JPH08321952A - Image forming device - Google Patents

Abstract

PURPOSE: To ensure the gradation by a multi-value output by allowing a parallel serial conversion section to output serially a multi-gradation bit map table synchronously with a plural-multiple clock signal so as to form an image of multi-gradation. CONSTITUTION: A main scanning direction counter 52 receives a dot clock VCLK from a plural multiple clock generator 51 and counts it to provide a binary count output to a lookup table 50. A subscanning direction counter 53 counts a signal HSYNC and provides a binary count output to the table 50. The table 50 decides a picture element data output pattern comprising white or black binary values as to a 16-gradation position and 4-bit output image data D0-D3 to be generated are written in a video buffer 45. The image data written in the buffer 45 are converted into a serial VDO signal synchronously with a 4-multiple clock outputted from the generator 51 in an S/P conversion circuit 46 to a laser driver, from which a 16-gradation output is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binary output image forming apparatus using an electrophotographic system, which is capable of forming an image by multi-value output.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic system has a superior print speed and print quality as compared with an image forming apparatus of another system such as a heat-sensitive system, and has a low price in recent years. As a result, printers, plain paper faxes, digital copiers, etc., as output terminals for personal computers or workstations, etc. are rapidly becoming popular.

An image forming apparatus in a conventional laser beam printer will be described below with reference to FIGS. 4 to 8 as an example of the image forming apparatus using the electrophotographic system as described above. 4 is a configuration diagram showing an internal structure of a conventional image forming apparatus, FIG. 5 is a perspective view of an optical system showing an image forming operation in the image forming apparatus shown in FIG. 4, and FIG. 6 is an image in the image forming apparatus shown in FIG. FIG. 7 is a block diagram of a controller unit for controlling data processing, and FIG. 7 is an explanatory view showing a method of forming a pseudo lattice and outputting multivalued data to the pseudolattice to form a multivalued image in the conventional image forming apparatus shown in FIG. FIGS. 8A and 8B are explanatory views showing a method of determining the irradiation period of the laser beam by comparing the density level of each pixel with the comparative triangular wave in the conventional image forming apparatus shown in FIG.

In FIG. 4, 1 is a photosensitive drum such as an OPC rotating in the direction of arrow A, 2 is a cleaning blade for scraping off the toner adhering to the photosensitive drum 1 into a waste toner container (not shown), and 3 is a cleaning blade. A charge eliminating lamp for irradiating the photoconductor layer on the surface of the photosensitive drum 1, a charger 4 for charging the surface of the photosensitive drum 1, and a reference numeral 5 for irradiating the surface of the photosensitive drum 1 with a potential of a portion corresponding to an image. A laser beam for raising 7 is a rotating cylinder for attaching the toner particles 6 to the surface of the developing unit and supplying the toner particles 6 to the surface of the photosensitive drum 1, 8
Is a transfer unit for transferring the toner particles 6 attached to the photosensitive drum 1 to the print paper 9, 10 is a corona assembly for generating electrostatic charges on the back surface of the print paper 9 for transferring the toner particles 6 to the print paper 9, and 11 is An electrostatic charge remover that removes the positive charge of the print paper 9 to prevent the print paper 9 from winding around the photosensitive drum 1, and a fixing unit 12 having a high-intensity lamp 13, a heating roller 14, and a pressure roller 15. .

In FIG. 5, 16 is a semiconductor laser, and 1
Reference numeral 7 is a collimator lens, 18 is a cylindrical lens, 19 is a scanning mirror of a polygonal mirror composed of six surfaces that rotates at a constant speed, 20 is a scanner motor that rotates the scanning mirror 19 at a constant speed, 21 is a converging lens, and 22 is a reflecting mirror. Reference numeral 24 is a beam detection mirror for detecting one end of the laser beam from the converging lens 21 for synchronization, 23 is an optical fiber for transmitting the laser beam reflected from the beam detection mirror 24, and 25 is sent from an external device or the like. The controller unit 26 converts the print data into image bitmap data and serially outputs it to the laser drive unit 26, and the controller unit 26.
5 is a laser driving unit that modulates a laser beam based on the bitmap data of the image sent from the device 5 and generates a signal for driving the semiconductor laser 26 and the scanner motor.

The structure of each part in the conventional image forming apparatus has been briefly described above, and the operation thereof will be described below with reference to FIGS. 4 and 5. First, before printing, the surface of the photosensitive drum 1 is destaticized by the cleaning blade 2 and the destaticizing lamp 3. Next, the photosensitive drum 1 is rotated, and the surface of the photosensitive drum 1 is charged by the charger 4 to a uniform potential of about -600V.

The laser beam 5 generated by the semiconductor laser 16 is collimated by a collimator lens 17 and focused on a scanning mirror 19 by a cylindrical lens 18. The laser beam 5 reflected by the scanning mirror 19 rotating at a constant speed scans the surface of the photosensitive drum 1 through the converging lens 21 and the reflecting mirror 22, and the portion irradiated with the laser beam 5 is charged to about -100V. An electrostatic latent image is formed.

The speed of the motor (not shown) for rotating the photosensitive drum 1 is, for example, in the case of a 600 DPI laser printer, the surface is rotated in the direction of 1/600 inch each time the laser beam 5 scans one line. Synchronized to move, the laser beam 5 is modulated to hit a dot of light every 1/600 inch. as a result,
Dots per square inch (DPI) is 600 x 6
00, a resolution of 600 DPI can be obtained.

At the start of each scan, the laser beam 5 is reflected by the beam detection mirror 24 before reaching the photosensitive drum 1 and sent to the controller section 25 by the optical fiber 23, where it is converted into an electrical signal called HSYNC. It is used to synchronize the output of data related to scanning with other data, and is also used for the control and test functions of other printers.

In the developing section, the rotating cylinder 7 having the toner particles 6 adhered to the surface thereof is brought close to the photosensitive drum 1 to adhere the toner particles 6 to the electrostatic latent image formed on the surface of the photosensitive drum 1. Since the toner particles 6 are negatively charged, they adhere to the portions exposed by the laser beam 5, but do not adhere to the portions not exposed.

In the transfer section 8, the toner image formed on the surface of the photosensitive drum 1 gives a positive charge to the print paper 9, and the toner particles 6 charged on the surface of the photosensitive drum 1 are negatively charged.
To be attached to the print paper 9. The electrostatic charge remover 11 removes the negative charges on the surface of the photosensitive drum 1 to prevent the print paper 9 from winding around the photosensitive drum 1. The print paper 9 to which the toner particles 6 adhere is transferred between the heating roller 14 and the pressure roller 15, and the toner particles 6 are melted and fixed on the print paper 9 by heat and pressure.

Next, the control of the image data in the controller section will be described with reference to FIG. First, the configuration of each part of the controller unit 25 will be described. Reference numeral 27 is a central processing unit (CPU) that controls the operation of the controller unit 25, and 28 is a CPU 2 stored in a program read-only memory (referred to as program ROM in the figure) 29.
Program data to be executed by 7 or font ROM
ROM controller for inputting image pattern data of character fonts stored in 30, font cards 31 and 32 via the data bus 33 according to address information from the CPU 27 and outputting to the main data bus 34, 31 and 3
Reference numeral 2 denotes a font card that stores image data of optional character fonts and is configured in a connector-in type ROM card format.

Further, 35 is a printer engine section showing all other such systems including a control panel (not shown) related to actual image print processing, and 36 controls address information from the CPU 27. Then, the printer engine unit 35 is controlled so that data is read from the printer engine unit 35 through the engine interface 37, coded image data is input from the external device 38 through the parallel interface 39, and further from the CPU 27. E according to the address information of
The engine controller 40 controls reading and writing of information to and from the EPROM 40, and the EEPROM 40 stores information such as print status and page count from the control panel of the printer engine unit 35.

Reference numeral 41 is a large capacity random access memory (referred to as DRAM in the figure) for storing coded image data input from the external device 38, bitmap data such as character fonts and other data, and 43 and 44 are D.
An expansion DRAM capable of expanding the memory area of the RAM 41, 42 is a D required for reading and writing data to and from the DRAM 41 in accordance with address information from the CPU 27.
Generates RAM address information and timing signal to generate DR
D for performing data access to the AM 41, arbitrating the main data bus 34, and refreshing the DRAM 41
It is a RAM controller.

Further, 45 is a video band buffer (referred to as VBB in the drawing) for holding bitmap data which is output image data for output, and 46 is parallel serial conversion of the output image data stored in the video band buffer 45. Then, in synchronization with the dot clock (VCLK) generated by the reference clock generated from the clock generator 47 (where VCLK has the same cycle as the resolution of the printer), it is output to the laser drive unit 26 as image dot data. It is a parallel-to-serial converter.

Similarly, referring to FIG. 6, the operation of the controller section 35 will be described. External device 38
The coded image data input from is input via the parallel interface 39. The input coded image data is stored in the DRAM 41 according to the setting contents of the EEPROM 40 referred to by the engine controller 36. The coded image data held in the DRAM 41 is stored in the CPU 2 according to the contents of the program ROM 29.
It is converted by 7 into an intermediate language called a display list and held there.

In the display list, font, image, graphic distinguishing information, coordinate position on the print paper 9, font type and size, if code, image itself if image, graphic itself. For example, it includes information such as circles, ellipses, lines, and line thickness. If the contents of the display list are characters, the font ROM 30 and the font cards 31 and 32 are referenced to determine the bitmap data of the corresponding characters. If the image itself is the bit map data of the image portion of the coded image data input from the external device 38, if the bit map data is binary, it is as it is, if it is multi value indicating multiple gradations. It is converted into a binary value using a method described later and then stored in the DRAM 41.

When the display list is created for all the coded image data, the printer engine unit 3
Printing starts on 5. When printing is started, bitmap data representing binary information at each bit position of the image is formed from the display list and written in the video band buffer (VBB) 45. The bitmap data written in the video band buffer 45 is sent to the parallel / serial conversion unit 46. The parallel-serial conversion unit 46 converts the bitmap data into serial data, and the main scanning direction (the direction perpendicular to the traveling direction of the print paper 9) is the dot clock VCLK, and the sub-scanning direction (the traveling direction of the print paper 9) is. VD synchronized with the HSYNC signal
An O signal is serially output to the laser drive unit 26.

[0019]

However, in the conventional image forming apparatus configured as described above, only two types of output (binary output) of white dots and black dots can be obtained, so that an intermediate gradation is obtained. It was difficult to output (multilevel output), that is, output having a density level. As one of the conventional techniques for solving this, when multi-valued data is input from the external device 38, for example, as shown in FIG. 7, 4 × 4 dots, 8 × 8 dots, 4 × 4 dots are used. , 16
The matrix of each grid such as × 16 dots is virtually regarded as one pixel, and processing such as the systematic dither method such as the halftone dot method, the spiral method, and the Bayer method is performed, and the pseudo image is multi-valued using binary image data. Some have been designed to output values. For example, as shown in FIGS. 7 (B) and 7 (C), one pixel is formed virtually or pseudo by 4 × 4 dots or 8 × 8 dots in a thick line, and each dot is formed into that pixel. The white or black dot that determines the gradation of the pixel is changed, and the gradation of the pixel is changed according to the position and the number.

Another conventional method for multi-value output is proposed in Japanese Patent Laid-Open No. 1-280965 as shown in FIG. It is a method that forms a comparative triangular wave for each pixel, compares the density level of each pixel with the comparative triangular wave, and excites the laser beam only when the value of the comparative triangular wave is lower than the density level of the pixel. is there.

However, in the case of using the first systematic dither method, if the gradation is improved, the resolution is lowered,
There is a problem that gradation is lowered if the resolution is improved. For example, in a printer having a resolution of 600 DPI, when a matrix of 4 × 4 dots is used, the number of gradations is 16 (= 4 × 4) and the resolution is 150 DPI, while a matrix of 8 × 8 dots is used. , The number of gradations increases to 64 (= 8 × 8), but the resolution is 75D.
There is a problem that the quality of the output image is greatly deteriorated due to the decrease in PI.

In the case of adopting the method of comparing the density level of the pixel with the comparative triangular wave using the latter comparative triangular wave,
An analog circuit such as a triangular wave generation circuit and a comparison circuit is required, which may lead to a significant increase in cost. Although many high-end printers use this method, there is a problem that a low-cost low-end printer cannot be a realistic solution.

The present invention has been made in view of the above problems, and minimizes the reduction in resolution without requiring the increase in complexity and cost due to the addition of analog circuits such as a triangular wave generation circuit and a comparison circuit. It is an object of the present invention to provide an image forming apparatus capable of ensuring gradation by multi-valued output while holding down.

[0024]

In order to achieve the above object, the image forming apparatus according to the present invention serializes the bit map data and a video band buffer which stores binary bit map data forming an output image. An image forming apparatus including a parallel-serial conversion unit for converting and outputting to a laser driving unit, the image forming apparatus forming an image by binary dots based on multi-valued input image information. Image data input buffer to be converted to the image data of the image, and the output pattern expressing the image is determined by referring to the converted multi-tone image data and stored in the video band buffer as multi-tone bitmap data. Generates a lookup table to output and a multiple clock signal having a period that is a multiple of a dot clock (VCLK) that determines the resolution. And a plurality times clock generator,
A multi-gradation image is formed by outputting multi-gradation bitmap data input in the parallel-to-serial conversion unit serially in synchronization with a multiple-time clock signal. .

Further, in order to achieve the above object, the image forming apparatus according to the present invention further has a dot clock (VCL
K) is included in the main scanning direction counter and the sub scanning direction counter, and the resolution and the number of gradations of pixels in the resolution are determined by the counts of the main scanning direction counter and the sub scanning direction counter. It is characterized in that a multi-tone image is formed according to the tones.

In order to achieve the above object, the image forming apparatus according to the present invention has a dot clock (VCLK) cycle of a multiple clock signal having a cycle that is a multiple of a dot clock (VCLK). 1 time 1/4 time
It is characterized in that it has a cycle of double, 1/8 or 16 times.

Further, in order to achieve the above object, the image forming apparatus according to the present invention further has a dot clock (VCL
K) 1/2 times, 1/4 times, 1/8 times or 16
It is characterized in that a clock signal selecting means capable of selecting any one of a plurality of clock signals having a period of one-tenth is provided.

[0028]

The image forming apparatus according to the present invention is configured as described above, and in particular, in its controller section, a display list is created from input multi-tone input image data and the number of gray levels is converted to obtain a multi-valued image. An image data input buffer that outputs (multi-gradation) image data, and a binary output pattern that represents a multi-gradation image based on multi-valued image data is determined by referring to a table, and the output image data is output. A look-up table to be stored in the video band buffer, a multiple clock generator for generating a signal of a multiple of (n) times the dot clock VCLK, and a counter in the main scanning direction and the sub-scanning direction are provided. A plurality of (n) times the number of gradations is set in the scanning direction, and the resolution and the gradation of that pixel are determined by the count values of the main scanning direction counter and the sub-scanning direction counter. By which is adapted to determine,
Realization of an image forming apparatus capable of ensuring gradation by multi-value output while minimizing deterioration of resolution without increasing complexity and cost due to addition of analog circuits such as a triangular wave generation circuit and a comparison circuit. Became possible.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings and FIGS.
1 is a block diagram showing in detail a part of a controller unit of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of an entire controller unit of the image forming apparatus including the part shown in FIG. 1, and FIG. FIG. 6 is an explanatory diagram showing a state of multi-value output in one embodiment of the present invention with one pixel.

First, referring to FIG. 1 and FIG.
The configuration of the image forming apparatus according to the embodiment will be described in detail. In FIGS. 1 and 2, the blocks having the same numbers as the numbers shown in the conventional controller unit 25 in FIG. 6 are the same, so the description thereof will be omitted. In FIGS. 1 and 2, reference numeral 48 is a controller unit constructed according to the present embodiment, and 49 is a temporary holding unit for input multi-tone input image data, which will be described later.
An image data input buffer for converting into image data of gradation, 50 is an output pattern which refers to a table and expresses a pixel of multi gradation (16 gradations) to be printed for a value of input image data of multi gradation. It is a lookup table to be determined.

Further, 51 generates a plurality of (n) -fold clocks having a period (that is, a plurality of times) that is 1 / n times the resolution of the printer (in this embodiment, 4).
1 × period or 4 × frequency) Multiple Clock Generator, 4VCLK is Multiple Clock Generator 5
The dot clock VCLK generated in 1 is further frequency 4
4 times the dot clock which determines the number of gradations in the main scanning direction by doubling (cycle is 1/4), 52 is the binary main scanning direction counted by the dot clock VCLK generated from the multiple clock generator 51 A counter 53 is a binary sub-scanning direction counter that is counted by a clock HSYNC that synchronizes in the sub-scanning direction.

In this embodiment, the resolution of the printer itself is 6
It is assumed that binary output by 00 DPI is possible, and the number of expressible gradations is 16 gradations at a resolution of 300 DPI. In this case, the multiple clock generator 51 uses, for example, one pixel of 600 DPI as shown in the middle thick line in FIG. 3 by 4 pixels (or 300 D as shown in the thick line).
Since 16 gradations are output by one pixel of PI, the frequency of 4 times the dot clock VCLK (4
The signal of 1 / cycle is generated and controlled.

Next, with reference to FIGS. 1 to 3, the operation of the image forming apparatus constructed as described above according to this embodiment will be described. In a series of printing operations, a display list is created as in the above-mentioned conventional example. Here, in the case of the conventional example, the display list of multi-valued data is converted into binary and held in the DRAM 41, but in the case of the present embodiment, the input multi-valued (multi-tone) image data itself and its floor are displayed. Temporarily hold the key number in the image data input buffer 49,
I convert it to a multi-valued display list and hold it there.

Then, temporarily, the image data input buffer 4
The multivalued image data of the display list held in 9 is changed or converted into the number of gradations that can be output by the printer.
In the case of this embodiment, the display list is converted in the image data input buffer 49 from 8-bit 256-gradation image data (Din0 to dDin7) to 4-bit 16-gradation image data (Dout0 to Dout3). Addresses A0 to 0 of the lookup table 50
Input to A3.

On the other hand, the main scanning direction counter 52 inputs and counts the dot clock VCL from the multiple clock generator 51, and outputs the binary count output to the address A4 of the lookup table 50. The sub-scanning direction counter 53 counts the signal HSYNC from the beam detection mirror 24 (FIG. 5) and outputs the binary count output to the address A5 of the look-up table 50.

In the look-up table 50, referring to the table based on the data input to the addresses A0 to A5, as described below, white or black is generated for each 16 gradation position in one pixel having 16 gradations. The binary image data output pattern is determined, and the 4-bit output image data D0 to D3 created thereby are written in the video band buffer 45. Video band buffer 4
In the parallel-serial conversion circuit 46, the image data written in 5 is synchronized with the quadruple clock 4VCLK output from the multiple clock generator 51 and serial V
It is converted into a DO signal and output to the laser drive unit 26. As a result, as shown in FIG. 3, 16 gradations can be output by 4 pixels of 600 DPI (= 1 pixel of 300 DPI).

As described above, according to this embodiment,
Image data input for creating a display list from multi-tone input image data and converting the number of gray levels to output multi-value (multi-tone) image data in a controller unit of an image forming apparatus having binary output Based on the buffer and the multi-valued image data from the image data input buffer, a binary output pattern expressing a multi-tone image or pixel is determined by referring to the table, and the output image data is output to the video band buffer. And a lookup table stored therein, a multiple clock generator for outputting a clock signal having a cycle of a plurality (n) of the resolution in the main scanning direction, a main scanning direction and sub-scanning direction counter, The number of gradations can be set multiple times in the main scanning direction, and
The resolution and the number of gradations at the resolution are determined by the count values of the main scanning direction counter and the sub-scanning direction counter, so that the multi-value output using the area gradation that can change the gradation for each pixel. Is what makes it possible.

In the present embodiment, the multiple clock generator generates the 4 × dot clock 4VCLK having a quarter period of the dot clock VCLK.
8 times gradation at 300DPI at double, 300D at 1/8 times
32 gradations with PI, 64 with 300 DPI at 1/16 times
It can be easily inferred that multi-value output of gradation is possible by changing the value of the look-up table. Further, the multiple clock generators are each one half, one quarter
It is configured to selectively generate a clock signal having a cycle of double, ⅛ times, or ⅙ times, and is either selected by an external device or set by a clock signal selection means such as a control panel. You may make it select the signal of a period.

[0039]

The image forming apparatus according to the present invention is configured as described above, and in particular, the controller section thereof is provided with a display list from input image data of multiple gradations, and the number of gradations is converted to a large number. An image data input buffer that outputs image data of multiple values (multi-gradation), and a binary output pattern that represents a multi-gradation image based on the multi-valued image data is determined by referring to the table, and the output image data Is stored in the video band buffer, a multiple clock generator for generating a signal of a multiple (n) times the dot clock VCLK, and a main scanning direction and sub-scanning direction counter are provided. The number of gradations can be set multiple times for each direction, and the resolution and the number of gradations at that resolution can be determined by the count values of the main scanning direction counter and the sub scanning direction counter. By doing so, the gradation deterioration is ensured by the multi-value output while minimizing the decrease in resolution without increasing the complexity and cost due to the addition of analog circuits such as the triangular wave generation circuit and the comparison circuit. It is possible to realize an image forming apparatus capable of performing the above.

[Brief description of drawings]

FIG. 1 is a block diagram showing in detail a part of a controller unit of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of the entire controller unit of the image forming apparatus including the portion shown in FIG.

FIG. 3 shows a state of multi-value output in one embodiment of the present invention.
Explanatory drawing shown in pixels

FIG. 4 is a configuration diagram showing an internal structure of a conventional image forming apparatus.

5 is a perspective view of an optical system showing an image forming operation in the image forming apparatus shown in FIG.

6 is a block diagram of a controller unit that controls processing of image data in the image forming apparatus shown in FIG.

7 is an explanatory diagram showing a method of forming a pseudo lattice and outputting multivalued data to the pseudolattice in the conventional image forming apparatus shown in FIG. 4 to form a multivalued image.

FIG. 8 is an explanatory diagram showing a method of determining the laser beam irradiation period by comparing the density level of each pixel with a comparative triangular wave in the conventional image forming apparatus shown in FIG.

[Explanation of symbols]

 1 Photosensitive Drum 2 Cleaning Blade 3 Charge Eliminating Lamp 4 Charging Device 5 Laser Beam 6 Toner Particles 7 Rotating Cylinder 8 Transfer Part 9 Print Paper 10 Corona Assembly 11 Static Charge Remover 12 Fixing Part 13 High Brightness Lamp 14 Heating Roller 15 Pressure Roller 16 Semiconductor Laser 17 Collimator Lens 18 Cylindrical Lens 19 Scanning Mirror 20 Scanner Motor 21 Converging Lens 22 Reflecting Mirror 23 Optical Fiber 24 Beam Detecting Mirror 25 Controller Section 26 Laser Driving Section 27 CPU 28 ROM Controller 29 Program ROM 30 Font ROM 31 Font Card 32 font card 33 data bus 34 main data bus 35 printer engine section 36 engine controller 37 engine interface 38 external device 39 Parallel interface 40 EEPROM 41 DRAM 42 DRAM controller 43 Extended DRAM 44 Extended DRAM 45 Video band buffer 46 Parallel-serial conversion unit 47 Clock generator 48 Controller unit 49 Image data input buffer 50 Look-up table 51 Multiple clock generator 52 Main scanning direction Counter 53 Sub-scanning direction counter

Claims (4)

[Claims] 1. A multi-value conversion system comprising: a video band buffer for storing binary bit map data forming an output image; and a parallel / serial conversion section for converting bit map data into serial data and outputting the serial data to a laser driving section. An image forming apparatus for forming an image by binary dots based on input image information, comprising an image data input buffer for converting multi-valued input image information into multi-tone image data, and the converted multi-tone image data. A lookup table for determining an output pattern expressing the image by referring to the image data and outputting it to the video band buffer as multi-tone bitmap data, and a dot clock (VCL) for determining the resolution.
K), and a multiple clock generator that generates a multiple clock signal having a cycle of a multiple of K), and the multi-gradation bitmap data is synchronized with the multiple clock signal in the parallel-serial conversion unit. An image forming apparatus is characterized in that a multi-gradation image is formed by serially outputting the images. 2. The image forming apparatus includes a main scanning direction counter and a sub scanning direction counter that count the dot clock (VCLK), and the resolution and the resolution in the resolution are determined by the main scanning direction counter and the sub scanning direction counter. The image forming apparatus according to claim 1, wherein a multi-gradation image based on area gradation is formed by determining the number of gradations of pixels. 3. A cycle of a clock signal having a cycle that is a multiple of a multiple of the dot clock (VCLK) is 1/2, a quarter, or a eighth of the dot clock (VCLK). 3. The image forming apparatus according to claim 1, wherein the image forming apparatus has a cycle of 1/16 times. 4. The image forming apparatus further comprises a half, a quarter, and a eighth of the dot clock (VCLK).
4. The image forming apparatus according to claim 3, further comprising a clock signal selection unit capable of selecting either a clock signal having a cycle of double or 1/16.