JP4347238B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine.

  2. Description of the Related Art Image forming apparatuses that form an image on recording paper by an electrophotographic process using an image carrier such as a photosensitive drum or a transfer belt are widely known. In this type of image forming apparatus, the density of an image output on recording paper may change due to a change in development performance.

  In order to solve this problem, conventionally, a plurality of types of patch patterns are experimentally output on a recording sheet, and the image on the recording sheet is read, and the image value obtained by the reading operation and a predetermined reference value are obtained. A method is known in which density comparison is performed by changing a threshold table used for screen processing when generating the patch pattern in accordance with the comparison result.

  On the other hand, a method is also known in which density adjustment is performed by changing a γ correction table used for γ correction processing.

  For example, in Patent Document 1 below, a first pattern is formed on a recording medium, and the image forming conditions on the image carrier are controlled based on the image characteristics of the first pattern formed on the recording medium. The second pattern is formed on the image carrier, the image characteristics of the second pattern formed on the image carrier are detected, and the detected information is used as reference information. The second pattern is formed on the image carrier, and the post-control image formation condition is corrected based on the difference between the image characteristics of the second pattern formed on the image carrier and the reference information. Techniques to do this are disclosed.

Further, in Patent Document 2 below, regarding the γ correction table used for the density adjustment, a continuous γ correction table is created based on discrete γ correction data, and the printer γ conversion circuit for converting the printer γ characteristic has this γ. A technique for setting a correction table is disclosed.
Japanese Patent No. 3542582 JP 2001-94788 A

  Since the above-described threshold table changing operation is complicated, it is usually performed by a specialized person (serviceman), and it is difficult for general users to easily perform density adjustment. was there. Although Patent Documents 1 and 2 disclose that the density adjustment is performed by changing the γ correction table used for the γ correction processing, in the image forming apparatus capable of adjusting the density by changing the threshold table as described above. It is not intended to enable general users to adjust the density.

  The present invention has been made in view of the above circumstances, and in the case where there is a change in density, an image forming apparatus capable of improving the color reproducibility of a printed matter without imposing a complicated operation on the user as described above. The purpose is to provide.

According to a first aspect of the present invention, there is provided an image forming apparatus capable of adjusting the density of an image formed on a recording sheet by changing a threshold value table used for screen processing, and an image carrier and a toner image on the image carrier. An image forming unit to be formed; an image forming control unit for causing the image forming unit to form a predetermined toner image on the image carrier; and a density of the toner image formed on the image carrier. Density detecting means for performing γ correction processing on input image data using a γ correction table, γ correction table changing means for changing the γ correction table, and on the image carrier A determination unit configured to cause the density detection unit to detect the density of the predetermined toner image formed, and to determine whether or not the γ correction table changing process is required by the γ correction table changing unit according to the detected value ; Drawing on paper Input operation means for inputting a formation instruction, and a plurality of image quality modes for performing image processing corresponding to the type of document to be copied, it is necessary to change processing of the γ correction table by the determining means Is determined, the γ correction table changing means changes the γ correction table, and the γ correction means performs the γ correction processing based on the γ correction table changed by the γ correction table changing means. When the γ correction table changing process is executed by the γ correction table changing unit when the photo mode is selected from the plurality of image quality modes, the image forming instruction by the input operation unit is not accepted. When a warning process for outputting a warning prompting adjustment of gradation by changing the threshold table is performed and the photo mode is not selected, the γ correction table When the changing process of the γ correction table is performed by the changing means is characterized in that not implementing the warning process.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when the image forming control unit causes the image forming unit to perform a toner image forming operation, a predetermined target density is determined in advance. the operation of forming a toner image based on the image data set in advance so as to have a difference was made in the image forming means, said determining means, each concentration of the respective toner images formed on the image bearing member When the density detection unit detects the difference in detected density between the toner images that are targets of density detection by the density detection unit exceeds a predetermined threshold, the γ correction table change unit performs a γ correction table change process. It is characterized in that it is performed.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image forming apparatus includes a notifying unit that notifies that the change of the γ correction table is executed by the γ correction table changing unit. To do.

  According to the first aspect of the present invention, the density detecting unit detects the density of the predetermined toner image formed on the image carrier, and the γ correction table changing unit changes the γ according to the detected value. Since it is determined whether or not the correction table change processing is necessary, if it is determined that the γ correction table change processing by the γ correction table changing means is necessary, the γ correction table change processing is automatically performed. Done. As a result, the density is automatically adjusted, so that even if there is a change in density due to a change in development performance, the color reproducibility of the printed matter is improved without imposing complicated operations on the user. be able to.

  Note that whether or not the γ correction table needs to be changed depends on the density value of the image data obtained by the reading operation for the predetermined image output on the recording paper and the reference density value corresponding to the image data constituting the predetermined image. It is preferable to make a determination in accordance with the density correction value relating to the toner image forming operation of the image forming means derived based on the above.

When the γ correction table is changed by the γ correction table changing means when a photo mode is selected from among a plurality of image quality modes for performing image processing according to the type of document to be copied. Since the warning process for outputting the warning prompting the adjustment of the gradation by changing the threshold value table is performed without accepting the image formation instruction by the input operation means, the photograph in which the reproducibility of the gradation is regarded as important When the mode is set, it is possible to prevent an image from being formed in a state where there is room for further improvement in gradation.

As in the second aspect of the invention, the change of the γ correction table is set in advance so as to have a predetermined target density difference when the image forming unit is caused to perform a toner image forming operation. the operation of forming a toner image based on the image data is detected in each of the concentration detecting means the concentration of each of the toner image formed on the image bearing member by causing said image forming means, the density detection The detection may be performed when the difference between the detected densities of the toner images that are the targets of density detection by the means exceeds a predetermined threshold. In addition to this method, each image forming unit performs each operation of forming a toner image based on the same image data with a predetermined time difference between the toner images formed on the image carrier. It may be performed when the difference in detected density exceeds a predetermined threshold .

  According to the third aspect of the invention, since the gamma correction table changing means notifies that the change of the gamma correction table has been executed, the user can determine whether or not the density adjustment is more accurate. Can do.

  Hereinafter, an embodiment of a color copier as an example of an image forming apparatus according to the present invention will be described. FIG. 1 is a diagram showing an internal configuration of a color copying machine.

  As shown in FIG. 1, the color copying machine 1 includes an image reading unit 10 that reads an image of a color original P placed on a contact glass 11, and forms an image on a recording sheet by the image reading unit 10. The image forming unit 20, the paper discharge unit 30 that discharges the paper after the image formation by the image forming unit 20, and the control unit 40 that controls the image reading unit 10, the image forming unit 20, and the paper discharge unit 30. ing.

  The image reading unit 10 irradiates the color original P placed on the contact glass 11 with the light from the exposure lamp 12, and reflects the reflected light to the reflecting mirrors 13a, 13b, 13c, the lens 14, and R (red). , G (green) and B (blue) color separation filters are used to receive light by the photoelectric conversion element 15 such as a CCD, thereby color-separating the image information of the color original P into R component, G component, and B component. Color image data R, G, B proportional to the light intensity of the component is read. The color image data read in this way is A / D converted into RGB digital image data composed of digital values, and used as input image data to the control unit 40. The control unit 40 determines whether the image of the document P is a color image or a monochrome image based on YUV digital image data obtained by converting RGB digital image data using a predetermined determinant.

  The image reading unit 10 includes an opening / closing lid 16 that is rotatably supported by the apparatus main body so that the front side (front side in FIG. 1) can move upward. A document placing portion 16a for placing a document to be read is formed. When the document is placed on the document placement unit 16a, the image reading unit 10 feeds the images on the contact glass 11 one by one from the lowest document in order to read the image of the document.

  The image forming unit 20 forms a toner image based on the output image data on the recording paper fed from the paper feed cassettes 211, 212, 213 or the manual feed tray 214 disposed at the lower part of the apparatus. Then, the toner image is fixed by the heating roller 231 and the pressure roller 232 of the fixing unit 23. The duplex unit 25 reverses the front and back sides of the recording paper on which one side has been formed and feeds it to the image transfer unit 22 again when forming images on both sides of the recording sheet.

  The image transfer unit 22 is a corona discharge from a charging wire (not shown) to which a high voltage is applied in order along the rotation direction around a photoconductive drum 221 that is rotatably supported by a photoconductor. And a charger 222 for applying a predetermined potential to the surface of the photosensitive drum, and a laser beam corresponding to the output image data from the laser oscillator 223a via the mirror 223b to selectively attenuate the potential of the surface of the photosensitive drum 221. An exposure unit 223 for forming an electrostatic latent image, a developing unit 224 for developing the electrostatic latent image formed on the surface of the photosensitive drum 221 with toner, and a toner image formed on the photosensitive drum 221 for recording paper. A transfer device 225 for transferring to the surface, a static eliminator 226 for discharging the surface of the photosensitive drum 221 and a cleaner for removing residual toner on the surface of the photosensitive drum 221. It has been.

  In the color copying machine 1, in order to form a color image, the exposure unit 223 is configured to form an electrostatic latent image for each color component of the output image data, and the development unit 224 includes C (cyan), M ( Four developing devices 224c, 224m, 224y, and 224k for developing toner images of each color of magenta), Y (yellow), and K (black) are provided.

  When forming a color image, the transfer device 225 temporarily transfers the color toner images developed on the surface of the photosensitive drum 221 onto the transfer belt 225a once, and C (( The toner images of cyan, M (magenta), Y (yellow), and K (black) are superimposed, and then secondarily transferred onto the recording paper conveyed onto the transfer roller 225b. Further, in the case of forming a monochrome image, the transfer unit 225 primarily transfers the black toner image developed on the surface of the photosensitive drum 221 onto the transfer belt 225a, and then the recording is carried onto the transfer roller 225b. Secondary transfer onto paper.

  The density sensor 26 measures the toner density on the surface of the transfer belt 225a to which the toner image is transferred.

  The paper discharge unit 30 includes a discharge branch guide 31 and a plurality of discharge bins. The uppermost discharge bin is a non-sort bin 32, and the other multiple discharge bins are a sort bin 33. Has been. The discharge branch guide 31 can switch the paper discharge direction between the non-sort bin 42 side (conveying path 34 side) and the sort bin 33 side (conveying path 35 side) by a drive unit (not shown). The paper discharged in this way is guided to the non-sort bin 32 side (conveyance path 34 side) or the sort bin 33 side (conveyance path 35 side).

  For example, an input operation unit 50 as shown in FIG. 2 is provided at an appropriate position on the upper surface of the color copying machine 1. The input operation unit 50 includes various button groups 51 including a start button 51a for issuing a print execution instruction, and a display unit 52 including a liquid crystal display or the like for displaying various operation guide information regarding an image forming operation. The display unit 52 has a touch panel function and can appropriately input an operation signal from the operator. The operation signal is output to the control unit 40.

  The color copying machine 1 is provided with a character mode and a photo mode as image quality modes. The character mode is a mode in which when a document to be copied includes a character image, the character image is subjected to image processing suitable for the character image. In the photo mode, the document includes a photographic image. In this case, this is a mode for performing image processing suitable for the photographic image. These image quality modes can be selected by the input operation unit 50.

  FIG. 3 is a block diagram showing the configuration of the color copying machine 1.

  As shown in FIG. 3, the color copying machine 1 includes an image reading unit 10, an image forming unit 20, a density sensor 26, an input operation unit 50, a γ correction processing unit 60, and a control unit 40. The image reading unit 10, the image forming unit 20, the density sensor 26, and the input operation unit 50 correspond to the image reading unit 10, the image forming unit 20, the density sensor 26, and the input operation unit 50 shown in FIG.

  The γ correction processing unit 60 performs γ correction processing described later on the image data. The γ correction process is a process for adjusting brightness, and is performed by converting the pixel value of each pixel with an exponential function. In an image sensor such as a CCD, there is usually a relationship of D = Eγ between the input light amount E and the output value D. Adjusting the value of γ is γ correction. Further, the input-to-output conversion for correcting with the optimum γ value is tabulated as a γ correction table.

  The control unit 40 governs the overall operation of the color copying machine 1. For example, a storage unit (not shown) that stores a control program for controlling the operation of the color copying machine 1, a control program, and the like are stored in the storage unit. It is comprised from the microcomputer etc. which read from and run.

  By the way, in the color copying machine 1, for example, the development performance changes due to changes in the environment such as the temperature, and the expressed density may change even for the same image data. In the present embodiment, when this density change occurs, the density can be adjusted by changing a threshold table used for screen processing, which will be described later, and a γ correction table used for γ correction processing. ing. In the screen processing, when the color or gradation of a photographic part is expressed by a halftone dot (screen), the halftone dot pattern and the laser light output time of the laser emitter 213a are determined and output to the laser oscillator 223a. This is processing for setting the pulse width of the pulse signal.

  Here, a screen processing method will be schematically described. FIG. 4 is a diagram for explaining a screen processing method.

  First, as shown in FIG. 4, the entire predetermined image is divided into a predetermined number of blocks (hereinafter referred to as pixel blocks) both vertically and horizontally. Here, it is assumed that the block is divided into 8 × 8 (pieces). Next, output data is derived from input data in each pixel block using the matrix table T1 and the threshold table T2. The threshold table T2 is a table in which gradation is set according to the combination of the threshold table number and the pulse width of the laser pulse, and the matrix table T1 is a table indicating the threshold table number corresponding to each pixel block.

  For example, as shown in FIG. 4B, when the input data of the pixel block B1 is “60”, the threshold table number “1” corresponding to this pixel block B1 is derived from the matrix table T1, and When the input data of the pixel block B2 is “71”, the threshold table number “8” corresponding to the pixel block B2 is derived from the matrix table T1.

Then, based on the derived threshold value table number and input data, the laser pulse width is determined from the threshold value table T2. That is, in the threshold value table T2, comparison of the level value y of the input data and the gray level value x set in the threshold table number corresponding to the position of the pixel block is performed, in the laser pulse width satisfying x <y The largest one is derived as output data. For example, in the above example, the output data “15” is derived for the pixel block B1, and the output data “3” is derived for the pixel block B2. Output data is similarly derived for other pixel blocks.

  By changing the threshold value table T2 used for the screen processing as described above, the gradation can be adjusted with high accuracy, and good gradation reproducibility can be realized.

  However, in order to change the threshold table T2 used for the screen processing, it is necessary for the user or a specialized operator to perform it manually, and the method of adjusting the density by changing the threshold table T2 is complicated and experienced. It is necessary. For this reason, it is difficult for a general user to perform density adjustment by changing the threshold value table T2, and it is usually performed by a specialized operator.

  Therefore, in the present embodiment, the change of the γ correction table used for the γ correction process is inferior to the case where the gradation reproducibility is changed compared to the threshold table used for the screen process, but the density adjustment is relatively easy ( Therefore, under the predetermined conditions to be described later, the γ correction table is automatically changed, so that the density can be easily adjusted and the gradation reproducibility is included. When high-precision density adjustment is required, a specialized operator or user is allowed to perform density adjustment by changing the threshold table T2.

  In order to realize the above functions, as shown in FIG. 3, the control unit 40 functionally includes a patch pattern formation instruction unit 41, a determination unit 42, a table change unit 43, and a display control unit 44. And an input operation reception prohibition unit 45.

  When the main power supply of the color copying machine 1 is turned on, the patch pattern formation instructing unit 41 has a plurality of patch patterns including 0% and 10% patch patterns with respect to the image forming unit 20 (image transfer unit 22). An instruction to form a toner image having toner on the transfer belt 225a is given.

  The determination unit 42 causes the density sensor 26 to measure the density of a toner image having 0% and 10% patch patterns formed by an instruction from the patch pattern formation instructing unit 41, and the toner image obtained from the density sensor 26. It is determined whether or not the difference in density is greater than a predetermined value.

  FIG. 5 illustrates patch pattern data values (input values) in a normal case where no change in density occurs (curve A) and in a case where a so-called gradation jump occurs due to a change in density (curve B). 3 is a graph showing an output value of a density sensor 26. Note that the output value of the density sensor 26 is normalized with the output value when the gradation is the maximum level 255 being 1.

As shown in FIG. 5, for example, in a normal case where no density change occurs, the output value when a 10% patch pattern is measured by the density sensor 26 is about 0.18, whereas the density change occurs. When it occurs, the output value when the 10% patch pattern is measured by the density sensor 26 is about 0.36. The output value when the 0 % patch pattern is measured by the density sensor 26 is 0 in all cases.

  The determination unit 42 calculates the difference between the output value corresponding to the 0% patch pattern and the output value corresponding to the 10% patch pattern in each of the above cases (when the density change has occurred in the normal case). It is determined whether or not the difference is greater than or equal to a threshold value. In the case of the previous example, this threshold value is set to a value larger than an output value difference 0.18 in a normal case where no density change occurs.

  The table changing unit 43 corrects the γ correction table used for the γ correction processing when the determination unit 42 determines that the toner density difference is larger than a predetermined value. The reason why the γ correction table is corrected when the toner density difference is larger than a predetermined value is that a relatively large gradation jump occurs when the toner density difference is larger than the predetermined value.

  When the photographic mode is set as the image quality mode of the color copying machine 1 and the γ correction table is corrected by the table changing unit 43, the display control unit 44, for example, “Color” "The tone reproducibility of the image is not good. Please adjust the tone (copying in the photo mode is prohibited)." The display unit 52 displays a warning indicating that copying in the mode is prohibited and a warning that prompts the user to correct the gradation by changing the threshold table used for screen processing.

  The input operation acceptance prohibition unit 45 accepts a print execution instruction from the start button 51a when the photo mode is set as the image quality mode of the color copying machine and the γ correction table is corrected by the table change unit 43. Is prohibited.

  Hereinafter, the density adjustment process in the color copying machine 1 will be described. FIG. 7 is a flowchart showing density adjustment processing performed by the color copying machine 1.

  As shown in FIG. 7, when the main power supply of the color copier 1 is turned on (YES in step # 1), the control unit 40 generates a 100% patch pattern (step # 2) and sets a plurality of development biases. A 100% patch pattern is formed on the transfer belt 225a while switching to the stage (step # 3), and the density sensor 26 measures the density of the toner image of the formed 100% patch pattern (step # 4). Then, the control unit 40 determines an optimum bias value based on the measured density (Step # 5).

  Next, the control unit 40 generates patch patterns including, for example, 0% and 10% patch patterns (step # 6), and forms these patch patterns on the transfer belt 225a (step # 7). Then, the control unit 40 causes the density sensor 26 to measure the density of the toner image related to the formed patch pattern (step # 8), and determines an optimum density correction value based on this density (step # 9). .

  The control unit 40 calculates the difference between the density of the toner image of the 0% patch pattern and the density of the toner image of the 10% patch pattern, and determines whether or not the density difference exceeds the threshold (Step # 10). .

  As a result, if the density difference does not exceed the threshold value (NO in step # 10), the process ends. On the other hand, when the density difference exceeds the threshold value (YES in step # 10), the control unit 40 resets the γ correction table and the threshold value table (step # 11), and 0% and 0% are transferred on the transfer belt 225a. A 10% patch pattern is formed (step # 12), and the density sensor 26 measures the density of the toner image of the formed patch pattern (step # 13).

  Then, a density correction value is calculated according to the relationship between the measured density and the reference density (step # 14), and the γ correction table is corrected based on the density correction value (step # 15).

  Thereafter, the control unit 40 determines whether or not the currently set image quality mode is the photo mode (step # 16). If the image quality mode is not the photo mode (NO in step # 16), the process ends. In the case of the photo mode (YES in step # 16), the display unit 52 is caused to display a warning indicating that the γ correction table has been changed and a tone for correcting the gradation. A print start instruction is not accepted (step # 17).

  As described above, when a toner image related to the 0% patch pattern and the 10% patch pattern is formed on the transfer belt 225a, and the density difference between these toner images is larger than a predetermined value, the γ correction used for the γ correction processing is performed. Since the table is corrected, the density can be automatically adjusted without imposing a density adjustment work on the user.

  In addition, when the γ correction process is executed, the fact is notified so that the user can determine whether or not the density adjustment by the correction of the threshold value table used for the screen process is more accurate. Can do.

  In addition, when the γ correction table is changed when the photo mode is selected, a notification that the γ correction table has been changed and a warning prompting the user to correct the gradation are given, and the printing operation is performed. Since it is prohibited, it is possible to avoid image formation in a state where there is room for improvement in gradation reproducibility by changing the γ correction table in spite of the mode in which gradation reproducibility should be emphasized. can do.

  In addition to the said embodiment, it can replace with the said embodiment, and the deformation | transformation form demonstrated to following form [1]-[3] is also employable for this invention.

  [1] In the above-described embodiment, the processing shown in FIG. 7 is executed when the color copying machine is turned on (started up). However, the present invention is not limited to this. For example, the processing shown in FIG. Alternatively, the color copier 1 may be executed every time the operation time of the color copying machine 1 elapses, and the execution timing can be set as appropriate.

  [2] In the embodiment, the γ correction process is performed based on the difference between the output value corresponding to the 0% patch pattern and the output value corresponding to the 10% patch pattern in the normal case and in the case where the density change occurs. However, the present invention is not limited to this. Based on the difference between the output values corresponding to the 10% patch pattern between the normal case and the case where the density change occurs. Thus, the necessity of correction of the γ correction table used for the γ correction process may be determined. That is, a threshold value for the difference between the output values may be set in advance, and the γ correction table used for the γ correction process may be corrected when the derived output value difference is larger than the threshold value.

  In the above embodiment, whether to change the γ correction table is determined according to the density difference between the toner images of the 0% patch pattern and the 10% patch pattern. The density difference between the toner images of the 0% patch pattern and the 10% patch pattern is not limited to the density difference between the toner images of the 0% patch pattern and the 15% patch pattern.

  [3] In the above embodiment, the developer drums 224c, 324m, 324y, and 324k that develop toner images of each color of C (cyan), M (magenta), Y (yellow), and K (black) are provided. Each color toner image developed on the surface of 221 is primarily transferred onto the transfer belt 225a, and the toner images of each color are superimposed on the transfer belt 225a, and then transferred onto the recording paper conveyed onto the transfer roller 225b. However, the present invention is not limited to this, and is provided with a plurality of image forming units each including a photosensitive drum, a charging unit, an exposure unit, a developing unit, and the like for each color. The present invention can also be applied to a so-called tandem type copying machine in which recording paper is conveyed in the arrangement direction of the forming units and toner images of respective colors are transferred onto the recording paper.

1 is a diagram showing an internal configuration of a color copying machine that is an example of an image forming apparatus according to the present invention. FIG. It is an external appearance block diagram of an input operation part. 1 is a block diagram illustrating a configuration of a color copying machine. It is a figure for demonstrating the method of a screen process. The output of the density sensor with respect to the patch pattern data value (input value) in the normal case where the density change has not occurred (curve A) and in the case where a so-called gradation jump occurs due to the density change (curve B). It is a graph which shows a value. FIG. 6 is a diagram illustrating contents displayed on a display unit when a photo mode is set as an image quality mode of a color copying machine and a γ correction table is corrected by a table changing unit. 5 is a flowchart showing density adjustment processing performed by a color copying machine.

41 Patch Pattern Formation Instruction Unit 42 Judgment Unit 43 Table Change Unit 44 Display Control Unit 45 Input Operation Acceptance Prohibition Unit 52 Display Unit

Claims (3)

An image forming apparatus capable of adjusting the density of an image formed on recording paper by changing a threshold table used for screen processing,
An image carrier;
Image forming means for forming a toner image on the image carrier;
Image forming control means for causing the image forming means to perform a predetermined toner image forming operation on the image carrier;
Density detecting means for detecting the density of the toner image formed on the image carrier;
Γ correction means for performing γ correction processing on input image data using a γ correction table;
Γ correction table changing means for changing the γ correction table;
The density detecting unit detects the density of the predetermined toner image formed on the image carrier, and determines whether or not the γ correction table changing process is required by the γ correction table changing unit according to the detected value. and determination means for,
An input operation means for inputting an instruction to form an image on the recording paper;
A plurality of image quality modes for performing image processing according to the type of document to be copied , and
When it is determined by the determining means that the γ correction table needs to be changed, the γ correction table changing means changes the γ correction table,
The γ correcting means, have rows the γ correction process on the basis of the γ correction table changed by the γ correction table changing means,
When a photographic mode is selected from the plurality of image quality modes and the γ correction table changing process is executed by the γ correction table changing unit, the threshold value is not received without receiving an image forming instruction from the input operation unit. Perform warning processing that outputs a warning prompting you to adjust the gradation by changing the table,
An image forming apparatus , wherein when the photographic mode is not selected and the γ correction table changing process is executed by the γ correction table changing means, the warning process is not performed . The image formation control unit performs a toner image formation operation based on each image data set in advance so as to have a predetermined target density difference when the image formation unit performs a toner image formation operation. to perform said image forming means, said determining means is a said image bearing formed on said body to detect the density of the toner image on each of the concentration detecting means, the density detection by the density detecting means each target The image forming apparatus according to claim 1, wherein when the difference in detected density between toner images exceeds a predetermined threshold, the γ correction table changing unit performs a γ correction table changing process.   The image forming apparatus according to claim 1, further comprising a notifying unit that notifies that the change of the γ correction table has been executed by the γ correction table changing unit.

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