JP2007243432A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for preventing inability to detect additional information being electronic watermarks and the reduction in confidentiality, even when performing automatic gradation correction control. <P>SOLUTION: The image forming apparatus for generating additional information FJ to be embedded to image data by using dots in a first size and dots in a second size that is greater than the first size and forming an image on paper on the basis of the generated additional information, includes: a detection section 36 for detecting the size of a dot image formed by the first size dots DH; a determination section 37 for determining whether the size of the dot image detected by the detection section is greater or smaller than a prescribed size ST; and a first correction section 39 that increases the size of the dot image by revising an image forming condition until the determination section determines that the size of the dot image is greater than the prescribed size when the determination section determines that the size of the dot image is smaller than the prescribed size. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that creates additional information for embedding in image data using a plurality of types of dots having different sizes and forms an image on a recording medium.

  In recent years, a technique for applying a digital watermark to an image of a document using human visual characteristics has been used in the field of image formation (Patent Documents 1 and 2). By inserting a digital watermark, it is possible to confirm the originality of the document, to display a copy prohibition warning, to add various auxiliary information, or to control the device.

  Conventionally, in a multi-function copying machine called a multi-function peripheral or MFP (Multi Function Peripherals), additional information is created using a plurality of types of dots of different sizes, and this additional information is combined with an image of a document. Embedding is done.

For example, two types of dots having different sizes are used, a background is formed by small dots, and an embedded character (check character) is formed by large dots. The background and embedded characters by these two types of dots are combined as a background pattern for the image of the document.
JP 2001-36724 A JP 2001-103285 A

  As described above, when using small dots for the background area and large dots for the embedded character area, the background area and the embedded character area are It is necessary to obtain an equivalent concentration.

  However, in a copying machine or the like, automatic gradation correction control (AIDC) is usually performed so that gradation of an image to be formed is appropriate. When the automatic gradation correction control is performed, the image forming conditions such as the developing conditions and the beam diameter of the laser light change, and the diameters of the dots of the background and embedded characters change accordingly. As a result, it is possible that the dot becomes small and the additional information cannot be detected, or the average density of the background area and the embedded character area is changed, resulting in a decrease in confidentiality.

  In addition, due to the secular change of the copy machine and the difference in density characteristics for each model, the difference in average density between the background area and the embedded character area may become large and the confidentiality may be lowered.

  The present invention has been made in view of the above-described problems. In an image forming apparatus that creates additional information using a plurality of types of dots having different sizes, even if automatic gradation correction control is performed, the addition is performed. An object is to prevent information from being detected and to prevent a decrease in confidentiality.

  The image forming apparatus according to the present invention creates additional information for embedding in image data using a first size dot and a second size dot larger than the first size, and based on the created additional information An image forming apparatus for forming an image on a recording medium, the detecting means for detecting the size of a dot image formed by the first size dots, and the size of the dot image detected by the detecting means A determination unit that determines whether the size is larger or smaller than a predetermined size; and when the determination unit determines that the size is smaller than the predetermined size, the image forming condition is determined until the determination unit determines that the size is larger than the predetermined size. And a first correction unit that changes the size of the dot image to increase the size of the dot image.

  Preferably, an average density of an image formed by the second size dots matches an average density of an image formed by the first size dots corrected by the first correction unit. As described above, a second correction unit that corrects the dots of the second size is provided.

  In addition, the tint block is constituted by the first size dots and the second size dots, and the second correction unit is configured to obtain an average density of an image formed by the first size dots. And the average density of the image formed by the dots of the second size are corrected to be the same.

  The second correction unit corrects the average density of the image by changing the number of dots of the second size.

  The second correction unit corrects the image formed by the second size dots so that the image can be detected separately from the image formed by the first size dots.

  An image forming apparatus for embedding additional information in image data to form an image on a recording medium, wherein the addition is performed using a first size dot and a second size dot larger than the first size. Means for creating information, a print engine for forming an image on a recording medium based on the created additional information, detection means for detecting the size of a dot image formed by the dots of the first size, A determination unit that determines whether the size of the dot image detected by the detection unit is larger or smaller than a predetermined size; and the determination unit determines that the size is smaller than the predetermined size. First correction means for changing the image forming condition of the print engine to increase the size of the dot image until it is determined that the first image is larger than the first correction means; Under the image forming conditions changed by the positive means, the average density of the image formed by the second size dots matches the average density of the image by the first size dots. And second correcting means for correcting the dots of the second size.

  Preferably, the print engine is an electrophotographic print engine, and automatic gradation correction control is performed so that gradation of an image formed on the recording medium is appropriate.

  Further, the density detection sensor used for the automatic gradation correction control is used to detect the density of an image formed by the dots of the first size and the second size.

  According to the present invention, even when automatic gradation correction control is performed, it is possible to prevent additional information from being detected and to prevent confidentiality from being lowered.

  1 is a block diagram showing a configuration of an image forming apparatus 1 according to an embodiment of the present invention, FIG. 2 is a block diagram showing a functional configuration of an embedding information creation unit, and FIG. 3 is a diagram showing a configuration of a print engine. 4 is a diagram showing an example of a background dot pattern and an embedding dot pattern, FIG. 5 is a diagram showing a state in which an original image and additional information are combined, and FIG. 6 is a state of correction processing of dots constituting the additional information FJ. FIG. 7 is a flowchart showing an outline of processing in the image forming apparatus 1.

  1, the image forming apparatus 1 includes a scanner 11, a processing unit 12, a print engine 13, and the like.

  The scanner 11 reads a document image and outputs a document image FG. The document image FG is “data” about the document image, but is described as “document image FG” in this specification. The same applies to other cases.

  The processing unit 12 performs various image processes on the document image FG output from the scanner 11. In the present embodiment, as shown in FIG. 5, an information embedding process is performed in which a document image FG and additional information FJ are combined to generate a combined image FS.

  As shown in FIG. 5, the additional information FJ includes an embedded character “copy prohibited”. The additional information FJ is formed as a copy-forgery-inhibited pattern (background pattern) made up of embedded characters “copy prohibited” and the background. When the composite image FS is printed by the image forming apparatus 1, the user can see the original image FG and the background pattern, but cannot see the “copy prohibited” which is an embedded character. This is because the embedded character is buried in the background and concealed. When this printed matter is copied, the embedded character “copy prohibited” is brought up and is visible to the user.

  For information embedding processing, an embedding information creation unit 21 and a synthesis unit 22 are provided. Details will be described later.

  The print engine 13 performs color printing by an electrophotographic method and is a publicly known printer. In the print engine 13, automatic gradation correction control (AIDC) is performed so that gradation of an image formed on a recording medium such as paper is appropriate. A density detection sensor SE1 is provided for automatic gradation correction control.

  That is, as shown in FIG. 3, the print engine 13 includes a rotating photosensitive drum 61, and the charging charger 62, Y, M, C, A K developing device 63, a transfer belt 64, a transfer charger 65, and a cleaning unit 66 are disposed. Laser light is emitted from the laser diode 67 of the exposure unit toward the surface of the photosensitive drum 61 charged by the charging charger 62. The CPU 68 that controls the print engine 13 outputs a drive signal that changes in accordance with the image signal, and the laser diode 67 is modulated in luminance by the drive signal to emit light. As a result, an electrostatic latent image corresponding to the image signal is formed on the surface of the photosensitive drum 61. When the image signal is based on the composite image FS, the same electrostatic latent image as the composite image FS is formed, and when the image signal is based on the patch pattern, the same electrostatic latent image as the patch pattern is formed.

  The electrostatic latent image on the photosensitive drum 61 is developed by the developing unit 63 and becomes a toner image. The toner image on the photosensitive drum 61 is transferred onto the transfer belt 64 by the transfer charger 65. The toner image transferred onto the transfer belt 64 is transferred to a sheet (not shown), fixed, and discharged. In addition, toner remaining on the photosensitive drum 61 is scraped off by the cleaning unit 66.

  At a predetermined position of the transfer belt 64, the above-described density detection sensor SE1, which is an optical sensor for detecting the density of the toner patch (patch pattern toner image) TP on the transfer belt 64, is disposed. .

  Next, the processing unit 12 will be described in detail.

  As shown in FIG. 2, the embedding information creation unit 21 includes a background dot storage unit 31, an embedding dot storage unit 32, a background dot selection unit 33, an embedding dot selection unit 34, a patch control unit 35, and a background pattern. A creation unit 41 and the like are provided. The patch control unit 35 includes a dot size detection unit 36, a determination unit 37, a threshold storage unit 38, a first correction unit 39, a second correction unit 40, and the like.

  It should be noted that the function of the embedded information creation unit 21 can be realized by software by the CPU executing an appropriate program, hardware by a hardware circuit, or a combination thereof.

  The background dot storage unit 31 and the embedding dot storage unit 32 store various background dot patterns DH and embedding dot patterns DU as shown in FIG. The background dot pattern DH is composed of a plurality of background dots TH having a small diameter, and the embedding dot pattern DU is composed of embedding dots TU having a larger diameter than the background dots TH.

  Embedding information is embedded in the background pattern by utilizing the difference in size (diameter) of these two types of dots. That is, meaningful information is expressed by the embedding dots TU in the background image formed by the background dots TH. The background dots TH and the embedding dots TU are separated from each other by a copying machine or the like at the time of copying after they are actually recorded (image formation) on the paper as dot images. It will be detected separately. Accordingly, the background dots TH and the embedding dots TU need to be different in size so that they can be distinguished and detected as such.

  Further, as described in the section of the prior art, both the background dots TH and the embedding dots TU have a certain size or more so as to be recognized or detected by a copying machine or the like. Need to be. In addition, in order to maintain the confidentiality of the embedded information, the average density of the background region where the background dots TH are present and the embedded region where the embedded dots TU are present must be the same or approximately the same.

  FIG. 4 shows background dot patterns DH1 to DH3 and embedding dot patterns DU1 to DU9. The background dot patterns DH1 to DH3 have the same dot size but different dot arrangements. The background is determined by the dot arrangement. When automatic gradation correction control is performed, the dot size changes, but if the dot size becomes too small, it may not be detected. Therefore, in this case, correction processing (first dot correction processing) for increasing the dot size is performed. Details will be described later. These background dot patterns DH1 to DH3 are patterns or lines made up of combinations of dots. For example, when the resolution is 600 dpi, the minimum value of the interval (pitch) between dots is about 40 μm in the horizontal direction or the vertical direction.

  The embedding dot patterns DU1 to DU9 shown in FIG. 4 have the same dot size, but the number of dots is different and is 1 to 9, respectively. As the number of dots is different, the embedding dot patterns DU1 to DU9 have different average densities. The dot arrangement in the embedding dot pattern DU may be different.

  The background dot selection unit 33 selects the background dot pattern DH to be used as the background from the background dot patterns DH stored in the background dot storage unit 31.

  The embedding dot selection unit 34 selects an embedding dot pattern DU to be used as embedding information from among the embedding dot patterns DU stored in the embedding dot storage unit 32.

  In order to check whether or not the selected background dot pattern DH and embedding dot pattern DU are appropriate as the background pattern, the patch control unit 35 controls the print engine 13 to generate a patch pattern based on them. And various controls or processes are performed so that the created patch pattern becomes appropriate.

  That is, a patch pattern is created based on the background dot pattern DH selected and read from the background dot storage unit 31, and the signal S2 is sent to the print engine 13 so as to form a toner image of the patch pattern. send. The formed toner image is detected as an image by the density detection sensor SE1, and a detection signal S1 is sent. Based on the detection signal S1, the dot size detection unit 36 detects the dot of the toner image, that is, the size of the dot image. Further, based on the detection signal S1, the second correction unit 40 detects the average density of the toner image.

  The patch control unit 35 also creates a patch pattern based on the embedding dot pattern DU selected and read from the embedding dot storage unit 32, and forms a toner image of the patch pattern on the print engine 13. To send a signal S2. The formed toner image is similarly detected as an image by the density detection sensor SE1, and a detection signal S1 is sent. Based on the detection signal S1, the second correction unit 40 detects the average density of the toner image.

  The determination unit 37 compares the size of the dot image detected by the dot size detection unit 36 with the threshold value ST stored in the threshold value storage unit 38, and determines whether the dot image is larger or smaller than the threshold value ST. Judging. When it is determined that the dot image is smaller than the threshold value ST, the first correction unit 39 outputs a signal S3 to the print engine 13 so as to enlarge the dot image. The print engine 13 changes the image forming condition in response to the signal S3. For example, the laser beam diameter is increased so that the size of the latent image formed by the background dots TH is increased, and the development conditions are changed so that more toner adheres to the same latent image. In this way, the first correction unit 39 adjusts so that the size of the dot image formed by the background dots TH is larger than the threshold value ST.

  The threshold value ST is set so that the dot image PF can be detected. Various threshold values ST having different values may be prepared, and the threshold value ST may be selected according to the model or purpose.

  After the dot image by the background dot TH becomes larger than the threshold value ST, in this state, the patch pattern created by the background dot pattern DH and the patch pattern created by the embedding dot pattern DU are in this state. The second correction unit 40 outputs a signal S4 for adjusting the number of embedding dots TU so that the average densities of and are the same. In response to the signal S 4, the embedding dot selection unit 34 selects an appropriate embedding dot pattern DU from the embedding dot storage unit 32.

  That is, by increasing the size of the dot image by the background dots TH, the average density of the background dot pattern DH increases and the average density of the embedding dot pattern DU also increases, but the balance between them changes. The average density of each other may not be the same. In this case, the second correction unit 40 corrects the average density of the embedding dot pattern DU by changing the number of embedding dots TU (second dot correction process).

  For example, if the embedding dot pattern DU6 is appropriate before the size of the background dot TH is adjusted, the average density of the background dot pattern DH is that of the embedding dot pattern DU after the size of the background dot TH is adjusted. If so, the signal S4 is output so that the embedding dot pattern DU7 having one more dot is selected in order to increase the average density of the embedding dot pattern DU. Using the embedding dot pattern DU7, patch patterns are created again and the average densities are compared. If the average density of the embedding dot pattern DU7 is still low, the signal S4 is output so as to select one more embedding dot pattern DU8. The process is repeated until a dot pattern having an equivalent average density is found.

  In this way, the average density of the background dot pattern DH and the average density of the embedding dot pattern DU are adjusted to be substantially the same. As a result, the embedded information and the background in the background pattern have the same density in the clear vision distance observation, and the confidentiality of the embedded information is maintained.

  The copy-forgery-inhibited pattern creating unit 41 uses the background dot pattern DH and the embedding dot pattern DU that are finally selected as described above, so that these dot patterns have the same size as the size of the document image FG. In addition, the ground pattern, that is, the additional information FJ is created by using a predetermined arrangement.

  Since the background pattern creation unit 41 arranges the background dot pattern DH and the embedding dot pattern DU, the background pattern creation unit 41 manages the positions of the background region and the embedded region in the entire image. It is possible.

  Processing of the first correction unit 39 and the second correction unit 40 will be described with reference to FIG.

  FIG. 6 shows toner patches TP <b> 1 to TP <b> 5 based on a patch pattern created by the background dot pattern DH and the embedding dot pattern DU.

  In FIG. 6, the toner patch TP1 is based on the background dot pattern DH1, and the toner patch TP2 is based on the embedding dot pattern DU6. The toner patches TP1 and TP2 are equivalent in density. However, since the size of the dot image PF of the toner patch TP1 is equal to or smaller than the threshold value ST, the signal S3 is output from the first correction unit 39 so as to enlarge the dot image PF. As a result, the image forming conditions are changed in the print engine 13, and the toner patch TP1 becomes the toner patch TP3 and the toner patch TP2 becomes the toner patch TP4. As a result, the average density of the toner patch TP4 due to the embedding dot pattern DU was relatively lowered, and the density of toner patches TP3 and TP4 was not equivalent. Therefore, the second correction unit 40 outputs a signal S4 to the embedding dot selection unit 34 so as to increase the number of dots of the embedding dot pattern DU. The embedding dot selection unit 34 selects the embedding dot pattern DU7 having one more dot, and based on this, the toner patch TP5 is created.

  As a result, since the average density of the toner patch TP3 and the average density of the toner patch TP5 are equivalent, the additional information FJ is created using the background dot pattern DH1 and the embedding dot pattern DU7. became. The created additional information FJ is combined with the document image FG to become a combined image FS, which is printed on a sheet by the print engine 13.

  As described above, even when there is a change in the dot size due to the automatic gradation correction control or a change in the dot size due to the secular change of the image forming apparatus 1 or the difference in density characteristics for each model, the first correction is performed. The size of the dot image PF is detected without changing the arrangement of the dots in the background dot pattern DH by the dot correction processing (first dot correction processing and second dot correction processing) by the unit 39 and the second correction unit 40. It is maintained at a possible level, so that dots can be reliably detected, and the density of the background area and the embedded area is kept at the same level, thereby preventing a decrease in confidentiality.

  In FIG. 6, the size of the dot image PF of the toner patch TP1 is equal to or smaller than the threshold value ST. However, the toner patch TP1 temporarily maintains the shape of one dot. However, depending on aging and deterioration of toner and the like, one dot may be thinned and diffused, or dispersed to a plurality of small points. Even in such a case, it is detected that the size of the dot image PF is equal to or smaller than the threshold value ST.

The timing for performing the dot correction processing described above is as follows.
(1) When an operation means for executing dot correction processing is provided on an operation panel or the like, and the user operates the operation means.
(2) When a new background dot pattern DH or embedding dot pattern DU is registered in the background dot storage unit 31 or the embedding dot storage unit 32. In addition, when such dot pattern registration can be performed via a network from a terminal device or a server, the dot pattern is registered via the network. Thereby, the compatibility between the newly registered dot pattern and the print engine 13 is checked.
(3) When a performance check operation key related to creation of the additional information FJ is provided, and when a predetermined state is obtained by operating the key. That is, when the key is operated, the additional information FJ with a predetermined background pattern is printed. When the printed additional information FJ is copied, the image obtained by reading the additional information FJ with the scanner 11 is compared with the electronic data of the original additional information FJ, and the confidentiality of the background pattern is checked and the background pattern is erased / raised. The degree is checked. As a result of these checks, it is automatically determined whether or not dot correction processing is necessary. If the background pattern has a code, the internal electronic data can be specified from the code, so the above-described processing may be performed using the code.
(4) When the process of adding the additional information FJ, that is, the combining process in the combining unit 22, is performed, the dot correction process is performed immediately before that.
(5) When the image forming apparatus 1 is turned on. That is, it is performed when the image forming apparatus 1 is warmed up.
(6) Performed in parallel with automatic gradation correction control. Usually, since the automatic gradation correction control is performed periodically, dot correction processing is performed periodically in accordance with it.

  In the embodiment described above, in order to change the average density of the embedding dot pattern DU, the embedding dot patterns DU1 to DU1-9 having different numbers of dots are selected. The number of dots may be increased or decreased with respect to the embedding dot pattern DU.

  Next, the embedding process will be described with reference to a flowchart.

  In FIG. 7, gradation correction by automatic gradation correction control is performed (# 11). A toner patch TP with a patch pattern for dot correction processing is created, and it is checked whether the dot image PF with the background dot TH is larger than the threshold value ST (# 12). When the dot image PF is smaller than the threshold value ST (No in # 12), a process for adjusting the size of the dot image PF, that is, a first dot correction process is performed (# 13). When the dot image PF becomes larger than the threshold value ST (Yes in # 12), it is checked whether or not the average density of the background area and the embedded area match (# 14). If the average density does not match (No in # 14), a process for adjusting the number of dots in the embedding dot pattern DU, that is, a second dot correction process is performed (# 15). If the average density matches (Yes in # 14), the background pattern (additional information FJ) created thereby and the original image FG are combined (# 16) and printed (# 17).

  In the automatic gradation correction control in step # 11, the size of the dot image PF by the background dots TH is not taken into consideration. When the answer is YES in step # 12, gradation correction by automatic gradation correction control may be performed immediately after that. The gradation correction in this case is performed so as to maintain that the size of the dot image PF of the background dots TH is equal to or larger than the threshold value ST.

  In the embodiment described above, as a method of increasing the size of the dot image PF, the image forming conditions are changed. However, instead of or in addition to this, one pixel is constituted by a plurality of dots, and black dots The density of the pixel may be increased by increasing the number. That is, the density pattern method may be applied. Although the background dot TH is made smaller and the embedding dot TU is made larger, conversely, the background dot TH may be made larger and the embedding dot TU may be made smaller. Further, although the toner patch TP is detected using the density detection sensor SE1 used for the automatic gradation correction control, an optical sensor separate from the automatic gradation correction control may be used.

  In the embodiment described above, the configuration of the embedded information creation unit 21 can be various configurations other than those shown in FIG. In the print engine 13, the part that creates the toner patch TP based on the patch pattern may also serve as the part that creates the toner patch for automatic gradation correction control.

  In addition, the configuration, structure, shape, dimensions, function, number, arrangement, processing content, processing order, etc. of the entire processing unit 12 or each part of the image forming apparatus 1 are other than those described above in accordance with the spirit of the present invention. It can be various.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows the functional structure of an embedding information creation part. It is a figure which shows the structure of a print engine. It is a figure which shows the example of the dot pattern for backgrounds, and the dot pattern for embedding. It is a figure which shows a mode that a document image and additional information are synthesize | combined. It is a figure which shows the mode of the correction process of the dot which comprises additional information. 5 is a flowchart illustrating an outline of processing in the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Scanner 12 Processing part 13 Print engine 31 Background dot storage part 32 Embedding dot storage part 33 Background dot selection part 34 Embedding dot selection part 35 Patch control part 36 Dot size detection part (detection means)
37 Judgment Unit (Judgment Unit)
38 threshold value storage unit 39 first correction unit (first correction means)
40 Second correction unit (second correction means)
41 Ground pattern creation unit (means for creating additional information)
TH Background dot (first size dot)
TU embedding dots (second size dots)
Image PF Dot image ST Threshold (predetermined size)
FJ additional information (background pattern)
SE1 Concentration detection sensor

Claims (8)

Using the first size dot and the second size dot larger than the first size, additional information for embedding in the image data is created, and an image is formed on the recording medium based on the created additional information. An image forming apparatus,
Detecting means for detecting a size of a dot image formed by the dots of the first size;
Determination means for determining whether the size of the dot image detected by the detection means is larger or smaller than a predetermined size;
When the determination unit determines that the size is smaller than the predetermined size, the first correction unit increases the size of the dot image by changing the image forming condition until the determination unit determines that the size is larger than the predetermined size. When,
An image forming apparatus comprising: The average density of the image formed by the dots of the second size matches the average density of the image formed by the dots of the first size corrected by the first correction unit. Comprising second correcting means for correcting the dots of the second size;
The image forming apparatus according to claim 1. A tint block is constituted by the dots of the first size and the dots of the second size,
The second correction unit corrects the average density of the image formed by the first size dots to be equal to the average density of the image formed by the second size dots. To
The image forming apparatus according to claim 2. The second correction unit corrects an average density of the image by changing the number of dots of the second size.
The image forming apparatus according to claim 2. The second correction unit corrects the image formed by the second size dots so that the image can be detected separately from the image formed by the first size dots.
The image forming apparatus according to claim 2. An image forming apparatus for embedding additional information in image data to form an image on a recording medium,
Means for creating the additional information using a first size dot and a second size dot larger than the first size;
A print engine that forms an image on a recording medium based on the created additional information;
Detecting means for detecting a size of a dot image formed by the dots of the first size;
Determination means for determining whether the size of the dot image detected by the detection means is larger or smaller than a predetermined size;
When the determination unit determines that the size is smaller than the predetermined size, the image forming condition of the print engine is changed to increase the size of the dot image until the determination unit determines that the size is larger than the predetermined size. First correction means;
Under the image forming conditions changed by the first correction unit, the average density of the image formed by the second size dots is changed to the average density of the image by the first size dots. Second correction means for correcting the dots of the second size so as to match,
An image forming apparatus comprising: The print engine is an electrophotographic print engine,
Automatic gradation correction control is performed so that the gradation of the image formed on the recording medium is appropriate.
The image forming apparatus according to claim 6. Detecting a density of an image formed by each dot of the first size and the second size using a density detection sensor used for the automatic gradation correction control;
The image forming apparatus according to claim 7.