JP5157285B2 - 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.

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 this invention is to provide the technique which can suppress generation | occurrence | production of a latent image ghost.

The invention according to claim 1 exposes the surface of the rotating body that is driven to rotate and whose surface potential changes in response to light irradiation, and the pixel value included in the input image data. An image output means having an exposure means for writing an electrostatic latent image by means of, 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; The position of the pixel in the main scanning direction on the rotator, the first image data, the second image data, and the first image data are input after one rotation of the rotator. When the second image data is input, the second image is adjusted such that the density of the image transferred to the recording medium based on the second image data approaches the density corresponding to the second image data. Pair with correction amount to correct data Storage means for attaching and storing a correction amount corresponding to the image data input before only one rotation of the rotating body than the input image data and the image data, the main scanning direction on said rotating body A correction amount determining means for determining each pixel position based on the stored contents of the storage means, and a correcting means for correcting the input image data using the correction amount determined by the correction amount determining 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 plurality of test images having a corresponding second area, wherein the first area is provided with a first color chart having a maximum density, and the second area is arranged in a predetermined direction. A second color chart composed of a plurality of small regions having the same density arranged is provided, and the density of the small region is different for each test image, and the first region is superimposed on the second region. A reading unit that reads a test image in which the first and second color charts are arranged so that a part of each of the small areas overlaps the first color chart, and a test image read by the reading unit The density of the portion where the second color chart overlaps the first color chart for each of the small areas And recalculating means for obtaining a difference between the second color chart and a density of a portion not overlapping the first color chart and writing the difference as a correction amount in the first storage means. To do.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image forming apparatus further includes a position specifying unit that specifies a writing position of the electrostatic latent image on the rotating body in the sub-scanning direction by the exposure unit. The storage means stores the position of the pixel in the main scanning direction and the sub-scanning direction on the rotating body, the first image data, the second image data, and the correction amount in association with each other. The correction amount determining means determines the correction amount corresponding to the input image data and the image data input before the image data by one rotation of the rotating body, in the main scanning direction of the exposure means and Each pixel position in the sub-scanning direction is determined based on the storage contents of the storage means .

According to a fourth aspect of the present invention, a rotating body that is driven to rotate and changes the surface potential in response to light irradiation, and the surface of the rotating body is exposed based on a pixel value included in input image data. An image output apparatus comprising: an exposure unit that writes an electrostatic latent image by a developing 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 position of the pixel in the main scanning direction on the rotator , the first image data, the second image data, and the first image data are input after the first rotation of the rotator. When the second image data is input, the second image data is set such that the density of the image transferred to the recording medium based on the second image data approaches the density corresponding to the second image data. Corresponding to the correction amount to correct Only storage means for storing the correction amount than the input image data and the image data corresponding to the image data input before only one rotation of the rotating body, the main scanning direction on said rotating body A correction amount determining means for determining each pixel position based on the stored contents of the storage means, and a correcting means for correcting the input image data using the correction amount determined by the correction amount determining means; An image processing apparatus is provided.

In the invention according to claim 5, the computer is rotated and the surface of the rotating body is changed based on the pixel value included in the input image data, and the rotating body whose surface potential changes in response to light irradiation. An image having exposure means for writing an electrostatic latent image by exposure, developing means for developing the electrostatic latent image using a developer, and transfer means for transferring an image obtained by the development to a recording medium The position of the pixel in the main scanning direction on the rotator of the output device , the first image data, the second image data, and the one rotation of the rotator after the first image data is input. When the second image data is input later, the second image data is transferred so that the density of the image transferred to the recording medium approaches the density corresponding to the second image data. Correcting image data Storage means for storing in association with each correction amount, the correction amount corresponding to the image data input before only one rotation of the rotating body than the input image data and the image data, the rotator For each pixel position in the upper main scanning direction , the input image data is converted using a correction amount determination unit that is determined based on the stored contents of the storage unit, and a correction amount that is determined by the correction amount determination unit. Provided is a program for functioning as correcting means for correcting.

According to the first, fourth, and fifth aspects of the present invention, the occurrence of the latent image ghost can be suppressed.
According to the second aspect of the present invention, the amount of latent image ghost generated varies with time and environmental fluctuations by using the test image to grasp the amount of latent image ghost generated in the image forming apparatus and changing the correction amount. Even so, the occurrence of the latent image ghost can be reliably suppressed. In addition, the correction amount can be determined with a small amount of calculation compared to the case without the present configuration.
According to the third aspect of the present invention, the occurrence of the latent image ghost can be suppressed even when the degree of occurrence of the latent image ghost differs depending on the circumferential position of the rotating body.

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.
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 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. 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.

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 correction amount determination circuit 102 as the 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 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 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 correction amount determination circuit 102 in synchronization with the input of the image data K, the image data K and the image data K1 are synchronized in the correction amount determination circuit 102. Will be entered.

  Further, the correction amount determination circuit 102 inputs a position X in the main scanning direction on the photosensitive drum 20K on which an electrostatic latent image based on the image data K is formed in synchronization with the input of the image data K. Since each pixel is associated with a unique coordinate value in the area for one page, the CPU 44 outputs the component in the main scanning direction included in this coordinate value as the position X to the correction amount determination circuit 102.

  The correction amount determination circuit 102 has a memory therein, and a three-dimensional LUT (Look Up Table) 201 is written in the memory. The three-dimensional LUT 201 stores a position X in the main scanning direction on the photosensitive drum 20, a pixel value of the image data K, a pixel value of the image data K1, and a correction amount α for the image data K in association with each other. It is. In the three-dimensional LUT 201, a correction amount α obtained by a predetermined method is written in advance.

Here, a procedure for obtaining the correction amount α will be described. FIG. 5 is a diagram illustrating a procedure for obtaining the correction amount α.
In order to obtain the correction amount α, 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 obtaining the correction amount α. The length of the color charts A and B in the figure is equal to the circumference of the photosensitive drum 20K. That is, the color charts A and B are areas corresponding to one rotation 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. The color chart B is divided into five in the main scanning direction, and each of the small areas obtained by the division forms a patch having a uniform density. Each small region corresponds to a position X = 0 to 70 mm, 70 to 140 mm, 140 to 210 mm, 210 to 280 mm, and 280 to 350 mm in the main scanning direction from the left in the drawing. All concentrations are Cin = 15%. Each patch of the color chart B has an area that can cover the patches for one column in the color chart A at a time when the color chart A is superimposed on the color chart B.

Next, a test image is formed on the recording medium 10 by the image output unit 6 based on the test image data (step A02). FIG. 7 is a diagram illustrating a test image formed on the recording medium 10 based on the test image data. In this example, the color chart A image is formed by one rotation of the photosensitive drum 20K, and the color chart B image is formed by the next rotation. As shown in the figure, in color chart B, negative ghost of color chart A is generated, and the density of the area corresponding to the patch of color chart A is lower than the surrounding density. In this example, since the density of the color chart B is low, negative ghost is strongly generated regardless of the density 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.

  Processing similar to the above is performed using test image data in which Cin of color chart B is changed to 30, 50, and 70%. 8, 9, and 10 are images formed by the image output unit 6 based on test image data in which Cin of the color chart B is changed to 30, 50, and 70%, respectively. When Cin = 30, 50%, the density of the negative ghost varies depending on the position X in the main scanning direction. Further, when Cin = 70%, negative ghost is not as remarkable as when Cin = 50% or less.

  Next, the portion of the color chart B shown in FIGS. 7, 8, 9, and 10 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 Cin value in the color chart A and for each position X in the main scanning direction. FIG. 11 is a diagram showing the relationship between the reflectance of the ghost generation portion corresponding to the Cin = 100% patch of the color chart A and the Cin of the color chart B at the position X = 0 mm in the main scanning direction, and the horizontal axis represents the horizontal axis. Cin of the color chart B, the vertical axis is the reflectance. 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, in order to suppress the negative ghost, the image data K is corrected so that the reflectance of the ghost generation part matches the reflectance of the background part. Therefore, as shown in the figure, a correction amount α of the image data K for obtaining the same reflectance as that of the background portion is obtained (step A04). Specifically, for each reflectance value, a value obtained by subtracting Cin of the background portion from Cin of the ghost occurrence portion of the color chart B is set as the correction amount α. In the illustrated negative ghost example, the correction amount α is a positive value. In the case of positive ghost, the correction amount α is a negative value.
FIG. 12A is a diagram showing the relationship between the correction amount α obtained by the above procedure and Cin of the color chart B. At the position X = 0 mm in the main scanning direction, the color chart A, that is, the image data K1. The horizontal axis is plotted as the color chart B, that is, the Cin of the image data K, with respect to the correction amount α obtained by the ghost generation portion of Cin = 100%. FIGS. 12B, 12C, and 12D show the correction amounts obtained by the ghost generation portion of Cin = 80, 60, 0% of the color chart A at the position X = 0 mm in the main scanning direction, respectively. This is a plot of α.
13, 14, 15, and 16 are plots of the correction amount α obtained for each Cin of the color chart A in the same manner as in FIG. 12 for the positions X = 70, 140, 210, and 280 mm in the main scanning direction. .

In a three-dimensional LUT (Look Up Table) 201 provided in the correction amount determination circuit 102, the correction amount α obtained in advance by the above procedure includes the value of the image data K, the value of the image data K1, and the position X in the main scanning direction. It is written in association with.
The correction amount determination circuit 102 calculates a correction amount α corresponding to the input image data K, the image data K1, and the position X in the main scanning direction for each pixel. Then, the obtained correction amount α is output to the adder 103.

The adder 103 inputs the same image data K in synchronization with the input of the image data K by the correction amount determination circuit 102 and adds the correction amount α output from the correction amount determination circuit 102 to the image data K. , And 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 recalculation circuit 106 are provided to recalculate the correction amount α. The reason why the correction amount α is 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 increases, the wear of the photosensitive drum 20K advances, and the degree of occurrence of the latent image ghost also changes depending on the degree of wear. The degree of occurrence of the latent image ghost also changes depending on changes in temperature, humidity, etc. in the image forming apparatus 1. In order to maintain good image quality, it is necessary to recalculate the correction amount α corresponding to such a change.

Therefore, the present embodiment is configured such that the content of the three-dimensional LUT 201 can be rewritten by recalculating the correction amount α. Specifically, it is as follows.
The recalculation of the correction amount α 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 the latent image ghost is visually recognized, 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. Specify the item.

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 according to the procedure of FIG. The recalculation circuit 106 performs the processing of steps A03 to A04. The recalculation circuit 106 is, for example, a computer having a CPU, a ROM, and a RAM, and a program that describes the procedure of steps A03 to A04 is stored in the ROM. When the CPU reads this program on the RAM and executes it, the processing from steps A03 to A04 is performed, and the correction amount α is obtained. The obtained correction amount α is written in the three-dimensional LUT 201, and is thereafter used by the correction amount determination circuit 102 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 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 ghost is corrected according to the position of the photosensitive drum 20 in the main scanning direction. However, the ghost may be corrected according to the position of the photosensitive drum 20 in the sub-scanning direction. . An example of the configuration is as follows.
The photosensitive drums 20Y, 20M, 20C, and 20K are provided with sensors 71Y, 71M, 71C, and 71K that measure and output the rotation angle of each photosensitive drum 20. The rotation angle of the photosensitive drum 20 at the time when the exposure device 19 writes the electrostatic latent image on the photosensitive drum 20 is measured, and this rotation angle is set as a position Y in the sub-scanning direction. Then, for example, for each range of Y = 0 to 90 °, 90 to 180 °, 180 to 270 °, and 270 to 0 °, the correction amount α is obtained according to the procedure shown in FIG. 5 and written in the three-dimensional LUT 201 in advance. . When performing image formation, a correction amount α corresponding to the image data K and the image data K1 is obtained from the three-dimensional LUT 201 for each range to which the rotation angle obtained from the sensor belongs, and an image is obtained using the correction amount α. Data K is corrected.
Note that a circumferential distance from a predetermined reference point on the photosensitive drum 20 to the writing position may be calculated based on the rotation angle, and this distance may be used as the position Y.

  The ghost may be corrected according to both the position X in the main scanning direction and the position Y in the sub scanning direction. In this case, the correction amount α is obtained for each combination of the position X in the main scanning direction and the position Y in the sub-scanning direction, and is written in the four-dimensional LUT. When performing image formation, the position Y in the sub-scanning direction corresponding to the image data K is obtained for each pixel based on the rotation angle obtained from the sensor, and the image data K, the image data K1, the position X in the main scanning direction, A correction amount α corresponding to the position Y in the sub-scanning direction is obtained from the four-dimensional LUT, and the image data K is corrected using this correction amount α.

<Modification 2>
In the above-described embodiment, an example in which the user gives an instruction to recalculate the correction amount α to the image forming apparatus 1 when the user determines that recalculation is necessary has been described, but the recalculation is performed in the following cases. You may comprise. 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 recalculation. Further, the image forming apparatus 1 includes a temperature sensor and a humidity sensor, and the CPU 44 may instruct the ghost correction unit 100 to execute recalculation when the temperature and humidity in the image forming apparatus 1 reach predetermined values. Good.

<Modification 3>
The latent image ghost tends to occur more strongly as the density of the image before one rotation of the photosensitive drum increases. 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 amount α, test image data in which the color chart A is composed only of patches with Cin = 100% may be used.

<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 has a developing roller that is a cylindrical member. The developing roller is charged with a polarity opposite to that of the photosensitive drum 20, toner is attached to the surface thereof, and is driven to rotate in a predetermined direction. Then, the toner moves to the surface of the photosensitive drum 20 by the 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 accumulated 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 α is obtained by subtracting the Cin of the background portion from the Cin of the ghost generation portion for each reflectance value.For example, the Cin of the ghost generation portion with respect to Cin of the background portion is shown. The ratio may be obtained and used as the correction amount α. In this case, by dividing the image data K by the correction amount α, the density of the ghost generation part can be made to coincide with the density of the background part.

<Modification 6>
In the above embodiment, the correction amount α is written in the three-dimensional LUT 201 in advance. However, the correction amount α may not be written in advance. In this case, in the first correction of the latent image ghost by the image forming measure 1, the correction amount α is obtained by the same procedure as the above-described recalculation, and the correction amount α is written in the three-dimensional LUT 201 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 may be stored in the image memory 101 and output to the correction amount determination circuit 102 as the image data K1 after one rotation of the photosensitive drum 20.

<Modification 8>
In the above-described embodiment, an example in which the components other than the recalculation circuit 106 of the ghost correction unit 100 are configured by hardware has been described. However, a program for causing the computer to function as the ghost correction unit 100 is stored in the storage unit 5 and the CPU 44. However, the same processing as that of the ghost correction unit 100 may be executed by executing this program.
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 written to 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, when the correction amount α is recalculated, the test image transferred to the recording medium 10 is read by the image input unit 12, but the test image formed on the transfer belt 8 is read. You may make it read. For example, a reading device composed of a CCD or the like is provided facing the outer peripheral surface of the transfer belt 8, a test image transferred from the photosensitive drum 19 to the transfer belt 8 is read using the reading device, and the obtained image data is reflected. The correction amount α is obtained by the procedure shown in step A04 of the embodiment.

2 is a diagram illustrating a hardware configuration of the image forming apparatus 1. FIG. It is a figure showing the example of the image in which the negative ghost has not occurred. It is a figure showing the example of 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 an example of the image formed based on test image data. It is an example of the image formed based on test image data. It is an example of the image formed based on test image data. It is an example of the image formed based on test image data. It is a figure showing the relationship between the reflectance of a ghost generating part, and Cin of the color chart B. It is a figure showing the relationship between correction amount (alpha) and Cin of the color chart B. FIG. It is a figure showing the relationship between correction amount (alpha) and Cin of the color chart B. FIG. It is a figure showing the relationship between correction amount (alpha) and Cin of the color chart B. FIG. It is a figure showing the relationship between correction amount (alpha) and Cin of the color chart B. FIG. It is a figure showing the relationship between correction amount (alpha) and Cin of the color chart B. FIG.

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, 7 ... Image forming engine, 20 ... Photosensitive drum, 21 ... Charging device, 19 ... Exposure device, 22 ... Development , 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 ... Correction amount determination circuit 201 ... Three-dimensional LUT 103 ... Adder 104 ... Selector 105 ... Test image data generation circuit 106 ... Recalculation circuit

Claims (5)

Rotating body that is driven to rotate and changes the surface potential in response to light irradiation, and exposure that writes an electrostatic latent image by exposing the surface of the rotating body based on pixel values included in input image data Image output means comprising: means; developing means for developing the electrostatic latent image using a developer; and transfer means for transferring an image obtained by the development to a recording medium;
The position of the pixel in the main scanning direction on the rotator, the first image data, the second image data, and the first image data are input after the first rotation of the rotator. When the second image data is input, the second image data is set such that the density of the image transferred to the recording medium based on the second image data approaches the density corresponding to the second image data. Storage means for associating and storing a correction amount for correcting
The correction amount corresponding to the input image data and the image data input before one rotation of the rotator before the image data is determined for each pixel position in the main scanning direction on the rotator. Correction amount determining means for determining based on the storage contents of the storage means;
An image forming apparatus comprising: a correction unit that corrects the input image data using the correction amount determined by the correction amount determination unit. A plurality of test images having a first area corresponding to one rotation of the rotating body and a second area corresponding to one rotation of the rotating body following the first area, The first color chart having the maximum density is provided in one area, and the second color chart including a plurality of small areas having the same density arranged in a predetermined direction is provided in the second area. The density of the small area is different for each test image, and when the first area is overlapped with the second area, a part of each small area overlaps the first color chart. Reading means for reading a test image in which the first and second color charts are arranged;
For each small region of the test image read by the reading unit, the density of the portion where the second color chart overlaps the first color chart, and the second color chart overlaps the first color chart. 2. The image forming apparatus according to claim 1, further comprising: a recalculating unit that obtains a difference from the density of the portion that should not be obtained and writes the difference as a correction amount in the first storage unit. A position specifying means for specifying a writing position in the sub-scanning direction on the rotating body of the electrostatic latent image by the exposure means;
The storage means stores the pixel positions in the main scanning direction and the sub-scanning direction on the rotating body, the first image data, the second image data, and the correction amount in association with each other,
The correction amount determining means determines a correction amount corresponding to the input image data and the image data input by one rotation of the rotating body before the image data. The image forming apparatus according to claim 1 , wherein each pixel position in the scanning direction is determined based on a storage content of the storage unit. Rotating body that is driven to rotate and changes the surface potential in response to light irradiation, and exposure that writes an electrostatic latent image by exposing the surface of the rotating body based on pixel values included in input image data A main scanning direction on the rotator of the image output apparatus including: 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 position of the pixel, the first image data, the second image data, and the second image data are input after one rotation of the rotating body after the first image data is input. The correction amount for correcting the second image data so that the density of the image transferred to the recording medium based on the second image data approaches the density corresponding to the second image data. storage means for attaching stores ,
The correction amount corresponding to the input image data and the image data input before one rotation of the rotator before the image data is determined for each pixel position in the main scanning direction on the rotator. Correction amount determining means for determining based on the storage contents of the storage means;
An image processing apparatus comprising: a correction unit that corrects the input image data using the correction amount determined by the correction amount determination unit. Computer
Rotating body that is driven to rotate and changes the surface potential in response to light irradiation, and exposure that writes an electrostatic latent image by exposing the surface of the rotating body based on pixel values included in input image data A main scanning direction on the rotator of the image output apparatus including: 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 position of the pixel, the first image data, the second image data, and the second image data are input after one rotation of the rotating body after the first image data is input. The correction amount for correcting the second image data so that the density of the image transferred to the recording medium based on the second image data approaches the density corresponding to the second image data. storage means for attaching stores ,
The correction amount corresponding to the input image data and the image data input before one rotation of the rotator before the image data is determined for each pixel position in the main scanning direction on the rotator. Correction amount determining means for determining based on the storage contents of the storage means;
A program for functioning as correction means for correcting the input image data using the correction amount determined by the correction amount determination means.