JP2005039603A - Method and system for electronic watermark detection, information providing system, and information providing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic watermark detection system which reduces the quantity of data transmitted from a mobile information terminal to a server while suppressing the amount of arithmetic executed in the mobile information terminal. <P>SOLUTION: The mobile information terminal is provided with a blocking part 201 for making an electronic watermark inserted image into blocks, a discrete Fourier transform part 202 for subjecting the blocks to discrete Fourier transformation, an amplitude calculation part 203 for calculating amplitudes, and an amplitude integration part 204 for integrating amplitudes among blocks. The server is provided with a scale factor detection part 205 for detecting the scale factor on the basis of an integrated amplitude, a rotation angle detection part 206 for detecting the rotation angle on the basis of the integrated amplitude and the scale factor, and a data detection part 207 for detecting data on the basis of the integrated amplitude, the scale factor, and the rotation angle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a digital watermark detection system and a digital watermark detection method for detecting a digital watermark from image data in which the digital watermark is inserted, and an information providing system and information providing method for providing information using the detected digital watermark.

  In recent years, a technique for inserting a digital watermark of image data has been developed, and information for identifying a person who has a copyright, etc., information on usage methods and conditions for permitting the use of a copyrighted work, etc. in the form of a digital watermark. Insertion into image data has been put into practical use.

  Normally, a digital watermark is inserted and detected in the form of electronic data, but a digital watermark corresponding to printing has also appeared. This makes it possible to detect a digital watermark from the printed image data even when the image data into which the digital watermark is inserted is printed.

Prior art documents related to the present invention include the following.
Japanese Patent Application Laid-Open No. 2002-259249 Although not disclosed, the applicant of the present invention has filed Japanese Patent Application No. 2002-165628 as an application related to the present invention.

  However, the digital watermark corresponding to conventional printing is premised on reading a printed matter using a scanner. Under such a premise, the scale of the read image is known in advance, and the image is never rotated. Further, since the scanner has a high resolution of about 600 dpi and 1200 dpi, it can detect a digital watermark embedded in a high frequency component. Further, unlike the case of reading with a camera, there is no case of camera shake. Further, since the image is emitted from the scanner with a constant light source, the signal-to-noise ratio and the contrast are good.

  On the other hand, in recent years, portable information terminals having a built-in camera and having an electronic mail function and a WWW (World Wide Web) browser function have become widespread. If an image with a digital watermark inserted is read by the camera of such a portable information terminal, and the image is sent from the portable information terminal as an email attachment or form information on a homepage, the WWW server detects the digital watermark. Based on this, information is retrieved from the database, and the portable information terminal can receive various services such as provision of such information from a WWW server, a mail server, or the like.

  Therefore, the advent of a digital watermark insertion method and apparatus and a digital watermark detection method and apparatus capable of detecting a digital watermark from an image read by a built-in camera or the like of a portable information terminal is desired.

  However, the scale of an image read by a built-in camera or the like of the portable information terminal is indefinite because the distance between the image and the camera is a variable factor. In addition, an image read by a built-in camera or the like of a portable information terminal is often rotated not a little because of a variation factor such as a relative rotation angle between the image and the camera. Furthermore, the resolution of the image read by the built-in camera of the portable information terminal is low. For example, the number of pixels when a 3 cm × 4 cm image is read by a 600 dpi scanner is 670,000, and the number of pixels when it is read by a 1200 dpi scanner is 2.68 million. It is clear from the fact that the number of pixels of the built-in camera of the terminal is about 300,000. Further, an image read by a built-in camera or the like of the portable information terminal may have a camera shake. Furthermore, since an image read by a built-in camera or the like of a portable information terminal is read under general external light, the signal-to-noise ratio and contrast are often insufficient.

  Therefore, the present invention has an indefinite scale, is rotated, has a low resolution, has shakes, has a poor signal-to-noise ratio, and has a poor contrast. An object of the present invention is to provide a robust digital watermark detection apparatus and method capable of stably detecting data.

  Further, if all detection of digital watermarks is performed by the server, all image data in which the digital watermarks are embedded must be transmitted. Even if the image data is compressed, the volume of the image data is large, and the communication time and communication cost are not negligible. In particular, if the user wants to receive information frequently, the total communication time is considerably long, and the total communication cost is considerable. Therefore, it is conceivable that the digital information is detected by the portable information terminal and only the detected digital watermark is transmitted to the server. However, processing for detecting a digital watermark is complicated and requires a large amount of computation. And a portable information terminal cannot perform a lot of calculations at high speed. Accordingly, it is impossible to cause the portable information terminal to perform a large amount of computation for detecting the digital watermark.

  Therefore, the present invention provides a digital watermark detection system and method capable of reducing the amount of data transmitted from the portable information terminal to the server while keeping the amount of computation performed by the portable information terminal low. With the goal.

  According to the present invention, an imaging unit that reads an image in which a digital watermark is embedded, and a first processing unit that performs a part of the processing for detecting the digital watermark from the image read by the imaging unit. And second processing means for performing the remaining part of the processing for detecting the digital watermark from the image read by the imaging means, using the processing result by the first processing means, There is provided a digital watermark detection system, wherein the imaging means and the first processing means are provided in a portable information terminal, and the second processing means is provided in a server.

  In the above-described digital watermark detection system, the first processing unit converts the image into a plurality of blocks, and converts or converts the data of each block from a spatial domain to a frequency domain. Means for obtaining the amplitude of each frequency component of each block, and means for obtaining the total amplitude for each frequency by adding the amplitude of each frequency component between the blocks, the second Processing means for detecting the enlargement / reduction ratio of the image by detecting one corresponding to a non-zero frequency component for detecting the enlargement / reduction ratio of the image in the frequency domain in the frequency domain; In the frequency domain, by detecting the sum amplitude corresponding to the non-zero frequency component for detecting the rotation angle of the image, A relative angle between the means for detecting a turning angle, and the summed amplitude in which the position in the frequency domain is corrected by the enlargement / reduction ratio and the rotation angle, and is in the first predetermined number of candidate positions. And a means for detecting an inserted digital watermark based on a combination of positions of a second predetermined number of total amplitudes smaller than the first predetermined number.

  In the above digital watermark detection system, the first processing means includes means for dividing an image into blocks, means for converting the data of each block from a spatial domain into a frequency domain, and blocks vector amplitudes of each frequency component. Means for obtaining a vector sum by performing vector addition between them, and means for obtaining an amplitude of the vector sum of each frequency component, wherein the second processing means includes: Means for detecting the enlargement / reduction ratio of the image by detecting the one corresponding to the non-zero frequency component for detecting the enlargement / reduction ratio, and detecting the rotation angle of the image in the amplitude in the frequency domain Means for detecting a rotation angle of the image by detecting a component corresponding to a non-zero frequency component, and the enlargement / reduction ratio and the rotation angle. A second predetermined number less than the first predetermined number that has a relatively large value among the corrected amplitudes in the first predetermined number of candidate positions. And a means for detecting a digital watermark inserted based on the combination of the positions of the amplitudes.

  In the above digital watermark detection system, the non-zero frequency component for detecting the enlargement / reduction ratio of the image is generated in the first radius region in the frequency region at the time of generation. The non-zero frequency component for detecting the rotation angle is generated in the region of the second radius having a predetermined proportional relationship with the first radius at the time of generation, and the first predetermined number of the frequency components are detected. The candidate position may be in one or a plurality of regions of a radius having a predetermined proportional relationship different from the first proportional relationship with the first radius.

  In the above digital watermark detection system, the non-zero frequency component for detecting the enlargement / reduction ratio of the image may also serve as the non-zero frequency component for detecting the rotation angle of the image.

  In the above digital watermark detection system, the non-zero frequency component for detecting the enlargement / reduction ratio of the image is generated in the first radius region in the frequency region at the time of generation, and the first The predetermined number of candidate positions may be in one or a plurality of regions having a radius that is in a predetermined proportional relationship with the first radius.

  In the digital watermark detection system, the first radius may correspond to an intermediate frequency in the frequency domain.

  In the above digital watermark detection system, the first processing means further comprises means for encoding the total amplitude necessary for the three detections of the total amplitude and information related thereto, and the second processing means. May further comprise means for decoding the encoded sum amplitude and information associated therewith.

  In the above digital watermark detection system, the first processing means further comprises means for encoding amplitudes necessary for the three detections of the vector sum amplitude and information related thereto, and the second processing. The means may further comprise means for decoding the encoded vector sum amplitude and associated information.

  According to a second aspect of the present invention, the above-described digital watermark detection system, means for searching for information corresponding to the detected digital watermark, and means for transmitting the searched information to the portable information terminal; An information providing system characterized by comprising:

  According to the present invention, a part of the process for detecting the digital watermark from the image read by the imaging unit is performed by the first processing unit, and the processing result of the first processing unit is used to perform the processing. The remaining portion is performed by the second processing means, the first processing means is provided in the portable information terminal, and the second processing means is provided in the server. If it is small and the data amount of the processing result by the first processing means is small, it is possible to reduce the amount of computation and computation time performed in the portable information terminal, and further reduce the amount of data transmitted from the portable information terminal to the server. Then, the server performs processing with a large amount of calculation, but such processing does not become overloaded for the server. Accordingly, when viewed as a whole, the total calculation time is only slightly increased as compared with the case where all calculations are performed by the server, and the amount of data transmitted from the portable information terminal to the server can be reduced. Further, when viewed as a whole, the total calculation time can be greatly reduced as compared with the case where all calculations are performed by the portable information terminal. Since the data amount of the processing result by the first processing means is very small, the time and cost required for transmitting the processing result from the portable information terminal to the server are very small.

  Further, according to the present invention, the enlargement / reduction ratio detection pattern is inserted into the image by the digital watermark insertion apparatus, and the enlargement / reduction ratio is corrected by using the enlargement scale ratio detection pattern by the digital watermark detection apparatus. Even if the scale is indefinite, data embedded in the form of a digital watermark can be detected stably.

  Furthermore, according to the present invention, the rotation angle detection pattern is inserted into the image by the digital watermark insertion device, and the rotation angle is corrected by using the rotation angle detection pattern by the digital watermark detection device, so that the image is rotated. However, it is possible to stably detect data embedded in the form of a digital watermark.

  Furthermore, according to the present invention, since the digital watermark is detected by the amplitude of the frequency component instead of the complex frequency component by the digital watermark detection apparatus, even if the image is shaken, the data embedded in the form of the digital watermark can be stabilized. Can be detected.

  Furthermore, according to the present invention, the second predetermined number of frequency components that are less than the first predetermined number and are non-zero in the first predetermined number of candidate positions that are combined with each other by the data, Even an image with a low signal-to-noise ratio and a low contrast can stably detect data embedded in an electronic form.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1]
FIG. 1 is a block diagram showing a configuration of a digital watermark insertion apparatus according to Embodiment 1 of the present invention.

  Referring to FIG. 1, the digital watermark insertion apparatus according to the present embodiment includes an enlargement / reduction detection pattern generation unit 101, a rotation angle detection pattern generation unit 102, a data holding unit 103, a data pattern generation unit 104, a synthesis unit 105, and an inverse. A discrete Fourier transform unit 106, a binarization unit 107, and an addition unit (or subtraction unit) 108 are provided.

  The enlargement / reduction ratio detection pattern generation unit 101 is an electronic watermark detection apparatus that generates an enlargement / reduction ratio pattern in the frequency domain for detecting the enlargement / reduction ratio of the input image.

  An example of the enlargement / reduction ratio pattern is shown in FIG. Referring to FIG. 2, the enlargement / reduction ratio detection pattern is composed of 20 points out of 24 points evenly distributed on the outermost circle of the circles shown in FIG. 2 in the frequency domain. Note that an enlargement / reduction rate detection pattern including all of the 24 points may be generated. Each point of the enlargement / reduction ratio detection pattern is a non-zero frequency component with a non-zero real part amplitude and an imaginary part amplitude of zero, and the non-zero frequency component of the enlargement / reduction ratio detection pattern is a point in the frequency domain. By adopting a symmetric distribution, an imaginary part is prevented from being generated when an inverse discrete Fourier transform is performed on the enlargement / reduction ratio detection pattern. This condition is also satisfied in a rotation angle detection pattern and a data pattern described later. In addition, the distribution in the frequency domain of the non-zero frequency components forming the enlargement / reduction ratio detection pattern is not only point-symmetric but also bilaterally symmetric and vertically symmetric. The radius of the outermost circle corresponds to an intermediate frequency when the maximum frequency in the set frequency region is set to a high frequency. This is because when the enlargement / reduction rate detection pattern is set to a high frequency, the detection accuracy is improved, but the enlargement / reduction rate detection pattern frequency does not exceed the Nyquist frequency even when an image is taken small by the camera. This is because a margin must be provided. For example, if the maximum frequency of the one-side frequency is 1024 [cycle / unit length], the radius of the outermost circle is set to a value corresponding to any frequency of 64 to 512 [cycle / unit length]. To do. Here, the unit length is the length of one side of the inverse discrete Fourier transform block.

  The rotation angle detection pattern generation unit 102 generates a rotation angle detection pattern in the frequency domain for detecting the rotation angle of the input image by the digital watermark detection apparatus.

  An example of the rotation angle detection pattern is shown in FIG. Referring to FIG. 3, the rotation angle detection pattern includes 10 out of 24 points that are evenly distributed on one inner circle of the outermost circle of the circles shown in FIG. 3 in the frequency domain. Consists of points. The rotation angle detection pattern may be composed of a number other than ten. The distribution of the non-zero frequency components forming the rotation angle detection pattern in the frequency domain is left-right asymmetric and up-down asymmetric. That is, the distribution of the non-zero frequency components forming the rotation angle detection pattern in the frequency domain is biased so that rotation can be detected. Although the circumference for setting the rotation angle detection pattern is set to the inside of the circumference for setting the enlargement / reduction ratio detection pattern, it may be set to the outside.

  The data holding unit 103 holds data to be embedded in the image in the form of a digital watermark.

  The data pattern generation unit 104 generates a data pattern corresponding to the data value held by the data holding unit.

The data pattern is obtained by adding all the patterns shown in FIGS. For the purpose of explanation, it is divided into FIGS. FIG. 4 shows a portion of the data pattern distributed on the outermost circumference, FIG. 5 shows a portion of the data pattern distributed on the center circumference, and FIG. 6 shows a data pattern on the innermost circumference. The distributed part is shown. The outermost part of the data pattern is composed of 10 points out of 20 points evenly distributed on the circumference in the frequency domain. These ten points are non-zero frequency components of equal amplitude. Of the three parts of the data pattern (the outermost part, the central circumferential part, and the innermost part), the number of non-zero frequency components forming the outermost part is unchanged, and the data to be inserted The distribution of 10 non-zero frequency components is changed according to the value of. Since the ten non-zero frequency components are distributed point-symmetrically, in practice, according to the data value, the degree of freedom to set the non-zero frequency components at five positions out of the ten candidate positions. The position of 10 points will be determined. Therefore, ₁₀ C ₅ = 252 types of data can be expressed in the outermost part. The reason why non-zero frequency components are set in five positions out of the ten candidate positions is that the number of combinations is maximized. The central circumferential portion of the data pattern is composed of 6 points out of 12 points evenly distributed on the circumference in the frequency domain. These six points are equal amplitude non-zero frequency components. Of the three parts of the data pattern (the outermost part, the central circumferential part, and the innermost circumferential part), the number of non-zero frequency components constituting the central circumferential part 6 is invariant. The distribution of the six non-zero frequency components is changed according to the value. Since the six non-zero frequency components are distributed point-symmetrically, actually, the non-zero frequency components are set at three positions among the six candidate positions in accordance with the value of the data to be inserted. The positions of six points are determined with a degree of freedom. Therefore, ₆ C ₃ = 20 types of data can be represented in the central circumferential portion. The reason why non-zero frequency components are set in three positions instead of other numbers among the six candidate positions is that the number of combinations is maximized. The innermost part of the data pattern is composed of two points out of four points that are evenly distributed on the circumference in the frequency domain. These two points are non-zero frequency components of equal amplitude. Of the three parts of the data pattern (the outermost part, the central circumferential part and the innermost part), the number 2 of non-zero frequency components forming the innermost part is invariant and should be inserted. The distribution of the two non-zero frequency components is changed according to the data value. Since the two non-zero frequency components are distributed point-symmetrically, in practice, according to the data value, there is a degree of freedom to set the non-zero frequency component at one of the two candidate positions. The positions of the two points will be determined. Therefore, ₂ C ₁ = 2 types of data can be represented by the innermost circumference.

  252 types of data can be represented in the outermost circle part, 20 types in the center part circle, and two kinds of data in the innermost circle part. By combining these, it is possible to represent 1,080 kinds of data. Become.

  Of the 18 candidate positions including the 10 candidate positions of the outermost circle part, the 6 candidate positions of the center circle part, and the 2 candidate positions of the innermost circle part The non-zero frequency component may be set at nine positions corresponding to the data value of this data. In this case, 48620 kinds of data can be represented. Further, although the types of data are reduced, the data pattern may be placed on only two or one of the three circles. Conversely, in order to increase the types of data, data patterns may be placed on more than three circles.

  Also, all the circles that set the data pattern are inside the circle that sets the enlargement / reduction ratio detection pattern and the circle that sets the rotation angle detection pattern, but some or all of the circles that set the data pattern The circle outside the circle setting the enlargement / reduction ratio detection pattern and the circle setting the rotation angle detection pattern, or between the circle setting the enlargement / reduction ratio detection pattern and the circle setting the rotation angle detection pattern It is good.

  The radii of the circle on which the enlargement / reduction ratio detection pattern rides, the circle on which the rotation angle detection pattern rides, and the three circles on which the data pattern rides are in a predetermined proportional relationship.

  The combining unit 105 combines the non-zero frequency components generated by the enlargement / reduction ratio detection pattern generation unit 101, the rotation angle detection pattern generation unit 102, and the data pattern generation unit 104. Note that the term “synthesis” here means addition.

  The inverse discrete Fourier transform unit 106 performs an inverse discrete Fourier transform on the non-zero frequency component synthesized by the synthesis unit 105 to generate a pattern in the spatial domain. The size of the pattern output from the inverse discrete Fourier transform unit 106 is determined by the number of samples handled by the inverse discrete Fourier transform, and is, for example, a size of 256 × 256 pixels, 512 × 512 pixels, 1024 × 1024 pixels, or the like. FIG. 7 shows a pattern in which such a size is repeated over the size of the original image. Note that the pattern in the spatial domain generally has a negative value pixel because the value of the direct current component of the output of the data pattern generation unit 104 is zero, but this pattern has a negative value for convenience of printing. FIG. 7 shows the result of adding an offset that eliminates pixels.

  The binarization unit 107 binarizes the pattern generated by the inverse discrete Fourier transform unit 106 into a predetermined value a or −a using zero as a threshold value. Although the binarized pattern also has a pixel of −a, an example of repeating the binarized pattern obtained by adding an offset that eliminates a negative value pixel is shown in FIG. Shown in

  The addition unit (or subtraction unit) 108 adds (or subtracts) the binarized pattern to some or all of the blue components of the original image. The blue component is selected because the blue component noise is not visually noticeable. Note that the binarization processing by the binarization unit 107 is performed because an experimental result has been shown that the accuracy of digital watermark detection in the digital watermark detection apparatus is improved. Therefore, binarization processing is not necessarily required. In this case, the adding unit (or subtracting unit) 108 multiplies the pattern output from the inverse discrete Fourier transform unit 106 by a predetermined coefficient to the original image. Add (or subtract) some or all of the blue components. Further, it is presumed to be due to the characteristics of the optical system or electrical processing system of the camera, but the pattern output by the inverse discrete Fourier transform unit 106 or a binarized pattern is also slightly added to the other components of the blue component ( (Or subtraction) in comparison with the case where the pattern output from the inverse discrete Fourier transform unit 106 or the binarized pattern is added (or subtracted) to only the blue component. Since an experimental result has been shown that the accuracy is improved, a pattern output by the inverse discrete Fourier transform unit 106 or a binarized pattern is slightly added to some or all blocks of other components of the blue component (or Subtraction).

  FIG. 9 shows an example of an original image, and FIG. 10 shows an example of an image after adding a binarized pattern to the original image shown in FIG.

  Next, the operation of the digital watermark insertion apparatus according to the present embodiment will be described with reference to FIG.

  First, the enlargement / reduction rate detection pattern generation unit 101 generates an enlargement / reduction rate detection pattern as shown in FIG. 2 (step S151). Next, the rotation angle detection pattern generation unit 102 generates a rotation angle detection pattern as shown in FIG. 3 (step S152). Next, the data pattern generation unit 104 generates a data pattern (obtained by combining the non-zero coefficients in FIGS. 4, 5, and 6) determined by the data value held by the data holding unit 103 (step S103). ). Next, the pattern synthesis unit 105 synthesizes the patterns generated by the enlargement / reduction ratio detection pattern generation unit 101, the rotation angle detection pattern generation unit 102, and the data pattern generation unit 104 (step S154). Next, the inverse discrete Fourier transform unit 106 performs inverse discrete Fourier transform on the pattern obtained by the synthesis unit 105 to generate a pattern in the spatial domain (step S155). Next, the binarization unit 107 binarizes the pattern in the spatial domain generated by the inverse discrete Fourier transform unit 106 (step S156). Finally, the adding unit (or subtracting unit) 108 adds (or subtracts) the binarized pattern to the blue component of the original image and other components as necessary (step S157). If binarization is not required, step S156 is omitted.

  The image in which the digital watermark is inserted is printed on a book, a magazine or the like and waits to be photographed by a camera or the like of a portable information terminal.

  FIG. 12 is a block diagram showing the configuration of the digital watermark detection apparatus according to Embodiment 1 of the present invention.

  Referring to FIG. 12, the digital watermark detection apparatus according to the present embodiment includes a blocking unit 201, a discrete Fourier transform unit 202, an amplitude calculation unit 203, an amplitude integration unit 204, an enlargement / reduction rate detection unit 205, a rotation angle detection unit 206, and the like. A data detection unit 207 is provided.

  The blocking unit 201 blocks the blue component of the digital watermark insertion image input by the camera of the portable information terminal. In addition, since a camera or the like shoots an image printed on a book, magazine, or the like, the digital watermark insertion image input by the camera or the like is generally compared with the digital watermark insertion image output by the digital watermark insertion device. Are shifted, enlarged or reduced, rotated, and have different contrast, brightness and saturation. As described above, when a digital watermark is inserted into other components of the blue component, the other components of the blue component are also blocked. The block is a block composed of a number of pixels equal to the number of pixels converted by the inverse discrete Fourier transform unit 106 of the digital watermark insertion apparatus. For example, a block of 256 × 256 pixels, 512 × 512 pixels, 1024 × 1024 pixels, or the like It is. Note that the number of pixels constituting the block created by the blocking unit 201 is equal to the number of pixels converted by the inverse discrete Fourier transform unit 106 of the digital watermark insertion apparatus, but the image input by the blocking unit 201 is a camera or the like. Therefore, the block created by the blocking unit 201 is generally an enlarged or reduced version of the inverse discrete Fourier transform block by the inverse discrete Fourier transform unit 106 of the digital watermark insertion apparatus.

  The discrete Fourier transform unit 202 performs discrete Fourier transform on all blocks output from the blocking unit 201 and outputs all frequency components of all blocks output from the blocking unit 201.

  The amplitude calculation unit 203 obtains the amplitude (absolute value) of a frequency component that is generally a complex number output from the discrete Fourier transform unit 202, and outputs the amplitude of all frequency components of all the blocks output from the blocking unit 201.

  Based on the amplitude of the frequency component output from the amplitude calculation unit 203, the amplitude integrating unit 204 adds the amplitude of each frequency component between all the blocks, thereby summing up each frequency as shown in FIG. Get the amplitude.

  The enlargement / reduction rate detection unit 205 detects the enlargement / reduction rate of the digital watermark insertion image taken by the camera or the like based on the total amplitude for each frequency output from the amplitude integration unit 204. The detection of the enlargement / reduction ratio is performed by detecting the radius of the enlargement / reduction ratio detection pattern. Since the enlargement / reduction ratio detection pattern is composed of a predetermined number of non-zero frequency components on the circumference of a predetermined radius, the predetermined number or a predetermined range from the predetermined number on the circumference of any radius. If a total amplitude having a particularly large amplitude is detected, the camera images the ratio of the radius and the radius of the enlargement / reduction rate detection pattern generated by the enlargement / reduction rate detection pattern generation unit 101 of the digital watermark insertion apparatus. The enlargement / reduction ratio of the digital watermark inserted image can be set.

  The rotation angle detection unit 206 detects the rotation angle of the digital watermark insertion image photographed by the camera or the like based on the total amplitude for each frequency output from the amplitude integration unit 204 and the enlargement / reduction rate output from the enlargement / reduction rate detection unit 205. To do. The rotation angle is detected by detecting the angle of the rotation angle detection pattern. First, the magnification is normalized by the enlargement / reduction ratio output by the enlargement / reduction ratio detection unit 205 with respect to the total amplitude for each frequency output by the amplitude integration unit 204, and the total amplitude corresponding to the rotation angle detection pattern is obtained. Appear at a predetermined radius. Then, among the total amplitude appearing at a predetermined radius, a pattern constituted by a total amplitude having a particularly large amplitude is detected, and the angle of the pattern and the rotation angle detection generated by the rotation angle detection pattern generation unit 102 of the digital watermark insertion device are detected. By detecting the difference in the angle of the pattern for use, the rotation angle of the digital watermark inserted image taken by the camera or the like is detected.

  Note that the enlargement / reduction ratio detection pattern may also serve as the rotation angle detection pattern by making the distribution of the non-zero frequency components of the enlargement / reduction ratio detection pattern asymmetric. In this case, the enlargement / reduction ratio is detected by detecting the radius of the enlargement / reduction ratio detection / rotation angle detection pattern. Since the enlargement / reduction ratio detection / rotation angle detection pattern is composed of a predetermined number of non-zero frequency components on the circumference of a predetermined radius, the predetermined number or the predetermined number on the circumference of any radius. If a total amplitude having a particularly large amplitude within a certain range is detected, the radius and the detection of the enlargement / reduction rate detection / rotation angle detection pattern generated by the enlargement / reduction rate detection pattern generation unit 101 of the digital watermark insertion apparatus are detected. The ratio of the radii is defined as the enlargement / reduction ratio of the digital watermark inserted image captured by the camera. The rotation angle is detected by detecting the angle of the enlargement / reduction ratio detection / rotation angle detection pattern. First, the magnification is normalized by the enlargement / reduction ratio output by the enlargement / reduction ratio detection unit 205 with respect to the total amplitude for each frequency output by the amplitude integrating unit 204, and the pattern for enlargement / reduction ratio detection / rotation angle detection is obtained. The corresponding total amplitude appears at a predetermined radius. Then, by detecting a pattern constituted by a summed amplitude having a particularly large amplitude among the summed amplitudes appearing at a predetermined radius, and detecting a difference between the angle of the pattern and the angle of the enlargement / reduction ratio detection / rotation angle detection pattern The rotation angle of the digital watermark inserted image taken by the camera or the like is detected.

  The data detection unit 207 is photographed by a camera or the like based on the total amplitude for each frequency output from the amplitude integration unit 204, the enlargement / reduction ratio output from the enlargement / reduction rate detection unit 205, and the rotation angle output from the rotation angle detection unit 206. Data embedded in the form of a digital watermark is detected from the inserted digital watermark image. Data is detected by detecting a data pattern. First, the magnification is normalized by the enlargement / reduction ratio output by the enlargement / reduction ratio detection unit 205 with respect to the total amplitude for each frequency output by the amplitude integrating unit 204, and the rotation angle output by the rotation angle detection unit 206 is used. The rotation is corrected so that the total amplitude corresponding to the data pattern appears at a candidate position with a predetermined radius. Then, the summed amplitude after correction of the enlargement / reduction ratio and the rotation angle is passed through a filter that passes frequency components only at the candidate positions. Then, the total amplitude of the filter output for each radius of the three radii is compared with a common threshold value that changes from a high value to a low value, and the total amplitude whose value exceeds the threshold value is a predetermined number ( Of the three parts of the data pattern, when the outermost part is reached, 5 if it is a part on the center circumference, and 3 if it is the innermost part, the threshold value change is reached. Stop (see FIG. 14). At this time, the value of data embedded in the form of a digital watermark is detected from the pattern formed by the total amplitude exceeding the threshold.

  Since the pattern has only a real part in the frequency domain and is distributed point-symmetrically, the enlargement / reduction ratio detection unit 205, the rotation angle detection unit 206, and the data detection unit 207 are arranged in the first quadrant of the frequency domain. Detection may be performed using frequency components of only two quadrants among the frequency components of four quadrants.

  Next, the operation of the digital watermark detection apparatus according to the present embodiment will be described with reference to FIG.

  First, the blocking unit 201 blocks the blue component of the digital watermark insertion image photographed by the camera or the like and other color components as necessary (step S251). Next, the discrete Fourier transform unit 202 performs a discrete Fourier transform on each block generated by the blocking unit 201 (step S252). Next, the amplitude calculation unit 203 obtains the amplitude of each complex frequency component output from the discrete Fourier transform unit 202 (step S253). Next, the amplitude integrating unit 204 integrates the amplitude output by the amplitude calculating unit 203 for each frequency between blocks, and obtains a total amplitude for each frequency (step 254). Next, the enlargement / reduction rate detection unit 205 obtains the enlargement / reduction rate of the digital watermark inserted image photographed by the camera or the like based on the total amplitude for each frequency output from the amplitude integration unit 204 (step S255). Next, the rotation angle detection unit 206 rotates the digital watermark insertion image captured by the camera or the like based on the total amplitude for each frequency output from the amplitude integration unit 204 and the enlargement / reduction rate output from the enlargement / reduction rate detection unit 205. A corner is obtained (step S256). Finally, the data detection unit 207 performs digital watermarking based on the total amplitude for each frequency output from the amplitude integration unit 204, the enlargement / reduction rate output from the enlargement / reduction rate detection unit 205, and the rotation angle output from the rotation angle detection unit 206. The data embedded in the form is detected (step S257).

[Embodiment 2]
Since the digital watermark insertion apparatus and operation of the second embodiment are the same as those of the first embodiment, description thereof is omitted.

  FIG. 16 is a block diagram showing a configuration of a digital watermark detection apparatus according to Embodiment 2 of the present invention.

  As is apparent from a comparison of FIG. 16 with FIG. 12, the digital watermark detection apparatus according to the second embodiment is compared with the digital watermark detection apparatus according to the first embodiment. In contrast to the latter stage of the amplitude calculation unit 203, in the digital watermark detection apparatus according to the second embodiment, the amplitude integration unit 204 is replaced with the frequency component integration unit 303, and the frequency component integration unit 303 is located before the amplitude calculation unit 304. Is different. The other parts of the digital watermark detection apparatus according to the second embodiment and their operations are the same as those of the first embodiment, and a description thereof will be omitted.

  The frequency component accumulating unit 303 adds the frequency components expressed by complex numbers output from the Fourier transform unit 202 between the blocks for each frequency.

  The amplitude calculation unit 304 obtains the amplitude of the frequency component represented by the complex number output from the frequency component integration unit 303.

  According to the configuration of the second embodiment, the pattern inserted into the image by the digital watermark insertion apparatus has the same phase in the frequency domain in all blocks, whereas the frequency components of the image are random in phase. This makes it possible to increase the signal-to-noise ratio when the frequency component of the pattern is regarded as a signal and the frequency component of the image is regarded as noise.

  Next, the operation of the digital watermark detection apparatus according to the present embodiment will be described with reference to FIG.

  As is clear from comparing FIG. 17 with FIG. 15, the operation of the digital watermark detection apparatus according to the second embodiment is compared with the operation of the digital watermark detection apparatus according to the first embodiment, and steps S252 and S253 are omitted. , Steps S353 and S354 are added. In step S353, the frequency component 303 vector-adds the frequency component represented by the complex number output from the Fourier transform unit 202 between the blocks for each frequency. In step S354, the amplitude calculation unit 304 includes the frequency component integration unit 303. The amplitude of the frequency component represented by the complex number to be output is obtained.

[Embodiment 3]
In the first and second embodiments, the digital watermark is detected by the digital watermark detection apparatus. Then, it is assumed that the digital watermark detection apparatus is mounted on one computer such as a server.

  On the other hand, in the third embodiment, the digital watermark detection apparatus is divided into two processing units. And a 1st process part is mounted in a portable information terminal, and a 2nd process part is mounted in computers, such as a server. The two processing units constitute a digital watermark detection system.

  The first processing unit performs processing with a small amount of calculation, reduces the data amount, and transmits the reduced data to the second processing unit. The second processing unit detects a digital watermark by performing processing with a large amount of calculation using the data received from the first processing unit.

  FIG. 18 is a block diagram showing a configuration of a portable information terminal according to Embodiment 3 of the present invention. Referring to FIG. 18, the portable information terminal according to the third embodiment includes an imaging unit 401, an image encoding unit 402, an image decoding unit 403, a blocking unit 201, a discrete Fourier transform unit 202, an amplitude calculation unit 203, and an amplitude integration unit. 204, a point candidate encoding unit 411, an information receiving unit 416, and an information using unit 417.

  FIG. 19 is a block diagram showing a configuration of a server according to Embodiment 3 of the present invention. Referring to FIG. 19, the server according to the third embodiment includes a point candidate decoding unit 412, an enlargement / reduction rate detection unit 205, a rotation angle detection unit 206, a data detection unit 207, a database 413, an information search unit 414, and an information transmission unit 415. Is provided.

  The first processing unit includes an imaging unit 401, a blocking unit 201, a discrete Fourier transform unit 202, an amplitude calculation unit 203, an amplitude integration unit 204, and a point candidate encoding unit 411 shown in FIG. Further, the first processing unit may include an image encoding unit 402 and an image decoding unit 403.

  In the second processing unit, the point candidate decoding unit 412, the enlargement / reduction rate detection unit 205, the rotation angle detection unit 206, and the data detection unit 207 illustrated in FIG. 19 include the second processing unit.

  The information providing system includes a digital watermark detection system including a first processing unit and a second processing unit, an information search unit 413 and an information transmission unit 414 shown in FIG. 19, and an information reception unit 415 and an information use unit 416 shown in FIG. Is provided.

  Returning to FIG. 18, the blocking unit 201, discrete Fourier transform unit 202, amplitude calculation unit 203, and amplitude integration unit 204 are the same as those in the first embodiment, and thus description thereof is omitted.

  The imaging unit 401 is a CCD camera, a CMOS camera, or the like, and captures an image. The image encoding unit 402 compresses and encodes the image captured by the imaging unit 401 according to, for example, the JPEG format. The compressed and encoded image data is stored in a storage unit or a memory card of the portable information terminal. The image decoding unit 403 decodes the stored compressed image data. Note that the image encoding unit 402 and the image decoding unit 403 are not necessary if the blocking unit 201 can directly input data of an image captured by the imaging unit 401. Further, the image encoding unit 402 and the image decoding unit 403 are not necessary even when the image data captured by the imaging unit 401 is stored in a storage unit or a memory card without being compressed.

  The point candidate encoding unit 411 encodes the point candidate as follows based on the integrated amplitude for each frequency output from the amplitude integrating unit 204. Here, the point candidates are the points of the enlargement / reduction rate detection pattern, the rotation angle detection pattern point, and the data pattern point in the enlargement / reduction rate detection unit 205, the rotation angle detection unit 206, and the data detection unit 207, respectively. It is a candidate point.

  A window having a size of 5 × 5 shown in FIG. 20 is applied to the integrated amplitude of each frequency while shifting the frequency by one frequency in the horizontal direction and the vertical direction. The accumulated amplitude of interest is the accumulated amplitude at the position indicated by reference numeral 13 in FIG. The maximum amplitude of the integrated amplitudes of Nos. 7, 8, 9, 12, 14, 17, 18, and 19 adjacent to the integrated amplitude at the position indicated by No. 13 is obtained, and the integrated amplitude of No. 13 is larger than this maximum amplitude. In this case, it is assumed that the integrated amplitude currently focused on is a point candidate. If it is determined that the current integrated amplitude is a point candidate, the X coordinate, the Y coordinate, the integrated amplitude of the point candidate, and the integrated amplitude that is currently focused on and the average value of the second adjacent integrated amplitude Find the difference. Here, the difference between the integrated amplitude currently focused on and the average value of the second adjacent integrated amplitudes is more specifically, from the integrated amplitude of No. 13 to Nos. 1 to 5, 6, 10, 11, It is the difference obtained by subtracting the average value of accumulated amplitudes of 15, 16, 20-25.

  When the above processing is repeated for all the accumulated amplitudes, the X coordinates, Y coordinates, accumulated amplitudes, and the differences of all point candidates are compressed and encoded in, for example, the ZIP format, the LHA format, or the like.

  Referring to FIG. 19, the point candidate decoding unit 412 decodes the compression code created by the point candidate encoding unit 411 and obtains the X coordinate, Y coordinate, integrated amplitude, and the difference of all point candidates.

  The enlargement / reduction ratio detection unit 205, rotation angle detection unit 206, and data detection unit 207 are the same as those in the first embodiment, and conceptually perform the same processing as in the first embodiment. The detection using the X coordinate, the Y coordinate, the accumulated amplitude, and the above difference of all point candidates obtained by the decoding unit 412 will be described more specifically.

  The enlargement / reduction ratio detection unit 205 uses the X coordinates, Y coordinates, and integrated amplitudes of all point candidates to shift the radius of the circle from the maximum radius to the minimum radius, and the number of point candidates that ride on the circle of each radius. Is a predetermined number or a certain range from the predetermined number, and the enlargement / reduction ratio is obtained from the radius of the circle that satisfies such a condition.

  The rotation angle detection unit 206 includes the above-described integrated amplitude among the point candidates that ride on a circle that should have a rotation angle detection pattern in coordinates whose size is normalized by the enlargement / reduction rate detected by the enlargement / reduction rate detection unit 205. Predetermined predetermined number of point candidates having a large sum obtained as a result of adding the differences are points constituting the angle detection pattern, and the rotation angle is obtained from these points.

  The data detection unit 207 normalizes the size based on the enlargement / reduction ratio detected by the enlargement / reduction rate detection unit 205 and corrects the data pattern at the coordinates whose angle is corrected by the rotation angle detected by the rotation angle detection unit 206. The sum obtained by adding the above difference to the accumulated amplitude is calculated for point candidates at positions where the constituent points should be, and a predetermined number of upper point candidates having a large sum are points constituting the data pattern. The data is detected from these points.

  The database 413 stores detection data and information corresponding thereto in association with each other. The information corresponding to the detection data is, for example, a homepage URL (Uniform Resource Locator), image data, audio data, text data, and the like. The information search unit 414 searches the database 413 for information corresponding to the detection data detected by the data detection unit 207 from the digital watermark. The information transmission unit 415 transmits the information searched by the information search unit 414 to the portable information terminal.

  Returning to FIG. 18, the information receiving unit 416 receives information transmitted from the server. The information using unit 417 uses the information received by the information receiving unit 416. For example, when the information is a URL, the information using unit 417 accesses a home page having the URL via the Internet. For example, if the information is image data, the information utilization unit 417 displays the image data on the screen. If the information is audio data, the information utilization unit 417 outputs the audio data from the speaker. If it is data, the text data is displayed on the screen.

[Embodiment 4]
The third embodiment is configured based on the first embodiment. In contrast, the fourth embodiment is configured based on the second embodiment.

  FIG. 21 is a block diagram showing a configuration of a portable information terminal according to Embodiment 4 of the present invention. As is clear when FIG. 21 is compared with FIG. 18, the portable information terminal according to the fourth embodiment is different from the portable information terminal according to the third embodiment in that the amplitude calculation unit 203 and the amplitude integration unit 204 are the frequency component integration unit 303 and the amplitude. Only the points replaced by the calculation unit 304 are different, and the other parts are the same. Since the frequency component integrating unit 303 and the amplitude calculating unit 304 are the same as those of the second embodiment, description thereof will be omitted.

  The server according to the fourth embodiment of the present invention is the same as that of the third embodiment shown in FIG.

[Embodiment 5]
In Embodiments 1 to 4, a discrete cosine transform or a discrete sine transform may be used instead of the discrete Fourier transform. In this case, a pattern is set in only one quadrant.

  1, 12, 16, 18, 19, and 21 (except for the imaging unit 401 and the database 413), the computer reads and executes a program for causing the computer to function as these parts. The steps shown in FIGS. 11, 15 and 17 can also be realized by the computer reading and executing a program for causing the computer to execute these steps.

  The present invention can be used for digital watermark detection.

It is a block diagram which shows the structure of the digital watermark insertion apparatus by Embodiment 1 of this invention. It is a figure which shows the example of the pattern for the expansion / contraction rate detection by Embodiment 1 of this invention. It is a figure which shows the example of the pattern for rotation angle detection by Embodiment 1 of this invention. It is a figure which shows the 1st part of the example of the data pattern by Embodiment 1 of this invention. It is a figure which shows the 2nd part of the example of the data pattern by Embodiment 1 of this invention. It is a figure which shows the 3rd part of the example of the data pattern by Embodiment 1 of this invention. It is a figure which shows the example of the pattern which the inverse Fourier transform part of the digital watermark detection apparatus by Embodiment 1 of this invention outputs. It is a figure which shows the example of the binarization pattern which the binarization part of the digital watermark detection apparatus by Embodiment 1 of this invention outputs. It is a figure which shows the example of an original image. FIG. 10 is a diagram illustrating a digital watermark inserted into the original image illustrated in FIG. 9 by the digital watermark insertion apparatus according to the first embodiment of the present invention. It is a flowchart which shows operation | movement of the digital watermark insertion apparatus by Embodiment 1 of this invention. It is a block diagram which shows the structure of the digital watermark detection apparatus by Embodiment 1 of this invention. It is a figure which shows the example of distribution of the sum total amplitude which the amplitude integration part of the digital watermark detection apparatus by Embodiment 1 of this invention outputs. It is a figure for demonstrating operation | movement of the data detection part of the digital watermark detection apparatus by Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the digital watermark detection apparatus by Embodiment 1 of this invention. It is a block diagram which shows the structure of the digital watermark detection apparatus by Embodiment 2 of this invention. It is a flowchart which shows operation | movement of the digital watermark detection apparatus by Embodiment 2 of this invention. It is a block diagram which shows the structure of the portable information terminal by Embodiment 3 of this invention. It is a block diagram which shows the structure of the server by Embodiment 3 of this invention. It is a figure for demonstrating point candidate extraction by Embodiment 3 of this invention. It is a block diagram which shows the structure of the portable information terminal by Embodiment 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Enlargement / reduction ratio detection pattern generation part 102 Rotation angle detection pattern generation part 103 Data holding part 104 Data pattern generation part 105 Synthesis | combination part 106 Inverse discrete Fourier transform part 107 Binarization part 108 Addition part (subtraction part)
201 Blocking Unit 202 Discrete Fourier Transform Unit 203 Amplitude Calculation Unit 204 Amplitude Integration Unit 205 Enlargement / Reduction Ratio Detection Unit 206 Rotation Angle Detection Unit 207 Data Detection Unit 303 Frequency Component Integration Unit 304 Amplitude Calculation Unit 401 Imaging Unit 402 Image Coding Unit 403 Image decoding unit 411 Amplitude encoding unit 412 Amplitude decoding unit 413 Database 414 Information search unit 415 Information transmission unit 416 Information reception unit 417 Information utilization unit

Claims (21)

An imaging means for reading an image in which a digital watermark is embedded;
First processing means for performing a part of processing for detecting the digital watermark from the image read by the imaging means;
Second processing means for performing the remaining part of the processing for detecting the digital watermark from the image read by the imaging means using the processing result by the first processing means;
With
The imaging means and the first processing means are provided in a portable information terminal,
The digital watermark detection system, wherein the second processing means is provided in a server. The digital watermark detection system according to claim 1,
The first processing means includes
Means for dividing the image into a plurality of blocks;
Means for obtaining the amplitude of each frequency component of each block by transforming the data of each block from the spatial domain to the frequency domain, or after the transformation;
Means for obtaining a total amplitude for each frequency by adding the amplitude of each frequency component between blocks;
With
The second processing means includes
Means for detecting the enlargement / reduction ratio of the image by detecting one corresponding to a non-zero frequency component for detecting the enlargement / reduction ratio of the image in the frequency domain in the frequency domain;
Means for detecting the rotation angle of the image by detecting one corresponding to a non-zero frequency component for detecting the rotation angle of the image in the frequency domain in the frequency domain;
The first amplitude indicating a relatively large value among the summed amplitudes whose positions in the frequency domain are corrected by the enlargement / reduction ratio and the rotation angle and among the first predetermined number of candidate positions. Means for detecting an inserted digital watermark based on a combination of positions of a second predetermined number of total amplitudes less than a predetermined number of
An electronic watermark detection system comprising: The digital watermark detection system according to claim 1,
The first processing means includes
Means for dividing the image into blocks;
Means for transforming the data of each block from the spatial domain to the frequency domain;
Means for adding a vector amplitude of each frequency component between blocks to obtain a vector sum;
Means for obtaining the amplitude of the vector sum of each frequency component;
With
The second processing means includes
Means for detecting an enlargement / reduction ratio of the image by detecting one corresponding to a non-zero frequency component for detecting the enlargement / reduction ratio of the image in the frequency domain;
Means for detecting the rotation angle of the image in the frequency domain by detecting the amplitude corresponding to a non-zero frequency component for detecting the rotation angle of the image;
Of the amplitudes whose positions in the frequency domain have been corrected by the enlargement / reduction ratio and the rotation angle and being in the first predetermined number of candidate positions, the first value indicating a relatively large value therebetween Means for detecting a digital watermark inserted based on a combination of positions of a second predetermined number of amplitudes less than the predetermined number;
An electronic watermark detection system comprising: The digital watermark detection system according to claim 2 or 3,
The non-zero frequency component for detecting the enlargement / reduction ratio of the image is generated in the region of the first radius in the frequency region at the time of generation,
The non-zero frequency component for detecting the rotation angle of the image is generated in a region of a second radius having a predetermined proportional relationship with the first radius at the time of generation,
The first predetermined number of candidate positions are in one or more regions of a radius having a predetermined proportional relationship different from the first proportional relationship to the first radius. Detection system. The digital watermark detection system according to claim 2 or 3,
The digital watermark detection system, wherein the non-zero frequency component for detecting the enlargement / reduction ratio of the image also serves as a non-zero frequency component for detecting the rotation angle of the image. The digital watermark detection system according to claim 5, wherein
The non-zero frequency component for detecting the enlargement / reduction ratio of the image is generated in the first radius region in the frequency region at the time of generation,
The digital watermark detection system according to claim 1, wherein the first predetermined number of candidate positions are in one or a plurality of regions having a radius in a predetermined proportional relationship with the first radius. The digital watermark detection system according to claim 4 or 6,
The digital watermark detection system according to claim 1, wherein the first radius corresponds to an intermediate frequency in the frequency domain. The digital watermark detection system according to claim 2,
The first processing means further comprises means for encoding a total amplitude required for the three detections of the total amplitude and information related thereto,
The digital watermark detection system according to claim 2, wherein the second processing means further comprises means for decoding the encoded total amplitude and information related thereto. The digital watermark detection system according to claim 3.
The first processing means further comprises means for encoding amplitudes necessary for the detection of the three vector amplitudes and information related thereto,
The digital watermark detection system, wherein the second processing means further comprises means for decoding the amplitude of the encoded vector sum and related information. The digital watermark detection system according to any one of claims 1 to 9,
Means for retrieving information corresponding to the detected digital watermark;
Means for transmitting the retrieved information to the portable information terminal;
An information providing system comprising: An imaging step of reading an image with an embedded digital watermark;
A first processing step for performing a part of processing for detecting the digital watermark from the image read by the imaging step;
A second processing step for performing the remaining part of the processing for detecting the digital watermark from the image read by the imaging step using the processing result of the first processing step;
With
The imaging step and the first processing step are performed by a portable information terminal,
The digital watermark detection method, wherein the second processing step is performed by a server. The digital watermark detection method according to claim 11.
The first processing step includes:
Dividing the image into a plurality of blocks;
Obtaining the amplitude of each frequency component of each block by transforming the data of each block from the spatial domain to the frequency domain, or after the transformation,
Adding the amplitude of each frequency component between blocks to obtain a total amplitude for each frequency;
With
The second processing step includes
Detecting the enlargement / reduction ratio of the image in the frequency domain by detecting one corresponding to a non-zero frequency component for detecting the enlargement / reduction ratio of the image among the total amplitude;
Detecting the rotation angle of the image by detecting one corresponding to a non-zero frequency component for detecting the rotation angle of the image in the frequency domain,
The first amplitude indicating a relatively large value among the summed amplitudes whose positions in the frequency domain are corrected by the enlargement / reduction ratio and the rotation angle and among the first predetermined number of candidate positions. Detecting an inserted watermark based on a combination of positions of a second predetermined number of total amplitudes less than a predetermined number of
An electronic watermark detection method comprising: The digital watermark detection method according to claim 11.
The first processing step includes:
Dividing the image into blocks;
Transforming the data of each said block from the spatial domain to the frequency domain;
Vector addition of the vector amplitude of each frequency component between blocks to obtain a vector sum;
Obtaining the amplitude of the vector sum of each frequency component;
With
The second processing step includes
Detecting the scaling ratio of the image by detecting the amplitude corresponding to a non-zero frequency component for detecting the scaling ratio of the image in the frequency domain;
Detecting the rotation angle of the image in the frequency domain by detecting the amplitude corresponding to a non-zero frequency component for detecting the rotation angle of the image;
Of the amplitudes whose positions in the frequency domain have been corrected by the enlargement / reduction ratio and the rotation angle and being in the first predetermined number of candidate positions, the first value indicating a relatively large value therebetween Detecting a watermark inserted based on a combination of positions of a second predetermined number of amplitudes less than the predetermined number;
An electronic watermark detection method comprising: The digital watermark detection method according to claim 12 or 13,
The non-zero frequency component for detecting the enlargement / reduction ratio of the image is generated in the region of the first radius in the frequency region at the time of generation,
The non-zero frequency component for detecting the rotation angle of the image is generated in a region of a second radius having a predetermined proportional relationship with the first radius at the time of generation,
The first predetermined number of candidate positions are in one or more regions of a radius having a predetermined proportional relationship different from the first proportional relationship to the first radius. Detection method. The digital watermark detection method according to claim 12 or 13,
A digital watermark detection method, wherein a non-zero frequency component for detecting an enlargement / reduction ratio of the image also serves as a non-zero frequency component for detecting a rotation angle of the image. The digital watermark detection method according to claim 15, wherein
The non-zero frequency component for detecting the enlargement / reduction ratio of the image is generated in the first radius region in the frequency region at the time of generation,
The digital watermark detection method according to claim 1, wherein the first predetermined number of candidate positions are in one or a plurality of regions having a radius that is in a predetermined proportional relationship with the first radius. The digital watermark detection method according to claim 14 or 16,
The digital watermark detection method according to claim 1, wherein the first radius corresponds to an intermediate frequency in the frequency domain. The digital watermark detection method according to claim 12, wherein
The first processing step further comprises a step of encoding a total amplitude required for the three detections of the total amplitude and information related thereto,
The digital watermark detection method according to claim 2, wherein the second processing step further comprises a step of decoding the encoded total amplitude and information related thereto. The digital watermark detection method according to claim 13,
The first processing step further includes a step of encoding amplitudes necessary for detection of the three of the vector sum amplitudes and information related thereto,
The digital watermark detection method according to claim 2, wherein the second processing step further comprises a step of decoding the encoded vector sum amplitude and information related thereto. The digital watermark detection method according to any one of claims 11 to 19,
Searching for information corresponding to the detected digital watermark;
Transmitting the retrieved information to the portable information terminal;
An information providing method comprising:   A program for causing a computer to perform the method according to any one of claims 11 to 20.