JP4924261B2 - 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

  It is an object of the present invention to provide a technique capable of suppressing the occurrence of in-plane unevenness and the occurrence of latent image ghosts.

The invention according to claim 1, is rotated, a rotating body potential of the surface is changed in accordance with the irradiation of light, an electrostatic latent image by exposing the surface of the rotating body on the basis of images data An image output means comprising: an exposure means for forming; 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; and a first image When the second image data is inputted after one rotation of the rotating body after the data value, the second image data value, and the first image data are inputted, the second image data is inputted. A first correction amount for correcting the second image data so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data based on the image data; First storage means for storing the information in association with each other; A value of image data, a second correction amount for correcting the image data so that a density of an image transferred to the recording medium by the image output unit approaches a target value based on the image data, and the exposure unit Second storage means for storing the pixel positions in the main scanning direction in association with each other, input image data, and image data input by one rotation of the rotating body before the image data. The first determination means for determining the corresponding first correction amount based on the stored contents of the first storage means, and the first correction amount determined by the first determination means are used for the input. A first correction unit for correcting the image data, and a second correction amount corresponding to the image data corrected by the first correction unit based on the storage contents of the second storage unit. And determining means of the second Using the second correction amount constant means is determined, and having a second correcting means for outputting to said image output means by correcting the image data corrected by said first correction means 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 first area corresponding to one rotation of the rotating body and the one rotation of the rotating body following the first area. a first test image data to be perforated and the corresponding second region, said the first region is provided with a first color chip density is maximum, in the second region A second color chart composed of a plurality of small areas with different densities is provided, and when the first area is superimposed on the second area, a part of each small area is the first color area. A first test image transferred to a recording medium by the image output means based on first test image data representing an image in which the first and second color charts are arranged so as to overlap with one color chart. A reading means for reading, and for each small region of the first test image read by the reading means The concentration of the portion where the small area is overlapped with the first color chart is, to approach the concentration of the portion where the small region does not overlap with the first color chart, a correction amount for correcting the second image data The correction amount is obtained as the first correction amount, and is written in the first storage means in association with the value of the first test image data corresponding to the first color chart and the small area. 1 arithmetic means .

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the second image data is transferred to the recording medium by the image output unit based on the second test image data representing an image having a uniform density. A test image is read by the reading means, and a ratio of the density of the read second test image to the target value is obtained for each pixel, and a value obtained by dividing the second test image data by the ratio is the second value. As a correction amount, there is provided a second calculation means for writing to the second storage means in association with the value of the second image data and the pixel position in the main scanning direction of the exposure means .

The invention according to claim 4, is rotated, a rotating body potential of the surface is changed in accordance with the irradiation of light, an electrostatic latent image by exposing the surface of the rotating body on the basis of images data An image output means comprising: an exposure means for forming; 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; and a first image When the second image data is inputted after one rotation of the rotating body after the data value, the second image data value, and the first image data are inputted, the second image data is inputted. A first correction amount for correcting the second image data so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data based on the image data; First storage means for storing the information in association with each other; A value of image data, a second correction amount for correcting the image data so that a density of an image transferred to the recording medium by the image output unit approaches a target value based on the image data, and the exposure unit Second storage means for storing the pixel positions in the main scanning direction in association with each other, and a second correction amount corresponding to the input image data is determined based on the stored contents of the second storage means. A second determining unit; a second correcting unit that corrects the input image data using the second correction amount determined by the second determining unit; and the second correcting unit that corrects the input image data. Image data after correction by the second correction means, image data after correction by the second correction means of image data input by one rotation of the rotating body before the input image data, First corresponding to A first determination unit that determines a correction amount based on the storage content of the first storage unit, and a first correction amount that is determined by the first determination unit, and the input image data. An image forming apparatus comprising: a first correction unit that corrects the image data corrected by the second correction unit and outputs the corrected image data to the image output unit .

According to a fifth 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, based on image data. An image that outputs the image data to an image output unit that includes an exposure unit, 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. A processing device, the first image data value, the second image data value, and the second image data after one rotation of the rotating body after the first image data is input. Is input to the recording medium by the image output means based on the second image data so that the density of the second image approaches the density corresponding to the second image data. First complement to correct data First storage means for storing the amount in association with each other, the value of the image data, and the density of the image transferred to the recording medium by the image output means based on the image data so as to approach the target value A second storage unit that stores a second correction amount for correcting the image data in association with a pixel position in the main scanning direction of the exposure unit; the input image data; and the rotation based on the image data. First determination means for determining a first correction amount corresponding to image data input by one rotation of the body before based on the stored contents of the first storage means; and the first determination means A first correction unit that corrects the input image data using the first correction amount determined by the first correction unit, and a second correction amount corresponding to the image data corrected by the first correction unit. The stored contents of the second storage means And correcting the image data after correction by the first correction unit using the second determination unit determined based on the second determination unit and the second correction amount determined by the second determination unit. There is provided an image processing apparatus comprising: a second correction unit for outputting.
According to a sixth 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 and image data. An image that outputs the image data to an image output unit that includes an exposure unit, 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. A processing device, the first image data value, the second image data value, and the second image data after one rotation of the rotating body after the first image data is input. Is input to the recording medium by the image output means based on the second image data so that the density of the second image approaches the density corresponding to the second image data. First complement to correct data First storage means for storing the amount in association with each other, the value of the image data, and the density of the image transferred to the recording medium by the image output means based on the image data so as to approach the target value A second storage unit that stores a second correction amount for correcting image data and a pixel position in the main scanning direction of the exposure unit in association with each other; and a second correction amount corresponding to the input image data The second determination means for determining the input image data using the second determination means determined based on the stored contents of the second storage means and the second correction amount determined by the second determination means. 2 correction means, the image data after the input image data is corrected by the second correction means, and the image data input before the input image data by one rotation of the rotating body. The second correction hand And a first determination unit that determines a first correction amount corresponding to the image data after correction based on the storage contents of the first storage unit, and a first determination unit determined by the first determination unit. And a first correction unit that corrects image data after the correction by the second correction unit using the correction amount and outputs the corrected image data to the image output unit. A processing device is provided.

According to a seventh 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 and image data. A computer that outputs the image data to an image output unit that includes an exposure unit, 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. The first image data value, the second image data value, and the first image data are input, and the second image data is input after one rotation of the rotating body. In this case, based on the second image data, the second image data is corrected so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data. The first correction amount and The image data is stored so that the density of the image transferred to the recording medium by the image output unit based on the image data value and the image data value is stored in association with the image data. Second storage means for storing the second correction amount to be corrected and the pixel position in the main scanning direction of the exposure means in association with each other, input image data, and 1 of the rotating body based on the image data. First determination means for determining a first correction amount corresponding to image data input before the rotation amount based on the stored contents of the first storage means, and the first determination means A first correction unit that corrects the input image data using a first correction amount, and a second correction amount that corresponds to the image data that has been corrected by the first correction unit. Based on the storage contents of the storage means Using the second determining means to be determined and the second correction amount determined by the second determining means, the image data corrected by the first correcting means is corrected and output to the image output means. A program for functioning as second correction means is provided.
According to an eighth 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, based on image data. A computer that outputs the image data to an image output unit that includes an exposure unit, 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. The first image data value, the second image data value, and the first image data are input, and the second image data is input after one rotation of the rotating body. In this case, based on the second image data, the second image data is corrected so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data. The first correction amount and The image data is stored so that the density of the image transferred to the recording medium by the image output unit based on the image data value and the image data value is stored in association with the image data. A second storage unit that stores a second correction amount to be corrected and a pixel position in the main scanning direction of the exposure unit in association with each other, and a second correction amount that corresponds to input image data. A second correction unit that corrects the input image data by using a second determination unit that is determined based on the storage contents of the second storage unit and a second correction amount that is determined by the second determination unit. Means, image data after the input image data is corrected by the second correction means, and the first of the image data input by one rotation of the rotating body before the input image data. By the correction means of 2 First correction means for determining a first correction amount corresponding to the corrected image data based on the stored contents of the first storage means, and a first correction determined by the first determination means A program for correcting the image data after the correction by the second correction unit of the input image data by using the amount and outputting it to the image output unit is provided.

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 photoreceptor drum 20Y is a cylindrical photoreceptor, and the outer peripheral surface has photoconductivity. Encoders (not shown) are provided on the rotating shafts of the photosensitive drums 20Y, 20M, 20C, and 20K, and an index signal is output from each encoder each time the photosensitive drums 20Y, 20M, 20C, and 20K make one rotation. Is done.
The charging device 21Y charges the surface of the photosensitive drum 20Y that is rotationally driven in the direction of arrow A 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 using toner as a developer. The toner cartridge 23Y contains yellow toner, and a predetermined amount of toner is supplied to the developing device 22Y. The developing device 22Y supplies this toner to the surface of the photoreceptor drum 20Y. Then, the toner adheres to the portion where the potential is lowered by the irradiation of the exposure beam LB, 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. 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.

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. Regions A and B in the figure are images composed of white crosses and black crosses. The areas C and D are each composed of a plurality of rectangles 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. Then, from the left in the figure, Cin = 100, 80, 60, 40, 20%. The lengths in the vertical direction in the drawing of the part consisting of areas A and B and the part consisting of areas C and D 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 areas A, B, C, and D 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. is there. That is, the images of the areas A and B are formed by the first rotation of the photosensitive drum 20, and the images of the areas C and D are formed by the subsequent one rotation. As shown in the figure, a black cross mark is raised in the region C at a position corresponding to the white cross mark 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. Further, in the region D, a black cross mark is projected at a position corresponding to the white cross mark in the region B. In addition, a white cross mark is raised at a position corresponding to the black cross mark. The figure is exaggerated for easy understanding.

  Further, in this example, when the rectangular areas having the same density are compared between the area C and the area D, the density of the negative ghost is different. That is, in-plane unevenness occurs in the main scanning direction of the photosensitive drum 20. As one of the causes, it is conceivable that the film thickness of the protective layer and the charge transport layer of the photosensitive drum 20 is not uniform in the main scanning direction. If the film thickness is non-uniform, even if a uniform voltage is applied to the surface of the photosensitive drum 20, the charged potential becomes non-uniform, resulting in in-plane unevenness. Also, the accuracy of the mounting position of each device is considered to be a factor. That is, the charging device 21 and the developing device 22 are charged and developed by a charging roller and a developing roller, which are cylindrical members, respectively, but the surface of the charging roller and the developing roller and the surface of the photosensitive drum 20 are in the main scanning direction. If they are not parallel, the charging potential and the density of the toner image are not uniform in the main scanning direction, resulting in in-plane unevenness.

  Next, the configuration of the ghost correction unit 100 will be described. 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). 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 having an area that can cover the patches of one column in the vertical direction of the color chart A at a time, 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 the image data K. 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 the image data K. 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 test image data generation circuit 105 and the ghost correction amount calculation circuit 106 are provided to recalculate the correction amounts β and γ. The reason why the correction amounts β and γ are recalculated 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. For example, as the cumulative operation time of the image forming apparatus 1 is extended, the surface of the photosensitive drum 20 is worn, and the degree of occurrence of the latent image ghost changes depending on the degree of wear. In addition, when the worn photosensitive drum 20 is replaced with a new one, the degree of occurrence of the latent image ghost is different from that before the replacement. The degree of occurrence of the latent image ghost also changes depending on the change in temperature or the like in the image forming apparatus 1. In order to maintain good image quality, it is necessary to change the correction amounts β and γ corresponding to such changes.

Therefore, in the present embodiment, the contents of the one-dimensional LUTs 201 and 202 can be rewritten by recalculating the correction amounts β and γ. Specifically, it is as follows.
The recalculation of the correction amounts β and γ 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 “ghost correction amount recalculation” therein is displayed. The item is specified by the user.

When the above instruction is input to the instruction receiving unit 41, the test image data generation circuit 105 generates test image data representing the test image shown in FIG. 6 and outputs it to the selector 104.
The selector 104 outputs the input test image data to the image output unit 6. Then, processing is performed in accordance with the procedure of steps A01 to A05 described above. The processing of steps A03 to A05 is performed by the ghost correction amount calculation circuit 106. The ghost correction amount calculation circuit 106 is, for example, a computer having a CPU, a ROM, and a RAM, and a program that describes the processing procedure of steps A03 to A05 is stored in the ROM. When the CPU reads this program onto the RAM and executes it, the processing from steps A03 to A05 is performed, and the correction amounts β100 and γ are obtained. The obtained correction amounts β100 and γ are written in the one-dimensional LUTs 201 and 202, respectively, and thereafter, the ghost correction amount determination circuit 102 is used to determine the correction amount α.
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 above is the description of the configuration of the ghost correction unit 100.

  Next, the configuration of the in-plane unevenness correction unit 300 will be described. Since the contents of the processing performed by the in-plane unevenness correction units 300Y, 300M, 300C, and 300K are the same, the following description will be made on the in-plane unevenness correction unit 300K.

FIG. 4 shows the configuration of the in-plane unevenness correcting unit 300K together with the ghost correcting unit 100K.
The in-plane unevenness correction value determination circuit 302 outputs, as image data K2, a correction value corresponding to the pixel value of each pixel included in the image data K + α according to the position X of each pixel in the main scanning direction. Specifically, it is as follows.

  The in-plane unevenness correction value determination circuit 302 is provided with a two-dimensional LUT 401. The two-dimensional LUT 401 is a table that holds the pixel value and correction value of each pixel in association with each position in the main scanning direction. The correction value is obtained in advance by a predetermined method.

Here, a procedure for obtaining a correction value for correcting the in-plane unevenness will be described. FIG. 11 is a diagram illustrating a procedure for obtaining a correction value.
In order to obtain the correction value, first, test image data representing a test image is input to the image output unit 6 (step B01). FIG. 12 is an example of a test image used when obtaining a correction value. The test image is composed of a plurality of band-like regions extending in the main scanning direction. Each region has a uniform density, and the image area ratio of each region is Cin = 15, 30, 50, 70, 100% from the top in the figure.

Next, a test image is formed on the recording medium 10 by the image output unit 6 using the test image data (step B02).
Next, the test image formed in step B02 is read by the image input unit 12, and the obtained image data is converted into reflectance (step B03). Specifically, for example, the reflectance of each pixel on a line that divides each band-like region into two vertically is obtained. FIG. 13 is a diagram showing the input / output characteristics of the image output unit 6 for each pixel using reflectance. In this embodiment, a number (pixel = 0 to 7000) is assigned to each pixel in order from the left in each band-like region, and the position X in the main scanning direction is represented by this number. The horizontal axis of each graph is a value obtained by converting the test image data input to the image output unit 6 into reflectance, and the vertical axis indicates that the test image output from the image output unit 6 is read by the image input unit 12. Is a value obtained by converting the image data obtained by the above into reflectance. In the figure, a solid line is an actual measurement value, and a broken line is a target value. The target value is the same for each pixel.

  As shown in the figure, the difference between the actually measured value and the target value is different for each pixel. That is, in-plane unevenness occurs. In the present embodiment, the image data is corrected so as to remove in-plane unevenness in the main scanning direction (step B04). Specifically, for each pixel value of the image data, a correction value obtained by correcting the image data so that the measured reflectance value matches the target value is obtained. For example, when the measured reflectance value at a certain pixel value is 1.2 times the target value, a value obtained by dividing the pixel value by 1.2 is set as a correction value for the pixel value. Then, the correction value is written in the two-dimensional LUT 401 in association with the pixel value and the position X in the main scanning direction. FIG. 14 is a diagram showing the relationship between the pixel value written in the two-dimensional LUT 401 and the correction value for each position X in the main scanning direction.

  The above is the procedure for obtaining the correction value. In the two-dimensional LUT 401, the correction value obtained by the above procedure is written in advance in association with the pixel value of the image data and the position X in the main scanning direction. The in-plane unevenness correction value determination circuit 402 receives the image data K + α output from the selector 104 of the ghost correction unit 100 and the position X of the pixel in the main scanning direction. The in-plane unevenness correction unit 300 extracts a correction value corresponding to the pixel value represented by the image data K + α and the position X in the main scanning direction from the two-dimensional LUT 401, and outputs the correction value to the selector 304 as the image data K2. .

  The selector 304 outputs the image data K2 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 K2.

The in-screen unevenness correction test image data generation circuit 305 and the in-plane unevenness correction value calculation circuit 306 are provided for recalculation of correction values. The reason why the correction value is recalculated is as follows.
In-plane unevenness may occur in accordance with the passage of time, changes in the environment within the image forming apparatus 1, and the like. For example, as the cumulative operation time of the image forming apparatus 1 increases, the surface of the photosensitive drum 20 is worn, and the degree of occurrence of in-plane unevenness varies depending on the degree of wear. Further, when the photoconductor drum 20 with advanced wear is replaced with a new one, the degree of in-plane unevenness is different from that before the replacement. The degree of occurrence of in-plane unevenness also changes depending on changes in temperature or the like in the image forming apparatus 1. In order to maintain good image quality, it is necessary to change the correction value in response to such a change.

Therefore, the present embodiment is configured such that the correction value can be recalculated and the contents of the two-dimensional LUT 401 can be rewritten. Specifically, it is as follows.
The recalculation of the correction value is performed when the user inputs a predetermined instruction to the instruction receiving unit 41. For example, when a user observes an image formed by the image forming apparatus 1 and the occurrence of in-plane unevenness is visually recognized, the user inputs a predetermined instruction. For example, when the user designates the 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 the “in-plane unevenness correction value recalculation” is displayed. The user designates the item.

When the above instruction is input to the instruction receiving unit 41, the in-screen unevenness correction test image data generation circuit 305 generates test image data representing the test image shown in FIG.
The selector 304 outputs the input test image data to the image output unit 6. Then, processing is performed in accordance with the procedure of steps B01 to B04 described above. The processing in steps B03 to B04 is performed by the in-plane unevenness correction value calculation circuit 306. The in-plane unevenness correction value calculation circuit 306 is, for example, a computer having a CPU, a ROM, and a RAM, and a program that describes the processing procedure of steps B03 to B04 is stored in the ROM. When the CPU reads this program on the RAM and executes it, the processing from step B03 to B04 is performed, and the correction value is obtained. The obtained correction value is written in the two-dimensional LUT 401, and thereafter, the in-plane unevenness correction value determination circuit 402 is used to determine the correction value.
The above is the description of the in-plane unevenness correction unit 300.

  The recalculation of the latent image ghost correction amounts β and γ and the recalculation of the in-plane unevenness correction value may be performed separately. That is, only the correction amounts β and γ may be recalculated to recalculate the in-plane unevenness correction value, or in-plane unevenness correction may be performed without recalculating the correction amounts β and γ. Only recalculation of values may be performed. However, in many cases, since the latent image ghost is accompanied by in-plane variation, it is desirable to recalculate the correction value for in-plane unevenness together with the correction amounts β and γ. In that case, it can be seen that if the correction values β and γ are recalculated after recalculating the correction values for in-plane unevenness, better results are obtained than in the reverse order. Yes. Specifically, the two-dimensional LUT 401 is rewritten by first performing the above-described processing from step B01 to B04. Subsequently, processing from steps A01 to A05 is performed. That is, in the recalculation of the correction amounts β and γ, in-plane unevenness correction is performed using the recalculated correction value when the test image is formed on the recording medium. The test image is read by the image input unit 12 and the correction amounts β and γ are recalculated.

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 recalculation instruction to the image forming apparatus 1 when the user determines that recalculation of the correction amount β, γ or in-plane unevenness correction value is necessary has been described. You may comprise so that recalculation may be performed in the following cases. For example, the CPU 44 may instruct the ghost correction unit 100 or the in-plane unevenness correction unit 300 to execute recalculation every time the number of pages of an image formed by the image forming apparatus 1 reaches a predetermined value. Further, the image forming apparatus 1 includes a temperature sensor, and when the temperature in the image forming apparatus 1 reaches a predetermined value, the CPU 44 instructs the ghost correction unit 100 or the in-plane unevenness correction unit 300 to execute recalculation. May be.

<Modification 3>
As shown in FIG. 7, the latent image ghost tends to be generated more strongly as the density of the image before one rotation of the photosensitive drum is higher. Further, as shown in FIG. 10, the latent image ghost is generated only when the density of the image before one rotation of the photosensitive drum is at or near the maximum density value (Cin = 100%). Therefore, in the recalculation of the correction amounts β and γ, test image data in which the color chart A is configured only by patches with Cin = 100% may be used. In this case, for Cin = 100%, the correction amount β100 is obtained by the procedure shown in the above embodiment. For other Cin, the correction amount α is determined by multiplying the correction amount β100 by the correction amount γ previously written in the one-dimensional LUT 202.

<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 same procedure as the recalculation described above, and the correction amounts β and γ are written in the one-dimensional LUTs 201 and 202. What is necessary is just to use for correction. The same applies to the in-plane unevenness correction value.

<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.

<Modification 10>
In the above embodiment, the example in which the in-plane unevenness correcting unit 300 is provided after the ghost correcting unit 100 is shown. However, the in-plane unevenness correcting unit 300 may be provided before the ghost correcting unit 100. However, since it has been found that a better image can be obtained by providing the in-plane unevenness correction unit 300 at the subsequent stage of the ghost correction unit 100, it is preferable to configure as such.

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. 2 is a diagram illustrating a configuration of a ghost correction unit 100. FIG. 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 procedure which calculates | requires a correction value. It is an example of the test image used when calculating | requiring a correction value. It is the figure which represented the input-output characteristic of the image output part 6 for every pixel using the reflectance. FIG. 6 is a diagram showing the relationship between pixel values and correction values written in a two-dimensional LUT 401 for each position X in the main scanning direction.

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 calculation circuit, 300 ... In-plane unevenness correction unit, 302 ... In-plane unevenness correction value determination circuit, 401 ... Two-dimensional LUT, 304 ... Selector, 305 ... In-screen unevenness correction test image data generation circuit 306: In-plane unevenness correction value calculation circuit

Claims (8)

Is rotated, a rotating body potential of the surface is changed in accordance with the irradiation of light, an exposure means for forming an electrostatic latent image by exposing the surface of the rotating body on the basis of images data, the static 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;
When the value of the first image data, the value of the second image data, and the second image data are input after one rotation of the rotating body after the input of the first image data. First correcting the second image data based on the second image data so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data. First storage means for storing the correction amount in association with each other;
A value of image data, a second correction amount for correcting the image data so that a density of an image transferred to the recording medium by the image output unit approaches a target value based on the image data, and the exposure unit Second storage means for storing the pixel positions in the main scanning direction in association with each other;
A first correction amount corresponding to the input image data and the image data input by one rotation of the rotating body before the image data is determined based on the stored contents of the first storage means. A first determining means;
First correction means for correcting the input image data using the first correction amount determined by the first determination means;
Second determination means for determining a second correction amount corresponding to the image data corrected by the first correction means based on the stored contents of the second storage means;
A second correction unit that corrects the image data corrected by the first correction unit using the second correction amount determined by the second determination unit and outputs the corrected image data to the image output unit; An image forming apparatus. A first region corresponding to one rotation of the rotating body, a first test image data to have a second area corresponding to one rotation of the rotating body subsequent to the first region , said the first region is provided with a first color chips concentration is maximum, the second color chart comprising a plurality of small areas from each other with different concentration in the second region is provided The first and second color charts are arranged so that a part of each small area overlaps the first color chart when the first area is overlapped with the second area. Reading means for reading the first test image transferred to the recording medium by the image output means on the basis of the first test image data representing the image being processed;
For each small area of the first test image read by the reading means, the density of the portion where the small area overlaps the first color chart is the portion where the small area does not overlap the first color chart. A correction amount for correcting the second image data is obtained so as to approach the density of the first color, and the correction amount is used as the first correction amount, and the first color chart and the first region corresponding to the small region are obtained. 2. The image forming apparatus according to claim 1, further comprising: a first calculation unit that writes to the first storage unit in association with a value of the test image data . The second test image transferred to the recording medium by the image output unit based on the second test image data representing a uniform density image is read by the reading unit, and the density of the read second test image For each pixel, a value obtained by dividing the second test image data by the ratio is used as the second correction amount, and the value of the second image data and the main scanning of the exposure unit 3. The image forming apparatus according to claim 2, further comprising: a second calculation unit that writes to the second storage unit in association with a pixel position in a direction . Is rotated, a rotating body potential of the surface is changed in accordance with the irradiation of light, an exposure means for forming an electrostatic latent image by exposing the surface of the rotating body on the basis of images data, the static 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;
When the value of the first image data, the value of the second image data, and the second image data are input after one rotation of the rotating body after the input of the first image data. First correcting the second image data based on the second image data so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data. First storage means for storing the correction amount in association with each other;
A value of image data, a second correction amount for correcting the image data so that a density of an image transferred to the recording medium by the image output unit approaches a target value based on the image data, and the exposure unit Second storage means for storing the pixel positions in the main scanning direction in association with each other;
Second determination means for determining a second correction amount corresponding to the input image data based on the storage content of the second storage means;
Second correction means for correcting the input image data using the second correction amount determined by the second determination means;
The second correction of the input image data after the correction by the second correction means and the image data input by one rotation of the rotating body before the input image data. First determination means for determining a first correction amount corresponding to the image data corrected by the means based on the storage content of the first storage means;
A first correction amount determined by the first determination unit is used to correct the image data after the correction by the second correction unit of the input image data and to output to the image output unit an image forming apparatus, comprising a correction means. A rotating body that is driven to rotate and changes the surface potential in response to light irradiation; an exposure unit that forms an electrostatic latent image by exposing the surface of the rotating body based on image data; An image processing apparatus that outputs the image data to an image output unit that includes a developing unit that develops an image using a developer and a transfer unit that transfers an image obtained by the development to a recording medium,
When the value of the first image data, the value of the second image data, and the second image data are input after one rotation of the rotating body after the input of the first image data. First correcting the second image data based on the second image data so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data. First storage means for storing the correction amount in association with each other;
A value of image data, a second correction amount for correcting the image data so that a density of an image transferred to the recording medium by the image output unit approaches a target value based on the image data, and the exposure unit Second storage means for storing the pixel positions in the main scanning direction in association with each other;
A first correction amount corresponding to the input image data and the image data input by one rotation of the rotating body before the image data is determined based on the stored contents of the first storage means. A first determining means;
First correction means for correcting the input image data using the first correction amount determined by the first determination means;
Second determination means for determining a second correction amount corresponding to the image data corrected by the first correction means based on the stored contents of the second storage means;
Second correction means for correcting the image data corrected by the first correction means using the second correction amount determined by the second determination means and outputting the corrected image data to the image output means;
An image processing apparatus comprising: A rotating body that is driven to rotate and changes the surface potential in response to light irradiation; an exposure unit that forms an electrostatic latent image by exposing the surface of the rotating body based on image data; An image processing apparatus that outputs the image data to an image output unit that includes a developing unit that develops an image using a developer and a transfer unit that transfers an image obtained by the development to a recording medium,
When the value of the first image data, the value of the second image data, and the second image data are input after one rotation of the rotating body after the input of the first image data. First correcting the second image data based on the second image data so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data. First storage means for storing the correction amount in association with each other;
A value of image data, a second correction amount for correcting the image data so that a density of an image transferred to the recording medium by the image output unit approaches a target value based on the image data, and the exposure unit Second storage means for storing the pixel positions in the main scanning direction in association with each other;
Second determination means for determining a second correction amount corresponding to the input image data based on the storage content of the second storage means;
Second correction means for correcting the input image data using the second correction amount determined by the second determination means;
The second correction of the input image data after the correction by the second correction means and the image data input by one rotation of the rotating body before the input image data. First determination means for determining a first correction amount corresponding to the image data corrected by the means based on the storage content of the first storage means;
A first correction amount determined by the first determination unit is used to correct the image data after the correction by the second correction unit of the input image data and to output to the image output unit Correction means and
An image processing apparatus comprising: A rotating body that is driven to rotate and changes the surface potential in response to light irradiation; an exposure unit that forms an electrostatic latent image by exposing the surface of the rotating body based on image data; A computer that outputs the image data to an image output unit that includes a developing unit that develops the image using a developer and a transfer unit that transfers the image obtained by the development to a recording medium;
When the value of the first image data, the value of the second image data, and the second image data are input after one rotation of the rotating body after the input of the first image data. First correcting the second image data based on the second image data so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data. First storage means for storing the correction amount in association with each other;
A value of image data, a second correction amount for correcting the image data so that a density of an image transferred to the recording medium by the image output unit approaches a target value based on the image data, and the exposure unit Second storage means for storing the pixel positions in the main scanning direction in association with each other;
A first correction amount corresponding to the input image data and the image data input by one rotation of the rotating body before the image data is determined based on the stored contents of the first storage means. A first determining means;
First correction means for correcting the input image data using the first correction amount determined by the first determination means;
Second determination means for determining a second correction amount corresponding to the image data corrected by the first correction means based on the stored contents of the second storage means;
Second correction means for correcting the image data corrected by the first correction means and outputting the corrected image data to the image output means by using the second correction amount determined by the second determination means.
Program to function as. A rotating body that is driven to rotate and changes the surface potential in response to light irradiation; an exposure unit that forms an electrostatic latent image by exposing the surface of the rotating body based on image data; A computer that outputs the image data to an image output unit that includes a developing unit that develops the image using a developer and a transfer unit that transfers the image obtained by the development to a recording medium;
When the value of the first image data, the value of the second image data, and the second image data are input after one rotation of the rotating body after the input of the first image data. First correcting the second image data based on the second image data so that the density of the image transferred to the recording medium by the image output means approaches the density corresponding to the second image data. First storage means for storing the correction amount in association with each other;
A value of image data, a second correction amount for correcting the image data so that a density of an image transferred to the recording medium by the image output unit approaches a target value based on the image data, and the exposure unit Second storage means for storing the pixel positions in the main scanning direction in association with each other;
Second determination means for determining a second correction amount corresponding to the input image data based on the storage content of the second storage means;
Second correction means for correcting the input image data using the second correction amount determined by the second determination means;
The second correction of the input image data after the correction by the second correction means and the image data input by one rotation of the rotating body before the input image data. First determination means for determining a first correction amount corresponding to the image data corrected by the means based on the storage content of the first storage means;
A first correction amount determined by the first determination unit is used to correct the image data after the correction by the second correction unit of the input image data and to output to the image output unit Correction means
Program to function as.