JPH08171252A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device having the uniformity of an image in a highlight density area. CONSTITUTION: The black color out of four colors of yellow 23, magenta 21, cyan 22 and black being the color separation components of a full color image is separated as individual image information for the highlight density area 24 and a dark density area 25, and the colors of five kinds of toner images are superimposed so as to form the full color image. At such a time, the black toner density of the highlight density area is set about 1/2 of the black toner density of the dark density area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer or a copying machine, and more particularly to an image forming apparatus for recording image information on a transfer material such as paper using an electrophotographic process to visualize it. It is about.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus for forming an image using an electrophotographic process is an apparatus for forming an image using a toner of a single density in an apparatus for forming a single color image, and an apparatus for forming a full color image. In the above, full-color image information is decomposed into three primary colors of subtractive color mixture of yellow, magenta, and cyan, or a black component is extracted by UCR (undercolor removal) processing in order to reduce the consumption of all toner, and yellow and magenta are extracted. An image was formed by separating the toner into four colors of cyan, black and four corresponding single density toners.

[0003]

However, with respect to image quality, there is a drawback in that such an image forming method and the image characteristics of electrophotography are not well integrated. To explain this, in an image using an electrophotographic process, since the density of the image is expressed by the amount of toner adhered to the transfer material, the maximum amount of toner adhered to the transfer material is semipermanent by the fixing unit. The amount of toner that can be fixed is limited. Therefore, in order to express an image with a light density, it is necessary to form an image with a small amount of toner.

Therefore, in order to express an image having a uniform light density, it is required to arrange a small number of toners uniformly, but it is very difficult to satisfy this requirement. That is, non-uniformity of image density (unevenness or roughness) occurs, and the image quality significantly deteriorates in the highlight density region. Further, this phenomenon remarkably occurs in a black color having a high visual density, while it is almost unrecognizable in a yellow color having a low visual density.

That is, in the case where an image is formed by expressing the lightness and darkness of an image by the toner adhesion amount as described above, and making a unique toner correspond to the basic color obtained by color-separating the full-color image information, in the highlight density area. There is a drawback that the image uniformity is impaired and the image quality is significantly deteriorated.

Accordingly, it is an object of the present invention to provide an image forming apparatus having image uniformity even in a highlight density area.

[0007]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
In the image forming apparatus, the electrostatic latent image formed on the image carrier according to the image information is visualized by the toner contained in the developing means, and the visualized toner image is transferred to the transfer material to obtain an image. Includes a low-density toner and a high-density toner separately, and the low-density toner is used for a highlight density area of image information, and the high-density toner is used for a dark density area to form an image. Image forming apparatus.

It is preferable that the image information is divided into a highlight density area and a dark density area, and the highlight density area image information is formed with a low density toner and the dark density area image information is formed with a high density toner.

Preferably, the image information is full-color image information, and of the four color separation components of the full-color image, yellow, magenta, cyan, and black, black is divided into a highlight density region and a dark density region. Separated as individual image information, a full-color image is formed by color superposition of five types of toner images of yellow, magenta, cyan, black in highlight density area, and black in dark density area. At this time, the toner density in black in the highlight density area is formed. Is lower than the toner density of black in the dark density region.

It is preferable to have a mode for forming an image with four colors of yellow, magenta, cyan and black, and a mode for forming an image with five colors of yellow, magenta, cyan, highlight density area black and dark density area black.

Preferably, the image information is full-color image information, and among the four color separation components of the full-color image, yellow, magenta, cyan, and black, the magenta color, cyan color, and black color are respectively highlighted. Decomposes as individual image information of the density area and dark density area, yellow, highlight density area magenta,
Dark density area magenta, highlight density area cyan,
Dark density area cyan, highlight density area black,
A full-color image is formed by superimposing seven kinds of black in the dark density region, and at this time, the toner density of each highlight density region of magenta, cyan, and black is set to be lower than the toner density of each dark density region.

A mode for forming an image with four colors of yellow, magenta, cyan and black, and yellow, highlight density area magenta, dark density area magenta, highlight density area cyan, dark density area cyan, highlight density area black and dark. It is preferable to have a mode in which an image is formed with seven colors of density area black.

The developing means for developing a highlight density area image and a dark density area image of the same hue preferably contain toners of different densities separately in a single developing device.

It is preferable that the toner density in the highlight density area of the same hue is approximately ½ of the toner density in the dark density area.

[0015]

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

First Embodiment A first embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. The image forming apparatus of this embodiment is a color copying machine.

In FIG. 1, the image forming apparatus separates a color original for each pixel by a conventional color image sensor and digitally reads it as an electric signal, and a full color print image is obtained by an electrophotographic method in a color laser beam printer section. I will get it. The image forming apparatus includes an image reading unit A and an image printing unit B.

In the image reading section A, the document exposure lamp 2
Illuminates the color document 1 placed on the document table,
The color reflected light image reflected from the color original is imaged on the color image sensor 3 which moves in parallel to the original and scans.

The color image signal color-separated for each pixel by the color image sensor 3 is subjected to signal processing by the color signal processing circuit 4 and input to the image processing circuit 5 through the cable 29. The image processing circuit 5 decomposes the color information by digitizing the input signal and digital image processing of the color signal, and then sends the digital image processing to the image printing section B.
According to the image data sent to the print section B via the cable 6, the semiconductor laser 8 is modulated by the semiconductor laser drive section 7, reflected by the polygon mirror 9, and further reflected by the mirror 10, and then the primary charger. A monochromatic latent image that has been color-separated into a raster is formed on the photosensitive drum 11, which is an image carrier uniformly charged at 19.

The formed latent image is visualized in each of the five developing devices, that is, a magenta developing device 21, a cyan developing device 22, a yellow developing device 23, a highlight density region black developing device 24, and a dark density region black developing device 25. A toner image that has been colorized and color-separated is formed on the photosensitive drum 11.

On the other hand, the transfer material supplied from the cassette 17 is timing-adjusted by the registration roller 18 at the front end of the image, and then wound around the transfer drum 12 by electrostatic attraction so as to be synchronized with the above-described color-separated toner image. The toner image is transferred by the transfer charger 30.

As is apparent from the figure, since only one color image is formed in one image forming process, the color separation process of the original is performed by the number of toner colors, that is, magenta, cyan, yellow and highlight density. Region black and dark density region black are repeated five times, and similarly, the steps of latent image formation, development, and transfer according to each color component are also repeated in synchronization with each color separation.

In this way, the transfer material is the transfer drum 12.
After being rotated five times to complete the transfer of the five colors while being wound around, the separation claws 13 are forcibly separated from the transfer drum 12, and the heat pressure fixing roller 1 is conveyed through the conveying member 14.
Then, the toner images of a plurality of colors are fixed on the transfer material and discharged to the outside of the apparatus. Through the above steps, one full-color copying step is completed. The photosensitive drum 11
The upper residual toner is removed by the cleaner 20.

In the image forming operation described above, the signal value of black read by the color image sensor is decomposed into the dark density area black and the highlight density area black. At this time, the toner density of the highlight density area black is determined. Dark density area Set to half the black toner density.

Further, as shown in the graph of FIG. 2, for the black signal value, the dark density area black data is distributed to a density area darker than half of the black signal density area, while the highlight density is increased. The area black data is distributed to the density areas lighter than the remaining half value, and the data value is increased by the amount corresponding to the toner density being set low, and the output data is obtained. In the case of this embodiment, the toner density is reduced to 1/2.
And the data value is doubled.

In this way, the read data of black is decomposed into two image data of black in the highlight density region and black in the dark density region, and when outputting a full color image, all five colors (magenta, cyan, yellow) are output. ,
An image is formed in the highlight density area black and the dark density area black) by the copying operation described above.

By forming an image as described above, unevenness and roughness are eliminated even in a highlight density region,
Image uniformity can be maintained and high quality images can be obtained.

In the above-mentioned image forming apparatus, an image forming mode is formed by four colors of yellow, magenta, cyan and black, and an image is formed by five colors of yellow, magenta, cyan, highlight density area black and dark density area black. The image forming mode may be provided, and any one of the modes may be selected according to the image forming condition.

The mode selection gives the user the freedom of switching the copying method depending on the user's request, that is, whether a high quality image is desired or a copying work time is desired to be shortened.

Second Embodiment Next, a second embodiment of the image forming apparatus according to the present invention will be described.
This will be described with reference to FIG.

The structure and operation of the image forming apparatus are similar to those of the first embodiment, but in this embodiment, the highlight density area magenta developing device 121, the dark density area magenta developing device 122, and the highlight density area cyan. Developing unit 12
3, dark density region cyan developing device 124, yellow developing device 125, highlight density region black developing device 126,
It is different in that it includes a developing device for seven colors of the dark density region black developing device 127.

Of the color separation data of the color original read by the color image sensor, magenta, cyan, and black colors were processed in the same manner as black in Example 1, and in magenta, highlight density areas magenta and dark were also used. It is decomposed into two image data of density area magenta, and is also decomposed into two image data of cyan, which is a highlight density area cyan and dark density area cyan. Further, in black, it is also decomposed into highlight density area black and dark density area black. Decompose into two image data. Then, seven images are superposed on the highlighted image using a toner having a low density. Note that the highlight and dark density areas are not divided for yellow, which has a bright brightness.

As described above, the embodiment in which not only black but also black and magenta and cyan are used to develop the highlight density region by using a toner having a low density, so that only black is divided into the highlight and dark density regions. Compared with No. 1, it is possible to significantly improve the unevenness and roughness of the image in the highlight density region, and it is possible to maintain the uniformity of the image.

As in the first embodiment, a mode for forming an image with four colors of yellow, magenta, cyan, and black, and yellow, highlight density area magenta, dark density area magenta, highlight density area cyan, and dark density area. A mode in which an image is formed with seven colors of cyan, highlight density area black, and dark density area black is provided, and any one of the modes may be selected according to the image forming conditions.

The mode selection allows the user to freely change the copying method depending on the user's request, that is, whether a high-quality image is desired or a copying work time is desired to be shortened.

Further, in the image forming apparatus in the future, the demand for high pixel density is expected to increase, but as the pixel density increases, the pixel size becomes relative to the light beam spot diameter of the exposure system. And the contrast of the latent image of each pixel is low, which makes it difficult to uniformly adhere and develop the toner. Therefore, the unevenness or roughness of the image in the highlight density region is more likely to occur, and the effect of applying the present invention, which is capable of developing a deep latent image using a toner with a low density in the highlight density region, is It is increasing.

On the other hand, although full-color images have been described in both Examples 1 and 2, the recorded image is divided into highlight density areas by using toners having different densities in the single-color image forming apparatus, and each density area is dealt with. An image may be formed by developing with a toner having a density.

In the description of Embodiments 1 and 2, it is assumed that one developing device corresponds to each toner of a predetermined type, but one developing device has the same hue in each developing device. Low density toner and high density toner are stored separately, and by utilizing the difference in physical properties such as chargeability and particle size of each toner, the same developing device develops the same hue image component, It is also possible to make the highlight density region and the dark density region visible with individual toners without increasing the number, and to form an image.

[0039]

As is apparent from the above description, in the image forming apparatus according to the present invention, the toner separately contains the low density toner and the high density toner, and the low density area is included in the highlight density area of the image information. By using toner and forming an image in the dark density area using the high density toner, an image having uniformity in the highlight density area can be obtained, and therefore a high quality image can be obtained. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a graph showing division into highlight density region data and dark density region data of an input signal in the first embodiment.

FIG. 3 is a schematic configuration diagram showing a second embodiment of the image forming apparatus according to the present invention.

[Explanation of symbols]

 11 Photosensitive Drum (Image Carrier) 12 Transfer Drum 21 Magenta Developer 22 Cyan Developer 23 Yellow Developer 24 Highlight Density Area Black Developer 25 Dark Density Area Black Developer 121 Highlight Density Area Magenta Developer 122 Dark Density Area Magenta developing device 123 highlight density region cyan developing device 124 dark density region cyan developing device 125 yellow developing device 126 highlight density region black developing device 127 dark density region black developing device

Claims (8)

[Claims] 1. An image forming method in which an electrostatic latent image formed on an image carrier according to image information is visualized by a toner contained in a developing unit, and the visualized toner image is transferred to a transfer material to form an image. In the apparatus, the toner separately includes a low-density toner and a high-density toner, and the low-density toner is used for a highlight density area of image information, and the high-density toner is used for a dark density area to form an image. An image forming apparatus characterized by forming. 2. The image information is divided into a highlight density area and a dark density area, and the highlight density area image information is formed with a low density toner and the dark density area image information is formed with a high density toner. The image forming apparatus according to claim 1. 3. The image information is full-color image information, in which the black color of the four color separation components of the full-color image, yellow, magenta, cyan, and black, is individually separated into a highlight density area and a dark density area. Of the toner images of yellow, magenta, cyan, highlight density area black, and dark density area black to form a full-color image. At this time, the toner density of the highlight density area black is changed. The image forming apparatus according to claim 1, wherein the density is lower than the toner density of the dark density area black. 4. An image forming mode using four colors of yellow, magenta, cyan, and black, and an image forming mode using five colors of yellow, magenta, cyan, highlight density area black, and dark density area black. The image forming apparatus according to claim 3, which is characterized in that. 5. The image information is full-color image information, and in four color separation components of a full-color image, yellow, magenta, cyan, and black, a magenta color, a cyan color, and a black color respectively have a highlight density. Areas and dark density areas are decomposed as individual image information, and yellow, highlight density area magenta, dark density area magenta, highlight density area cyan, dark density area cyan, highlight density area black, dark density area black A full-color image is formed by superimposing seven kinds of colors, and at this time, the toner density of each highlight density area of magenta, cyan, and black is set to be lower than the toner density of each dark density area. Image forming apparatus. 6. A mode for forming an image with four colors of yellow, magenta, cyan and black, and yellow, highlight density area magenta, dark density area magenta, highlight density area cyan, dark density area cyan and highlight density area black. 6. The image forming apparatus according to claim 5, wherein the image forming apparatus has a mode in which an image is formed by seven colors of dark dark area black. 7. The developing means for developing a highlight density area image and a dark density area image of the same hue individually contain toners having different densities in a single developing device. The image forming apparatus according to any one of 1 to 6. 8. The image forming apparatus according to claim 1, wherein the toner density in the highlight density area of the same hue is approximately ½ of the toner density in the dark density area.