JP2007166227A - Apparatus, method and program for image processing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of improving a compression rate of an original image having embedded control information. <P>SOLUTION: The apparatus has a separation section 3 for separately extracting control information from a synthesized image in which an original image is synthesized with control information for controlling duplication of the original image; a compression section 4 for compressing the original image data from which the control image is extracted; and a storage section 12 for storing the compressed original image data. As described above, since the control information is separated from the synthesized image in which the original image is synthesized with the control information and only the original image data are compressed, the compression rate of the original image can be improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for preventing unauthorized copying of a document image.

  In recent years, copying of documents has become extremely simple due to the widespread use of image processing apparatuses having a copying function, such as personal computers, printers, and copying machines. In such a situation, a manuscript to which copyright has been granted, or a manuscript that prohibits unauthorized duplication such as “copy prohibited”, “restrict copying”, “confidential”, etc. (hereinafter collectively referred to as “confidential manuscript”) There is a drawback that copying is easily performed. In other words, it is a manuscript image containing character strings, figures, tables, graphs, etc., and it is necessary to prevent leakage of important information. The leakage of important information (confidential content) has become a problem. Therefore, it is necessary for an image processing apparatus having a copying function to have a function of preventing the abused copying of confidential documents.

  For example, in Patent Document 1, copying prohibition information (whether copying is prohibited), copying permission condition information (information for permitting copying when the conditions are met), latent image information (a latent image that floats when copied) In this technology, additional information such as information) is recorded as a background copy-forgery-inhibited pattern pattern of image data, and a user who can copy is restricted.

JP 2003-280469 A

  However, control information recorded as a background tint pattern is generally embedded on the entire surface of the paper in order to increase the recognition rate. For this reason, when compressing a document in which control information is embedded, the compression rate does not increase as compared with a normal document, and more memory is required.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an image processing apparatus, an image processing method, and an image processing program capable of increasing the compression rate of a document image in which control information is embedded.

In order to achieve such an object, the image processing apparatus of the present invention includes a separating unit that separates and extracts the control information from a composite image obtained by combining the original image and the control information for controlling reproduction of the original image, The apparatus includes a compression unit that compresses original image data from which the control information has been extracted, and a storage unit that stores the compressed original image data.
As described above, according to the present invention, the control information is separated from the synthesized image obtained by synthesizing the original image and the control information, and only the original image data is compressed. Therefore, the compression rate of the original image data can be increased. Therefore, it is not necessary to use a large capacity storage means for storing image data.

The image processing apparatus may include storage control means for associating the control information with the compressed original image data and storing them in the storage means.
Therefore, the control information embedded in the original image data can be easily recognized.

  In the image processing apparatus, decompression means for reading and decompressing the compressed image data from the storage means, encoding means for encoding the control information, and the control information encoded in the decompressed image data It is preferable to have superimposing means for superimposing and forming means for forming an image of the image data on which the control information is superimposed.

The image processing method of the present invention includes a separation step of separating and extracting the control information from a combined image obtained by combining the original image and control information for controlling the reproduction of the original image, and the original image from which the control information has been extracted. And a storing step for storing the compressed original image data.
According to the present invention, since the control information is separated from the synthesized image obtained by synthesizing the original image and the control information and only the original image data is compressed, the compression rate of the original image data can be increased. Therefore, it is not necessary to use a large capacity storage means for storing image data.

The image processing method may include a storage control step of storing the control information and the compressed original image data in the storage step in association with each other.
As a result, the control information embedded in the original image data can be easily recognized.

In the image processing method, a decompression step for reading and decompressing the compressed image data from the storing step, an encoding step for encoding the control information, and the control information encoded in the decompressed image data And a forming step of forming an image of the image data on which the control information is superimposed.
As a result, the same image data can be easily output even when the original image is output again.

An image processing program according to the present invention includes a separation step of separating and extracting the control information from a combined image obtained by combining the original image and control information for controlling reproduction of the original image, and the original image from which the control information has been extracted. And a storage step for storing the compressed original image data are executed by a computer.
According to the present invention, since the control information is separated from the synthesized image obtained by synthesizing the original image and the control information and only the original image data is compressed, the compression rate of the original image data can be increased. Therefore, it is not necessary to use a large capacity storage means for storing image data.

The image processing program may further include a storage control step for storing the control information and the compressed original image data in the storage step in association with each other.
As a result, the control information embedded in the original image data can be easily recognized.

In the image processing program, a decompression step for reading and decompressing the compressed image data from the storing step, an encoding step for encoding the control information, and the control information encoded in the decompressed image data It is preferable to further include a superimposing step for superimposing and a forming step for forming an image of the image data on which the control information is superimposed.
As a result, the same image data can be easily output even when the original image is output again.

  The present invention can increase the compression rate of a document image in which control information is embedded.

  Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

The image processing apparatus according to the present exemplary embodiment is configured to read the additional information embedded in the background copy-forgery-inhibited image from the confidential document in which the background copy-forgery-inhibited pattern image is embedded, and to print the confidential document only to authorized users. .
Additional information embedded in the background pattern image includes the following.
(A) Copy prohibition information (whether or not to prohibit copying)
(B) ... Copy permission condition information (information for permitting copying if the conditions are met)
For example, a personal identification number, a user ID number that permits copying (employee number, etc.), a date and time for canceling copy prohibition, a machine number of a copier that permits copying (C) ... latent image information (related to a latent image that floats when copied) information)
For example, latent image character string, font type, font size, latent image character string direction (angle), background tint image color

  Here, the background copy-forgery-inhibited pattern image will be described in detail with reference to FIG. The background copy-forgery-inhibited pattern image includes a latent image IP and a background pattern PB that covers the entire surface of the output image O.

  The background pattern PB and the latent image IP are different from each other. However, the output image O is formed with a pattern having the same pixel area and pixel color per unit area so that it can be seen by the human eye as a uniform gray background.

  The latent image IP is composed of finer dots than other portions so that the image appears to the extent that the latent image IP can be identified by human eyes in the copied document.

  The background pattern PB is composed of codes. The code is composed of a condition code CD representing arbitrary code data and a prohibited copy code CP that restricts copying.

  The code is composed of a hatched pattern PS representing arbitrary code data. In the oblique line pattern PS, the one represented by a half line inclined 45 degrees counterclockwise with respect to the scanning direction D represents bit 0 of the code data, and the one inclined 135 degrees represents bit 1 of the code data.

  The forbidden copy code CP is composed of a pattern in which the entire hatched pattern PS represents bit 0 and a bit 1. The forbidden copy code CP is used to determine that a copy is restricted when two or more types of forbidden copy codes CP are detected.

The condition code CD is composed of a synchronization code area AS and a data code area AC.
The synchronous code area AS is a code area in which the outer periphery of a rectangular area of a predetermined size surrounding the data code area AC is composed of a hatched pattern PS1 in which all bits 1 are represented.
In the data code area, a code number, a user ID number permitting copying (employee number, etc.), a date and time for canceling copying prohibition, a machine number of a copying machine permitting copying, etc. are encoded and embedded as a condition code CD. ing.

  Next, the configuration of the image processing apparatus 1 of the present embodiment will be described with reference to FIG. 2 includes a scanner unit 2, a separation unit 3, a compression unit 4, an image storage unit 5, an expansion unit 6, an image superposition unit 7, and a print unit 8. , A copy prohibition information detection unit 9, a copy permission condition information detection unit 10, a control unit 11, a storage unit 12, a copy permission condition information encoding unit 13, and a user interface unit 14.

  The scanner unit 2 reads a document placed on the platen glass and outputs the read image data to the separation unit 3.

The separation unit 3 deletes the pattern portion of the background ground image included in the background in the input image. Image data obtained by separating the background pattern image is output to the compression unit 4. The separation unit 3 will be described in detail with reference to FIG.
First, the image data output from the scanner unit 2 is input to the gray scale unit 51 and the color extraction unit 57. The gray scale conversion unit 51 converts the input image (RGB or YMCK) to gray scale. The image data converted to grayscale is input to the two binarization processing units 52 and 55, and binarized with a predetermined threshold value. The first binarization processing unit 52 performs binarization for performing subsequent pattern detection processing.

  The binarized image data is input to the noise removal processing unit 53, and noise removal processing is performed. The image data from which the noise has been removed is input to the pattern detection processing unit 54, and two types of oblique line pattern detection processing are performed. When the pattern is detected, the result is output to the area signal generation unit 56, and a binary image having the same shape as the pattern detected at the position of the detected pattern is generated. The generated binary image becomes a region image (1) for image deletion. The generated region image is output to the selection unit 58.

  In parallel with the above processing, the image data output from the gray scale conversion unit 51 is binarized by the second binarization processing unit 55. This binarized pixel becomes a region image (2) for image deletion. The generated binary image is output to the selection unit 58.

  In parallel with the above processing, the image data input to the separation unit 3 is input to the color extraction unit 57, and pixels having a predetermined range of colors are extracted. If it is a pixel in a predetermined range of color, a binary image having a pixel value “1”, otherwise a pixel value “0” is generated. This binary image becomes a region image (3) for image deletion. The generated binary image is output to the selection unit 58.

  A region image (1), a region image (2), and a region image (3) are input to the selection unit 58 in parallel. The selection unit 58 receives a selection signal from the control unit 11, selects one of the three region signals according to the selection signal, and outputs the selected signal to the image deletion unit 59.

  The image deletion unit 59 receives input image data to the separation unit 3 and a region image input from the selection unit 58. The image deletion unit 59 deletes the pixel of the input image corresponding to the pixel value “1” of the region signal (binary image) (replaces it with a white pixel).

  Through the above processing, the pattern portion (or high-density background pixel portion or specific color pixel portion) of the background tint block image included in the background in the input image is deleted.

The compression unit 4 is a device that compresses image data in order to effectively store a large amount of image data in a storage device having a limited capacity. Various algorithms can be used for the compression method, and as an example, data can be compressed by an adaptive predictive coding method. The compressed image data is stored in the storage unit 12 under the control of the image storage control unit 5. At this time, the image storage control unit 5 stores the copy prohibition information, copy permission condition information, latent image information and image data detected by the copy prohibition information detection unit 9 and the copy permission condition information detection unit 10 in association with each other. Accumulate in unit 12.
Copy prohibition information, copy permission condition information, and latent image information are input from the control unit 11 to the image accumulation control unit 5.

  Further, the image accumulation control unit 5 reads out the image data accumulated in the accumulation unit 12 and outputs it to the expansion unit 6. The decompressing unit 6 restores the compressed image data to the original image data in order to supply the image data to the printing unit 8. The restored image data is output to the image superimposing unit 7.

  The image superimposing unit 7 outputs the decompressed image data to the printing unit 8. If the control unit 11 is set to synthesize a background copy-forgery-inhibited pattern image, the print unit 8 superimposes the encoded data encoded by the copy permission condition information encoding unit 13 on the decompressed image data. Output to. The image superimposing unit 7 performs a logical sum (OR) synthesis on a predetermined color plane of the image data, and outputs the synthesized image data to the printing unit 8. The print unit 8 records the composite image data or image data output from the image superimposing unit 7 on a sheet.

Next, the copy prohibition information detection unit 9 will be described with reference to FIG. FIG. 4 shows a detailed configuration of the copy prohibition information detection unit 9.
The image data output from the scanner unit 2 is input to the gray scale conversion unit 21 and converted from full color to gray scale. Thereafter, it is binarized by the binarization processing unit 22.

  The binarized image data is input to the noise removal processing unit 23, and noise removal processing is performed. Specifically, a pixel block in which black pixels are connected is obtained, and each pixel of the pixel block whose size (number of connected pixels) is not within a predetermined range is replaced with a white pixel. The predetermined range is set to an appropriate range so that the hatched pattern is not deleted, and other patterns (isolated dot patterns, characters and figures in the document, etc.) are deleted.

  The image data from which noise has been removed is input to the pattern detection unit 24, where two types of oblique line pattern detection processing are performed, and the result is output as image data of 2 bits per pixel. Specifically, the pattern shown in FIGS. 5A and 5B is applied at the position of each pixel in the image data, and detection is performed by template matching. Here, when the pattern (A) shown in FIG. 5 is detected, the pixel value 0 is output, and when the pattern (B) shown in FIG. 5 is detected, the pixel value 1 is output and the pattern is not detected. , Pixel value 2 is output.

  The image data output from the pattern detection processing unit 24 is input to the blocking processing unit 25. Here, the block size is set to a size smaller than half the size of the copy prohibition code and the condition code, and is set to a size such that one or more blocks are completely included in the code. The blocking processing unit 25 divides the input image data into blocks of a predetermined size and outputs them to the number calculation unit 26.

  The number calculation unit 26 calculates the number of pixels having a pixel value 0 and the pixel having a pixel value 1 in the block, and outputs the result to the ratio calculation unit 27. The total is output to the determination processing unit 28. The ratio calculation unit 27 calculates the ratio of pixels with a pixel value of 0 and outputs the result to the determination processing unit 28.

  The determination processing unit 28 performs determination processing based on the total number input from the number calculation unit 26 and the ratio input from the ratio calculation unit 27.

  Here, when the inside of the block being processed is located inside the copy prohibition code of all bits 0, a diagonal line pattern corresponding to a predetermined number of bits 0 or more is detected in the block, and bit 1 Since the hatched pattern corresponding to is hardly detected, the ratio of the hatched pattern corresponding to bit 0 should be high and almost close to 1.0.

  If the block currently being processed is located inside the copy prohibition code of all bits 1, a hatched pattern corresponding to a predetermined number of bits 1 or more is detected in the block, and bit 0 is set. Since the corresponding diagonal pattern is hardly detected, the ratio of the diagonal pattern corresponding to bit 0 should be low and almost close to 0.0.

  If the block currently being processed includes at least a part of the condition code, a diagonal line pattern corresponding to a plurality of bits 0 and a diagonal line pattern corresponding to a plurality of bits 1 are detected in the block. The ratio of the hatched pattern corresponding to 1 should be much lower than 1.0 and much higher than 0.

  If the input image data is an image in which copy prohibition information is embedded, a copy prohibition code with all bits 0 in the block and a copy prohibition code with all bits 1 in the block are included in the image. There should be more than one embedded.

The following determination process is performed using the above characteristics.
If the total number> the first threshold value and the ratio> the second threshold value, the block is determined to be the copy prohibition code 0.
If the total number> the first threshold value and (1-ratio)> the second threshold value, the block is determined to be the copy prohibition code 1.
In cases other than the above, it is determined that the block is not a copy prohibition code. Also, the first threshold value is set by adding a margin to the number of theoretical patterns included in the block from the block size and pattern size. The second threshold value is set to a value close to 1.0.

  The determination processing unit 28 separately counts the number of blocks determined to be the copy prohibition code 0 and the number of blocks determined to be the copy prohibition code 1. If the number of blocks determined as copy prohibition code 0 is equal to or greater than the third threshold value and the number of blocks determined as copy prohibition code 0 is equal to or greater than the third threshold value, the image is determined to be a copy prohibited document. The determination result is output to the control unit 11.

Next, details of the copy permission condition information detection unit 10 will be described with reference to FIG.
The image data output from the scanner unit 2 is input to the gray scale conversion unit 31, converted from full color to gray scale, and then binarized by the binarization processing unit 32.

  The binarized image data is input to the noise removal processing unit 33, and the noise removal processing 33 is performed. The image data from which the noise has been removed is input to the pattern detection processing unit 34, where two types of oblique line pattern detection processing are performed, and the data of the processing result is stored in the buffer memory 35. In this image data, the pixel value at the position where the diagonal line pattern corresponding to bit 0 is detected is 0, the pixel value at the position where the diagonal line pattern corresponding to bit 1 is detected is 1, and other values are 2 The image data is 2 bits per pixel.

  The image data stored in the buffer memory 35 is input to the skew angle detection processing unit 36, and the skew angle is detected. Here, the skew angle of the input image data is obtained. As a specific method, Hough transform is performed on a pixel having only a pixel value of 0 or 1, and the peak of the projection distribution on the angle axis is obtained. The obtained skew angle is output to the code detector 37.

  Further, the image data stored in the buffer memory 35 is read out and input to the code detection unit 37, and the two-dimensional code is detected. Specifically, the image is scanned at the obtained skew angle to extract a pixel value of 0 or 1 (corresponding to 0 or 1 of the bit). A synchronization code is found from the extracted bit string. The synchronization code is defined as a code in which the outer periphery of a rectangular area having a predetermined vertical and horizontal size is entirely composed of bits 1. A bit array surrounded by the synchronization code is a two-dimensional code (condition code). This bit array is rearranged into a one-dimensional bit string and output to the error correction decoding unit 38.

  The error correction decoding unit 38 performs a predetermined error correction decoding process on the input bit string and decodes it as condition information. The decrypted copy permission condition information is output to the control unit 11.

Next, the additional condition encoding unit 13 will be described with reference to FIG.
Additional information (copy prohibition information, condition information, latent image information) is input from the control unit 11 to the additional condition encoding unit 13. The control unit 11 reads the additional information of the image data to be decoded from the storage unit 12 and supplies it to the copy permission condition information encoding unit 13. Of these, copy prohibition information and copy permission condition information are input to the additional information encoding unit 42, and latent image information is input to the latent image generation unit 41.

  The latent image generation unit 41 generates a latent image based on the input latent image information. The latent image information is information indicating what kind of latent image character is embedded in the pattern image. Specifically, the latent image character string, font type, font size, and direction of the latent image character string (angle) ) Etc. Upon receiving the latent image information, the latent image generation unit 41 draws a latent image character string in the specified direction with the specified font type and font size, and generates a binary latent image image. The generated latent image is output to the additional information encoding unit 42. Note that the resolution of the latent image is a resolution obtained by dividing the resolution of the printer by the size of a pattern to be described later. For example, when the printer resolution is 600 dpi and the pattern size is 12 pixels × 12 pixels, the resolution of the latent image is 50 dpi.

  The additional information encoding unit 42 encodes the input copy prohibition information and condition information. First, when the copy prohibition information indicates that the document that has been printed out is not to be copied by the image processing apparatus, two types of copy prohibition codes shown in FIGS. 8A and 8B are generated. Here, the copy prohibition code shown in FIG. 8A is all bit 0 inside the code, and the copy prohibition code shown in FIG. is there. When copy prohibition information is not input, or when it does not indicate that a document that has been printed out is not to be copied by the image processing apparatus, two types of codes shown in FIGS. 8A and 8B are generated. Is not done.

  Next, when condition information is input, an error correction code is applied to the condition information to generate a condition code as shown in FIG. The code in FIG. 8C represents a bit string of the encoded condition information by the arrangement of bit 0 and bit 1. The outer periphery of the cord has a special bit pattern for facilitating the positioning of the cord.

  Next, a plurality of generated codes are repeatedly arranged as shown in FIG. 9A to generate a pattern number array having the same size as the latent image. Here, the hatched rectangle in the figure is the copy prohibition code of FIG. 8A, the vertical hatched rectangle is the copy prohibition code of FIG. 8B, and the dot hatched rectangle is FIG. 8C. This is the condition code. If a copy prohibition code is not generated, a condition code is placed in the copy prohibition code portion in the figure. If the condition code is not generated, a copy prohibition code is placed in the condition code portion in the figure. At this time, the value of each element of the pattern number array is 0 or 1.

  Next, referring to the latent image, the pattern number of the element of the pattern number array corresponding to the coordinates of the black pixels in the latent image is changed to 2. If this is performed for all the black pixels in the latent image, the pattern number arrangement is such that the latent image characters are drawn with the pattern number 2 on the background in which the copy prohibition code and the condition code are arranged side by side. This state is shown in FIG. A black “COPY” portion in the figure indicates a portion in which the pattern array number is changed to “2”. The pattern number array is output to the pattern image generation unit 44.

  The pattern image generation unit 44 refers to each element of the input pattern number array, reads a pattern corresponding to the pattern number from the pattern storage unit 43 and converts it into a pattern image, thereby generating a background pattern image. The generated background tint block image is stored in a memory (not shown) in the image composition unit 18.

The procedure of this embodiment will be described with reference to FIGS.
First, the operation during image accumulation will be described with reference to the flowchart shown in FIG.
When the image data is input (step 1), first, the separating unit 3 extracts additional information from the image data (step S2). The image data from which the additional information is separated is output to the compression unit 4. The image data from which the additional information is extracted is compressed by the compression unit 4 and output to the image accumulation control unit 5. The image data with additional information input from the scanner unit 2 is input to the copy prohibition information detection unit 9 and the copy permission condition information detection unit 10. The copy prohibition information detection unit 9 and the copy permission condition information detection unit 10 take out copy prohibition information and copy permission condition information, respectively, and output them to the control unit 11. The control unit 11 outputs these pieces of information to the image accumulation control unit 5. The image storage control unit 5 stores the compressed image data and the additional information in the storage unit 12 in association with each other.

Next, an operation when an image is decompressed and output will be described with reference to the flowchart shown in FIG.
The image accumulation control unit 5 takes out the compressed image data from the accumulation unit 12 and outputs it to the decompression unit 6. Further, the additional information is output to the control unit 11. The decompression unit 6 performs decompression processing on the compressed image data (step S12). The additional information is output to the additional permission condition information encoding unit 13 and encoded there (step S13). The expanded image data and the encoded additional information are superimposed by the image superimposing unit 7 (step S14), and an image is formed by the printing unit 8 (step S15).

  As described above, the present embodiment separates the additional information embedded in the original image data and encodes only the original image data, so that the compression rate of the image data can be increased.

  The image processing program of the present invention can be realized as a program that is executed by controlling a computer. This program can be provided by being stored and distributed in a magnetic disk, an optical disk, a semiconductor memory, or other recording media, or distributed via a network.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

It is a figure which shows a background tint block image. It is a block diagram which shows the structure of an image processing apparatus. It is a block diagram which shows the structure of a separation part. It is a block diagram which shows the structure of a copy prohibition information detection part. It is a figure which shows an example of the image used for template matching. It is a block diagram which shows the structure of a copy permission condition information detection part. It is a block diagram which shows the structure of a background tint block image generation part. It is a figure which shows copy prohibition information and condition information. It is a figure which shows a pattern number arrangement | sequence. It is a flowchart which shows the procedure at the time of image accumulation. It is a flowchart which shows the procedure at the time of image output.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image processing apparatus 2 Scanner part 3 Separation part 4 Compression part 5 Image accumulation control part 6 Decompression part 7 Image superposition part 8 Print part 9 Copy prohibition information detection part 10 Copy permission condition information detection part 11 Control part 12 Accumulation part 13 Copy permission Condition information encoding unit 14 User interface unit

Claims (9)

Separating means for separating and extracting the control information from a combined image obtained by combining the original image and the control information for controlling reproduction of the original image;
Compression means for compressing original image data from which the control information has been extracted;
An image processing apparatus comprising: storage means for storing the compressed original image data.   The image processing apparatus according to claim 1, further comprising a storage control unit that stores the control information and the compressed original image data in the storage unit in association with each other. Decompression means for reading and decompressing the compressed image data from the storage means;
Encoding means for encoding the control information;
Superimposing means for superimposing the encoded control information on the decompressed image data;
The image processing apparatus according to claim 1, further comprising a forming unit that forms an image of the image data on which the control information is superimposed. A separation step of separating and extracting the control information from a composite image obtained by combining the original image and the control information for controlling reproduction of the original image;
A compression step of compressing original image data from which the control information has been extracted;
A storage step for storing the compressed original image data.   5. The image processing method according to claim 4, further comprising a storage control step of storing the control information and the compressed original image data in the storage step in association with each other. A decompression step of reading and decompressing the compressed image data from the storage step;
An encoding step for encoding the control information;
A superimposing step of superimposing the encoded control information on the decompressed image data;
6. The image processing method according to claim 4, further comprising a forming step of forming an image of the image data on which the control information is superimposed. A separation step of separating and extracting the control information from a composite image obtained by combining the original image and the control information for controlling reproduction of the original image;
A compression step of compressing original image data from which the control information has been extracted;
An image processing program for causing a computer to execute a storing step for storing the compressed original image data.   8. The image processing program according to claim 7, wherein a storage control step is executed in which the control information and the compressed original image data are stored in the storage step in association with each other. A decompression step of reading and decompressing the compressed image data from the storage step;
An encoding step for encoding the control information;
A superimposing step of superimposing the encoded control information on the decompressed image data;
The image processing program according to claim 7, further comprising: a forming step of forming an image of the image data on which the control information is superimposed.

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