JPH10153899A - Color image forming method and device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming method where color reproducibility is improved by KNC (image forming method for performing transferring on recording paper after superposing a multicolor toner image on an image forming body) processing performing image exposure from inside. SOLUTION: In this color image forming method superposing and forming the toner image by electrifying the image forming body, performing the image exposure from the rear face of the image forming body and repeating reversal developing; the image exposure is performed from the inside of the image forming body, and the exposure for a first color and a second color at the time of forming a secondary color is made nearly the same, and is also made smaller than a primary color, and also is made equal to or above the half exposure E1/2 of the image forming body and equal to or below twice of the half exposure E1/2 of the image forming body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method for forming a color-separated electrostatic latent image on an image forming body, superimposing a multicolor toner image on the image forming body, and then transferring it onto recording paper. In particular, the present invention relates to a color image forming method for improving color reproduction of edges, thin lines, and isolated points of an image, and a color image forming apparatus used as a printer or a copying machine employing the method. .

[0002]

2. Description of the Related Art In the KNC process, a multicolor toner image is superposed on an image forming body by repeating a charging process, an image exposing process, and a reversal developing process, and then transferred onto a recording paper. In the developing process, DC and AC biases are applied to each developing sleeve, and reversal development is performed on the image forming body without contact. The adhesion state of the toner obtained by such a KNC process is not simply determined by the exposure light modulated based on the image density data. The image exposure means is arranged outside the image forming body, and the image exposure is performed from outside the image forming body. The following phenomena are involved when an external exposure method is used.

The first phenomenon is a phenomenon that makes it difficult for the next toner to adhere to a solid portion of a toner image because of a toner layer potential and a shielding property that the toner does not easily transmit light. This is abbreviated as an average shift due to the structure of the previous image. The second phenomenon is the deformation of an electrostatic latent image (hereinafter, simply referred to as a latent image) caused by the structure of a previously formed toner image, that is, an isolated point, an isolated dotted line,
This is a halo effect that appears as an edge effect or a pseudo contour phenomenon occurring at the edge of a character or a solid portion, and has the same cause as the edge effect, but is a phenomenon unique to the KNC process due to superposition. A shift due to such a phenomenon is abbreviated as a local shift due to a structure between images. The third phenomenon is the deformation of a latent image caused by the type of image regardless of the structure of the previously formed toner image or a state in which a toner image has not yet been formed on the image forming body, that is, electrophotography. This is a peculiar edge effect phenomenon, which is a shift between image data and a reproduced image, and is hereinafter abbreviated as a shift due to the structure of the image. The edge effect and the halo effect depend on the development method and the characteristics of the photosensitive layer, but may be as large as about 0.5 to 2 mm. In order to suppress such a phenomenon, conventionally, as described in JP-A-6-218991, a toner image is formed in a well-balanced manner in a lower layer and an upper layer in units of recording dots for binary recording image data. Therefore, the color reproducibility is improved by modulating the pulse width at the time of image exposure and modulating the exposure beam to a solid portion that is an isolated pixel or a continuous pixel or a pixel at the end thereof. Specifically, when the recording dots overlap, the correction is performed such that the first color is weak and the second color is strong.

FIG. 3 is a graph showing KNC correction by an external exposure method.

The graph shows the photosensitive characteristics of the image forming body, the vertical axis of the graph shows the surface potential of the image forming body, and the horizontal axis of the graph shows the exposure.

[0006] Curve a represents the photosensitive characteristic when the toner image is not carried on the surface of the image forming body, E _1/2 represents the exposure required to attenuate the initial charging potential V ₀ by half, This is called a half-exposure dose. Exposure E _c is the exposure amount for obtaining a first color having the maximum image density, the exposure amount E _a is
This is the exposure amount of the first color for obtaining the secondary color having the maximum image density. Exposure E _a, to the first color and the toner adhesion amount of the dichroic subsequent to obtain the secondary color substantially identical, are weaker than the exposure amount E _c.

[0007] Curve b shows the photosensitive characteristic in a state where the toner layer of the first color has already been carried on the surface of the image forming body in order to obtain a secondary color. Curve b is a curve in which the degree of attenuation is smaller than curve a due to the light shielding property of the toner,
In addition, the residual potential also increases due to the potential of the toner layer formed earlier. Thus, for example, by performing image exposure of the first color image exposure and second color to obtain a secondary color in the same exposure amount E _a, the latent image potential as shown in the graph does not sufficiently decrease,
Not the same. As a result, a toner image with a low color balance with a small toner adhesion amount for the second color is obtained. In order to correct the deformation of such a color balance, as much as possible to correct stronger than the first color exposure amount E _a for the second color exposure amount E _b1 to obtain a secondary color to obtain a secondary color. This exposure amount E _b1 is nearly twice or more than E _a , and is a correction amount that is almost the same as or larger than E _c . In this way, the amount of the toner layer attached to the first color for obtaining the secondary color having the maximum density is made equal to the amount of the toner layer attached to the second and subsequent colors. This is the basic principle of the KNC correction by the external exposure method, and it is difficult to stabilize a color image because the correction amount is large.

The KNC process to which the KNC correction is applied by the external exposure method will be described below.

FIG. 4 is a schematic diagram showing the surface potential on the image forming body in the external exposure type KNC process.

FIG. 4A is a schematic diagram showing the initial charging, and it can be seen that the surface potential of the image forming body is set uniformly to the charging potential. 4 (b) is a schematic view showing an exposure process for forming a latent image of a first color, E _c, is shown an exposure amount for obtaining a first color having the maximum image density, E _a indicates the exposure amount of the first color for obtaining the secondary color having the maximum image density. Since E _a is weaker than E _c, it can be seen that the latent image potential is high.

FIG. 4C is a schematic view showing the state after the development process of the first color, and it can be seen that toner according to the potential difference between the latent image potential and the development bias is attached.

FIG. 4D is a schematic diagram showing the surface potential of the image forming body after the second charging process. It can be seen that the charging potential is uniform regardless of the presence of the toner.

FIG. 4E is a schematic view showing an exposure process for forming a second color latent image. E _c, is shown an exposure amount for obtaining a first color having the maximum image density, E _b1 is shown an exposure amount of the second color to obtain the secondary color having the maximum image density. By making E _b1 equal to or stronger than E _c , the influence of the toner layer potential of the first color and the light shielding property of the toner is corrected, and becomes equal to the potential of the toner latent image of the first color.

FIG. 4F is a schematic view showing a state after the development process of the second color, in which toner corresponding to the potential difference between the latent image potential and the developing bias adheres. In other words, it can be seen that the amount of adhesion of the toner layer of the first color for obtaining the secondary color and the amount of adhesion of the toner layers of the second and subsequent colors are the same as corrected by the exposure amount.

The same exposure amount correction is performed on the primary color and secondary color regions having intermediate image densities ranging from low to medium according to the potential characteristics shown in FIGS.

[0016]

However, when the KNC process for performing image exposure from the inside is performed, compared with the KNC process using the external exposure method, the light shielding of the toner image and the light by the toner image are performed. The effect of the spread of the beam diameter resulting from the scattering is eliminated. Specifically, at the above point, the image exposure is performed without being affected by the previous toner image, while the potential of the toner layer increases the residual potential. The first and second phenomena are reduced due to the elimination of light absorption and light scattering.
C correction cannot be applied, and a correction unique to the internal exposure method is required.

Further, proposals in the conventional external exposure method are as follows.
It is limited to superimposition of two colors on the value image data and focuses on the adjacent pixel information of the image. The colors of the edges, thin lines and isolated points including the case of multi-valued image data The quality of reproduction has not been improved. Also, there is no correspondence for a full-color image in which three or four colors overlap. This is because the range over which the edge effect reaches is expanded to about 1 mm, so that a wide range of correction is indispensable. Further, since it is multi-valued color image data, the correction level needs to be performed with high accuracy. Conventionally, correction based on adjacent pixel information is insufficient, which means that correction according to the structure and spread of an image is required.

A first object of the present invention is to solve the above problems,
An object of the present invention is to provide a color image forming method for improving color reproducibility by a KNC process for performing image exposure from the inside.

A second object of the present invention is to solve the above problems,
When superimposing toner images based on multi-valued color image density data, the image data is corrected in consideration of the image density distribution, that is, new recording image data is created for each color, and thus light modulation is performed. An object of the present invention is to provide a color image forming apparatus which improves color reproduction of edges, fine lines, and isolated points by recording.

[0020]

Means for achieving the above object are as follows to achieve the above object.

(1) A color image forming method in which the image forming body is charged, the image is exposed from the back surface of the image forming body, and reversal development is repeated to form a superposed toner image. A color image forming method, wherein the exposure amounts of the first and second colors when forming the next color are smaller than the exposure amounts when forming the primary color having the maximum density.

(2) A color image forming method in which the image forming body is charged, the image is exposed from the back surface of the image forming body, and reversal development is repeated to form a toner image by superimposition. The exposure amount of the first color when forming the next color is set to be substantially equal between the first color and the second color, and is smaller than the exposure amount when forming the primary color having the maximum density, and the half of the image forming body is reduced. A color image forming method, wherein the exposure amount is not less than _{1/2 and not} more than twice.

(3) The color image forming method according to (1) or (2), wherein the second color is corrected by 5 to 50% more than the first color in the image exposure amount of the secondary color having the maximum density. .

(4) In the image exposure amount of the secondary color having the maximum density, the solid color of the second color is 5 to 30% of the first color.
The color image forming method according to any one of (1) to (3), wherein a large amount of correction is performed.

(5) In the image exposure amount of the secondary color having the maximum density, the second color has 10 to 50 isolated points with respect to the first color.
%. The method for forming a color image according to any one of (1) to (4), wherein the correction is performed by%.

(6) The image exposure amount of the first and second colors of the secondary color having the maximum density is set to be weaker than that of the primary color having the maximum density. Item 1. The color image forming method according to Item 1.

(7) The correction of the image exposure amount for the second color is increased with an increase in the image exposure amount.
(6) The color image forming method according to any one of the above (6).

(8) A color image forming apparatus which charges an image forming body, exposes the image from the back side of the image forming body, and repeats reversal development to form a superposed toner image. Arrange the exposure means to expose from
Color image formation wherein the exposure amounts of the first and second colors from the exposure means when forming a secondary color having a maximum density are smaller than the exposure amounts when forming a primary color having a maximum density. apparatus.

(9) A color image forming apparatus in which the image forming body is charged, the image is exposed from the back surface of the image forming body, and reversal development is repeated to form a superposed toner image. Arrange the exposure means to expose from
The exposure amount of the first color from the exposure means when forming the secondary color having the maximum density is substantially equal between the first color and the second color, and the exposure amount when forming the primary color having the maximum density And the half-life exposure amount E of the image forming body.
A color image forming apparatus characterized by being at least _1/2 and at most twice as large.

(10) The image exposure for each color is optically modulated for each recording dot based on multi-valued recording image data, and the recording image data is corrected by image density and image density distribution data. The color image forming apparatus according to (8) or (9), wherein the light modulation based on the image data is performed by pulse width modulation or intensity modulation.

(11) A correction unit for forming multi-valued recording image data used for image exposure for each color includes a first correction unit for correcting an average shift between images, and a local shift due to a structure between images. (10) The color image forming apparatus according to (10), further including a second correction unit that corrects the color image.

(12) The color image forming apparatus according to (11), wherein the first correction section and the second correction section correspond to either pulse width modulation or intensity modulation.

(13) The color image forming apparatus according to any one of (8) to (11), wherein the correction of the image exposure amount of the second color is increased as the image exposure amount increases.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) First, a mechanical schematic configuration of a color image forming apparatus 400 according to an embodiment of the present invention will be described.

An embodiment of the color image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus, and FIG. 2 is a cross-sectional view illustrating a support structure of an image forming body.

In the color image forming apparatus 400 according to the present embodiment, the substrate of the image forming body 10 is made transparent and the exposure optical system 1 is used in order to eliminate the lack of space on the peripheral surface of the image forming body 10.
2Y, 12M, 12C, 12K are cylindrical support members 20
The intermediate transfer belt 14 is attached to the base of the image forming body 10, and the image is exposed from the inside of the image forming body 10. The developing units 13Y, 13M, 13C, and the developing units 13Y, 13M, 13C
The abutting rollers provided at 13K abut against the ends of the image forming body 10, and the roller members provided at the ends of the chargers 11Y, 11M, 11C, and 11K abut against the image forming body 10 to maintain a gap. is there. The chargers 11Y, 11M, 11C, 11K,
Exposure optical system 12Y, 12M, 12C, 12K, developing unit 1
3Y, 13M, 13C, 13K, intermediate transfer belt 14,
The support structure of the transfer roller 15 and the like will be described.

Each of the chargers 11Y and 11 including the image forming body 10
M, 11C, 11K, developing units 13Y, 13M, 13
C, 13K and the cleaning device 19 are housed in a cartridge (not shown) and are integrally housed in the apparatus main body.

On the other hand, each exposure optical system 12Y, 12M, 12
C and 12K are also integrated with the support member 20 as a common support, supported and housed in a cartridge, and
It is attached to and detached from the apparatus main body together with 0. Further, a toner storage container (not shown) is stored in the upper part of the cartridge, and each of the developing devices 13Y, 13
M, 13C, and 13K are respectively connected via toner supply tubes (not shown).

Exposure optical systems 12Y, 12M, 12C, 12
As shown in FIG. 2, K is bonded to both ends of a pair of front and rear support members 20 fixed to the rotary support shaft 30 by adjusting the distance to the photosensitive surface through a wedge-shaped attaching member 21 in a predetermined positional relationship. For this reason, it is housed inside the base of the image forming body 10. Image forming body 10 has flange members 10A provided at both ends.
And 10B are rotatably supported by the support member 20 via the bearing B, respectively, and the gear 1 provided in the flange member 10B is provided.
The rotation of the rotation support shaft 30 in the fixed state is performed by the drive of 0G.

As described above, the rotary support member 30 integrally supporting the image forming body 10 and the exposure optical systems 12Y, 12M, 12C, and 12K is formed in a U-shape and connected in a symmetrical front and rear direction. The bearing is supported between the respective drum support plates 40.

The abutment reference member has a disk-like shape, and is fixed to the left and right support members 20 by screws (not shown) with the center axis aligned with the image formation member 10 through the rotary support shaft 30. And are fixed concentrically. An abutting surface (not shown) of an abutting reference member provided concentrically with the image forming body 10
The developing roller 13 is positioned coaxially with the image forming body 10 by abutting rollers 131 of the respective developing devices 13. The abutting rollers 131 are gap maintaining members in which bearings (not shown) are included in shafts at both ends of a developing sleeve of the developing device 13. For example, a member having a thickness of 3 mm and an outer diameter of 20 mm is used as the abutting roller 131, and the abutting roller 131 is held by a bearing (not shown) fitted on the rotating shaft of the developing device 13 so as to rotate individually with the developing sleeve. Provided.
The developing sleeve is brought into contact with the image forming body 10 by a predetermined gap, for example, 300, by the abutting roller 131 abutting against the abutting reference member.
The developing unit 13 is mounted while being kept in a non-contact state with an interval of about 600 μm.

The abutting reference members are the chargers 11Y, 11M, 1
1C, 11K, an abutment surface for the cleaning device 16 or the intermediate transfer belt 14 is provided.
A gap holding member is provided for each of the chargers 11Y, 11M, 11C, 11
K, the cleaning device 16, the intermediate transfer belt 14, etc., and then the chargers 11Y, 11M,
1C, 11K, a cleaning device 16, a gap holding member provided on the intermediate transfer belt 14 and the like are abutted to position the image forming body 10 coaxially. With such a configuration, the developing devices 13Y, 13M, 13C, 13K,
When the gaps of the image forming units such as the chargers 11Y, 11M, 11C, and 11K, the cleaning device 16, and the intermediate transfer belt 14 are maintained, the gap holding members are positioned on the abutting reference member. Image forming body 10
Are not directly pressed, and the image forming body 10 is not deformed or damaged.

The drum support plate 40 is provided with a suspension means (not shown) at the front and rear connection portions, and is inserted into and engaged with a guide member (not shown) provided in the apparatus main body so as to be in a suspended state. The image forming body 10 and the exposure optical systems 12Y, 12M, 12C and 12K held at 30 are arranged at substantially set positions. When the rotation support shaft 30 is inserted to a regular position, the shaft end 30B protruding from the rear drum support plate 40 from the above-described suspended state fits into the receiving seat 72 of the rear plate 71 as the device substrate. The shaft end 30A protruding from the front drum support plate 40 is supported by a screw member 82 taperedly fitted to a receiving seat 81 provided on the drum support substrate 80, so that the image forming body 10 is set at a regular set position. The gear 10G is meshed with the gear on the driving side by precisely regulating, while each of the exposure optical systems 12Y, 12M, 12
C and 12K are further accurately engaged and fixed at a predetermined angular position with respect to the apparatus main body by engaging the through pin P1 of the shaft end 30B with the V-shaped groove formed in the receiving seat 72. State.

The drum supporting substrate 80 has upper and lower reference holes H.
1 is engaged with a pair of reference pins P2 provided on a front side plate 70 as a front device board, and its mounting position is determined, and is fixed to the front side plate 70 by a plurality of screwing screws. A plurality of windows 80A are formed with openings, and charging devices 11Y, 11M, 11C, and 11K in the form of bars are inserted from the outside of the drum supporting substrate 80 to set them at predetermined intervals with respect to the image forming body 10 and to form electrodes. Are fixed and supported by screwing screws in a state where is connected.

The above is the support structure of the image forming member. Next, a schematic configuration of each image forming member will be described.

The image forming body 10 includes a transparent conductive layer, an organic photoreceptor (OPC), and an α-transparent layer formed on the outer periphery of a cylindrical substrate formed of a transparent member such as optical glass or transparent acrylic resin.
It is provided with a photosensitive layer made of Si or the like. The image forming body 10 has, for example, a cylindrical transparent resin substrate formed of a transparent member of glass or transparent acrylic resin provided inside, and a transparent conductive layer and an organic photoconductor layer (OPC) formed on the outer periphery of the substrate. And rotated counterclockwise as indicated by the arrow in FIG.

In the present embodiment, it is sufficient that the photoconductor layer of the image forming body 10 has an exposure amount that can provide an appropriate contrast. Therefore, the light transmittance of the transparent resin substrate of the image forming body 10 in the present embodiment does not need to be 100%, and may have a characteristic such that a certain amount of light is absorbed when the exposure beam is transmitted. . As a material of the light-transmitting substrate, an acrylic resin, particularly one polymerized using a methyl methacrylate monomer, has transparency, strength,
Although it is excellent in accuracy, surface properties, and the like, it is preferably used, but various translucent resins such as fluorine, polyester, polycarbonate, polyethylene terephthalate, and the like used for other general optical members can be used.

Further, as long as it has a light transmitting property to the exposure light, it may be colored. The refractive index of these resins is approximately 1.5. Examples of the method for forming the light-transmitting conductive layer include a vacuum deposition method, an active reaction deposition method, various sputtering methods, and various C methods.
Using the VD method, indium tin oxide (IT
O), alumina, tin oxide, lead oxide, indium oxide, copper iodide, or a thin film of light transmissivity such as Au, Ag, Ni, Al or the like is used, or a dip coating method, a spray coating method, or the like is used. A conductive resin composed of the above-mentioned metal fine particles and a binder resin is used. Various organic photoconductor layers (OPC) can be used as the photoconductor layer.

Also, after adding a catalyst for synthesizing and polymerizing the plastic material monomer, pour it into a cylindrical mold, seal and fix with a side plate, rotate it at high speed, and heat it appropriately. This promotes uniform polymerization. After completion of the polymerization, the mixture is cooled, the obtained transparent resin substrate is removed from the mold, cut, and if necessary, a finishing step is performed to produce a transparent resin substrate for an image forming body of an image forming apparatus (centrifugal polymerization method). .

As the material of the transparent resin substrate of a transparent plastic molded by centrifugal polymerization, those obtained by polymerization using a methyl methacrylate monomer as described above are the best in terms of transparency, strength, precision, surface properties and the like. And other polyethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polybutyl acrylate, polystyrene, polyimide, polyester, polyvinyl chloride, and the like, or a copolymer thereof, and the like. In the centrifugal polymerization method, since the roundness is determined by the mold used for molding, a highly accurate substrate can be obtained. In addition, uneven thickness varies depending on rotation unevenness and viscosity during polymerization and heating conditions during polymerization.

The use of the plastic cylindrical transparent resin substrate produced by the above-described production method provides an image forming body having a uniform thickness and excellent cylindricality and circularity of the cylindrical substrate. You.

Charger 11Y, Charger 11M, Charger 11
C and a charger 11K are charging means used in an image forming process for each of yellow, magenta, cyan and black, and include a grid and a wire which are held at a predetermined potential with respect to the organic photoconductor layer of the image forming body 10. A charging action is performed by corona discharge by the electrodes, and a uniform potential is applied to the image forming body 10.

Exposure optical systems 12Y, 12M, 12C, 12
K denotes LEDs, FL, E arranged in the axial direction of the image forming body 10.
An image exposure means comprising a light emitting element such as L and PL and an image forming element such as a selfoc lens. Image signals of respective colors read by a separate image reading device are sequentially taken out of a memory, and an exposure optical system is provided. 12Y, exposure optical system 12
M, and are input as electrical signals to the exposure optical system 12C and the exposure optical system 12K, respectively. Note that the exposure optical system 12Y,
12M, 12C, 12K are LCD, LI as light emitting elements
It can also be composed of a combination of optical shutter members such as SA and PLZT and an imaging element such as a selfoc lens.

In order to stabilize the temperature in the image forming body 10 and prevent the temperature from rising due to the heat generated by the exposure optical systems 12Y to 12K, a material having good heat conductivity is used for the support member 20. In the case of high temperature, a heater is used to radiate heat to the outside through a heat pipe.

The developing units 13Y, 13M, 13C, and 13K are developing means for containing yellow, magenta, cyan, and black developers, respectively, with a predetermined gap from the peripheral surface of the image forming body 10 in the same direction. And a developing sleeve that rotates. Each of the developing devices 13Y, 13M, 13C, and 13K includes a pressing device (not shown), and presses the abutting member at the shaft end of the developing sleeve outside the image forming area on the peripheral surface of the image forming body 10, A fixed amount (0.2 mm to 1.0 mm) of gap amount is set between the developing sleeve and the peripheral surface of the image forming body 10.

Each of the developing units 13Y, 13M, 13C and 13
K denotes charging by the chargers 11Y, 11M, 11C, and 11K, and exposure optical systems 12Y, 12M, 12C, and 12K.
The reverse development of the electrostatic latent image formed on the image forming body 10 by the image exposure by the non-contact phenomenon method under the application of the developing bias voltage.

The intermediate transfer belt 14 has a thickness of 0.5 to 2.0.
mm, a semiconductive substrate of silicon rubber or urethane rubber having a resistance of 10 ⁸ to 10 ¹² Ω · cm, and a toner filming prevention layer of 10 ¹⁰ to 10 ^{16 on} the outside of the rubber substrate. Ω · cm resistance, thickness 5
It has a two-layer structure with a 50 μm fluorine coating. This layer also preferably has a similar semiconductivity. Instead of the rubber belt substrate, semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate or the like having a thickness of 0.1 to 0.5 mm can be used. Intermediate transfer belt 14 has rollers 14A, 14B, 14C and 14D
And is conveyed while circulating clockwise in synchronization with the peripheral speed of the image forming body 10 by the power transmitted to the roller 14D.

The intermediate transfer belt 14 contacts the belt surface between the rollers 14A and 14B with the peripheral surface of the image forming body 10,
On the other hand, the outer peripheral belt surface of the roller 14C is in contact with a transfer roller 15 as a transfer member, and a transfer area of a toner image is formed at each contact point.

The intermediate transfer belt 14 is provided with the above-described structure, so that the color toner image adhered to the peripheral surface of the image forming body 10 is firstly contacted with the toner to the roller 14B at the contact point with the intermediate transfer belt 14. The transfer is sequentially performed on the peripheral surface side of the intermediate transfer belt 14 by application of a bias voltage having an opposite polarity. That is, the color toner image on the image forming body 10 is conveyed to the transfer area without scattering the toner by the guidance of the grounded roller 14A, and the color toner image on the image forming body 10 is applied to the roller 14B with a bias voltage of 1 to 2 kV. The transfer is efficiently performed on the intermediate transfer belt 14 side by the application.

Here, the KNC correction in the internal exposure system will be described.

FIG. 5 is a graph showing the KNC correction by the internal exposure method.

The graph shows the photosensitive characteristics of the image forming body 10, the vertical axis of the graph shows the surface potential of the image forming body 10, and the horizontal axis of the graph shows the exposure.

The curve a shows the photosensitive characteristic when the toner image is not carried on the surface of the image forming body 10, and E _1/2 is the exposure amount required to attenuate the initial charging potential V ₀ to half. This is called half-exposure dose. Exposure E _c is the exposure amount for obtaining a first color having the maximum image density, the exposure amount E
_a is the exposure amount of the first color for obtaining the secondary color having the maximum image density. The image forming body 10 is charged and the image forming body 1
0, a color image forming method for forming a toner image by superposing a toner image by repeating image reversal and reversal development,
The exposure amount when forming the secondary color having the maximum density is substantially equal between the first color and the second color, and the exposure amount of the secondary color is smaller than the exposure amount of the primary color, thereby obtaining the maximum image density. , The amount of adhesion of the first and second colors can be the same. Exposure E _c in this embodiment are larger than twice the half decay exposure E _1/2. Usually, this value is preferably 2-3 times. Exposure E _a is described with reference to FIG. 5, E _a for obtaining a secondary color having the maximum image density, to the first color and the toner adhesion amount of the second color after approximately the same, the exposure It is weaker than the quantity E _c. A color image forming method in which the image forming body 10 is charged, the image is exposed from the back surface of the image forming body 10, and reversal development is repeated to form a superimposed toner image to form a secondary color having a maximum density. The exposure amount of the first color is set to be substantially equal between the first color and the second color, smaller than the exposure amount for forming the primary color having the maximum density, and the half-exposure amount E ₁ of the image forming body 10 is reduced. _{/ 2} or more and twice or less.

A curve c shows the photosensitive characteristic in a state where the toner layer is carried on the image forming body 10 in order to obtain a secondary color. The curve b is substantially the same as the curve a and has a slightly delayed attenuation because the influence of the light shielding property of the toner is removed because the internal exposure method is adopted. For this reason, in the region where the exposure amount is small, that is, in the region where the toner adhesion of the second color is small, the exposure amounts of the first color and the second color may be set to be approximately the same or slightly higher. On the other hand, it can be seen that as the exposure amount increases, the shift of the light attenuation curve increases, and the influence of the residual potential increases due to the potential of the previously formed toner layer. Accordingly, for example, the exposure amount of the first color image exposure and the exposure amount of the second color image exposure for obtaining a secondary color having a low image density are substantially the same, but the secondary color having the maximum image density is obtained. The exposure amount of the second color is corrected more strongly than the low image density portion. When forming the secondary color having the maximum image density from this that, first exposure amount of the second color to an exposure amount E _a Ogle E _b2 are required large correction than that of the low density portion, preferably 5 to It is strongly corrected in the range of 50%. Thereby, as shown in the graph, the latent image potential becomes 1
This can be the same as the color, so that the amount of the first color toner layer for obtaining the secondary color and the amount of the second and subsequent color toner layers can be the same.

Further, depending on the toner layer potential and the edge effect, 1
The second color has a maximum exposure of 5 to 50 with respect to the first color in the image exposure amount of the secondary color having the maximum density so that the secondary color is guaranteed even under the influence of the toner image potential of the color and the latent image potential of the second color. %
Make many corrections. Preferably, in the image exposure amount of the secondary color having the maximum density, the solid portion of the second color is 5 to 3 with respect to the first color.
It is preferable that the correction is performed by 0% more and that the isolated point is corrected by 10% to 50%. For a low density, the above correction amount is small.

The image forming body 10 is charged, and the image forming body 10 is charged.
In a color image forming method in which a toner image is exposed from the back surface and a toner image is formed by repeating reversal development, the exposure amount when forming a secondary color having the maximum density is substantially equal for the first color and the second color. In addition, the exposure amount of the secondary color is smaller than the exposure amount of the primary color.

[0067] exposure of the second color image exposure for obtaining the exposure amount E _a and secondary colors of the image exposure of the first color to obtain a secondary color E _b2 is half exposed in half-life exposure E _1/2 or more It is set to less than twice the amount E _1/2 . It is difficult to obtain a sufficient image density at the exposure amount is less than half decay exposure E _1/2, also equal to the adhesion amount of a plurality of colors the toner layer exceeds twice the half-decay exposure E _1/2 This is because it is difficult to control.

[0068] Also, since the exposure amount correction is a back exposure, secondary colors of an exposure amount E _a, it is preferably set smaller than at least the primary colors of an exposure amount E _c between E _b2. The image exposure amounts of the first and second colors of the secondary color having the maximum density are set to be weaker than the image exposure amounts of the primary colors having the maximum density.

When the image density of the secondary color is low, the correction amount of the second color is reduced because the difference between the potential characteristics of the first color and the potential of the second color is small as shown in FIG. That is, it is preferable to increase the correction amount of the second color as the image density increases. This correction is preferably increased as the image density of the first color increases.

Next, a color image forming process in the color image forming apparatus of the present embodiment will be described with reference to FIG.

FIG. 6 is a schematic view showing a KNC process of the internal exposure system.

FIG. 6A is a schematic diagram showing initial charging, FIG. 6B is a schematic diagram showing an exposure process for forming a latent image of the first color, and FIG. FIG. 6D is a schematic diagram showing a state after the development process of the first color, FIG. 6D is a schematic view showing a surface potential of the image forming body 10 after the second charging process, and FIG. FIG. 6F is a schematic diagram illustrating an exposure process for forming a second color latent image, and FIG. 6F is a schematic diagram illustrating a state after the second color development process.

The KNC process in the present embodiment is
After the image forming body 10 is uniformly charged, the multi-level digital image density data from a computer or a scanner is D / A converted to a pulse width modulated spot light based on a modulation signal obtained on the image forming body 10 to form a spot light on the image forming body 10. The method is based on a process of forming a dot-shaped electrostatic latent image and reversal-developing the electrostatic latent image with toner to form a dot-shaped toner image. The charging, exposure, and reversal development steps, which are the basic steps, are repeatedly performed to form a color toner image on the image forming body 10 in a superimposed manner. After transferring the color toner image onto the recording paper, the recording paper is transferred to the image forming body. Separated from 10 and fixed to obtain a color image.

In an image reading apparatus separate from this apparatus, image data obtained by reading an original image by an image pickup device or image data edited by a computer is processed, and each color of Y, M, C and K is processed. It is once stored and stored in the memory as another image signal. At the start of image recording, the image forming body driving motor is started to rotate the image forming body 10 clockwise, and at the same time, the application of a potential to the image forming body 10 is started by the charging action of the charger 11Y (FIG. 6A )reference).

In the exposure optical system 12Y, a spot light modulated by yellow data (for example, 8-bit digital image density data) is emitted. In FIG. 6 (b), E _c, is shown an exposure amount for obtaining a first color having the maximum image density, E _a is the exposure of the first color to obtain a secondary color having the maximum image density The amount is indicated. E
Since _a is weaker than E _c, it can be seen that the latent image potential is high. Of course, intermediate density these E _a, and has a smaller amount of exposure than E _c.

The latent image shown in FIG. 6B is applied with a developing bias voltage obtained by applying a direct current and an alternating current to the developing sleeve in the developing device 13Y, and the jumping development by the one-component or two-component developer contained in the developing device is performed. Then, non-contact reversal development is performed on the image forming body 10 that grounds the transparent conductive layer, and a yellow toner image is formed according to the rotation of the image forming body 10. From FIG. 6C, it can be seen that toner according to the potential difference between the latent image potential and the developing bias is attached.

FIG. 6D is a schematic diagram showing the surface potential of the image forming body after the second charging process. It can be seen that the charging potential is uniform regardless of the presence of the toner.

Next, spot light modulated by magenta data (8-bit digital density data) is irradiated onto the image forming body 10 to form an electrostatic latent image. FIG.
In (e), E _C indicates an exposure amount for obtaining a primary color having a maximum image density, and E _b2 indicates an exposure amount of a second color for obtaining a secondary color having a maximum image density. Is shown. The electrostatic latent image shown in FIG.
, A magenta toner image is sequentially superimposed on the yellow toner image. As shown in FIG. 6F, it can be seen that toner according to the potential difference between the latent image potential and the developing bias is attached.
That is, the adhesion amount of the toner layer of the first color for obtaining the secondary color and the adhesion amount of the toner layers of the second and subsequent colors are made uniform.

The charger 11C and the exposure optical system 12C are processed in the same process as described with reference to FIGS. 6 (d) to 6 (f).
The developing unit 13C sequentially develops the toner image to form a third toner image (cyan toner image), and a three-color toner image sequentially stacked on the image forming body 10 is formed.

Finally, a black (K) toner image corresponding to the fourth color signal is sequentially superimposed and formed by the charger 11K, the exposure optical system 12K, and the developing device 13K, and within one rotation of the image forming body 10. A color toner image is formed on the peripheral surface. The toner image for each color is an overlap of three or four colors depending on the image.

On the other hand, the recording paper is carried out by the operation of the paper feed roller 17 of the paper feed cassette (not shown) and fed to the timing roller 18, and is synchronized with the transport of the color toner image on the intermediate transfer belt 14. The paper is fed to the transfer area of the transfer roller 15.

The transfer roller 15 is rotated counterclockwise in synchronization with the peripheral speed of the intermediate transfer belt 14, and the fed recording paper is moved between the transfer roller 15 and the above-mentioned grounded roller 14C. In the transfer area formed by the nip portion, the color toner image is closely adhered to the color toner image on the intermediate transfer belt 14, and the color toner image is sequentially transferred onto the recording paper by applying a bias voltage having a polarity opposite to that of the toner of 1 to 2 kV to the transfer roller 15. .

The recording paper to which the color toner image has been transferred is neutralized, conveyed to the fixing device 91 via the conveyance plate 19, and
After being nipped and transported between the heat roller 91A and the pressure roller 91B and heated, the toner is fused and fixed, and then discharged to the outside of the apparatus via the paper discharge roller 92.

A cleaning device 16 and an intermediate transfer belt cleaning device 18 are installed on the image forming body 10 and the intermediate transfer belt 14, respectively, and the blades of the cleaning devices 16 and 18 are constantly pressed to remove the remaining adhered toner. The surrounding surface is always kept clean.

The above-described exposure optical systems 12Y, 12M, 12
Image exposure of the photosensitive layer of the image forming body 10 by C and 12K is performed from the inside of the image forming body 10 through the above-mentioned transparent substrate. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without transmitting the previously formed toner image, and is equivalent to the image corresponding to the first color signal. Can be formed.

As described above, the color image forming method according to the present embodiment employs the exposure optical systems 12Y, 12M, 12M.
C and 12K are arranged in the image forming body 10, and color reproducibility can be improved by color correction suitable for a KNC process of performing image exposure from the inside using a photosensitive body of a transparent base.

(Embodiment 2) Next, an embodiment in which the present invention is applied to a binary recording printer will be described.

In the binary recording, the recording dots are Y,
Color recording is performed in seven colors including M and C, and secondary colors B, G and R, and black.

When red (R) is reproduced by the color toner superimposition method, it is necessary to adjust the toner adhesion amounts of the toner and magenta in the same manner. A desired color image is obtained by adjusting.

Further, in order to improve the image quality, it is effective to perform the exposure of the second color in consideration of the influence of the toner layer of the first color when charging and image-exposing the color toner on the first color.

The color image forming apparatus according to the present embodiment
A color image is formed by sequentially performing charging, image exposure, and development of each color within one rotation of one image forming body 10, and an exposure optical system is arranged in the image forming body, and a transparent base photoconductor is used. By using the KNC process in which image exposure is performed from the inside, it is possible to eliminate the influence of the light blocking of the previous toner image and the spread of the beam diameter resulting from the light scattering by the toner image. it can.

Specifically, unlike the external exposure method, the internal exposure method is a color correction that does not include correction of light absorption and light scattering in a low density portion and corrects the toner layer potential in a high density portion. is there. As a result, the correction associated with the KNC process is also changed from the external exposure method, but the degree is reduced, so that more stable color reproduction can be performed.

The color image forming apparatus according to the present embodiment has the same mechanical configuration as that described with reference to FIGS. 1 and 2, and a detailed description thereof will be omitted.

On the other hand, the color image forming apparatus according to the present embodiment has a plurality of exposure optical systems 12Y, 12M, 12C,
Since the image is formed and transferred collectively within one rotation using 12K, if the exposure optical systems 12Y, 12M, 12C, and 12K used for each color are different, the exposure optical systems 12Y, 12M, 12C, 12K tilt, bend,
A color shift or bleeding occurs due to a shift in the mounting position or the like. Color shifts and bleeding are easily visible (0.03 m
m), which poses a practical problem.

FIG. 7 shows a scanning circuit 30 according to the present embodiment.
FIG.

The scanning circuit 300 divides the LED array into a plurality of blocks, and adjusts the exposure timing of each block to the timing of the transfer of the normal image data and the timing of the image exposure from the upstream side in the main scanning direction. By controlling according to the direction and direction, by correcting the inclination and bending of the attached LED array and controlling the light emission,
The inclination and the bend of the LED array in the main scanning line are raster-scanned so as not to appear as the inclination and the bend of the image as they are. The distribution circuit 310 and the LED blocks 321 to 32n in which the LEDs are integrated in an array state, m Delay circuits 331 to 33n having a capacity of K times the bit, digital switches 341 to 34n, m-bit shift registers 351 to 35n, and a counter 361 for adjusting a reference time for determining a light emission start timing of the LED block.
, A counter 362, and LED blocks 321 to 32n
Each LED block 32 with the block number of
A memory 363 for storing a delay time from the start of light emission of 1 to 32n, a comparator 364, a multiplexer 365,
m-bit parallel-in parallel-out type memory 37
1 to 37n.

Next, the operation of the scanning circuit 300 in this embodiment will be described with reference to FIGS.

FIG. 8 is a time chart showing the operation of the scanning circuit 300, and FIG. 9 is a schematic diagram showing the shift of the light image from the LED array from the previously desired dot line in the main scanning direction.

As shown in FIG. 9, each LED array is linearly arranged in a direction orthogonal to the moving direction of the image forming body 10 and is divided into, for example, 17 blocks. 321 each block from the left
322 to 32n.

FIG. 8A shows a recording start signal S ₁ , and FIG. 8B shows a signal indicating data write timing. At this timing, image data is input to the distribution circuit 310. LED blocks 321 to 32
Output according to the array of n. Here, the image data Q is serial data for one line in the main scanning direction. The data output from the distribution circuit 310 is
Digital switch 3 after being delayed by K times of m bits at 33n
It is output to the NC terminals 41-34n. Here, the value of K can be set individually by the delay circuits 331 to 33n. Thus, when the arrangement direction of the LED blocks is the main scanning direction and the rotation direction of the image forming body 10 is the sub-scanning direction, for example, to obtain a resolution of 5 lines / mm in the sub-scanning direction, The interval y is 200 μm. In FIG. 9, L
When the optical image on the photosensitive surface of the ED block is viewed in the sub-scanning direction from a predetermined dot line (shown by a dashed line) in the main scanning direction, and is represented by Δy (Δy _{1 to} Δy _n ), Δy / LED block 321-32n
Of K.

In this way, each LED block 321
If the value of K for every ~ 32n is determined, the LED block 321
The capacitances of the delay circuits 331 to 33n corresponding to .about.32n are determined. If K = 0, the distribution circuit 310 needs to be connected to the shift registers 351 to 35n without delay, and the digital switches 341 to 34n may be set to the NO terminal side.

Also, for the decimal part of Δy / y,
For example, W is obtained by an expression of Δy / 128 and written to the memory 363. Here, the number 128 on the right side denominator means that the line interval y in the sub-scanning direction is divided into 128 equal parts, and is determined by the counter 361.

The counter 361 counts the clock S ₄ and outputs a count value S ₆ shown in FIG. 8D for dividing the recording time _Sw into, for example, 128 equal parts. Count value S ₆ that such means reference time for determining the emission start time of the LED blocks.

[0104] Counter 362 is set to "1" for each count value S ₆ of the counter 361, counts the n times of the clock S ₇ of the clock S _4. This count value S ₈ is
FIG. 8E shows an LED block 321.
Means block numbers 1 to n of 32n to 22n.

The memory 363 stores a light emission start time adjustment amount W (W _{1 to} W _n ) corresponding to the count value S ₈ shown in FIG.
Is output. The light emission start time adjustment amount W is output in one round for each count value S ₅ shown in Figure 8 (c).

The comparator 364 outputs “1” when the light emission start time adjustment amount W matches the count value S ₅ which is the reference time. Konosai, memory 371~37n multiplexer 365 which decodes the count value S _8, corresponding to S ₈
Set the data in. The light image is formed on the photosensitive surface in a straight line by turning on or off the LED according to the data "1" or "0" stored in the memories 371 to 37n.

This shift amount can be easily measured at the time of assembling and adjusting the color image forming apparatus. By writing the shift amount into the memories 371 to 37n at the time of assembly,
Almost no mounting adjustment is required when assembling the LED array, and the adjustment time is greatly reduced.

As described above, if the linearity or the directionality is not uniform between the LED arrays provided, a deviation occurs in the superimposed toner images, so-called color deviation or color bleeding occurs in the formed image. To prevent color image quality from deteriorating.

FIG. 10 shows a seven-color multi-color image from four color toners in which the image formation order in this embodiment is yellow (Y), magenta (M), cyan (C) and black (BK). It shows the process of doing.

First color Second color Superimposed color YY + M → Red (R) Y + C → Green (G) M M + C → Blue (B) C BK Of the above seven colors, particularly in the case of a single color Although there is no problem, red (R), green (G), and blue (B), which are formed by superposing two color toners, have a problem with the amount of adhered toner.
It is necessary that the color toner adhesion amount and the second color toner adhesion amount be equal in order to obtain a proper color tone. A color image method for obtaining a multicolor image of seven colors by superposing two color toners in the present embodiment will be described with reference to FIG. 6 again.
FIG. 6A illustrates a state in which the peripheral surface of the image forming body 10 whose back surface is grounded by the charger is uniformly charged with the surface potential V ₀ . In FIG. 6B, after the image forming body 10 is uniformly charged, image exposure based on an image signal is performed by an exposure optical system, and the image exposed portion is erased to have a low potential. FIG.
(C) is a case where reversal development of the first color is performed and 1
This shows a state in which the toner of the color is adhered and development is performed. FIG. 6D shows a state where the second charging is performed by the charger. FIG. 6E shows a state in which the second image exposure is performed on the first color toner. In the portion where the second color image exposure has been performed, a latent image is formed with the toner layer potential of the toner itself due to the toner attached to the first color. FIG. 6F shows a case where reversal development of the second color is performed and 1
This shows a state where the second color toner is superimposed on the color toner. If the image exposure amounts of the first color and the second color are the same, the toner adhesion amount of the second color is smaller than the toner adhesion amount of the first color, and the balance between the first color and the second color is lost. The image exposure pulse width or power of the color is reduced. For red (R), green (G), and blue (B), the exposure power for forming the maximum image density of the primary color is 10
When it is set to 0, it is preferable in terms of balance to set the exposure power of the secondary color to the following value, for example. The exposure power 100 was set to 2.4 times the half-exposure light amount E1 _{/ 2} .

Y (50) + M (70) → RY (55) + C (70) → GM (60) + C (75) → B As described above, by reducing the pulse width or output power of the first color, The color balance is greatly improved. But still not enough. There are cases where the color balance is good and bad depending on the image pattern. For example, when the color balance is good for a halftone image, it is bad for a solid image, and when the color balance is good for a solid image, it is a halftone image. In the case of, it becomes defective. This tendency causes a difference in hue in the order of solid image, thin line (character), and isolated point. FIG. 11 illustrates the reason.

FIG. 11 is a schematic diagram showing factors that cause a difference in hue depending on an image pattern.

Although the image exposure is spot exposure, it actually has a spread, and therefore, even if the solid image and the halftone image are subjected to image exposure with the same power, a difference occurs in the charged potential on the image forming body 10. This causes a difference in hue depending on the image pattern, and this tendency appears regardless of the toner color. When the correction coefficient of the output power based on the image pattern is di ₁ (i ₁ = 1 to 5), for example, the following values are experimentally obtained as appropriate values.

Y (50) × di ₁ + M (70) → RY (55) × di ₁ + C (70) → GM (60) × di ₁ + C (75) → B

[0115]

[Table 1]

When the image pattern of one page is a single image pattern such as solid graphics or a 9-point character image, a print image of a good hue was obtained by the above setting conditions. Instead of a single image pattern, for example, there are many composite image patterns in which, for example, some graphics are solid and others are 9-point character images. Analyzing the image information for one page, performs a 10% correction as di ₁ for the determination portion and solid graphics, 15% as di ₁ for the determination portion 9 point character Is corrected to obtain the output power of the first color, it is possible to obtain a print image having a favorable hue even for the composite image pattern.

Since the image pattern of one page may be a more complex image pattern, the page is divided into blocks by image discrimination, and the following weighted average correction coefficient di ₂ ( By setting i ₂ = 1 to 5), significant hue disturbance in the page can be prevented.

Y (50) × di ₂ + M (70) → RY (55) × di ₂ + C (70) → GM (60) × di ₂ + C (75) → B

[0119]

[Table 2]

The weighted average correction coefficient d _i2 is calculated by the following equation (1).

[0121]

(Equation 1)

FIG. 12 is a circuit diagram of a color image forming apparatus for adjusting a first image exposure amount and a second image exposure amount of two colors in accordance with an image pattern when the above multi-color toner images are superimposed. It is shown.

In the present embodiment, the printer controller 5
03 (including the operation board 504) and the printer body 5
05.

The printer controller 503 decodes the image information (mainly a page description language) from the host computer 502, develops it into bitmap data, and sends it to the video interface 600 in the printer main body 505. The host 502, the operation board 504, and the video interface 60.
It works to send a command to 0. As a component, high-speed C
PU 506, plane memory 509 (a to c) for holding data of one page developed by bitmap, RAM
510, a dot condition determination circuit 511, and the like. The plane memories 509a, 509b, and 509c store dot data of each color of Y, M, and C, respectively. When the data of these three memories are all "1",
It means K (Y + M + C).

The printer main body 505 includes a CPU and a mechanical controller 516 (which controls charging, exposure, transfer, fixing, etc.)
A video interface (one-chip gate array) 600 for performing image data processing (for generating timing for reading and writing image data, processing image data, selecting command data, and the like); and a timing generation circuit 51
5, an optical control unit 517, and a printing unit 518.

The video interface 600 in charge of image signal processing includes a test pattern generator (TP) 551 and a selector 552 in addition to the input conversion circuit 512.
A single / multicolor detection circuit 554, an image pattern discrimination circuit 555, a hue correction circuit 556, a correction coefficient calculation circuit 557, a video control circuit 558, a smoothing processing control circuit (SO) 559, and a register group. RG1 to RG28 (5
14), OR circuit 560, and laser control circuit 562
And a control circuit 563 for controlling the operation of these circuits (outputting the control circuits CL1 to CLn to each circuit while transmitting and receiving information to and from the CPU and the mechanical controller 516).

The input conversion circuit 512 converts the video signal from the printer controller 503 into Y,
The signal is converted into a 4-bit signal of M, C, and BK. The test pattern generator (TP) 551 is a ROM for enabling output of a fixed test pattern without a controller. The selector 552 selectively passes the test pattern and the normal video input signal.

The video interface 600 has an input conversion circuit 512, and the plane memories 509a and 509
b, 509 c are converted into video (dot) data and input to the selector 552. FIG. 13 shows this video (dot) data input mechanism. In the selector 552, the single-color / multi-color detection circuit 554 uses the superimposed dot data (Y + M, Y + C, M +
The detection for C) is made. The image pattern discrimination circuit 555 is (1) a character as image pattern information. (1.1) Character size (printing point number).
(2) Graphics. (2.1) Solid, other (halftone) (3) The determination of (1) to (3) of the ratio of the above 1 and 2 occupying in one page is made. The correction coefficient calculation circuit 557 calculates the weighted average correction coefficient d0 by the above equation (1) based on the determination result of the image pattern determination circuit 555, and inputs it to the hue correction circuit 556. The hue correction circuit 556 includes a single color / multicolor detection circuit 554.
[Y (100), M (100), C (100), KB]
[Y (50) × di ₂ + M (70), Y (55) × di ₂
+ C (70), M (60) × di ₂ + C (75)].

This data is subjected to color correction and smoothing processing for each dot by the video control circuit 558 and the smoothing processing control circuit 559, and access is made to registers RG1 to RG28 which store printing conditions for the dot. Condition data is output from the accessed register (any one of RG1 to RG28), and the optical control unit 5
Reference numeral 17 controls the printing operation according to the data. The timing of all operations is performed in dot units with reference to an index signal IND (a signal indicating that the beam has come to a predetermined position near the front end of the image on the photoconductor) obtained from the printing unit 518. That is, the index signal IND is supplied to the timing generation circuit 515, and based on the index signal IND, a high-speed clock (5 MHZ) in units of dots whose phases are synchronized is generated.
03, etc., dot data is transferred in synchronization with this, signal processing is performed in real time, and printing is performed.

The optical controller 517 of the exposure optical system 12 has a pulse width modulation circuit 571, an LED on / off signal generator 572, and an LED driver 573. Also,
The printing unit 518 includes the image forming body 10 also illustrated in FIG. 1, the chargers 11Y, 11M, 11C, and 11K, and four colors (Y, M, and
C, BK) developing units 13Y, 13M, 13C, 13K. The rotation of the image forming body 10 is controlled by a stepping motor 583, and the number of rotations is detected by an encoder and sent to the CPU and the mechanical controller 516.

With this circuit configuration, for a color image in which two colors are superimposed, in the present embodiment, the image exposure amount of the first color is changed according to the image pattern.
The power output level is subjected to pulse width modulation by a pulse width modulation circuit 571. FIG. 14 shows a pulse width modulation circuit 57.
FIG. FIG. 14A is a circuit diagram, and FIG.
FIG. 4B is an operation explanatory diagram. The output level of the LED power is converted to an analog level by the D / A converter 571A, while the triangular wave output from the triangular wave generation circuit 571B as a comparison wave is compared with the write level by the comparison circuit 571C, and the resulting signal is pulsed. Output from the width modulation circuit 571 as a PWM signal.

In order to apply the present invention to multi-level recording, color correction is performed on image density data, that is, multi-level data of yellow, magenta, cyan, and black.
The degree of the color correction is small in the low-density part and large in the high-density part according to the potential characteristics shown in FIG.

Although the embodiment in which the pulse width is changed to change the image exposure amount has been described, the LED power for each dot may be changed instead of the pulse width. In the case where three or more colors are superimposed, exposure conditions for each color may be set in accordance with a pattern as in the case of two colors.

In addition to the automatic identification of the image pattern by the printer controller, the user may switch and adjust the image pattern by manual switching means such as "graphics", "character", and "solid image".

As the color image forming apparatus of the present embodiment, an image forming method in which a toner image is superimposed on the image forming body 10 using an intermediate transfer body has been described.
In addition to this method, the present embodiment is also applied to a color image forming apparatus that directly transfers a toner image to transfer paper.

(Embodiment 3) An embodiment in which the present invention is applied to a color image forming apparatus for reproducing a multi-valued image represented by a color copying machine will be described.

The color image forming apparatus according to the present embodiment has the same mechanical configuration as that described with reference to FIGS. 1 and 2, and a detailed description thereof will be omitted.

The adhesion state of the toner obtained by the KNC process when reproducing multi-valued gradations is not determined simply by exposure light modulated based on image density data, but involves the following phenomena.

The first phenomenon is a phenomenon that makes it difficult for the next toner to adhere to the solid portion of the toner image due to the potential of the toner layer. This is abbreviated as an average deviation due to the structure of the preceding image. The second phenomenon is the deformation of the latent image caused by the structure of the previously formed toner image, that is, the edge effect or the pseudo contour phenomenon that occurs at the edge of the isolated point, the isolated dotted line, the character, or the solid portion when the colors are superimposed. This is a halo effect that appears and has the same cause as the edge effect, but is a phenomenon unique to the KNC process due to superposition. A shift due to such a phenomenon is abbreviated as a local shift due to a structure between images. The third phenomenon is that a latent image is deformed due to the type of an image regardless of the structure of the previously formed toner image or a state in which a toner image has not yet been formed on the image forming body 10, that is, electrophotography. This is an edge effect phenomenon peculiar to the method, and is a shift amount between image data and a reproduced image, and is hereinafter abbreviated as a shift due to an image structure. The edge effect and the halo effect depend on the developing method and the characteristics of the photoreceptor, but may be as large as about 0.5 to 2 mm.

In the present embodiment, the edge effect and the halo effect are simplified as correction of the adjacent pixel level.

FIG. 30 is a schematic diagram showing a process for determining the toner adhesion state in the KNC process. In Figure 30, V ₀ is the initial charging potential of the image forming body 10 surface, V _s is the DC bias potential applied to the developing sleeve _{surface, V L1, V L21, V} L22 in the potential of the latent image portion is there. Not only the potential difference between V _s and V _L1 but also the 1
Due to the images (1) to (3), the formed electric field acts so as to attract the toner onto the image forming body 10 with deviation from the image exposure amount, that is, with deviation from the image data.

FIG. 30A shows the potential relationship immediately before the developing process using the first color toner. In such a development process, image exposure is performed by performing multi-level modulation on the multi-level image density data of each color in consideration of the overlapping state of the toner images, but here, the latent image potential shown in FIG. V _L1 . L _a is a latent image showing an isolated point or isoline. L _b shows the latent image corresponding to the solid having a large area.

[0143] Depending on the counter electrode effect, general occur at the edges of the extent of the latent image is strong electrostatic field there is a difference L _a and the latent image L _b is a development method (hereinafter, simply referred to as edge effect ), whereas since the electric field is weakened in the central portion of the latent image L _b, the solid portion of the latent image L _b has become difficult to adhere the toner, while a line or edge portion of the toner as compared with the solid portion center It is easy to adhere. This is the third phenomenon described above.

FIG. 30B is a sectional view showing a state where each latent image is visualized with the first color toner under the potential relationship shown in FIG.

[0145] P denotes the image forming body 10, T ₁ denotes a toner image formed an isolated point which is visualized by the first color toner. T ₂ are illustrates a toner image having a large area which is visualized in a first color toner. The toner image T ₂ where such is composed of an edge portion in and around the central portion.
The toner image T ₂ are, by the edge effect described above, and indicates that an uneven shape of a toner image with toner less adhere to the central portion than the edge portion (which is the third phenomenon). The edge effect not only acts when the latent image that becomes an isolated point or the latent image that becomes a thin line that is an isolated line is enhanced and visualized, but when the latent image becomes too small,
Conversely, it acts in a direction that makes visualization difficult.

FIG. 30 (c) shows a state in which the image exposure of the second color has been performed after recharging, that is, the potential relation immediately before the development process using the second color toner.

Here, the image exposures _La1 and _Lb1 are different from those of the first exposure.
_a1 is assumed to have exposure by shifting the position in the same position, only L _b1. In the figure, V _L1 and V _L21 , V _L22 have a mixed and disturbed potential distribution. V _L21, L _L22 is the potential of the latent image portion formed on the first color toner image is higher than the V _L1. Other symbols are omitted because they are described.

The reason why the potential distribution of L _b1 and the electric field shown in FIG. 30C are disturbed will be described below.

As described above, the development process for the second and subsequent colors is performed in a state where the previously visualized toner image is carried on the image forming body 10. Therefore, the already formed toner image fluctuates the latent image potential and the electric field of the second and subsequent colors. Stated in detail, T ₂ is in a state of adhering more toner to the edge portion as described above, it is fewer adhesion of the toner to the vicinity of the central portion. These toners have the effect of increasing the potential and hindering toner adhesion. These are the first phenomena described above.

FIG. 30D is a cross-sectional view showing the electric field formed on each latent image in the potential relationship shown in FIG. 30C.

The state of the electric field in the newly formed latent images L _a1 and L _b1 is indicated by arrows of electric lines of force.

[0152] The new latent image L _a1 is formed on the toner image T ₁ corresponding to the isolated point is visualized by the first color toner. It can be seen that such _a toner image T ₁ affects the electric field formed on the latent image La from the toner layer potential described above. Specifically by local electric field generated in the vicinity of the toner image T ₁ center, since the electric field of attaching toner is weakened,
It can be seen that the second color toner is hard to adhere. This is the second phenomenon described above. Although not shown, the second color toner easily adheres around the first color toner, and may adhere under some conditions.

[0153] latent image L _b1 newly formed, is formed by image exposure by shifting the position similar images over uneven toner image T _2. Thus it was formed a new latent image L _b1 field is considered part overlapping with the toner image T ₂ and its vicinity are distorted.

[0154] latent image L _b1 is latent L _b11 from differences adhesion amount of a toner image that is formed previously, the latent image L _b21, 3 of the latent image L _b31
Area. The latent image _Lb11 is formed on the image forming body 10 where the first color toner is not attached. Latent image L _b21 is obtained by forming the edge of the toner image T _2, is formed on the highest location of the toner adhesion amount of change. Latent image L _b31 in the central portion of the toner image T _2, those are of the edge due to the influence of the edge effect which is formed on the attachment portion of the thin toner. Latent image L _b11 , latent image L _b21 , latent image L
_b31 does not become the same potential from the toner potential even if the same amount of light is irradiated.

Further, it can be seen from the state of the lines of electric force that the halo effect is generated in the latent image _Lb21 . Here, the halo effect is a kind of the edge effect, and means that the second color toner is hard to adhere to the edge of the first color toner image, and the development occurs in which the second color toner easily adheres to the periphery. That is, the latent image _Lb21 is an area where the edge effect is generated by the first color toner. In other words, weak electric field for attaching toner from field of the latent image L _b31 formed in the central portion of the toner image T ₂ are at the edge, adhering the toner than the electric field formed in the location L _b11 absence of the toner image in the peripheral This indicates that the electric field has increased.

FIG. 30E is a cross-sectional view showing an overlapping state of the toner images visualized under the potential condition shown in FIG. 30C.

The toner image T formed by the second color toner
₃ is a slight amount of adhesion from the electric field condition shown in FIG. In other words, rather than secondary colors obtained by the adhesion amount of the toner image T ₁ and the toner image T ₃ in the same, which is intended to color-balance out the color of the first color toner is strong. The toner image T ₄ formed of the second color toner adheres to the latent image L _b11 ′ by the same amount as the first color toner due to the electric field described above, and the latent image L _{b21 forms the} toner image under the influence of the halo effect. a second color toner less adhere to the edge portion of the T _2, the second color toner often adheres to the peripheral portion, less adhered than near the center of the toner image T ₂ in the latent image L _b31, the edges You can see that it is slightly raised. Therefore, the portion where the edge portion of the toner image T ₂ and the toner image T ₄ was formed by superimposed is it is understood that the that collapse of the density and color balance out strong halo effect. This is the second phenomenon.

On the other hand, the solid portion formed between the solid portions of the toner image T ₂ and the toner image T ₄ has a lower density of the second color. This is the first phenomenon.

Next, the overall configuration of the image processing circuit employed in the image forming apparatus of the present embodiment will be described.

FIG. 15 is an overall block diagram of the image processing circuit according to the present embodiment.

The image processing circuit according to the present embodiment is a circuit constituting a driving circuit for a scanning optical system. As shown in FIG. 15, the image processing circuit includes a driving circuit for an image data processing circuit 100, a modulation signal generating circuit 200, and a scanning circuit 300. Become.

The schematic configuration of each circuit will be described below with reference to FIG.

The image data processing circuit 100 is a circuit for interpolating and outputting the edge portion of the font data. The image data processing circuit 100 receives the data from the input circuit 110 composed of a computer, the font data generation circuit 120, the font data storage circuit 130, and the interpolation data generation circuit 140. The character code signal, the size code signal, the position code signal, and the color code signal from the input circuit 110 are converted into the font data generation circuit 1
20. The font data generation circuit 120
An address signal is selected from the various input signals and sent to the font data storage circuit 130. The font data storage circuit 130 sends font data corresponding to one character corresponding to the address signal to the font data generation circuit 120. The font data generation circuit 120 sends the font data to the interpolation data generation circuit 140. The interpolation data generation circuit 140 interpolates jaggies and jumps in the image density data generated at the edge portion of the font data using the intermediate density, and sends the result to the linear masking circuit 154 as, for example, 8-bit image density data. Further, the linear masking circuit 154 changes the corresponding color to each of yellow (Y), magenta (M), cyan (C), and black (BK) according to the color code.
And sends it to the image density data storage circuit 210 composed of a page memory. In this way, a multi-valued font is multi-valued developed in a page memory for each color in a state where each color has the same shape and a different density ratio.

The image density data storage circuit 210 is a normal page memory (hereinafter simply referred to as a page memory 210), a RAM (random access memory) for storing in page units, and corresponds to at least one page (one screen). It has a capacity to store multi-valued image density data.
Also, if the device is used in a color printer,
This means that a page memory only for storing image density signals corresponding to a plurality of colors, for example, yellow, magenta, cyan, and black color components is provided.

The modulation signal generation circuit 200 includes the read circuit 2
20, latch circuit 230, image discriminating circuit 231, MTF
Correction circuit 232, γ correction circuit 233, reference wave phase determination circuit 240, select circuits 250A, 250B, 250
C, 250D, modulation circuits 260A, 260B, 260
C, 260D, a reference clock generation circuit 280, a triangular wave generation circuit 290, a delay circuit group 291, and a KNC correction circuit 1000 for correcting the adhesion state of the toner required for the KNC process.

Modulated signal generating circuit 200 of the present embodiment
Indicates that one pixel of interest in the image density data is m × n (width ×
Vertical) small pixels, the distribution of density data of adjacent pixels including the target pixel is replaced with the distribution of m × n small pixels in the one pixel, and the distribution of the target pixel multiplied by a constant P Based on the image density data of the small pixels obtained by distributing the data according to the distribution, the latent image by displacing the writing position of the dot of the nth row by displacing the phase of the reference wave of each row of the small pixel. Can be formed. Displacing the dot writing position is called recording position modulation. The process of converting the target pixel into image density data of small pixels divided into m × n is referred to as a resolution improvement process (RE process). High-density recording is performed by such RE processing.

[0167] reading circuit 220 reads the image density data of consecutive one scan line units continuously in synchronization with the reference clock DCK ₀ with an index signal as a trigger from the page memory 210, the reference wave phase determination circuit 240,
It is sent to the image discriminating circuit 231 and the KNC correction circuit 1000.

The latch circuit 230 is a circuit that latches the image density data for the time during which the process of the reference wave phase determination circuit 240 described later is executed.

The image discriminating circuit 231 discriminates whether the image is a character area or a halftone area, and determines the MTF.
Determine the degree of correction and gamma correction. The KNC correction circuit 1000 includes an MTF correction circuit 232 and a γ correction circuit 233.
15 are provided at the front stage in FIG. 15, but are preferably provided at the latter stage. In particular, when the correction value of the image density data is large, hue cannot be compensated.

Although not shown, it is also preferable that a magnification change circuit for changing the magnification of the output image and a color conversion circuit for changing the color tone and hue be similarly arranged before the KNC correction circuit.

If the image discriminating circuit 231 discriminates the character area of a character or a line drawing, the modulating circuit 26 converts the triangular wave selected by the reference wave phase determining circuit 240 for all color components.
0A, 260B, 260C, and 260D are output to select circuits 250A, 250B, 250C, 2
50D, the MTF correction circuit 232, the γ correction circuit 2
Reference numeral 33 denotes an inoperative state, and the modulation circuits 260A, 260B, 2
60C and 260D. As a result, clear characters and edge portions without color tone change are reproduced. On the other hand, when the image discriminating circuit 231 determines that the image is in the halftone area, it outputs a selection signal similar to that of the character area only for the achromatic component, that is, black data, and the reference wave phase determining circuit 240 selects the other color components. The selection signal that outputs only the reference triangular wave φ0 without outputting the selected triangular wave is output to the selection circuit 250A,
The signals are sent to 250B, 250C, and 250D to operate the MTF correction circuit 232 and the γ correction circuit 233. As a result, the image density data other than black read out from the readout circuit 220 is corrected by the MTF correction circuit 232 and the γ correction circuit 233, and then is transmitted to the modulation circuit 2 via the latch circuit 230.
60A, 260B, 260C and 260D.
As a result, an image without moiré or color skipping can be formed in the halftone region, while an effect of giving sharpness and closeness to the image by the black image is produced.

The MTF correction circuit 232 is composed of a Laplacian filter, has visual sharpness, and has a size of about 5 × 5 pixels. The value of this filter is determined experimentally from the development characteristics.

The modulation circuits 260A, 260B, 260C,
260D is a reference wave phase determination circuit 2 as shown in FIG.
The latch circuit 2 is operated by the triangular wave which is the reference wave selected at 40.
The signal of the image density data input through 30 is modulated to generate a pulse width-modulated signal, which is sent to the scanning circuit 300.

The description of the scanning circuit 300 is omitted because it has been described above.

On the other hand, the reference clock generation circuit 280 is a pulse generation circuit, generates a pulse signal having the same repetition cycle as the pixel clock, and reads out the readout circuit 220, the triangular wave generation circuit 290, the delay circuit group 291, the modulation circuits 260A and 260A.
Output to 60B, 260C, 260D. For convenience the clock referred to as a reference clock DCK _0.

The triangular wave generation circuit 290 has a reference clock DC.
Based on K ₀ , waveform shaping of a reference triangular wave φ0 which is a reference wave having the same cycle as the pixel clock is performed. Also, delay circuit group 2
Reference numeral 91 denotes a plurality of clocks D having a phase difference at regular intervals (in this example, 1/6 cycle) with respect to the reference clock DCK _0.
CK1～DCK ₄ produced on the basis of this, the triangular wave is a reference wave having different phases .phi.1 to .phi.4 (triangular wave delayed triangular wave φ1,2 / 6 cycle delay 1/6 cycle here Fai2,1 /
Triangular wave φ advanced 6 cycles, triangular wave φ advanced 2/6 cycles
4) is output.

Select circuits 250A, 250B, 250
C and 250D have input sections for triangular waves φ1 to φ4 whose phases are shifted from the reference triangular wave φ0, and select one of the triangular waves according to a selection signal from a reference wave phase determination circuit 240 to be described later to modulate the modulation circuit. 260A, 260B, 260C, 2
It sends out to the input terminal T of 60D. The above is the schematic configuration of the image processing circuit according to the present embodiment.

Hereinafter, each part of the image processing circuit according to the present embodiment will be described in detail in order.

(First Embodiment) First, the KNC correction circuit 1
15 to 19 and FIG.
2. Description will be given with reference to FIG.

FIGS. 16 and 17 are block diagrams each showing a specific main configuration of the KNC correction circuit 1000 shown in FIG.

The KNC correction circuit 1000 has a function of correcting the adhesion state of the toner for each color required for the KNC process from the image density data and the image density distribution data of each color. The image exposure is intensity and pulse width modulated according to the image density and image density distribution of each color, and the modulation changed according to the overlapping state of the toner images is the exposure intensity of the preceding image exposure and the subsequent image exposure when overlapping. And the exposure time are both changed. KNC correction circuit 10
00, an input 16 and Y ₁ data D ₁ i.e. each color multi-valued image density data obtained by the linear masking as shown in FIG. 17, M ₁ data, C ₁ data, the K ₁ data, corrected recorded image data D ₄ words each color to Y ₄ data, M ₄ data, C ₄ data, consists of three correction circuits 1300,1400,1500 for outputting K ₄ data.

It is to be noted that these correction circuits can be collectively formed as one circuit having the same function.
In this case, it is preferable that the correction algorithm can be operated by simplifying the calculation, the look-up table method is used, or the correction algorithm is used in combination. The first correction circuit 1300 performs correction corresponding to the image density of each color (corresponding to correction of an average shift corresponding to the first development). The second correction circuit 1400 corrects a structural shift between images corresponding to the second phenomenon. The third correction circuit 1500 corrects a shift between the image data corresponding to the third phenomenon and the reproduced image. Assuming that the recorded image data D ₄ subjected to the KNC correction is Y ₄ , M ₄ , C ₄ and K ₄ , the recorded image data is separated and output as shown in FIGS. Configuration. And the recorded image density data D ₄ is MT
The data is sent to the F correction circuit 232 and processed.

In the present embodiment, the exposure optical system is arranged in the image forming body, and the KNC process of exposing the image from inside using the image forming body of the transparent substrate is used. It is possible to eliminate the influence of the spread of the beam diameter resulting from light shielding and light scattering caused by the toner image. Further, by performing correction for the first and second phenomena, the overlay can be improved. Thereby, stable color reproduction can be performed by the above-described correction accompanying the KNC process.

More specifically, unlike the external exposure method, the correction according to the potential characteristic of the image forming body 10 shown in FIG. 5, that is, does not include the correction of light absorption and light scattering, but incorporates the toner layer potential. I do. For this reason, the correction at the time of masking in the first term and the correction f due to the structure of the toner image in the second term can be simplified, and the correction coefficient can use the approximate expression 1 + α.

In the correction of the present embodiment, the expression of the product of the first to third corrections has been shown as an example for convenience of calculation. However, in the backside exposure, the degree of correction is reduced. The approximation as a product of the correction of 3 and the simplified expression (1) become effective.

The filter 1100 is composed of a Laplacian filter and detects the structure of the toner image. Specifically, the filter 1100 is used to determine the second correction coefficient and the third correction coefficient from the calculated values. . The second correction coefficient is the second
The third correction coefficient is a parameter for determining the correction amount in the correction circuit 1400 of FIG.
This is a parameter for determining the correction amount at 00. The filter 1100 corresponds to the density change of each color.
That is, the Laplacian values ΔY, ΔM, ΔC, and ΔK are obtained for the target pixel according to the edge effect for each color, and a correction parameter that is a correction amount for each pixel of each color is determined from these values.
The image density data is corrected based on the correction parameters. The size of the filter for obtaining the Laplacian value is 600 if an edge effect of about 1 mm is generated.
In the case of dpi, the size is about 20 × 20 pixels.
Since the edge effect varies depending on the developing method and the photoreceptor, the above-described coefficient is experimentally determined.

The delay circuit 1200 includes a first correction circuit 130
0, delay by the processing time of the second correction circuit 1400.

Before describing the structure of the three correction circuits, the operation in the KNC correction by the internal exposure method will be described.

FIG. 22 is a schematic diagram showing the operation of the KNC correction circuit 1000 in the color image forming process.

FIG. 22A shows the potential relationship during the developing process using the first color toner.

The first correction circuit 1300 for performing average deviation correction between images modifies image data so as to perform modulation based on the image density of each color in consideration of the overlapping state of toner images. Therefore, a position also to form a latent image L _a and the latent image L _b2 which are to form the latent image by the exposure process by the next color toner, a latent image potential of forming this round of exposure process V
_It can be seen that _L2 is set higher than the latent image potential _VL1 of the latent image _Lb1 where no other color toner is superimposed. The third correction circuit 1500 corrects the deviation between the image data and the reproduced image. Thus, also, it can be seen that exposure to the edge effect is prevented is controlled potential is set high in the latent image L _b1 and the latent image L _b2.

FIG. 22B is a cross-sectional view of a state in which each latent image is visualized with the first color toner under the potential relationship shown in FIG.

The toner images T ₁ , T ₂ and T ₃ are shown in FIG.
As shown in the figure, the edge effect is removed by the third correction value to make the surface flat. Moreover, the toner images T ₁ and T ₃ are formed thinner than the toner image T ₂ by the first correction value.

FIG. 22C shows the potential relationship during the developing process using the second color toner.

The first correction circuit 1300 for correcting the average deviation between images corrects image data so as to perform modulation based on the image density of each color and the overlapping state of toner images based on the image density. Therefore, the latent image _Lb4 is set to V _L2 which is the same potential as the previous image. Since the latent image L _a1 , the latent image L _b6, and the edge position of the latent image L _b5 form a latent image even in the exposure process using the next color toner, strong image exposure is performed to lower the potential. . As a result, the potential drops by the same degree. This correction has been described with reference to FIGS. When the exposure amount is small, the light attenuation curves of the first color and the second color of the image forming body 10 are similar, but it is preferable to increase the correction amount of the second color as the exposure amount increases.

The second correction circuit 1400 corrects a shift due to a structure between images. Such correction is performed by the edge effect of the previous toner image as indicated by the arrow, even if a latent image is formed from above, assuming that the previous toner image is reproduced according to the image data. The image is deformed (shown in FIG. 30 (d)). Thus, in order to prevent edge effects in the latent image L _a1 and the latent image L _b5, the strong image exposure on the weak image exposure around the L _a1 L _a1, latent image L
Correction was made such that the edge of _b5 was strongly exposed and the periphery of _Lb5 was weakly exposed. This is the correction of L _a1 and L _b5 .

The third correction circuit 1500 corrects the deviation between the image data and the reproduced image, and corrects the image density data to form toner images T _{1 to} T ₆ having no edge effect. This is the same as described above with reference to FIG.

FIG. 22D shows electric fields formed on the latent images L _{b4 to} L _b6 by lines of electric force. It can be seen that the effects of the halo effect and the edge effect have all been removed.

FIG. 22E is a cross-sectional view showing a state where each latent image is visualized with the second color toner under the potential relationship shown in FIG. 22C. Each of the toner images T _{4 to} T ₆ is flattened by removing the edge effect and the halo effect. Moreover, the toner image T ₄ through T ₇ are are formed thinner than T ₁ and T ₃ in the same manner as in the toner image T _2, T _6. In this way, it is shown that the color balance of the secondary color is corrected as compared with FIG.

Subsequently, the following three correction circuits 1300 to 1
The configuration example of 500 will be described more specifically.

The first correction circuit 1300 corrects average deviation between images, and includes the following.

As a first example of the first correction circuit 1300, a look-up table method for executing a color correction process by a direct conversion method (hereinafter, simply referred to as a direct conversion method).
Or a look-up table method (abbreviated as a three-dimensional interpolation method) for executing a color correction process by a three-dimensional interpolation method.

In the color correction processing by the direct conversion method, generally, the color correction processing is regarded as a coordinate conversion from a simple color separation signal space to a color correction signal space, and color correction signal data corresponding to each color separation signal coordinate is converted. It is stored in a memory table, and the coordinate conversion is directly performed by referring to this table.

The three-dimensional interpolation method will be described with reference to FIG.

FIG. 18 is a schematic diagram showing the color correction processing by the three-dimensional interpolation method. FIG. 18A is a schematic diagram showing the division of the color separation signal space in the color correction processing by the three-dimensional interpolation method, and FIG. 18B is a schematic diagram showing the eight-point interpolation method. (c) is a schematic diagram showing a method of dividing into tetrahedrons.

In the color correction processing by the three-dimensional interpolation method, the correspondence table between the color separation signal coordinates and the color correction signal data is limited to a limited number of colors, and the input of coordinates not in the table uses nearby known data. Lookup table method for three-dimensional interpolation and color correction by a neural network.

In the three-dimensional interpolation method, as shown in FIG. 18A, a color separation signal space is separated into a plurality of unit cubes, and optimal color correction signal data at the vertex coordinates of each unit cube is obtained in advance. As shown in FIG. 18 (b), a calculation method of interpolating from data of eight vertices of a unit cube belonging thereto is general. Thereby, the memory capacity which is a problem in the direct conversion method can be reduced. Also, the three-dimensional interpolation method is
As shown in FIG. 18C, the unit cube is further divided into a plurality of 4
There is also a method of dividing into tetrahedrons and interpolating from the data of the four vertices of the tetrahedron to which they belong. According to such a method, the interpolation operation can be in the form of adding a constant term to the linear masking method.
Hardware load can be reduced by reducing the number of adders and multipliers.

As a second example of the first correction circuit 1300, a first correction circuit 1300 that performs average deviation correction between images
Will be described with reference to FIGS. 19 to 21.

FIG. 19 is a block diagram showing a second example of the first correction circuit 1300 shown in FIGS. 16 and 17, and FIG.
21 is a graph showing seven colors that can be color-separated by the first correction circuit 1300 based on the previous image, and FIG. 21 is a schematic diagram showing the processing operation of the color extraction circuit 1330.

First correction circuit 1300 shown in FIG.
Performs average deviation correction between images in the same manner as in the first example described above, and ₁ is set in accordance with an image represented by Y ₁ , M ₁ , C ₁ , and BK data subjected to normal masking.
Y ₂ , M ₂ , C ₂ , and K ₂ , which are separated into black K, primary colors, and secondary colors at the time of 00% UCR, then subjected to color correction of primary colors and secondary colors, and then mixed with black to correct them It outputs data, and comprises a lower color processing circuit 1310, an achromatic color correction circuit 1320, a color extraction circuit 1330, and a color addition circuit 1340.

The lower color processing circuit 1310 converts the Y ₁ , M ₁ , C ₁ , and B ₁ data after normal masking processing into 100% UCR
Sent to achromatic color correction circuit 1320 extracts a black component BK in value, and sends the Y _11, M _11, C ₁₁ data after UCR processing to the color extraction circuit 1330.

The color extraction circuit 1330 separates the Y ₁₁ , M ₁₁ , C ₁₁ data into primary colors Y, M, C and secondary colors B, G, R as shown in FIG. Blue, cyan,
After correcting green and yellow to match the reproduction color,
It is sent to the color addition circuit 1340. As shown in FIG.
The primary colors are the colors of the Y, M, and C color toners. The secondary color is a color obtained by adding the primary colors Y, M, and C, and B is G
And R are obtained. G is obtained by adding Y and C. R is obtained by adding Y and M. Gray is obtained by adding the primary colors Y, M, and C at the same ratio, and is separated by the lower color processing circuit 1310 by 100% UCR. Such correction is performed, for example, when the red color is Y and M
To reduce the data of Y ₂ when shifted color superposition, to increase the M ₂ data. As a result, the exposure amount is corrected, and the thickness of each color toner layer to be superimposed can be made the same as described with reference to FIG.

The color addition circuit 1340 selects the correction value so that the boundary of the hue indicated by the dotted line in FIG. 20, for example, red, magenta, blue, cyan, green, and yellow, matches the reproduced color, and selects the primary color Y _2. , M ₂ , C ₂ , and K ₂ data.

In the correction described in the first and second examples of the first correction circuit 1300, the toner layers overlap.
In other words, although the correction is performed in the solid area, the correction is performed for image structures such as green, peripheral portions, isolated points, and lines between the toner image formed earlier and the toner image formed later. Absent. Therefore, the second correction circuit 1400 is required as the correction based on the structure of the image.

If the function is expressed as a function f, the second correction circuit 1400 originally has the image density data Y, M,
F _Y (Y, M, C,
K), f _M (Y, M, C, K), f _C (Y, M, C,
K) and f _K (Y, M, C, K), which are generally expressed as functions. Since it is sufficient to consider only the influence of the previous toner image only, there is no difference due to the toner color. In a simplified manner, the development order is Y → M → C → K, and each f is f _Y = 1, f _M =
1 + α _Y , f _C = 1 + α _{Y + M} , f _K = 1 + α _{Y + M + C}

If the function of the third correction circuit 1500 is expressed as a function g, the image data Y, M, and
G _Y (Y, M, C, g) determined from the change in the concentration of C and K
K), g _M (Y, M, C, K), g _C (Y, M, C,
K) and g _K (Y, M, C, K). Since the influence of the previous toner image is not considered, there is no difference due to the color of the toner. When simplify this function, each g is the image data Y, M, C, and each color shift correction of K the reproduced image _{g Y = (1 + β Y} ), g M = (1 + β M), g C =
The function of the third correction circuit 1500 can be expressed as (1 + β _C ) and g _K = (1 + β _K ). Here, since there is no correction of interference between toner images, the correction coefficient 1 + β determined from the Laplacian value obtained from the image density data of each color is used.

Further, the first to third corrections D ₄ = D ₂ × f ×
Equation (1) is obtained by simplifying g.

Equation (1) Y ₄ = Y ₂ × 1 × (1 + β _Y ) M ₄ = M ₂ × (1 + α _Y ) × (1 + β _M ) C ₄ = C ₂ × (1 + α _{Y + M} ) × (1 + β _C K ₄ = K ₂ × (1 + α _{Y + M + C} ) × (1 + β _K ) In this embodiment, the recorded image data Y ₄ , M ₄ , C
₄ and K ₄ are distributed to intensity modulation data and pulse width data.

The above equation (1) shows the KNC correction when developing in the order of Y, M, C and K.
This is a formula in which the development order is limited to Y → M → C → K,
It is not limited to this. For example, K → C → M →
Y, K → Y → M → C, etc. In such a case, the correction coefficient is changed accordingly.

The first row of recorded image data Y ₂ , M ₂ , C ₂ ,
K ₂ is the image density data obtained by correcting the average deviation between the images first.

The second column is a correction term for correcting a shift due to the structure between the images. The shift due to the subsequent image is not corrected for simplification taking into account only the influence of the previous image. is there. Such a second term is originally f _Y (Y, M, C,
K), f _M (Y, M, C, K), f _C (Y, M, C,
K) and f _K (Y, M, C, K).

The third column is a correction item for correcting a shift between the image data and the reproduced image. α, f, and β are variables indicating the density distribution of each color toner, and are obtained by multiplying a Laplacian filter by a coefficient or by experimentally creating a correspondence table. These are the first to third rows, the first to third rows explained earlier.
This corresponds to the third correction.

Since the third correction circuit 1500 corrects the deviation between the image data and the reproduced image, the MTF correction circuit 23 is used instead of the correction circuit 1500.
2. This is a correction circuit that can include only the γ correction circuit 233.

In addition, it is also possible to correct image data by using the above equation as a look-up table system.

As a method of sharing the data transmitted from the KNC correction circuit 1000 to the modulation circuits 260A, 260B, 260C and 260D into the intensity modulation and the pulse width modulation, the first correction circuit 1300 to the third correction circuit 1500 Table 3 shows combinations of outputs. The first embodiment shown in Table 3 corresponds to the KNC correction circuit 10 shown in FIG.
00, and the second embodiment shown in Table 3 corresponds to the KNC correction circuit 1000 shown in FIG.

[0226]

[Table 3]

In Table 3, the data corresponding to the pulse width has the meaning of modulating the exposure width, that is, the area of the latent image.
In the data corresponding to the intensity modulation is the exposure intensity,
This has the meaning of modulating the latent image potential.

In Table 3, the first correction circuit 130
0 indicates the output data D _{2, that} is, Y ₂ , M ₂ , C ₂ , K _2, and indicates the corrected output data f _Y (Y, M, C, K), f from the second correction circuit 1400. _M (Y, M, C,
K), f _C (Y, M, C, K), f _K (Y, M, C, K)
Indicates correction output data g _Y (Y, M, C, K) from the third correction circuit 1500, and g _M (Y, M, C,
K), g _C (Y, M, C, K), g _K (Y, M, C, K)
Is shown.

The KNC correction circuit 1000 shown in FIG.
Data D ₂ corresponding to the pulse width by the combination shown in Table 3, that _{is, Y 2, M 2, C} 2, data corresponding to K ₂ and the intensity modulation _{f Y (Y, M, C} , K) × g Y (Y, M, C,
K), f _M (Y, M, C, K) × g _M (Y, M, C,
K), f _C (Y, M, C, K) × g _C (Y, M, C,
K), f _K (Y, M, C, K) × g _K (Y, M, C, K)
Modulation circuits 260A, 260B, 260C,
260D.

The KNC correction circuit 1000 shown in FIG.
Data D ₂ × f corresponding to the pulse widths in combinations shown in Table 3, ie, Y ₂ × f _Y (Y, M, C, K), M ₂ × f
_M (Y, M, C, K), C ₂ × f _C (Y, M, C, K),
Data corresponding to K ₂ × f _K (Y, M, C, K) and intensity modulation g _Y (Y, M, C, K), g _M (Y, M, C, K), g
_C (Y, M, C, K) and g _K (Y, M, C, K) are divided into modulation circuits 260A, 260B, 260C, 260D.
Will be sent to

[0231]

[Table 4]

Table 4 specifically shows Table 3 using the simplified equation (1). The KNC correction circuit 1000 converts the toner image based on the multi-valued image density data and the image density distribution of each color. The recording image data of each color is created so as to be superimposed. Then, the multi-valued recording image data subjected to the KNC correction is transmitted to the modulation circuits 260A, 260B, 260C, and 260D.
Sent to. D ₂ indicates the first column of the equation (1), and corresponds to Table 3 below. (1 + α) indicates the second column of the equation (1), and corresponds to Table 3. (1 + β) indicates the third column of the equation (1), and corresponds to Table 3 below. D ₂ , α, β
Has already been described, and its description is omitted.

FIG. 23 is a block diagram showing a modulation circuit according to the present embodiment.

The modulation circuits 260A, 260B, 260C,
260D has the same circuit configuration as shown in FIG.
D / A conversion circuit 261, comparator 262, differential amplifier 263, D / A conversion circuit 264, input of data corresponding to a pulse width and a reference triangle wave φ ₀ or a triangle wave whose phase is shifted by ６ cycle. and parts T, an input unit D of the data corresponding to the intensity modulation, the reference clock DCK have input CK of _0, Table 3 or Table 4 based on the data corresponding to the intensity modulation as shown in clock DCK0 D / A conversion is performed by the D / A conversion circuit 264 in synchronism with. On the other hand, the triangular wave input from the select circuits 250A, 250B, 250C, and 250D is used as a reference wave by the comparator 262.
And generates a uniform pulse width signal using a predetermined threshold value for cutting off the reference wave. That is, the threshold signal is applied to the negative input terminal of the comparator 262 and compared with the reference wave to obtain a pulse width modulation signal. Next, a pulse width modulated signal and data from the input section D are amplified by the differential amplifier 263 to obtain a pulse width signal whose intensity is modulated.

FIG. 24 is a block diagram showing a reference wave phase determining circuit according to the present embodiment.

The reference wave phase determination circuit 240 includes a one-line delay circuit 242, a one-clock delay circuit 243, and an arithmetic processing circuit 241 as shown in FIG. A delay of two line scanning time is given to the image density data of the first one scanning line of three scanning lines of the received image density data.
One line scanning time is delayed for the intermediate image data of one scan line (no delay is applied to the last image data of one scan line). Further, each image data is delayed by one clock delay circuit 243 by two reference clocks or one reference clock, and all image density data of pixels including the target pixel and adjacent to the target pixel are simultaneously processed by the arithmetic processing circuit 241. To send to. The arithmetic processing circuit 241 performs an operation of adding the density data of each small scanning line to obtain the center of gravity of the original density data in one pixel, and outputs different selection signals as follows depending on the position of the center of gravity. Select circuit 250A, 250B, 250C, 250D
Output to

Hereinafter, the modulation operation in the image processing circuit of this embodiment will be described in relation to the reference wave phase determination.

First, the operation of the reference wave phase determination circuit 240 will be described.

FIG. 25 is a diagram showing an example of the relationship between a triangular wave having a different phase and a target pixel. FIG. 26A is a plan view showing the target pixel as m5, and adjacent pixels including the target pixel m5 as m1 to m9 when the target pixel m5 is divided into 3 × 3. Is 3 ×
It is an enlarged view showing a case where each small part when divided into three small pixels is represented by s1 to s9. Here, it is assumed that m1 to m9 and s1 to s9 represent the concentration of that portion.

The arithmetic processing circuit 241 performs RE processing to obtain small pixel density data. The density data of such a small pixel is represented by s1, s2, s3,.
, A small scan line including s4, s5, s6,... And a small scan line including s7, s8, s9,. Three small scanning lines of these small pixels correspond to the original one pixel. The arithmetic processing circuit 241 performs an operation for calculating the center of gravity of the density data in the original one pixel of each small scanning line, and outputs different selection signals as follows from the output terminal O depending on the position of the center of gravity.
Output to 50A, 250B, 250C, 250D.

That is, the arithmetic processing circuit 241 adds the densities of s1, s2, and s3 (first small scanning line) of the pixel m5, and adds the densities of s4, s5, and s6 (second small scanning line) of the pixel m5. The densities are added, the densities of s7, s8, and s9 (third small scanning line) of the pixel m5 are added, and the center of gravity of the original pixel is detected from these added values. When the arithmetic processing circuit 241 detects that the center of gravity of the pixel m5 is in the vicinity of the second small scanning line, the reference triangular wave φ having no phase displacement shown in FIG.
Select ₀ and output. The arithmetic processing circuit 241 calculates the pixel m
When detecting that the center of gravity of 5 is near the boundary between the second small scanning line and the first small scanning line, the triangular wave φ1 whose phase is delayed by ６ cycle shown in FIG. 25 is selected and output. When the center of gravity of the pixel m5 is near the center of the first small scan line, the arithmetic processing circuit 241 selects and outputs the triangular wave φ2 whose phase is delayed by ／ cycle. The arithmetic processing circuit 241 includes:
When the center of gravity of the pixel m5 is near the boundary between the second small scan line and the third small scan line, the triangular wave φ ₃ whose phase is advanced by ６ cycle is selected and output. The arithmetic processing circuit 241 includes:
When the center of gravity of the pixel m5 is in the vicinity of the third small scanning line, a signal for selecting the triangular wave φ ₄ advanced by ／ cycle is sent from the output terminal O to the selection circuits 250A, 250B, 250C, 2
Output to 50D.

Next, the RE processing will be described with reference to FIG.

FIG. 27 shows the target pixel m5 divided into 3 × 3 pixels.
FIG. 2 is a schematic diagram showing an example when P = 0.5, and FIG.
7A is a schematic diagram illustrating an example of a density distribution of an adjacent pixel including the target pixel m5, and FIG. 27B is a schematic diagram illustrating a density distribution in the target pixel m5 calculated as P = 0.5. is there.

Here, taking the case of dividing the target pixel m5 into 3 × 3 small pixels as an example, the density of the small pixel si is determined by the following equation.

Si = (9 × m5 × P × mi / A) + (1−P) × m5 where i = 1, 2,..., 9 and P is a constant which can be called the intensity of RE processing. And a numerical value in the range of 0.1 to 0.9 is used. A is the sum of m1 to m9.

In the above equation, (9 × m5 × P × mi /
The term of (A) is obtained by multiplying the density of the target pixel m5 by P and allocating it according to the ratio of the density of the adjacent pixel.
The term of (P) × m5 is obtained by equally distributing the remaining density of the target pixel m5 to each of the small pixels, which means that the blur factor is taken into account.

Next, modulation circuits 260A, 260B, 260
The image exposure operation in C and 260D will be described with reference to FIGS.

As shown in FIG. 16, the image density data D ₂
The operation of modulation circuits 260A, 260B, 260C and 260D in the case where is included in data corresponding to the pulse width will be described with reference to FIG.

FIGS. 28A to 28F are time charts showing signals of respective parts of the modulation signal generating circuit when recording position modulation is performed.

In FIG. 28, (a) is Y ₂ , M ₂ , C ₂ , which is the image density data D ₂ transmitted based on the reference clock DCK ₀ using the index signal as a trigger from the shift correction circuit 1300 for the previous image. , K ₂ data is D / A
A part of the data converted into an analog value by the conversion circuit 261 is shown. A higher level indicates a lighter density, and a lower level indicates a higher density.

FIG. 28B shows select circuits 250A and 250A.
A triangular wave is sequentially selected from 50B, 250C, and 250D and is a selected reference wave including a delayed one.

FIG. 28 (c) shows an input signal of the comparator 262, which is shown in FIGS. 28 (a) and 28 (b).
Is the same as

FIG. 28D shows a reference signal generator 2 internally for converting the triangular wave shown in FIG. 28B into a pulse width signal.
6 shows a pulse width signal generated by generating a DC voltage generated by 61 and comparing the generated DC voltage with a comparator 262. This pulse width signal is applied to the differential amplifier 263
Is one of the input signals.

FIG. 28E shows correction data determined from the peripheral pixels of the target pixel. Data f × g or (1 + α) × (1+) corresponding to the intensity modulation shown in Table 3 or Table 4.
β), and such a signal becomes one input signal of the differential amplifier 263.

FIG. 28 (f) shows the state shown in FIG.
10E illustrates an intensity-modulated pulse width signal from the differential amplifier 263 that amplifies the difference between the two input signals illustrated in FIG. The modulated signal obtained in this manner is scanned by the scanning circuit 30.
0 to emit light from the LED array.

According to the modulation signal generation result, in the character area, the position of the small dot in the nth row in the target pixel is moved to a position along the line direction of the original character or line drawing from the density data of the original adjacent pixel. As a result of the position modulation, characters and images are clearly reproduced. Further, in the above-described recording position modulation, only the black component is performed in the halftone region to prevent a change in color tone, and the other color components are modulated by a triangular wave having no phase shift.

Further, by sequentially shifting the phase of the reference wave in the sub-scanning direction, it is possible to form a dot corresponding to a halftone dot having a screen angle. For example, the screen angle is 45 ° for the yellow component and 2 for the magenta component.
6.6 °, −26.6 ° for the cyan component, and 0 for the black component
° to improve the uniformity of color reproduction and prevent the occurrence of moiré fringes.

In particular, setting the black component to 0 ° has the advantage that the recording phase modulation means can be used without any change.

As shown in FIG. 17, modulation circuits 260A, 260B, 260C and 260D when image density data D ₂ and correction f are included in data corresponding to pulse width modulation.
Will be described with reference to FIG.

FIGS. 29A to 29F are time charts showing signals of respective parts of the modulation signal generating circuit when recording position modulation is performed.

In FIG. 29, (a) represents D ₂ × f, and is Y, which is image density data D ₂ transmitted from the shift correction circuit 1300 for the previous image based on the reference clock DCK ₀ using the index signal as a trigger. ₂ , M ₂ , C ₂ ,
D / A conversion circuit 261 after multiplying K ₂ data by f
Shows a part of the data converted into an analog value. A higher level indicates a lighter density, and a lower level indicates a higher density.

That is, the data corrected in accordance with the pulse modulation shown in Table 3 or Table 4, ie, data D ₂ × f or D ₂ × (1
+ Α), and as a result of correcting the deviation due to the previous image in D ₂ , this correction shows that the density change is large, and the corrected result indicates that the higher the level, the lower the density is recorded. The higher the level is, the higher the density is recorded, and this signal is one input signal of the comparator 262.

FIG. 29B shows select circuits 250A and 250A.
A triangular wave is sequentially selected from 50B, 250C, and 250D and is a selected reference wave including a delayed one.

FIG. 29 (c) shows the input signal of the comparator 262, the dashed line D ₂ × f is as shown in FIG. 29 (a), and the triangular wave shown by the solid line is as shown in FIG. 29 (c). Signal.

FIG. 29D shows an output signal from the comparator 262, which is internally generated by the D / A conversion circuit 261 to convert the triangular wave shown in FIG. 29B into a pulse width signal. A pulse width signal generated by generating a DC voltage and being compared by the comparator 262 is shown. This pulse width signal is applied to the differential amplifier 26
3 is one of the input signals.

FIG. 29 (e) shows an image shift correction circuit 1.
The D / A conversion circuit 261 converts a part of the intensity-modulated data consisting of g or 1 + β, which has been transmitted based on the reference clock DCK ₀ using the index signal as a trigger, from 300 into an analog value. Such a signal becomes one input signal of the differential amplifier 263.

FIG. 29 (f) shows the state shown in FIG. 29 (d) and FIG.
10E illustrates an intensity-modulated pulse width signal from the differential amplifier 263 that amplifies the difference between the two input signals illustrated in FIG. The modulated signal obtained in this manner is scanned by the scanning circuit 30.
0 to emit light from the LED array.

The color image forming apparatus 4 of this embodiment described above.
According to 00, even when spot light is irradiated from above the toner image based on the digital signal, a fringe-free, high-sharp, high-dot electrostatic latent image is formed. As a result,
A toner image with high sharpness can be obtained, and the quality of color reproduction such as edges, thin lines, and isolated points can be improved by performing correction in consideration of the image density distribution when the toner images are superimposed. .

In the present embodiment, as a result of an experiment in which the value of the RE processing coefficient P was variously changed, the value of P was 0.1 to
Good images were obtained in the range of 0.9. However, when P is small, the sharpness of the character is insufficient, and when P is large, a result is obtained in which the edge of the character or line drawing is emphasized too much. Therefore, the preferable range of the value of P is 0.3. ~ 0.7
Turned out to be in the range. As a result, when the original is a character or a line drawing, the edge portion clearly appears, and even small characters can be reproduced in detail. In addition, there was no adverse effect when the image had a halftone such as a photograph. This is because this method has a small effect on the halftone image due to the value of P.

In the present invention, it is possible to use P constant, but it is preferable to use P by changing it according to the image (character area or halftone area). Assuming that the value in the character area is P1 and the value in the halftone area is P2, it is preferable that P1> P2. That is, when the image is a character or the like, the value of P is large, preferably 0.9 to 0.4, and when the image is halftone, the value of P is small, 0.6 to 0.1.

In this example, as a result of an experiment in which the value of the coefficient P of the RE processing was variously changed, the value of P was 0.1 to
Good images were obtained in the range of 0.9. However, when P is small, the sharpness of the character is insufficient, and when P is large, a result is obtained in which the edge of the character or line drawing is emphasized too much. Therefore, the preferable range of the value of P is 0.3. ~ 0.7
Turned out to be in the range. As a result, when the original is a character or a line drawing, the edge portion clearly appears, and even small characters can be reproduced in detail. In addition, there was no adverse effect when the image had a halftone such as a photograph. This is because this method has a small effect on the halftone image due to the value of P.

In the present invention, it is possible to use P constant, but it is preferable to use P by changing it according to the image (character area or halftone area). Assuming that the value in the character area is P1 and the value in the halftone area is P2, it is preferable that P1> P2. That is, when the image is a character or the like, the value of P is large, preferably 0.9 to 0.4, and when the image is halftone, the value of P is small, 0.6 to 0.1.

The above-described flow of image data has been described as a printer which outputs data once stored in the page memory 210. However, the present invention is not limited to this. Instead of the image data processing circuit 100, the color scanner 151 and the A / D
An image data processing circuit 150 including a conversion circuit 152, a density conversion circuit 153, a linear masking circuit 154, and the like.
Instead of this, if a circuit for inputting image density data from a scanner and performing image processing can be applied to other image forming apparatuses such as a copying apparatus.

(Second Embodiment) In the first embodiment, each correction term is divided into pulse width modulation and intensity modulation. However, the schematic configuration of the color image forming apparatus is substantially the same as that of the first embodiment, and KN
A similar effect can be obtained by mixing the functions of the C correction circuit 1000 between pulse width modulation and intensity modulation as shown in Table 4 and performing pulse width modulation and intensity modulation.

[0275]

(Equation 2)

Here, if each γ _i is γ ₁ , γ ₂ , γ ₃ > 1, the correction amount of the second term is reduced, and the correction amount is added to the third term. If γ ₁ , γ ₂ , γ ₃ <1, the correction amount of the second term is increased. At γ _i = 0, it matches equation (1). Of course, the denominator of the third term is (1 + β)
A different structure can be obtained by multiplying this number by the second term at γ ⁱ .

The above equation (4) shows the KNC correction when developing in the order of Y, M, C and K.
This is a formula in which the development order is limited to Y → M → C → K,
It is not limited to this. For example, K → C → M → Y
Or K → Y → M → C.

In the first column, D _2, that is, Y ₂ , M ₂ , C ₂ , and K ₂ are image density data in which the average deviation between the images has been corrected.

The second column is a correction term for correcting a shift due to the structure between the images. When there is no previous toner image, α _Y
= 0, so that the latent image is not corrected. When there is a previous toner image, α _Yで な い 0 is not satisfied.
The correction is performed on the latent image. Specifically, γ
In the case of> 1, correction is performed so as to reduce the latent image area. Note that such correction is reflected in the data for intensity modulation.

The third column is a correction term for correcting the deviation between the image data and the reproduced image. When there is no previous toner image, α _Y = 0, and there is no correction for the latent image potential. When the previous toner image is present, α _Y ≠ 0 is not satisfied, so that the latent image potential is corrected. α, f, g, β
Is a variable of the density distribution of each color toner, which is obtained by multiplying a Laplacian filter by a coefficient or experimentally creating a correspondence table.

[0281]

As described above, according to the first to sixth aspects of the present invention, the color reproducibility can be improved in the KNC process using the internal exposure system by providing the above configuration. .

According to the seventh to thirteenth aspects of the present invention, by providing the above configuration, recording image data is created by performing correction in consideration of the image density distribution when superimposing toner images, By performing light modulation by this, the influence of superposition can be corrected, so that a color image forming apparatus capable of improving color reproduction and quality of edges, fine lines, and isolated point regions can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus.

FIG. 2 is a sectional view showing a support structure of the image forming body.

FIG. 3 is a graph showing KNC correction in an external exposure method.

FIG. 4 is a schematic diagram showing a surface potential on an image forming body in a KNC process of an external exposure method.

FIG. 5 is a graph showing KNC correction by an internal exposure method.

FIG. 6 is a schematic view showing a KNC process of an internal exposure system.

FIG. 7 is a block diagram illustrating a scanning circuit according to the present embodiment.

FIG. 8 is a time chart illustrating an operation of the scanning circuit.

FIG. 9 is a schematic diagram showing a shift of a light image from an LED array from a dot line in a main scanning direction which is previously desired.

FIG. 10 shows a process for realizing a seven-color multi-color image.

FIG. 11 is a schematic diagram showing factors that cause a difference in hue depending on an image pattern.

FIG. 12 is a circuit diagram of a color image forming apparatus that performs an adjustment process according to an image pattern.

FIG. 13 shows an input mechanism of video dot data.

FIG. 14 is an explanatory diagram of a pulse width modulation circuit.

FIG. 15 is an overall block diagram of an image processing circuit according to the present embodiment.

FIG. 16 is a configuration diagram of a specific main part of a KNC correction circuit.

FIG. 17 is a configuration diagram of a specific main part of a KNC correction circuit.

FIG. 18 is a schematic diagram showing a color correction process by a three-dimensional interpolation method.

FIG. 19 is a block diagram showing a second example of the first correction circuit shown in FIGS. 16 and 17;

FIG. 20 is a graph showing seven colors that can be color-separated by the first correction circuit 1300 based on the previous image.

FIG. 21 is a schematic diagram showing a processing operation of a color extraction circuit 1330.

FIG. 22 is a schematic diagram illustrating the operation of a KNC correction circuit in a color image forming process.

FIG. 23 is a block diagram showing a modulation circuit in the present embodiment.

FIG. 24 is a block diagram showing a reference wave phase determination circuit according to the present embodiment.

FIG. 25 is a diagram illustrating an example of a relationship between a triangular wave having a different phase and a pixel of interest.

FIG. 26 is a schematic diagram showing adjacent pixels when a target pixel m5 is divided into 3 × 3.

FIG. 27 divides a target pixel m5 into 3 × 3, and P = 0.5
It is a schematic diagram which shows an example in the case of it.

FIG. 28 is a time chart showing signals of each part of a modulation signal generation circuit when recording position modulation is performed.

FIG. 29 is a time chart showing signals of each part of a modulation signal generation circuit when recording position modulation is performed.

FIG. 30 is a schematic view showing a process of determining a toner adhesion state in the KNC process.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 image data processing circuit 200 modulation signal generation circuit 210 image density data storage circuit (page memory) 220 readout circuit 230 latch circuit 231 image discrimination circuit 232 MTF correction circuit 233 γ correction circuit 240 reference wave phase determination circuit 241 arithmetic processing circuit 250A 250B, 250C, 250D Select circuit 260A, 260B, 260C, 260D Modulation circuit 280 Reference clock generation circuit 290 Triangular wave generation circuit 291 Delay circuit group 300 Scanning circuit 400 Color image forming apparatus 1000 KNC correction circuit 1100 Filter 1300 First correction circuit 1400 Second correction circuit 1500 Third correction circuit

Claims (13)

[Claims] 1. A color image forming method in which an image forming body is charged, the image is exposed from the back surface of the image forming body, and reversal development is repeated to form a superimposed toner image. A color image forming method, wherein the exposure amounts of the first color and the second color at the time of forming are smaller than the exposure amounts at the time of forming a primary color having a maximum density. 2. A color image forming method comprising: charging an image forming body, exposing the image from the back surface of the image forming body, and repeating reversal development to form a superimposed toner image. The exposure amount of the first color at the time of formation is substantially equal to the first color and the second color, and is smaller than the exposure amount at the time of forming the primary color having the maximum density. A color image forming method characterized by being at least _1/2 and at most twice as large. 3. The color image forming method according to claim 1, wherein the second color is corrected by 5 to 50% more than the first color in the image exposure amount of the secondary color having the maximum density. . 4. The image processing apparatus according to claim 1, wherein the solid portion of the second color is corrected by 5 to 30% more than the first color in the image exposure amount of the secondary color having the maximum density. 3. The color image forming method described in 1. above. 5. The method according to claim 1, wherein the second color corrects the isolated point by 10 to 50% more than the first color in the image exposure amount of the secondary color having the maximum density. 3. The color image forming method described in 1. above. 6. The first and second secondary colors having the maximum density.
The color image forming method according to any one of claims 1 to 5, wherein an image exposure amount of a color is set to be weaker than a primary color having a maximum density. 7. The color image forming method according to claim 1, wherein the correction of the image exposure amount of the second color increases as the image exposure amount increases. 8. A color image forming apparatus which charges an image forming body, exposes an image from the back surface of the image forming body, and repeats reversal development to form a superposed toner image, thereby exposing from inside the image forming body. The exposure means is arranged in such a manner that the primary color from the exposure means when forming a secondary color having the maximum density
A color image forming apparatus, wherein the exposure amounts of the first and second colors are smaller than the exposure amounts when forming a primary color having a maximum density. 9. A color image forming apparatus which charges an image forming body, exposes the image from the back side of the image forming body, and repeats reversal development to form a superposed toner image, thereby exposing from inside the image forming body. The exposure means is arranged in such a manner that the primary color from the exposure means when forming a secondary color having the maximum density
The exposure amount of the color is substantially equal to the first color and the second color, and is smaller than the exposure amount when forming the primary color having the maximum density, and the half-exposure amount E _1/2 or more of the image forming body. A color image forming apparatus characterized in that it is not more than twice as large. 10. The image exposure for each color is light-modulated for each recording dot based on multi-valued recording image data, and the recording image data is corrected by image density and image density distribution data. 10. The color image forming apparatus according to claim 8, wherein the light modulation based on the data is performed by pulse width modulation or intensity modulation. 11. A correction unit for forming multi-valued recording image data used for image exposure for each color, a first correction unit for correcting an average shift between images, and a local shift due to a structure between images. The color image forming apparatus according to claim 10, further comprising a second correction unit that corrects the color image. 12. The color image forming apparatus according to claim 11, wherein the first correction unit and the second correction unit correspond to one of pulse width modulation and intensity modulation. 13. The color image forming apparatus according to claim 8, wherein the correction of the image exposure amount of the second color increases as the image exposure amount increases.