JP3004281B2 - Image forming device - Google Patents

Description

Description: 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 that forms an image with a plurality of resolutions.

[Related Art] Conventionally, in this type of apparatus, the resolution of a natural image and that of a character image in one image output are made different according to an image area separation method or an instruction from a CPU. By the way, there is a case where it is desired to combine a natural image and a character image which exist independently.

[Problems to be Solved by the Invention] However, according to the conventional method, there is a waste that an image area is separated on the printer side from an image synthesized on the host side in advance.

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art, and an object thereof is to form a high-quality single image from images of different gradations, for example, a multi-valued image and a binary image such as a character. An object of the present invention is to provide an image forming apparatus and an image forming control device.

[Means for Solving the Problems] In order to achieve the above object, an image forming apparatus according to the present invention has a first input unit for inputting multi-valued image information and a first input unit for synthesizing the multi-valued image information. A second input unit for inputting the second image information to the multi-valued image information in synchronization with the clock, and a unit for forming an image of the image information input by the first and second input units. Image forming means for forming an image at a resolution of or a second resolution different from the first resolution;
A control unit for selectively controlling the first and second resolutions based on a level of the second image information input by the second input unit.

Further, in order to achieve the above object, an image forming apparatus according to the present invention includes a first memory for storing multi-valued image information, a second memory for storing binary image information, and the second memory. Converting means for converting the binary image information into multi-valued image information; selecting means for selecting one of first and second resolutions according to the level of the binary image information in the second memory; At the resolution selected by the means, the image information obtained by combining the multi-valued image information of the first memory and the multi-valued image information converted by the conversion means is converted into a binary signal corresponding to the density of the combined image information. It is characterized by comprising a binarizing unit for converting, and an image forming unit for forming an image in accordance with the binarized signal converted by the binarizing unit. Preferably, the first memory stores color-separated color multi-valued image information.

Further, in order to achieve the above object, the image forming control device of the present invention includes a first input unit for inputting multi-valued image information, and a second image information to be combined with the multi-valued image information. A second input unit for inputting in synchronization with the multi-valued image information, and a unit for forming an image based on the image information, wherein the second input unit has a first resolution or a second resolution different from the first resolution. A first supply unit that supplies the image forming unit that forms an image in combination with the multi-valued image information and the second image information, and a level of the second image information that is input by the second input unit And a second supply unit for supplying a control signal for selectively controlling the first and second resolutions to the image forming unit based on the first and second resolutions.

[Description of Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a sectional view of a printer mechanism of a color laser beam printer (C-LBP) of the embodiment. In the printer unit 2000, a laser beam emitted from a laser element (not shown) is scanned at high speed in the main (horizontal) scanning direction by a polygon mirror 2289, further reflected by a mirror 2290, and
Line dot exposure is performed on the photosensitive drum 2900 uniformly charged at 2297 with a resolution of up to 16 lines / mm. In this embodiment, one horizontal scanning length of the laser corresponds to one horizontal scanning length of the image information.
On the other hand, the photosensitive drum 2900 is rotating at a constant speed in the direction of the arrow,
Thereby, a planar image (latent image) is formed. Next, for example, if the exposed image is yellow image data, the latent image is developed by a yellow developing device (Y) 2292, and further transferred onto a sheet on a transfer drum 2296 by a transfer charger 2298.
In this way, the above is repeated for each image data of magenta (M), cyan (C), and black (B _K ), and a color image is formed by superimposing images of each color on the same sheet.

FIG. 1 is a block diagram of the C-LBP80 of the embodiment. The C-LBP 80 of the embodiment includes an interface unit 100 and a printer unit 2000.

In the interface unit 100, reference numeral 2 denotes an external interface circuit, which is connected to the host system 30 via the cable 1.
Connect to 0 to exchange control information and image data. A control unit 3 interprets and executes a control command or the like sent via the external interface circuit 2 and controls an image memory described later. In the control unit 3, reference numeral 3-1 denotes a CPU, which performs main control of the control unit 3. 3
Reference numeral -2 denotes a ROM, which stores, for example, a control program shown in FIG. 6 to be executed by the CPU 3-1. The ROM 3-2 also stores a font table for converting character code data into character pattern data. A ROM 3-3 temporarily stores character code data and the like sent from the host system 300, and is also used by the CPU 3-1 as a work area. Reference numeral 3-4 denotes a direct memory access controller (DMAC) which manages image memories 5 to 5 under the control of the CPU 3-1.
8 for DMA transfer of color image data. The image memories 5 to 8 respectively store color-separated color image data. That is, the R memory 5 is red (R) or cyan (C), the G memory 6 is green (G) or magenta (M), and the B memory 7 is blue (B) or yellow (Y).
Are respectively stored. The B _K memory 8 stores loiter image data or by connexion expanded character pattern data to CPU3-1 of (B _K) (2-value data). Also 27
Numeral F denotes an F memory, which stores, when a different image is synthesized in the image memories 5 to 8, the synthesized position in a bit map system. Reference numeral 10 denotes a synchronization signal processing circuit which reads image data from the image memories 5 to 8 in synchronization with a synchronization signal BD from the printer unit 2000 and sends the image data to the printer unit 2000.

In the printer unit 2000, an image processing circuit 2121 performs color conversion of input R, G, B data into Y, M, C, _BK data when necessary. Reference numeral 2160 denotes a gradation control circuit which makes the Y, M, C, _BK data correspond to the color reproduction density of the printer unit 2000 and performs PWM conversion according to the density. Reference numeral 2200 denotes a laser driver, which outputs a video signal output from the gradation control circuit 2160 to the laser element 22.
Drive 23. A control unit 2500 controls the printer unit 2000. The control unit 2500 is connected to the control unit 3 via the line 24.
Exchange information with the In the control unit 2500, 2110
Denotes a CPU, which performs main control of the control unit 2500. Reference numeral 2502 denotes a ROM, which is a control program executed by the CPU 2110 (for example, a sixth
(Part of the figure). 2504 is RAM, CPU 2110
Is used as a work area. Reference numeral 2600 denotes a potential sensor, which detects a charge amount of the photoconductor 2900. Reference numeral 2700 denotes a potential measurement unit (PDU), which amplifies the output of the potential sensor 2600 and inputs it to the A / D converter 2503. Reference numeral 2800 denotes a sensor which detects a tip position to output an image and outputs an image tip signal IT.
Output OP. Further, reference numeral 2298 denotes a humidity sensor, and 2299 denotes a temperature sensor, which detect humidity and temperature for correcting development characteristics, respectively. Reference numeral 2285 denotes a drive motor of the printer mechanism.

In such a configuration, the host system 300 communicates with the CPU 3-1 via the external interface circuit 2. For example, the host system 300 specifies the type of image data to be sent, and the specified information is stored in the RAM 3-3.

The following are conceivable as combinations of images to be sent. R, G, B data and character code data (black or color designation), R, G, B data and binary font data (black or R,
G, B), Y, M , C, B K data and character code data (black or color specification), Y, M, C, B K data and binary font data (black or R, G, B), And so on. Instead of the binary font data, image data having three or more gradations and a relatively small number of gradations (for example, color image data created by computer graphics) may be used. The CPU 3-1 manages the DMAC 3-4, so that the R, G, and B data are stored in the image memories 5-7.
In, also Y, M, C, sequentially DMA-transferred to the image memory 5-8 for B _K data.

In the case of R, G, B data and black character code data A), the CPU 3-1 temporarily stores the character code data in the RAM 3-3, converts this into character pattern data by the ROM 3-2, and The interface circuit 2 is controlled to control the signal line 11
And the signal line 13 are connected, the address line 14 is incremented, and the character pattern data is
Develop in _BK memory 8

In the case of R, G, B data and black font data B),
The font stored data once the RAM3-3, deployed to B _K memory 8 the font data in the bit map method while incrementing the address line 14 in the same manner as described above.

In the case of R, G, B data and character code data of color designation C), the character code data is temporarily stored in the RAM 3-3, and this is converted into character pattern data in the ROM 3-2. The address line 14 is incremented and the character pattern data is developed in the F memory 27. Further, the character pattern data is converted into multi-valued R, G, B
The data is color-separated, and the respective data are combined into R, G, B memories 5 to 7.

Also, R, G, B data and multi-valued color fonts, that is, R,
In the case of font data having components G and B, D), the font data is temporarily stored in the RAM 3-3, the address line 14 is incremented in the same manner as described above, and the R, G, and
The B font data is combined with the R, G, B memories 5-7. In addition, at the time of this combination, when any of the R, G, and B font data is data other than “0”, the CPU 3-1 writes a bit of logic “1” in a corresponding position of the F memory 27.

In the case of Y, M, C, B _K data and black character code data E)
Temporarily stores the character code data in the RAM 3-3, converts the character code data into character pattern data in the ROM 3-2, increments the address line 14 in the same manner as described above, and develops the character pattern data in the F memory 27. I do. Further, the character pattern data is converted into corresponding two types of multi-value data (for example, 00H or FFH) and is synthesized with the _BK memory 8.

In the case of Y, M, C, _BK data and character code data for color designation F), first, binary character pattern data is developed in the F memory 27 in the same manner as described above. Further color separation of the character pattern data Y of the slave connexion multivalued the designated color, M, C, the B _K data, synthesizing the respective image memory 5-8. Other combinations can be considered in the same manner as described above.

Thereafter, the CPU 3-1 sends a data processing end flag to the host system 300. The host system 300 knows from the flag transfer that the printer is in a printable state, and sends a print request command. As a result, CPU3−
1 activates the printer unit 2000.

FIG. 5 is a block diagram of a B _K memory 8 embodiment. In the figure, a decoder 802 decodes a bit plane selection signal from the CPU 3-1 into chip selection signals CS0 to CS7. Reference numeral 803 denotes a selector, which outputs a chip selection signal CS0 output from the decoder 802 in response to a selection signal from the CPU 3-1.
〜CS7 or all chip simultaneous selection signal is output. Thus, B _K memory 8 is also accessible as a normal image data memory even bit plane memory.

FIG. 3 is a block diagram of the image processing circuit 2121 of the embodiment. In the figure, reference numeral 901 denotes a gamma (γ) RAM, which performs γ conversion of input color image data. The contents of the γRAM 901 can be set by an instruction (or γ data) from the host system 300. For example, when Y, M, is stored C, and B _K data into the image memory 5-8, the contents of γRAM901 may be a non-conversion (input-output the same) properties. The selector 905 in accordance with the visible color information in the printer unit (Y → M → C → order of B _K) γRAM9
01Select the output Y, M, C, _BK data in order and then select selector 90
Output from 6. At this time, the binary signal F from the F memory 27 is input to the black processing circuit 903, and is output as it is from the line 2116 as the output pixel advances. The binary signal F output from the line 2116 controls the printing resolution in real time.

When the R, G, and B data are stored in the image memories 5 to 7, the contents of the γRAM 901 are so-called gamma conversion (R, G, B →
(Y, M, C) characteristics. By the way, the color material of the printer unit is toner in the case of the electrophotographic system as in the present embodiment, and other ink, for example, the ink jet system, and the thermal transfer ink in the thermal transfer system. Generally, since these color materials have different unnecessary absorption portions, it is not efficient to perform a masking operation for each printer on the host system 300 side. Therefore, UCR is added to the image processing circuit 2121.
A masking circuit 902 is provided so that the output
The Y, M, and C data are subjected to masking processing and the undercolor is removed, and at the same time, inking data B _K 2 ｛= (Y, M, C) _min ｝ is generated.

The binary data B _K has no conversion (input / output is the same) characteristic, and the output is referred to as binary pattern data B _K 1.
On the other hand, it outputs the black data B _K 3 based binary pattern data B _K 1 black processing circuit in 903 inking data B _K 2 or the later the multi-value conversion data. The selector 904 in accordance with the visible color information of the printer unit Y, M, C, and selectively outputs one data of the B _K. A serial signal of binary pattern data B _K1 is output to a line 2116.

FIG. 4 is a block diagram of the black processing circuit 903 of the embodiment. In the figure, the binary pattern data B _K1 is converted by a multiplexer 907 into a serial binary signal synchronized with the pixel output. 908 is a buffer;
The output serial binary signal is converted into multi-level data. For example, when the bit of the binary signal is logic 0, the multi-level data 00H (H
Is converted to multi-value data FFH when the bit of the binary signal is logic 1. Reference numeral 909 denotes an OR circuit for multi-value data, which includes inking data B _K 2 and multi-value data (00H or FFH).
OR the two. Thus, R, G, of the natural image based on the B data, black data B _K 3 of the synthesized portion of the logical 1 of the character pattern data is forced to FFH, is image synthesis. Further, in the portion where the character pattern data is logical 0, the print output remains a natural image. 910 is a selector, which is a CPU
2110 and outputs the black data B _K 3 were accordance connexion selected specified.
That is, for example, when the combination of the image data sent from the host system 300 is R, G, B data and black character code data (or black font data), the output of the OR circuit 909 is selected. At this time, binary pattern data that has been serially converted is output from a line 2116 and used as a resolution selection signal to be described later. For other combinations of image data, the multiplexer 907 is controlled by the CPU so that the F memory 27 is used, and its output signal F is used as a resolution selection signal.

FIG. 6 is a flowchart of a control procedure of the control unit 3 of the embodiment. In step S1, it waits for a control command to be sent from the host system 300. When the control command is sent, the process proceeds to step S2, for example, to initialize the interface unit 100. At this time, the setting of γ data of the image processing circuit 2121, the setting of the UCR coefficient, and the image data of R, G, B or Y, M, C,
Specify B _K. The CPU 3-1 provides information on the printer unit 2000. For example, paper size, whether or not the printer is in a wait state, and the like. In step S3, it is determined whether or not there is command data (character code data or the like). If not, in step S11, it is determined whether or not it is image data. If image data, DM in step S112
A, and all image data (R, G, B or C, M,
Y, B _K ) is determined. If not, the process returns to step S12. If the process is completed, the process proceeds to step S13.

If the command data is determined in step S3, the
Proceeding to S4, the character code data is temporarily stored in the RAM3-3. Determine whether the step S5, B _K data, to prohibit the data expansion in step S15 if there B _K data to the B _K memory 8. The process proceeds to step S6 if no B _K data, deploying character pattern data corresponding to the character code data into B _K memory 8. At this time, up to eight character pattern data can be developed in the _BK memory 8. In step S7, it is determined whether or not the development is completed. If the development is not completed, the process returns to step S6.
If the development is completed, the process proceeds to step S8, and the presence or absence of a print output command is detected. If it is not a print output command, the process returns to step S11. If the command is a print output command, the flow advances to step S9 to activate the printer unit via the control line 24, and at the same time, drive the synchronous signal processing circuit 10. Meanwhile, the printer unit 20
The CPU 2110 of 00 is the selector 904 or 905 of the image processing circuit 9,
And 906 are selected to selectively output color image information corresponding to the developed color. In step S10, it is determined whether or not the printing is completed. If the printing is completed, the host system 300 is notified of the completion and the process returns to step S1. If the processing is not completed for a predetermined time or more, the process proceeds to step S14, and the host system 300 is notified of the error. This error state is restored by a reset button (not shown) of the printer.

FIG. 7 is a circuit diagram of the gradation control circuit 2160 of the embodiment.
The main function of the gradation control circuit 2160 is to read and write image data, and to control the image clock signal (RCL) of the interface unit 100.
K) and synchronization of the image clock signal (VCLK) of the printer unit 2000, gradation conversion of the input video data in accordance with the image output mode, and further, the gradation-converted video data is subjected to PWM modulation. For example, conversion into a binary signal corresponding to the density.

In the figure, 8-bit image data output from the image processing circuit 2121 is a horizontal synchronizing signal (RHS) from the interface unit 100.
YNC) and the video clock signal (RCLK) in synchronization with the buffer memory (FIFO) 2105. Also, this image data is output from a horizontal synchronization signal (HSYN
C) and the video clock signal (VCLK). As a result, the interface unit 100 and the printer unit 2
000 speed matching is achieved.

The image data read from the buffer memory 2105 is a look-up table for printer characteristic correction {LUT (2)} 2
Enter in 106. The LUT (2) adjusts the input image data to match the output characteristics of the printer (eg, beam spot diameter, toner particle diameter, etc.) (the gradation of the output density increases and becomes linear). It is for creating data. The image data output from the LUT (2) is input to the D / A converter 2107, where it is converted into an analog video signal that changes in steps, and input to one terminal of each of the comparators 2117 and 2118. To the other terminals of the comparators 2117 and 2118, pattern signals (1) and (2) for binarizing (PWM modulation) the analog video signal in accordance with the density are input. Pattern signal (1)
Is for reproducing, for example, a character image, a line image or the like. In this case, since the resolution is a problem, a pattern signal having the same frequency (for example, 400 lines) as the video signal is used. That is, one pattern signal is generated per pixel. The pattern signal (2) is for reproducing, for example, a halftone image. In this case, since it is necessary to increase the gradation, for example, the frequency of the line drawing pattern signal is 1/2 (for example, 200 lines). The pattern signal is as follows. That is, the relationship is such that one pattern signal is generated for every two pixels.

Explaining the circuit, a crystal oscillator (XTAL) 2112 generates a clock signal having a frequency four times or more the frequency of the image clock signal. The synchronization control circuit 2113 synchronizes with the BD signal and the ITOP signal to synchronize the main scanning synchronization signal (HSYNC) and the basic clock signal (S).
CLK). The frequency dividing circuit 2114 frequency-divides the SCLK signal to generate a clock signal for generating a pattern (TVCLK and PVCLK). This TVCLK signal is a clock signal having a frequency twice as high as the video data signal and a duty ratio of 50%.
The pattern generation circuit 2115 generates an analog pattern signal (1) according to the TVCLK signal. In this embodiment, for example, a triangular wave signal is used. The comparator 2117 compares the analog video signal with the pattern signal (1), and outputs a PWM signal (1) obtained by subjecting the video density to pulse width modulation (PWM modulation).

The PVCLK signal is a clock signal having a frequency 1/2 that of the video data signal and a duty ratio of 50%. The pattern generation circuit 2116 generates an analog pattern signal (2) according to the PVCLK signal. In this embodiment, for example, this is also a triangular wave signal. The comparator 2118 compares the analog video signal with the pattern signal (2) and outputs a PWM signal (2) obtained by pulse width modulation of the video density. The selector 2103 selects a serial binary image signal 2116 or a selection signal from the CPU 2110 according to a control signal 2123 of the CPU 2110. When the control signal 2123 selects the serial binary image signal 2116, the selector 2119 selects the PWM signal (1) or the PWM signal (2) according to the logic 1 or 0 of the binary image signal 2116. As a result, the character pattern portion is output at a high resolution (400 lines), and the other natural image portions are output at a low resolution (200 lines). That is, in the modes shown in C), D) and F) among the above-mentioned modes, since 1 is set in the F memory in the character code or font portion, the input of the input terminal 9 is input to the multiplexer 907. If selected, a high resolution is set for the character or font portion by the signal on line 2116, and high-quality image reproduction can be performed. When the control signal 2123 selects a selection signal from the CPU, the resolution can be set according to the control of the CPU 2110. In this way, the selected PWM signal (1) or (2) is further matched with the operation of the material to be transferred by the gate circuit 2120 and is input to the laser driver 2200, where the semiconductor signal is output for a time corresponding to the pulse width of the PWM signal. Drive laser 2223 at constant current,
An electrostatic latent image is formed on the surface of the photosensitive drum 2900.

FIG. 8 is a timing chart of main signals in the printer unit. The figure shows an example of a horizontal synchronizing signal BD, a blanking signal, a reference clock signal SCLK, clock signals TVCLK and PVCLK for pattern generation, a video clock signal VCLK, and the like. Although not shown, the blanking signal is formed by a counter that measures a time shorter than a BD signal cycle reset at the falling edge of the BD signal.

FIG. 9 is a block diagram of an image processing circuit of another embodiment, and FIG. 10 is a block diagram of a black processing circuit of another embodiment. The UCR masking circuit 902 performs a matrix operation on the input image data with predetermined parameters and performs a UCR operation.
Enable to set parameters from 2110. Also UCR
A configuration in which a parameter value by which min (Y, M, C) is multiplied is set also in the calculation part. Further, in this embodiment, the LU for color correction is used.
T911 to 913 and LUT 914 for black correction are added, each of which is CPU 21
An arbitrary curve (conversion characteristic) can be set from 10. As a result, parameters can be set in accordance with the performance of the color material of the printer and the fixing roller. For example, inking data B _K 2
If you add the correction to Y, M, may be substituted for the overlapping portion by C data of three colors in inking data B _K 2. As a result, swelling due to three-color toner can be avoided, and the life of the fixing roller is prolonged. In addition, since the three-layer toner of Y, M, and C is easily scattered,
If this to B _K toner 1 layer, prevent splattering.

The printer unit of the above embodiment is Y, M, C, has been described in four colors of B _K is not limited thereto. The developing material of the printer unit may be composed of three colors of Y, M and C.

The density binarization means is not limited to PWM modulation. The dither method may be used.

Further, in the above-described embodiment, the case of synthesizing and outputting two systems of image data has been described, but the present invention is not limited to this. For example, the other binary image data for one multi-valued image data may be used only for switching the resolution. That is, for example, the fourth
In the figure, the signal on line 2116 is used as a resolution selection signal, but the multi-value data of the encoder 908 output is always “0”.
If the control is performed so as to make it impossible, the composite of the substantially binary image data is not performed. Accordingly, the host system can prepare multi-valued image data and binary image data (resolution selection signal) corresponding to the multi-valued image data, so that a high degree of freedom and fine-grained resolution control can be performed.

[Effects of the Invention] As described above, according to the present invention, images of different gradations,
For example, since a multi-valued image and a binary image such as a character and a figure can be input in synchronization with a clock, an image in which these images are combined can be easily formed. Therefore, especially in a region where a multi-valued image is combined with a character graphic or the like, the gradation of the multi-valued image can be maintained, and the character graphic or the like can be formed with high resolution.
High quality images can be obtained.

[Brief description of the drawings]

FIG. 1 shows a color laser beam printer (C
2 is a block diagram of the printer mechanism of the C-LBP80 of the embodiment, FIG. 3 is a block diagram of the image processing circuit 2121 of the embodiment, and FIG. 4 is a black diagram of the embodiment. block diagram of a processing circuit 903, block diagram of a B _K memory 8 in Fig. 5 embodiment, Figure 6 is a control procedure of the control unit 3 of the embodiment flow chart, the gradation of Fig. 7 example FIG. 8 is a timing chart of a main signal in the printer unit, FIG. 9 is a block diagram of an image processing circuit of another embodiment, and FIG. 10 is a block diagram of a black processing circuit of another embodiment. It is a block block diagram. In the figure, 80 ... Color laser beam printer (C-LB
P), 300: Host system, 100: Interface unit, 2000: Printer unit, 2289: Polygon mirror, 22
90 ... Mirror, 2297 ... Charging device, 2900 ... Photosensitive drum,
2292: Yellow developing unit, 2293: Magenta developing unit, 22
94 ... Cyan developing device, 2295 ... Black developing device, 2298 ...
... Transfer charger.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/387

Claims (4)

(57) [Claims] A first input unit for inputting multi-valued image information; and a second input for inputting second image information to be combined with the multi-valued image information in synchronization with the multi-valued image information. Means for forming an image of image information input by the first and second input means, wherein the image formation is performed at a first resolution or a second resolution different from the first resolution. Means for controlling the selection of the first and second resolutions based on the level of the second image information input by the second input means. 2. A first memory for storing multi-valued image information, a second memory for storing binary image information, and a conversion for converting the binary image information in the second memory into multi-valued image information. Means for selecting one of first and second resolutions in accordance with the level of the binary image information in the second memory; and multiple memories in the first memory at the resolution selected by the selection means. Binarizing means for converting image information obtained by combining value image information and multi-valued image information converted by the converting means into a binary signal corresponding to the density of the combined image information; An image forming apparatus comprising: an image forming unit that forms an image in accordance with a converted binary signal. 3. An image forming apparatus according to claim 2, wherein said first memory stores color-separated multi-valued image information. 4. A first input means for inputting multi-valued image information, and a second input means for inputting second image information to be combined with the multi-valued image information in synchronization with the multi-valued image information. Means for forming an image based on image information, the image forming means for forming an image at a first resolution or a second resolution different from the first resolution; A first supply unit that supplies a combination of the first and second image information, and a first and a second resolution that are selectively controlled based on a level of the second image information that is input by the second input unit. A second supply unit for supplying a control signal to the image forming unit.