JP2005257834A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the print density of the image data of a document is corrected based upon the density of the image data of images on a sheet printed on its one side, which is to be supplied to an image forming part for printing the image data of the document, and the image data after the correction is printed on the sheet. <P>SOLUTION: A control part uses a close-contact type sensor to read images printed on a sheet from the unprinted side of the sheet which has images on its one side (i.e., images seen through from the unprinted side) and creates image data of the image. Next, the control part performs the process of correcting the density of the image data of a document, which corresponds to the area where the created image data is detected. Thereafter, based on the image data after the correction, the control part prints the image onto the unprinted side of the sheet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that prints an image of a read original on an unprinted surface of a sheet that has been printed on one side in an image forming unit, and in particular, on the sheet supplied to the image forming unit The present invention relates to an image forming apparatus that corrects the print density of image data of the original based on the density of image data of the image and prints the corrected image data on the sheet.

Recently, for example, when copying materials to be distributed to an in-house company using an image forming apparatus configured as a copier, printer, facsimile, or a complex machine in a company or the like, reasons for environmental countermeasures and cost reduction, etc. Therefore, in general, the unprinted side of a sheet on which one side is already printed (hereinafter referred to as a backing paper) is often used. However, when replenishing the backing paper to the paper feed cassette, if the accommodation direction of the printed surface of the backing paper is wrong, a new image is further printed on the already printed surface of the backing paper, that is, overwrite printing. There is a problem that wasteful printing processing is performed. In order to solve such a problem, for example, in the printing apparatus (an example of an image forming apparatus) disclosed in Patent Document 1, an image data reading unit is used, and in the image forming apparatus illustrated in Patent Document 2, a sensor is already used. Each printed surface is detected, and based on these detection results, control is performed so that a new image is printed on the unprinted surface of the backing paper. Thus, in the printing apparatus or the image forming apparatus, even if the user mistakenly accommodates the printed side of the backing paper in the paper feeding cassette, the above overwrite printing is not performed. It has become.
JP-A-9-76588 JP 10-97112 A

However, when printing is performed using the backing paper, the surface of the backing paper opposite to the surface on which the image is printed, that is, the image on the backing paper is already printed on the backing paper. There is a problem that the displayed image can be seen through. This problem is particularly noticeable when the backing paper is a thin sheet. In the region where the printed image on the backing paper and the newly printed image overlap the unprinted surface, Since the image becomes dark, the new image may be uneven and difficult to see.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image of an image on a single-side printed sheet supplied to an image forming unit for printing image data of a document. An object of the present invention is to provide an image forming apparatus that corrects the print density of image data of the original document based on the density of the data and prints the corrected image data on the sheet.

  To achieve the above object, the present invention provides a document image reading means for reading an image of a document, a document image data generating means for generating image data of the document read by the document image reading means, and the document image. A sheet image reading device for reading an image on a single-side printed sheet supplied to the image forming unit in an image forming apparatus comprising an image forming unit for printing the image data generated by the data generating unit And the print density of the image data of the original printed on the unprinted surface of the sheet based on the density of the image data of the image on the sheet read by the sheet image reading means, and the corrected And a corrected image printing means for printing an image on an unprinted surface of the sheet in the image forming unit based on the image data. That it is configured as an image forming apparatus.

  In the image forming apparatus, for example, the sheet image reading unit reads an image on the sheet from a surface opposite to a surface on which the image is printed, and the corrected image printing unit includes the sheet. Based on the image data detected from the area where the image is read by the image reading means, the print density of the image data corresponding to the area in the original image data generated by the original image data generating means is corrected. It is possible.

Further, since the image forming apparatus includes a density threshold value storage unit that stores a density threshold value of the image data of the image on the sheet, in the image forming apparatus, for example, the sheet image reading unit is arranged on the sheet. The image is read from the surface on which the image is printed, and the corrected image printing means has a density higher than the threshold density stored in the density threshold storage means in the image data of the image on the sheet. Based on the distribution data of the difference density between the density of the image data in the area and the threshold density, the print density of the image data corresponding to the area in the original image data generated by the original image data generation means is corrected. It may be a thing.
In this case, it is desirable that the density threshold value is stored in a stepwise manner in the density threshold value storage unit corresponding to the thickness of the sheet.

As described above, in the image forming apparatus according to the present invention, when the image on the sheet is read from the surface opposite to the surface on which the image is printed by the sheet image reading unit, the corrected image is displayed. The printing means corrects the print density of the image data corresponding to the same area in the image data of the original based on the image data detected from the area where the image on the sheet is read. As a result, even if the image already printed on the sheet can be seen through the unprinted surface of the sheet, the corrected image printing means prints the image data corresponding to the area. By correcting the density so as to reduce the density, for example, the unevenness of the image in the same area (the area where the image already printed on the sheet overlaps the image of the original newly printed on the unprinted surface) is corrected. Can be prevented. As a result, an easy-to-see image can be provided even when the sheet is thin.
According to the present invention, when the image on the sheet is read from the surface on which the image is printed by the sheet image reading means, the corrected image printing means is configured to make the original image based on the difference density distribution data. There is also provided an image forming apparatus that corrects the print density of image data corresponding to the same area in the original image data generated by the data generation means. Therefore, similarly, even when an image already printed on the sheet is seen through the unprinted side of the image on the sheet, the corrected image printing means does not display the image data corresponding to the area. By correcting the print density so as to be light, for example, unevenness of the image in the same area (the area where the image already printed on the sheet overlaps the image of the original newly printed on the unprinted surface). Can be prevented. As a result, an easy-to-see image can be provided even when the sheet is thin.
When the corrected image printing unit corrects the image density to be thin, it is possible to save the amount of toner used for printing the original image in the image forming apparatus.

Hereinafter, embodiments and examples of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. It should be noted that the following embodiments and examples are examples embodying the present invention, and do not limit the technical scope of the present invention.
FIG. 1 is a schematic cross-sectional view of the image forming apparatus X1 (X2) according to the embodiment of the present invention. FIG. 2 is a block diagram of the main part of the control system of the image forming apparatus X1 according to the first embodiment. FIG. 3 is a flowchart showing image density correction processing when a new image is printed on the unprinted side of the backing paper, which is executed by the control unit 31a included in the image forming apparatus X1, and FIG. 4 is related to the second embodiment. FIG. 5 is a block diagram of the main part of the control system of the image forming apparatus X2. FIG. 5 is an image density correction when a new image is printed on the unprinted surface of the backing paper, which is implemented by the control unit 31b of the image forming apparatus X2. It is a flowchart showing a process.
Note that the image forming apparatuses X1 and X2 cited as examples of the present invention are monochrome development image forming apparatuses, but the present invention can also be applied to color development image forming apparatuses. The developing method in the image forming apparatuses X1 and X2 may be a dry or wet toner type, or an ink jet type. Further, the image forming apparatuses X1 and X2 may be image forming apparatuses that perform printing processing independently, or image formation that performs printing processing by receiving data signals from an external terminal or the like via a network. It may be a device.

<First Embodiment>
First, the configuration of the image forming apparatus X1 according to the first embodiment of the present invention will be described with reference to FIGS.
The image forming apparatus X1 is detachably provided with a plurality of paper feed cassettes 5 that contain sheets for printing images. The sheet feeding cassette 5 accommodates sheets of different forms. The different types of sheets refer to, for example, sheets having different sizes and sheets having different paper qualities and directions, such as plain paper and the backing paper. A duplex unit 6 is disposed above the paper feed cassette 5, and an image forming unit 7 for printing image data of the read original is provided above the duplex unit 6. A fixing device 20 for fixing toner onto a sheet such as transfer paper is provided at a side portion of the image forming unit 7, and a scanner 8 (an example of a document image reading unit in the present invention) for reading an image is provided above the automatic device. A document conveying device (hereinafter referred to as ADF) 9 is attached. The image forming unit 7 and the fixing device 20 are examples of the image forming unit in the present invention.
Here, a contact-type sensor 30a (in which an optical photosensitive element for reading the image density on the sheet surface is arranged in the vertical conveyance path of the sheet provided between the sheet feeding cassette 5 and the image forming unit 7). contact image sensor: an example of a sheet image reading means in the present invention is provided. In this embodiment, using the contact type sensor 30a, an image in which the printed image on the backing paper as an example of the sheet can be seen through to an unprinted surface is opposite to the surface on which the image is printed. The surface, that is, the image is read from the unprinted surface. In addition, about the installation position of the contact | adherence type | mold sensor 30a, FIG. 1 is an example, Comprising: It does not restrict to this.

A display operation unit 3 such as a liquid crystal touch panel is disposed on the upper surface of the main body of the image forming apparatus X1, and the display operation unit 3 is provided with a plurality of buttons, switches, and the like. When the user operates these buttons and switches, the image quality setting, variable magnification setting, selection of a sheet used for printing (that is, selection of the paper feed cassette 5), or an original image read by the scanner 8 described later Settings for various functions of the image forming apparatus X1, such as setting whether to correct the density (hereinafter referred to as setting of the image density correction mode). The setting of the image density correction mode for the backing paper, which will be described later with reference to FIG.
Further, the image forming unit 7 is provided with an image forming unit 15 in which a charging device 12, a developing device 13, and a cleaning device 14 are disposed around a photosensitive drum 11 as an image carrier. The transfer device 16 is disposed opposite to the photosensitive drum 11. The photosensitive drum 11 has a photosensitive layer formed on the surface of an aluminum cylinder having a diameter of 84 mm, for example, and is driven to rotate clockwise in FIG. The charging device 12 charges the surface of the rotating photosensitive drum 11 to several hundred volts by corona discharge. On the downstream side of the charging device 12 on the surface of the photosensitive drum 11 in the rotational direction, the surface of the photosensitive drum 11 is exposed by an exposure device 18 including an LED array head and a selfoc lens to form an electrostatic latent image. Is done. Image data used for controlling the light emission output of the exposure device 18 is output from the image processing unit 4.

Hereinafter, the operation during the printing process when printing an image on the backing paper in the image forming apparatus X1 will be described mainly with reference to FIG.
First, when a scanner 8 as a light source scans a document placed on a document table of the image forming apparatus X1, reflected light from the document is converted into a CCD 10 (Charge-Coupled Device; image signal into an electrical signal) via a mirror. Device), where it is A / D converted and input to the image processing unit 4 as digital image data (original image data). Next, the input document image data is subjected to appropriate image processing by the image processing unit 4. After that, when the original image data after image processing is input to the exposure apparatus control means 19, the exposure apparatus control means 19 controls the exposure apparatus 18 so that exposure is performed according to the input original image data. To do.
On the other hand, when an image based on the original image data is printed on the non-printed side of the backing paper, first, a pickup roller and a pick-up roller and The backing paper is conveyed from the paper feed cassette 5 toward the image forming unit 7 by a conveying roller that rotates in the same direction as the pickup roller. In this embodiment, when a new image is printed on the unprinted surface of the backing paper, the contact sensor 30a causes the image already printed on the backing paper to be printed on the unprinted surface of the backing paper. When the image data is read from the image data, based on the image data detected from the read image area, the print density of the image data corresponding to the same area in the original image data to be printed on the unprinted surface of the backing paper is determined. It is corrected. Details will be described later.

Further, in the developing device 13, a developing roller (not shown) rotates so that the magnetic brush formed on the surface of the developing roller comes into contact with the surface of the photosensitive drum 11 and attaches charged toner to the electrostatic latent image. Thus, a toner image is formed. This toner image is transferred between the photosensitive drum 11 and the transfer belt 17 in which the backing paper conveyed by the conveying roller from the paper feeding cassette 5 moves at the same speed as the peripheral speed of the photosensitive drum 11 in the transfer device 16. The toner image is transferred to the unprinted surface of the backing paper by being charged while being conveyed while being held between them.
Further, a cleaning device 14 is disposed on the downstream side of the transfer device 16, and toner and other deposits remaining on the surface of the photosensitive drum 11 are removed. The backing paper onto which the toner image has been transferred by the transfer device 16 is conveyed to a fixing device 20 provided downstream in the transport direction. The transfer device 16 included in the image forming apparatus X1 employs a transfer belt, but it can be replaced with a transfer roller.
The fixing device 20 includes a fixing roller 1 and a pressure roller 2 provided with a pressure mechanism facing the fixing roller 1. The toner image adhering to the non-printed surface of the backing paper conveyed from the transfer device 16 by the transfer belt or the transfer roller is used while the backing paper passes between the fixing roller 1 and the pressure roller 2. The toner image is melted and fixed by the heat of the fixing roller 1, and the sheet is pressed against the fixing roller 1 by the pressure roller 2, whereby the toner image is fixed on the unprinted surface of the backing paper. The backing paper on which the toner image has been fixed by the fixing device 20 is then sent to the sheet processing apparatus B side, subjected to predetermined processing, and then discharged from a predetermined sheet discharge port.

Here, the configuration of the main part of the control system of the image forming apparatus X1 will be described with reference to FIG.
The entire image forming apparatus X1 is controlled by a control unit 31a including a CPU that performs various arithmetic processes, a ROM, a RAM, and the like, which are semiconductor memories. The control unit 31a is connected to the image processing unit 4, the paper feed cassette 5, the image forming unit 7, the scanner 8, the contact type sensor 30a, and the like via buses. Further, the control unit 31a executes programs (document image data generation function 32, corrected image printing function 33a, etc.) stored in the storage unit such as the ROM, thereby performing various controls and calculations in the image forming apparatus X1. Processing is performed, and details will be described later.

Next, referring to the flowchart of FIG. 3, the image density when a new image is printed on the unprinted side of the backing paper (one-side printed sheet), which is implemented by the control unit 31a included in the image forming apparatus X1. The correction process will be described.
In this process, when a new image is printed on the unprinted surface of the backing paper, the contact sensor 30a reads the image already printed on the backing paper from the unprinted surface of the backing paper. In this case, based on the image data detected from the read image area, the print density of the image data corresponding to the same area in the image data of the original printed on the unprinted side of the backing paper is corrected. Is.
Here, it is assumed that the user has previously set the image density correction mode from the display operation unit 3 as a premise of this processing. In this process, there is no problem as long as the storage unit in which image data is stored in the processes of steps S3, S7, and S8 described later is an appropriate storage unit provided in the image forming apparatus X1.
This process is started when, for example, a start button (not shown) provided in the display operation unit 3 is pressed.
S1, S2,... Described in the following description represent processing procedure (step) numbers.

When it is detected from the input signal that the start button provided on the display operation unit 3 is pressed by the user (Yes side of S1), the control unit 31a first uses the scanner 8 to place a document table (not shown). The image of the placed document is read (S2). The read original image is A / D converted by the CCD 10 to generate image data (hereinafter referred to as original image data), and then temporarily stored in an appropriate storage unit (S3).
Further, the control unit 31a drives the motor (not shown) to rotate the pickup roller and the conveyance roller as described above, thereby conveying the backing paper from the paper feed cassette 5 toward the image forming unit 7. (S4). Here, when the user has not set the image density correction mode from the display operation unit 3 (No side of S5), the control unit 31a sets the normal image processing (that is, the image density of the document). After performing the printing process without performing the correction process, the present process is terminated (S9). In this process, since it is assumed that the user has set the image density correction mode from the display operation unit 3, the control unit 31a performs the process of step S6 (Yes in S5).
In the subsequent step S6, the controller 31a uses the contact-type sensor 30a provided in the vicinity of the paper feed cassette 5, and the image already printed on the backing paper from the unprinted side of the backing paper. Read. That is, among the images already printed on the backing paper, an image in which the image has passed through the unprinted surface of the backing paper due to a particularly high density is read. At this time, an appropriate threshold value is set in advance, and only an image that is darker than the appropriate threshold density, that is, an image of an area that has passed through the unprinted surface of the backing paper because it is particularly dark is read. Also good. Further, image data generated by A / D conversion of the read image (hereinafter referred to as image data on the back paper) is temporarily stored in an appropriate storage unit (S7).
Next, the control unit 31a applies to the image data of the original stored in the process of step S3 corresponding to the area where the image data of the back paper stored in the process of step S7 is detected. After performing the density correction process, the corrected image data is stored in an appropriate storage unit (S8). In this density correction process, for example, the density of image data in the area where the image data of the backing paper is detected is 30 and the density of image data in the same area in the image data of the original is 70. In this case, the density of the image data in the same area in the image data of the original is reduced from density 70 to density 40 as a differential density.
Thereafter, the control unit 31a prints an image based on the corrected image data stored in the process of step S8 on the unprinted side of the backing paper, and ends this process (S9). At this time, the image data stored in steps S3, S7, and S8 is erased from the storage unit.
Note that the original image data generation function 32 (an example of the original image data generation means in the present invention) is used for the process in step S3 in the present process, and the corrected image print function 33a (in the present invention) The control unit 31a uses an example of the corrected image printing unit in FIG.

<Second Embodiment>
Next, the configuration of the image forming apparatus X2 according to the second embodiment of the present invention will be described with reference to FIG. 1, FIG. 4, and FIG. Note that members, functions, and the like common to the image forming apparatus X2 and the image forming apparatus X1 according to the first embodiment of the present invention are denoted by the same reference numerals and description thereof is omitted.
As shown in FIG. 1, an optical for reading the image density on the sheet surface is provided in the vertical sheet conveyance path provided between the paper feed cassette 5 and the image forming unit 7 provided in the image forming apparatus X2. A contact type sensor 30b (contact image sensor: an example of sheet image reading means in the present invention) is provided. In this embodiment, the contact-type sensor 30b is used to read the printed image on the backing paper from the surface on which the image is printed. In addition, about the installation position of the contact | adherence type | mold sensor 30b, FIG. 1 is an example, Comprising: It does not restrict to this.
When the image forming apparatus X2 prints an image based on the original image data on the unprinted side of the backing paper, first, the paper feeding that accommodates the backing paper among the plurality of paper feeding cassettes 5 is performed. The backing paper is conveyed from the cassette toward the image forming unit 7 by a pickup roller and a conveyance roller that rotates in the same direction as the pickup roller. In this embodiment, the contact-type sensor 30b reads an image of the printed surface of the backing paper being conveyed, so that the threshold value stored in an internal storage unit 34 to be described later in the image data of the image is read. The print density of the image data corresponding to the same area of the original image data is corrected based on the distribution data of the difference density between the density of the image data in the higher density area and the threshold density. Details will be described later.

Next, the configuration of the main part in the control system of the image forming apparatus X2 will be described with reference to FIG.
The entire image forming apparatus X2 is controlled by a control unit 31b including a CPU that performs various arithmetic processes, a ROM, a RAM, and the like, which are semiconductor memories. The control unit 31b includes an image processing unit 4, a paper feeding cassette 5, an image forming unit 7, a scanner 8, a contact sensor 30a, and a threshold value of density of image data of a printed image on the backing paper (hereinafter referred to as threshold density). ) And the like, and an internal storage unit 34 (an example of a density threshold storage unit in the present invention) that stores various information relating to the operation of the image forming apparatus X2, and the like. Here, the threshold density stored in the internal storage unit 34 is for extracting a high-density print area that is transparent to the back (non-printing surface) of the sheet. Whether to show through is related not only to the density of the image on the printing surface but also to the thickness of the sheet (hardness of see-through), so the threshold density is stored stepwise corresponding to the thickness of the backing paper. That is, a higher density is used for the threshold density used when the thick backing paper is printed, and a lower density is used for the threshold density used when the thin backing paper is printed. , Stored in the internal storage unit 34 in a previously associated state. In the image forming apparatus X2, the control unit 31b automatically sets the threshold density when the user selects the type of the backing paper used for printing from the display operation unit 3.
Further, the control unit 31b executes programs (document image data generation function 32, corrected image printing function 33b, etc.) stored in the storage unit such as the ROM, whereby various controls and arithmetic processing in the image forming apparatus X2 are performed. The details will be described later.
Note that all or some of the information stored in the internal storage unit 34 may be stored in the RAM included in the control unit 31b or in an appropriate storage unit included in the image forming apparatus X2.

Next, an image density correction process when a new image is printed on the unprinted surface of the backing paper, which is performed by the control unit 31b included in the image forming apparatus X2, will be described with reference to the flowchart of FIG.
In this process, when a new image is printed on the unprinted surface of the backing paper, the printed image on the backing paper is read from the surface on which the image is printed by the contact sensor 30b. In addition, based on the distribution data of the difference density between the density of the image data of the area having a density higher than the threshold density stored in the internal storage unit 34 and the threshold density in the image data of the read image, The print density of the image data corresponding to the same area of the image data is corrected.
Here, it is assumed that the user has previously set the image density correction mode from the display operation unit 3 as a premise of this processing. In this process, there is no problem as long as the storage unit in which image data is stored in the processes of steps S22, S26, S30, and S31 described later is an appropriate storage unit provided in the image forming apparatus X2.
This process is started when, for example, a start button (not shown) provided in the display operation unit 3 is pressed.
S20, S21,... Described in the following description represent processing procedure (step) numbers.

When it is detected from the input signal that the start button provided on the display operation unit 3 is pressed by the user (Yes side of S20), the control unit 31b is first implemented by the image forming apparatus X1 described above. The same processing as in steps S2 to S5 is performed. Next, in this process, since it is assumed that the user has set the image density correction mode from the display operation unit 3, the control unit 31b performs the process of step S25 (Yes side of S24).
In the subsequent process of step S25, the control unit 31b reads the image from the surface of the backing paper on which the image has already been printed, using the contact type sensor 30b provided in the vicinity of the paper feed cassette 5. Image data obtained by A / D conversion of the read image (hereinafter referred to as backing paper image data) is temporarily stored in an appropriate storage unit (S26). Next, the control unit 31b acquires the threshold density from the internal storage unit 34 (S27), and compares the threshold density with the density of the image data on the backing paper (S28). Here, when the density of the image data of the entire area in the image data of the backing paper is lower than the acquired threshold density (No side of S29), the control unit 31b performs the process of step S22. After printing an image based on the generated image data on the unprinted side of the backing paper, the present process is terminated (S32).
In the process of step S29, when image data having a density higher than the threshold density acquired from the image data of the backing paper is detected (Yes side of S29), the control unit 31b Distribution data (bitmap data) describing the difference density between the density of the image data having a density higher than the density and the threshold density is generated, and the distribution data is stored in an appropriate storage unit (S30). In this case, since the image already printed on the backing paper and the image of the original to be corrected are in an axisymmetric relationship, the distribution data is stored in an appropriate storage unit at the coordinate position after coordinate conversion. . Thereafter, based on the stored distribution data and the image data of the original stored in step S22, the same process as in step S8 is performed (S31).
Thereafter, the controller 31b prints an image based on the corrected image data stored in the process of step S31 on the unprinted side of the backing paper, and ends this process (S32). At this time, the image data stored in the processes of steps S22, S26, S30, and S31 are erased from the storage unit.
Note that the original image data generation function 32 (an example of the original image data generation means in the present invention) is used for the process in step S22 in the present process, and the corrected image print function 33b (in the present invention) The control unit 31b uses an example of the corrected image printing unit in FIG.

1 is a schematic sectional view of an image forming apparatus X1 (X2) according to an embodiment of the present invention. FIG. 3 is a configuration block diagram of a main part in a control system of the image forming apparatus X1 according to the first embodiment. 7 is a flowchart showing an image density correction process when a new image is printed on an unprinted surface of a backing paper, which is executed by the control unit 31a included in the image forming apparatus X1. FIG. 9 is a configuration block diagram of a main part in a control system of an image forming apparatus X2 according to a second embodiment. 6 is a flowchart showing an image density correction process when a new image is printed on an unprinted surface of a backing paper, which is implemented by the control unit 31b included in the image forming apparatus X2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fixing roller 2 ... Pressure roller 3 ... Display operation part 4 ... Image processing part 5 ... Paper feed cassette 6 ... Duplex unit 7 ... Image forming part 8 ... Scanner 9 ... Automatic document feeder (ADF)
10 ... CCD
DESCRIPTION OF SYMBOLS 11 ... Photoconductor drum 12 ... Charging device 13 ... Developing device 14 ... Cleaning device 15 ... Image forming unit 16 ... Transfer device 17 ... Transfer belt 18 ... Exposure device 19 ... Exposure device control means 20 ... Fixing device 30a, 30b ... Contact type Sensors 31a, 31b ... control unit 32 ... original image data generation function 33a, 33b ... corrected image printing function 34 ... internal storage unit

Claims (4)

A document image reading means for reading a document image;
Document image data generating means for generating image data of the document read by the document image reading means;
An image forming apparatus comprising: an image forming unit for printing the image data generated by the document image data generating unit;
Sheet image reading means for reading an image on a single-side printed sheet supplied to the image forming unit;
Based on the density of the image data of the image on the sheet read by the sheet image reading means, the print density of the image data of the document printed on the unprinted surface of the sheet is corrected, and the corrected image data An image forming apparatus comprising: a correction image printing unit that prints an image on an unprinted surface of the sheet in the image forming unit. The sheet image reading means is
The image on the sheet is read from the surface opposite to the surface on which the image is printed,
The corrected image printing means is
Correcting the print density of image data corresponding to the same area in the original image data generated by the original image data generation means based on the image data detected from the area where the image was read by the sheet image reading means The image forming apparatus according to claim 1, wherein A density threshold value storage means for storing a density threshold value of the image data of the image on the sheet;
The sheet image reading means is
The image on the sheet is read from the surface on which the image is printed,
The corrected image printing means is
The original based on the distribution data of the difference density between the density of the image data in the region having a density higher than the threshold density stored in the density threshold storage means in the image data of the image on the sheet and the threshold density 2. The image forming apparatus according to claim 1, wherein the print density of the image data corresponding to the same area in the image data of the document generated by the image data generating means is corrected.   The image forming apparatus according to claim 3, wherein the density threshold value is stored stepwise in the density threshold value storage unit in correspondence with the thickness of the sheet.

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