JP2002082499A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing an image from getting irregular at a highlight part (low density part) and also improving the tone reproduction in a dynamic range at a high density part by performing the processing of image density data by the use and the combination of image data for thin toner and thick toner. SOLUTION: In this image forming device, image exposure is performed by separating the image data into the image data for thick toner and the image data for thin toner accompanied with the image density data respectively.

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 for forming an image using toner by electrophotography,
In particular, the present invention relates to an image forming apparatus that develops an image by using two types of toners of the same color, a light color toner and a dark color toner, and forms an image.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic method, an image forming body is uniformly charged by a charging means and then exposed to an image to form a latent image. The latent image portion is developed by the subsequent developing means to form a toner image. In a digital image forming apparatus, image exposure is performed by, for example, dots that have been subjected to pulse width modulation, and reversal development in which toner adheres to the dot portions is performed. The amount of toner adhering to the dot portion is determined by the area and potential state of the dot portion on the image forming body, the developing bias for the dot portion, the state of the charge of the toner, and the like.

A high-density image portion recorded on an image forming body by an image exposure means has a large number of dots per area,
The size of the dots is also large. On the other hand, the low-density image portion has a small number of dots per area and a small size of one dot. Thus, after development, the amount of toner adhered to the high density image portion on the image forming body is large, and the amount of toner adhered to the low density image portion is small. The difference in the density of the recorded image is expressed by the amount of toner adhering to the area of the image formed on the image forming body by development.

[0004]

However, it is difficult to form an image with good gradation with one type of toner. Highlight part (low density part)
In this case, since the dots are small, the adhesion of a very small amount of toner per area is unstable, and image unevenness (image roughness) is likely to occur, and it is difficult to obtain stable gradation. Further, in the high-density portion, the toner is in an excessively adhered state, and the image density is likely to be saturated, and there is a problem that the gradation is not good in a wide area (dynamic range).

The present invention is applied to a monochrome or color image forming apparatus, and includes two kinds of toners of the same color, a light color and a dark color (for example, cyan (C), magenta (M), yellow (Y), An image forming apparatus that performs development using any of black (K) and performs processing of image density data
By using and combining the image data for dark toner, it is possible to prevent the occurrence of image roughness in the highlight area (low density area) and to improve the reproduction of the gradation in the dynamic range in the high density area. It is an object of the present invention to provide an image forming apparatus aiming at the above.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to form an image on an image forming body by image exposure and development with a dark toner and image exposure and development with a light toner after charging, based on image data. In the image forming apparatus, the image data is decomposed into image data for dark toner and image data for light toner accompanied with image density data, and image exposure is performed.

[0007]

Embodiments of the present invention will be described below. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope.

An image forming process and each mechanism of an embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a color image forming apparatus showing an embodiment of the image forming apparatus according to the present invention, FIG. 2 is a sectional view showing another example of the image forming apparatus, and FIG. 4 is a block diagram of an image processing system. FIG. 4 is a graph showing a relationship between a toner adhesion amount and a print image density. FIG. 5 is a potential state of an electrostatic latent image and a toner adhesion state to a latent image portion. FIG.
FIG. 4 is a diagram showing a relationship between input image density data and recorded image density in a state where image data is decomposed.

According to FIG. 1, the color image forming apparatus shown in FIG. 1 is a tandem type color image forming apparatus using an intermediate transfer member. Y), four sets of process units 1 consisting of magenta (M), cyan (C) and black (K)
In each process unit 100, Y, M, C, and K toner images are formed using dark and light toners, and the toner images are superimposed and transferred on the transfer belt 14a. The formed color toner images are collectively transferred onto recording paper as a transfer material, fixed, and discharged outside the apparatus.

Since the four process units 100 have a common structure, only one of them will be described. The photoreceptor drum 10 as an image forming body includes a light-transmitting conductive layer and an organic photosensitive layer (OPC) on the outer periphery of a cylindrical base formed of a light-transmitting member such as glass or light-transmitting acrylic resin. Is formed.

The photosensitive drum 10 is rotated counterclockwise as indicated by an arrow with the light-transmitting conductive layer grounded by power from a drive source (not shown) or by the transfer belt 14a.

Numeral 11 denotes a scorotron charger as charging means, which is attached to the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10 so as to face and be close to the photosensitive drum 10.
The photosensitive drum 1 is driven by corona discharge having the same polarity as the toner.
A uniform potential is given to 0.

An exposure optical system 12 (H) as an image exposure means for dark toner and an exposure optical system 12 (L) as an image exposure means for light toner each have an LED (light emitting element) as a light emitting element for image exposure. A linear exposure element (not shown) in which a plurality of diodes are arranged in an array in parallel with the axis of the photosensitive drum 10.
Selfoc lens (not shown)
Are configured as an exposure unit attached to the holder. An exposure optical system 12 (H) is provided on a cylindrical holding member,
12 (L) is attached and housed inside the base body of the photosensitive drum 10. In addition, as the exposure element, a linear element in which a plurality of light emitting elements such as FL (phosphor emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used. The exposure optical system 12 (H) is an image exposure unit that performs image exposure using image density data of image data for dark toner, and the exposure optical system 12 (L) is an image exposure unit that performs image exposure based on image density data of image data for light toner. Image exposure means.

The exposure optical system 12 (H) for the dark toner uses the scorotron charger 1 to determine the exposure position on the photosensitive drum 10.
Developing device 13 (H) for dark toner containing 1 and dark toner
Between the photosensitive drum 10 and the developing device 13 (H).
Is disposed inside the photoreceptor drum 10 in a state provided on the upstream side in the rotation direction. Exposure optical system 12 (L) for light toner
The exposure position on the photosensitive drum 10 is on the downstream side of the developing unit 13 (H) for the dark toner, and the developing unit 13 (H) and the developing unit 13 (L ), The developing unit 13 (L) is disposed inside the photosensitive drum 10 in a state provided on the upstream side in the rotation direction of the photosensitive drum 10 with respect to the developing unit 13 (L).

Developing device 13 as developing means for the dark toner
(H) contains a one-component dark toner or a two-component developer of a dark toner and a magnetic carrier, and performs reversal development by contact or non-contact. The developing device 13 (L), which is a developing means for the light toner, incorporates a one-component light toner or a two-component developer of a light toner and a magnetic carrier that enables superposition development without destroying the toner image. Then, reversal development is performed by soft development or more preferably non-contact development.

In forming an image, Y, M, C and K
As described in detail later, the image data of each color
Each of the image data is divided into dark toner image data and light toner image data accompanied by image density data, and the image exposure of the image density data of the dark toner image data is performed by an exposure optical system 12.
(H), and development with the dark toner is performed by the developing roller 131 (H) of the developing unit 13 (H).
Image exposure of image density data of light toner image data is performed by the exposure optical system 12 (L), and the developing device 13 (L)
Is developed by the developing roller 131 (L), and a toner image of the light toner is formed on the photosensitive drum 10 on the toner image of the dark toner. The dark and light toner images are transferred at a transfer position onto a transfer belt 14a described later. The transfer residual toner remaining on the photosensitive drum 10 after the transfer is cleaned by a cleaning device 19 that electrostatically collects the toner.

Process units for four colors of Y, M, C and K
The transfer belt 14a to which the rollers 100 face in parallel is a volume resistor.
Resistance rate is 10^Ten-10^FifteenΩ · cm, surface resistivity is 10^Ten~
10 ^FifteenΩ / □ endless belt, for example, modified polyimid
, Thermosetting polyimide, ethylene tetrafluoroethylene
Copolymer, polyvinylidene fluoride, nylon alloy, etc.
Disperse conductive materials in engineering plastics
Of a semiconductive film substrate having a thickness of 0.1 to 1.0 mm.
On the outside, preferably as a toner filming prevention layer
2 layer structure with fluorine coating of 5 to 50 μm
It is a seamless belt. Base of transfer belt 14a
Other than these, silicone rubber or urethane rubber
0.5-2.0mm thick semiconductive material with conductive material dispersed
An electrically conductive rubber belt can also be used. Transfer belt 1
4a is a driving roller 14d, a driven roller 14e,
External roller 14k and backup roller 14j
During image formation, a drive motor (not shown)
The drive roller 14d is rotated by the drive of
At the transfer position of the photosensitive drum 1 by the primary transfer device 14c.
0, the transfer belt 14a is pressed.
It is rotated in the direction indicated by the arrow in the figure.

A primary transfer device 14c, which is a transfer roller for each color, is provided to face the photosensitive drum 10 for each color with the transfer belt 14a interposed therebetween, and the transfer belt 14a and the photosensitive member for each color are provided. A transfer area (no reference numeral) for each color is formed between the transfer area and the drum 10. Primary transfer unit 14 for each color
By applying a DC voltage of the opposite polarity (positive polarity in the present embodiment) to c, and forming a transfer electric field in the transfer area, the dark and light toner images on the photosensitive drum 10 for each color are transferred. The image is transferred onto the belt 14a.

The static eliminator 14m, which is a static eliminator for each color,
Preferably, the primary transfer unit 1 is constituted by a corona discharger.
The transfer belt 14a charged by 4c is neutralized.

The process unit 1 of black (K) is started by starting a photoconductor drive motor (not shown) when image recording is started.
The photoconductor drum 10 is rotated in the direction indicated by the arrow in the figure, and at the same time, the application of a potential to the K photoconductor drum 10 is started by the charging action of the K scorotron charger 11.

After a potential is applied to the K photosensitive drum 10, the exposure optical system 12 (H) for K dark toner converts the first color signal, that is, the image data of K dark toner image data into image data. Image writing by the corresponding electric signal is started, and an electrostatic latent image for dark toner corresponding to the K image of the original image is formed on the surface of the K photosensitive drum 10.

The latent image for dark toner is subjected to reversal development in a contact state by a developing device 13 (H) for dark toner of K, and a toner image of dark toner of K is formed in accordance with the rotation of the photosensitive drum 10 of K. It is formed. Subsequently, an electrostatic latent image for light toner corresponding to the image density data of K is formed by the exposure optical system 12 (L) for light toner of K, and the developing unit 1 for light toner is formed.
By 3 (L), a toner image of K light toner is formed on the previously formed toner image of K dark toner.

The K toner image formed of the dark and light toners formed on the K photoreceptor drum 10 as the image forming body by the above-described image forming process is the first toner image in the K transfer area (no sign). The image is transferred onto the transfer belt 14a by a K primary transfer device 14c as a transfer unit.

Next, the transfer belt 14a is synchronized with the C toner image, and the cyan (C) process unit 10
0, the density of C formed on the photosensitive drum 10 of C,
Toner image composed of light toner is transferred area of C (no sign)
, The primary transfer device 14c of C as the first transfer means
As a result, a toner image composed of C dark and light toners is superposed on the toner image composed of K dark and light toners.

By the same process, the image is synchronized with the superposed toner images of K and C, and is formed on the photosensitive drum 10 of M by the process unit 100 of magenta (M). A toner image composed of M dark and light toners corresponding to the image density data of
In the M transfer area (no sign), the M primary transfer device 14c, which is the first transfer means, superimposes the toner images composed of the M dark and light toners on the K and C toner images from above. Formed on the Y photoreceptor drum 10 by the yellow (Y) process unit 100 in synchronism with the K, C, and M superimposed toner images. The toner image composed of the dark and light Y toners corresponding to the image density data of the image data is transferred to the Y transfer area (no sign) of Y 1
By the next transfer device 14c, toner images composed of dark and light toners of Y are formed on the K, C, and M toner images in a superimposed manner, and K, C, M, and Y are formed on the transfer belt 14a.
Is formed.

The transfer residual toner remaining on the peripheral surface of the photosensitive drum 10 for each color after the transfer is cleaned by a cleaning device 19 which is a cleaning means of the image forming body for each color.

On the other hand, in synchronism with the formation of the superimposed color toner image on the transfer belt 14a, the recording paper P is transferred from the paper supply cassette 15 as the transfer material storage means via the timing roller 16 as the transfer material supply means to the second paper. Is transferred to a transfer area (no symbol) of a secondary transfer unit 14g, which is a transfer unit, and a DC voltage having a polarity opposite to that of toner is applied to the secondary transfer unit 14g.
Thereby, the superimposed color toner images on the transfer belt 14a are collectively transferred onto the recording paper P.

The recording paper P on which the color toner image has been transferred is
The charge is removed by a charge removing electrode 16b, which is a separating means formed of a saw-toothed electrode plate, conveyed to a fixing device 17 as a fixing means, and recorded by applying heat and pressure between the fixing roller 17a and the pressure roller 17b. After the toner image on the paper P is fixed, it is discharged to a tray outside the apparatus.

The untransferred toner remaining on the peripheral surface of the transfer belt 14a after the transfer is cleaned by a cleaning device 19a which is a transfer belt cleaning means provided opposite to the driven roller 14e with the transfer belt 14a interposed therebetween. .

As described above, it is possible to provide a small-sized image forming apparatus in which color reproduction can be easily performed by widening a reproduction area using dark and light toners.

In the present embodiment, development with dark and light toners is performed for the four colors Y, M, C, and K. However, development with only dark toner is performed for Y, M, and C, and development with only K is performed. , The excellent effects of the present invention can be obtained. In this case, the developing device is an image forming apparatus provided with five sets.

According to FIG. 2, the image forming apparatus shown in FIG. 2 has the same effect as the image forming apparatus described with reference to FIG. Y, M, C using dark and light toner
1 and the process units 100 for forming the toner images of K and K are arranged in parallel, but in this embodiment, the toner images are superimposed on the transfer material without the intermediate transfer member. I am doing it. Only the differences from the case of the image forming apparatus of FIG. 1 will be described. In the image formation, the recording paper P discharged from the paper feed cassette 15 is synchronized with the toner image formation on the process unit 100 by a timing roller. 16
Is transported to the transport belt 14 via the

The transported recording paper P is charged to the same polarity as the toner by the paper charger 14n, and the rotating transport belt 1 is rotated.
The toner image formed of the dark and light Y toner formed on the process unit 100Y is transferred onto the recording paper P by the primary transfer unit 14c, and the process units 100M and 100C are transferred onto the recording paper P. , 100K, M, C, and K toner images formed of dark and light toners are transferred in a superimposed manner to form a superimposed color toner image.

The recording paper P carrying the color toner image is neutralized by the neutralizing electrode 16b, separated from the conveyor belt 14 and transported to the fixing device 17, where the color toner image on the recording paper P is fixed and Discharge to an external tray.

Also in the case of FIG. 2, it is possible to provide an image forming apparatus in which the reproduction area is widened by using dark and light toners, and which is small in size and in which color superposition is easily performed.

Also, in the embodiment shown in FIG. 2, it is also possible to adopt a configuration in which development with only dark toner is performed for Y, M and C, and development with dark and light toner is performed only for K. It is also possible to adopt a configuration in which development is performed using only dark toner for Y and K, C and M for dark and light toners, and the excellent effects of the present invention can be obtained.

Although the color image forming apparatus has been described as an example of each of the above image forming apparatuses, the present invention is not necessarily limited to this, and a process similar to that described with reference to FIG. 1 or FIG. The present invention is also applied to a monochrome image forming apparatus.

In the image forming apparatus of the present invention,
Decomposes image density information into image data for dark toner and image data for light toner, and forms a dark toner image by image exposure based on the image density data of the image data for dark toner and development using dark toner Then, based on the image density data of the light toner image data, a light toner image is formed by image exposure and development using the light toner, and the light toner image is superimposed on the dark toner image to form an image. Device
In the present invention, the image density data of each color of Y, M, C and K is divided into image density data for dark toner and image density data for light toner, and the image density data for dark toner is dark toner. The image density data for the light toner is converted by the exposure optical system 12 (H) for the light toner.
(L) performs image exposure on the photosensitive drum 10.

According to FIG. 3, an original image is read by image reading means using a solid-state image sensor such as a CCD (F1). The amplified analog image signal output from the CCD is converted to an 8- to 10-bit digital signal by A / D conversion.
After the conversion, shading correction and subsequent image processing (1) such as color space conversion, logarithmic conversion, black generation, and color correction are performed (F2). The image data may be read from the stored memory and subjected to the same processing.

The image data obtained in the image processing (1) is
By checking the density distribution of the data and the density difference between adjacent dots, it is possible to determine whether the original image is a halftone image such as a photograph or a picture or a character image such as a character or a line drawing. (F3).

The image data obtained in the image processing (1) is
Image data for dark toner (F5A) accompanied by image density data based on the determination result as to whether the image is a halftone image or a character image, or based on the specified output form (F3);
Image data for light toner with image density data (F5
B) is created.

The image data for dark and light toner accompanying the decomposed image density data is subjected to γ correction for each toner (F6A, F6B), and MTF correction (F7A, F7).
B), PWM modulation is performed (F8A, F8B). In the PWM modulation, it is preferable to form large dots and increase the recording unit so as to improve dot reproduction in a highlight portion (low density portion). For example, with respect to the image data for dark toner, one pixel PWM
Do with. On the other hand, the image data for light toner is subjected to two-pixel PWM in order to enhance the gradation, and the recording unit is increased. Note that intensity modulation may be used instead of PWM modulation.

The image exposure (input of the image density data of the dark toner) corresponding to the image density data of the image data for the dark toner after the PWM modulation is performed on the photosensitive drum 10 by the exposure optical system 12 (H) (F9A). ), An image exposure (input of light toner image density data) corresponding to the image density data of the light toner image data after the PWM modulation is performed by the exposure optical system 12.
(H) is performed on the photosensitive drum 10 (F9B).

It is preferable that these correction values are sequentially changed in accordance with the image discrimination. That is, in the half tone, the form in which the γ correction is performed is used, the MTF correction is weakened, and the PWM recording unit is increased. On the other hand, for character images, it is preferable to make changes such as setting the γ correction higher, increasing the MTF correction, and reducing the PWM recording unit.

For an image forming apparatus using a dark toner and a light toner, in order to obtain a sufficient effect according to the present invention, the toner adhesion amount and the print image shown in FIG. It is desirable to have a relationship of concentration. The difference in density between the dark and light toners is caused by a difference in the amount of pigment contained in the toner particles. Further, the amount of toner adhered at the time of saturation depends on the toner particle size. For example, for dark toner, the amount of toner adhering to white paper is 1 mg /
The recording density becomes saturated at about cm ² . It is necessary that the saturated concentration value _Dmax (H) in the saturated state be 1.7 to 2.5. As shown in FIG. 4, the density value at the point of substantially saturation is defined as D _max (H). To be exact, the concentration gradually increases as shown by the broken line.

On the other hand, the density of the light toner does not reach a saturation state when the amount of toner attached to white paper is 1 mg / cm ² , for example. When the light toner has the same toner adhesion amount as the dark toner reaching the saturation density value, that is, when the density of the dark toner is saturated, the recording density D (L) of the light toner is D (L) = 0. It must be between 0.3 and 0.8. Before the toner adhesion amount to the white paper reaches the saturation density value, for example, the ratio to the recording density D _S (L) when using a light toner with the toner adhesion amount of 0.5 mg / cm ² , that is, the light toner DOO slope ratio of recording density of the dark toner _{D S (L) / D S} (H) = 0.2~0.
It must be between 5 and 5.

The recording density needs to have the above relationship between the dark toner and the light toner, but the toner particle diameter and the charge amount may be the same for the dark and light toners. preferable. For toner particle size,
Because both dark and light toners ensure image quality and developability,
It is preferable that the volume average particle size is between 3 and 10 μm, and even if there is a difference, it is ± 20% or less. The charge amount is between 5 and 30 μC / g for both the dark and light toners. In particular, when the toner particle size is small, a high charge amount is required. Preferably, there is. By satisfying these conditions,
A similar γ characteristic can be obtained between the dark and light toners, and the design can be made so that the sum of the adhesion amounts of the dark toner and the light toner in the middle to high density areas is substantially the same and the change in the recording density changes linearly. It will be easier.

Note that the gradation characteristics shown in FIG. 4 also change depending on the toner particle size and the contained coloring material. In the case of a toner having a small particle diameter, the toner may saturate even with a smaller amount of adhesion of 0.5 mg / cm ² , but is important in designing a toner having a high saturation density and a low slope ratio.

According to FIG. 5, the relationship between the potential state of the electrostatic latent image based on the dark and light image data and the toner adhesion state of the dark and light toners is shown in FIG. Here, as the arrow becomes →, the density changes from low density to high density. First, as shown in FIG. 5A, the scorotron charger 11 described above with reference to FIG. 1 has the same polarity (minus polarity in the present embodiment) as the toner polarity to be used, and is usually −500 to −1000V.
The photosensitive layer of the photosensitive drum 10 uniformly charged to the charging potential V ₀ of the photosensitive drum 10 is exposed by the exposure optical system 12 (H) for dark toner.
Image exposure of image density data for dark toner is performed, and a latent image is formed in accordance with image density data of dark toner having a different potential.

Subsequently, as shown in FIG.
And the same polarity as the toner polarity used (in this embodiment,
In this case, the charge of the photosensitive drum 10 is negative.
Rank V ₀0.8V₀Degree or this
A developing bias potential Vb is applied,
Inversion of dark toner by developing unit 13 (H) for dark toner
Development takes place. Here, depending on the developing bias potential Vb
The shape is formed between the photosensitive drum 10 and the developing roller 131 (H).
The developed electric field causes the dark toner to be transferred to the photosensitive drum 10.
The latent image is electrostatically attached to the latent image, and the dark toner is developed.
You.

Further, as shown in FIG. 5 (C), the image exposure of the image density data for the light toner is performed by the light toner exposure optical system 12 (L), and the image of the light toner having a different potential is obtained. A latent image is formed according to the density data. At this time, the potential contrast of the latent image potential portion to which the dark toner adheres also decreases, but a small amount of the light toner adheres. Next, as shown in FIG. 5 (D), housing a light toner, toner having the same polarity to be used (negative polarity in this embodiment), relative to the charge potential V ₀ photoreceptor drum 10,
0.8, which is the same value as the developing bias for the dark toner.
Non-contact reversal development of the light toner is performed by the light toner developing unit 13 (L) in which a developing bias for superimposing an AC voltage is applied to a developing bias potential Vb of a DC voltage of about V ₀ . The photosensitive drum 10 and the developing roller 131 by the developing bias potential Vb by the DC voltage and the AC voltage.
(L), the light toner flying by the developing electric field is electrostatically formed on the latent image of the light toner formed in accordance with the image density data of the light toner on the photosensitive drum 10, and The light toner is developed on the latent image of the dark toner formed on the photosensitive drum 10.

As shown in FIG. 5 (D), the obtained recorded image density is a low density area, the first image exposure is not performed, the second image exposure is performed, and only the light toner is used. A dot is formed.

Reference numeral denotes low to medium density portions, in which the first image exposure is not performed, the second image exposure is performed, and dots are formed only with light toner.

Reference numeral denotes a medium density portion, in which the first image exposure is weakly performed and a small amount of dark toner adheres, and the second image exposure is weakly performed and a small amount of light toner is superimposedly adhered. is there.

Is a middle to high density area, the first image exposure was performed strongly, a large amount of dark toner was adhered, the second image exposure was performed weakly, and a small amount of light toner was further superimposedly adhered. Things.

Is a high density area, the first image exposure is performed strongly, a large amount of dark toner adheres, the second image exposure is not performed, but a small amount of light toner is overlapped because the potential contrast remains. Is attached.

The relationship between the recorded image densities (image densities recorded with dark and light toners) indicated by in FIG. 5D and the original image densities is shown in FIG. The original image data is decomposed, and is formed as a sum of the image density data of the dark toner and the image density data of the light toner by image exposure of the image data (dotted line in the figure) corresponding to the decomposed dark and light toners. The toner image is developed with dark and light toners (solid lines in the figure). That is, FIG. 6 shows the image exposure (image density data of the original dark toner) according to the image density data of the image data for the dark toner after the charging, the development with the dark toner, and the image density data of the image data for the light toner. The photosensitive drum 1 is formed by the corresponding image exposure (image density data of the original light toner) and development with the light toner.
It shows the relationship with the image density formed (recorded) at the same position on 0. Due to the overlap of the dark and light toner images, a recorded image density corresponding to the original image density is obtained.

As described above, the processing of the image density data is
By using and combining the image data for the light and dark toners, it is possible to prevent the occurrence of image roughness in the highlight portion (low-density portion) and to achieve the gradation in the dynamic range in the high-density portion. An image forming apparatus with improved reproduction can be provided.

[0059]

According to the present invention, the processing of the image density data is performed in combination with the use of the image data for the light and dark toners, whereby the occurrence of image roughness in the highlight portion (low density portion) is prevented. Thus, it is possible to provide an image forming apparatus in which the reproduction of gradation in a dynamic range in a high-density portion is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a sectional view illustrating another example of the image forming apparatus.

FIG. 3 is a block diagram of an image processing system.

FIG. 4 is a graph showing a relationship between a toner adhesion amount and a print image density.

FIG. 5 is a diagram illustrating a potential state of an electrostatic latent image and a state of toner adhesion to a latent image portion.

FIG. 6 is a diagram illustrating a relationship between input image density data and recorded image density in a state where image data is decomposed.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum 11 scorotron charger 12 (H), 12 (L) exposure optical system 13 (H), 13 (L) developing device 14 transport belt 14 a transfer belt 14 c primary transfer device 14 g secondary transfer device 15 paper feed Cassette 16 Timing roller 17 Fixing device 100 Process unit 131 (H), 131 (L) Developing roller

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) G03G 15/08 503 H04N 1/29 H 5C074 H04N 1/29 B41J 3/00 A (72) Inventor Yotaro Sato 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Corporation F-term (reference) EA11 GA13 GA17 5C074 AA05 BB02 BB26 CC26 DD03 EE11 GG02 GG09 GG12 GG13

Claims (3)

[Claims] 1. An image forming apparatus that forms an image by image exposure and development with a dark toner and image exposure and development with a light toner after charging the image forming body based on the image data. An image forming apparatus for decomposing the image data into image data for dark toner and image data for light toner accompanied by image density data, and performing image exposure. 2. The image forming apparatus according to claim 1, wherein the dark toner is used before the light toner. 3. The image forming apparatus according to claim 1, wherein the gray image data is formed at the same position.