JP2001249503A - Image forming device and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device and an image forming method by which an image deteriorated little is outputted even when image adjustment is not aimed but image contrast must be adjusted for the purpose of reducing toner consumption and taking measures to cope with the leak of an electrifying device. SOLUTION: Required γ conversion characteristic is obtained by performing interpolation arithmetic operation by two kinds of γconversion tables according to VcontNow (=Vcont+ΔVcont1) obtained by correcting basic developing contrast Vcont by developing correction amount ΔVcont1 for reducing the toner consumption and taking the measures to cope with the leak of the electrifying device. Thus, the density of a halftone area is maintained and the deterioration of the image by visual observation is restrained to be little.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine and a printer, and more particularly to a gamma conversion thereof.

[0002]

2. Description of the Related Art In an image forming apparatus, a method for adjusting an image density includes a digital image processing method and an analog adjustment method. Digital image processing methods include adjustment by a brightness / density converter for converting a received original luminance signal into an original density signal, adjustment by an output / density converter for converting an original density signal to an output density signal, and output. The adjustment is performed by the γ-conversion means, which is an inverse function of the printer characteristic indicating the output density signal corresponding to the signal. Generally, the place where the image density is most easily adjusted is the adjustment by the γ-conversion means, which is more direct and accurate in determining the characteristics of the printer.

As an analog adjustment method, it is general to adjust a latent image potential and a development potential. There are some other parts that can be adjusted, such as the amount of toner in the developing means, the developing frequency, each adjustment gap inside the developing means, and the gap between the developing means and the electrophotographic photoreceptor. A latent image potential and a development potential are used. In particular, a development contrast which is a difference between a latent image potential to which toner on an electrophotographic photoreceptor adheres and a development potential of the latent image means is a most general parameter which influences flying of the toner.

[0004]

In the digital image adjustment represented by adjusting the conversion contents of the γ conversion means, the density adjustment in the halftone area can be adjusted as desired. . However, the adjustment is not effective for the density (hereinafter, Dmax) of the portion where the toner is most applied and the fog of the portion where the toner is not applied.

On the other hand, in analog image adjustment represented by adjustment of development contrast, not only the density of a halftone area but also Dmax is adjusted in conjunction with the adjustment. It should be noted that the fog of the portion where the toner is not applied hardly changes unless the back contrast applied to the difference between the development potential and the potential of the portion where the toner is not applied is not changed.

Conventionally, although the digital image adjustment and the analog image adjustment have been individually designated,
There has been no algorithm or sequence that automatically operates in the image forming apparatus main body.

It is important to change the development contrast without the purpose of adjusting the image, such as reducing the amount of consumed toner or taking measures against leakage of charging means for forming a potential applied to the photosensitive member. There is that. If only the development contrast as described above is changed, the density of the halftone area and Dmax change in conjunction. As a result, a very degraded impression is given to the user as an image.

The present invention has been made under such circumstances, and even when the image contrast has to be adjusted without aiming at the image adjustment, the halftone density can be maintained by the γ conversion and the deterioration is small. It is an object of the present invention to provide an image forming apparatus and an image forming method capable of outputting an image.

[0009]

Means for Solving the Problems The present inventors have studied means for reducing the amount of toner consumption and taking measures against leakage of the charging means so as not to give an impression of deterioration as an image even when the development contrast is changed. did. In studying the present invention, two experimental rules were found by the study of the present inventors.

First, what gives the impression of image deterioration is the density of the halftone area. Therefore Dm
It is not so dependent on ax, and even if Dmax is slightly reduced, as long as the halftone area can be maintained, many users will be given a satisfactory impression. For example, in the observation of a general image by visual observation, if the reflection density is 1.1 or more, it does not appear that the image quality is degraded.

Secondly, even if the halftone is output a little more, the toner consumption is reduced by lowering Dmax. Compared to the halftone area of the image,
The above phenomenon is caused by a large amount of applied toner in the Dmax region.

In view of the above two experimental rules, when the development contrast is changed, if the halftone density can be maintained by adjusting the conversion content of the γ-conversion means, Dmax is reduced because the development contrast is changed. The toner consumption is reduced, or it is established as a countermeasure against leakage of the charger,
At the same time, since the halftone density is maintained, it is possible to create an optimal image that does not give an impression of a deteriorated image. When the development contrast is insufficient, the content of the γ-conversion means may be adjusted so that the halftone density becomes higher than usual.

For this reason, in the present invention, the construction is such that the development contrast in the printer portion is read, and the γ conversion means indicates the conversion result in accordance with the development contrast.

In addition to the above-described development contrast adjustment for the purpose of image adjustment, which is not intended for image adjustment such as reduction of toner consumption or countermeasures against leakage of the charging device, γ The content of the conversion by the conversion means is not adjusted. Image density adjustments such as image adjustment and environmental fluctuations in the developing means are required to reduce the development contrast and reduce the heart tone density. This is because it works so as to reproduce the density densely and cancels the effect.

Therefore, in the present invention, the image forming apparatus is configured as in the following (1) to (7), and the image forming method is configured as in the following (8).

(1) Luminance density conversion means for converting an original luminance signal into an original density signal, output density conversion means for converting the original density signal obtained by the luminance density conversion means into an output density signal, and output density Γ-conversion means for γ-converting the output density signal obtained by the conversion means to obtain an output signal, charging means for uniformly charging the electrophotographic photosensitive member, and the electrophotographic photosensitive member after being charged by the charging means. Exposure means for turning the body into a latent image by exposure with the output signal, and development means for developing the latent image by the exposure means with toner,
An image forming apparatus that visualizes an image by forming a latent image potential, which is a surface potential on an electrophotographic photosensitive member formed by the charging unit and the exposure unit, and a developing potential applied to the developing unit. An image forming apparatus according to claim 1, wherein the conversion content of said γ conversion means is modulated in accordance with a development contrast which is a difference between a latent image potential at which toner flying from said developing means onto said electrophotographic photosensitive member adheres and said development potential.

(2) In the image forming apparatus described in (1), the target development contrast in the development contrast is a basic development contrast Vcon.
t, and a first development contrast correction amount Δ for correcting this
Vcont1 and the second development contrast correction amount ΔVco
nt2, and the conversion content of the γ conversion means is the first development contrast correction amount ΔVcont1
Only or the basic development contrast Vcon
t and the first development contrast correction amount ΔVcont1 and the second development contrast correction amount ΔV
An image forming apparatus that does not depend on the value of cont2.

(3) The image forming apparatus according to (2), wherein the first development contrast correction amount ΔVcont
An image forming apparatus 1 is used to reduce the amount of toner consumed by the developing unit or to prevent leakage of the charging unit.

(4) In the image forming apparatus described in (2), the second development contrast correction amount ΔVcont
Reference numeral 2 denotes an image forming apparatus used for adjusting image density or adjusting a fluctuation due to an environment.

(5) The image forming apparatus according to (2), further comprising means for storing conversion contents of the two types of the γ conversion means in two types of development contrast prepared in advance, and An image forming apparatus for calculating an output result of the γ-conversion means in a sum of a contrast Vcont and the first development contrast correction amount ΔVcont1 from the two types of stored conversion contents.

(6) The image forming apparatus according to any one of (1) to (4), further comprising a plurality of image processing means for characterizing a lighting pattern of the exposure means, wherein each of the image processing means has An image forming apparatus having two types of γ-conversion conversion contents and modulating the output result of the γ-conversion means according to the processing method of each image processing means.

(7) Developing contrast adjusting means not intended for image adjustment such as reduction of toner consumption and countermeasures against leakage of the charging device, and γ converting means whose γ converting characteristics are changed according to the adjustment by the adjusting means. An image forming apparatus comprising:

(8) Step A for adjusting the development contrast not for the purpose of image adjustment such as reduction of toner consumption and countermeasures against leakage of the charging device, and step of changing the γ conversion characteristic according to the adjustment in Step A B. An image forming method comprising:

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to examples of a laser printer. The present invention is not limited to a laser printer, but can be implemented in an appropriate digital image forming apparatus.

Further, the present invention is not limited to the form of the apparatus, but may be carried out in the form of an image forming method supported by the description of the embodiments.

[0026]

(Embodiment 1) FIG. 1 shows a schematic configuration of a "laser printer" which is Embodiment 1. This printer has a cylindrical photosensitive drum 2 as an electrophotographic photosensitive member substantially at the center of an apparatus main body 1. The photosensitive drum 2 includes the apparatus main body 1
, And is rotatably supported in the direction of arrow R1. Around the photosensitive drum 2, in order along the rotation direction, a voltage reducer 3 for erasing the potential on the photosensitive drum 2, a photosensitive drum 2
A primary charger 4 as charging means for uniformly charging the surface; an exposure means 5 for exposing the surface of the photosensitive drum 2 to form an electrostatic latent image; a potential sensor 6 for measuring a potential on the photosensitive drum 2 after exposure; A developing device 7 as a developing means for forming a toner image by attaching toner to the electrostatic latent image; a transfer charger 8 for transferring the toner image onto the transfer material P; and a separation charging device for separating the transfer material P from the photosensitive drum 2 The device 9 and a cleaner 10 for removing residual toner on the photosensitive drum 2 are provided.

A transfer material P to which the toner image is transferred is supplied from a paper feed deck 11. Below the photosensitive drum 2, that is, below the inside of the apparatus main body 1, a paper feed deck 11 for storing the transfer material P is arranged. The transfer material P in the paper feed deck 11 is fed by a paper feed roller 12, and is supplied between the photosensitive drum 2 and the transfer charger 8 via a transport roller 13 and a registration roller 15. The transfer material P transfers the toner image from the photosensitive drum 2 here, and is conveyed to the fixing device 17 by the conveyance belt 16. Transfer material P on which the toner image is fixed by heat and pressure applied by fixing device 17
Is discharged onto a discharge tray 20 by a discharge roller 19 as a final output image.

In the above-described printer, the exposing means 5
Is scanned by a polygon mirror 31 with a laser beam emitted according to an image signal from a semiconductor laser 30, and is guided to the photosensitive drum 2 via a coupling lens 32 and a reflection mirror 33.

FIG. 2 is a diagram schematically illustrating an electric configuration around a control board for measuring a potential on the photosensitive drum 2. As shown in FIG. In FIG. 2, in the control board, a ROM in which a control program is described and a RAM which is a temporary storage element of necessary data on the program are connected to a CPU which is a central element of processing. I / O which is an interface element
A / D converter and D / A which are data conversion elements
The converter is connected to external peripheral devices, and information is input and output to and from the control board. As a peripheral device, a potential sensor can measure the potential on the photosensitive drum after charging and exposure. Further, it is possible to control the applied voltage of the primary charger and the applied output value of the semiconductor laser in order to form a desired dark portion potential or light portion potential on the photosensitive drum 2. Further, it is possible to form a developing potential in the developing device 7 to cause the toner to fly onto the photosensitive drum 2.
The potential actually applied to the developing device 7 is a superposition of a DC component and an AC component, but here, the developing potential is substituted by a DC component.

FIG. 3 is a schematic configuration diagram of a digital image processing portion. The document image is input to the image processing unit via a reader / scanner network as a reading device or as an 8-bit signal from a storage device such as a hard disk. A filtering process is performed on the original image by a filter processing unit in order to make the edge portion of the image change in intensity. Next, in order to convert a luminance signal as a document image into a density signal, a luminance / density conversion unit performs a luminance / density conversion process. Then, an output density conversion unit performs an output density conversion process in order to convert the original image which has become the density signal into an output density corresponding to the output density pattern selected by the user. Here, the output density pattern is a character mode that emphasizes the contrast of an output image in order to mainly output a character original, or a photo mode in which the tone of an output image is emphasized in order to mainly output a photographic original. The mode is selected by a user using an operation panel (not shown in FIG. 1) which is a user interface, such as a mode or a text / photo mode for outputting an intermediate image between the text mode and the photo mode. The output density signal obtained as a result is subjected to γ conversion in consideration of the output characteristics of the printer by the γ conversion unit. The output signal for obtaining the output density is determined by the γ conversion. The table of the γ-conversion unit is configured by obtaining an inverse function with respect to the correlation table between the output signal to be output to the exposure system of the printer and the density signal which has been obtained in advance. Then, this output signal is converted into a binary level by an error diffusion processing unit in order to convert the 8-bit multi-level signal into a binary signal. By outputting this binary output signal to the semiconductor laser 30 which is an exposure system, the converted latent image of the original image is written on the photosensitive drum 2. Due to the error diffusion processing unit, it is microscopically a binary level,
From a macro perspective, the image becomes a binary image that can be recognized as multi-valued.

FIG. 4 shows the characteristics of the conversion table in the luminance / density conversion unit. The brightness-density conversion unit is an application of logarithmic conversion, and has a function of compressing a signal change in a dark part that is difficult to recognize with the naked eye and a function of extending a signal change in a bright part that is easy to catch the change with the naked eye.

FIG. 5 shows the characteristics of the conversion table in the output density converter. In the present embodiment, there are three types of tables, and in a character mode in which the output image is mainly output, the contrast is gained at a steep rise in a character mode in which the contrast of the output image is emphasized. In the photographic mode in which the tone of the output image is emphasized because the output of the photographic document is mainly used, the density signal of the document and the output density signal have a relatively gentle linear relationship, and the tone is maintained. On the other hand, the character photograph mode has an intermediate property between the character mode and the photograph mode.

FIG. 6 shows the characteristics of the conversion table in the γ conversion unit. The γ conversion unit holds the relationship of output signals for obtaining a desired density. As shown in FIG. 7, the density characteristics for an arbitrary output signal are examined in advance, and approximated or interpolated by a curve or a straight line. The γ conversion table is given by an inverse function of the obtained table Γ.

FIG. 8 is a view for explaining the latent image potential and the developing potential in this embodiment. In this embodiment, the background exposure method is adopted in which the toner mainly flies to a portion that has not been exposed to the semiconductor laser, so that the toner adheres to the dark portion potential portion of the photosensitive drum 2. The light-potential side is a so-called white background although some fogging occurs.
Indicates the DC component of the bias applied to the developing device as the development potential. The amount of toner adhesion changes depending on the magnitude of the development contrast, which is the difference between the dark potential and the development potential, and the halftone density also changes in digital machines. . In this embodiment, the basic dark portion potential is 390 V and the bright portion potential is 50.
V, the developing potential is set to 200V, and the developing contrast is set to 190V. In this embodiment, the development contrast is adjusted by modulating the voltage applied to the primary charger to adjust the dark portion potential. The back contrast, which is the difference between the development potential and the light portion potential, is not changed in this embodiment.

FIG. 9 is a diagram for explaining the adjustment items for determining the development contrast according to the present invention. Basic development contrast (hereinafter, basic development contrast Vcon
t) is 190 V as described in FIG. In this embodiment, the first development contrast correction amount ΔVcont1 and the second development contrast correction amount ΔVcont2, which are two types of contrast correction amounts, are added to or subtracted from the basic development contrast.
Therefore, the total development contrast when the printer actually outputs is the value of the following equation.

Total development contrast = Vcont + ΔVcont1 + ΔVcont2 Expression (2) As described later, the second development contrast correction amount ΔV
The development contrast not including cont2 is defined as VcontNow as in the following equation.

VcontNow = Vcont + ΔVcont1 (1) The first development contrast correction amount ΔVcont1 is further divided into two types of uses, one for reducing toner consumption and one for preventing charging device leakage. ΔVco for toner consumption reduction
-20V, -40 including 0V which does not change nt1
V, -60V. This is performed because the toner that adheres to the dark portion potential is reduced by lowering the development contrast, and the toner consumption is reduced. In the charger countermeasures, including the unmeasured 0V,
It can be switched between -30V and -60V. Leak countermeasures are intended to prevent adverse effects caused by spark discharge in the primary charger of a printer placed in a low pressure area when the voltage to be applied to the primary charger increases to increase the dark area potential. Inevitably, the dark portion potential is reduced.

Second development contrast correction amount ΔVcon
t2 is also divided into two types of uses, one for image adjustment and one for environmental correction. For image adjustment, fine settings from -50V to + 50V are possible. The purpose is to use a printer serviceman or user to adjust the overall dark / light looking at the output image. For environmental correction, the detection result from the temperature and humidity sensor provided inside the printer is read, the amount of moisture in the environment where the printer is placed is calculated, and the development contrast in accordance with the amount of moisture is continuously adjusted from 0 to -75V. And automatically change it. This is because the environment in which the amount of water is excessive is more dilute than the environment in which the amount of moisture is excessive, so that the developing property of the developing device inside the printer is higher, and even when the surface potential of the photosensitive drum is constant, the phenomenon that the amount of toner attached increases is suppressed. . Of course, it depends on the developing characteristics of the developing device. In the case of the present embodiment, it is necessary to increase the amount of decrease in ΔVcont2 as the amount of water decreases.

What is important is that the second development contrast correction amount ΔVcont2 is used for image adjustment when development is confirmed and is environmental correction corresponding to the state of the developing device.
Manual or automatic adjustment according to the image. Therefore, different from the first development contrast correction amount ΔVcont1, the change of the development contrast acts to optimize the quality of the image. In other words, the second development contrast correction amount ΔVcont2 is operated when the density of Dmax and halftone is adjusted to be low because of the high density, or when the density of Dmax and halftone is adjusted to be low because of the low density. Yes, further density adjustments should not be digital.

On the other hand, the first development contrast correction amount ΔV
cont1 is to change the development contrast regardless of the quality of the image. Here, in the case where there is one table for γ conversion shown in FIG. 6, the density of the toner adhering to the dark portion potential Dmax decreases, and also the macro halftone density decreases. It gives a strong impression.

Therefore, in this embodiment, the first development contrast correction amount ΔVCont1 is used as digital density adjustment.
By preparing a γ conversion table according to the above, it is possible to prevent image deterioration without reducing the halftone density.

FIG. 10 is an explanatory diagram of two types of γ conversion tables provided in the printer of this embodiment in advance. The two types of γ conversion tables indicate that when the first development contrast correction amount ΔVcont1 is 0 V, that is, when the second development contrast correction amount ΔVcont2 is any value together with the basic development contrast Vcont 190 V, Vcont + ΔVcont1 is 190 V Case (V
contα) and the first developing contrast correction amount ΔVcont1 is −50 V, that is, the basic developing contrast Vcont 190 V
And the second development contrast correction amount ΔVcon
Regardless of the value of t2, Vcont + ΔVcon
7 is a γ conversion table (γβi) when t1 is 140 V (Vcotnβ). Here, the suffix i of the γ conversion table is the value of the output density signal of the table and has a value of 0 to 255 since it is 8 bits long.

In this embodiment, the gamma conversion unit shown in FIG. 11 is replaced with the gamma conversion unit shown in FIG. That is, the gamma conversion unit in FIG. 11 has two types of gamma conversion tables. Further FIG.
As shown in, the basic development contrast Vcont,
The sum of the first development contrast correction amount ΔVcont1 is obtained and set as VcontNow. The value of VcontNow varies from 190 V to 70 V from the set value in FIG. In practice, it is not possible to use both the toner consumption reduction and the leak countermeasures together.
It is often used in the range of 0V. This VcontNo
w value, the relationship between Vcontα and Vcontβ, and Vc
Using the γ conversion table for ont α and the γ conversion table for Vcont β, the calculation is performed by the interpolation calculator of FIG. As an expression representing the interpolation calculation at this time,

[0044]

(Equation 1)

Here, the suffix i of the γ conversion table is the value of the output density signal of the table, and has a value of 0 to 255 since it is 8 bits long. The above equation gives VcontNow =
In the case of Vcontα, γNowi = γαi, and Vc
In the case of ontnow = Vcontβ, γNowi = γβ
Needless to say, i.

FIG. 12 is a view for explaining an example of the result of the interpolation calculation formula. In the figure, γ conversion tables γαi and γβi prepared in advance, a basic development contrast Vcont, and a first development contrast correction amount ΔV
From the current value of the current sum VcontNow of cont1, γNowi obtained by interpolation is obtained.

Finally, γNowi obtained by interpolation is 8
In order to reduce the quantization error caused by the shortage of the dynamic range due to the bit signal, the value is adjusted through the averaging process provided in the γ-conversion unit in FIG.

In this embodiment, the calculation method according to the equation is executed, but the output density j with the subscript j is given as follows.
May be used.

[0049]

(Equation 2)

Here, Γ is a table of the output density signal with respect to the output signal j, and has an inverse function relationship with γ.

As described above, the embodiment using the γ conversion table according to the development contrast has the characteristics shown in Table 1 below as compared with the conventional example. Conventional example 1
In the case where only the analog type image adjustment is performed, the case where only the development contrast is generally changed,
Here, a comparison was made in a case where image adjustment was performed only with a digital system, and in a case where only the γ conversion table was arbitrarily changed. In analog image adjustment as in Conventional Example 1,
This leads to a decrease in Dmax and a decrease in halftone density at the same time, which significantly degrades the apparent image quality. For example, the reduction in density itself causes development such as a poor impression of an image, a deterioration in gradation, and a thinning line. On the other hand, in the digital image adjustment as in the conventional example 2, the toner reduction effect is weaker than that of the analog type, so that not only the halftone density is extremely lowered to obtain the desired reduction effect, No effect can be exerted against the leak countermeasures.

However, as in this embodiment, by lowering the development contrast and automatically modulating the γ conversion table (changing the γ conversion characteristics) at the same time, the Dmax is reduced, but the halftone density is maintained. Does not give a poor impression to the image. Dmax is 1.1 in reflection density.
This is because if the value is not divided, the response to the density of the naked eye is dull in the dark part, so that a bad impression is not given. At the same time, in the present embodiment, it is also possible to achieve toner reduction and leakage countermeasures, and it is possible to achieve both image quality and required items which are not found in the conventional examples 1 and 2.

[0053]

[Table 1]

As described above, according to the present embodiment,
A gamma conversion table corresponding to two types of development contrast is provided in advance, and an optimal gamma conversion table is set according to the current development contrast.
By calculating the conversion table, it is possible to maintain the quality of the image as much as possible at the time of reducing the toner consumption or taking measures against the leakage of the charger so that the development contrast has to be reduced.

(Embodiment 2) In Embodiment 1, as shown in FIG. 8, a printer which forms a potential of a background exposure system in which toner mainly flies in a dark portion potential has been described. The present invention can also be applied to a printer that employs an image exposure method in which toner mainly flies at a light portion potential. This example will be described as a second embodiment.

In the image exposure method, the difference between the development potential and the light portion potential becomes the development contrast, and the difference between the dark portion potential and the development potential becomes the back contrast. In this embodiment, the basic dark portion potential is 400 V, the bright portion potential is 50 V,
The basic development potential is set to 250 V, and the development contrast is set to 200 V.

In the first embodiment, the development contrast is modulated by modulating the dark area potential. In this embodiment, the development contrast is also modulated simultaneously with the dark area potential.
This is because the dark portion potential has to be reduced for the leak countermeasures of the first embodiment as shown in FIG. 9, but the image exposure method does not directly involve the dark portion potential in the development contrast. Therefore, if the development potential is also slid by the amount corresponding to the decrease in the dark portion potential, the value of the back contrast does not change, and therefore, there is no change such as an increase or decrease in fog, and only the development contrast can be reduced. The back contrast involved in fogging, as it is smaller, causes extra adhesion of proper toner called ground fogging, but if it is too large, it causes fogging mainly composed of toner charged to reverse polarity with toner called inverted fogging,
This causes image stains called shadowing. Therefore, it is important to keep the value within a certain value, and if the development potential is lowered in conjunction with the dark portion potential, the back contrast does not change, which is very convenient. As in the first embodiment, the printer of this embodiment in which the development potential is lowered can achieve both the countermeasure against leakage, the reduction in toner consumption, and the image quality.

In the first embodiment, the printer is of the background exposure type. However, as in the present embodiment, if it is considered as the development contrast, it can be implemented by an image exposure type printer. That is, by lowering the developing potential at the same time as lowering the dark area potential, measures are taken to prevent leakage of the charger and reduce toner consumption by lowering the developing contrast, and at the same time, perform optimal γ conversion to suppress deterioration in image quality. .

(Embodiment 3) In FIG. 3 of the embodiment 1, the error diffusion unit after the γ conversion is converted to a binary level. In this embodiment, an example of a printer using a plurality of image processing methods including error diffusion processing will be described. FIG. 14 is a schematic configuration diagram of a digital image processing portion of the present embodiment.
The original luminance signal read from a reader scanner or network, or a storage device such as a hard disk is added to the intensity of the image edge by the filter unit, converted to the original density signal by the luminance density conversion unit, and output by the output density conversion unit. This is a density signal. In this embodiment, the error diffusion processing, dither screen processing, and pulse width modulation processing (hereinafter, PWM processing) described in the first embodiment are mounted as methods for generating signal data for driving the semiconductor laser.

The feature of this embodiment is that
For each type of image processing method, two types of gamma conversion tables are provided, that is, a total of six types of gamma conversion tables are provided. The purpose is to create a corresponding γ conversion table. In the error diffusion process, the toner dots formed on the photosensitive drum are less likely to concentrate than the dither screen, and the dots tend to be fine. Therefore γ
The conversion table has a different tendency even with the same development contrast. Similarly, the PWM processing also has a well-known feature that dots are easily connected in the main scanning direction and dots are easily connected in the sub-scanning direction. Therefore, a γ conversion table different from error diffusion processing and dither screen processing is required. Therefore, two types of γ conversion tables are required for each of the three types of image processing methods. The output image by the error diffusion process is
Although it has a very high resolution, it is used in a character mode and the like because of its characteristics such as inferior gradation stability compared to other processes. On the other hand, an output image obtained by the dither screen processing is used in a photographic mode or the like because it has a low resolution but is excellent in gradation stability. The PWM processing has an intermediate property between the two, and is used in a text / photo mode or the like.

FIG. 15 is a diagram showing a second example in the dither screen processing.
FIG. 1 is a gamma conversion table of various types of development contrast, and FIG.
6 is γ of two types of development contrast in the PWM processing.
It is a conversion table. The gamma conversion unit has two types of gamma conversion tables for three types of image processing in addition to the gamma conversion table of FIG. 10, and performs gamma conversion according to the current development contrast through an interpolation calculation unit and an average processing unit. A table is created. As described above, in this embodiment, the optimum γ conversion table according to each image processing method and the current development contrast is automatically selected, so that a stable image is always obtained even when the development contrast has to be reduced. It is possible to provide.

As described above, according to this embodiment,
In a printer equipped with a different image processing method, by providing two types of γ conversion tables for each image processing method, it is possible to provide an optimum image according to the image processing method and the development contrast. I have.

[0063]

As described above, according to the present invention,
Even when the image contrast has to be adjusted without the purpose of image adjustment, an image with little deterioration can be output.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a first embodiment;

FIG. 2 is a diagram showing an electric configuration around a control board.

FIG. 3 is an explanatory diagram of an image processing unit.

FIG. 4 is an explanatory diagram of a conversion table of a luminance / density conversion unit.

FIG. 5 is an explanatory diagram of a conversion table of an output density conversion unit.

FIG. 6 is an explanatory diagram of a conversion table of a γ conversion unit.

FIG. 7 is an explanatory diagram of a Γ conversion table showing a density characteristic with respect to an output signal.

FIG. 8 is an explanatory diagram of a latent image potential and a development potential of a background exposure system.

FIG. 9 is an explanatory diagram of adjustment items for determining a development contrast.

FIG. 10 is an explanatory diagram of a gamma conversion table provided in advance.

FIG. 11 is an explanatory diagram of a γ conversion unit.

FIG. 12 is a diagram showing an example of γNowi

FIG. 13 is an explanatory diagram of a latent image potential and a development potential of an image exposure system according to a second embodiment.

FIG. 14 is an explanatory diagram of an image processing unit according to a third embodiment.

FIG. 15 is an explanatory diagram of a gamma conversion table for dither screen processing.

FIG. 16 is an explanatory diagram of a γ conversion table for PWM processing.

[Explanation of symbols]

 2 Photosensitive Drum 5 Exposure Means 30 Semiconductor Laser VD Dark Part Potential VL Light Part Potential Vcont Basic Development Contrast ΔVcont1 First Development Contrast Correction Amount γ Conversion Table for Vcontα γ Conversion Table for Vcontβ γ Conversion Table for VcontNow

Continued on the front page F term (reference) 2H027 DA02 DA13 DA14 DB01 EA01 EA02 EA05 EB01 EB02 EB03 EC04 EC06 EC07 EC10 HB04 2H073 AA02 AA03 BA04 BA13 BA23 BA33 5C074 AA05 AA11 AA15 BB03 BB26 DD03 H08H04 BB20

Claims (8)

[Claims] 1. A brightness density conversion means for converting a document brightness signal into a document density signal; an output density conversion means for converting a document density signal obtained by the brightness density conversion means into an output density signal; Converting means for obtaining an output signal by gamma converting the output density signal obtained by the means, charging means for uniformly charging the electrophotographic photosensitive member, and the electrophotographic photosensitive member charged by the charging means An exposure means for forming a latent image by exposure with the output signal, and a developing means for developing a latent image by the exposure means with toner, on the electrophotographic photosensitive member formed by the charging means and the exposure means. An image forming apparatus that visualizes an image by forming a latent image potential, which is a surface potential of the electrophotographic photosensitive member, and a developing potential applied to the developing unit. Depending on the development contrast toner Xiang is the difference of the development potential and latent image potential to be deposited, the image forming apparatus characterized by modulating the converted content of the γ conversion unit. 2. The image forming apparatus according to claim 1, wherein
In the development contrast, a target development contrast is a basic development contrast Vcont,
A first development contrast correction amount ΔVco for correcting this
nt1 and second development contrast correction amount ΔVcont2
The conversion content of the γ conversion means is modulated according to only the first development contrast correction amount ΔVcont1 or the sum of the basic development contrast Vcont and the first development contrast correction amount ΔVcont1. An image forming apparatus which does not depend on the value of the second development contrast correction amount ΔVcont2. 3. The image forming apparatus according to claim 2, wherein
The first development contrast correction amount ΔVcont1 is
An image forming apparatus, which is used for reducing the amount of toner consumed by the developing unit or for preventing leakage of the charging unit. 4. The image forming apparatus according to claim 2, wherein
The second development contrast correction amount ΔVcont2 is
An image forming apparatus, which is used for adjusting image density or for adjusting fluctuation due to environment. 5. The image forming apparatus according to claim 2, wherein
Means for storing conversion contents of the two types of γ conversion means in two types of development contrast prepared in advance,
The basic development contrast Vcont and the first
Wherein the output result of the γ conversion means in the sum of the development contrast correction amount ΔVcont1 is calculated from the two types of stored conversion contents. 6. The image forming apparatus according to claim 1, further comprising a plurality of image processing units that characterize a lighting pattern of the exposure unit, wherein each image processing unit includes two types of image processing units. An image forming apparatus having a conversion content of γ conversion, and modulating an output result of the γ conversion unit according to a processing method of each image processing unit. 7. A developing contrast adjusting means which does not aim at image adjustment such as reduction of toner consumption and a countermeasure against leakage of a charging device, and a γ converting means which changes a γ converting characteristic according to the adjustment by the adjusting means. An image forming apparatus comprising: 8. A step A for adjusting the development contrast not for the purpose of image adjustment such as a reduction in toner consumption and a measure against leakage of the charging device, and a step B for changing the γ conversion characteristic in accordance with the adjustment in the step A. An image forming method comprising: