded color is changed to the representative color according to the embedding method. The image processing apparatus according to claim 1, wherein: 5. The image processing apparatus according to claim 2, wherein the color set candidate extraction unit adjusts the color range according to a resolution of the color image. The color set candidate extracting unit, when the color image is compressed though the image, the color range, claim 5 be adjusted according to the degree of compression from claim 2, wherein The image processing apparatus according to item 1.   An image processing program for causing a computer to execute the function of the image processing apparatus according to any one of claims 1 to 6.

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