JPH05265287A - Color image forming method - Google Patents

Abstract

PURPOSE:To provide a color image forming method of enabling the formation of an glossy copy image only in the photographic region or the whole face of a document regardless of the quality of transfer material. CONSTITUTION:A color toner image of yellow toner Y, magenta toner M, cyanogen toner C, black toner BK is formed on a photoconductor 30 by developing apparatus 36Y, 36M, 36C, 36BK, and a photographic region and a character region are discriminated by the region discriminating CPU of an image signal processing part. In the photographic region, a transparent toner layer is formed by a developing apparatus 36T so as to obtain a glossy image. In the character region, a transparent toner layer is not formed so as to obtain an unglossy image. A total face glossy mode or a total face unglossy mode is further selected in a control panel so as to enable the total face of the copy image to be glossy or unglossy in this color image forming method.

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 an electrophotographic copying machine, which is provided with an image reading section for reading an original image by a device such as a CCD and outputting the image, and extracting the characteristics of the image to obtain a copy image. The present invention relates to a color image forming method capable of forming an image having a gloss on a part or the entire surface.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus such as an electrophotographic copying machine is provided with means for automatically replenishing toner by monitoring the toner density of a developer so as to keep the developing conditions constant, or the average density of an original document. Is known, and the developing conditions are changed according to the result to obtain a copy which is as faithful to the original as possible and easy to read. But,
A color image forming method capable of reproducing the glossiness of an original image has not yet been realized.

[0003]

Therefore, in the conventional image forming apparatus, since the copy of the original having gloss is made of a plain paper as the transfer material, the copy feels different from the original, and the character due to the change of the image data is generated. There is a problem that the density of a part is lowered, or the saturation is lowered in a color copy.

Looking at an image recorded on a transparent sheet used for an overhead projector or the like,
Since a diffused reflection of transmitted light is prevented by giving gloss to the image surface and a clear and highly saturated projection image can be obtained, a transferred image with high gloss is required.

Also, regarding an image transferred onto a recording paper, it is preferable that a part of the original has a photographic area as shown in FIG. 5, for example, the part is glossy, thereby further improving the quality of the image. It can also be increased.

According to the present invention, in order to meet the above demands, the image area is separated, and in the photographic area, a copy image on the transfer material can be recorded as a glossy image regardless of the material of the transfer material. The purpose is to provide.

[0007]

The object is to have means for separating an image area into a photograph area and a character area, and a transparent layer is selectively provided for the separated image area. And a color image forming method. Also, a preferred embodiment is a color image forming method in which the setting of the transparent layer is variable with respect to the separated photographic area by an external command.

[0008]

First, the image processing method of the present invention will be described.

According to the image processing method of the present invention, the entire original image is scanned (prescanned) by the image reading unit in advance, thereby globally separating the image regions.

The basic configuration of the image signal processing performed by the present invention is roughly divided into an image reading system, a memory for storing image data and discrimination data, and further discrimination based on the image data stored by prescan, and the memory again. It is configured by a CPU that performs a process of storing in.

The image data is taken into the memory during the prescan. Since this data does not necessarily require fine data, the reading interval can be thinned and the number of bits can be reduced. 16 dots / mm in each main scan, each B
Although 8 bits are used for (blue), G (green), and R (red), 2 dots / mm and 6 bits are sufficient for pre-scan sampling in some cases, so the memory capacity is for image density data. This is a value that is sufficient for practical use, since it is sufficient to use one thousandth of the memory.

Based on this data, the CPU performs discriminant calculation and returns the result (characters, photographs, etc.) to the memory again. Since this calculation is completed within a few seconds, it can be executed without much delay until the main scan. Further, because of such a configuration, it is possible to provide a system that does not require special hardware other than the CPU, has a simple mechanism, and can easily change algorithms and parameters. The above CP
Even if U has an independent structure, the scanner and the control CPU may also play the role.

At the time of the main scan, the discrimination data is transferred in synchronization with the image data. If they have been thinned out, the neighborhood is transferred as the same determination data. By using this determination data for the subsequent processing, it is possible to obtain higher-level processing and output.

Next, the structure of the image signal processing unit of the present invention will be described. FIG. 2 shows an example thereof, and 60 is an image signal processing unit. The image data read by the prescan of the image reading system A is sent to the global discrimination CPU 61, which is a means for thinning and separating the image area.
The global discrimination CPU 61 uses the method described later to
A photo area, a monochrome image area, and a color image area are discriminated. Although this result is temporarily stored in the discrimination memory, it is thinned out data of at most 2 bits, and does not require much capacity.

In the main scan, the image data read by the image reading system A is sent to the local discrimination CPU 62 and the masking unit 63. The above image data is masking part
63 at y (yellow), m (magenta), c (cyan),
After being converted into a bk (black) signal, it is processed through a filter unit 64 for adjusting sharpness (MTF), a γ conversion unit 65 for adjusting gradation, etc., and a modulation circuit group 66 having independent modulation circuits. Sent to.

The local discrimination CPU 62 discriminates in real time whether it is a character area or a photograph area by a method described later. This result is used together with the result determined by the global determination CPU 61 to selectively use the filter unit 64 and γ.
It becomes a processing command of the conversion unit 65.

In the modulation circuit group 66, the above y, m,
Along with the c and bk signals, a signal corresponding to the maximum density in the photographic area and a transparent signal t corresponding to the density 0 in the character area, which are sent from the global discrimination CPU 61, are received, and pulse width modulation is performed respectively to the laser writing system B. Sent out. As a result, a solid transparent toner layer is formed in the photographic area. FIG. 4A shows a glossy area to which the transparent toner is attached and a non-glossy area to which the transparent toner is not attached, which are formed on the photoconductor.

T is a transparent toner and G is a color toner.

In the global discrimination CPU 61, (a) a character area of a binary image area such as a character, a line drawing, and a figure has a spatial frequency characteristic different from that of a photographic area having continuous gradation. Orthogonal transformation method for discriminating a region using (b) autocorrelation method, (c) concentration distribution method, (d)
A method with high discrimination performance such as a hierarchical discrimination method is used.

Further, in the local CPU 62, (a) a density gradient method for discriminating a region by paying attention to the fact that the density gradient of the image is large in the character region and small in the photographic region, and the structure is constituted by the region (b). A pattern discrimination method for discriminating a region while paying attention to the fact that the patterns are different, or (c) a combination method for dividing the image data into a plurality of blocks and discriminating a region from at least two or more kinds of values representing the property in the block,
Etc. are used.

FIG. 1 is a sectional view showing an example of an image forming apparatus to which the present invention is applied so that a glossy or non-glossy copy can be obtained. This image forming apparatus comprises an image reading system A, a laser writing system B, an image forming section H and the like.

An original table made of a transparent glass plate or the like is provided above the image forming apparatus, and an original D placed on the original table.
There is a document placing section 11 composed of a document cover or the like for covering the first mirror unit in the main body of the apparatus below the document table.
12, second mirror unit 13, main lens 20, color CCD
An image reading system A composed of 23 etc. is provided. The first mirror unit 12 includes an illumination lamp 14 and a first mirror 15,
It is mounted parallel to the document table and linearly movable in the horizontal direction in the drawing, and optically scans the entire surface of the document D. The second mirror unit 13 integrally includes a second mirror 16 and a third mirror 17, and linearly moves in the left-right direction at a speed half that of the first mirror unit 12 so as to always maintain a predetermined optical path length. As a matter of course, the movement of the second mirror unit 13 is parallel to the platen like the first mirror unit 12. The image of the document D on the document table illuminated by the illumination lamp 14 is converted by the main lens 20 into the first mirror 15,
An image is formed on the color CCD 23, which is a scanner, through the second mirror 16 and the third mirror 17. When the scan is completed, the first mirror unit 12 and the second mirror unit 13 return to their original positions and wait until the next scan.

Image data obtained from the color CCD 23 at the time of pre-scanning and main scanning by the above-mentioned scanning is processed by the image signal processing unit 60 shown in FIG. 2, and is output to the laser writing system B as an image density signal through a selector not shown. It

The image forming unit H includes a charger 35, an image exposing unit 55, developing units 36T, 36Y, 36M, 36C, 36BK, a transfer unit 37, which are arranged around the periphery of the photosensitive drum 30 which is an image forming body. Separator 3
8, a cleaning device 39, a conveyor belt 44, a fixing device 45 and the like.

The developing devices 36T, 36Y, 36M, 36C, 36BK are those which contain the transparent toner T in the most upstream part of the peripheral edge of the photosensitive drum 30, and the developing device 36BK which contains the black toner BK in the most downstream part. Are arranged. Developer 36Y, 36M, 36C, 36BK
Since well-known color toners are used as the color toners stored in the above, description thereof will be omitted. However, as the black toner BK, a toner having infrared transmissivity is used, and therefore, a toner not restricted by the image forming order is selected.

Transparent toner T contained in the developing device 36T
Is a resin that does not contain a colorant. For example, a styrene-based monomer such as styrene and an acrylic ester monomer such as butyl acrylate and / or a methacrylic ester monomer such as methyl methacrylate are used. A styrene-acrylic copolymer resin obtained by copolymerization, and a thermoplastic resin such as a polyester resin is used.

The fixing device 45 has a fixing temperature of non-gloss mode,
It can be switched according to the gloss mode,
In the gloss mode, the fixing device sets the fixing temperature so that the toner image is sufficiently fused and fixed to have gloss.

In the image forming apparatus of this embodiment, any one of the full gloss mode, the full non-gloss mode and the automatic gloss mode can be selected, and the image forming apparatus shown in FIG.
A desired copy mode is selected by the operation panel 100 shown in.

That is, the automatic gloss button 101 is used for automatic gloss copy in which the image area of the original is automatically determined and separated and the photograph area is used as the gloss image. To make the entire copy image a non-glossy image, the full-glossy button 103 is selected and pressed. Next, the operation of each mode will be described.

(1) In case of automatic gloss mode By pressing the automatic gloss button 101, the fixing device 45 is first set to a temperature suitable for gloss fixing. When the copy button 104 is pressed, the image reading system A performs prescan prior to the image forming process (copy process) and sends the image data to the image signal processing unit 60. In the image signal processing unit 60, the global discrimination CPU 61 discriminates / separates the image area, and the data is stored in the global discrimination CPU 61. When the main scan is performed after the pre-scan, the read image data is processed based on the global discrimination of the pre-scan and the local discrimination of the main scan, and is sent to the laser writing system B, and the image exposure unit Image exposure is performed on the photosensitive drum 30 at 55.

The image area determined to be a character area by the global determination is subjected to image exposure based on the image data that has been γ-corrected so that the γ characteristic stands, and then a latent image is formed, and then BK by the developing device 36BK. Although development is performed, the transparent toner T is not subjected to image exposure and development.

In the image area determined as the photographic area by the global determination, the image exposure of Y, M, C, BK is performed on the photosensitive drum 30.
Each time the image is rotated, the developing devices 36Y, 36M, 36C and 36BK perform development, respectively, and four color toner images are superposed on the photosensitive drum 30, and image exposure of the transparent toner T is further performed thereon.
Development is performed. Image exposure in the photographic area is γ-corrected so as to have gradation.

The image signal from the image reading system A by the main scan is input to the drive motor 31, the rotary polygon mirror 32, and the laser writing system B including a semiconductor laser, an fθ lens, a correction lens and the like, which are not shown, and the copy process is performed. Start. That is, the photosensitive drum 30 rotates in the clockwise direction as shown by the arrow and is uniformly charged by the charger 35. In the image exposure unit 55, the image on the original D is processed through the image signal processing unit 60. The writing of the yellow (Y) image is performed by the laser beam from the laser writing system B, and the electrostatic latent image of the Y image is formed. The electrostatic latent image on the photosensitive drum 30 is subjected to reversal development with Y toner by the developing device 36Y to become a visible Y toner image. That is, the developing device
The developing sleeve with a built-in 36Y magnet roll
A DC or further AC bias voltage is applied to perform non-contact development with a two-component developer which is a developing means to form a Y toner image. The photoconductor drum 30 on which the Y toner image is formed passes under the retracted cleaning device 39, and is subsequently charged by the charger 35, and the laser writing system B is used to generate a magenta (M) image laser. Beam writing is performed and an electrostatic latent image of a magenta (M) image is formed on the Y toner image. This latent image is subjected to reversal development by the developing device 36M containing magenta toner to form an M toner image. Subsequently, similarly, cyan (C) toner image and black (B
K) A toner image is formed. Finally, a transparent toner T layer is formed by the transparent signal t that uniformly forms the transparent toner T layer in the photographic area determined by the global determination, as shown in FIG. On the upper side, a color toner image in which a transparent toner T layer is added on the color toner G only in the photographic area is formed. FIG. 4A shows a state of the toner formed on the photosensitive drum 30.

The transfer paper P fed by the paper feed roller 41 one by one from the paper feed cassette 40 containing the white transfer paper P as a transfer material is synchronized with the toner image on the photosensitive drum 30. It is delivered onto the photoconductor drum 30 by an operating timing roller 42. This transfer paper P has a transfer device 37
By the action of, the color toner image including the transparent toner T layer on the photoconductor drum 30 is transferred, separated from the photoconductor drum 30 by the separator 38, and then sent to the fixing device 45 via the conveyor belt 44. After being sandwiched and pressed by the heat fixing roller and the pressure bonding roller to perform gloss fixing with the transparent toner T layer as the lower layer, the tray outside the apparatus is ejected by the paper discharge roller 46.
It is discharged to 47.

On the other hand, the photosensitive drum 30 continues to rotate,
The toner remaining on the surface without being transferred is collected and cleaned by the cleaning device 39 having the cleaning blade 39A or the like that has been retracted, and stands by for the next copy.

(2) In case of full gloss mode When the full gloss button 102 is pressed, the fixing device 45 is set to a temperature suitable for gloss fixing, and pre-scan is controlled so as not to be performed. Subsequently, the copy process is performed, but the transparent toner T is controlled so that image exposure and development for forming the transparent toner T layer on the entire surface are performed. Therefore, the latent image is formed by the image data of Y, M, C, and BK, and the latent image is formed for the formation of the entire transparent toner T layer.
The transfer paper P on which the toner image has been transferred after being developed with the M, C, BK and T toners is fixed by the transport belt 44 to the fixing device 45.
After being conveyed to the sheet and subjected to gloss fixing, the sheet is discharged by a sheet discharge roller 46 to a tray 47 outside the apparatus.

(3) In the case of the full non-gloss mode When the full non-gloss button 103 is pressed in the operation unit to specify the full non-gloss mode, the fixing temperature of the fixing device 45 is set to the normal fixing temperature. The prescan is controlled not to be performed. Also in the copying process, the image exposure with the transparent toner T is not performed, and the developing device 36T
Is controlled not to operate. Therefore, Y, M, C, BK
The latent image is formed by the image data of Y and the development is performed by Y, M, C, and BK toners, and the transfer paper P on which the toner image is transferred is conveyed to the fixing device 45 by the conveyance belt 44 and is normally fixed. After that, the paper is ejected to the tray 47 outside the apparatus by the paper ejection roller 46.

As described above, when the automatic gloss mode is designated, the transparent toner T layer is formed only in the photographic area and the entire surface is gloss-fixed. If you specify the full gloss mode,
The transparent toner T layer is formed on the entire surface of the transfer material so as to be superposed on the color toner G, and the gloss is fixed. Further, in the case of the full non-gloss mode, the full transparent toner T layer is not formed and the normal fixing is performed.

The adhering amount of the transparent toner T is determined in the image signal processing section 60 in consideration of the adhering amount of color toner,
A large amount of the transparent toner T is formed in a portion where the amount of adhered color toner G is small, and a small amount of the transparent toner T is formed in a portion where the amount of adhered color toner G is large. As shown in FIG. It is also possible to obtain a uniform and even copy. In this case, in FIG. 2, the signal corresponding to the adhesion amount of the transparent toner T may be replaced with the signal t for which the adhesion amount of the transparent toner T is constant, and may be realized by t- (y + m + c + Bk). As a result, the amount of transparent toner attached can be changed according to the amount of color toner attached.

[0040]

According to the present invention, by the method described above, a copy having an excellent gloss in the photographic area can be obtained even if a general transfer paper is used for an original having a photographic area in a part thereof. Also, the entire surface can be made into a glossy image or a non-glossy image by an external command, and when a transparent sheet is used as the transfer material, the transparency is good and there is no irregular reflection,
It is possible to provide a method capable of obtaining an excellent copy capable of projecting a clear and highly saturated image.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a color image forming apparatus to which the present invention is applied.

FIG. 2 is a block diagram showing an example of an image signal processing unit of the present invention.

FIG. 3 is a main-portion plan view illustrating an example of an operation unit according to the present embodiment.

FIG. 4 is a cross-sectional view showing a toner layer structure on a photoconductor formed according to the present invention.

FIG. 5 is a diagram showing an example of a document having a photo area.

[Explanation of symbols]

 30 Photosensitive drum 35 Charging device 36 T, 36Y, 36M, 36C, 36BK Developing device 37 Transfer device 38 Separator 39 Cleaning device 40 Paper cassette 45 Fixing device 60 Image signal processing unit A Image reading system B Laser writing system BK Black toner C Cyan toner H Image forming part M Magenta toner P Transfer paper T Transparent toner Y Yellow toner

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[Procedure amendment]

[Submission date] April 30, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (2)

[Claims] 1. A color image forming method, comprising means for separating an image area into a photographic area and a character area, and a transparent layer is selectively provided to the separated image area. 2. The color image forming method according to claim 1, wherein the setting of the transparent layer is variable with respect to the separated photographic area by an external command.