JP2009033443A - Image processor, and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of stably extracting auxiliary information at high speed from synthetic image information obtained by embedding additional auxiliary information in main image information at an invisible state, resulting in reduction in extraction processing time. <P>SOLUTION: The auxiliary information is extracted by recording the synthetic image information obtained by embedding the additional auxiliary information in the main image information at the invisible state on a recording medium at a visible state, further recording code information as extraction auxiliary information for assisting extraction of the auxiliary information by overlapping the code information at the invisible state to the synthetic image information recorded at the visible state, and using both of the synthetic image information including the auxiliary information recorded at the visible state and the code information as the extraction auxiliary information recorded at the invisible state in extraction processing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention, for example, embeds additional sub information (security information, etc.) in the invisible state with respect to the main image information (face image, etc.) in the visible state for analog information that is output to a recording medium. Image processing apparatus and image processing for recording generated composite image information in a visible state on a recording medium, reading the composite image information recorded on the recording medium, and extracting the sub-information from the read composite image information Regarding the method.

  In recent years, with the digitization of information and the spread of the Internet, techniques such as digital watermarks and digital signatures have come to be regarded as important in order to prevent forgery and alteration of images. In particular, a digital watermark technique for embedding additional sub-information in the main image information in an invisible state has been proposed as a measure against illegal copying, forgery, and falsification of a personal authentication medium such as an ID card or a photograph embedded with copyright information.

For example, there is a digital watermark insertion method for embedding data by using the characteristics of high spatial frequency components and color difference components that are difficult for humans to sense for image data to be output to a recorded matter, thereby removing the human classification ability. It is known (for example, refer to Patent Document 1).
Also, a digital watermark recording apparatus that can be confirmed with an optical filter is known (see, for example, Patent Document 2).

In these digital watermark embedding processing methods,
(1) Utilizing human visual characteristics
・ The gradation discrimination ability decreases as the frequency of the image increases.
-Color difference information is more difficult to distinguish than luminance information
(2) Complementary color relationship Example: Red + cyan color = achromatic color (white) (in case of additive color mixture)
(3) Applying complementary color relationship and color difference information to high frequency carrier pattern images (color difference modulation processing)
By using, it is possible to embed sub information (sub image information) in the main image information in an invisible state without causing image quality degradation.

  In the example of (2) above, red and cyan (= green + blue) are complementary colors in the case of additive color mixing, and even if red and cyan are adjacent to each other, they are discriminated by the human eye. Difficult to see and looks achromatic.

  As in the example of (3) above, by using a high-frequency carrier pattern, red-rich pixels and cyan-rich pixels are repeatedly arranged, so the human eye cannot identify these small color difference differences. The human visual characteristic that the color difference amount is determined to be plus or minus “0” is used.

  If it is necessary to determine the authenticity of a recorded material on which an image to which the above-mentioned digital watermark technology is applied is recorded, the restoration process described in the above-mentioned patent document is performed using the key information, and the invisible state The authenticity determination is performed by extracting the sub-information recorded in (1).

Specifically, first, using an image input device such as a scanner or a digital camera, composite image information in which sub-information is embedded as color difference information and recorded on a recorded matter such as a card is read as digital information. Next, by applying a digital filter having a frequency component corresponding to the specific frequency information of the key information to the composite image information, the sub-information embedded as the color difference information is restored. Finally, authenticity determination is performed from the result obtained by restoration.
Japanese Patent Laid-Open No. 9-248935 JP 2001-268346 A

  However, when the digital watermarked image information recorded on the recording medium is read and restored using the above method, the color change at the time of reading, the input range, the resolution, the position, the inclination, the background of the recording medium, etc. Restoration performance deteriorates due to the influence of. In order to obtain a better restoration extraction result, it is necessary to improve the influence factors described above, but there are many factors that cannot be controlled in consideration of the use environment. For this reason, the controllable resolution is increased and a high-resolution read image is used, but there is a problem that the extraction process takes a long time.

  Therefore, the present invention makes it possible to stably extract the sub information from the composite image information in which the sub information additional to the main image information is embedded in an invisible state, and to perform image processing that can reduce the extraction processing time. An object is to provide an apparatus and an image processing method.

  The image processing apparatus of the present invention records the composite image information created by embedding additional sub-information in the invisible state with respect to the main image information in the visible state in a visible state on the recording medium. In the image processing apparatus for reading the composite image information recorded in the image and extracting the sub-information from the read composite image information, the main image information is composed of code information expressed as a binary or multi-value gray image Composite image generation means for creating composite image information by embedding the sub information in an invisible state, extraction auxiliary information generation means for generating code information for assisting the extraction of the sub information from the composite image information, Visible information recording means for recording the composite image information generated by the composite image generating means on a recording medium using a visible material, and a code generated by the extraction auxiliary information generating means Invisible information recording means for recording information using an invisible material superimposed on the composite image information recorded by the visible information recording means, and visible information for reading the composite image information recorded on the recording medium by the visible information recording means Sub-information is extracted from the composite image information from the information reading means, the invisible information reading means for reading the code information recorded on the recording medium by the invisible information recording means, and the code information read by the invisible information reading means. Sub-information is extracted from the composite image information read by the visible information reading means by using the extraction auxiliary information restoring means for restoring the extraction auxiliary information necessary for this purpose, and the extraction auxiliary information restored by the extraction auxiliary information restoring means. Sub-information extracting means for extracting.

  Further, the image processing method of the present invention records the composite image information created by embedding additional sub information in the invisible state with respect to the main image information in the visible state in a visible state on the recording medium. Code information expressed in binary or multi-value gray image with respect to main image information in an image processing method for reading composite image information recorded on a medium and extracting the sub-information from the read composite image information A composite image generation step for generating composite image information by embedding the sub-information configured in a non-visible state, and an extraction auxiliary information generation step for generating code information for assisting the extraction of the sub information from the composite image information A visible information recording step for recording the composite image information generated in the composite image generation step on a recording medium using a visible material, and the extraction auxiliary information generation step. Recorded on the recording medium by the visible information recording step, and the invisible information recording step for recording the code information generated by the image information using the invisible material on the composite image information recorded by the visible information recording step. From the visible information reading step for reading the composite image information, the invisible information reading step for reading the code information recorded on the recording medium by the invisible information recording step, and the composite image information from the code information read by the invisible information reading step. Extraction auxiliary information restoring step for restoring extraction auxiliary information necessary for extracting sub-information from the image, and using the extraction auxiliary information restored by this extraction auxiliary information restoration step, the synthesis read by the visible information reading step A sub information extracting step of extracting sub information from the image information.

  According to the present invention, it is possible to stably extract the sub-information at high speed and stably from the composite image information in which the sub-information additional to the main image information is embedded in an invisible state, and image processing that can reduce the extraction processing time An apparatus and an image processing method can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a configuration of an image processing system to which an image processing apparatus and an image processing method according to the present invention are applied. This image processing system is roughly divided into an image input device 11 as an image input means, a printer 12 as a recording means, a computer 13 for performing various processes, and the image input device 11, the printer 12 and the computer 13 can communicate with each other. It is comprised by the bidirectional | two-way communication means 14 and 15 connected to.

  The image input device 11 inputs a multi-tone image such as a face image on the photograph (printed material) P1 as a digital image of R (red), G (green), and B (blue). It consists of a video camera and flatbed scanner. In this embodiment, for example, a scanner is used.

  The printer 12 outputs a recorded material P2 used as a personal authentication medium such as an ID card by recording a binary image such as a multi-tone image or a character on a recording medium. The printer 12 includes a visible image recording unit 12a and an invisible image recording unit 12a. An image recording unit 12b is provided, and in this embodiment, a dedicated intermediate transfer printer is used.

  The computer 13 includes a recording image processing unit 16 as a recording image processing unit that performs recording image processing such as color conversion processing on multi-gradation image information input by the image input device 11, and a recording image processing unit. A digital watermark embedding unit 17 as composite image generation means for creating composite image information by embedding sub-information in a state invisible to the human eye with respect to the multi-tone image information subjected to image processing for recording by 16; Based on the information used in the digital watermark embedding unit 17, the information is processed into information for assisting the process of extracting the sub-information from the obtained composite image information on the recording medium, and a two-dimensional barcode (hereinafter referred to as 2DBC) An extraction auxiliary information generation unit 18 as extraction auxiliary information generation means for converting the code information into code information.

  Here, the computer 13 may be, for example, a personal computer (hereinafter simply referred to as a personal computer) or a dedicated board composed of a CPU, a semiconductor memory, a hard disk device, an image capture board, and the like. In this embodiment, a personal computer is often used.

  Note that the recording image processing unit 16, the digital watermark embedding unit 17, and the extraction auxiliary information generation unit 18 in the present embodiment are configured by a part of an application program that operates on a personal computer.

  The bidirectional communication means 14 and 15 may be any means capable of bidirectionally communicating signals such as USB and SCSI. In this embodiment, USB 2.0 is used.

The overall processing operation of the image processing system configured as described above will be described below.
First, a multi-tone image such as a face image is input by the image input device 11. Here, the multi-tone image is, for example, a color face image on the photograph (printed material) P1, but is not limited thereto. The input image information is sequentially subjected to preprocessing, recording image processing, digital watermark embedding processing, extraction auxiliary information generation processing, and postprocessing, which are part of the application program, in the computer 13 and sent to the printer 12. It is done.

  That is, first, the recording image processing unit 16 performs color conversion processing on the face image input by the image input device 11. For example, image information of red, green, and blue (hereinafter referred to as R, G, and B) used in an image input system such as a digital camera is converted into cyan, magenta, and yellow (hereinafter referred to as C, M, and so on) held by a printer. Color conversion processing for converting into image information (referred to as Y) is performed. The face image thus subjected to the recording color conversion process is sent to the digital watermark embedding unit 17.

  In the digital watermark embedding unit 17, the sub information is embedded in a face image that has been subjected to the recording color conversion processing by the recording image processing unit 16 in a form that is not recognized by humans. The face image thus subjected to the digital watermark embedding process is sent to the extraction auxiliary information generation unit 18.

  Based on the information used in the digital watermark embedding process, the extraction auxiliary information generation unit 18 processes the composite image information on the recording medium into information that is the key to the process of reading the sub information by some method, and Code information converted into information such as 2DBC is generated so that the information is unknown.

  The face image subjected to the digital watermark embedding process by the digital watermark embedding unit 17 and the code information as the extraction auxiliary information generated by the extraction auxiliary information generation unit 18 are respectively sent to the printer 12. In the printer 12, the face image in which the sub-information is embedded is recorded on a recording medium with a material having transmission characteristics at the visible wavelength and transmission at the invisible wavelength, and the code information as the extraction auxiliary information is at the visible wavelength. It is recorded on the face image with a material that is transmissive and reflective at invisible wavelengths. By this recording process, a recorded material P2 such as an ID card is obtained.

Here, the digital watermark embedding process and the sub information restoration process (extraction process) will be described.
First, for the sake of simplicity, the principle of digital watermark embedding processing using digital data and sub information restoration processing will be described.

  As described in the Background Art section, in the digital watermark embedding processing technique using color difference, sub-information is embedded by adding or subtracting the color difference amount from 8-bit digital data. In addition, the process for restoring (extracting) the sub information is performed by a digital band pass filter process. The digital watermark technique for embedding the sub information as the color difference used in the present embodiment embeds the sub information by superimposing the color difference on the image of the high frequency carrier pattern. Therefore, sub information can be extracted by a band pass filter that passes only the frequency of the carrier pattern.

  As the color difference of the carrier pattern, that is, the amplitude of the carrier pattern is larger, it is easier to pass through the band-pass filter, and the recoverability is improved. In order to improve the resilience, it is necessary to increase the color difference. However, if the color difference is increased, the carrier pattern can be recognized by the human eye, and the image quality deteriorates.

Next, restoration (extraction) of sub information from a recording medium (analog data) on which digital watermarks are recorded instead of digital data will be described.
The sub information is restored from the recording medium in which the digital watermark is recorded by applying a frequency filter to the information digitized by the image acquisition means of the recording medium in which the digital watermark is embedded, as in the case of the digital data. Restore information. The restoration result is generally worse than that of digital data due to various causes.

As a factor of deterioration,
(1) Up to recording processing (color conversion, gradation processing, etc.), recording processing (area gradation conversion, etc.) to the medium recording processing,
(2) Background recording of the recording medium itself, noise such as paper fibers,
(3) Some of them are caused by an image input unit such as gradation, color reproducibility, angle, distortion, and color reproducibility when inputting an image from a recording medium.

  Considering the same restoration process, it is necessary to improve the parts (1) to (3) in order to improve the restoration property. (1) is optimized for color reproducibility according to the recording method, and (2) cannot be changed due to the characteristics of the recording medium. Therefore, at present, in order to ensure a certain degree of restoration result, the restoration process is performed by relatively increasing the amount of information by acquiring image information with an increased resolution. However, since the amount of information is large, there is a problem that it takes a long processing time.

  Therefore, in the present embodiment, the composite image information in which the additional sub-information is embedded in the invisible state with respect to the main image information is recorded in the visible state on the recording medium, and the composite image information recorded in the visible state is recorded. On the other hand, the extraction auxiliary information for assisting the extraction of the sub information is recorded in an invisible state, and in the extraction process, the composite image information including the sub information recorded in the visible state and the extraction auxiliary recorded in the invisible state are recorded. By using both pieces of information, sub-information is stably extracted at high speed.

  Hereinafter, processing up to output of recorded matter in the image processing system according to the present embodiment will be described with reference to the flowchart shown in FIG.

  First, the main image information 101 is acquired by the scanner input process 201 or the camera photographing process 202. Next, the pattern image information 102 which is sub-information embedded by the pattern image input process 203 or the pattern image creation process 204 is acquired. These processes are performed by the image input device 11.

  Next, the computer 13 generates the composite image information 103 by performing the above-described composition processing (digital watermark embedding processing) 205 using the color difference using the main image information 101 and the pattern image information 102 obtained by the above processing. To do.

  Also, by performing extraction auxiliary information generation processing 206 using the main image information 101 and / or pattern image information 102, information used for reading the composite image information on the recording medium and restoring the sub information is generated, Further, by performing encoding such as 2DBC, code information 104 as extraction auxiliary information is generated. Here, description will be made assuming that the code information 104 as extraction auxiliary information used when sub-information is restored is a frequency carrier pattern used in the synthesis process 205 and the information of the carrier pattern image is converted to 2DBC.

  Next, the composite image information 103 and the code information 104 are sent to the printer 12, and a recording process 207 is performed. At this time, the composite image information 103 is recorded by a visible image recording process 208 (visible image recording unit 12a) that records with a material that reflects at a visible wavelength and transmits at an invisible wavelength, and the code information 104 transmits at a visible wavelength. / The invisible image recording process 209 (invisible image recording unit 12b) that performs recording with a material that reflects at an invisible wavelength performs recording on the composite image information 103 recorded in the visible image recording process 208. By performing these recording processes, the recording medium 105 (recorded material P2) is obtained.

  3 and 4 show the flow of processing from reading the composite image information embedded with the digital watermark from the recording medium in the image processing system according to the present embodiment to restoring (extracting) the sub information. Explain about it.

  First, the composite image information 302 is obtained by acquiring a visible image by the visible information reading process 401 in the area where the composite image information including the sub information of the recording medium 301 (recording medium 105) is recorded. Next, an invisible image (code information) 303 as extraction auxiliary information is obtained by the invisible image reading process 402 without changing the reading position. Specifically, each image having a desired resolution can be acquired by an imaging device having four cells having sensitivity in the R, G, B and invisible bands.

  Next, information (mask image) 304 necessary for restoring the sub information is obtained from the acquired code information 303 by performing extraction according to the determined code restoration procedure by the extracted information restoration processing 403. Here, it is assumed that the restored mask image 304 is a frequency carrier pattern image in order to match the illustration in the extraction auxiliary information generation processing 206.

  Next, a difference image 305 is generated by a difference image generation process 404 using the composite image information 302 and the mask image 304 as inputs. Since a visible image and an invisible image are superimposed and recorded at the time of recording, the necessary difference image 305 can be efficiently generated without performing a search for a mask position. Since there is an extraction mask image 304 this time, the composite image 302 is masked with the extraction mask image 304. The difference image 305 is generated by this processing.

  Finally, sub information is extracted from the difference image 305 by performing sub information extraction processing 405.

  5 to 7 are schematic diagrams for explaining the sub information extraction processing 405, which will be described below.

  As described above, the digital watermark embedding method using the color difference used in the present embodiment has frequency information. As shown in FIG. 6, the period of a unit of four pixels constituted by a red pixel RS indicated by halftone dots and a cyan pixel CS indicated by diagonal lines corresponds to that. Here, 8 × 8 pixels are defined as one block, and by changing the frequency direction by 90 degrees, information of “1” and “0” is given to each block, and “1” and “0” are given from the left block. , Sub information “1” can be obtained.

A method for obtaining the sub information by actual processing will be described. First, when the mask image as shown in FIG. 5 is superimposed on the composite image information shown in FIG. 6 (the cross hatched portion Ma indicates the portion where the mask is closed, and the white portion Mb indicates the portion where the mask is open), An image as shown in FIG. 7 can be obtained. In FIG. 7, when the four horizontal pixels of the mask image in which the mask is open (white portion Mb) are viewed, the portion A in which the cyan pixels CS are continuous, the cyan pixel CS, and the red pixel RS alternate. There will be a portion B that appears in The same result as above can be obtained by calculating the color difference with the adjacent pixels and determining “0” when the continuity is large and “1” otherwise. Specifically, for example, as shown in FIG. 7, ΔE1, ΔE2, ΔE3, ΔE3, ΔE5, ΔE6, ΔE7, ΔE8,.
ΔE1 <ΔE3: 1
ΔE5> ΔE7: 0
The comparison judgment is performed.

  FIG. 8 shows a specific example of the image recording layer configuration in the printer 12 according to the present embodiment. This is an intermediate transfer image forming method in which an image is formed on a film and then transferred to paper. A visible image is formed on the film with cyan, magenta, and yellow, and the image and the medium are transferred. 2 shows a cross section of an image formed on a medium via an adhesive layer for the purpose of maintaining adhesiveness.

  Specifically, an adhesive layer 507 for ensuring adhesion between an image composed of cyan, magenta, and yellow on the medium 508 and the medium, and a yellow layer (Y, infrared) for forming an image. Transmission) 506, magenta layer (M, infrared transmission) 505, cyan layer (C, infrared transmission) 504, image receiving layer 503 serving as a basis for forming an image, and protective layer 502 for protecting the formed image from the outside. Are stacked in order, and together these constitute a recording medium 501 (recording medium 105). In this example, the adhesive layer 507 is configured to also serve as an IR (visible transmission, infrared absorption) layer, and invisible information (code information as extraction auxiliary information) is recorded in the adhesive layer 507. .

In the above embodiment, the case where a scanner or a camera is used as the main image information input unit has been described. However, the present invention is not limited to this as long as the image input unit obtains digitized data.
The main image information is a human face image, but the present invention is not limited to this.

In addition, the information included in the code information as the auxiliary extraction information is a frequency carrier pattern used at the time of generating the composite image. But there are similar effects.
In addition, the encoding of the code information as the extraction auxiliary information is 2DBC, but there is no problem with other code systems.

Further, the invisible image recording process 209 is performed after the visible image recording process 208 is performed in the recording process 207, but the effect is not changed even if this order is changed.
In addition, when reading an image from a recording medium, an invisible image reading process 402 is performed after the visible information reading process 401. However, even if this order is changed, the effect is not changed.

  In addition, as a specific method at the time of image reading, acquisition is performed with an image sensor having a cell having sensitivity in R, G, B and invisible bands, but the cell itself has broad sensitivity, and each image is captured by a light source. There is no problem even if it is obtained and combined as needed.

  Further, the specific process of the difference image generation process 404 is a mask process, but is not limited thereto. The extraction auxiliary information can be changed in any way by having the difference image processing method and the difference data.

  As described above, according to the above embodiment, the composite image information in which the additional sub-information is embedded in the invisible state with respect to the main image information is recorded in the visible state on the recording medium, and is recorded in the visible state. Code information as auxiliary extraction information for assisting the extraction of sub information is further overlapped and recorded in the invisible state with respect to the synthesized image information, and the extraction process includes a composite image including the sub information recorded in the visible state. By extracting the sub information by using both the information and the code information as the extraction auxiliary information recorded in the invisible state, the sub image is subtracted from the composite image information in which the additional sub information is embedded in the main image information in the invisible state. Information can be extracted stably at high speed, and the extraction processing time can be reduced.

Further, since the extraction auxiliary information is coded, there is another effect that the extraction auxiliary information can be generated even when a recording processing problem occurs and a part of the extraction auxiliary information is lost.
Further, since the extraction auxiliary information is coded, the extraction auxiliary information cannot be easily confirmed. Therefore, the embedding method cannot be estimated from the extraction of the sub information, and the security can be improved.

1 is a block diagram schematically showing the configuration of an image processing system to which an image processing apparatus and an image processing method according to the present invention are applied. The flowchart explaining the flow of a process until the recorded matter output of an image processing system. 7 is a flowchart for explaining a flow of processing from reading composite image information embedded with a digital watermark from a recording medium to restoring (extracting) sub-information. 6 is a flowchart for explaining a flow of processing from reading composite image information embedded with a digital watermark from a recording medium to restoring (extracting) sub-information. The enlarged view of the designation | designated area of the mask image for extraction. The enlarged view of the designated area of synthetic image information. The enlarged view of the designation | designated area of the difference image after performing a difference image generation process. FIG. 3 is a schematic diagram illustrating a specific example of an image recording layer configuration in a printer.

Explanation of symbols

  P1 ... photograph (printed matter), P2 ... recorded matter, 11 ... image input device (image input means), 12 ... printer (recording means), 12a ... visible image recording portion, 12b ... invisible image recording portion, 13 ... calculator, 14 , 15 ... bidirectional communication means, 16 ... recording image processing section (recording image processing means), 17 ... digital watermark embedding section (composite image generation means), 18 ... extraction auxiliary information generation section (output auxiliary information generation means) .

Claims (7)

The composite image information created by embedding additional sub information in the invisible state with respect to the main image information in the visible state is recorded in a visible state on the recording medium, and the composite image information recorded on the recording medium is recorded. In the image processing apparatus that reads and extracts the sub-information from the read composite image information,
Composite image generation means for creating composite image information by embedding sub-information composed of code information represented by binary or multi-value gray images in the invisible state with respect to the main image information;
Extraction auxiliary information generating means for generating code information for assisting extraction of sub-information from the composite image information;
Visible information recording means for recording the composite image information generated by the composite image generating means on a recording medium using a visible material;
Invisible information recording means for recording the code information generated by the extraction auxiliary information generating means using an invisible material superimposed on the composite image information recorded by the visible information recording means,
Visible information reading means for reading the composite image information recorded on the recording medium by the visible information recording means;
Invisible information reading means for reading code information recorded on a recording medium by the invisible information recording means;
Extraction auxiliary information restoring means for restoring extraction auxiliary information necessary for extracting sub-information from composite image information from code information read by the invisible information reading means;
Sub-information extraction means for extracting sub-information from the composite image information read by the visible information reading means using the extraction auxiliary information restored by the extraction auxiliary information restoration means;
An image processing apparatus comprising:   2. The image according to claim 1, wherein the extraction auxiliary information generated by the extraction auxiliary information generation unit is at least one of main image information and spatial frequency information required by the composite image generation unit. Processing equipment. The sub information extraction means includes
Differential image generation means for generating a differential image using the extraction auxiliary information obtained by the extraction auxiliary information restoration means from the composite image information read by the visible information reading means;
A color difference calculation means for calculating a color difference with surrounding data from the difference image generated by the difference image generation means;
The image processing apparatus according to claim 1, further comprising:   The invisible information recording unit is an intermediate transfer type image forming method in which image information is formed on an intermediate transfer medium and then the formed image information is transferred to the recording medium. Cyan, magenta, 2. An image processing apparatus according to claim 1, wherein the image processing apparatus is recorded with an adhesive used for the purpose of maintaining adhesion between an image composed of yellow and the intermediate transfer medium. The composite image information created by embedding additional sub information in the invisible state with respect to the main image information in the visible state is recorded in a visible state on the recording medium, and the composite image information recorded on the recording medium is recorded. In an image processing method of reading and extracting the sub-information from the read composite image information,
A composite image generation step of creating composite image information by embedding sub-information composed of code information represented by binary or multi-value gray images in the invisible state with respect to the main image information;
An extraction auxiliary information generation step of generating code information for assisting the extraction of sub-information from the composite image information;
A visible information recording step of recording the composite image information generated by the composite image generation step on a recording medium using a visible material;
Invisible information recording step of recording the code information generated by the extraction auxiliary information generating step by using an invisible material to be superimposed on the composite image information recorded by the visible information recording step;
A visible information reading step of reading the composite image information recorded on the recording medium by the visible information recording step;
An invisible information reading step of reading the code information recorded on the recording medium by the invisible information recording step;
From the code information read by the invisible information reading step, an extraction auxiliary information restoring step for restoring extraction auxiliary information necessary for extracting sub-information from the composite image information;
A sub-information extraction step for extracting sub-information from the composite image information read by the visible information reading step using the extraction auxiliary information restored by the extraction auxiliary information restoration step;
An image processing method comprising:   6. The image according to claim 5, wherein the extraction auxiliary information generated in the extraction auxiliary information generation step is at least one of main image information and spatial frequency information required in the composite image generation step. Processing method. The sub information extraction step includes:
A difference image generation step for generating a difference image using the extraction auxiliary information obtained by the extraction auxiliary information restoration step from the composite image information read by the visible information reading step;
A color difference calculation step for calculating a color difference with the surrounding data from the difference image generated by the difference image generation step;
6. The image processing method according to claim 5, further comprising:

Images