JP6855775B2 - Image forming device and gradation correction method - Google Patents

Description

The present invention relates to an image forming apparatus and a gradation correction method.

In general, an image forming apparatus (printer, copier, facsimile, etc.) using electrophotographic process technology produces an electrostatic latent image by irradiating (exposing) a charged photoconductor with a laser beam based on image data. Form. Then, toner is supplied from the developing device to the photoconductor drum (image carrier) on which the electrostatic latent image is formed, so that the electrostatic latent image is visualized and the toner image is formed. Further, after the toner image is directly or indirectly transferred to the paper, the toner image is formed on the paper by heating and pressurizing with the fixing nip to fix the toner image.

In the developing apparatus, carriers to which toner is attached are supported on the developing roller by magnetic force, and a magnetic brush composed of a plurality of carriers is formed on the developing roller. Then, the toner on the magnetic brush is supplied to the photoconductor drum at the developing nip which is the opposite portion between the developing roller and the photoconductor drum.

The developing method as described above includes a with method in which the developing roller and the photoconductor drum are rotated in the same direction at the developing nip, and a counter method in which the developing roller and the photoconductor drum are rotated in the opposite directions. In the counter method, the developing roller and the photoconductor drum rotate in opposite directions at the developing nip, so that the toner is transferred from the tip of the toner image to the rear end by the spikes of the magnetic brush. The phenomenon of being swept up occurs. This phenomenon is called fading or sweeping, and an image defect occurs in which the density becomes low in the front end region and the density becomes high in the rear end region of the toner image.

In the with method, the same phenomenon as in the counter method occurs. In the case of the with method, since the developing roller and the photoconductor drum rotate in the same direction at the developing nip, the density becomes high in the front end region of the toner image and becomes low in the rear end region, resulting in an image defect.

In order to suppress the above-mentioned image defects, for example, Patent Document 1 discloses a technique for predicting and correcting the occurrence of the image defects from the input image data for the image defects such as white spots.

Japanese Unexamined Patent Publication No. 11-196277

However, in the technique described in Patent Document 1, the level of image defect changes due to individual differences in the apparatus and changes in environmental durability, so that the correction amount becomes insufficient or the correction amount becomes excessive. Therefore, there is a possibility that the image based on the input image data cannot be accurately corrected.

An object of the present invention is to provide an image forming apparatus and a gradation correction method capable of accurately correcting an image based on input image data.

The image forming apparatus according to the present invention is
An image forming portion having a rotatable image carrier and forming an image on the image carrier,
A control unit that controls the image forming unit so as to form a patch image having gradation included in the input image data on the image carrier.
A density-related information detection unit that detects density-related information in the rotation direction of the image carrier of the patch image,
With
The control unit
Among the density-related information detected by the density-related information detection unit, the first information corresponding to the first position in the rotation direction and the position closer to the end of the patch image than the first position. The correction amount of the second information is determined based on the difference between the second information corresponding to the two positions and the gradation table showing the relationship between the density-related information and the gradation information.
Based on the correction amount, it is related to the input image data so that the gradation of the portion corresponding to the second position in the image based on the input image data becomes the gradation of the portion corresponding to the first position. Correct the gradation of image data.

The gradation correction method according to the present invention
A gradation correction method for an image forming apparatus having a rotatable image carrier and including an image forming portion for forming an image on the image carrier.
The image forming unit is controlled so as to form a patch image having gradation included in the input image data on the image carrier.
The density-related information of the patch image in the rotation direction of the image carrier was detected.
Among the detected density-related information, the first information corresponding to the first position in the rotation direction and the second information corresponding to the second position which is a position closer to the end of the patch image than the first position. The correction amount of the second information is determined based on the difference between the above and the gradation table showing the relationship between the density-related information and the gradation information.
Based on the correction amount, it is related to the input image data so that the gradation of the portion corresponding to the second position in the image based on the input image data becomes the gradation of the portion corresponding to the first position. Correct the gradation of image data.

According to the present invention, an image based on input image data can be accurately corrected.

It is a figure which shows schematic the whole structure of the image forming apparatus which concerns on this embodiment. It is a figure which shows the main part of the control system of the image forming apparatus which concerns on this embodiment. It is an enlarged view of the development nip. It is a figure which shows the patch image. It is a figure which shows the detection result of the patch image by the density detection part in the paper passing direction. It is a figure which shows the relationship between the reference density | concentration | detection density | density | concentration gradation table, and the relationship | concentration | correction table. It is a figure which shows the plurality of patch images which have different gradations. It is a figure which shows the relationship between the reference density | concentration | detection density | density | concentration gradation table, and the relationship | concentration | correction table. It is a figure which shows a plurality of patch images which have different widths in a paper-passing direction. It is a figure which shows the relationship between the width of a patch image, and the amount of sweeping. It is a flowchart which shows an example of the operation example of the gradation correction control in an image forming apparatus.

Hereinafter, the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing an overall configuration of an image forming apparatus 1 according to the present embodiment. FIG. 2 is a diagram showing a main part of the control system of the image forming apparatus 1 according to the present embodiment.

As shown in FIG. 1, the image forming apparatus 1 is an intermediate transfer type color image forming apparatus using an electrophotographic process technique. That is, the image forming apparatus 1 primary transfers the Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photoconductor drum 413 to the intermediate transfer belt 421. An image is formed by superimposing toner images of four colors on the intermediate transfer belt 421 and then secondary transfer to the paper S sent from the paper feed tray units 51a to 51c.

Further, in the image forming apparatus 1, the photoconductor drums 413 corresponding to the four colors of YMCK are arranged in series in the traveling direction of the intermediate transfer belt 421, and the toner images of each color are sequentially transferred to the intermediate transfer belt 421 in one procedure. The tandem method is adopted.

As shown in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper conveying unit 50, a fixing unit 60, and a control unit 101.

The control unit 101 includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, and the like. The CPU 102 reads a program according to the processing content from the ROM 103, develops it in the RAM 104, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the expanded program. At this time, various data stored in the storage unit 72 are referred to. The storage unit 72 is composed of, for example, a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive.

The control unit 101 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or WAN (Wide Area Network) via the communication unit 71. Do. The control unit 101 receives, for example, image data (input image data) transmitted from an external device, and causes the paper S to form an image based on the image data. The communication unit 71 is composed of a communication control card such as a LAN card.

As shown in FIG. 1, the image reading unit 10 includes an automatic document feeding device 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.

The automatic document feeding device 11 conveys the document D placed on the document tray by the conveying mechanism and sends it out to the document image scanning device 12. The automatic document feeding device 11 makes it possible to continuously read a large number of images (including both sides) of documents D placed on the document tray at once.

The document image scanning device 12 optically scans the document conveyed on the contact glass from the automatic document feeding device 11 or the document placed on the contact glass, and the reflected light from the document is a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and the original image is read. The image scanning unit 10 generates input image data based on the scanning result by the document image scanning device 12. The image processing unit 30 performs predetermined image processing on the input image data.

As shown in FIG. 2, the operation display unit 20 is composed of, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image states, operation statuses of each function, and the like according to the display control signals input from the control unit 101. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 101.

The image processing unit 30 includes a circuit or the like that performs digital image processing according to initial settings or user settings on the input image data. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table) under the control of the control unit 101. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, compression processing, and the like, in addition to gradation correction, on the input image data. The image forming unit 40 is controlled based on the image data subjected to these processes.

As shown in FIG. 1, the image forming unit 40 forms an image forming unit 41Y, 41M, 41C for forming an image with each colored toner of Y component, M component, C component, and K component based on the input image data. , 41K, intermediate transfer unit 42 and the like.

The image forming units 41Y, 41M, 41C, 41K for the Y component, the M component, the C component, and the K component have the same configuration. For convenience of illustration and description, common components are indicated by the same reference numerals, and when distinguishing them, they are indicated by adding Y, M, C, or K to the reference numerals. In FIG. 1, the reference numerals are given only to the components of the image forming unit 41Y for the Y component, and the reference numerals are omitted for the other components of the image forming units 41M, 41C, and 41K.

The image forming unit 41 includes an exposure device 411, a developing device 412, a photoconductor drum 413, a charging device 414, a drum cleaning device 415, and the like. The photoconductor drum 413 corresponds to the "image carrier" of the present invention.

The photoconductor drum 413 is made of an organic photoconductor in which, for example, a photosensitive layer made of a resin containing an organic photoconductor is formed on an outer peripheral surface of a drum-shaped metal substrate.

The control unit 101 rotates the photoconductor drum 413 at a constant peripheral speed by controlling the drive current supplied to the drive motor (not shown) that rotates the photoconductor drum 413.

The charging device 414 is, for example, a charging charger, and by generating a corona discharge, the surface of the photoconductive drum 413 is uniformly negatively charged.

The exposure apparatus 411 is composed of, for example, a semiconductor laser, and irradiates the photoconductor drum 413 with a laser beam corresponding to an image of each color component. As a result, an electrostatic latent image of each color component is formed in the image region irradiated with the laser beam on the surface of the photoconductor drum 413 due to the potential difference from the background region.

The developing device 412 is a two-component reversing type developing device, and a toner image is formed by visualizing an electrostatic latent image by adhering a developer of each color component to the surface of the photoconductor drum 413.

For example, a DC development bias having the same polarity as the charging polarity of the charging device 414 or a development bias in which a DC voltage having the same polarity as the charging polarity of the charging device 414 is superimposed on the AC voltage is applied to the developing device 412. As a result, reverse development is performed in which toner is adhered to the electrostatic latent image formed by the exposure apparatus 411.

The drum cleaning device 415 has a flat plate-shaped drum cleaning blade or the like made of an elastic body, which is in contact with the surface of the photoconductor drum 413, and remains on the surface of the photoconductor drum 413 without being transferred to the intermediate transfer belt 421. Remove the toner.

The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

The intermediate transfer belt 421 is composed of an endless belt, and is stretched in a loop on a plurality of support rollers 423. At least one of the plurality of support rollers 423 is composed of a driving roller, and the other is composed of a driven roller. For example, it is preferable that the roller 423A arranged on the downstream side in the belt traveling direction with respect to the primary transfer roller 422 for the K component is the drive roller. This makes it easier to keep the running speed of the belt in the primary transfer unit constant. As the drive roller 423A rotates, the intermediate transfer belt 421 travels at a constant speed in the direction of arrow A.

The intermediate transfer belt 421 is a belt having conductivity and elasticity, and has a high resistance layer on the surface. The intermediate transfer belt 421 is rotationally driven by a control signal from the control unit 101.

The primary transfer roller 422 is arranged on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photoconductor drum 413 of each color component. By pressing the primary transfer roller 422 against the photoconductor drum 413 with the intermediate transfer belt 421 sandwiched between them, a primary transfer nip for transferring the toner image from the photoconductor drum 413 to the intermediate transfer belt 421 is formed.

The secondary transfer roller 424 is arranged on the outer peripheral surface side of the intermediate transfer belt 421 so as to face the backup roller 423B arranged on the downstream side of the drive roller 423A in the belt traveling direction. By pressing the secondary transfer roller 424 against the backup roller 423B with the intermediate transfer belt 421 sandwiched between them, a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper S is formed.

When the intermediate transfer belt 421 passes through the primary transfer nip, the toner image on the photoconductor drum 413 is sequentially superimposed on the intermediate transfer belt 421 and the primary transfer is performed. Specifically, the toner image is obtained by applying a primary transfer bias to the primary transfer roller 422 and applying a charge having the opposite polarity to the toner on the back surface side of the intermediate transfer belt 421, that is, the side in contact with the primary transfer roller 422. It is electrostatically transferred to the intermediate transfer belt 421.

After that, when the paper S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the paper S. Specifically, a toner image is obtained by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner on the back surface side of the paper S, that is, the side in contact with the secondary transfer roller 424. Is electrostatically transferred to the paper S. The paper S on which the toner image is transferred is conveyed toward the fixing portion 60.

The belt cleaning device 426 removes the transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer.

The fixing portion 60 is arranged on the fixing surface of the paper S, that is, the upper fixing portion 60A having the fixing surface side member arranged on the surface side on which the toner image is formed, and the back surface of the paper S, that is, the surface opposite to the fixing surface. It is provided with a lower fixing portion 60B having a back surface side support member to be formed, a heating source, and the like. By pressing the back surface side support member against the fixing surface side member, a fixing nip that sandwiches and conveys the paper S is formed.

The fixing unit 60 fixes the toner image on the paper S by secondarily transferring the toner image and heating and pressurizing the conveyed paper S with the fixing nip. The fixing unit 60 is arranged as a unit in the fixing device F.

The upper fixing portion 60A has an endless fixing belt 61, a heating roller 62, and a fixing roller 63, which are members on the fixing surface side. The fixing belt 61 is stretched by a heating roller 62 and a fixing roller 63.

The lower fixing portion 60B has a pressure roller 64 which is a back surface side support member. The pressure roller 64 forms a fixing nip that sandwiches and conveys the paper S with the fixing belt 61.

Further, a concentration detecting unit 73 is provided on the downstream side of the fixing unit 60. The density detection unit 73 is an in-line sensor that reads an image fixed on the paper S, and detects density information of the patch image in the paper passing direction of the paper S, that is, the rotation direction of the photoconductor drum 413. The concentration detection unit 73 corresponds to the "concentration-related information detection unit" of the present invention. Further, the concentration information corresponds to the "concentration-related information" of the present invention. In the following description, the paper-passing direction of the paper S is simply referred to as the "paper-passing direction".

The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. Paper S (standard paper, special paper) identified based on the basis weight, size, etc. is stored in the three paper feed tray units 51a to 51c constituting the paper feed unit 51 for each preset type. .. The transport path portion 53 has a plurality of transport roller pairs including a resist roller pair 53a. The resist roller portion on which the resist roller pair 53a is arranged corrects the inclination and deviation of the paper S.

The paper S housed in the paper feed tray units 51a to 51c is sent out one by one from the uppermost portion, and is conveyed to the image forming unit 40 by the transfer path unit 53. In the image forming section 40, the toner image of the intermediate transfer belt 421 is collectively secondarily transferred to one surface of the paper S, and the fixing step is performed in the fixing section 60. The image-formed paper S is discharged to the outside of the machine by the paper ejection unit 52 provided with the paper ejection roller 52a.

By the way, as shown in FIG. 3, in the developing apparatus 412, the carrier C to which the toner (indicated by black dots in FIG. 3) is attached is supported on the developing roller 412A by a magnetic force, and the magnetic brush B composed of a plurality of carriers C is formed. Is formed on the developing roller 412A. Then, the toner on the magnetic brush B is supplied to the photoconductor drum 413 at the developing nip which is the opposite portion between the developing roller 412A and the photoconductor drum 413.

The developing method as described above includes a with method in which the developing roller 412A and the photoconductor drum 413 are rotated in the same direction at the developing nip, and a counter method in which the developing roller 412A and the photoconductor drum 413 are rotated in the opposite directions. FIG. 3 illustrates the case of the counter method.

In the counter method, the developing roller 412A and the photoconductor drum 413 rotate in opposite directions at the developing nip, so that the toner is supplied to the photoconductor drum 413 by the spikes of the magnetic brush B, and the toner is supplied to the photoconductor drum 413 at the tip of the image. The phenomenon of being swept to the rear end occurs.

This phenomenon is called fading or sweeping. For example, when a patch image T having a constant gradation is formed in the paper passing direction as shown in FIG. 4, when this phenomenon occurs, the density detection unit 73 detects it. The result is as shown in FIG. Specifically, as shown in FIG. 5, an image defect occurs in which the toner concentration becomes low at the front end portion of the image region and the toner density becomes high at the rear end portion.

In the example shown in FIG. 5, the image defect in which the first pixel, the second pixel, and the third pixel from the rear end of the image region have a higher toner density than the fourth and subsequent pixels from the rear end is exemplified. doing.

Further, in the with method, the same phenomenon as in the counter method occurs. In the with method, contrary to the counter method, an image defect occurs in which the density is high at the front end of the image area and low at the rear end.

In order to suppress the occurrence of such image defects, for example, in a technique such as the technique described in Patent Document 1 in which the occurrence of the image defect is predicted and corrected from the input image data, the individual difference of the device may vary. Due to changes in environmental durability, the level of image defects may change and correction at the edge of the image may not be performed accurately.

Further, in the technique described in Japanese Patent Application Laid-Open No. 7-1753667, in which the development bias is changed based on the detection result of the density detection unit to suppress the occurrence of image defects, the development bias is changed. Image defects such as insufficient density and deterioration of graininess may occur.

Therefore, in the present embodiment, the control unit 101 controls the image forming unit 40 so as to form the patch image having the gradation included in the input image data on the photoconductor drum 413, and is based on the density information of the patch image. To correct the gradation of the input image data. As a result, the image based on the input image data can be accurately corrected. Hereinafter, the gradation correction control of the present case will be described in detail.

The patch image formed on the photoconductor drum 413 in the gradation correction control of the present invention is an image having a constant gradation in the paper passing direction.

The control unit 101 acquires the density information of the patch image in the paper passing direction from the density detection unit 73. From the density information of the acquired patch image, the control unit 101 uses the density information of the first position, which is the position of the central portion of the patch image in the paper passing direction, as the reference density information (first information).

Further, as shown in FIG. 6, the storage unit 72 stores a density gradation table that shows the relationship between the toner density and the gradation, which has been measured in advance (the second quadrant or the fourth quadrant of FIG. 6). See quadrant). The density gradation table is a table having a curved shape in which the density of toner increases as the gradation increases. The density gradation table corresponds to the "gradation table" of the present invention.

In FIG. 6 and FIG. 8 described later, the first quadrant (upper right portion) shows the relationship between the density in the central portion (vertical axis) of the patch image and the density detected by the density detection unit 73 (horizontal axis). , The second quadrant (upper left part) shows the relationship between the density (vertical axis) and the gradation. Further, in FIGS. 6 and 8, the fourth quadrant (lower right portion) shows the relationship between the detected density (horizontal axis) and the correction gradation (vertical axis).

The control unit 101 refers to the density gradation table and creates a correction table based on the reference density information and the density gradation table. The correction table is a table showing the relationship between the correction gradation information that cancels the fluctuation amount of the gradation with respect to the reference gradation corresponding to the reference density in the density gradation table and the density information. The correction table may be stored in the storage unit 72 or the like in advance.

For example, when the difference between the reference gradation and the gradation at the second position, which is the first pixel from the rear end, is the difference shown in FIG. 6, the correction gradation at the second position in the correction table is The gradation cancels out the fluctuation amount with respect to the reference gradation. As a result, the correction amount of the portion corresponding to the second position where the difference in the density information is large with respect to the first position in the central portion of the patch image is determined.

Based on the determined correction amount, the control unit 101 determines the gradation of the input image data so that the portion corresponding to the second position in the image based on the input image data has the same gradation as the portion corresponding to the first position. To correct. By doing so, it is possible to perform correction according to the current state of the device, so that correction at the edge of the image can be performed accurately.

The control unit 101 adjusts the correction amount of each position according to the difference between the reference density information at the first position and the correction density information (second information) at all positions (second position) other than the first position. It is determined whether or not to perform the determination process.

For example, when the difference between the reference density and the density at the predetermined position in the paper passing direction in the patch image is equal to or larger than the predetermined density (for example, 0.3), the control unit 101 corrects in the portion corresponding to the predetermined position. Performs the process of determining the correction amount based on the table. Further, when the difference is less than a predetermined concentration, the control unit 101 does not perform a process of determining the correction amount.

As a result, correction can be performed without excess or deficiency according to the difference, and by extension, an image based on the input image data can be formed more accurately.

Further, as shown in FIG. 7, the control unit 101 controls the image forming unit 40 so that a plurality of patch images T1 to T10 having different gradations are arranged in the paper direction and formed on the photoconductor drum 413.

When a plurality of patch images T1 to T10 are formed in this way, as shown in FIG. 8, density information in each patch image T1 to T10 can be obtained. In FIG. 8, only the density information in the first pixel, the second pixel, the third pixel, and the fourth pixel from the rear end of the patch image is shown, and only the density information in the first pixel portion is shown. It is plotted and illustrated.

Then, the control unit 101 creates a plurality of correction tables according to the gradation. By doing so, even if images having different gradations exist in the input image data, appropriate correction can be performed according to the gradations.

Further, as shown in FIG. 9, the control unit 101 may control the image forming unit 40 so as to form a plurality of patch images T11 to T19 having different widths in the paper passing direction. Then, the control unit 101 sets the same width as the width of the patch image having a portion of the plurality of patch images T11 to T19 in which the difference between the reference density information and the correction density information is a predetermined density (predetermined value) or more. Only the image of the input image data to be included is subjected to the process of correcting the gradation.

If the width in the paper-passing direction in the image is small, the amount of toner swept by the magnetic brush is small, so that the sweep does not occur, and if the width is large, the toner is swept when the width exceeds a certain level. It is known that the amount is saturated (see FIG. 10). Therefore, by forming a plurality of patch images T11 to T19 having different widths in the paper passing direction, it is possible to determine the width of the image in which sweeping does not occur. As a result, when the width of the image in the paper passing direction is equal to or less than the width at which sweeping does not occur, the control unit 101 can prevent the process of determining the correction amount from being performed.

Further, when forming a plurality of patch images, the control unit 101 controls so that the patch images are formed on the photoconductor drum 413 at intervals. By doing so, it is possible to confirm that the sweeping phenomenon occurs accurately in each patch image, so that accurate correction can be performed.

Further, when the control unit 101 performs the process of determining the correction amount, the paper transport speed in the paper transport unit 50 is higher than the transport speed when the image based on the input image data is transferred to the paper by the image forming unit 40. It is preferable to control the paper transport unit 50 so as to slow down.

By doing so, the density detection unit 73 can increase the resolution when reading the image. For example, in the case of a normal transport speed, the resolution is 400 dpi, but if the speed is one-third of the speed, the resolution is 1200 dpi.

Next, an operation example of the gradation correction control in the image forming apparatus 1 will be described. FIG. 11 is a flowchart showing an example of an operation example of gradation correction control in the image forming apparatus 1. The process shown in FIG. 11 is appropriately executed during the execution of the print job.

As shown in FIG. 11, the control unit 101 controls the image forming unit 40 so as to form a patch image (step S101). Next, the control unit 101 acquires the density information of the patch image detected by the density detection unit 73 (step S102). Next, the control unit 101 acquires the reference concentration information from the acquired concentration information (step S103).

Next, the control unit 101 has a portion where the difference between the reference density information at the first position and the correction density information at all positions (second position) other than the first position is large, that is, a portion having a predetermined density or more. Whether or not it is determined (step S104).

As a result of the determination, if there is no portion having a large difference (step S104, NO), this control ends. On the other hand, when there is a portion having a large difference (step S104, YES), the control unit 101 determines the correction amount in the portion (step S105).

Next, the control unit 101 corrects the gradation of the input image data based on the correction amount so that the image based on the input image data becomes uniform in the paper passing direction (step S106). After step S106, this control ends.

According to the present embodiment configured as described above, the correction density information is corrected based on the difference between the reference density information and the correction density information and the density gradation table by forming the patch image. The amount is determined, and the gradation of the input image data is corrected based on the correction amount. As a result, the image based on the input image data can be accurately corrected.

Further, since the gradation correction is performed by forming the patch image, the correction can be performed according to the current state of the device. Therefore, unlike the configuration in which the occurrence of image defects is predicted and corrected from the input image data, the correction amount is not insufficient or the correction amount is not excessive, and accurate correction can be performed. ..

Further, in order to correct the gradation in the input image data, accurate correction can be performed without causing insufficient density or deterioration of graininess, unlike the configuration in which the correction is performed by changing the development bias.

Further, since the density information at the position of the central portion of the patch image in the paper passing direction, which is not affected by the sweeping, is used as the reference density information, the image based on the input image data can be corrected more accurately.

In addition, since the portion where the difference in the density information is large is corrected at a position other than the position at the center of the patch image, the correction can be performed without excess or deficiency according to the difference, and the image based on the input image data can be obtained. It can be formed more accurately.

Further, since a plurality of patch images having different gradations are formed and gradation correction control is performed, it is possible to create a plurality of correction tables according to the gradations. Therefore, even when one image has a plurality of gradations, the correction can be performed more accurately.

In the above embodiment, the process of determining the correction amount is always performed at all positions other than the position of the central portion of the patch image, but the present invention is not limited to this. For example, the control unit 101 receives the reference density information and the density information of at least the first pixel from the edge of the image before performing the process of determining the presence / absence of the process of determining the correction (steps S102 to S104 in FIG. 11). Depending on the difference between the above, it may be determined whether or not the process of determining the correction amount is performed.

For example, when the difference between the reference density information and the density information of the first pixel is smaller than the predetermined density, it is highly possible that the difference between the density information of the entire image and the reference density information is small, and it is considered that correction is not necessary. .. In such a case, by determining that the process of determining the correction amount is not performed, it is possible to suppress unnecessary correction and shorten the time for gradation correction control.

Further, as an example of the flowchart in the case of performing the above control, before step S102 in FIG. 11, a process of acquiring only the density information of the first pixel and the reference density information is performed, and then the difference between them is predetermined. Performs a process of determining whether or not the concentration is higher than the concentration. Then, when NO is determined in the process, this control is terminated, and when YES is determined, the process after step S102 in FIG. 11 (process for determining whether or not to perform the process for determining the correction amount) is performed. It may be performed for a plurality of pixels, that is, the second position. By doing so, it is only necessary to acquire the information of only the density information of the first pixel when the sweeping or the like does not occur, so that the time for acquiring other density information can be shortened.

Further, in the above embodiment, the density-related information is the density information of the image, but the present invention is not limited to this, and may be, for example, the brightness information of the image or the brightness information of the image.

Further, in the above embodiment, the position of the central portion of the patch image is set as the first position, but the present invention is not limited to this, and for example, a position slightly deviated from the position of the central portion may be set as the first position. .. However, in order to form an image based on the input image data more accurately, it is desirable that the first position is a position other than the end where sweeping is likely to occur, and it is considered that the first position is not easily affected by sweeping. It is even more desirable to have a central position.

Further, in the above embodiment, the photoconductor drum 413 is exemplified as the image carrier, but the present invention is not limited to this, and for example, an intermediate transfer belt 421 or the like may be used.

Further, in the above embodiment, the density detection unit 73 is an in-line sensor that reads the density of the image fixed on the paper S, but the present invention is not limited to this, for example, the image on the photoconductor drum 413. It may be a sensor capable of detecting the concentration.

In addition, the above-described embodiments are merely examples of embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

1 Image forming device 40 Image forming unit 50 Paper transport unit 73 Density detection unit 101 Control unit 413 Photoreceptor drum

Claims (14)

An image forming portion having a rotatable image carrier and forming an image on the image carrier,
A control unit that controls the image forming unit so as to form a patch image having gradation included in the input image data on the image carrier.
A density-related information detection unit that detects density-related information in the rotation direction of the image carrier of the patch image,
With
The control unit
Among the density-related information detected by the density-related information detection unit, the first information corresponding to the first position in the rotation direction and the position closer to the end of the patch image than the first position. The correction amount of the second information is determined based on the difference between the second information corresponding to the two positions and the gradation table showing the relationship between the density-related information and the gradation information.
Based on the correction amount, it is related to the input image data so that the gradation of the portion corresponding to the second position in the image based on the input image data becomes the gradation of the portion corresponding to the first position. Correct the gradation of image data,
Image forming device. The first position is the position of the central portion of the patch image in the rotation direction.
The image forming apparatus according to claim 1. The control unit determines the correction amount at each of the second positions according to the difference between the second information of all the second positions other than the first position in the rotation direction and the first information. Judge whether or not
The image forming apparatus according to claim 1 or 2. Whether or not the control unit performs a process of determining the correction amount according to the difference between the first information and the density-related information of at least the first pixel portion from the end portion in the rotation direction in the patch image. To judge whether
The image forming apparatus according to any one of claims 1 to 3. When the control unit determines that the process of determining the correction amount is to be performed, the control unit determines whether or not to determine the correction amount at the second position.
The image forming apparatus according to claim 4. The control unit controls the image forming unit so as to form a plurality of patch images having different gradations on the image carrier.
The image forming apparatus according to any one of claims 1 to 5. The control unit
The image forming unit is controlled so as to form a plurality of patch images having different widths in the rotation direction on the image carrier.
Of the plurality of patch images, only the image of the input image data having the same width as the width of the patch image having a portion where the difference between the first information and the second information is equal to or more than a predetermined value is the gradation. Perform the process of correcting
The image forming apparatus according to any one of claims 1 to 6. The control unit controls the image forming unit so as to form a plurality of patch images in the rotation direction on the image carrier at intervals.
The image forming apparatus according to any one of claims 1 to 7. The density-related information is image density information.
The image forming apparatus according to any one of claims 1 to 8. The density-related information is image brightness information.
The image forming apparatus according to any one of claims 1 to 8. The density-related information is brightness information of an image.
The image forming apparatus according to any one of claims 1 to 8. The density-related information detection unit is an in-line sensor that reads an image fixed on paper.
The image forming apparatus according to any one of claims 1 to 11. A paper transport unit that transports paper and
When performing the process of determining the correction amount, the control unit sets the paper transport speed in the paper transport unit from the transport speed when the image forming unit transfers an image based on the input image data to the paper. Control the paper transport section so as to slow down
The image forming apparatus according to claim 12. A gradation correction method for an image forming apparatus having a rotatable image carrier and including an image forming portion for forming an image on the image carrier.
The image forming unit is controlled so as to form a patch image having gradation included in the input image data on the image carrier.
The density-related information of the patch image in the rotation direction of the image carrier was detected.
Among the detected density-related information, the first information corresponding to the first position in the rotation direction and the second information corresponding to the second position which is a position closer to the end of the patch image than the first position. The correction amount of the second information is determined based on the difference between the above and the gradation table showing the relationship between the density-related information and the gradation information.
Based on the correction amount, it is related to the input image data so that the gradation of the portion corresponding to the second position in the image based on the input image data becomes the gradation of the portion corresponding to the first position. A gradation correction method that corrects the gradation of image data.

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