JPH09247452A - Image processor and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image processor capable obtaining a picture output with a stable density by forming first pattern image in a first area and forming a second pattern image in a second area except the first area. SOLUTION: A low density patch is formed in the image area 121 and a high density patch is in the non-image area 122 in a transfer drum 5. Halftone control is started by COPU after a prescribed time elapses from a time for turning-on a power source or in a proper timing such as a point if time when the number of printing reaches to the prescribed number. In halftone control, a pattern generator generates seven patches PY1-PY7 (corresponding to a Y- component), PM1-PM7 (corresponding to the M-component) and PBK1-PBK7 (corresponding to the BK-component) in the transfer drum 5 at every color in order to set proper LUT in a gradation correcting part. PY1 is the lowest in a density in PY1-PY7 and the density successively becomes deeper toward PY7. Of course, the same is executed for the other color component patches.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and a method thereof, and more particularly, to an image processing apparatus and a method thereof for performing halftone control by forming a patch and measuring the density thereof.

[0002]

2. Description of the Related Art In a so-called electrophotographic color image processing apparatus for forming an image by using a conventional laser beam, a multiple transfer method for developing and transferring each color component to form a color image on a recording sheet. There is a multi-developing method in which development is performed for each color component and a color image is formed by batch transfer onto recording paper.

In image formation by either method,
It is necessary to drive the laser by the laser driver based on the input image signal. However, the relationship between the image signal input to the laser driver and the image density actually formed and output on the recording paper, that is, the gradation characteristic, has an ideal relationship (straight line) as shown in FIG. Don't
Therefore, it becomes necessary to perform halftone control by correcting this gradation characteristic to an ideal relationship (straight line).

In the conventional image processing apparatus, the above-mentioned halftone control is realized as follows.

As shown in FIG. 10, the interval (2
Image signal a1 that changes with 0H, 40H, 60H, 80H, ... (H indicates hexadecimal notation)
Based on .about.an, a toner image for density detection (hereinafter referred to as a patch) is formed on the transfer drum in the image processing apparatus of the multiple transfer system and on a photosensitive drum in the image processing apparatus of the multiple development system. Then, the density of the patch is measured, and the initial gradation characteristic is obtained by linearly or curvedly interpolating the measurement result, and a look-up table (LUT) for gradation correction is created based on the gradation characteristic. . Then, at the time of image formation, an input image signal to the laser driver is corrected by referring to the LUT, that is, density conversion is performed by referring to the LUT, so that an output image having an ideal gradation characteristic can be obtained.

[0006]

In the above-mentioned halftone control method, the following method can be considered as a method for measuring the density of the patch formed on the drum (transfer drum or photosensitive drum).

First, the surface of the drum (hereinafter referred to as the base) corresponding to the position where the patch is formed is measured by a density sensor, and the sensor output is Su. Next, a patch is formed on the drum and measured by a density sensor, and the sensor output is Sp
And The sensor output Sp when this patch is measured includes the influence of the base (drum surface).

Here, in the image processing apparatus, a "density conversion table" for obtaining the density of the patch based on the sensor output Sp of the patch when the sensor output Su of the background is a predetermined value Sdef is stored in advance. Prepare

Therefore, when the patch density is measured, the difference between the measured values Su and Sdef of the background is obtained, and this difference is used as the measured value S of the patch.
By subtracting from p, the normalized value Sp- (Su-Sd
ef). Then, the standardized value Sp- (Su-S
def) by referring to the density conversion table above,
An appropriate patch density can be obtained.

As described above, by standardizing the patch density by the above method, it is possible to perform measurement with accuracy even when the reflectance of the drum surface changes to some extent due to contamination due to aging. Therefore, it is possible to create an LUT with high accuracy, and it is possible to perform appropriate density conversion in halftone control.

However, in the halftone control of the above-described image processing apparatus, the density conversion can be performed with high accuracy only when the reflectance of the drum surface does not change extremely. Therefore, it is preferable that the patch created in the halftone control, that is, in the calibration mode is formed in a portion where the surface of the drum is less deteriorated. The temporal change of the drum surface does not occur uniformly in all areas of the drum surface, and exhibits a predetermined bias depending on whether or not there is contact with another member such as transfer paper. Therefore, the reflectance of the base of the drum forming the patch may be locally different.

Therefore, in order to avoid creating a patch on a base having different reflectance, the patch is not directly related to image formation on the drum surface, and therefore the patch is applied only to a region (non-image region) with little deterioration. It is also conceivable to form However, it is necessary to increase the number of patches when performing high-precision halftone control, and the drum itself must be enlarged accordingly. With this,
This is not an effective method because the drum size must be increased for halftone control.

The present invention has been made in order to solve the above-mentioned problems in view of the above situation, and it is possible to effectively use an area on a medium on which an image is formed to perform halftone control. It is an object of the present invention to provide an image processing apparatus and method capable of obtaining an image output with stable density.

[0014]

As one means for achieving the above object, an image processing apparatus according to the present invention has the following arrangement.

That is, an image processing apparatus for sequentially forming images of respective color components on an image carrier and sequentially transferring the images to a transfer material held by a transfer material holder, wherein an input image is obtained based on gradation correction characteristics. Gradation correcting means for performing the gradation correction, pattern forming means for forming a plurality of pattern images having different density values on the transfer material holder, and density detecting means for detecting the density value on the transfer material holder. And a control unit for controlling the gradation correction characteristic based on the density value of the pattern image detected by the density detection unit, wherein the pattern image forming unit is a first unit on the transfer material holder. A first pattern image is formed in a region, and a second pattern image is formed in a second region other than the first region on the transfer material holder.

For example, the second region is a region that is more deteriorated than the first region.

For example, the first region corresponds to a minimum size of the transfer material that can be held on the transfer material holding body.

For example, the first area corresponds to the size of the transfer material that is most frequently used.

For example, the second pattern image has a higher density than the first pattern image.

For example, the density detecting means detects a density value of the pattern image in a first detection mode, and a density mode of the surface of the transfer material holder before the pattern image is formed in a second detection mode. A detection mode, and the control means controls the gradation correction characteristic based on the pattern image detected by the first and second modes of the density detection means and the density value on the surface of the transfer material holder. It is characterized by doing.

For example, the area on the transfer material holder in which the surface density is detected in the second mode of the density detecting means corresponds to the area where the pattern image is formed by the pattern forming means. To do.

For example, the control means sets the average of the density values on the transfer material holder corresponding to the first pattern detected by the second mode of the density detection means to the second pattern. The gradation correction characteristic is controlled as a corresponding density value on the transfer material holder.

Further, there is provided notifying means capable of notifying the state of the apparatus, and the control means controls the density value of the first area of the density value on the transfer material holder detected in the second mode of the density detecting means. When the absolute value of the difference between the average value of the density values and the average value of the density values of the second area is a predetermined value or more, or the average value of the density values of the second area is a predetermined value or more, the notification is given. Means for notifying that the transfer material holder is abnormal.

Further, each color component image is formed on the image carrier,
An image processing apparatus for collectively transferring the image onto a transfer material,
Gradation correction means for performing gradation correction of an input image based on gradation correction characteristics, pattern forming means for forming a plurality of pattern images having different density values on the image carrier, and density on the image carrier The pattern image forming means includes a density detecting means for detecting a value and a controlling means for controlling the gradation correction characteristic based on the density value of the pattern image detected by the density detecting means. Forming a first pattern image on a first region on the body, the first pattern image on the image carrier;
The second pattern image is formed in the second area other than the area.

For example, the first region is a region that is more deteriorated than the second region.

For example, the first area corresponds to the maximum size of an image that can be formed on the image carrier.

For example, the first area corresponds to an image size having the highest formation frequency.

For example, the first pattern image has a higher density than the second pattern image.

For example, the density detecting means detects a density value of the pattern image in a first detection mode and a second detection mode of detecting a density value on the surface of the image carrier before the pattern image is formed. A mode, the control means, based on the density value of the pattern image and the image carrier surface detected by the first and second modes of the density detection means,
It is characterized in that the gradation correction characteristic is controlled.

For example, the area on the image carrier where the surface density is detected in the second mode of the density detecting means corresponds to the area where the pattern image is formed by the pattern forming means. .

For example, the control means may calculate the average of the density values on the image carrier corresponding to the second pattern detected by the second mode of the density detection means as the first value.
As the density value on the image carrier corresponding to the pattern of,
It is characterized in that the gradation correction characteristic is controlled.

Further, there is provided a notifying means capable of notifying the state of the apparatus, and the control means controls the density value of the first area of the density value on the transfer material holder detected in the second mode of the density detecting means. When the absolute value of the difference between the average value of the density values and the average value of the density values of the second region is a predetermined value or more, or the average value of the density values of the first region is a predetermined value or more, the notification is given. Means for notifying that the transfer material holder is abnormal.

Further, the image forming means for forming an image on the medium, the reading means for reading the image formed on the medium, and the image forming characteristics of the image forming means are controlled based on the read data of the reading means. In the image processing apparatus having the control means, the reference image in the calibration mode is formed in both the first region and the second region outside the first region that can be imaged in the normal mode. It is characterized by For example, the medium is a transfer drum. For example, the medium is a photosensitive drum. For example, the reading unit reads the background density of the first and second areas on the medium and the reference images formed in the first and second areas, respectively. For example, the control means is characterized in that the background density of the first region is used to replace the background density of the second region. Further, as one method for achieving the above object, the image processing method according to the present invention includes the following steps.

That is, an image processing method in an image processing apparatus in which images of respective color components are sequentially formed on an image carrier and the images are sequentially transferred to a transfer material held by a transfer material holder, Background density detecting step for detecting the surface density value of the pattern, a pattern forming step for forming a plurality of pattern images having different density values on the transfer material holder, and a pattern density detecting for detecting the density value of the plurality of pattern images And a gradation correction characteristic control step for controlling gradation correction characteristics referred to when gradation correction of an input image is performed based on the surface density value of the transfer material holder and the density value of the pattern image. In the pattern forming step, a first pattern image is formed in a first area on the transfer material holder, and a second pattern image other than the first area on the transfer material holder is formed. Second putter in the area And forming an image.

For example, the second region is a region that is more deteriorated than the first region.

For example, the second pattern image has a higher density than the first pattern image.

For example, the area on the transfer material holder whose surface density is detected in the background density detecting step corresponds to the area where the pattern image is formed in the pattern forming step.

For example, in the control step, the average of the density values on the transfer material holder corresponding to the first pattern detected in the background density detecting step is calculated as the average of the density values corresponding to the second pattern. The gradation correction characteristic is controlled as a density value on the transfer material holder.

Further, each color component image is formed on the image carrier,
An image processing method in an image processing apparatus for collectively transferring the image to a transfer material, comprising: a background density detecting step of detecting a surface density value of the image carrier, and a plurality of patterns having different density values on the image carrier. A pattern forming step of forming an image, a pattern density detecting step of detecting density values of the plurality of pattern images, a surface density value of the image carrier and a density value of the pattern image, based on a density of the input image. A gradation correction characteristic control step of controlling a gradation correction characteristic referred to when performing the tone correction, and in the pattern forming step, a first pattern image is formed in a first region on the image carrier. Forming a second area other than the first area on the image carrier.
The second pattern image is formed in the area of.

For example, the first region is a region which is more deteriorated than the second region.

For example, the first pattern image has a higher density than the second pattern image.

For example, the area on the transfer material holder whose surface density is detected in the background density detecting step corresponds to the area where the pattern image is formed in the pattern forming step.

For example, in the control step, the average of the density values on the image carrier corresponding to the second pattern detected in the background density detection step is set to the first value.
As the density value on the image carrier corresponding to the pattern of,
It is characterized in that the gradation correction characteristic is controlled. Also,
An image forming step of forming an image on a medium, a reading step of reading an image formed on the medium, and a control step of controlling image forming characteristics in the image forming step based on read data by the reading step. An image processing method having: in both a first region on the medium imageable in a normal mode and a second region outside the first region,
It is characterized in that a reference image in the calibration mode is formed.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below in detail with reference to the drawings.

<First Embodiment> First, an image processing apparatus to which the present embodiment is applicable will be described with reference to FIG. FIG. 1 is a side sectional view of a color image processing apparatus using an electrophotographic multiple transfer system. In FIG. 1, 1 is a photosensitive drum, 2 is a roller charger, and a plurality of developing devices 4a, 4b, 4c, 4d are carried on the left side thereof by a rotatable support member 3. Further, on the right side of the photosensitive drum 1, there is arranged a transfer drum 5 which holds a transfer paper (not shown) and has a function of transferring an image on the photosensitive drum 1 onto the transfer paper. Photosensitive drum 1, transfer drum 5, developing device 4a
4d are driven to rotate in the direction of the arrow in the figure by a driving means (not shown).

Above the inside of the apparatus main body, a laser diode 7 constituting an exposure apparatus, a polygonal mirror 9 driven to rotate by a high speed motor 8, a lens 10, and a folding mirror 11 are provided.
Is arranged.

When a signal according to the image of the yellow (Y) component is input, the laser driver 22 causes the laser diode 7 to emit light. Then, this light is applied to the photosensitive drum 1 through the optical path 12. The photosensitive drum 1 is uniformly charged by the primary charger 2, and a latent image is formed according to the optical information applied. When the photosensitive drum 1 further rotates in the direction of the arrow, this latent image is visualized with the Y toner by the developing device 4a.

In synchronization with the image on the photosensitive drum 1,
When a transfer paper (not shown) is supplied from the transfer paper cassette 13 by the pickup roller 14, the transfer paper is held by the gripper 15, and then the suction roller 16 and the transfer drum 5 that supports and conveys the transfer paper. The transfer paper is electrostatically adsorbed on the transfer drum 5 by applying a voltage during the period. After that, the toner image on the photosensitive drum 1 is transferred onto the transfer paper on the surface of the transfer drum 5.

By sequentially performing the above steps for magenta (M), cyan (C) and black (Bk), toner images of a plurality of colors are transferred onto the transfer paper. The transfer paper is peeled off from the transfer drum 5 by the separating claw 17, and the fixing device 18 melts and fixes the toner image to obtain a permanently visualized color image.

On the other hand, the toner remaining on the photosensitive drum 1 is cleaned by a cleaning device 6 such as a fur brush or blade means. Further, the toner on the transfer drum 5 is also cleaned by the transfer drum cleaning device 19 such as a fur brush or a wave, and then the residual charge on the transfer drum 5 is removed by the charge removing roller 20.

A density sensor 21 can measure the density on the surface of the transfer drum 5. Here, FIG.
The detailed configuration of the density sensor 21 is shown in FIG. In FIG. 2, 2
Reference numeral 11 denotes a light emitting element such as an LED, 212 a photodiode, a light receiving element such as CdS, and 213 a holder. As shown in the figure, the light emitting element 211 irradiates the patch T on the transfer drum 5 with light, and the reflected light is received by the light receiving element 212
The density of the patch T is measured by reading with.

Returning to FIG. 1, reference numeral 25 denotes a control unit, which includes a halftone process for an image signal input from an external device (not shown) in a normal image forming mode (hereinafter referred to as "normal mode"). Appropriate image processing is performed and output to the laser driver 22 for each color component. 26 is an operation unit,
It has various keys and a display panel such as an LCD, and is used by the operator to input commands and notify the device status.

In the image processing apparatus of the multiple transfer system described above, it is possible to form a halftone image. Next, a detailed block configuration of the control unit 25 is shown in FIG. In FIG.
A logarithmic conversion unit 304 converts R, G, B color image signals input from an external device (not shown) such as a host computer into C, M, Y signals. A black generation unit 305 generates a Bk signal from the C, M and Y signals.
Reference numeral 306 denotes a gradation correction unit, which performs conversion by the LUT so that the relationship (gradation characteristics) between the input image signal and the density of the image actually formed is linear. When forming and outputting a color image, accurate reproduction of halftones is particularly important, and therefore the quality of the output image depends on how the LUT corrects. The contents of this LUT are determined as described below. Reference numeral 307 denotes a pulse width modulator, which is based on the image signal after gradation conversion and is used by the laser driver 2
Grayscale is expressed by modulating the pulse width for driving 2. Reference numeral 309 denotes a pattern generator that is a feature of the present embodiment. As will be described later, an image signal for generating a patch of a predetermined density for each color is provided in advance at a predetermined position on the drum, and is used during halftone control, that is, during LUT creation. , And outputs an image signal for generating the patch to the pulse width modulator 307.

Reference numeral 310 is a CPU, and the ROM 31
The overall control of the entire apparatus including the components of the control unit 25 and the concentration sensor 21 and the operation unit 26 described above with reference to the control program stored in No. 1 is performed. The ROM 311 holds various control programs including an LUT update program in the gradation correction unit 306, variables, and the like, which are shown in a flowchart described later. The image data corresponding to each patch output by the pattern generator 309 described above is R
It may be stored in the OM 311. In addition, RAM31
2 is used as a work area of the CPU 310, and the LUT described above may exist in the RAM 312, for example.

In the image processing apparatus of this embodiment having the above-described configuration, the input image signal has a linear gradation characteristic or a desired gradation characteristic before being input to the laser driver 22 by the LUT in the gradation correction unit 306. Correction is performed so that the gradation characteristics are suitable for the image to be displayed. In this embodiment, an 8-bit image signal from "00H" to "FFH" is handled, and the image density increases from "00H" to "FFH".

As described in the above-mentioned conventional example, this LU
In the initial state where T is not set, the image signal is sent to the laser driver 22 as it is, and thus the obtained gradation characteristic does not become a straight line as shown in FIG. Therefore, in order to obtain ideal gradation characteristics, the pattern generator 3
09, a patch is formed on the drum, and the patch is measured by the density sensor 21 and further standardized.
T can be updated appropriately to cope with the deterioration of the drum surface.

However, as the operating period becomes longer and the number of printed sheets increases, the portion of the surface of the transfer drum 5 where the transfer paper is wound (image area) and the portion where the transfer paper is not wound (non-image area) The roughening will be different.

The cause is considered as follows. That is,
During printing, since the transfer paper is wrapped around the image area, the photosensitive drum 1 and the surface of the transfer drum 5 do not rub directly, but unlike the image area, the non-image area always rubs directly on the photosensitive drum 1. . Therefore, the non-image area on the surface of the transfer drum 5 always has a large amount of sliding friction with the photosensitive drum 1 as compared with the image area. The surface of the transfer drum 5 is polyvinylidene fluoride (PVdF), polyethylene terephthalate (PET),
As it is a film or sheet made of resin such as polycarbonate or polyurethane, it is easily damaged. Therefore, as the number of printed sheets increases, the difference in the roughness between the image area and the non-image area becomes noticeable on the surface of the transfer drum 5, resulting in a large difference in the reflectance.

In order to prepare the LUT for performing the appropriate gradation conversion in the gradation correction unit 306, it is desirable that the reflectance of the surface of the transfer drum 5 forming the patch does not change extremely. Therefore, the patch may be formed in the image area of the transfer drum 5, that is, in a portion having less roughness.

However, in order to improve the accuracy of gradation correction in the gradation correction unit 306, it is necessary to increase the number of patches formed on the drum. Will end up creating a patch.

Here, as a method of avoiding the formation of patches on the bases having different reflectances such as image areas and non-image areas, the patches are formed only on the non-image areas on the transfer drum 5 as shown in FIG. 4, for example. There are possible ways to do this. In FIG. 4, 51 on the surface of the transfer drum 5 is an image area, and
2 is a non-image area. Further, the patches 53 to 56 are formed, that is, the patches 53 to 56 are formed on the non-image areas at both ends of the drum. Then, as the transfer drum 5 rotates in the direction of the arrow in the drawing, the patches 53 to 56 are sequentially read by the fixed density sensor 21.

However, according to this method, the patches 53-
The area where 56 can be formed is limited to both ends of the drum.
Therefore, especially when highly accurate gradation correction is performed, the width of the transfer drum 5 must be increased only for the purpose of creating a large number of patches. In addition, since the non-image area on the transfer drum 5 generally does not have good image forming accuracy, it is not preferable to form the patch on the non-image area.

Therefore, in the present embodiment, during the halftone control in the image processing apparatus of the multiple transfer system, a large number of patches are efficiently formed on the surface of the transfer drum 5 where deterioration may occur, and an appropriate LUT is derived. Is characterized by.

Hereinafter, referring to the flowchart of FIG.
The halftone control in this embodiment will be described. still,
The control program shown in the flowchart of FIG. 5 is stored in the ROM 311 as described above.

The halftone control of the present embodiment is started by the CPU 310 at an appropriate timing such as when the power of the main body is turned on, when a predetermined time has elapsed since the power was turned on, or when the number of printed sheets reaches a predetermined number. .

In the halftone control of this embodiment, in order to set an appropriate LUT in the gradation correction unit 306,
The pattern generator 309 uses seven patches P for each color.
Y1 to PY7 (corresponding to Y component), PM1 to PM7 (corresponding to M component), PC1 to PC7 (corresponding to C component), PBk1 to PBk7 (B
(corresponding to the k component) is created on the transfer drum 5. In addition, PY1
.About.PY7, PY1 has the lowest concentration, and the concentration gradually increases until PY7. Of course, the same applies to other color component patches.

FIG. 6 shows the state of the Y component patch formed on the transfer drum 5 in this embodiment. In FIG. 6, reference numeral 121 is an image area, 122 is a non-image area, and a low-density patch on the image area 121 is a non-image area 122.
A state in which a high-density patch is formed is shown.

In the present embodiment, it is known that a patch having a high density value of "80H" or more is hardly affected by the background. Therefore, it is easily influenced by the base, for example, “08H”, “10H”, “30H”, “5”.
0H "," 70H ", etc. patches of relatively low density (PY1 ~
PY5, PM1 to PM5, PC1 to PC5, and PBk1 to PBk5 respectively) are created in the image area in which the reflectance of the background is relatively stable. Then, relatively high density patches (PY6 to PY7, PM6 to PM7, PC6 to PC7, PBk6 to PBk7) such as "90H" and "C0H" which are hardly influenced by the background.
In the non-image area where the reflectance of the background largely changes depending on the number of printed sheets. Here, the image area refers to an area on the transfer drum 5 around which the transfer paper of the smallest size that can be printed by the apparatus is wrapped, and the other area is a non-image area. Alternatively, the area around which the transfer paper of the most frequently used size is wound may be used as the image area. As a result, it is possible to effectively use the area of the surface of the transfer drum 5 when forming the patches, so that a larger number of patches can be formed, and therefore, high-precision halftone control can be performed.

When the halftone control is started, first in step S
At 21, the transfer drum 5 is rotated to measure the background density of the portion forming the patch. That is, the patches PY1 to PY7, PM1 to PM7, PC1 created in this embodiment.
To PC7, PBk1 to PBk7 are formed in the background density UY1
˜UY7, UM1 to UM7, UC1 to UC7, UBk1 to UBk7 are measured by the density sensor 21 and stored in the RAM 312. These background densities are UY1 to UY5, UM1 to UM5, U as described above.
C1 ~ UC5, UBk1 ~ UBk5 correspond to the image area, UY6, U
Y7, UM6, UM7, UC6, UC7, UBk6 and UBk7 correspond to non-image areas.

Next, the process proceeds to step S22, and the pattern generator 309 reads out the image data aY1 to aY7 corresponding to the Y component patches PY1 to PY7 stored in advance, and sends the data to the laser driver 22. As a result, a latent image of the Y density detection patch is formed on the photosensitive drum 1, and the latent image is developed by the developing device 4a.
Toner images of Y1 to PY7 are formed and transferred onto the transfer drum 5 at predetermined positions where the background densities UY1 to UY7 have been measured.
Then, in step S23, the density values of the Y patches PY1 to PY7 formed on the transfer drum 5 are measured by the density sensor 21.
The sensor output S
Save Y1 to SY7 in the RAM312.

Next, in step S24, the CPU 310
Reads the background measurement values UY1 to UY7 of the Y patch stored in the RAM 312, and calculates the average value UYL of UY1 to UY5 and U
The average value UYH of Y6 and UY7 is calculated, and the absolute value of the difference ΔUY
Is calculated. Then, in step S25, the ΔUY is compared with a predetermined threshold (“10H” in this embodiment), and
If UY is equal to or greater than the threshold value, it is determined that the surface of the transfer drum 5 is severely deteriorated, and the operator is informed that the surface of the transfer drum 5 is abnormal from the LCD panel or the like on the operation unit 26 in step S26. And proceeds to step S27.

If ΔUY is less than the threshold value in step S25, the average value UYA of the background densities UY1 to UY5 is determined in step S27.
ve is calculated, and the average value UYAve is substituted into UY6 and UY7. Then, in step S28, the patch densities DY1 to DY7 are calculated by using the bases UY1 to UY7 of the Y patch as the above Su and the measured values SY1 to SY7 of the patch as the above Sp. Then, in step S29, a gradation correction LUT for the Y component is created based on the obtained patch densities DY1 to DY7.

With the above processing, the LUT for the Y component is created. Next, in steps S30 and S31, other M, C,
By performing the same processing on the Bk component, an appropriate LUT is created for each color component. The order of the color components for generating the LUT may be arbitrary.

As described above, according to this embodiment, in the color image processing apparatus of the multiple transfer system, the patches formed on the transfer drum 5 at the time of the halftone control have the deterioration of the drum surface at the low density portion. Is formed in a non-image area where the deterioration of the drum surface is large, and the patch density is measured to generate a gradation correction LUT.
As a result, it is possible to effectively use the area of the surface of the transfer drum 5 and perform the halftone control while suppressing the influence of the deterioration of the surface of the transfer drum 5 as much as possible, and obtain a stable output image density.

<Second Embodiment> The second embodiment of the present invention will be described below.
An embodiment will be described.

First, with reference to FIG. 7, a color image forming apparatus of an electrophotographic multiple developing system which is an image processing apparatus of the second embodiment will be described. In FIG. 7, the same numbers are given to the configurations that bring about the same operations as those in FIG. 1 described in the first embodiment.

In FIG. 7, 1 is a photosensitive drum, 2 is a primary charging device, and a plurality of developing devices 4a, 4b, 4 are provided on the right side thereof.
c and 4d are arranged. The photosensitive drum 1 is rotationally driven in the direction of the arrow in the figure by a driving unit (not shown).

When the signal according to the image of the Y component is input, the laser driver 22 causes the laser diode 7 to emit light. Then, this light is applied to the photosensitive drum 1 through the optical path 12. The photosensitive drum 1 is uniformly charged by the primary charger 2, and a latent image is formed according to the optical information applied. When the photosensitive drum 1 further rotates in the direction of the arrow, this latent image is visualized with the Y toner by the developing device 4a.

When the photosensitive drum 1 makes one revolution, the photosensitive drum 1 is again uniformly charged by the primary charger 2. Then, light information corresponding to the image information of M of the second color is radiated thereon, and a latent image is formed. Next, this latent image is visualized by the M toner in the developing device 4b. When the photosensitive drum 1 further rotates once, the photosensitive drum 1 on which the Y toner image and the M toner image are formed is charged again by the primary charger 2, and the optical information corresponding to the image information of C of the third color is formed on the photosensitive drum 1. It is illuminated and a latent image is formed. Then, this latent image is visualized by the C toner in the developing device 4c. When the photosensitive drum 1 further rotates once, the photosensitive drum 1 on which the Y toner image, the M toner image, and the C toner image have been formed again becomes the primary charger 2 again.
Are charged, and light information corresponding to the image information of Bk of the fourth color is radiated thereon to form a latent image. And
This latent image is visualized by Bk toner in the developing device 4d.

Subsequently, when a transfer paper (not shown) is supplied from the transfer paper cassette 13 by the pickup roller 14, the transfer charger 23 applies the toner of Y, M, C, Bk on the photosensitive drum 1 to the transfer paper. Images are transferred at once. Further, the fixing device 18 fuses and fixes the toner image on the surface of the transfer paper to obtain a permanently visualized color image.

On the other hand, the toner remaining on the photosensitive drum 1 is cleaned by the cleaning device 6. Here, the cleaning device 6 has a configuration that can be switched on and off, and when the image is formed on the photosensitive drum 1, the photosensitive drum 1
Is in an off state apart from the above, and is in an on state in which the photosensitive drum 1 is contacted only when the transfer residual toner is cleaned.

A density sensor 21 can measure the density of the surface of the photosensitive drum 1, that is, the density of patches formed on the photosensitive drum 1. Reference numeral 25 denotes a control unit, which performs appropriate image processing including halftone control on an image signal input from an external device (not shown) and outputs the image signal to the laser driver 22 for each color component. An operation unit 26 has various keys and a display panel such as an LCD, and is used by the operator to input commands and notify the device status.

The above-described image processing apparatus of the multiple development system can form halftone images. The control unit 2
Since the detailed configuration of 5 is the same as that of FIG. 3 shown in the above-described first embodiment, the description thereof will be omitted. Note that the second embodiment also handles 8-bit image signals from “00H” to “FFH”, and shows that the image density increases from “00H” to “FFH”.

Also in the second embodiment, as in the first embodiment, the image signal is sent to the laser driver 22 as it is in the initial state where no LUT is set in the gradation correction unit 306. The obtained gradation characteristic does not become a straight line as shown in FIG. Therefore, in order to obtain an ideal gradation characteristic, a patch is formed on the drum by the pattern generator 309, and the patch is applied to the density sensor 21.
It is necessary to update the LUT as appropriate by measuring with.

However, also in the image processing apparatus of the second embodiment, when the toner image formed on the photosensitive drum 1 is transferred onto the transfer paper, the image area on the surface of the photosensitive drum 1 is rubbed by the transfer paper. . Therefore, since only the image area on the surface of the photosensitive drum 1 is damaged or the toner is fused and contaminated, if the operation period becomes long and the number of printed sheets increases, the reflectance becomes large between the image area and the non-image area. Will be different.

Therefore, in order to prepare the LUT for performing the appropriate gradation conversion in the gradation correction unit 306, it is desirable that the reflectance of the surface of the photosensitive drum 1 forming the patch does not change extremely. Therefore, the patch may be formed in the non-image area of the photosensitive drum 1, that is, in the portion where the roughness is small. However, in the case of performing the high-precision halftone control, a large number of patches must be formed. It is not preferable that the area where the patch can be formed on the drum 1 is limited.

Therefore, in the second embodiment, a large number of patches are efficiently formed on the surface of the photosensitive drum 1 where deterioration may occur during halftone control in the image processing apparatus of the multiple development system, and an appropriate LUT is derived. It is characterized by

Hereinafter, with reference to the flowchart of FIG.
The halftone control in the second embodiment will be described.
The control program shown in the flowchart of FIG. 8 is stored in the ROM 311 as described above.

The halftone control of this embodiment is started by the CPU 310 at an appropriate timing such as when the power of the main body is turned on, when a predetermined time has elapsed since the power was turned on, or when the number of printed sheets reaches a predetermined number. .

In the halftone control of the second embodiment, the pattern generator 309 sets seven patches PY1 to PY7 (corresponding to the Y component) for each color in order to set an appropriate LUT in the gradation correction unit 306. PM1 to PM7 (corresponding to M component), PC1 to PC7 (corresponding to C component), PBk1 to PBk7
(Corresponding to Bk component) is created on the photosensitive drum 1. still,
Among PY1 to PY7, PY1 has the lowest concentration, and the concentration gradually increases up to PY7. Of course, the same applies to other color component patches.

FIG. 9 shows the state of the Y component patch formed on the photosensitive drum 1 in the second embodiment. In FIG. 9, 91 is an image area and 92 is a non-image area, and a high-density patch is formed on the image area 91 and a low-density patch is formed on the non-image area 122.

Also in the second embodiment, it is known that a patch having a high density value of "80H" or more is hardly affected by the background. Therefore, "10H", "30H", "50H", "70H" that are easily affected by the base
Patch with relatively low density (PY1 to PY4, PM1 to P
M4, PC1 to PC4, and PBk1 to PBk4 respectively) are created in the non-image area where the reflectance of the background is relatively stable. And, the "90
"H", "B0H", "C0H" with relatively high density patches (PY5 to PY7, PM5 to PM7, PC5 to PC7, PBk5)
(Corresponding to PBk7) is created in an image area in which the reflectance of the background greatly changes depending on the number of printed sheets. Here, the image area refers to an area on the photosensitive drum 1 that is in contact with a transfer paper of the maximum size that can be printed by the apparatus, and the other area is a non-image area. Alternatively, the area where the image is formed most frequently in the apparatus may be the image area.
Therefore, the non-image area on the photosensitive drum 1 is preferably wider so that more patches can be formed. As a result, the area of the surface of the photosensitive drum 1 can be effectively used during patch formation, so that a larger number of patches can be formed, and therefore, high-precision halftone control can be performed.

When the halftone control is started, first, step S
At 41, the photosensitive drum 1 is rotated, and the background density of the portion where the patch is formed is measured. That is, the patches PY1 to PY7, PM1 to PM7, P created in the second embodiment.
Base density U of the portion where C1 to PC7 and PBk1 to PBk7 are formed
Y1 to UY7, UM1 to UM7, UC1 to UC7, UBk1 to UBk7 are measured by the density sensor 21 and stored in the RAM 312. These background densities are, as described above, UY1 to UY4, UM1 to UM4,
UC1 to UC4 and UBk1 to UBk4 correspond to the non-image area, and UY5
.About.UY7, UM5 to UM7, UC5 to UC7, UBk5 to UBk7 correspond to the image areas.

Next, the process proceeds to step S42, and the pattern generator 309 reads out the image data aY1 to aY7 corresponding to the Y component patches PY1 to PY7 stored in advance, and sends the data to the laser driver 22. As a result, a latent image of the Y density detection patch is formed on the photosensitive drum 1, and the latent image is developed by the developing device 4a.
Toner images Y1 to PY7 are formed on the photosensitive drum 1 at predetermined positions where the background densities UY1 to UY7 are measured. In step S43, the density values of the Y patches PY1 to PY7 formed on the photosensitive drum 1 are measured by the density sensor 21 at appropriate timings, and the sensor outputs SY1 to
Save SY7 in RAM312.

Next, in step S44, the CPU 310
Reads the background measurement values UY1 to UY7 of the Y patch stored in the RAM 312, and calculates the average value UYL of UY1 to UY4 and U
Calculate the average value UYH of Y5 to UY7 and calculate the absolute value of the difference ΔUY
Is calculated. Then, in step S45, the ΔUY is compared with a predetermined threshold value (“10H” in the second embodiment),
If ΔUY is greater than or equal to the threshold value, it is determined that the surface of the photosensitive drum 1 is severely deteriorated, and the operator is informed that the surface of the photosensitive drum 5 is abnormal from the LCD panel or the like on the operation unit 26 in step S46. And proceeds to step S47.

If ΔUY is less than the threshold value in step S45, the average value UYA of the background densities UY1 to UY4 is calculated in step S47.
ve is calculated, and the average value UYAve is substituted into UY5 to UY7. Next, in step S48, the densities DY1 to DY7 of the patch are calculated using the bases UY1 to UY7 of the Y patch and the measured values SY1 to SY7 of the patch. Then, in step S29, a gradation correction LUT for the Y component is created based on the obtained patch densities DY1 to DY7.

The Y component LUT is created as described above, and then, in steps S50 and S51, other M, C, and
By performing the same processing on the Bk component, an appropriate LUT is created for each color component. The order of the color components for generating the LUT may be arbitrary.

In the second embodiment, an example has been described in which of the seven patches, four with relatively low density are formed in the non-image area and three with relatively high density are formed in the image area. Of course, the same density patches as in the first embodiment may be prepared to form five relatively low densities in the non-image area and two relatively high densities in the image area.

As described above, according to the second embodiment,
In a multi-developing color image processing apparatus, a patch formed on the photosensitive drum 1 during halftone control forms a low-density portion in a non-image area where deterioration of the drum surface is small, and a high-density portion forms a drum surface. Formed in the image area where the deterioration of
This patch density is measured to generate a gradation correction LUT. As a result, it is possible to effectively use the area of the surface of the photosensitive drum 1 and perform halftone control while suppressing the influence of deterioration of the surface of the photosensitive drum 1 as much as possible, and obtain a stable output image density.

The image processing apparatus according to the present invention is not limited to the examples shown in the above-mentioned embodiments, but can be variously modified within the scope of the gist.

For example, the present invention can be applied to an image processing apparatus for forming a color image using an intermediate transfer member.

In the color image processing apparatus of the first and second embodiments described above, the color image is formed based on the image signal input from an external device (not shown) such as a host computer. However, the present invention is not limited to this example. For example, a copier or the like has an image processing apparatus itself provided with a document table and a scanner section for optically reading a document placed on the document table, and the image is read by itself. It may be a device that forms a document image.

The number of patches formed during halftone control is not limited to seven, and may be set appropriately for each device in accordance with the precision of halftone control and the drum size.

In the color image forming apparatus of the first and second embodiments, the RGB image data is used as an input signal for conversion into YMCBk inside the apparatus, but this processing is performed by an external device such as a host. Done by YM
The image data of CBk may be used as an input signal.

Although the halftone is generated by pulse width modulation, it can be used in any image forming apparatus that generates a halftone, such as an image forming apparatus that generates a halftone by a binary image such as dither or error diffusion method. The present invention is applicable.

Further, although the photosensitive drum and the transfer drum are used in the above example, a photosensitive member such as a photosensitive belt or a transfer member such as a transfer belt may be used.

Further, the invention is not limited to the case where the patch is formed on the transfer drum and the photosensitive drum, and for example, an intermediate transfer belt,
In an apparatus using an intermediate transfer drum, it may be formed on these media.

In the halftone control, the developing bias, the contrast potential, etc. may be controlled in addition to controlling the gradation correction characteristic.

Further, even when the present invention is applied to a system composed of a plurality of devices (for example, host computer, interface device, reader, printer, etc.), a device composed of one device (for example, a copying machine or a facsimile machine). Etc.) may be applied.

Further, an object of the present invention is to supply a storage medium having a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to supply a computer (or CPU or MPU of the system or apparatus).
It goes without saying that the above can also be achieved by reading and executing the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, C
DR, magnetic tape, nonvolatile memory card, ROM
Etc. can be used.

Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also the OS or the like running on the computer actually operates based on the instruction of the program code. It goes without saying that a case where a part or all of the processing of (1) is performed and the functions of the above-described embodiments are realized by the processing is also included.

Furthermore, after the program code read from the storage medium is written in the memory provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer, based on the instruction of the program code, It goes without saying that a case where the CPU or the like included in the function expansion board or the function expansion unit performs a part or all of the actual processing and the functions of the above-described embodiments are realized by the processing is also included.

[0115]

As described above, according to the present invention, it is possible to obtain an image with a stable density by performing halftone control by effectively utilizing the area on the medium on which an image is formed. It will be possible.

[0116]

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an image processing apparatus of a multiple transfer system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a concentration sensor according to the present embodiment.

FIG. 3 is a block diagram showing a detailed configuration of a control unit in the present embodiment.

FIG. 4 is a diagram showing an example of forming a patch in a non-image area on the surface of a transfer drum.

FIG. 5 is a flowchart showing a halftone control procedure in this embodiment.

FIG. 6 is a diagram showing an example of forming a patch on a transfer drum in the present embodiment.

FIG. 7 is a diagram showing a schematic configuration of an image processing apparatus of a multiple development system according to a second embodiment of the present invention.

FIG. 8 is a flowchart showing a halftone control procedure in the second embodiment.

FIG. 9 is a diagram showing an example of forming a patch on a photosensitive drum in the second embodiment.

FIG. 10 is a diagram showing gradation characteristics obtained when a gradation correction LUT is not set.

[Explanation of symbols]

 1 Photosensitive Drum 5 Transfer Drum 22 Laser Driver 25 Control Unit 26 Operation Unit 304 Logarithmic Conversion Unit 305 Black Generation Unit 306 Gradation Correction Unit 307 Pulse Width Modulation Unit 309 Pattern Generator 310 CPU 311 ROM 312 RAM

Claims (36)

[Claims] 1. A color component image is sequentially formed on an image carrier,
An image processing apparatus for sequentially transferring the image to a transfer material held by a transfer material holder, a gradation correcting unit for performing gradation correction of an input image based on a gradation correction characteristic, and the transfer material holder. Pattern forming means for forming a plurality of pattern images having different density values, density detecting means for detecting the density value on the transfer material holder, and based on the density value of the pattern image detected by the density detecting means The pattern image forming means forms a first pattern image in a first area on the transfer material holder, and the pattern image forming means forms a first pattern image on the transfer material holder. An image processing apparatus, wherein a second pattern image is formed in a second area other than the first area. 2. The image processing apparatus according to claim 1, wherein the second area is an area that is more deteriorated than the first area. 3. The image processing apparatus according to claim 2, wherein the first area corresponds to a minimum size of the transfer material that can be held on the transfer material holder. 4. The image processing apparatus according to claim 2, wherein the first area corresponds to the size of the transfer material that is most frequently used. 5. The image processing apparatus according to claim 1, wherein the second pattern image has a higher density than that of the first pattern image. 6. The density detecting means detects a density value of the pattern image in a first detection mode, and a density value of a surface of the transfer material holder before the pattern image is formed in a second detection mode. A detection mode, wherein the control unit controls the gradation correction characteristic based on the pattern image detected by the first and second modes of the density detection unit and the density value of the surface of the transfer material holder. The image processing apparatus according to any one of claims 1 to 5, characterized in that: 7. The area on the transfer material holder in which the surface density is detected in the second mode of the density detecting means is:
7. The image processing apparatus according to claim 6, which corresponds to an area where a pattern image is formed by the pattern forming unit. 8. The control means sets an average of density values on the transfer material holder corresponding to the first pattern detected by the second mode of the density detection means to the second pattern. The image processing apparatus according to claim 7, wherein the gradation correction characteristic is controlled as a corresponding density value on the transfer material holder. 9. The apparatus further comprises an informing unit capable of informing the state of the apparatus, wherein the control unit is the first of the density values on the transfer material holder detected in the second mode of the density detecting unit. When the absolute value of the difference between the average value of the density values of the area and the average value of the density values of the second area is a predetermined value or more, or when the average value of the density values of the second area is a predetermined value or more, The image processing apparatus according to claim 8, wherein the notification unit notifies that the transfer material holder is abnormal. 10. An image processing apparatus for forming images of respective color components on an image carrier and transferring the images to a transfer material at a time, the gradation correction performing gradation correction of an input image based on gradation correction characteristics. Means, pattern forming means for forming a plurality of pattern images having different density values on the image carrier, density detecting means for detecting density values on the image carrier, and the pattern detected by the density detecting means A control unit that controls the gradation correction characteristic based on a density value of an image, wherein the pattern image forming unit forms a first pattern image in a first region on the image carrier, An image processing apparatus, wherein a second pattern image is formed on a second area other than the first area on the image carrier. 11. The first region is a region that is more deteriorated than the second region.
The image processing apparatus according to any one of the preceding claims. 12. The image processing apparatus according to claim 11, wherein the first area corresponds to a maximum size of an image that can be formed on the image carrier. 13. The image processing apparatus according to claim 11, wherein the first area corresponds to an image size having the highest formation frequency. 14. The image processing apparatus according to claim 10, wherein the first pattern image has a higher density than that of the second pattern image. 15. The density detecting means detects a density value of the pattern image in a first detection mode and a second detection mode detects a density value of the surface of the image carrier before the pattern image is formed. The control means controls the gradation correction characteristic based on the pattern image detected by the first and second modes of the density detection means and the density value of the image carrier surface. The image processing apparatus according to any one of claims 10 to 14, characterized in that. 16. The area on the image carrier where the surface density is detected in the second mode of the density detecting means corresponds to the area where a pattern image is formed by the pattern forming means. The image processing apparatus according to claim 15. 17. The control unit corresponds to the first pattern an average of density values on the image carrier corresponding to the second pattern detected by the second mode of the density detection unit. 17. The image processing apparatus according to claim 16, wherein the gradation correction characteristic is controlled as a density value on the image carrier. 18. A notifying unit capable of notifying the state of the apparatus, wherein the control unit is the first of the density values on the transfer material holder detected in the second mode of the density detecting unit. When the absolute value of the difference between the average value of the density values of the area and the average value of the density values of the second area is a predetermined value or more, or when the average value of the density values of the first area is a predetermined value or more, 18. The image processing apparatus according to claim 17, wherein the notifying unit notifies that the transfer material holder is abnormal. 19. An image processing method in an image processing apparatus, wherein images of respective color components are sequentially formed on an image carrier, and the images are sequentially transferred to a transfer material held by a transfer material holder. A background density detecting step of detecting a surface density value of a pattern, a pattern forming step of forming a plurality of pattern images having different density values on the transfer material holder, and a pattern density detecting detecting a density value of the plurality of pattern images A step, and a gradation correction characteristic control step of controlling a gradation correction characteristic to be referred to when gradation correction of an input image is performed based on a surface density value of the transfer material holder and a density value of the pattern image. In the pattern forming step, a first pattern image is formed in a first area on the transfer material holder, and a second pattern image other than the first area on the transfer material holder is formed. Second putter in the area Image processing method characterized by forming an image. 20. The second region is a region that is more deteriorated than the first region.
The image processing method described in the above. 21. The image processing method according to claim 20, wherein the second pattern image has a higher density than that of the first pattern image. 22. The area on the transfer material holder, the surface density of which is detected in the background density detecting step, corresponds to the area where a pattern image is formed in the pattern forming step. Image processing method. 23. In the control step, an average of density values on the transfer material holder corresponding to the first pattern detected in the background density detecting step is set to the second value.
23. The image processing method according to claim 22, wherein the gradation correction characteristic is controlled as a density value on the transfer material holder corresponding to the pattern. 24. An image processing method in an image processing apparatus for forming images of respective color components on an image carrier and transferring the images to a transfer material at a time, the background density detection detecting a surface density value of the image carrier. A step, a pattern forming step of forming a plurality of pattern images having different density values on the image carrier, a pattern density detecting step of detecting density values of the plurality of pattern images, and a surface density value of the image carrier And a gradation correction characteristic control step of controlling a gradation correction characteristic referred to when performing gradation correction of the input image based on the density value of the pattern image, and in the pattern forming step, A first pattern image is formed on a first area on the image carrier, and a second pattern image is formed on a second area other than the first area on the image carrier. Image processing method. 25. The first region is a region that is more deteriorated than the second region.
The image processing method described in the above. 26. The image processing method according to claim 25, wherein the first pattern image has a higher density than that of the second pattern image. 27. The area on the transfer material holder, the surface density of which is detected in the background density detecting step, corresponds to the area where a pattern image is formed in the pattern forming step. Image processing method. 28. In the control step, the average of the density values on the image carrier corresponding to the second pattern detected in the background density detection step is set to the image corresponding to the first pattern. 28. The image processing method according to claim 27, wherein the gradation correction characteristic is controlled as a density value on a carrier. 29. An image processing apparatus for forming an image on an image carrier and transferring the image onto a transfer material, comprising: gradation correction means for correcting gradation of an input image based on gradation correction characteristics; Pattern forming means for forming a plurality of different pattern images; density detecting means for detecting the density value of the pattern image; and controlling the gradation correction characteristic based on the density value of the pattern image detected by the density detecting means. The pattern image forming unit forms the first pattern image in the first region and the second pattern image in the second region other than the first region. An image processing device characterized by: 30. An image processing method in an image processing apparatus for forming an image on an image carrier and transferring the image onto a transfer material, the background density detecting step of detecting a background density value when forming an image, and the density value. Pattern forming step of forming a plurality of different pattern images, a pattern density detecting step of detecting the density value of the plurality of pattern images, based on the background density value and the density value of the pattern image of the input image A gradation correction characteristic control step of controlling a gradation correction characteristic that is referred to when performing gradation correction, and in the pattern forming step, a first pattern image is formed in a first base region, An image processing method, comprising: forming a second pattern image in a second background area other than the first background area. 31. An image forming unit for forming an image on a medium, a reading unit for reading the image formed on the medium, and an image forming characteristic of the image forming unit based on read data of the reading unit. In the image processing apparatus having the control means, the reference image in the calibration mode is formed in both the first area and the second area outside the first area that can be imaged in the normal mode. An image processing device characterized by the above. 32. The image processing apparatus according to claim 31, wherein the medium is a transfer drum. 33. The image processing apparatus according to claim 31, wherein the medium is a photosensitive drum. 34. The reading means is a first device on the medium.
32. The image processing apparatus according to claim 31, wherein the background density of the second area and the reference image formed in the first area are read. 35. The image processing apparatus according to claim 34, wherein the control unit replaces the background density of the second area with the background density of the first area. 36. An image forming step of forming an image on a medium; a reading step of reading the image formed on the medium; and an image forming characteristic in the image forming step based on read data by the reading step. An image processing method including: a reference image in a calibration mode in both a first region on the medium that can be imaged in a normal mode and a second region outside the first region. An image processing method comprising: forming an image.