JP5444595B2 - Image forming apparatus, image processing apparatus, and program - Google Patents

Description

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

  In the electrophotographic image forming apparatus, the history of the formed latent image remains on the photosensitive drum, and this influence may cause uneven density in an image formed after one rotation of the photosensitive drum. This uneven density is called a latent image ghost. In addition, the latent image ghost is not necessarily generated uniformly in the plane, and the degree of the occurrence may vary in the plane.

For example, Patent Document 1 proposes a technique for suppressing latent image ghost by adjusting the material of a photoconductor and the film thickness of a charge transport layer, and Patent Document 2 discloses a static elimination device that removes the charge on the surface of the photoconductor. Techniques have been proposed for suppressing the occurrence of latent image ghosts while controlling.
JP 2002-6527 A JP 2003-76076 A

  An object of the present invention is to provide a technique capable of suppressing a latent image ghost even when the generation amount of the latent image ghost is changed.

According to the first aspect of the present invention, an electrostatic latent image is formed by exposing a surface of a rotating body that is rotationally driven and whose surface potential changes in response to light irradiation to the input image data. An image output means comprising: an exposure means for forming the electrostatic latent image; a developing means for developing the electrostatic latent image using a developer; and a transfer means for transferring an image obtained by the development to a recording medium; Image data, second image data for forming an electrostatic latent image in an area overlapping with the electrostatic latent image based on the first image data of the rotating body, and the first image data are input. When the second image data is input after one rotation of the rotating body from the above, the density of the area of the image transferred to the recording medium by the image output means based on the second image data is Density corresponding to the second image data Storage means for storing in association with each correction amount for correcting the second image data so as to approach, and the second image data corresponding to the input image data, said than image data which has been the input A correction amount determining means for determining a correction amount corresponding to the first image data corresponding to the image data input before one rotation of the rotating body based on the storage content of the storage means; and the correction amount A correction unit that corrects the input image data using the correction amount determined by the determination unit and outputs the corrected image data to the exposure unit; A thickness of a protective layer provided on the rotating body; C. temperature and humidity around the rotating body; A current value of a transfer current generated by the transfer means; Rewriting means for detecting any one or more of the length of the period during which the power was last turned off, and rewriting the correction amount stored in the storage means in accordance with the result of the detection. An image forming apparatus is provided.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the rewriting unit decreases the correction amount as the thickness of the protective layer decreases.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the rewriting unit increases the correction amount as the temperature increases, and the correction as the humidity increases. It is characterized by increasing the amount.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the rewriting unit increases the correction amount as the current value increases.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the rewriting unit increases the correction amount as the length of the period increases.

According to a sixth aspect of the present invention, there is provided a rotating body that is driven to rotate and whose surface potential changes in response to light irradiation, and the surface of the rotating body is exposed based on input image data. The image data is supplied to an image output device having an exposure unit for forming the electrostatic latent image, a developing unit for developing the electrostatic latent image using a developer, and a transfer unit for transferring an image obtained by the development to a recording medium. An image processing apparatus that outputs the second image data for forming an electrostatic latent image in a region overlapping the first image data and the electrostatic latent image based on the first image data of the rotating body When the second image data is input after one rotation of the rotating body after the first image data is input, the recording is performed by the image output means based on the second image data. the territory of the image to be transferred to the medium Storage means for the concentration in association with a correction amount for correcting the second image data so as to approach the concentration corresponding to the second image data, the second corresponding to the input image data And the correction amount corresponding to the first image data corresponding to the image data input by one rotation of the rotating body before the input image data. A correction amount determining means that is determined based on the stored contents of the means; a correction means that corrects the input image data using the correction amount determined by the correction amount determining means and outputs the corrected image data to the exposure means; A thickness of a protective layer provided on the rotating body; C. temperature and humidity around the rotating body; A current value of a transfer current generated by the transfer means; Rewriting means for detecting any one or more of the length of the period during which the power was last turned off, and rewriting the correction amount stored in the storage means in accordance with the result of the detection. An image processing apparatus is provided.

According to a seventh aspect of the present invention, there is provided a rotating body that is driven to rotate and whose surface potential changes in response to light irradiation, and the surface of the rotating body is exposed on the basis of input image data. The image data is supplied to an image output device having an exposure unit for forming the electrostatic latent image, a developing unit for developing the electrostatic latent image using a developer, and a transfer unit for transferring an image obtained by the development to a recording medium. A computer for output includes: first image data ; second image data for forming an electrostatic latent image in an area overlapping with the electrostatic latent image based on the first image data of the rotating body; When the second image data is input after one rotation of the rotating body after the first image data is input, the second image data is transferred to the recording medium based on the second image data. dark of the area of that image The second image but corresponding to the image data storage means, which is input in association with the correction amount for correcting the second image data so as to approach the concentration corresponding to the second image data The correction amount corresponding to the data and the first image data corresponding to the first image data corresponding to the input image data one rotation before the input image data is based on the stored contents of the storage means. A correction amount determining means determined by the correction amount, a correction means for correcting the input image data using the correction amount determined by the correction amount determining means, and outputting to the exposure means; A thickness of a protective layer provided on the rotating body; C. temperature and humidity around the rotating body; A current value of a transfer current generated by the transfer means; A program for detecting any one or more of the length of the period during which the power was last turned off and causing it to function as a rewriting means for rewriting the correction amount stored in the storage means according to the detection result provide.

  According to the present invention, it is possible to suppress the latent image ghost even when the generation amount of the latent image ghost is changed.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating a hardware configuration of an image forming apparatus 1 according to the present embodiment.
The control unit 4 includes a CPU (Central Processing Unit) 44, a ROM (Read Only Memory) 45, and a RAM (Random Access Memory) 46. The storage unit 5 is a non-volatile memory such as a hard disk device, and stores a program such as an OS (Operating System). The storage unit 5 is also used for storing data input to the image forming apparatus 1 from the outside. The ROM 45 stores an IPL (Initial Program Loader), and when the image forming apparatus 1 is turned on, the CPU 44 executes the IPL, whereby the OS is read onto the RAM 46. Then, the CPU 44 controls the image forming apparatus 1 by executing the OS.

The instruction receiving unit 41 includes a display unit 39 and a key input unit 40, and the user can input an instruction to the image forming apparatus 1 via the instruction receiving unit 41. The display unit 39 is a liquid crystal display screen, for example, and displays an image representing a menu. Further, the display unit 39 includes a sensor for recognizing an area touched by the user on the screen, thereby specifying a menu item touched by the user. The key input unit 40 includes start, stop, and reset keys and a numeric keypad. The instruction received by the instruction receiving unit 41 is sent to the CPU 44, and the CPU 44 controls the image forming apparatus 1 according to the sent instruction.
A communication interface (I / F) 48 is connected to a communication network (not shown) such as a LAN (Local Area Network) and mediates communication between the image forming apparatus 1 and another apparatus.

  A cover 51 covering the platen glass 2 is provided with a document feeder 52. The document feeder 52 includes a document table 53 on which a document is placed, a roller 54 that feeds documents placed on the document table 53 one by one, and a roller 55 that guides the sent document onto the platen glass 2. The originals placed one on top of another can be conveyed onto the platen glass 2 one by one.

  The image input unit 12 optically reads a document and generates image data. Specifically, the light source 13 irradiates light on the document placed on the platen glass 2, and the reflected light is received by the light receiving unit 18 through the optical system 3 including the mirrors 14, 15, 16 and the lens 17. Received light. The light-receiving unit 18 includes a photoelectric conversion element such as a CCD (Charge Coupled Device), and generates image data representing reflected (R), G (Green), and B (Blue) color images of reflected light. The CPU 44 converts this image data into image data representing an image of Y (Yellow) color, M (Magenta) color, C (Cyan) color, and K (Black) color, and writes the image data in a buffer area secured on the RAM 46. When the image forming apparatus 1 functions as a copying machine, this image data is supplied to the image output unit 6 every time one page of image data is written in the buffer area. On the other hand, when the image forming apparatus 1 functions as a scanner, the image data written in the buffer area is converted into, for example, TIFF (Tagged Image File Format) format image data and stored in the storage unit 5.

The image output unit 6 includes image forming engines 7Y, 7M, 7C, and 7K, a transfer belt 8, a fixing device 11, and the like. The image forming engines 7Y, 7M, 7C, and 7K respectively perform Y (Yellow) color, M (Magenta) color, C (Cyan) color, and K (K) by electrophotography based on the image data supplied from the buffer area. A black toner image is formed on the surface of the transfer belt 8. Since the configuration of each image forming engine is common, only the image forming engine 7Y will be described here.
The image forming engine 7Y includes a charging device 21Y, an exposure device 19Y, a developing device 22Y, a transfer device 25Y, and the like around the photosensitive drum 20Y.

The photosensitive drum 20Y is a cylindrical photosensitive member that is rotationally driven in the direction of arrow A, and the outer peripheral surface has photoconductivity. An encoder (not shown) is provided on the rotating shaft of the photosensitive drum 20Y, and an index signal is output from the encoder every time the photosensitive drum 20Y rotates once.
In order to enhance the durability of the photosensitive drum 20Y, a protective layer made of resin or the like is provided on the surface thereof.
The charging device 21Y charges the surface of the photosensitive drum 20Y that is rotationally driven to a predetermined potential.

The exposure device 19Y is a scanning optical system that irradiates the surface of the photosensitive drum 20Y with an exposure beam LB. Specifically, the exposure device 19Y includes a semiconductor laser and a rotating polygon mirror (not shown). The exposure device 19Y receives the image data written in the buffer area, and generates an exposure beam LB representing a Y color image by the semiconductor laser based on the image data. The rotary polygon mirror is driven to rotate at a predetermined angular velocity. The exposure device 19Y deflects and scans the surface of the photosensitive drum 20Y at a predetermined speed in the main scanning direction by reflecting the generated exposure beam LB with the rotary polygon mirror and further reflecting with the mirror 191Y. Here, the main scanning direction coincides with the direction of the rotation axis of the photosensitive drum 20Y, and the exposure device 19Y causes the pixel value represented by the image data, that is, the latent image corresponding to the image area ratio of each pixel in the main scanning direction. Write. The arrangement of pixels in the main scanning direction is called a scanning line. The sub-scanning direction is a direction orthogonal to the main scanning direction, that is, a circumferential direction, and writing of the latent image in units of scanning lines is repeated in the sub-scanning direction by rotating the photosensitive drum 20Y.
On the surface of the photosensitive drum 20Y, the potential of the portion irradiated with the exposure beam LB is lowered to a predetermined level. In this way, an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 20Y.

The developing device 22Y develops the electrostatic latent image formed on the surface of the photoreceptor drum 20Y. The toner cartridge 23Y contains a developer composed of Y-color toner and a carrier, and a predetermined amount of developer is supplied to the developing device 22Y. The developing device 22Y charges the developer to a predetermined potential. Then, the toner adheres to the electrostatic latent image due to the potential difference between the electrostatic latent image on the photosensitive drum 20Y and the developer, and a toner image is formed.
The transfer belt 8 is stretched around rollers 26, 27, 28, and 29, and is driven to circulate in the direction of arrow B. Below the photosensitive drum 20Y, a transfer device 25Y is provided so as to sandwich the transfer belt 8, and a predetermined voltage is applied. The toner image formed on the surface of the photoreceptor drum 20Y is transferred to the surface of the transfer belt 8 (primary transfer) by the action of an electric field generated by a voltage applied to the transfer device 25Y.
The cleaner 24Y removes the toner remaining on the photosensitive drum 20Y.

  The above is the configuration of the image forming engine 7Y. In the image forming engines 7M, 7C, and 7K, toner images corresponding to the respective colors are formed and transferred onto the transfer belt 8 in an overlapping manner. Hereinafter, when it is not necessary to distinguish the image forming engines 7Y, 7M, 7C, and 7K, they are simply referred to as the image forming engine 7. Similarly, for other components, the Y, M, C, and K notations are omitted when it is not necessary to distinguish between Y, M, C, and K.

  A plurality of medium supply units 9 are provided and contain recording media 10 of different sizes. The recording medium 10 is paper, for example. When the toner image is formed on the surface of the transfer belt 8, the CPU 44 corresponds to one of the medium supply unit 9 according to the size designated by the user with the instruction receiving unit 41 or the size determined based on the image data. The rollers 33 are rotated to feed the recording medium 10 one by one. The sent recording medium 10 is conveyed along the conveyance path 36 by roller pairs 34, 35, and 37.

A predetermined voltage is applied to the transfer roller 30. The transfer belt 8 is circulated and driven in the direction of arrow B, and in synchronization with the toner image formed on the surface thereof approaching the transfer roller 30, the transfer roller 30 passes through the transfer belt 8 with a predetermined load. To form a contact area. Then, the recording medium 10 enters this contact area. The toner image on the transfer belt 8 is transferred to the surface of the recording medium 10 (secondary transfer) by the action of the electric field applied to the transfer roller 30 and the pressurization in the contact area.
The recording medium 10 on which the toner image is transferred is guided to the fixing device 11 by the roller pair 31. The fixing device 11 fixes the toner image on the surface of the recording medium 10 by heating and pressing the recording medium 10.

  A guide member 35 for determining the conveyance path of the recording medium 10 is provided on the downstream side of the fixing device 11, and a plate large enough to load the maximum size recording medium 10 is further provided on the downstream side thereof. A plurality of medium discharge portions 32 having a shape member are provided. The upper medium discharge unit 32 only discharges the recording medium 10. The lower medium discharge unit 32 has a post-processing function such as stapling, and the recording medium 10 is discharged to the lower medium discharge unit 32 only when the user designates post-processing with the instruction receiving unit 41. The direction of the guide member 35 is changed.

  The image forming apparatus 1 also has a function as a printer. Specifically, when the image forming apparatus 1 and the information processing apparatus are connected via a communication network, when document data described in, for example, a page description language is transmitted from the information processing apparatus to the image forming apparatus 1, The CPU 44 converts the received document data into image data and supplies it to the image output unit 6. It is also possible to form an image using image data stored in the storage unit 5. In this case, when the user designates desired image data stored in the storage unit 5, the designated image data is supplied to the image output unit 6.

The image forming apparatus 1 includes ghost correction units 100Y, 100M, 100C, and 100K. Here, the latent image ghost will be described.
There are several known causes of latent image ghosts, one of which is due to concentration of transfer current. As described above, when the toner image on the photosensitive drum 20 is transferred to the transfer belt 8, a predetermined voltage is applied to the transfer belt 8 by the transfer device 25. A current that flows on the surface of the photosensitive drum 20 by applying a voltage is called a transfer current. Although it is desirable that the transfer current flow uniformly on the surface of the photosensitive drum 20, it does not actually flow uniformly. That is, the transfer current hardly flows in the area where the toner is adhered on the photosensitive drum 20, and the transfer current tends to concentrate and flow in the area where the toner is not adhered. In the region where the transfer current is concentrated, the charging potential is lower than in the other regions. Therefore, the region where the toner is not attached has a lower charging potential than the region where the toner is attached. The distribution of the charged potential remains on the surface of the photosensitive drum 20 even after the toner image is transferred.

  Here, for the sake of convenience, an area where toner has adhered on the photosensitive drum 20 at the time of the previous transfer is referred to as a toner adhesion area, and an area where toner has not adhered is referred to as a non-toner adhesion area. That is, after the transfer of the toner image, the charging potential in the non-toner adhesion region is lower than the charging potential in the toner adhesion region.

  The portion where the toner image has been transferred on the photosensitive drum 20 is newly charged by the charging device 21 for the next exposure. In this charging, the charging device 25 applies a uniform voltage to the surface of the photosensitive drum 20. However, as described above, since the charging potential of the non-toner adhesion region is lower than that of the toner adhesion region, the charging potential of the non-toner adhesion region after charging is lower than the charging potential of the toner adhesion region.

  When exposure is performed on the photosensitive drum 20 in this state, the charged potential of the non-toner adhesion region becomes lower than the original charged potential. Then, when development is performed following exposure, a larger amount of toner adheres to the non-toner adhesion area than the amount that should be originally adhered, so the density of the non-toner adhesion area is based on the original density, that is, based on the image data. It becomes higher than the concentration. As a result, the toner image transferred to the transfer belt 8 is a toner image that is to be originally transferred and is superimposed at a low density by reversing the density of the toner image before one rotation of the photosensitive drum 20. . When this toner image is transferred to the recording medium 10, the area corresponding to the image before one rotation appears to have a relatively lowered density. An image overlaid with the contrast reversed is called negative ghost.

  In addition, depending on the conditions at the time of image formation, the charged potential in the non-toner-attached area may be higher than the charged potential in the toner-attached area. In this case, the image before one rotation of the photosensitive drum 20 inverts the density. Without being overlaid at a low concentration. This image is called positive ghost. Negative ghosts and positive ghosts are collectively referred to as latent image ghosts.

  Further, as a cause of the negative ghost, it is known that the sensitivity of the photosensitive drum 20 is lowered. In the area where the latent image is written on the photosensitive drum 20, the sensitivity to light decreases, and the lower the sensitivity of the latent image, the greater the decrease in sensitivity. For example, assume that a high-density latent image is written to form an image, and a low-density and uniform-density latent image is written after one rotation of the photosensitive drum 20. In this case, the sensitivity of the area where the latent image is written before one rotation is lowered, and the lowered amount of the potential with respect to the exposure beam LB having the same intensity is smaller in the portion where the sensitivity is lowered than in the portion where the sensitivity is not lowered. , The density of the latent image in that portion is lowered. Also in this case, the density of the area corresponding to the image before one rotation appears to be relatively lowered. Such a decrease in sensitivity is called light history.

Next, how a negative ghost occurs will be described using an example of a black and white image.
FIG. 2 is an example of an image in which no negative ghost is generated. A region A in the figure is an image composed of white crosses and black crosses. The area B is composed of a plurality of rectangles each filled with a uniform density, and the image area ratio of each rectangle is Cin = 20, 40, 60, 80, 100% from the left in the figure. The lengths of the areas A and B in the vertical direction in the figure are both equal to the circumference of the photosensitive drum 20.

  On the other hand, FIG. 3 is an example of an image in which a negative ghost is generated. This image is an image formed in the order of regions A and B on the recording medium 10 by inputting image data representing the image shown in FIG. 2 to an image forming apparatus that does not include the ghost correction unit 100. That is, the image of the area A is formed by the first rotation of the photosensitive drum 20, and the image of the area C is formed by the subsequent one rotation. As shown in the figure, a black cross is raised in the region B at a position corresponding to the white cross in the region A due to the occurrence of the negative ghost. In addition, a white cross mark is raised at a position corresponding to the black cross mark. The figure is exaggerated for easy understanding.

  Next, the configuration of the ghost correction unit 100 will be described. The ghost correction units 100Y, 100M, 100C, and 100K are provided in front of the exposure devices 19Y, 19M, 19C, and 19K, respectively. Since the ghost correction units 100Y, 100M, 100C, and 100K have the same configuration, the ghost correction unit 100K will be described in the following description.

FIG. 4 is a diagram illustrating the configuration of the ghost correction unit 100K.
The image data K is raster format data representing an image of K color, and is image data supplied from the image input unit 12, for example. The image data K may be image data obtained by converting the document data received via the communication I / F 48 into a raster format by the CPU 44. The image data K is data representing the image area ratio Cin of each pixel in 256 gradations from 0 to 255, with K = 0 corresponding to Cin = 0% and K = 255 corresponding to Cin = 100%. To do.

  The image memory 101 is, for example, a FIFO (First in First Out) memory, and its capacity is equal to the data amount of the image data K corresponding to the latent image for one rotation of the photosensitive drum 20K. When the image data K is supplied from the image input unit 12 or the CPU 44, the image memory 101 stores the image data K by the amount of data corresponding to the latent image for one rotation of the photosensitive drum 20K. In synchronization with the subsequent bit input, the bit with the oldest storage time is output to the ghost correction amount determination circuit 102 as image data K1. That is, the image data K1 is image data before the image data K input in synchronization therewith by one rotation of the photosensitive drum 20K.

The ghost correction amount determination circuit 102 determines a correction amount for correcting the image data K, and outputs the determined correction amount to the adder 103. Specifically, it is as follows.
First, the same image data K is input to the ghost correction amount determination circuit 102 in synchronization with the input of the image data K to the image memory 101. As described above, since the image memory 101 outputs the image data K1 to the ghost correction amount determination circuit 102 in synchronization with the input of the image data K, the ghost correction amount determination circuit 102 receives the image data K and the image data K1. It will be input synchronously.

  The ghost correction amount determination circuit 102 has a memory therein, and a one-dimensional LUT (Look Up Table) 201 and a one-dimensional LUT 202 are written in the memory. The one-dimensional LUT 201 is a table that holds the pixel value of the image data K and the correction amount β in association with each other. The one-dimensional LUT 202 is a table that holds the pixel value of the image data K1 and the correction amount γ in association with each other. The correction amounts β and γ are obtained in advance by a predetermined method.

Here, a procedure for obtaining the correction amounts β and γ will be described. FIG. 5 is a diagram illustrating a procedure for obtaining the correction amounts β and γ.
In order to obtain the correction amounts β and γ, first, test image data representing a test image is input to the image output unit 6 (step A01). When the user inputs a predetermined instruction to the instruction input unit 41, the test image data generation circuit 105 generates test image data, and this test image data is input to the image output unit 6.
FIG. 6 is an example of a test image used when calculating the correction amounts β and γ. The length of the color charts A and B in the figure is equal to the circumference of the photosensitive drum 20K. The color chart A is composed of a plurality of patches each having a uniform density, and patches having an image area ratio Cin = 100, 80, 60% are arranged from the top. Each patch of the color chart B is a patch of uniform density provided so that a part of the patch of the color chart A in the vertical direction overlaps a part thereof, and Cin = 15, 30, 50, 70,100%.

Next, a test image is formed on the recording medium 10 by the image output unit 6 using the test image data (step A02). FIG. 7 is a diagram illustrating the formed test image. In this example, the color chart A image is formed by the first rotation of the photosensitive drum 20K, and the color chart B image is formed by the next rotation. As shown in the drawing, in color chart B, negative ghost of color chart A occurs, and the density of the area corresponding to each patch of color chart A is lower than the surrounding density. Further, the higher the Cin in the color chart A, the greater the decrease in the density of the area corresponding to the patch. Further, the lower the Cin in the color chart B, the greater the decrease in the density of the area corresponding to the patch of the color chart A.
In the following description, an area where the density has decreased due to the occurrence of a negative ghost is referred to as a “ghost generation part”, and an area where no ghost is generated is referred to as a “background part”. That is, in the above example, in the color chart B, the area corresponding to the patch of the color chart A is the ghost generation section, and the other area is the background section.

  Next, the color chart B shown in FIG. 7 is read by the image input unit 12, and the obtained image data is converted into reflectance (step A03). This process is performed for each value of Cin in color chart A. FIG. 8 is a diagram showing the relationship between the reflectance of the ghost generation part corresponding to the patch of Cin = 100% of the color chart A and the Cin of the color chart B, the horizontal axis is Cin of the color chart B, and the vertical axis is Reflectivity. The broken line in the figure plots the reflectance of the ghost generation part, and the solid line plots the reflectance of the background part.

As shown in the figure, when the reflectance is compared for each Cin value, it can be seen that the reflectance of the ghost generation part is higher than the reflectance of the background part, that is, the density of the ghost generation part is lower than the density of the background part. . In the present embodiment, the image data K is corrected so that the reflectance of the ghost generation part matches the reflectance of the background part (step A04). Specifically, for each reflectance value, the correction amount β100 is obtained by subtracting the Cin of the background portion from the Cin of the ghost generation portion of the color chart B. Here, the subscript “100” of β represents the Cin value of the color chart A. In the illustrated negative ghost example, the correction amount β100 is a positive value. In the case of positive ghost, the correction amount β100 is a negative value.
FIG. 9A is a diagram showing the relationship between the correction amount β100 obtained by the above procedure and Cin of the color chart B. FIG. In this example, the correction amount β100 when the background portion is Cin = 15, 30, 50, 70, 100% is obtained and appropriately interpolated.

  Subsequently, the correction amount β is obtained for the ghost generation portion corresponding to the patches of Cin = 80% and 60% of the color chart A in the same procedure as described above. FIG. 9B is a diagram illustrating the relationship between the correction amount β80 of the ghost generation unit corresponding to the Cin = 80% patch of the color chart A and the Cin of the color chart B. FIG. 9C is a diagram illustrating the relationship between the correction amount β60 of the ghost generation unit corresponding to the Cin = 60% patch of the color chart A and the Cin of the color chart B.

Next, a ratio of β80 to β100 is obtained (step A05). For example, the ratio of β80 to β100 is obtained for Cin = 15%, 30%, 50%, 70%, and 100% of color chart B, and the average value thereof is obtained. Similarly for β60, the average value of the ratio to β100 is obtained for Cin = 15%, 30%, 50%, 70%, and 100% of color chart B. The average value obtained by this procedure is set as the correction amount γ. FIG. 10 is a diagram illustrating the relationship between the correction amount γ and Cin of the color chart A. As shown in the figure, the correction amount γ = 1 when Cin = 100% of the color chart A, and it can be seen that the correction amount γ rapidly decreases as the Cin of the color chart A decreases.
As the correction amount γ, respective maximum values may be used instead of the average value of the ratios of β80 and β60 to β100.
The above is the procedure for obtaining the correction amounts β and γ.

  In a one-dimensional LUT (Look Up Table) 201 provided in the ghost correction amount determination circuit 102, a correction amount β100 obtained in advance by the above procedure is written in association with the value of Cin. In the one-dimensional LUT 202, the correction amount γ obtained in advance by the above procedure is written in association with the value of Cin. The ghost correction amount determination circuit 102 obtains correction amounts β100 and γ corresponding to the input image data K and image data K1 for each pixel. That is, for each pixel, the correction amount β100 corresponding to the image data K is obtained from the one-dimensional LUT 201, the correction amount γ corresponding to the image data K1 is obtained from the one-dimensional LUT 202, and the correction amount α is obtained by multiplying β100 by γ. . Then, the obtained correction amount α is output to the adder 103.

The adder 103 inputs the same image data K in synchronism with the image data K input by the ghost correction amount determination circuit 102, and the correction amount α output by the ghost correction amount determination circuit 102 is input to the image data K. This is added, and this is output to the selector 104 as image data K + α.
The selector 104 outputs the image data K + α to the image output unit 6. Then, the image output unit 6 forms an image on the recording medium 10 based on the image data K + α. .

  The ghost correction amount calculation circuit 106 is provided for rewriting the correction amount β100 written in the one-dimensional LUT 201. The ghost correction amount calculation circuit 106 is, for example, a computer having a CPU, a ROM, and a RAM, and a program describing a correction amount rewriting procedure is stored in the ROM. When the CPU reads this program onto the RAM and executes it, processing for rewriting the correction amount β100 is executed.

  The rewriting of the correction amount β100 is performed when the user inputs a predetermined instruction to the instruction receiving unit 41. For example, when the user observes an image formed by the image forming apparatus 1 and the occurrence of a latent image ghost is visually recognized, or when the latent image ghost increases significantly, the user inputs a predetermined instruction. For example, when the user designates an item “image quality adjustment” displayed on the display unit 39 of the instruction receiving unit 41, a menu for adjusting the image quality is displayed, and an item “ghost correction amount rewriting” in the menu is displayed. Is specified by the user. When this item is designated, the ghost correction amount calculation circuit 106 executes a process of rewriting the correction amount β100.

The reason why the correction amount β100 is rewritten is as follows.
The amount of generation of the latent image ghost may change according to the passage of time or the change in the environment in the image forming apparatus 1. The causes of changes in the latent image ghost generation amount are listed as follows.

(1) Wear of the protective layer of the photosensitive drum When the cleaner 24 removes the toner remaining on the photosensitive drum 20, friction is generated between the cleaner 24 and the photosensitive drum 20. As the operation time increases, the wear of the protective layer proceeds. As the wear of the protective layer proceeds, the amount of latent image ghost changes. FIG. 11A is a diagram illustrating the relationship between the thickness of the protective layer and the latent image ghost generation amount. As shown in the figure, as the thickness of the protective layer decreases, the amount of latent image ghost generation decreases.

(2) Changes in temperature / humidity When the temperature / humidity around the photosensitive drum 20 changes, the electrical resistance on the surface of the photosensitive drum 20 changes, so the amount of latent image ghost changes. When a protective layer is provided on the surface of the photosensitive drum 20, a change in the latent image ghost generation amount due to a change in temperature and humidity is remarkable. FIG. 11B shows the relationship between the temperature / humidity around the photosensitive drum 20 and the latent image ghost generation amount. As shown in the figure, the amount of latent image ghost increases as the temperature and humidity around the photosensitive drum 20 increase.

(3) Change in Transfer Current The transfer device 25 adjusts the current value of the transfer current according to the toner density of the developer in the developing device 22 and the temperature and humidity around the photosensitive drum 20. When the transfer current value changes, the generation amount of the latent image ghost changes. FIG. 11C is a diagram illustrating the relationship between the transfer current value and the latent image ghost generation amount. As shown in the figure, the amount of latent image ghost increases as the transfer current value increases.

(4) Degree of light history recovery As described above, one of the causes of the latent image ghost is known to be due to the light history. Further, it has been found that the degree of the remaining light history depends on the length of the period during which the power of the image forming apparatus 1 is turned off (rest period). Accordingly, the generation amount of the latent image ghost due to the light history varies depending on the length of the pause period. FIG. 11D is a diagram showing the relationship between the number of pages on which an image is formed immediately after the power is turned on and the latent image ghost generation amount for each length of the pause period. As shown in the figure, the longer the pause period is, the more latent image ghosts are generated.

  The image forming apparatus 1 is configured to rewrite the correction amount β100 in accordance with changes in the latent image ghost generation amount due to the causes (1) to (4). In the description below. Rewrite modes of the correction amount β100 corresponding to the causes (1) to (4) will be described as first, second, third, and fourth embodiments, respectively.

<First Embodiment>
The first embodiment is an embodiment corresponding to the cause of the above (1), and is configured to rewrite the correction amount β100 according to the thickness of the protective layer of the photosensitive drum. As shown in FIG. 4, the image forming apparatus 1 includes a cycle counter 301 and a rotation speed storage unit 302.
The cycle counter 301 counts the number of rotations of the photosensitive drum 20 since the power was last turned on to the image forming apparatus 1, and outputs rotation number data representing the number of rotations to the rotation number storage unit 302.

  Each time the image forming apparatus 1 is powered off, the rotation speed storage unit 302 accumulates the rotation speed data output from the cycle counter 301 at that time, and stores the accumulated value. Accordingly, the rotational speed storage unit 302 stores cumulative rotational speed data representing the cumulative rotational speed of the photosensitive drum 20 from when the power is first turned on to the image forming apparatus 1 until the power is finally turned off. The

FIG. 12 is a diagram illustrating the relationship between the thickness t of the protective layer of the photosensitive drum 20 and the correction amount βpr. In the figure, t = t0, t1, t2, and t3 are the thicknesses of the protective layers, and their magnitude relationship is t0>t1>t2> t3. t = t0 is the thickness when the protective layer is not worn at all, and the correction amount (solid line in the figure) at this time is β100 obtained by the procedure of FIG. As the cumulative operation time of the image forming engine 7 increases, the thickness of the protective layer gradually decreases as t = t0, t1, t2, t3. When the thickness of the protective layer is reduced, the generation amount of latent image ghosts is also reduced. Therefore, it is necessary to make the correction amount βpr smaller than β100.
The relationship between the thickness t of the protective layer and the correction amount βpr is expressed by the following equation.
βpr = A × β100 Formula (1)
However, A = t / t0.

  The thickness t of the protective layer is obtained from the cumulative number of rotations of the photosensitive drum 20. The ghost correction amount calculation circuit 106 acquires rotation speed data from the cycle counter 201. Then, the rotation number represented by the rotation number data is added to the rotation number stored in the rotation number storage unit 302. As a result, the cumulative rotational speed N of the photosensitive drum 20 since the image forming apparatus 1 is first turned on is obtained.

The ROM of the ghost correction amount calculation circuit 106 stores the relationship between the cumulative rotational speed N of the photosensitive drum 20 and the protective layer thickness t, and the CPU is based on this relationship to determine the thickness corresponding to the rotational speed N. Find t. Next, the ghost correction amount calculation circuit 106 reads β100 from the one-dimensional LUT 201, and calculates the correction amount βpr by substituting the obtained thickness t and β100 into the equation (1). Then, the ghost correction amount calculation circuit 106 copies β100 written in the one-dimensional LUT 201 to another storage area of the one-dimensional LUT 201, and overwrites the obtained correction amount βpr on the copy source β100. The copied β100 is used when the correction amount is rewritten after the next time.
The above is the description of the first embodiment.

Second Embodiment
The second embodiment is an embodiment corresponding to the cause of the above (2), and is configured to rewrite the correction amount β100 according to the temperature and humidity around the photosensitive drum 20. As shown in FIG. 4, the image forming apparatus 1 is provided with a temperature / humidity sensor 303.
The temperature / humidity sensor 303 is provided in the vicinity of the photosensitive drum 20, measures the temperature and humidity around the photosensitive drum 20, and outputs temperature / humidity data representing the temperature and humidity to the ghost correction amount calculation circuit 106. To do.

FIG. 13 is a diagram showing the relationship between the temperature / humidity around the photosensitive drum 20 and the correction amount βh. The solid line in the figure is β100 obtained by the procedure of FIG. Here, the temperature around the photosensitive drum 20 is Te, the humidity is Hu, the temperature around the photosensitive drum 20 when β100 is obtained is Te0, and the humidity is Hu0. In the case of Te> Te0 and Hu> Hu0, the generation amount of latent image ghosts is increased as compared with the case of Te = Te0 and Hu = Hu0. Therefore, it is necessary to make the correction amount βh larger than β100. On the contrary, when Te <Te0 and Hu <Hu0, the generation amount of latent image ghosts is smaller than when Te = Te0 and Hu = Hu0, so the correction amount βh needs to be smaller than β100.
The relationship between the temperature / humidity around the photosensitive drum 20 and the correction amount βh is expressed by the following equation.
βh = B × β100 Formula (2)
However, B is a coefficient determined by the combination of the temperature Te around the photosensitive drum 20 and the humidity Hu, and B increases as the temperature increases and the humidity increases.

The ROM of the ghost correction amount calculation circuit 106 stores the relationship between the combination of the temperature Te and the humidity Hu and the coefficient B, and the CPU obtains the coefficient B corresponding to the temperature Te and the humidity Hu based on this relationship. Next, the ghost correction amount calculation circuit 106 reads β100 from the one-dimensional LUT 201, and calculates the correction amount βh by substituting the obtained coefficients B and β100 into the equation (2). Then, the ghost correction amount calculation circuit 106 copies β100 written in the one-dimensional LUT 201 to another storage area of the one-dimensional LUT 201, and overwrites the obtained correction amount βh on the copy source β100. The copied β100 is used when the correction amount is rewritten after the next time.
The above is the description of the second embodiment.

<Third Embodiment>
The third embodiment is an embodiment corresponding to the cause of the above (3), and is configured to rewrite the correction amount β100 according to the current value of the transfer current. As shown in FIG. 4, the image forming apparatus 1 is provided with a transfer current measuring unit 304.
The transfer current measuring unit 304 measures the current value of the transfer current generated on the surface of the photosensitive drum 20 and outputs current value data representing the current value to the ghost correction amount calculation circuit 106.

FIG. 14 is a diagram illustrating the relationship between the transfer current value and the correction amount βj. The solid line in the figure is β100 obtained by the procedure of FIG. Here, the transfer current value is J, and the transfer current value when β100 is obtained is J0. When J> J0, the generation amount of the latent image ghost increases as compared with the case where J = J0. Therefore, the correction amount βj needs to be larger than β100. On the other hand, when J <J0, the generation amount of the latent image ghost is smaller than that when J = J0, so the correction amount βj needs to be smaller than β100.
The relationship between the transfer current value and the correction amount βj is expressed by the following equation.
βj = C × β100 Formula (3)
However, C = j / j0.

The ROM of the ghost correction amount calculation circuit 106 stores the relationship between the transfer current value J and the coefficient C, and the CPU obtains the coefficient C corresponding to the transfer current value J based on this relationship. Next, the ghost correction amount calculation circuit 106 reads β100 from the one-dimensional LUT 201, and calculates the correction amount βj by substituting the obtained coefficients C and β100 into the equation (2). Then, the ghost correction amount calculation circuit 106 copies β100 written in the one-dimensional LUT 201 to another storage area of the one-dimensional LUT 201, and overwrites the obtained correction amount βj on the copy source β100. The copied β100 is used when the correction amount is rewritten after the next time.
The above is the description of the third embodiment.

<Fourth embodiment>
The fourth embodiment is an embodiment corresponding to the cause of the above (4), and is configured to rewrite the correction amount β100 according to the length of the suspension period. As shown in FIG. 4, the image forming apparatus 1 is provided with a pause period storage unit 305.
The pause period storage unit 305 stores the time when the power of the image forming apparatus 1 was last turned off, and determines the length of the pause period of the image forming apparatus 1 from the difference between this time and the time when the power was last turned on. The idle period data indicating the length of the idle period is obtained and stored.

FIG. 15 is a diagram illustrating the relationship between the length of the suspension period and the correction amount βr. The solid line in the figure is β100 obtained by the procedure of FIG. Since the latent image ghost generation amount increases as the length r of the pause period increases, it is necessary to increase the correction amount βr. The pause period immediately before β100 is determined is zero. Accordingly, βr is obtained by multiplying β100 by a coefficient corresponding to the length of the pause period.
The relationship between the length of the suspension period and the correction amount βr is expressed by the following equation.
βr = D × β100 Formula (4)
However, D is a coefficient determined from the length of the pause period, and D increases as the pause period increases.

The ROM of the ghost correction amount calculation circuit 106 stores the relationship between the length r of the pause period and the coefficient D, and the CPU obtains the coefficient D corresponding to the length r of the pause period based on this relationship. Next, the ghost correction amount calculation circuit 106 reads β100 from the one-dimensional LUT 201, and obtains the correction amount βr by substituting the obtained coefficients D and β100 into Equation (4). Then, the ghost correction amount calculation circuit 106 copies β100 written in the one-dimensional LUT 201 to another storage area of the one-dimensional LUT 201, and overwrites the obtained correction amount βr on the copy source β100. The copied β100 is used when the correction amount is rewritten after the next time.
The above is the description of the fourth embodiment.

  In the above description, an example in which a negative ghost is corrected has been described, but it is needless to say that a positive ghost can also be corrected by the above configuration.

The present invention is not limited to the form described above, and can be implemented in various forms. For example, the embodiment described above can be modified as follows.
<Modification 1>
In the above embodiment, the correction amounts β100 and γ corresponding to the image data K and K1 are read from the one-dimensional LUTs 201 and 202, respectively, and the correction amount α is determined. However, the two-dimensional LUT is used. Also good. That is, the correction amount determination circuit 102 is provided with a two-dimensional LUT that holds the correction amount α corresponding to the combination of the image data K and K1, and the correction amount α corresponding to the image data K and K1 is set for each pixel. It is configured to obtain from
Further, instead of the one-dimensional LUT, a function representing the correspondence relationship between the image data K and the correction amount β100 and a function representing the correspondence relationship between the image data K1 and the correction amount γ are stored in the memory, and these functions are stored. May be used to determine the correction amounts β and γ.

<Modification 2>
In the above-described embodiment, an example in which the user gives a rewriting instruction to the image forming apparatus 1 when the user determines that the correction amount β100 needs to be rewritten is described. However, the correction amount β100 is rewritten in the following cases. You may comprise as follows. For example, every time the number of pages of an image formed by the image forming apparatus 1 reaches a predetermined value, the CPU 44 may instruct the ghost correction unit 100 to execute rewriting of the correction amount β100. In the first embodiment, the CPU 44 may instruct rewriting of the correction amount when the thickness of the protective layer reaches a predetermined value. In the second embodiment, when the temperature / humidity reaches a predetermined value, the CPU 44 may instruct the rewriting of the correction amount. In the third embodiment, the CPU 44 may instruct the rewriting of the correction amount when the transfer current value reaches a predetermined value. Further, in the fourth embodiment, the CPU 44 may instruct rewriting of the correction amount when the suspension period reaches a predetermined value.

<Modification 3>
Two or more embodiments among the first to fourth embodiments may be combined. For example, the image forming apparatus 1 is provided with a cycle counter 301, a rotation speed storage unit 302, a temperature / humidity sensor 303, a transfer current measurement unit 304, and a pause period storage unit 305, and all the modes described as the first to fourth embodiments. The correction amount may be rewritten with the above.

<Modification 4>
In the above-described embodiment, an example in which the latent image ghost is corrected based on image data corresponding to one rotation before the photosensitive drum is shown, but the present invention is not limited to this configuration. For example, the developing device 22 includes a developing roller that is a cylindrical member. The developing roller is charged with a polarity opposite to that of the photosensitive drum 20, and is driven to rotate in a predetermined direction. The toner supplied from the toner cartridge 23 adheres to the surface of the developing roller, and the toner moves to the surface of the photosensitive drum 20 due to a potential difference between the developing roller and the electrostatic latent image. At this time, a difference occurs in the potential of the developing roller surface between the portion where the toner has moved and the portion where the toner has remained. During the next development, it is desirable that the developing roller is uniformly charged, but the amount of toner adhering becomes uneven due to the influence of the non-uniform potential generated during the development before one rotation, and as a result A latent image ghost may occur.
Even in such a case, the latent image ghost can be suppressed by using the configuration of the above embodiment. That is, the image data K for one rotation of the developing roller is stored in the image memory 101, and based on the image data K and the image data K1 corresponding to this before one rotation of the developing roller, The correction amount α may be obtained in the same procedure.

<Modification 5>
In the above embodiment, an example in which the correction amount β100 is obtained by subtracting the background portion Cin from the ghost generation portion Cin.For example, the ratio of the ghost generation portion Cin to the background portion Cin is obtained and calculated. The correction amount β100 may be used. In this case, a value obtained by multiplying β100 by γ is used as a correction amount α, and by multiplying the image data K by the correction amount α, the density of the ghost generation portion can be matched with the density of the background portion.

<Modification 6>
In the above embodiment, the correction amounts β and γ are written in the one-dimensional LUTs 201 and 202 in advance. However, the correction amounts β and γ may not be written in advance. In this case, in the first latent image ghost correction in the image forming measure 1, the correction amounts β and γ are obtained by the above-described procedure, and the correction amounts β and γ are written in the one-dimensional LUTs 201 and 202 and used for the correction. .

<Modification 7>
In the above embodiment, the FIFO memory is used as the image memory 101. However, the image memory 101 is not limited to this example. The input image data K is held, and the bit and the bit corresponding to one rotation before the photosensitive drum 20 are output to the correction amount determination circuit 102 in synchronization with the subsequent bit being input. It only has to be configured.

<Modification 8>
In the above-described embodiment, an example in which hardware other than the ghost correction amount calculation circuit 106 of the ghost correction unit 100 is configured. However, a program for causing the computer to function as the ghost correction unit 100 is stored in the storage unit 5. The CPU 44 may execute the program to execute the process of the above embodiment. The same applies to the in-plane unevenness correction unit 300.
Alternatively, the program may be recorded on a recording medium such as an optical disk, and the program may be read from the recording medium and written to the storage unit 5. Alternatively, the program may be received via a communication network, and the received program may be written in the storage unit 5.

<Modification 9>
In the above embodiment, an example in which the present invention is applied to an image forming apparatus having four image forming engines corresponding to different colors has been described. However, an image forming apparatus having three or less or five or more image forming engines is used. The present invention may be applied to.

2 is a diagram illustrating a hardware configuration of the image forming apparatus 1. FIG. It is a figure showing the image in which negative ghost has not occurred. It is a figure showing the image in which the negative ghost has generate | occur | produced. It is a figure showing the structure of the ghost correction | amendment part 100K. It is a figure showing the procedure which calculates | requires correction amount (beta) and (gamma). It is an example of a test image. It is a figure showing the test image formed based on the test image data. It is a figure showing the relationship between Cin of color chart B and reflectance, It is a figure showing the relationship between correction amount (beta) and Cin of the color chart B. FIG. It is a figure showing the relationship between correction amount (gamma) and Cin of the color chart A. FIG. It is a figure showing the mode of a change of the latent image ghost generation amount. It is a figure showing the relationship between the thickness t of a protective layer, and correction amount (beta) pr. It is a figure showing the relationship between temperature and humidity, and correction amount (beta) h. FIG. 6 is a diagram illustrating a relationship between a transfer current value and a correction amount βj. It is a figure showing the relationship between the length of a rest period, and correction amount (beta) r.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 4 ... Control part, 44 ... CPU, 45 ... ROM, 46 ... RAM, 5 ... Memory | storage part, 41 ... Instruction reception part, 39 ... Display part, 40 ... Key input part, 48 ... Communication I / F, 2 ... Platen glass, 52 ... Document feeder, 12 ... Image input unit, 6 ... Image output unit, 7Y, 7M, 7C, 7K ... Image forming engine, 20 ... Photosensitive drum, 21 ... Charging device, 19 ... Exposure device, 22 ... developing device, 25 ... transfer device, 8 ... transfer belt, 24 ... cleaner, 9a, 9b ... medium supply unit, 10 ... recording medium, 30 ... transfer roller, 11 ... fixing device, 32a, 32b ... medium Discharge unit 100 ... ghost correction unit 101 ... image memory 102 ... ghost correction amount determination circuit 201 ... one-dimensional LUT 202 ... one-dimensional LUT 103 ... adder 104 ... selector 105 ... test image data generation Circuit, 106 ... ghost correction amount calculating circuit, 301 ... cycle counter, 302 ... rotational speed storage unit, 303 ... temperature and humidity sensor, 304 ... transfer current measuring unit, 305 ... rest period storage unit

Claims (7)

A rotating body that is driven to rotate and whose surface potential changes in response to light irradiation; and an exposure unit that forms an electrostatic latent image by exposing the surface of the rotating body based on input image data; and An image output means having a developing means for developing the electrostatic latent image using a developer, and a transfer means for transferring the image obtained by the development to a recording medium;
First image data, second image data for forming an electrostatic latent image in a region overlapping with the electrostatic latent image based on the first image data of the rotating body, and the first image data The area of the image transferred to the recording medium by the image output unit based on the second image data when the second image data is input after one rotation of the rotating body after the input storage means for the concentration in association with a correction amount for correcting the second image data so as to approach the concentration corresponding to the second image data,
The second image data corresponding to the input image data and the first image data corresponding to the image data input before the input image data by one rotation of the rotating body. Correction amount determining means for determining a corresponding correction amount based on the stored contents of the storage means;
A correction unit that corrects the input image data using the correction amount determined by the correction amount determination unit and outputs the corrected image data to the exposure unit;
A. The thickness of the protective layer provided on the rotating body,
B. Temperature and humidity around the rotating body,
C. A current value of a transfer current generated by the transfer means;
D. The length of time the power was last disconnected,
An image forming apparatus comprising: a rewriting unit that detects any one or more of the above and rewrites a correction amount stored in the storage unit according to a detection result.   The image forming apparatus according to claim 1, wherein the rewriting unit reduces the correction amount as the thickness of the protective layer decreases. The image forming apparatus according to claim 1, wherein the rewriting unit increases the correction amount as the temperature increases, and increases the correction amount as the humidity increases.   The image forming apparatus according to claim 1, wherein the rewriting unit increases the correction amount as the current value increases.   The image forming apparatus according to claim 1, wherein the rewriting unit increases the correction amount as the length of the period increases. A rotating body that is driven to rotate and whose surface potential changes in response to light irradiation; and an exposure unit that forms an electrostatic latent image by exposing the surface of the rotating body based on input image data; and An image processing apparatus that outputs the image data to an image output apparatus having a developing unit that develops an electrostatic latent image using a developer and a transfer unit that transfers an image obtained by the development to a recording medium. ,
First image data, second image data for forming an electrostatic latent image in a region overlapping with the electrostatic latent image based on the first image data of the rotating body, and the first image data The area of the image transferred to the recording medium by the image output unit based on the second image data when the second image data is input after one rotation of the rotating body after the input storage means for the concentration in association with a correction amount for correcting the second image data so as to approach the concentration corresponding to the second image data,
The second image data corresponding to the input image data and the first image data corresponding to the image data input before the input image data by one rotation of the rotating body. Correction amount determining means for determining a corresponding correction amount based on the stored contents of the storage means;
A correction unit that corrects the input image data using the correction amount determined by the correction amount determination unit and outputs the corrected image data to the exposure unit;
A. The thickness of the protective layer provided on the rotating body,
B. Temperature and humidity around the rotating body,
C. A current value of a transfer current generated by the transfer means;
D. The length of time the power was last disconnected,
An image processing apparatus comprising: a rewriting unit that detects any one or more of the above and rewrites a correction amount stored in the storage unit according to a detection result. A rotating body that is driven to rotate and whose surface potential changes in response to light irradiation; and an exposure unit that forms an electrostatic latent image by exposing the surface of the rotating body based on input image data; and A computer that outputs the image data to an image output device having a developing unit that develops the electrostatic latent image using a developer and a transfer unit that transfers an image obtained by the development to a recording medium;
First image data, second image data for forming an electrostatic latent image in a region overlapping with the electrostatic latent image based on the first image data of the rotating body, and the first image data The area of the image transferred to the recording medium by the image output unit based on the second image data when the second image data is input after one rotation of the rotating body after the input storage means for the concentration in association with a correction amount for correcting the second image data so as to approach the concentration corresponding to the second image data,
The second image data corresponding to the input image data and the first image data corresponding to the image data input before the input image data by one rotation of the rotating body. Correction amount determining means for determining a corresponding correction amount based on the stored contents of the storage means;
A correction unit that corrects the input image data using the correction amount determined by the correction amount determination unit and outputs the corrected image data to the exposure unit;
A. The thickness of the protective layer provided on the rotating body,
B. Temperature and humidity around the rotating body,
C. A current value of a transfer current generated by the transfer means;
D. The length of time the power was last disconnected,
A program for functioning as a rewriting unit that detects any one or more of the above and rewrites the correction amount stored in the storage unit according to the detection result.