JP2017226074A - Image formation apparatus and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect image characteristics even when a sheet is a thin sheet in comparison to a case where countermeasures are not executed to the problem in which the color of a background member is transmitted through the sheet and read when detecting the image characteristics by reading an image on the sheet after print processing in a conveyance path.SOLUTION: An image reading unit 60 reads an image at a specific position of a print sheet after print processing in a sheet conveyance path. A printing control unit 40 prints a lining image at a specific position for reading the image by the image reading unit 60 to the print sheet before the image is read by the image reading unit 60, reverses the print sheet after printing the lining image by a reverse mechanism 70, and executes print processing to the print sheet after being reversed. An image processing unit 50 detects the presence/absence of the occurrence of toner fogging on the basis of the image data read by the image reading unit 60.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus and a program.

  Japanese Patent Application Laid-Open No. 2005-228561 discloses a document density detection apparatus configured such that a white reflecting roller is disposed on the back side of a document when the document density is detected.

  In Patent Document 2, any one of opacity, whiteness, and glossiness of a recording sheet to be conveyed is measured, and white toner whose adhesion amount is controlled based on the measurement result is formed as a background of an image. A color image forming apparatus is disclosed.

JP 09-222830 A JP 2002-268318 A

  For business printing, an image reading unit is used to read the image of the paper after the printing process in the conveyance path, and image characteristics are detected based on the read image data, and based on the detected image characteristics, Some are provided with a function of adjusting image quality such as gradation correction and in-plane unevenness adjustment.

  When detecting the position of the sheet by such an image reading unit, it is necessary to improve the detection accuracy of the sheet corner and the sheet edge. For this reason, black, which has a large difference in luminance value from white paper, is used as the background color when reading the paper. That is, the color of the conveyance path at the position where the image reading unit reads the image on the sheet is set to black.

  For this reason, when thin paper is used as the paper for performing the printing process, the black color of the background is seen, causing a problem that the image characteristics cannot be accurately detected.

  In particular, when the image reading means is used to detect the occurrence of an unintended minute transfer of toner called toner fog, if the background black is transparent, the toner fog is assimilated and hidden from the background. For this reason, it is impossible to accurately detect the presence or absence of toner fog.

  An object of the present invention is to execute a measure against the fact that the color of the background member is read through the paper when the image of the paper after the printing process in the conveyance path is read and the image characteristic is detected. In comparison, an object is to provide an image forming apparatus and a program capable of accurately detecting image characteristics even when the paper is thin.

[Image forming apparatus]
The present invention according to claim 1 is a reading unit that reads an image at a specific position of the paper after the printing process in the conveyance path;
Detecting means for detecting image characteristics based on image data read by the reading means;
An image forming apparatus comprising: a printing control unit that controls to print a background image at a position behind a specific position where the reading unit reads an image with respect to a sheet before the image is read by the reading unit. .

  According to a second aspect of the present invention, the print control unit prints a background image only on a position on the back side of a specific position where the image is read by the reading unit, on a sheet before the image is read by the reading unit. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled as described above.

  According to a third aspect of the present invention, in the first or second aspect, the print control unit changes a halftone dot area ratio of a backing image to be printed based on thickness information of a sheet on which printing processing is to be executed. An image forming apparatus.

  According to a fourth aspect of the present invention, the print control unit controls the printing process so that the halftone dot area ratio of the backing image increases as the thickness of the sheet on which the printing process is to be performed is thinner. The image forming apparatus described.

  The present invention according to claim 5 is the image forming apparatus according to any one of claims 1 to 4, wherein the backing image is formed of a white color material.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the detection unit detects the presence or absence of color material fogging based on the image data read by the reading unit. is there.

  The present invention according to claim 7 is further provided with a background member which is disposed so as to be positioned on the back side of the sheet when the image of the sheet is read by the reading unit, and which has a color different from the color of the sheet. 6. The image forming apparatus according to claim 6.

[program]
According to an eighth aspect of the present invention, there is provided a sheet on the back side of a specific position where an image is read by the reading unit with respect to a sheet before the image is read by a reading unit that reads an image at a specific position of the sheet after printing processing in the conveyance path. Printing a backing image at the position;
A step of reading an image at a specific position on the paper after the backing image is printed by the reading unit;
A program for causing a computer to execute an image characteristic detecting step based on image data read by the reading unit.

  According to the first aspect of the present invention, when the image of the paper after the printing process in the conveyance path is read and image characteristics are detected, the countermeasure against the color of the background member being read through the paper As compared with the case where the process is not executed, it is possible to provide an image forming apparatus capable of accurately detecting the image characteristics even when the paper is thin.

  According to the second aspect of the present invention, it is possible to provide an image forming apparatus capable of reducing the color material consumption as compared with a case where a background image is printed on the entire back side of the paper.

  According to the third aspect of the present invention, compared to a case where a background image is printed using a certain amount of color material, the color material is consumed while preventing the color of the background member from being read through the paper. An image forming apparatus capable of reducing the amount can be provided

  According to the fourth aspect of the present invention, compared to a case where a backing image is printed using a certain amount of color material, the color material is consumed while preventing the color of the background member from being read through the paper. An image forming apparatus capable of reducing the amount can be provided.

  According to the fifth aspect of the present invention, when the image characteristic is detected by reading the image of the white paper after the printing process in the conveyance path, the color of the background member is read through the paper. As compared with the case where no countermeasure is taken, it is possible to provide an image forming apparatus capable of accurately detecting image characteristics even when the paper is thin.

  According to the sixth aspect of the present invention, when the image characteristic is detected by reading the image of the white paper after the printing process in the conveyance path, the color of the background member is read through the paper. As compared with the case where no countermeasure is taken, it is possible to provide an image forming apparatus capable of accurately detecting whether or not color material fogging has occurred even when the paper is thin.

  According to the seventh aspect of the present invention, when the image characteristic is detected by reading the image of the paper after the printing process in the conveyance path, the color of the background member that is different from the color of the paper is transmitted through the paper. As compared with the case where no countermeasure is taken against the fact that the sheet is read, an image forming apparatus capable of accurately detecting whether or not color material fogging has occurred can be provided even when the sheet is thin.

  According to the eighth aspect of the present invention, when the image of the paper after the printing process in the conveyance path is read and the image characteristic is detected, the countermeasure against the color of the background member being read through the paper As compared with the case where the process is not executed, it is possible to provide a program capable of accurately detecting the image characteristics even when the paper is thin.

1 is a diagram illustrating a system configuration of an image forming system according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of an image forming apparatus 10 according to an embodiment of the present invention. 1 is a block diagram illustrating a hardware configuration of an image forming apparatus 10 according to an embodiment of the present invention. 4 is a diagram for explaining a configuration at a reading position when the image reading unit 60 reads an image on a printing paper 32. FIG. 6 is a diagram illustrating an example of a test chart image read by an image reading unit 60. FIG. It is a figure which shows the example of a reading area when the image reading part 60 reads an image from the printing paper on which the test chart image was printed. 6 is a diagram for explaining an example of an image reading position of the image reading unit 60. FIG. FIG. 6 is a diagram illustrating a state in which the image reading unit 60 does not read an image on a printing paper 32 on which a backing image is printed, and the printing paper 32 passes on a paper conveyance path. FIG. 6 is a diagram illustrating a state in which the printing paper 32 after the test chart image is printed is conveyed again to the reading position of the image reading unit 60. It is a figure which shows the example of reading at the time of reading a test chart image by the image reading part 60. FIG. 5 is a flowchart for explaining a determination process when determining whether or not toner fog is generated by the image processing unit 50. FIG. 10 is a diagram for describing a specific example of toner fog determination processing. It is a figure which shows the example of a graph which shows the relationship between the halftone dot area ratio of white toner, and the paper thickness (basis weight) of printing paper. FIG. 3 is a diagram illustrating a configuration example when an image reading unit 60 reads an image on a printing paper 32 from the side opposite to a printing surface.

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

  FIG. 1 is a diagram showing a system configuration of an image forming system according to an embodiment of the present invention.

  As shown in FIG. 1, an image forming system according to an embodiment of the present invention includes an image forming apparatus 10 and a terminal device 20 connected via a network 30. The terminal device 20 generates print data and transmits the print data generated via the network 30 to the image forming apparatus 10.

  The image forming apparatus 10 is a business high-speed printer called a so-called production printer. The image forming apparatus 10 prints an image based on the print data from the terminal device 20 on printing paper.

  FIG. 2 is a diagram illustrating a configuration of the image forming apparatus 10 of the present embodiment.

  As shown in FIG. 1, the image forming apparatus 10 includes image forming units 14C, 14M, 14Y, and 14K, an intermediate transfer belt 16, a paper tray 17, a paper transport path 18, a fixing device 19, a print control unit 40, and an image processing unit. 50, an image reading unit 60 and a paper reversing mechanism 70.

  First, the outline of the image forming apparatus 10 will be described. Image data input from the terminal apparatus 20 or the like via a network line such as a LAN is subjected to image processing such as gradation correction and resolution correction in the image processing unit 50. It is output to the image forming unit 14. The print control unit 40 controls the image forming units 14C, 14M, 14Y, and 14K, the intermediate transfer belt 16, the paper tray 17, the paper conveyance path 18, the fixing device 19, and the like, and the image processing unit 50 performs image processing. Based on the image data, a process of printing an image on the printing paper is executed.

  In the image forming apparatus 10 of the present embodiment, four image forming units 14 are arranged corresponding to the colors constituting the color image. In the present embodiment, four image forming units 14K, 14Y, 14M, and 14C correspond to the respective colors of black (K), yellow (Y), magenta (M), and cyan (C) along the intermediate transfer belt 16. Are arranged horizontally at regular intervals. The intermediate transfer belt 16 rotates as an intermediate transfer member in the direction of the arrow A in the figure, and these four image forming units 14K, 14Y, 14M, and 14C are configured based on the image data input from the image processing unit 50. The toner images are sequentially formed and transferred to the intermediate transfer belt 16 (primary transfer) at a timing at which the plurality of toner images are superimposed on each other. The order of the colors of the image forming units 14K, 14Y, 14M, and 14C is not limited to the order of black (K), yellow (Y), magenta (M), and cyan (C). ), Magenta (M), cyan (C), black (K), and the like.

  The sheet conveyance path 18 is disposed below the intermediate transfer belt 16. The printing paper 32 supplied from the paper tray 17 is transported on the paper transporting path 18, and the toner images of each color transferred onto the intermediate transfer belt 16 are collectively transferred (secondary transfer). The toner image thus fixed is fixed by the fixing device 19, passes below the image reading unit 60, and is discharged to the outside of the apparatus.

  The image reading unit 60 is a reading unit that reads an image at a specific position of the printing paper after the printing process in the paper conveyance path. When adjusting the settings of the image forming apparatus 10 and the like, a test chart generated in advance is printed on printing paper, and the image characteristics are detected by reading an image of the test chart by the image reading unit 60, and detection is performed. Based on the obtained image characteristics, image quality adjustment such as gradation correction and in-plane unevenness adjustment is performed.

  The paper reversing mechanism 70 includes a mechanism that can reverse the front and back of the printing paper after the fixing process is performed by the fixing device 19. Therefore, when performing duplex printing, the paper after the fixing process by the fixing device 19 is reversed by the paper reversing mechanism 70 and conveyed to the paper conveyance path 18.

  In the following description, as an example of the image characteristics, a case where the presence or absence of unintended minute transfer of toner called toner fog is detected using the image reading unit 60 will be described.

  Here, “toner fog” is a phenomenon in which a small amount of toner is transferred to a white background portion of paper that should not be printed, and the white background portion is slightly stained. Means. This toner fog is known to occur due to a change in the charging characteristics of the toner due to a high-temperature and high-humidity environment or the like, or because the charge amount is too low.

  The print control unit 40 controls the printing paper before the image is read by the image reading unit 60 to print a lining image at a position behind the specific position where the image reading unit 60 reads the image. In the present embodiment, since the ground color of the printing paper is white, the lining image is formed with white toner (white color material).

  Here, the print control unit 40 controls to print the background image only on the back side of the specific position where the image reading unit 60 reads the image on the printing paper before the image reading unit 60 reads the image. .

  Specifically, the print control unit 40 prints a lining image at a specific position where the image reading unit 60 reads an image on the printing paper before the image reading unit 60 reads the image, and the lining image is printed. The printed paper after being reversed is reversed by the reversing mechanism 70, and printing processing is executed on the reversed printed paper.

  The image processing unit 50 detects image characteristics based on the image data read by the image reading unit 60. In the present embodiment, the image processing unit 50 detects the presence or absence of toner fog based on the image data read by the image reading unit 60. A specific method for detecting toner fog will be described later.

  The image forming units 14K, 14Y, 14M, and 14C (image forming means) are configured in substantially the same manner except that the color of the image to be formed is different. Accordingly, the image forming unit 14K will be described below. The configuration of each image forming unit 14 is distinguished by adding K, Y, M, or C.

  The image forming unit 14K forms an electrostatic latent image by the optical scanning device 140K that scans the laser light according to the image data input from the image processing unit 50, and the laser light scanned by the optical scanning device 140K. And an image forming apparatus 150K.

  The optical scanning device 140K modulates the laser light according to the black (K) image data, and irradiates the laser light onto the photosensitive drum 152K of the image forming device 150K.

  The image forming apparatus 150K includes a photosensitive drum 152K as an image carrier that rotates at a predetermined rotational speed in the direction of arrow A, and a charging device as a charging unit that uniformly charges the surface of the photosensitive drum 152K. 154K, a developing device 156K that develops an electrostatic latent image formed on the photosensitive drum 152K, and a cleaning device 158K. The photosensitive drum 152K is uniformly charged by the charging device 154K, and an electrostatic latent image is formed by the laser light irradiated by the optical scanning device 140K. The electrostatic latent image formed on the photosensitive drum 152K is developed with black (K) toner by the developing device 156K and transferred to the intermediate transfer belt 16. Residual toner, paper dust, and the like adhering to the photosensitive drum 152K after the toner image transfer process are removed by the cleaning device 158K.

  The other image forming units 14Y, 14M, and 14C also form yellow (Y), magenta (M), and cyan (C) toner images in the same manner as described above, and intermediately transfer the formed toner images of the respective colors. Transfer to belt 16. The intermediate transfer belt 16 is circulated and driven at a predetermined speed in the direction of arrow A.

  The paper conveyance path 18 conveys the printing paper 32 taken out from the paper tray 17 by the paper feed roller and the printing paper 32 conveyed from the paper reversing mechanism 70. A secondary transfer roll 186 is disposed at the secondary transfer position on the paper conveyance path 18, and the toner images of each color transferred onto the intermediate transfer belt 16 in a multiple manner are transferred by the secondary transfer roll 186. Secondary transfer is performed on the printing paper 32 by the pressure and electrostatic force. The printing paper 32 to which the toner images of the respective colors are transferred is conveyed to the fixing device 19 by the conveying belt.

  The fixing device 19 melts and fixes the toner to the printing paper 32 by performing heat treatment and pressure treatment on the printing paper 32 to which the toner images of the respective colors are transferred.

  The residual toner adhering to the intermediate transfer belt 16 is removed by a cleaning blade or a brush of a belt cleaning device 189 provided downstream of the secondary transfer position.

  Next, FIG. 3 shows a hardware configuration of the image forming apparatus 10 in the image forming system of the present embodiment.

  As shown in FIG. 3, the image forming apparatus 10 transmits and receives data to and from a CPU 51, a memory 52, a storage device 53 such as a hard disk drive (HDD), and an external terminal device 20 via the network 30. A print interface 56 including a communication interface (IF) 54, a user interface (UI) device 55 including a touch panel or a liquid crystal display and a keyboard, and the image forming units 14K, 14Y, 14M, and 14C described above. These components are connected to each other via a control bus 57.

  The CPU 51 executes predetermined processing based on a control program stored in the memory 52 or the storage device 53, whereby the print control unit 40 and the image processing unit 50 described above are configured. In the present embodiment, the CPU 51 has been described as reading and executing a control program stored in the memory 52 or the storage device 53, but the program is stored in a storage medium such as a CD-ROM and stored in the CPU 51. It is also possible to provide.

  Next, the configuration at the reading position when the image reading unit 60 reads an image on the printing paper 32 will be described with reference to FIG.

  As shown in FIG. 4, the background of the reading position when the image reading unit 60 reads an image is a black image. FIG. 4 shows a configuration in which a black background member 80 is provided.

  The background member 80 is installed so as to be positioned on the back surface of the printing paper 32 when the image reading unit 60 reads the image of the printing paper 32, and is configured to have a black color different from the white color of the printing paper 32. Has been.

  The reason why the background of the printing paper 32 is black in this way is to improve the front and back registration accuracy by increasing the detection accuracy of the paper corner and paper edge. In other words, by making the background image of the printing paper black, which has a large difference in luminance value from that of the white printing paper, the paper corner and paper edge are reliably detected, and the position of the printing paper is reliably detected. This is the configuration.

  Next, an example of a test chart image read by the image reading unit 60 is shown in FIG. The test chart image example shown in FIG. 5 is an image in which three measurement patches 61 to 63 for measuring density values are arranged against a white background.

  Next, FIG. 6 shows an example of a reading area when the image reading unit 60 reads an image from the printing paper on which the test chart image shown in FIG. 5 is printed.

  As shown in FIG. 6, the image reading unit 60 includes density value detection areas 71 to 73 for measuring the densities of the measurement patches 61 to 63, and paper corner detection areas 81 to 81 for detecting the corner positions of the print paper 32. 84. The RGB values of the image in the toner fog detection area 91 for measuring the luminance value for determining whether or not the toner fog is generated are read.

  Next, in the image forming apparatus 10 of the present embodiment, white toner is printed at a position behind the reading position of the image reading unit 60, and the image on the printing paper 32 is transferred by the image reading unit 60 after the front and back sides of the printing paper are reversed. A state of reading will be described with reference to the drawings.

  First, as shown in FIG. 7, the print control unit 40 corresponds to density value detection areas 71 to 73, sheet angle detection areas 81 to 84, and a toner fog detection area 91 that are image reading positions of the image reading unit 60. Print the backing image with white toner at the position. As shown in FIG. 8, the image reading unit 60 does not read the image on the printing paper 32 on which the backing image is printed, and passes through the paper conveyance path.

  Then, the printing paper on which the backing image has been printed is reversed by the paper reversing mechanism 70 so that the backing image printed with the white toner is the back side of the printing paper (the side opposite to the side on which the printing process is performed). Become.

  Next, the print control unit 40 performs control to print the test chart image as shown in FIG. 5 on the printing paper after the front and back sides are reversed by the paper reversing mechanism 70.

  Then, the printing paper 32 on which the test chart image has been printed is conveyed again to the reading position of the image reading unit 60 through the paper conveyance path as shown in FIG.

  Then, the image reading unit 60 reads the images in the density value detection areas 71 to 73 of the printing paper 32 on the paper conveyance path, the paper corner detection areas 81 to 84, and the toner fog detection area 91. At this time, as shown in FIG. 9, the background image formed by the white toner is formed on the surface opposite to the surface on which the image is read by the image reading unit 60.

  Next, an example of reading when the test chart image is read by the image reading unit 60 will be described with reference to FIG. FIG. 10 shows an example of reading when the printing paper 32 is a thin paper.

  In the reading example shown in FIG. 10, toner fog occurs in the right region of the printing paper 32. In FIG. 10, since the printing paper is a thin paper, the black of the background image 80 is transmitted through the printing paper even in a region where toner fog does not occur.

  In the area where the toner fog occurs, the black color of the background image 80 is a color in which the color transmitted through the printing paper and the color due to the toner fog are mixed.

  However, since a background image of white toner is printed on the back side of the density value detection areas 71 to 73, the sheet angle detection areas 81 to 84, and the toner fog detection area 91, these detection areas are black by the background member 80. You can see that they are not so much affected.

  That is, the paper corner detection areas 81 and 82 are white images that are the ground color of the printing paper 32, and the paper corner detection areas 83 and 84 and the toner fog detection area 91 are images of colors due to toner fog. ing.

  Next, determination processing when determining whether or not toner fog has occurred by the image processing unit 50 will be described with reference to the flowchart of FIG.

  First, the image processing unit 50 acquires RGB values of the toner fog detection area 91 (step S101). Then, the image processing unit 50 determines whether or not the acquired RGB value of the toner fog detection area 91 satisfies a preset toner fog determination condition (step S102).

  Here, the image processing unit 50 reads the RGB value of the white ground color of the printing paper 32 in advance, and sets the toner fog determination condition based on the read RGB value.

  For example, in the case of 256 gradations, the RGB value should be (255, 255, 255) in the case of essentially perfect white, so that Rth, Gth, Bth (for example, as threshold values as toner fog determination conditions) 230) is set in advance.

  Then, the image processing unit 50 determines that the toner fog has occurred when at least one of the measured RGB values is equal to or less than any of Rth, Gth, and Bth.

  If the toner fog determination condition is satisfied in step S102, the image processing unit 50 determines that toner fog has occurred (step S103). If the toner fog determination condition is not satisfied in step S102, the image processing unit 50 determines that no toner fog has occurred (step S104). Then, the determination result of the toner fog determination is displayed via the user IF or the like (step S105).

  A specific example of the toner fog determination process will be described with reference to FIG.

  For example, as shown in FIG. 12A, when any of RGB measured luminance values measured by the image reading unit 60 is larger than Rth, Gth, and Bth, toner fog occurs. It is determined that it is not.

  Then, as shown in FIG. 12B, when the value of the G (green) signal is less than or equal to Gth among the RGB measured luminance values measured by the image reading unit 60, toner fog occurs. It is determined that

  Note that when the read value of the G signal is smaller than the threshold value Gth, it can be determined that toner fogging due to magenta toner has occurred. This is because when the toner fog due to magenta toner occurs, the reflection amount of the green (G) signal, which is a complementary color of magenta, is lower than that of white, so that the value of the G (green) signal is low. Thus, it can be determined that toner fogging due to magenta toner has occurred.

  The print control unit 40 does not keep the amount of white toner (halftone dot area ratio) for printing the backing image, but changes it based on the thickness information of the printing paper on which the printing process is to be executed. Also good.

  Specifically, the print control unit 40 controls the printing process so that the halftone dot area ratio of the backing image increases as the thickness of the sheet on which the printing process is to be performed is thinner.

  For example, it is experimentally determined in advance for each paper thickness (basis weight: weight per square meter of paper) how much the backing image can be printed to detect the toner fog, A graph as shown in FIG. 13 is created.

  The print control unit 40 stores paper information such as paper thickness and paper quality of the paper to be printed in advance, and refers to the paper information of the paper to be printed from now on and the graph as shown in FIG. Thus, white toner in an amount (halftone dot area ratio) corresponding to the paper to be printed is printed as a backing image.

  In the above-described embodiment, the configuration in which the image reading unit 60 is provided on the printing surface side has been described. However, the image reading unit 60 is provided on the opposite side to the printing surface, and is opposite to the printing surface. A configuration in which an image on the printing paper 32 is read from the side is also possible. An example of such a configuration is shown in FIG.

  In the configuration example illustrated in FIG. 14, the image reading unit 60 is installed below the paper conveyance path. For example, a part of the paper conveyance path is transparent or a gap, and the printing paper on which the image reading unit 60 is conveyed The image on the back side of 32 can be read. In the configuration example shown in FIG. 14, the black background member 80 is installed above the printing paper 32, and the image reading unit 60 is configured so that the printing paper 32 overlaid on the background member 80 is An image can be read.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image reading apparatus 14Y, 14M, 14C, 14K Image forming unit 16 Intermediate transfer belt 17 Paper tray 18 Paper conveyance path 19 Fixing device 20 Terminal device 30 Network 32 Printing paper 40 Print control part 50 Image processing part 51 CPU
52 Memory 53 Storage Device 54 Communication Interface (IF)
55 User Interface (UI) Device 56 Print Engine 57 Control Bus 60 Image Reading Unit 61-63 Measurement Patch 70 Paper Inversion Mechanism 71-73 Density Value Detection Area 81-84 Paper Angle Detection Area 91 Toner Cover Detection Area 140K Optical Scanning Device 150K Image forming device 152K, 152Y, 152M, 152C Photosensitive drum 154K Charging device 156K Developer 158K Cleaning device 162K, 162Y, 162M, 162C Primary transfer roll 186 Secondary transfer roll

Claims (8)

Reading means for reading an image at a specific position of the paper after printing processing in the conveyance path;
Detecting means for detecting image characteristics based on image data read by the reading means;
Print control means for controlling to print a lining image at a position on the back side of a specific position where the image is read by the reading means with respect to the paper before the image is read by the reading means;
An image forming apparatus.   2. The image according to claim 1, wherein the print control unit controls to print a lining image only at a position behind a specific position where the reading unit reads an image on a sheet before the reading unit reads the image. Forming equipment.   The image forming apparatus according to claim 1, wherein the printing control unit changes a halftone dot area ratio of a backing image to be printed based on thickness information of a sheet on which printing processing is to be executed.   The image forming apparatus according to claim 3, wherein the printing control unit controls the printing process such that the halftone dot area ratio of the backing image increases as the thickness of the sheet on which the printing process is to be performed is thinner.   The image forming apparatus according to claim 1, wherein the backing image is formed of a white color material.   The image forming apparatus according to claim 1, wherein the detection unit detects the presence or absence of color material fogging based on image data read by the reading unit.   7. The image forming apparatus according to claim 1, further comprising a background member that is disposed so as to be positioned on a back surface of the sheet when the reading unit reads an image of the sheet, and has a color different from the color of the sheet. . A step of printing a backing image at a position on the back side of the specific position where the image is read by the reading means on the paper before the image is read by the reading means for reading the image at the specific position of the paper after the printing process in the conveyance path. When,
A step of reading an image at a specific position on the paper after the backing image is printed by the reading unit;
A program for causing a computer to execute an image characteristic detecting step based on image data read by the reading unit.