JPH05292301A - Image forming method - Google Patents

Abstract

PURPOSE:To reduce character and line picture distortion, banding and picture noise by combining very small matrices with less deterioration in the resolution in the write of multi-value processing by one-dot modulation. CONSTITUTION:A 6-bit signal from a scanner is inputted to an adder 1105 and a ROM 1106 via line memories 1101, 1102, latches 1103, 1104 and switches SW1-SW4. The output is fed to a printer as an 8-bit data signal. The SW2 selects EVEN or ODD data for each one write block and the switches SW3, 4 are thrown to the down-position to select data from the latches 1103, 1104. Read main scanning 2-dots correspond to a write main scanning dot. Read dot data adjacent in the main scanning direction are divided into write dot data, two dots form one picture element and density data are sampled for each of two dots. Then a checker pattern is formed by deviating the phase of density occurrence dot.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method applied to a digital copying machine or the like. The present invention relates to an image forming method that realizes high-quality image formation by reducing cracking of character and line images and reducing banding and image noise in combination.

[0002]

2. Description of the Related Art For example, in writing processing in a digital copying machine, its resolution and gradation are important factors. Fine resolution and gradation that faithfully reproduce halftones are desired in copy processing for all originals including characters and photographs.

Conventionally, there is an area gradation method using a dither matrix as a method of expressing the gradation (for details of the area gradation method, see Japanese Patent Laid-Open No. 54-144126).
JP-A-56-17478, JP-A-57-7697
No. 7, etc.). However, in the above-mentioned area gradation method, since a pixel is composed of a plurality of dots and density is expressed by the number of written dots, the resolution is lowered. In this case, in the binary writing method, assuming that the number of dots forming a pixel is N, the number of gradations represents N gradations without including the background white portion, but in general, the resolution is high. Is reduced to 1 / N.

On the other hand, there has been proposed a 1-dot multi-value writing system which realizes multi-gradation without lowering the resolution. This is to modulate the density of one dot to be written in, for example, electrophotographic laser beam writing.
The optical modulation method of the laser diode for writing,
There are mainly a pulse width modulation method that modulates the exposure time and a power modulation method that modulates the exposure intensity. There is a conventional technique disclosed in Japanese Patent Laid-Open No. 62-49776 as a pulse width modulation system and Japanese Patent Laid-Open No. 64-1547 as a power modulation system.

Another method is to shift the writing phase with respect to the main scanning direction based on the image data to form a checkered pattern, or to resolve multi-value writing by one-dot modulation as shown in FIG. A two-dot multi-valued system has been proposed in which a minute matrix that does not deteriorate the property as much as possible is combined. In FIG. 19, (a) shows an image of 2 × 1 matrix and (b) shows an image of 1 × 2 matrix. In each of these images, weighting distribution of density is executed in the same direction.

Further, a digital image forming apparatus represented by a digital copying machine is required to reproduce halftones with high accuracy as one condition for achieving high image quality. In addition, it is said that the 1-dot multi-value writing method is preferable in order to achieve both resolution and gradation.

[0007]

However, the above-mentioned 1
The dot multi-value writing method has a problem that banding easily occurs. That is, for example, banding that occurs in the halftone area of a digital copying machine is
It is caused by uneven driving and vibration of the photoconductor, uneven scanning pitch of the writing optical system, and the like. The banding appears as continuous band-shaped density unevenness in the main scanning direction. In particular, in the 1-dot multi-value writing method, the skirts of the exposure beams in the intermediate exposure region overlap and banding occurs due to uneven scanning pitch of the laser diode in the sub-scanning direction during the exposure process.

Further, due to the higher resolution, the accuracy with respect to banding is being demanded. Further, in the one-dot multi-value writing at about 400 dpi, which is widely used at present, in the current electrophotographic process, image noise due to uneven density occurs in the solid halftone portion regardless of the modulation method, and the halftone There was a problem that it was not reproduced smoothly.

In addition, in the method of combining multi-valued writing by 1-dot modulation for reducing banding and image noise with a minute matrix with less deterioration of resolution, resolution in the direction of performing area gradation is achieved. Sex is reduced,
There is a problem that fine lines and cracks in letters are likely to become visible.

Further, in the method of forming a checkerboard pattern by shifting the writing phase with respect to the main scanning direction based on the image data, in order to actually embody the method using an electrophotographic process, , An isolated dot of 1 dot or less in the halftone by minimizing the writing beam diameter (for example, 1/2, 1 /
4) needs to be resolved, and there are many problems at the current technical level, such as difficulties.

Further, in the 2-dot multi-valued system (see FIG. 19) in which the multi-valued writing by the 1-dot modulation is combined with the minute matrix which does not reduce the resolution as much as possible, it is generated by the 1-dot multi-valued writing. Image noise is reduced due to banding and density unevenness in the halftone portion, and gradation is improved by smooth halftone reproduction. However, in the case of a 2-dot multi-valued line image forming 200 lines with a writing density of 400 dpi, characters and lines are cracked, and the image quality deteriorates as compared with the 1-dot multi-valued image.
In particular, there is a problem that abnormal images such as cracks of characters and lines, irregular pitch (density) of periodic lines, jaggies of edges of perfect circles, and the like occur.

The present invention has been made in view of the above, and achieves low banding in 2-dot multi-valued line image processing and maintains the advantage of smooth halftone reproducibility.
A first object of the present invention is to obtain high image quality by realizing reduction of characters and line cracks generated in a 2-dot multi-valued line image by simple image processing.

A second object is to reduce deterioration of resolution of characters and photographic images and improve gradation.

[0014]

In order to achieve the above-mentioned object, the present invention provides an image forming method for performing area gradation by multi-gradation writing for each dot and a plurality of adjacent read dot data. The present invention provides an image forming method for forming a checkerboard pattern by performing weighted distribution of density on write dot data based on a plurality of read dot data.

Further, in the image forming method in which the area gradation is performed by the multi-gradation writing for each dot and a plurality of read dot data adjacent to each other, the read dot data in the main scanning direction is delayed so as to be continuous in the main scanning direction. The density data of the dots is sampled and the density is weighted, distributed to adjacent two writing dot data in the main scanning direction, the dot formation start phase in the main scanning direction is periodically changed, and multi-level for each dot is performed. An image forming method for forming a checkerboard pattern by performing area gradation by two dots adjacent in the main scanning direction by gradation writing.

In addition, in the image forming method for performing the area gradation by the multi-gradation writing for each dot and a plurality of adjacent read dot data, the density of the write dot data is increased based on the plurality of adjacent read dot data. The present invention provides an image forming method in which a checkerboard pattern having a read pixel size or a dot size smaller than the read pixel size is formed by performing weighted distribution.

In addition, in the image forming method of performing the area gradation by the multi-gradation writing for each dot and the plural read dot data adjacent to each other, in the density of the write dot data based on the plural adjacent read dot data. Is performed, the dot formation start phase in the main scanning direction is periodically changed, and the density generation dots of the write dot data are periodically changed by the frequency division signal of the write clock signal to continuously change in the main scanning direction. An image forming method for forming a checkered pattern in units of 2 dots is provided.

Further, in the image forming method for performing the area gradation by the multi-gradation writing for each dot and a plurality of read dot data adjacent in the main scanning direction, the read dot data in the main scanning direction is delayed and the main scanning direction is delayed. The density data of a plurality of consecutive read dot data is sampled and the density is weighted and distributed to adjacent write dot data in the main scanning direction, and the dot formation start phase in the main scanning direction is divided by the write line signal. Image formation in which a density change dot of the write clock signal is changed cyclically by the frequency signal and the density generation dot of the write dot data is periodically changed by the frequency division signal of the write clock signal to form a checkered pattern of two dot units continuous in the main scanning direction. It provides a method.

Further, in the image forming method for performing the area gradation by the multi-gradation writing for each dot and a plurality of read dot data adjacent in the sub-scanning direction, two or more lines for storing the read density data in the main scanning direction are stored. By using the data storage means, the read dot data adjacent in the sub-scanning direction is sampled, the density is weighted, and distributed to the write dot data in the sub-scanning direction. Provides an image forming method for forming a checkerboard pattern.

Further, in the image forming method for performing the area gradation by the plural gradation writing for each dot by the power modulation of the laser output means and the plural adjacent read dot data,
The present invention provides an image forming method for forming a checkered pattern with dots having a size of 2 dots or more that are continuous in the main scanning direction.

Further, in the image forming method for performing the area gradation by the multi-gradation writing for each dot and the plural adjacent read dot data, the density data of the plural adjacent read dot data are sampled to weight the density. Done,
It is distributed to adjacent write dot data in the sub-scanning direction, the dot formation start phase in the main scanning direction is periodically changed by a divide-by-four signal of the write line signal, and it is continuous in the sub-scanning direction.
An image forming method for forming a checkered pattern in dot units.

Further, in the image forming method for performing the area gradation by the multi-gradation writing for each dot and a plurality of read dot data adjacent in the main scanning direction, the read dot data in the main scanning direction is delayed and the main scanning direction is delayed. Sampling density data of a plurality of read dot data consecutive to each other, weighting the densities, and distributing to adjacent write dot data in the main scanning direction, the dot formation start phase in the main scanning direction is 4 of the write line signal. It is an object of the present invention to provide an image forming method for forming a continuous checkered pattern of 2 dots or more in the sub-scanning direction by periodically changing it with a frequency division signal of frequency division or more.

Further, in the image forming method of performing the multi-gradation writing for each dot by the pulse width modulation of the laser output means and the area gradation by a plurality of read dot data adjacent to each other, two dot sizes consecutive in the sub-scanning direction or It is intended to provide an image forming method for forming a checkerboard pattern with more dots.

Further, in the image forming method for performing the area gradation by the multi-gradation writing for each dot and the plural adjacent read dot data, the density data of the plural adjacent read dot data are sampled to weight the density. Done,
It is distributed to adjacent write dot data, and the dot formation start phase in the main scanning direction is periodically changed by a frequency division signal of 4 or more of the write line signal and divided by 4 or more of the write clock signal. Provided is an image forming method for periodically changing density generation dots of write dot data by a circumferential signal to form a checkered pattern having a dot size of 2 dots or more in the main scanning direction and 2 dots or more in the sub scanning direction. ..

Further, in the image forming method for performing area gradation by multi-gradation writing for each dot and a plurality of read dot data adjacent in the main scanning direction, density data of a plurality of read dot data adjacent in the main scanning direction Are sampled, the densities are weighted, distributed to the adjacent write dot data in the main scanning direction, and the dot formation start phase in the main scanning direction is periodically divided by four or more divided signals of the write line signal. And the density generation dots of the write dot data are periodically changed by the frequency-divided signal of the write clock signal to form a checkered pattern with a dot size of 2 dots or more in the main scanning direction and 2 dots or more in the sub scanning direction. The present invention provides a method for forming an image.

[0026]

In the image forming method according to the present invention, the density is weighted from the adjacent read dot data, and the dots are formed so as to be distributed to the write dot data and form a checkered pattern. Further, the density is weighted from the read dot data adjacent in the main scanning direction, and the write dot data adjacent in the main scanning direction is distributed to form a checkerboard pattern without using a line memory. The writing is formed with a size of 2 dots or less.

Further, the image forming method according to the present invention forms a checkered pattern of 2 dot units continuous in the main scanning direction. Further, the density is weighted from the read dot data adjacent in the main scanning direction and distributed to the write dot data in the main scanning direction, and dots are formed so as to form a checkered pattern of two continuous dots in the main scanning direction. By doing so, a checkerboard pattern is formed in units of 2 dots without using a line memory. Also, using line memory,
A checkered pattern of dots having a size of 2 dots or more continuous in the main scanning direction is formed from the read dot data adjacent in the sub scanning direction. Further, the checkered pattern processing of concentrating two or more dots continuous in the main scanning direction and the one-dot multi-value writing by the power modulation of the semiconductor laser are combined.

Further, the image forming method according to the present invention forms a checkerboard pattern having a continuous 2-dot unit in the sub-scanning direction, that is, a vertical line basic tone. Further, by weighting the densities of the read dot data adjacent in the main scanning direction and distributing the weights to the write dot data in the main scanning direction, it is possible to continue in the sub-scanning direction with excellent development characteristics without using a line memory. A checkerboard pattern with vertical lines is formed. Further, the vertical line tone arranged in the sub-scanning direction by the checkered pattern processing with the dots of 2 dots size or more continuous in the sub-scanning direction and the one-dot multi-value writing by the pulse width modulation of the semiconductor laser are combined.

Further, in the image forming method according to the present invention, the density is weighted from the read dot data of adjacent two dots, the density is distributed to the write dot data of two dots, and the phase of the density generation dot is changed. , Main scanning direction 2
A checkered pattern of dots or more and two or more dots in the sub-scanning direction is formed.
In addition, the density is weighted by the read dot data to the two dots adjacent in the main scanning direction, the weight is distributed to the write dot data of the two dots adjacent in the main scanning direction, and the phase of the density generation dots is changed. A checkered pattern having a dot size of 2 dots or more in the main scanning direction and 2 dots or more in the sub scanning direction is formed without using a line memory.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. (1) Configuration of digital copying machine (2) Modulation method of write laser diode (3) Image reading processing (4) Image processing (5) 2-dot multi-valued circuit (6) Checkerboard pattern forming process (7) The effects of each embodiment will be described in detail in this order.

(1) Structure of Digital Copying Machine FIG. 1 shows a digital copying machine comprising a laser printer to which a general laser writing means is applied and an original reading device. In FIG. The contact glass 111 for mounting is illuminated by the light source 112, and the reflected light from the image surface of the read document is reflected by the mirror 113,
An image is formed on the light receiving surface of the CCD image sensor 117 via 114, 115 and the lens 116. Also, the light source 11
2 and the mirror 113, the traveling body 11 that moves the lower surface of the contact glass 111 in parallel with the contact glass 111.
It is installed in 8.

Main scanning is performed by solid-state scanning of the CCD image sensor 117. The original image is one-dimensionally read by the CCD image sensor 117, and the entire surface of the original is scanned by moving (sub scanning) the optical system. In this example, the read processing density is 40 for both main and sub-scanning.
Set to 0 dpi, A3 size (297 mm x 420
(mm) documents can be read.

Next, a laser printer constituting the above digital copying machine will be described. When the document reading device and the laser printer are integrally configured (this embodiment)
In some cases, the configurations are separate and only electrically connected. In this laser printer, various systems such as a laser writing system, an image reproducing system, and a paper feeding system are integrally configured.

The above laser writing system is shown in FIG. 1, FIG. 2 and FIG.
As shown in FIG. 3, a laser output unit 219, an imaging lens group 120, and a mirror 121 are provided. A laser diode LD1 which is a laser light source is provided inside the laser output unit 219, and a polygon mirror (polygon mirror) 21 that rotates at a high speed and a constant speed by a motor is provided in the writing unit.
9a is equipped. Laser light output from the laser writing system is applied to the photoconductor drum 122 equipped in the image reproducing system via the polygonal mirror 219a and the mirror 121.

As shown in FIG. 1, the photosensitive drum 12
Around the circumference of 2, a charging charger 123 that uniformly charges the surface of the photoconductor drum 122, a developing unit 125 that visualizes the formed electrostatic latent image, and a photoconductor drum on the conveyed recording paper. A transfer charger 126 that transfers the visible image formed on the surface 122, a separation charger 127 that separates the recording paper from the photosensitive drum 122, and a separation claw 128.
Further, a cleaning unit 129 for cleaning the surface of the photosensitive drum 122 after the transfer processing is provided. A beam sensor 330 that generates a main scanning synchronization signal (PMSYNC) is arranged at a position near one end of the photosensitive drum 122 where the laser light is emitted (see FIG. 3).

Further, 131 is a conveyor belt for conveying the recording paper after the transfer processing in a predetermined direction, and 132 is a conveyor belt 131.
The fixing unit for fixing the image on the recording paper conveyed by means of 133, 134 is a paper feed cassette for loading recording papers of different sizes, and 135 and 136 are for feeding the recording paper from the paper feed cassettes 133, 134. Paper feed roller, 1
A registration roller 37 conveys the recording paper to the transfer portion at a predetermined timing.

The operation of the above-mentioned structure will be described.
3 is uniformly charged to a high potential. When the surface of the photoconductor drum 122 is irradiated with laser light, the potential of the irradiated portion is lowered. Since the laser light is ON / OFF controlled according to the black / white of the recording pixel, the potential distribution corresponding to the recorded image on the surface of the photoconductor drum 122 by the laser light irradiation,
That is, an electrostatic latent image is formed.

When the portion on which the electrostatic latent image is formed passes through the developing unit 125, toner adheres according to the level of the potential, and a toner image is formed by visualizing the electrostatic latent image. The recording paper is conveyed by the registration roller 137 to the portion where the toner image is formed at a predetermined timing and overlaps with the toner image. After this toner image is transferred onto the recording paper by the transfer charger 126, the recording paper is separated by the separation charger 127 and the separation claw 128 from the photosensitive drum 122.
Separated from. The separated recording paper is conveyed by the conveyor belt 131.
Fixing unit 13 that is transported by
After being heat-fixed by 2, the sheet is discharged to a sheet discharge tray (not shown). After the transfer process is completed, the surface of the photosensitive drum 122 is cleaned by the cleaning unit 129 to prepare for the next copying process.

In the digital copying machine shown in FIG. 1,
The paper feeding system consists of two systems, one of which is
The paper feeding cassette 133 is equipped, and the paper feeding cassette 134 is equipped in the other paper feeding system. The recording paper in the paper feed cassette 133 is fed by the paper feed roller 135, and the recording paper in the paper feed cassette 134 is fed by the paper feed roller 136. The fed recording paper is temporarily stopped while being in contact with the registration roller 137, and is conveyed to the transfer portion of the photosensitive drum 122 at a timing synchronized with the progress of the recording process. Although not shown, each paper feed system
It is equipped with a size detection sensor that detects the size of the recording paper in the cassette.

(2) Modulation Method of Writing Laser Diode FIG. 4 shows a laser diode according to an embodiment of the present invention (L
It is a block diagram explaining the power modulation system of D), and the light emission level command signal is input into the 1st electric current conversion means 440 and the 2nd electric current conversion means 441.

The first current converting means 440 converts the light emission level command signal into a light emission level command signal current (output current) I _S according to its strength. The output current I _S of the first current converter 440 is the input current (I _S −I _L ), which is the difference between the output current I _S and the photocurrent I _L proportional to the optical output P _O generated in the light receiving element 442 of the laser diode LD1. Then, it is input to the current amplifier 443. It said current amplifier 443, the input current (I _S -I _L) of A multiplied by the output current A (I _S -I _L)
Is output.

On the other hand, the second current converting means 441 converts the light emission level command signal into an output current I ₁ which causes the set light quantity P _S to emit light. I, which is the sum of this output current I ₁ and the output current A (I _S −I _L ) of the current amplifier 443.
_{1 + A (I S -I L} ) is a forward current of the laser diode LD1.

In this way, the laser diode LD1
Obtains an optical output P _O determined by the forward current I ₁ + A (I _S −I _L ). That is, P _O = P {I ₁ + A (I _S -I _L )} P: The relational expression of the function representing the optical output of the LD 1-forward current characteristic is established.

Since I ₁ is set so that I _S ≈I _L , it can be approximated as follows.

[0045]

[Equation 1]

Letting the radiation sensitivity S of the light receiving element and the coupling efficiency with the laser diode LD1 be α, it can be expressed as P _O = P _S + η · A · (I _S −P _O · S · α)

[0047]

[Equation 2] Becomes

Assuming that the crossover frequency of the photoelectric negative period loop is f ₀ , the step response of the optical output P _O is: P _O = I _S / αS + {P _S −I _S / αS} · exp (-2πf ₀ It can be expressed approximately as t).

P set by the second conversion means 441
_S is set to be equal to I _S / αS,
For example, when P _S varies by 5% due to the droop characteristic, the time required for the error in P _O to be 0.4% or less is about 10 ns even if f ₀ = 40 MHz.

Further, the total amount of light (immediately after the light output P _O is changed to the set time τ ₀ (the integrated value of the light output ∫P
_OUT ) If the crossover frequency f ₀ for making the error 0.4% or less is τ ₀ = 50 ns, it suffices that f ₀ ≧ 40 MHz, and a crossover frequency of this level can be easily realized.

As described above, according to this method, a high-speed, high-accuracy, high-resolution laser diode control method can be realized. Furthermore, a laser diode LD using this method
By modulating the power of 1, 256 analog signals are input to the light emission level command signal, and image output of 256 gradations of 1 dot is realized in the laser printer.

Next, a power modulation method of a laser diode (LD) according to another embodiment using a plurality of constant current power supplies will be described. The drive control method of the laser diode in this embodiment utilizes the relationship (IL characteristic) between the forward current (I) and the emission intensity (L) of the laser diode shown in FIG. The IL characteristic of this laser diode is
The forward current that is equal to or higher than the threshold current (Ith) is substantially linear, and the differential quantum efficiency (n) at that time is treated as constant.

As shown in FIG. 6, the control method is such that the forward current is driven by the total current of a plurality of constant current sources 641, 642, 643, 644, and this is switched to the switch 6 by the write data.
It switches at 45, 646 and 647. A bias current larger than the threshold current is supplied by the constant current source 641, and the laser diode drive current is 3 bits 8 by the constant current sources 642, 643, 644 weighted so that the current value becomes 1: 2: 4. To control the value. The current values at that time are I ₁ , I ₂ , and I ₃ , respectively.
The minimum bias current that does not drive 646 and 647 is I
It is ₀ . Therefore, the light emission intensity (light quantity) by each current I _{0 to} I ₃ is as shown in FIG. 5, and the light quantity by all combinations of the currents I _{0 to} I ₃ is 8 from L _{0 to} L _7, and the light quantity difference is equal. can get.

The above setting procedure is executed as follows. The LD emission intensity range is set to P _{0 to} P _max (however,
P ₀ ≈0). LD minimum emission intensity P ₀ ← LD forward current I ₀ is determined. LD maximum emission intensity P _max ← LD forward current I ₀ + I
Determine I _max by _max . I1 = (1/7) · I _max , I2 = (2/7) · I
_max , I3 = (4/7) · I _max . From the above, assuming that the number of constant current sources is n, a light emission intensity of 2 ⁿ can be obtained. For example, if eight constant current sources are used and switching is performed by 8-bit emission data, 256 laser diode exposure outputs can be obtained. Is obtained.

(3) Image Read Signal Processing FIG. 7 shows a detailed block diagram of the image read signal processing. CC
D (charge coupled device) 117 has about 5000 pixels, 400
It is possible to perform dpi reading processing, and simultaneously reads the reflected light in the main scanning direction of the document. The optical data accumulated by the CCD 117 is converted into an electric signal (photoelectric conversion), waveform correction such as clamping, amplification, and A / D conversion are executed, and output as a 6-bit digital signal to the IPU (image processing device).

More specifically, the CCD 117
After being photoelectrically converted, the analog data output of is output separately for two systems of EVEN and ODD for high-speed transfer, amplified by amplifiers 702 and 703 (signal amplification) respectively, and sent to a switching IC 703 composed of analog switches. input. Here, they are combined into a serial analog signal (signal combination). The analog signal synthesized by the switching IC 703 is amplified (variably amplified) by the amplifier 704 and input to the A / D converter 705. The image transfer rate of one pixel after composition is about 10 MHz, and in synchronism with this, the A / D converter 705 converts it to a digital signal of 6-bit 64 gradations (signal digitization). Further, the (variable) amplifier 704 reads a reference white plate (not shown) before scanning a document and controls the amplification degree to an appropriate value in order to correct the light amount variation of the exposure fluorescent lamp.

(4) Image Processing A digital signal for each pixel indicating the original density is input to the IPU (image processing unit) 800 and subjected to image processing. IP
The flow of image processing by U800 is shown in FIG. IPU8
00 is composed of a plurality of LSIs, and executes the following control based on it in addition to image processing.

Shading correction processing Since a linear light source of a fluorescent lamp is used and light is condensed by a lens, the light amount becomes maximum at the central portion of the CCD 117 and decreases at the end portions. Further, the CCD 117 has variations in sensitivity among individual elements. In both of the above, the document data is corrected based on the reference white plate read data for each pixel.

MTF Correction Processing In an optical system using a lens or the like, the read output by the CCD 117 is read as blunt because the peripheral pixel information affects the performance of the lens and the like. Therefore, when one pixel data is obtained, correction is performed based on the peripheral pixel level to obtain an image with high reproducibility.

Main scanning direction scaling processing In this embodiment, the image reading and writing resolutions are the same 400 dpi, but the reading pixel frequency is about 1.
Since 0 MHz and the writing pixel frequency differ by about 12 MHz, frequency conversion is executed. The clock conversion is realized by reading and writing in the two-line memory, and the main scanning magnification is calculated by calculation using peripheral pixel data in the main scanning direction.

Γ-correction processing Both the density data conversion characteristics of the optical system using the CCD 117 (γ characteristics of the scanner) and the density reproduction characteristics of the laser printer using the electrophotographic method (γ characteristics of the printer) are not linear, and remain as they are. The original density is not reproduced faithfully. The above may be corrected individually, but in the present image forming apparatus, conversion processing is performed in consideration of both. Also, when adjusting the density manually, the density can be adjusted by changing this value.

Other Processing In addition to the above, the IPU (image processing device) 800 is
Controls such as auto gain control (auto gain control), image conversion such as masking, trimming, mirroring, black and white reversal, document size and density detection, image detection of markers and the like are also executed.

In this embodiment, one dot 256 gradation output by power modulation of the laser diode is combined with a matrix of 2 dots in the main scanning and sub scanning directions. FIG. 9A shows a 1 × 2 matrix, and FIG. 9B shows a 2 × matrix.
An optical writing method of one matrix is shown. In the low density area, the exposure power of one dot is increased to reach the maximum value, and then the exposure power of the next dot is increased. And 2 dots to 1
The original is reproduced while maintaining the density as pixels. As a result, one dot is fixed to white or black, the density is stable, and banding is reduced.

The density reproduction is executed by using two dots in the main scanning or sub-scanning direction as the target pixel. The read density of the CCD 117 is proportional to the amount of received light. Therefore, CCD 117
The amount of received light is linear with respect to the reflection density of the original, and the density data of 2 dots is added to the digital value, the added value is subjected to γ conversion, and converted into the writing density data by the above method.

As a result of the above, 512 gradations are realized with 2 dots in the main scanning and sub-scanning directions. Further, the chart of the formed halftone density region occurs as shown in FIG.
In the figure, the density is filled from the EVEN dots. 10A and 10C for executing area gradation in the sub-scanning direction 1 × 2
The matrix has a horizontal line tone in a continuous intermediate density region, and the 2 × 1 matrix in FIGS. 10B and 10D in which area gradation is performed in the main scanning direction has a vertical line tone in a continuous intermediate density region.

10 (c) and 10 (d) are respectively shown in FIG.
The writing phases of (a) and (b) are changed alternately,
Two dot lines are formed in the main scan and the sub scan to form an image of 100 lines. As a result, the number of gradations does not change, but the lines are concentrated and the apparent resolution is reduced by half.

(5) Two-dot multi-valued circuit FIG. 11 is a block diagram showing the configuration of a two-dot multi-valued circuit. Line memories 1101 connected in series for inputting a 6-bit signal input from the scanner. 1102
And the latches 1103 and 1104 and the line memory 11
01, 1102 and latches 1103, 1104 connected via switches SW1 to SW4, respectively.
105 and a ROM1 connected to the adder 1105
And 106. Output from the ROM is 8
It is output to the printer as a bit data signal.

The 1 × 2 matrix, the 2 × 1 matrix, and the dot concentration will be described in detail below. 1 × 2 matrix When performing area gradation with 2 dots in the sub-scanning direction (1 × 2
2 matrixes) are two line memories 1101 and 11
02 is used to delay the read data for two main scanning lines. After that, the two 6-bit data are added to the adder 1105.
ROM for γ conversion
Input to 1106. In the ROM 1106, one table is composed of 256 bytes, the first half 128 bytes of which is EVEN and the latter half 128 bytes of which is ODD data.

The first addition data is input to the address bus of the ROM 1106, and the EVEN data indicated by that address is output as write data. The same data is added on the next line, and the ODD data is output as write data from the data bus. Switching between EVEN and ODD is performed in synchronization with the line cycle (PMSYNC). After that, the process moves to the next 2 dots and the process is repeated.

In the block diagram of the 2-dot multi-valued circuit shown in FIG. 11, the switch SW1 and EVEN / ODD are switched for each main scanning line, and the switches SW3 and SW4 select the data from the line memories 1101 and 1102. Set it to the upper side. Further, A in FIG. 12 is a combination with the area gradation in the sub-scanning direction (1 × 2 matrix).
It is an explanatory view showing. Two sub-scanning dots for reading correspond to two sub-scanning dots for writing.

2 × 1 Matrix When area gradation is executed with 2 dots in the main scanning direction (2 × 1
One matrix) uses two latches 1103 and 1104 to delay the read data for two dots in the main scanning direction. Thereafter, as in the case of the 1 × 2 matrix, addition processing and γ conversion processing are executed, write data is output, and EVE
Switching between N and ODD is executed in synchronization with the write clock signal WCLOCK. After that, the process moves to the next 2 dots and the process is repeated.

In the block diagram of the 2-dot multi-valued circuit shown in FIG. 11, the switch SW2 and EVEN / ODD are switched every write clock, and the switches SW3 and SW4 are selected so that the data from the latches 1103 and 1104 are selected. Set to the lower side. 12B is an explanatory diagram showing a combination (2 × 1 matrix) with the area gradation in the main scanning direction. Two main scanning dots for reading correspond to two main scanning dots for writing.

Concentration of dots Converting the phase in writing to concentrate dots 1
When an image of 00 lines is formed, it is executed by dividing the EVEN / ODD switching cycle by two. As described above, no loss of gradation information occurs in all modes.

FIG. 13 shows an example of the γ conversion table (2-dot multi-value conversion table) used in this apparatus. FIG.
(A) is a γ conversion table used for the 1 × 2 matrix,
FIG. 13B is a γ conversion table used for the 2 × 1 matrix. Both tables are set so that the copy density is substantially equal to the document density. When one of the EVEN dots reaches the maximum value up to the intermediate density, the exposure intensity of the ODD dot is increased. As a result, the dots are concentrated while maintaining the density information of 2 dots. Moreover, the γ characteristic can be freely controlled by this γ conversion table, and the way of increasing 2 dots can also be changed. Further, since the density output characteristic also changes depending on the combination method with the area gradation, the γ conversion data is selected or RA conversion table is used.
Use M and rewrite it.

In general, the γ characteristic of the printer alone can be made linear by making the table value the inverse conversion of the γ characteristic in the printer, which is represented by the print density with respect to the writing exposure light amount. The 2-dot multi-valued circuit shown in FIG. 11 is configured in the IPU 800 and converts the image data for each dot from the scanner and outputs it to the writing system. As a result, the writing process of 512 gradations is realized by setting a unit of two dots in the main scanning direction and the sub scanning direction as one pixel.

(6) Checked Pattern Forming Processing Next, regarding the checkered pattern forming processing, a formation chart,
A detailed description will be given in the order of formation processing. Formation Chart FIGS. 14 and 15 are explanatory views showing a dot formation method chart according to the checkered pattern processing method according to the present invention. The hatched portions in the drawing show the density generation dots, and the arrow directions show the transfer of density data. .. FIG. 14 shows an example in which one pixel is formed by two dots in the main scanning direction, and FIG.
An example of forming one pixel with dots will be shown.

The checkered pattern processing method shown in FIG. 14 is 2 × 1.
In the matrix formation method, read dot data adjacent in the main scanning direction is distributed to write dot data adjacent in the main scanning direction, and in each case, one pixel is formed by two dots in the main scanning direction. At this time, the density data is sampled for every two dots adjacent in the main scanning direction. The checkered pattern processing method shown in FIG. 15 is a 1 × 2 matrix forming method in which read dot data adjacent in the sub-scanning direction is divided into adjacent write dot data in the sub-scanning direction, and both are sub-scanning. One pixel is formed by two dots in the direction.

Forming Process The forming process of the checkered pattern described above is the same as that shown in FIG.
It is performed by an EVEN / ODD input operation of the dot multi-valued circuit. That is, a checkerboard pattern is formed by shifting the phase of the density generation dots. Here, in order to eliminate character breakage in the main-scanning or sub-scanning direction that has occurred in the conventional 2-dot multi-valued / line image, the phase of write dots is changed to increase the dot density so as to form a checkered pattern. ..
Further, in order to form a more suitable horizontal line tone by analog modulation, two dots are concentrated in the main scanning direction to form a checkerboard pattern.

FIG. 16 is a block diagram showing the EVEN / ODD input phase converter, which is a phase converter 160 composed of a standard logic circuit such as a flip-flop.
1, the phase conversion circuit 1601 includes a write clock signal (WCLOCK) and a main scanning line synchronization signal (LG).
The input of (ATE) is divided by a predetermined dividing number according to the processing mode and is set to generate an EVEN / ODD signal. The write clock signal (WCLOCK) and the main scanning line synchronization signal (LGATE) are the same as the control signals of the 2-dot multi-valued circuit shown in FIG. 11 and are synchronized with each other.

FIG. 17 shows EVEN / OD of write phase control.
16 is a timing chart of the D signal, which is shown in FIGS.
The checkered pattern charts (a) to (o) of FIG. 18 and FIG. 19 are made to correspond to each other, which will be sequentially described.

FIG. 17A shows the phase control circuit 160.
By 1, the write clock signal (WCLOCK) is divided by 2, and the initial phase is set by the main scanning line synchronization signal (LGATE). That is, the checkered pattern is formed by changing the initial setting of the writing start in the density generation dots for each line in the main scanning direction. Further, FIG. 17B shows an EVEN / ODD signal obtained by dividing the main scanning line synchronization signal (LGATE) by two.

Further, in FIG. 17C, the write clock signal (WCLOCK) is divided by 2 as in the case of (a), and the main scanning line synchronizing signal (LGATE) is divided by 2 to set the initial value to the initial value. Set the phases so that they alternate. next,
In FIG. 17D, the write clock signal (WCLOCK) is divided by 4, and the initial phase is set by dividing the main scanning line synchronization signal (LGATE) by 2 as in the case of (c). Figure 1
7 (e) is a write clock signal (W
CLOCK) is divided by 2, and the main scanning line synchronization signal (LG
ATE) is divided by 4 and the initial value is set.

In FIG. 17 (f), the main scanning line synchronizing signal (LGATE) is divided by 6 to concentrate 3 dots in the sub-scanning direction as in (e) above. Depending on the number, it is possible to concentrate 3 or more dots. In addition, FIG. 17G shows the write clock signal (WCLOC
K) is divided by 4, and main scanning line synchronization signal (LGATE)
Is divided by 4 and the initial value is set. In FIG. 17 (h), the write clock signal (WCLOCK) is divided by 4 and the main scanning line synchronization signal (LGATE) is divided by 6 to set an initial value, and an EVEN / ODD signal is obtained.

Next, FIG. 16 (i) divides the write clock signal (WCLOCK) by 2 and the main scanning line synchronizing signal (LGATE) by 2, and FIG. 16 (j) shows the write clock signal. (WCLOCK) is divided by 2, the main scanning line synchronization signal (LGATE) is divided by 4, and in FIG. 16 (k), the write clock signal (WCLOCK) is divided by 4 and the main scanning line synchronization signal (LGATE) is divided. 16 (m), the write clock signal (WCLOCK) is divided by 4, and the main scanning line synchronization signal (LGATE) is divided by 4 so that the EVEN / ODD signal is divided. To get That is, (i), (j), (k) and (m) of FIG. 15 are the same EVEN as (c), (e), (d) and (g) shown in FIG.
The / ODD signal is generated, and the dot formation state becomes the same.

17 (l) and (n), the write clock signal (WCLOCK) is divided by 6, (l) is the main scanning line synchronization signal (LGATE) divided by 2, and (n) is The main scanning line synchronization signal (LGATE) is divided by 4 to set the initial phase. As a result, in FIGS. 15 (l) and 15 (n), the dot state in which the main scanning direction and the sub scanning direction in FIGS. 14 (f) and 14 (h) are interchanged is formed.

Next, formation of the checkered pattern shown in FIG. 18 (o) will be described. In FIG. 18 (o), a checkerboard pattern is formed with a half-size (1/2 size) dot as the minimum unit in the main scanning direction. That is, the first dot is formed in half of the 1-dot writing time, and the second dot is formed in the remaining half of the time. The write data at this time is
It is not necessary to add the read dot data of two adjacent dots and distribute it to the write dot data of two dots, which is performed by the two-dot multi-value image writing method. Then, after the writing density data is converted, the data is higher than the middle, that is, the presence or absence of the first dot is determined by the most significant bit, and the remaining lower bit data is formed in the first dot or the second dot.

In the checkered pattern forming process shown in FIG. 18 (o), the phase conversion circuit 1601 generates a write phase signal to execute dot formation, as described above. In addition, as shown in the timing chart of FIG.
In this case, the write modulation frequency is doubled with respect to the dot pattern of FIG. 14C, and the phase signal of dot generation is the write clock signal (WCLOCK) and its inversion signal, and the main scanning line synchronization signal. Switching is performed with a signal of (LGATE) divided by two.

As described above, in this embodiment, 1 is set in the main scanning direction.
Although the checkerboard pattern is formed with the / 2 dot size as the minimum unit, as another method, it is possible to perform the checkerboard pattern forming process with the ¼ dot size to improve the resolution. Further, in addition to the checkerboard pattern forming process with a dot size that is an integer multiple or a dot size that is a fraction of an integer, for example, a checkerboard pattern forming process with a 1.5 dot size or the like is performed to suit the performance of the writing output device. It is also possible to let. In such a case, the read dot size and the write dot size may differ, but it can be realized by calculating the write dot data from the surrounding read dot data.

(7) Effects of Each Embodiment Next, the check pattern forming contents and their effects in each of the above embodiments will be described. As described above, the density is weighted from the adjacent read dot data and distributed to the write dot data, and the checkered pattern is shown in FIGS. 14 (c) to 14 (h).
By forming as shown in FIGS. 15 (i) to (n) and FIG. 18 (o), banding caused by 1-dot multi-value writing and image noise due to density unevenness in the halftone portion are reduced, and characters and line cracks are generated. High image quality is obtained. Therefore, a good image can be reproduced for an image in which characters and photographs are mixed.

The checkered patterns shown in FIGS. 14C to 14H are weighted and distributed to the adjacent write dot data in the main scanning direction based on the adjacent read dot data in the main scanning direction. Because it is created, about 5000 bytes,
It is possible to form checkered dots without using a line memory for two lines, reduce banding and image noise with a low-cost configuration, and obtain high image quality with no characters or line cracks.

In FIG. 14 (c), FIG. 15 (i), and FIG. 18 (o), by making the checkerboard pattern to be formed within 1 dot size for writing, jaggies due to the checkerboard pattern image become inconspicuous. Image noise due to banding and density unevenness in the halftone portion generated by 1-dot multi-value writing are reduced, and high image quality without character and line cracks can be obtained. In this case, in particular, a jaggy caused by a checkered pattern image of 1 dot size in multi-value writing of 400 dpi has a resolution that cannot be visually confirmed and is inconspicuous, so that it becomes a practical image in which the character portion is slightly blurred. In addition, the writing density of 400 dpi or less, for example, in the printer of 200 dpi,
The dots that are formed are not easily resolved by visual observation, which is an effective means for reproducing high quality images.

Further, by generating writing dots so as to form a checkered pattern of two continuous dot units in the main scanning direction (FIG. 14 (d) and FIG. 15 (k)), one dot multi-value writing is performed. Image noise due to uneven banding and uneven density in the halftone area can be reduced, resulting in high image quality with less cracks in characters and lines. Also, by forming a checkerboard pattern by concentrating 2 dots in the main scanning direction, the features of a horizontal line basic image of a 2-dot multi-valued line image are incorporated, the smoothness of halftone is increased, and gradation is stable. To do.

Further, weighting distribution is performed on the write dot data based on the read dot data adjacent to each other in the main scanning direction to form a continuous checkered pattern of two dots in the main scanning direction (FIG. 14 (d)). Since dots are generated in a line, it is possible to form a checkered pattern in units of 2 dots without using a line memory. Therefore, it is possible to reduce banding and image noise with a low-cost configuration, and obtain high image quality with few character and line cracks.

Further, using the line memories 1101 and 1102, a checkered pattern (FIG. 15 (l)) is formed by dots having a size of two continuous dots or more in the main scanning direction based on the read dot data adjacent in the sub scanning direction. Therefore, the latent image is formed in a sufficiently long area in the main scanning direction, and the development characteristics are excellent, so that gradation can be stabilized and high image quality can be obtained, and banding and image noise can be further reduced.

In addition, the checkered pattern processing of concentrating two or more dots continuous in the main scanning direction is combined with the one-dot multi-value writing by the power modulation of the laser diode LD1 in FIG.
The method for forming the checkered pattern in (d), FIGS. 15 (k) and (l) blinks the beam exposure in the main scanning direction. In this case, since the checkered pattern is formed by the dots having a size of 2 dots or more continuously in the main scanning direction, the blinking is reduced. The power modulation of the laser diode LD1 modulates the writing exposure intensity for each dot, so that the latent image becomes long in the main scanning direction and has a horizontal linear potential distribution. That is,
Since the tendency of area gradation in the sub-scanning direction becomes high and the continuity of the horizontal line tone in the main scanning direction of the latent image is maintained, a deep engraving potential is obtained, and high gradation and smooth halftone reproduction are achieved. Become. Therefore, it is possible to obtain high image quality with few characters and line breaks.

Next, dots are formed in a continuous 2-dot unit in the sub-scanning direction, that is, in a checkerboard pattern of vertical lines (FIG. 14 (e)).
And (j)), the developing effect of electrophotography is improved. Further, it is possible to reduce image noise due to banding and density unevenness in the halftone portion, make cracks in characters and lines inconspicuous, and obtain high image quality. Further, since 2 dots are concentrated in the sub-scanning direction, it is possible to incorporate the advantages of the vertical line basic tone image in a 2-dot multi-valued line image, improve the smoothness of halftones, and provide stable gradation. Obtainable.

Further, based on the read dot data adjacent to each other in the main scanning direction, weighted distribution is performed to the write dot data in the main scanning direction, and the vertical line-based checkered pattern which is continuous in the sub-scanning direction and which is excellent in the developing characteristic. A pattern (FIGS. 14E and 14F) is formed. In this case, the line memory 110
Since a checkerboard pattern of 2 dots or more can be formed without using 1, 1102, banding with a low cost configuration,
Image noise is reduced, and cracks in characters and lines are less noticeable, and high image quality can be obtained.

The pulse width modulation of the laser diode LD1 modulates the writing exposure time for each dot. Therefore, when the latent image is located in the sub-scanning direction, a vertical line-shaped potential distribution is obtained. That is, the pulse width modulation increases the tendency of area gradation in the main scanning direction, and the latent image has vertical lines arranged in the sub scanning direction that are continuous in the sub scanning direction. e), (f), and FIG.
5 (j)). Therefore, the potential is deeply engraved, the gradation reproducibility is excellent, and smooth halftone can be reproduced. Furthermore, it is possible to obtain high image quality in which cracks in characters and lines are not noticeable.

Weighting distribution of density is performed on the write dot data of 2 dots based on the read dot data of adjacent 2 dots, and the phase of the density generating dot is changed, so that two or more dots in the main scanning direction or the sub-scanning direction is obtained. Scanning direction 2
A checkerboard pattern with a dot size larger than the dot (Fig. 14 (g),
(H) and FIGS. 15 (m) and (n) are formed. By this dot concentration, the tendency of area gradation can be increased, a checkered pattern that is faithful to read density data and has stable gradation can be realized, and banding can be eliminated. The checkerboard pattern is similar to the halftone dot image used in many printing techniques, and is an image that is easy to fit.

Further, the weighting distribution of the densities is executed for the write dot data based on the read dot data of two dots adjacent in the main scanning direction, and the phase of the density generation dots is changed, whereby the line memory 1101, 1102
It is possible to form a checkered pattern (FIGS. 14 (g) and 14 (h)) having a dot size of 2 dots or more in the main scanning direction and 2 dots or more in the sub scanning direction without using. Due to such a low-cost dot concentration method, the tendency of area gradation becomes high, it is faithful to the read density data, the gradation is excellently stabilized, high-quality halftone reproduction is realized, and banding is achieved. Can be eliminated. Further, this method is effective for reproducing high quality of halftone and character images by high-density writing of 400 dpi or more in the writing method by the electrophotographic process.

As described above, the image forming process using the checkered pattern according to the present invention is effective for reproducing characters and line images including halftones. Also, the checkered pattern image is positioned in the middle of the line image of the 1-dot multi-valued image and the 2-dot multi-valued image from the viewpoint of resolution and gradation, and has the advantages and disadvantages of both. Therefore, depending on the type of original image,
It becomes more effective by making the optimum writing method selectable and putting it into practical use. That is, in the case of a "character image", high resolution is essential in a black-and-white copying machine, so a 1-dot multi-value writing mode, and in a "photo image", a 2-dot multi-value / line processing mode, Then, for the "text / photograph mixed image", it is possible to cope with it, such as a 2-dot multi-valued / checkered pattern processing mode.

[0102]

As described above, according to the image forming method of the present invention, for example, in the image forming method of performing the area gradation by the multi-gradation writing for each dot and a plurality of adjacent read dot data, Weight density distribution is performed on the write dot data based on a plurality of adjacent read dot data to form a checkerboard pattern. Therefore, low banding and smooth halftone reproducibility in 2-dot multi-value line image processing are achieved. The advantages are maintained, and the reduction of characters and line cracks that occur in a 2-dot multi-valued line image can be realized by simple image processing, and high image quality can be obtained. In addition, the deterioration of the resolution of the characters and the photographic image is reduced, and the gradation can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a digital copying machine to which an image forming method according to the present invention is applied.

FIG. 2 is an explanatory diagram showing a configuration of a laser writing system in a digital copying machine.

FIG. 3 is an explanatory diagram showing a schematic configuration of a laser writing system in a digital copying machine.

4 is a block diagram showing a power modulation method of a laser diode (LD) used in the digital copying machine shown in FIG.

FIG. 5 is a graph showing the relationship (IL characteristic) between the forward current (I) and the emission intensity (L) of the laser diode.

FIG. 6 is a circuit diagram showing a control method of a laser diode.

FIG. 7 is a block diagram showing each unit that executes image reading signal processing.

FIG. 8 is a block diagram showing a flow of image processing.

FIG. 9 is an explanatory diagram showing a 1 × 2 matrix and a 2 × 1 matrix optical writing method.

FIG. 10 is a chart showing a halftone area.

FIG. 11 is a block diagram showing a configuration of a 2-dot multi-valued circuit.

FIG. 12 is an explanatory diagram showing a combination with area gradation in the main scanning / sub scanning direction.

FIG. 13 is a table showing 2-dot multi-valued γ conversion.

FIG. 14 is a chart showing a dot forming method by a checkered pattern processing.

FIG. 15 is a chart showing a dot forming method by a checkered pattern processing.

FIG. 16 is a block diagram showing a phase converter of an EVEN / ODD input.

FIG. 17 is a timing chart showing the timing of the EVEN / ODD signal for write phase control.

FIG. 18 is a chart showing a dot formation method by a checkered pattern processing.

FIG. 19 is a chart showing a dot formation method according to a conventional example.

[Explanation of symbols]

117 CCD image sensor 122 photoconductor drum 219 laser output unit 330 beam sensor 440 first current conversion unit 441 second
Current conversion means 442 light receiving element 641 642 643 644 constant current source 645 646 647 switch 702 704 amplifier 703 switching IC 705 A / D converter 800 IP
U (image processing device) 1101 1102 line memory 1103 1
104 Latch 1501 Phase conversion circuit

Claims (12)

[Claims] 1. An image forming method for performing area gradation by multi-gradation writing for each dot and a plurality of read dot data adjacent to each other, and a density for write dot data based on a plurality of adjacent read dot data. The image forming method is characterized in that a checkerboard pattern is formed by performing weighted distribution. 2. An image forming method in which multi-gradation writing is performed for each dot and area gradation is performed by a plurality of adjacent read dot data, and the read dot data in the main scanning direction is delayed so as to be continuous in the main scanning direction. The density data of the dots is sampled and the density is weighted, distributed to adjacent two writing dot data in the main scanning direction, the dot formation start phase in the main scanning direction is periodically changed, and multi-level for each dot is performed. An image forming method, characterized in that a checkerboard pattern is formed by performing area gradation with two dots adjacent in the main scanning direction by gradation writing. 3. An image forming method for performing area gradation by multi-gradation writing for each dot and a plurality of read dot data adjacent to each other, and a density for write dot data based on a plurality of adjacent read dot data. The image forming method is characterized in that a checkered pattern having a read pixel size or a dot size smaller than the read pixel size is formed. 4. An image forming method for performing multi-gradation writing for each dot and performing area gradation by a plurality of read dot data adjacent to each other, and a density for write dot data based on a plurality of adjacent read dot data. Is performed, the dot formation start phase in the main scanning direction is periodically changed, and the density generation dots of the write dot data are periodically changed by the frequency division signal of the write clock signal to continuously change in the main scanning direction. An image forming method characterized by forming a checkered pattern in units of 2 dots. 5. In an image forming method for performing area gradation by multi-gradation writing for each dot and a plurality of read dot data adjacent in the main scanning direction, the read dot data in the main scanning direction is delayed and the main scanning direction is delayed. The density data of a plurality of consecutive read dot data is sampled and the density is weighted and distributed to adjacent write dot data in the main scanning direction, and the dot formation start phase in the main scanning direction is divided by the write line signal. It is possible to form a checkered pattern in units of 2 dots that are continuous in the main scanning direction by periodically changing the frequency with a frequency signal and periodically changing the density generation dots of the write dot data with a frequency dividing signal of the write clock signal. A characteristic image forming method. 6. An image forming method for performing area gradation by multi-gradation writing for each dot and a plurality of read dot data adjacent in the sub-scanning direction, wherein two or more lines storing read density data in the main scanning direction are stored. Using the data storage means,
Sampling read dot data adjacent in the sub-scanning direction, weighting the density, and distributing to the write dot data in the sub-scanning direction, forming a checkerboard pattern with two or more continuous dots in the main scanning direction. And an image forming method. 7. An image forming method of performing multi-gradation writing for each dot by power modulation of a laser output means and area gradation by a plurality of read dot data adjacent to each other, in a two-dot size continuous in the main scanning direction or An image forming method characterized by forming a checkered pattern with the above dots. 8. An image forming method in which area gradation is performed by multi-gradation writing for each dot and a plurality of adjacent read dot data, and density is weighted by sampling density data of a plurality of adjacent read dot data. Performed, distributed to adjacent write dot data in the sub-scanning direction, and periodically changing the dot formation start phase in the main scanning direction by the divide-by-four signal of the write line signal, in units of 2 dots continuous in the sub-scanning direction. An image forming method, which comprises forming a checkered pattern. 9. An image forming method for performing area gradation by multi-gradation writing for each dot and a plurality of read dot data adjacent in the main scanning direction, wherein the read dot data in the main scanning direction is delayed and the main scanning direction is delayed. Sampling density data of a plurality of read dot data consecutive to each other, weighting the densities, and distributing to adjacent write dot data in the main scanning direction, the dot formation start phase in the main scanning direction is 4 of the write line signal An image forming method characterized by forming a continuous checkerboard pattern of 2 dots or more in the sub-scanning direction by periodically changing the frequency with a frequency-divided signal of frequency division or more. 10. An image forming method for performing multi-gradation writing for each dot by pulse width modulation of a laser output means and area gradation by a plurality of adjacent read dot data,
An image forming method, characterized in that a checkerboard pattern is formed by dots having a size of 2 dots or more that are continuous in the sub-scanning direction. 11. An image forming method in which multi-gradation writing is performed for each dot and area gradation is performed by a plurality of adjacent read dot data, and density data of a plurality of adjacent read dot data is sampled to weight the density. Then, it is distributed to adjacent write dot data, and the dot formation start phase in the main scanning direction is periodically changed by a frequency division signal of 4 or more of the write line signal, and 4 or more of the write clock signal is divided. The density generation dots of the write dot data are periodically changed by the frequency division signal of 2 dots or more in the main scanning direction and 2 dots in the sub scanning direction.
An image forming method characterized by forming a checkered pattern having a dot size equal to or larger than dots. 12. In an image forming method for performing area gradation by multi-gradation writing for each dot and a plurality of read dot data adjacent in the main scanning direction, density data of a plurality of read dot data adjacent in the main scanning direction. Are sampled, the densities are weighted, distributed to the adjacent write dot data in the main scanning direction, and the dot formation start phase in the main scanning direction is periodically divided by four or more divided signals of the write line signal. Change, the density generation dots of the write dot data are changed periodically by the divide-by-4 signal of the write clock signal, and the main scanning direction 2
An image forming method comprising forming a checkered pattern having a dot size of dots or more and 2 dots or more in the sub-scanning direction.