JPH0799588A - Image forming device - Google Patents

Abstract

PURPOSE:To conduct the image formation of a picture with high quality in response to the property of picture data. CONSTITUTION:A printer controller 3 receiving color picture data (RGB) outputs a PHIMG signal representing whether each picture element of picture data is a photographic picture or a character graphic picture. The color picture data (RGB) are converted into density picture data (YMC) at a color conversion section 81. The density picture data are subjected to under color reduction(UCR) processing according to the PHIMG signal at a UCR section 82 by using an LUT 86. Thus, the UCR processing depending on the property of the picture data is applied to the picture data.

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, and more particularly to an image forming apparatus such as an electrophotographic or electrostatic recording type copying machine or printer.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic system, for example, a bias roller transfer system or an electrostatic transfer system called a corona transfer system has been generally adopted in copying machines and printers.

In the bias roller transfer system, a transfer bias voltage having a polarity opposite to that of the charge of the toner of the developed image (toner image) on the photoconductor as an image carrier is applied to the transfer roller having a conductive layer on the transfer material. The toner image on the photoconductor is transferred. As a modification of this method, there is a method of using an endless belt having a conductive layer instead of the transfer roller.

On the other hand, in the corona transfer method, a dielectric film such as a polyester film is used as a transfer material carrier, and this dielectric film wound around a cylinder whose peripheral surface is greatly cut is used as a transfer drum. From the inside of the transfer drum, corona discharge is applied to the dielectric film to transfer the toner image onto the transfer material. As a modification of this method, there is a method of using an endless belt made of a dielectric film instead of the transfer drum.

In an electrophotographic color laser beam printer, an electrostatic latent image is formed by scanning a photosensitive drum, which is an image bearing member rotating at a constant speed, with laser beam light corresponding to an image signal. The electrostatic latent image is developed by a developing device and converted into a visible toner image. on the other hand,
After the transfer material fed by the paper feeding mechanism is wound around the transfer drum that also rotates at a constant speed, the toner image on the photosensitive drum is transferred at a predetermined transfer position, and Y
A total of 4 cycles of exposure-development-transfer process are executed for each color of (yellow), magenta (M), cyan (C), and black (K). When the superimposed transfer of the four-color toner images is completed, the toner images are sent to the fixing device, where they are fixed, and the paper is discharged to the paper discharge tray.

The rotary drive source of the photosensitive drum and the rotary drive source of the transfer drum are generally composed of one motor.

FIG. 7 shows an example of a side sectional view of the engine portion of the color laser printer having the above structure.

In FIG. 7, the paper 102 fed from the paper feed unit 101 is held at the outer periphery of the transfer drum 103 by holding the leading end thereof by a gripper 103f. The latent images formed in the respective colors by the optical unit 107 on the image carrier 100 (hereinafter referred to as the photosensitive drum) are formed in the respective color developing devices Dy,
After being developed by Dc, Db, and Dn, it is transferred to the paper on the outer periphery of the transfer drum a plurality of times to form another color image. After that, the paper 102 is separated from the transfer drum 103,
The image is fixed by the fixing unit 104 and is ejected from the paper ejection unit 105 to the paper ejection tray unit 106.

Here, the developing devices Dy, Dc, Db, D for the respective colors
n has a rotation support shaft at both ends thereof, and each is held by the developing device selection mechanism unit 108 so as to be rotatable around the shaft. As a result, the developing devices Dy, Dc, Db, Dn are not
As shown in FIG.
Even if 08 rotates about the rotation axis 110, its posture can be maintained constant. After the selected developing device moves to the developing position, the developing device selection mechanism unit 108 is integrated with the developing device and is a fulcrum 1
The selection mechanism holding frame 109 is pulled toward the photosensitive drum 100 by the solenoid 109a around the center 09b, and is moved toward the photosensitive drum 100.

Next, the color image forming operation of the color laser beam printer having the above structure will be specifically described.

First, the photosensitive drum 1 is charged by the charger 111.
00 is uniformly charged to a predetermined polarity, and laser beam light L
Is exposed on the photosensitive drum 100 by, for example, M
(Magenta) color latent image is M (magenta) color developing device Dm
Is developed, and a first toner image of M (magenta) color is formed on the photosensitive drum 100. On the other hand, the transfer paper P is fed at a predetermined timing, and the transfer bias voltage (+1.8 kV) having the opposite polarity (for example, positive polarity) to the toner.
Is applied to the transfer drum 103, the first toner image on the photosensitive drum 100 is transferred to the transfer paper P, and the transfer paper P is electrostatically adsorbed on the surface of the transfer drum 103. After that, the residual M (magenta) color toner is removed from the photosensitive drum 100 by the cleaner 112, and the photosensitive drum 100 is prepared for the next color latent image formation and development process.

Next, a second latent image of C (cyan) color is formed on the photosensitive drum 100 by the laser beam L.
Then, the second latent image on the photosensitive drum 1 is developed by the C (cyan) color developing device Dc to form a second toner image of C (cyan) color. Then, the second color of C (cyan)
The toner image of is transferred to the transfer paper P in accordance with the position of the first toner image of M (magenta) color that was previously transferred to the transfer paper P. In the transfer of the toner image of the second color, the transfer paper 103 is transferred to the transfer drum 103 immediately before the transfer paper P reaches the transfer portion.
A 2.1 kV bias voltage is applied.

Similarly, third and fourth latent images of Y (yellow) color and K (black) color are sequentially formed on the photosensitive drum 100, and are sequentially developed by the developing devices Dy and Db. The Y (yellow) color and the Bk (black) color third and fourth toner images are sequentially transferred in alignment with the toner image previously transferred to the transfer paper P. In this way, the four color toner images are formed on the transfer paper P in an overlapping state. In transferring the toner images of the third color and the fourth color, bias voltage images of +2.5 kV and +3.0 kV are applied to the transfer drum 103 immediately before the transfer paper reaches the transfer portion.

The reason why the transfer bias voltage is increased each time the toner image of each color is transferred is to prevent the transfer efficiency from being lowered. The main cause of this decrease in transfer efficiency is that when the transfer paper leaves the photosensitive drum 100 after transfer, the surface of the transfer paper is charged with a polarity opposite to that of the transfer bias voltage due to air discharge (the transfer paper carrying the transfer paper is charged). The surface of the drum is also slightly charged), and if this charging charge is accumulated for each transfer and the transfer bias voltage is constant, the transfer electric field decreases for each transfer.

During the transfer of the fourth color, when the leading edge of the transfer paper reaches the transfer start position (including immediately before and after), the fourth toner image of the fourth toner image is generated at an effective AC voltage of 5.5 kV (frequency is 500 Hz). A DC bias voltage +3.0 kV having the same polarity and the same potential as the transfer bias applied during transfer is superimposed and applied to the charger 111. In this way, when transferring the fourth color, when the leading edge of the transfer paper reaches the transfer start position, the charger 1
The operation of 11 is for preventing uneven transfer. In particular, in the transfer of a full-color image, even if slight transfer unevenness occurs, it is conspicuous as a difference in color. Therefore, it is necessary to apply the required bias voltage to the charger 111 to perform the discharge operation as described above. .

After that, when the front end of the transfer paper P on which the four color toner images are superposed and transferred approaches the separation position, the separation claw 113 is formed.
Comes close to each other and the tip thereof comes into contact with the surface of the transfer drum 103 to separate the transfer paper P from the transfer drum 103. The tip of the separation claw 113 maintains the contact state with the transfer drum surface,
After that, it is separated from the transfer drum 103 and returns to the original position. As described above, the charger 111 operates from when the front end of the transfer paper reaches the transfer start position of the final color (fourth color) to when the rear end of the transfer paper leaves the transfer drum 111, and the accumulated charge on the transfer paper ( The polarity opposite to that of the toner) is removed to facilitate separation of the transfer paper by the separation claw 113 and reduce air discharge during separation. The transfer bias voltage applied to the transfer drum 103 is turned off (ground potential) when the trailing edge of the transfer paper reaches the transfer end position (exit of the nip formed by the photosensitive drum 100 and the transfer drum 103). To do. At the same time, the bias voltage applied to the charger 111 is turned off. Next, the separated transfer paper P is conveyed to the fixing device 104, where the toner image on the transfer paper is fixed and is discharged onto the paper discharge tray 106.

In actual image formation, an output signal from a printer controller described below is input to the optical unit 107, and a semiconductor laser drive circuit (not shown) provided in the optical unit 107 is driven. .

Next, a printer controller for inputting an output signal to the engine section of the color laser beam printer having the configuration shown in FIG. 7 will be described.

In FIG. 8, a printer controller 302 receives image data 307 including a control signal and an image signal from a host computer (hereinafter referred to as a host) 301, performs image processing, and outputs an output signal to a semiconductor laser drive circuit. It is a figure which shows the processing concept at the time of outputting. As shown in FIG. 8, the image data 307 from the host is received by the interface unit 303. Next, of the received image data, the control signal 308 is sent from the interface unit 303 to the control signal processing unit 304, and the image signal 309 is sent to the image signal processing unit 305 for processing. Then, the semiconductor laser 306 is driven by the output signal of the image signal processing unit 305 via the semiconductor laser drive circuit. Also,
The control signal processing unit 304 outputs various control signals 310 for controlling the image signal processing unit 305. The control signal 310 also includes a 2-bit color designation signal (CNO). Here, the CNO bit pattern is "0.
It is assumed that M (magenta) is designated when it is 0, C (cyan) is designated when it is "01", Y (yellow) is designated when it is "10", and K (black) is designated when it is "11".

FIG. 9 is a block diagram showing the detailed arrangement of the image signal processing section 305.

When the image signal processing section 305 receives from the interface section 303 an image signal of a total of 24 bits in which each of the R, G and B color components is represented by 8 bits, the color processing section 3 receives.
At 51, color conversion, masking processing, and undercolor removal (UCR) are performed, and as shown in the time chart of FIG. 10, 1 sequentially in accordance with a page synchronization signal (TOPSNS) and a color designation signal (CNO). The VDO signal of the M (magenta) signal, the C (cyan) signal, the Y (yellow) signal, and the K (black) signal corresponding to the image for the page is output. M,
The C, Y, and K VDO signals are converted into signals that have been γ-corrected by the γ-correction unit 352, and the pulse-width modulation unit (hereinafter referred to as PWM
Input section 353.

In the PWM unit 353, as shown in the time chart of FIG. 11, the γ-corrected image signal (VDO signal) is latched by the latch 354 in synchronization with the rising edge of the image clock (VCLK), and the D / A converter is used. At 355, the image signal is converted into an analog voltage and input to the analog comparator 356. On the other hand, the image clock is converted into a triangular wave by the triangular wave generator 358, and the analog comparator 3
56 is input. The analog comparator 356 compares the triangular wave signal with the analog-converted image signal to obtain a pulse width modulated signal. The signal is inverted by the inverter 357 to obtain the PWM signal. As shown in FIG. 11, the PWM signal with the widest pulse width is output when the value of the image signal input to the PWM unit is maximum, and the PWM signal with the narrowest pulse width is output when the value of the image signal is minimum. It

[0023]

However, in the above-mentioned conventional example, since the UCR process (undercolor removal process) is performed to form an image regardless of the property of the image data, the image data may be displayed as characters or figures. If the image is close to the value image, there is a problem in that the edges of characters and lines are colored and high-quality images with sharp contours cannot be formed.

The present invention has been made in view of the above-mentioned conventional example, and an object thereof is to provide an image forming apparatus capable of performing high-quality image formation depending on the property of image data.

[0025]

In order to achieve the above object, the image forming apparatus of the present invention has the following constitution. That is, input means for inputting the brightness image data, analysis means for examining the properties of each pixel of the brightness image data, conversion means for converting the brightness image data into density image data, and according to the analysis result by the analysis means, An image comprising: an undercolor removing means for removing undercolor from the density image data; and an image forming means for forming an image based on the density image data subjected to the undercolor removal by the undercolor removing means. A forming device is provided.

[0026]

With the above structure, the present invention examines the properties of each pixel of the input luminance image data, converts the input luminance image data into density image data, and converts the density image data into the density image data.
It operates to perform undercolor removal according to the properties of each pixel.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a color laser beam printer (hereinafter referred to as a color LBP) which is a typical embodiment of the present invention.
3 is a block diagram showing a schematic configuration of FIG. Color LBP2
Is a printer controller 3 that receives image information from a host computer (hereinafter referred to as a host) 1 in a predetermined language and develops an image to generate image data 7, and a full-color image formation based on the generated image data 7. Performing a color image output up to 600 dpi (dots /
The printer engine 4 having a resolution of inch).

In the following description, the image data 7
Indicates that each pixel is represented by red (R), green (G), and blue (B) color components, and each color component is 8 bits,
It is assumed to be composed of a total of 24 bits of data.

In FIG. 1, the main signals exchanged between the printer controller 3 and the printer engine 4 are image data 7 (8 bits for each of R, G and B), an image transfer clock (VCLK) and a photo image designation signal (PHIMG). Line sync signal (LSYNC) and page sync signal (PSYNC)
C). The color components of the image data 7 are RDATA0-7, GDATA0-7, and BDATA0.
Represented as 7. Further, when simply referring to image data regardless of color components, they are represented as DATA0 to 7.

FIG. 2 is a block diagram showing the configuration of the printer controller 3.

The image information expressed in a predetermined language, which is sent from the host 1, is first processed by the image developing unit 5 to make each of RGB 8
Converted to a bit luminance signal. At this time, the image expansion unit 5 determines for each pixel whether the transmitted data is a character or a line drawing, or a photograph or a color character, and outputs the result as a PHIMG signal. In this embodiment, if the value of the PHIMG signal is "H", the image is a photographic image or a color character image, while if it is "L", the image is
Suppose it is a character or line drawing.

FIG. 3 is a block diagram showing the configuration of the signal processing unit included in the printer engine 4.

R sent from the printer controller 3
The 8-bit image data 7 for each GB is first transferred to the Y in the RF circuit 8.
Color conversion is performed on the MCK component, and masking processing and undercolor removal (UCR) processing are performed. Y processed by RF circuit 8
The MCK image data (DATA0 to 7) is written in the line memory 9 in synchronization with the write clock (VCLK). Next, the YMCK image data is read from the line memory 9 in synchronization with the rising edge of the read clock (PCLK) generated by the control clock generator 11, and γ
The correction unit 10 performs γ correction. The period of the read clock (PCLK) is 60 when the image recording density is 60.
It is generated so as to correspond to 0 dpi.

The γ correction unit 10 is a look-up table (LUT) composed of a ROM or a RAM. The image data is at addresses A0 to A7 and the PHIMG signal is at A8.
The 2-bit color designation signal (CNO) is A9 to A1.
Input to 0. This color designation signal (CNO) is the same signal as described in the prior art. The γ correction is performed differently depending on the type of image to which PWM is applied and the color component (toner characteristic) to be processed (that is, according to the PHIMG signal and CNO signal). The 8-bit multilevel signal output from the γ correction unit 10 is converted into an analog voltage by the D / A conversion unit 14 and input to the negative inputs of the comparators 15 to 16.

On the other hand, the triangular wave signals which are output signals from the triangular wave generators 12 and 13 are input to the positive inputs of the comparators 15 to 16, respectively. The triangular wave generator 12 generates the image clock (PCL) generated by the control clock generator 11.
K) is divided into 1 / 2PCLK by an integrator circuit to be converted into a triangular wave signal, and the triangular wave generator 13 outputs the image clock (P
CLK) is converted into a triangular wave signal by an integrating circuit. As a result, the comparator 15 outputs the PWM signal 20 corresponding to the recording density of 300 dpi to the selector 17, and the comparator 16 outputs the PWM signal 21 corresponding to the recording density of 600 dpi to the selector 17. Then, the selector 17 outputs one of the PWM signals 20 and 21 as an output signal 22 to the laser drive circuit (driver) according to the PHIMG signal. In this embodiment, the selector 17 outputs the PWM signal 2 if the value of the PHIMG signal is "H" (the image is a photographic image or a color character image).
On the other hand, if 0 is “L” (the image is a character or line drawing),
The PWM signal 21 is selected as the output signal 22.

FIG. 4 is a block diagram showing the structure of the RF circuit 8 according to this embodiment.

The RF circuit 8 includes a color conversion section 81 and a UCR section 8
2. By the masking unit 83, the RGB image data of 8 bits input from the printer controller 3 is YM
Color conversion is performed to C component image data, undercolor removal (UCR) processing according to the PHIMG signal is performed, and masking processing is performed. Then, the color designation signal (CN
In accordance with O), image data of Y (yellow), M (magenta), C (cyan), and K (black) components (each component is represented by 8 bits like RGB components) is output in a frame sequential manner.

The UCR unit 82 has the same RA as the γ correction unit 10.
Look-up table (LU
T) 86, 8-bit image data is input to addresses A0 to A7, PHIMG signal is input to A8, and color designation signal (CNO) is input to A9 and A10. Then, 8 bits corresponding to the values input to the respective addresses (A0 to A10) are obtained from the output addresses (D0 to D7).

The UCR unit 82 switches the memory bank of the LUT 86 according to the PHIMG signal and performs different undercolor removal (UCR) processing.

That is, if the value of the PHIMG signal is "H", the image is a photographic image or a color character image, and therefore the UCR processing is performed in which the amount of undercolor removal is reduced and the gradation is emphasized. On the other hand, if the value of the PHIMG signal is "L", the image is a character or line drawing, so the amount of undercolor removal is increased and UCR processing is performed so that the contour becomes sharper. When an achromatic image signal, that is, an image signal of R = G = B is input, the Y, M, and C signals are canceled, and the K component signal is expressed so that the image data is expressed only by the black component. Output only.

Therefore, according to the present embodiment, the UCR processing in which the amount of undercolor removal is reduced and the gradation is emphasized according to whether the input image data is a photographic image or a color character image, or a character or a line drawing. Alternatively, since UCR processing is performed so that the contour becomes sharper, it is possible to form a higher quality image depending on the property of the image data.

[0043]

Other Embodiments In the above-described embodiments, the printer controller 3 does not care whether the image data is monochrome image data or full-color image data based on the image information received from the host 1. It was In this embodiment, the printer controller 3 makes the distinction, and the result is sent from the printer controller 3 to the printer engine 4 as a monochrome / full color mode switching signal 8 as shown in FIG. A case will be described in which a grayscale image that is not subjected to color conversion is formed on a monochrome image according to the / full-color mode switching signal 8.

In the following description, when the value of the monochrome / full-color mode switching signal 8 is "L", the image data is monochrome (processing is monochrome mode), and when the value is "H", the image data is full-color (processing is full-color mode). ).

FIG. 6 shows a printer engine 4 according to this embodiment.
3 is a block diagram showing a configuration of an RF circuit 8 of FIG. Incidentally, in FIG. 6, the same components as those in the above-described embodiment are designated by the same reference numerals, and the description thereof will be omitted. Here, only the processing characteristic of this embodiment will be described.

When the monochrome mode is selected according to the monochrome / full-color mode switching signal 8 sent from the printer controller 3, the image data is directly input by the selector 85, and the processing by the color conversion unit 81 is passed. Further, the UCR process by the UCR unit 82 is also passed, and the masking unit 83 synthesizes the input RGB data and multiplies the RGB components by the following coefficients to obtain the sum, that is, (0.3 × R + 0.59 × G + 0.11 × B) is output. In this case, since the output from the masking unit 83 has the same value, the selector 84 selects one of the outputs and inputs the output to the selector 88.

When the monochrome mode is selected according to the monochrome / full-color mode switching signal 8, the selector 88 selects the output of the selector 84 and inputs it to the addresses A0 to A7 of the LUT 89. The monochrome / full-color mode switching signal 8 is input to the highest address (A11) of the LUT 89. Then, when the value of the monochrome / full-color mode switching signal 8 is “L”, the LUT 89 converts the image signal input to the addresses A0 to A7 into a black signal according to the conversion table stored in the LUT 89 and outputs it to the selector 87. Output.

The selector 87 selects the output from the LUT 89 when the value of the monochrome / full-color mode switching signal 8 is "L". As a result, only the black signal is output in the monochrome mode.

Now, when the processing is in the full-color mode, the data from the UCR section 82 is passed through the selector 88 to the L level.
The data is supplied to the UT 89, the data is converted by the LUT 89, and the data is input to the UCR unit 82. The configuration other than this is the same as the above-described embodiment.

Therefore, according to the present embodiment, according to the monochrome / full-color mode switching signal 8, it is possible to form a grayscale image which is not subjected to color conversion for a monochrome image.

The resolution of the PMW is not limited to that used in the above embodiment, and other resolutions such as 300 dpi and 150 dpi may be used.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0053]

As described above, according to the present invention, the property of each pixel of the input luminance image data is investigated, the input luminance image data is converted into the density image data, and the density image data of each pixel is converted. Since undercolor removal is performed according to the property, for example, undercolor removal that emphasizes gradation is applied to photographic images and color characters, and for example, undercolor removal is performed so that the outline of character graphics becomes sharper. Therefore, there is an effect that a high-quality image can be formed according to the property of the image.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a color laser beam printer which is a typical embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a printer controller 3.

FIG. 3 is a block diagram showing a configuration of a signal processing unit included in the printer engine 4.

FIG. 4 is a block diagram showing a configuration of an RF circuit 8.

FIG. 5 is a block diagram showing a schematic configuration of a color laser beam printer according to another embodiment.

FIG. 6 is a block diagram showing a configuration of an RF circuit 8 of a printer engine 4 according to another embodiment.

FIG. 7 is a side sectional view of an engine portion of a color laser printer according to a conventional example.

FIG. 8 is a diagram showing a processing concept when a printer controller receives image data from a host computer, performs image processing, and outputs an output signal to a semiconductor laser drive circuit according to a conventional example.

FIG. 9 is a block diagram showing a detailed configuration of an image signal processing unit 305 according to a conventional example.

FIG. 10 is a time chart showing a relationship between a color designation signal and an image signal according to a conventional example.

FIG. 11 is a time chart of a control signal and an image signal related to pulse width modulation according to a conventional example.

[Explanation of symbols]

 3 Printer Controller 4 Printer Engine 8 RF Circuit 12, 13 Triangle Wave Generation Unit 15, 16 Comparator 17 Selector 82 UCR Unit 86 LUT

Claims (4)

[Claims] 1. Input means for inputting luminance image data, analyzing means for examining properties of each pixel of the luminance image data, converting means for converting the luminance image data into density image data, and an analysis result by the analyzing means. In accordance with the above, there is provided an undercolor removing means for removing the undercolor of the density image data, and an image forming means for forming an image based on the density image data subjected to the undercolor removal by the undercolor removing means. Image forming apparatus. 2. According to the analysis result by the analysis means,
The image forming apparatus according to claim 1, further comprising a resolution control unit that controls a resolution of image formation. 3. The image forming apparatus according to claim 1, wherein the property examined by the analyzing means is a distinction between each pixel as a photographic image or a character graphic image. . 4. A determination means for checking whether or not the input brightness image data is monochrome data, and when the input brightness image data is monochrome data, the conversion means converts the density data into density image data. The image forming apparatus according to claim 1, wherein the conversion is bypassed.