JPH0969944A - Image forming device and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce a gray scale which is stable without being affected by characteristics of respective units without using a special optical system or developing device. SOLUTION: For each printer engine, spot diameter information and exposure quantity information on a scanner 3 and development bias voltage information on a high-voltage unit 4 which are measured and stored in advance are sent to a formatter 2 through a controller, and the formatter 2 determines a laser light emission time, a development contrast set value, etc., which are suitable to the printer engine and also makes tone curve corrections.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a digital copying machine or a printer for forming an image using an electrophotographic method and a control method thereof.

[0002]

2. Description of the Related Art Conventionally, image forming apparatuses such as digital copying machines and laser beam printers using electrophotography have
Printing commands and coded characters from external information processing equipment such as computers and workstations
An imager is provided with a formatter that receives image data and converts the code information into pixel information. And
At the time of conversion in the formatter, an image image having density information such as a photograph is binarized by a known image processing such as a dither matrix and an error diffusion method, and then converted into pixel information.

The converted pixel information is then printed in the electrophotographic engine section. That is, on the electrophotographic photosensitive member and electrostatic recording dielectric member that are uniformly charged in advance,
An electrostatic latent image is formed by an exposure unit such as an optical system that scans a semiconductor laser, which is modulated by pixel information. As an apparatus for developing the electrostatic latent image, for example, the developer is transferred onto the electrostatic latent image carrier from above the developer carrier having a predetermined minute gap in the developing area facing the electrostatic latent image carrier. It is known that an electrostatic latent image is developed by transferring and applying the electrostatic latent image. Further, the developed image is transferred to the transfer material by the transfer means.

The transfer material onto which the toner image has been transferred is separated from the electrostatic latent image carrier and sent to the fixing means of a known heat fixing device, where the toner image is fixed to the transfer material.
The transfer material that has passed through the fixing means is discharged to the outside of the image forming apparatus. The toner remaining on the electrostatic latent image carrier after the transfer is removed by a known cleaning means using a cleaning blade, and the next image is formed.

[0005]

However, the above-mentioned conventional example has the following problems.

Conventionally, the resolution of electrophotography, which has been about 300 dpi, has recently become higher, and the resolution has increased to 600.
Some are more than dpi. Along with this, the usage of printers and the like has changed, and the opportunities for printing image images such as photographs and graphics from the printing of characters are increasing. When printing an image image with a binary printer, the formatter converts the image data having the density data into density gradation by dither matrix processing or the like, converts it into bitmap data, and prints it. The number of lines (1
The image forming unit per inch) has been about 50 to 72 lines in the past, but has recently exceeded 100 lines, and the unit representing gradation has become smaller.

Further, in electrophotography, some variations in the line width and density are inevitable due to variations in each unit of the main body, usage state of the process cartridge, environment and the like. In the case of a character image, these fluctuations have only a slight variation in the line width and have almost no effect on the print result, but in the case of an image image, they affect the density of halftones, and the impression of the image is greatly different.

This phenomenon means that the resolution of the printer becomes large and the size of one pixel becomes small, whereas the diameter of the laser spot for exposure cannot be sufficiently narrowed down, or the latent image is diffused on the photoconductor to form one pixel. Becomes noticeable when is not sufficiently reproduced.

When the latent image is not sufficiently finely formed,
Binary development cannot be performed in development, and halftone development, that is, development is performed under such minute conditions that development is performed in a state in which the potential has not dropped sufficiently from the charging potential to the bright potential by exposure. The halftone density is greatly affected by the slight fluctuations in the line width and the density due to the use condition of the process cartridge and the environment. More specifically, the case where a 600 dpi printer receives 600 dpi density information-attached image data from a host computer and prints it will be considered. First, the formatter converts the image data with density information into binarized bitmap data by dither matrix processing or the like. For example, if the unit of binarization processing is 100 lines, 6 pixels × 6
The gradation is expressed by a dither matrix of pixels, but if one pixel cannot be reproduced stably at this time, the gradation cannot be reproduced stably. That is, 600d
One pixel of pi is about 42 μm × 42 μm, whereas the laser spot diameter for exposure generally has a size of about 80 μm to 100 μm, which is similar to halftone development with halftone reproduction. Development is carried out under such a minute condition that stable gradation cannot be reproduced.

Therefore, if the laser spot diameter is narrowed down to about the pixel size, this phenomenon is improved. However, narrowing the laser spot diameter down to about 42 μm requires an increase in the accuracy of the optical system, which is very costly. Get higher

The present invention has been made to solve the above-mentioned problems, and an image formation capable of reproducing a stable gray scale without being affected by the characteristics of each unit without using a special optical system or developing device. An object of the present invention is to provide an apparatus and a control method thereof.

[0012]

In order to achieve the above object, the image forming apparatus of the present invention has the following constitution.

That is, in an image forming apparatus having a formatter for converting coded image information received from an external information processing device into pixel information and visualizing the converted pixel information by an electrophotographic system, the formatter has a main body. A correction unit that corrects the characteristics of each unit and also performs tone curve correction is provided.

In such a configuration, the formatter controls so as to correct the characteristics of each unit of the main body and to perform the tone curve correction.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing the structure of the image forming apparatus according to the first embodiment. In the image forming apparatus,
A command relating to printing, coded characters, and image information from a host computer (not shown) are received as data, and the formatter 2 converts the code information into pixel information. In this conversion, an image image having density information such as a photograph is binarized after being subjected to a halftone process such as a dither matrix.

The electrophotographic engine portion (the portion surrounded by the broken line in FIG. 1) scans the electrophotographic photosensitive member 1 uniformly charged by the charging roller 5 with a laser scanner 3 for scanning a semiconductor laser modulated by pixel information. To form an electrostatic latent image with a resolution of 600 dpi.

The developing device 4 for developing the electrostatic latent image has a developing area facing the photoconductor 1 of about 300 μm.
The developer is used to develop the electrostatic latent image by transferring the developer to the electrostatic latent image on the photoconductor 1 by the developing contrast and applying the developer from the developing sleeve having a minute gap. The developed image is transferred to a transfer material by the transfer roller 7 to which a transfer bias is applied. The transfer material onto which the toner image has been transferred is separated from the photoconductor 1 and sent to the heat fixing device 8, where the toner image is fixed on the transfer material. Then, the transfer material that has passed through the fixing unit is discharged to the outside of the image forming apparatus through the conveyance path. Further, the toner remaining on the photoconductor 1 after the transfer is removed by the cleaning device 6 using the cleaning blade, and the next image formation is performed.

Conventionally, a method of sending characteristic data of each unit of the printer engine section to an engine controller and controlling a variable process condition in the engine controller has been performed. In this method, the image content to be printed is a character image, I couldn't distinguish between images, so I had to do the same control.

On the other hand, the embodiment is characterized in that the control is performed by the formatter, so that the control can be changed depending on the difference in the image content between the character image and the image image. For example, in the case of a character image, printing is performed without correction, and in the case of an image image, a method of applying optimum correction to low-density, medium-density, and high-density portions according to respective densities is applied.

According to the present embodiment, the image quality of an image image is improved without delaying the processing time of the character portion which generally occupies most of the print content by not particularly correcting the character image. It is possible to print at high speed and with high image quality. Hereinafter, this processing method will be described.

FIG. 2A shows a case where the image forming apparatus according to the embodiment is used to print a gray scale of 36 gradations by a 6 × 6 dither matrix as it is without performing tone curve correction in the formatter. This is a measurement of the change in concentration when For the concentration measurement, for example, RD-918 manufactured by Macbeth Co. is used.

The difference between a and b in FIG. 2A is due to the difference in laser spot diameter. In the image forming apparatus according to the embodiment, the spot diameter on the photoconductor 1 is about 80 ±.
Set to 10% (μm). In the figure, a is the case where the spot diameter is the minimum within the tolerance, that is, 72 μm, and b is the case where the spot diameter is the maximum within the tolerance, that is, 88 μm. The ideal density change is the straight line shown by the broken line.

Here, the tone curve correction shown in FIG. 2B is applied to the formatter. That is, by applying the inverse function of the gray scale density curve as the tone curve correction, the gray scale density change approaches an ideal straight line.

However, as shown in FIG. 2 (C), even after the tone curve correction, there is a difference in gray scale between the case where the spot diameter is a ', which is the minimum within the tolerance, and the case where the spot diameter is the maximum, b', within the tolerance. It can be seen that Especially, there is a difference of about 0.1 to 0.2 in the density of the 8th to 20th gradation,
For example, when a photograph of a person's face or the like is printed, a difference appears in facial expressions. Further, in the case of b ', it is found that the density is the same as that of solid black around the 30th gradation, and the high density area is collapsed. On the other hand, up to the 6th gradation, it cannot be reproduced with almost the same density as solid white, which means that the highlight part of the image image cannot be reproduced and is skipped.

As described above, if there is a difference such as a spot diameter variation on the printer engine side, it is not possible to correct the difference for each printer engine only by the tone curve correction. This also applies to the exposure amount, the high pressure, and the like.

Therefore, according to the present embodiment, as shown in FIG. 3, the spot diameter, the exposure amount, the high pressure, etc. are measured in advance for each printer engine, and the scanner unit 3, which is the engine side information based on the factory setting value, High voltage unit 4
Etc., and the information signal from each unit is sent to the formatter 2 via the controller 9. The formatter 2 determines the optimum laser emission time for the printer engine, the development contrast setting value, and the like based on the information signal from the controller 9, and also performs the tone curve correction.

In the case of the present embodiment, 600 dpi, 8 p
Since it is a pm printer, the laser emission time per pixel is usually 125 nsec. How to specifically control the light emission time will be described. Regarding the laser spot diameter, the spot diameter in FIG. 2 is the maximum within the tolerance, that is, 8
In the case of 8 μm, the laser emission time is 10% longer 138 nsec in the low density region 1 to 7 gradations, and the laser emission time is 5% longer 132 nsec in the medium density region 8 to 20 gradations.
In the high density range of 27 to 35 gradations, the laser emission time is shortened by 10% to 113 nsec, and solid black is obtained.
The 6 gradations are controlled inside the formatter 2 while keeping the laser emission time unchanged.

Further, the spot diameter is the smallest within the tolerance, that is, 7
In the case of 2 μm, since it is quite close to the ideal straight line, the laser emission time remains the same in the low and medium density regions, while in the high density region 27 to 35 gradations, the laser emission time is shortened by 3% to 121 μm. The 36 gradations of black are controlled inside the formatter 2 while keeping the laser emission time unchanged.

The control for each density range is possible because the coded data is handled inside the formatter 2, and cannot be controlled by an engine controller that has only pixel information.

As a result, it is possible to prevent a difference occurring in gray scale reproduction due to a difference in laser spot diameter, and the same gray scale as shown in FIG. The concentration can be changed. In particular, when there is a difference in the laser spot diameter, when the spot diameter is large, the density does not appear in the low density area and it tends to collapse in the high density area, so this method divides the density area into low, medium and high. Is valid.

When the spot diameter is measured in advance for each printer engine, if the spot diameter is out of the tolerance range, it may be considered that the center value may be adjusted and returned. It takes time to adjust the slight variations, which slows down the speed of the production line and makes it expensive.

Therefore, it is better to measure the spot diameter in advance and output it as the information of the engine side unit to the formatter 2 via the controller 9 and respond by the laser emission time as in the present embodiment.

Further, the difference in the halftone characteristic of each unit of the printer engine according to the present embodiment is not limited to the spot diameter of the laser, and the same problem occurs in the variation of the exposure amount, the developing bias and the like. Next, the case where the developing bias varies for each high-voltage unit will be described.

Similar to FIG. 2, FIG. 4 uses the image forming apparatus according to the present embodiment to perform gray scale of 36 gradations by a 6 × 6 dither matrix and perform the above-mentioned tone curve correction in the formatter. It is a measurement of density conversion when printed. C shown in FIG.
d is due to the difference in the developing bias DC voltage. The developing bias DC voltage is set to −500 ± 5% (V). Here, c in the drawing is the case where the developing bias DC voltage is maximum within the tolerance, that is, -525V, and d is the case where it is the minimum within the tolerance, that is, -475V. Figure 2 shows the ideal change in concentration.
Similarly, is a straight line indicated by a broken line.

It can be seen from FIG. 4 that even in the developing bias DC voltage, there is a difference in gray scale between the case of the maximum c within the tolerance and the case of the minimum d within the tolerance. Two
The halftone densities of 0th to 25th gray levels appear as a difference of about 0.2 to 0.3. Further, in the case of c, the density is the same as the solid black around the 29th gradation, and it can be seen that the high density area is collapsed. On the other hand, in the case of d,
Up to the fifth gradation, the density is almost the same as that of solid black, and it cannot be reproduced. This means that the highlight part of the image cannot be reproduced and is skipped.

Even in the variation of the developing bias DC voltage among the high voltage units, the developing bias DC voltage is measured in advance for each high voltage unit as in the case of the above-mentioned spot diameter, and the information of the engine side high voltage unit is set by the factory setting. An information signal is sent from the high voltage unit to the formatter 2 via the controller 9. Formatter 2
By setting the optimum laser emission time for the printer engine by the information signal from the controller 9, it is possible to prevent the difference in gray scale reproduction due to the difference in the developing bias DC voltage within the tolerance range.

Although the spot diameter and the developing bias DC voltage have been described above, the present invention is not limited to these, and the present invention can be applied to other conditions such as the exposure amount to prevent the difference in gray scale reproduction.

Further, in order to prevent the difference in gray scale reproduction, it is possible to deal with the situation by changing the development contrast by the formatter 2 in addition to adjusting the laser emission time. With modern printers,
The print density can be adjusted from the host computer.
Since the information is transmitted in both directions, the development contrast can be changed by the formatter 2.

[Second Embodiment] Next, a second embodiment of the present invention will be described in detail with reference to the drawings.

In the second embodiment, a difference in gray scale reproduction due to variations in the laser spot diameter, exposure amount, developing bias, etc. on the engine side is arithmetically processed by the printer engine side controller, and each variation amount is comprehensively calculated. The feature is that it is judged and the variable amount is changed as necessary. The apparatus in this embodiment is basically the same as the image forming apparatus having the configuration shown in FIG. Therefore,
To avoid complication of the description, the description is omitted unless it is necessary.

First, the arithmetic processing performed by the controller will be described. FIG. 5 is a block diagram showing the flow of signals. The controller 9'collects the halftone characteristic data of each engine unit, and the controller 9'calculates the sum of the halftone characteristic data and outputs it to the formatter 2. The formatter 2 changes the variable process amount (light emission time, development contrast) by an amount corresponding to the sent information.

As described above, various halftone characteristics are combined as compared with the case where the variations such as the laser spot diameter, the exposure amount and the developing bias are corrected by one or one by one by the calculation by the controller 9 '. To be effective when. For example, the laser spot diameter is maximum within the tolerance, that is, 88 μm, and the exposure amount is maximum 2.2 μ within the tolerance.
Consider the case of J / cm2. In this example, since the spot diameter is large, the reproduction of the grayscale highlight portion is poor, but it is covered by the large amount of exposure. On the other hand, in the high-density area of gray scale, the spot diameter is large and the exposure amount is large, but since both directions tend to be crushed, the gradation is crushed from a fairly early gradation.

From the calculation of this controller 9 ', the above is understood. Based on this judgment, the effects of changes in spot diameter, exposure dose, and high pressure can be
It is possible to calculate by dividing into each area of high concentration. Then, this effect is sent to the formatter, and the formatter adjusts so that the low-density portion remains as it is and the high-density portion shortens the laser emission time by about 20%.

By the above control, it becomes possible to stabilize the reproduction of the gray scale substantially constant.

[Third Embodiment] Next, the third embodiment of the present invention will be described.
Embodiments of will be described in detail.

The third embodiment is characterized in that the environment variation of the printer engine characteristic is monitored in the first or second embodiment and the tone curve is corrected accordingly. The image forming apparatus is basically the same as that of the above-described embodiment, and the description thereof will be omitted unless necessary.

The environment is detected by the charging roller 5 and the bias power source. As already known, a DC and AC weight bias is applied to the bias of the charging roller. Since the direct current determines the dark potential VD of the photoconductor, it is -700V with constant voltage control.
However, since the alternating current causes the resistance of the charging roller to fluctuate due to environmental fluctuations, the effective current value is controlled to be constant so that the leveling effect is constant. In the present embodiment, the applied voltage increases in a low temperature and low humidity environment and becomes 2.2 k.
V (peak-to-peak value), the applied voltage becomes small in a high temperature and hard environment and becomes 1.6 kV (peak-to-peak value). It is possible to detect temperature and humidity by monitoring this voltage value with a bias power supply and sending a signal to the controller 9.

The change in temperature and humidity changes the characteristics of the photoconductor and changes the bright potential VL. For example, VL in normal environment
= -150 V, VL = -130 V in a high temperature and high humidity environment, VL = -170 V in a low temperature and low humidity environment, and the change in development contrast is about 40 V.

When a character image is mainly used in a conventional low resolution printer of about 300 dpi, such a contrast fluctuation does not pose a problem, but when an image image or a graphic image is printed by a high resolution printer of 600 dpi or more, Similar to the embodiment described above, the problem of gray scale reproducibility arises due to a change in development contrast.

In the present embodiment, the temperature / humidity signal sent to the controller 9 is reflected in the correction function in the tone curve correction in the formatter 2 to cover the environmental fluctuation of the engine characteristics.

A method of sending the temperature / humidity signal sent to the controller 9 to the developing bias power source to control the developing vice DC voltage is also possible.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 6 is a view showing the arrangement of the image forming apparatus according to the fourth embodiment. Regarding the device of FIG.
Although the electrophotographic process cartridge 12 (a portion surrounded by a thick line) is used, it is basically the same as the image forming apparatus shown in FIG. Therefore, in FIG. 6, in order to avoid complication of description, the same members as those in FIG.

The above-mentioned problem of variations in gray scale reproduction in the high resolution printer is caused by the sensitivity of the photosensitive drum, the distance between the photosensitive drum and the developing sleeve (hereinafter abbreviated as SD interval), and the development of the magnet included in the developing sleeve for each process cartridge. This is also a problem caused by the size of the magnetic poles.

In the present embodiment, a memory 13 for measuring and storing the above-mentioned various conditions at the time of factory shipment is provided inside the process cartridge 12, information is sent from the memory 13 to the printer engine controller 9, and the printer 13 is sent to the printer engine controller 9. The information is transmitted to the formatter as information on the engine side, and the formatter 2 corrects the intermediate characteristics by adjusting the laser emission time, adjusting the development contrast, and the like.

Specifically, for example, regarding the sensitivity of the photosensitive drum, the bright potential VL varies by about 40 to 50 V, the SD interval varies by about 30 μm, and the developing magnetic pole of the magnet varies by about 10 mT (100 gauss). The variations in gray scale reproduction are similar to those described in the first embodiment. Therefore, the problem can be solved by performing the same halftone characteristic correction in the formatter 2 as in the first embodiment.

[Fifth Embodiment] Next, the fifth embodiment of the present invention will be described.
Embodiments of will be described in detail.

In the fifth embodiment, the difference in grayscale reproduction caused by the sensitivity of the photosensitive drum, the SD interval, and the size of the developing magnetic pole of the magnet inside the developing sleeve is arithmetically processed by the printer engine side controller for each process cartridge. It is characterized in that the amount of variation is comprehensively judged and the variable amount is changed as necessary. The configuration of the image forming apparatus is almost the same as that of the fourth embodiment.

As described in the fourth embodiment, the process cartridge 12 is provided with the memory 13 for measuring the above-mentioned various conditions at the time of factory shipment and storing the halftone characteristic. Information is sent to the controller 9. The controller calculates the sum of the halftone characteristic data and outputs it to the formatter 2. The formatter 2 changes the variable process amount (light emission time, development contrast) by an amount corresponding to the sent information.

By performing calculation by the controller, various halftone characteristics generated by the sensitivity of the photosensitive drum, the SD interval, the size of the developing magnetic pole of the magnet contained in the developing sleeve, etc. are combined and corrected for each process cartridge. For example, the SD interval is the maximum within the tolerance, that is, 330μ
m, the developing pole of the magnet is up to 75 mT within the tolerance.
Consider the case of (750 gauss). Since the SD interval and the development pole are large, the reproduction of the grayscale highlight part is poor. On the other hand, the high density area of gray scale is SD
Even if the distance and the developing pole are large, they do not change much. From the calculation of the controller, the above can be understood. This result is sent to the formatter, and in the formatter, the light emission time of the laser is increased by about 20% in the low density portion and the high density portion is adjusted as it is.

As described above, the variation for each process cartridge can be corrected by calculating on the printer engine side based on the signal from the process cartridge and outputting to the formatter.

[Sixth Embodiment] In the sixth embodiment, in the fourth or fifth embodiment, the sensitivity of the photosensitive drum, the SD interval, the size of the developing magnetic pole of the magnet included in the developing sleeve, and the like are set. It is characterized by monitoring the environmental fluctuation of the process cartridge characteristics and correcting the tone curve accordingly.

In this embodiment, the environmental change monitor uses a charging roller as in the third embodiment.
In the present embodiment, the applied voltage increases to 2.2 kV (peak value) in the low temperature and low humidity environment, and the applied execution voltage decreases to 1.6 kV (peak value) in the high temperature and high humidity environment. It is possible to detect temperature and humidity by monitoring this voltage value with a bias power supply and sending a signal to the controller 9.

The control described above can prevent not only the variations among the process cartridges but also the characteristic changes of the process cartridges due to environmental changes.

The present invention may be applied to a system composed of a plurality of devices such as a host computer, an interface and a printer, or to an apparatus composed of a single device such as a copying machine. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program stored in a storage medium to a system or an apparatus.

[0067]

As described above, according to the present invention,
The halftone characteristic signal of each unit of the printer engine is sent to the formatter side, and the halftone characteristic is corrected by the control of the formatter side, and the tone curve is corrected in the formatter.

Further, the halftone characteristic signals of the respective units of the printer engine section are detected, the image forming apparatus engine controller side performs arithmetic processing on them, and sends them to the formatter side, and the halftone characteristic is corrected by the control from the formatter side. Perform tone curve correction in the formatter.

Further, the difference in the halftone characteristics caused by the variation in the electrophotographic characteristics of each part of the process cartridge is sent to the formatter side by the signal from the process cartridge, and the halftone characteristics are corrected by the control of the formatter side, and the formatter The tone curve is corrected at.

By the above means, it is possible to correct the difference in gray scale reproducibility due to the difference in tone curve reproduction characteristics between the printer engine and the process cartridge.

[0071]

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of an image forming apparatus according to a first embodiment.

FIG. 2 is a diagram showing a grayscale density change in the first embodiment.

FIG. 3 is a diagram showing a signal flow in the first embodiment.

FIG. 4 is a diagram showing a grayscale density change in the second embodiment.

FIG. 5 is a diagram showing a signal flow in the second embodiment.

FIG. 6 is a diagram showing a configuration of an image forming apparatus according to a fourth embodiment.

[Description of numbering]

 1 Photosensitive Drum 2 Formatter 3 Laser Scanner 4 Developing Device 5 Charging Roller 6 Cleaner 7 Transfer Roller 8 Fixing Device 9 Print Controller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yozo Hotta 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (10)

[Claims] 1. An image forming apparatus having a formatter for converting coded image information received from an external information processing device into pixel information, and visualizing the converted pixel information by an electrophotographic method, wherein the formatter has a main body. An image forming apparatus comprising: a correction unit that corrects a characteristic of each unit and also performs a tone curve correction. 2. The image forming apparatus according to claim 1, wherein one of the characteristics of each unit of the main body is based on a laser spot diameter. 3. The image forming apparatus according to claim 1, wherein the characteristic of each unit of the main body is due to each portion of the process cartridge. 4. The image forming apparatus according to claim 1, wherein the correction unit monitors the environmental change of each unit of the main body and performs the tone curve correction according to the result. 5. The image forming apparatus according to claim 1, further comprising arithmetic processing means for arithmetically processing characteristics of each unit of the main body. 6. A method of controlling an image forming apparatus, comprising a formatter for converting coded image information received from an external information processing device into pixel information, and visualizing the converted pixel information by an electrophotographic method. A method for controlling an image forming apparatus, comprising: a control step of correcting the characteristics of each unit of the main body and controlling to perform tone curve correction. 7. A method of controlling an image forming apparatus according to claim 6, wherein one of the characteristics of each unit of the main body is based on a laser spot diameter. 8. The method of controlling an image forming apparatus according to claim 6, wherein the characteristic of each unit of the main body depends on each portion of the process cartridge. 9. The image forming apparatus according to claim 6, wherein in the control step, the environmental change of each unit of the main body is monitored and the tone curve correction is performed according to the result. 10. The method according to claim 6, further comprising an arithmetic processing step for arithmetically processing the characteristics of each unit of the main body.
10. A control method for an image forming apparatus according to claim 9.