JP2000125128A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the image forming device by which a highlight part of an image is stably reproduced from a low density part and resolution and stability are attained for a medium density part and a high density part. SOLUTION: The image forming device has amplifier that adds image data of an adjacent pixel to data from a gradation processing circuit 78 or the like of an image processing section, a means that generates a density from a specific pixel based on the sum data, a means that replaces the pixel from which the density is generated with other pixel in a subscanning direction, and the means replacing the density generating pixel with other pixel couples adjacent pixels in the subscanning direction. Thus, in the case that image data consisting of plural dots are summed in the subscanning direction and a density is being generated from specific pixels, coupled dots in the subscanning direction are reproduced by properly placing the specific pixels generating the density and potential concentration and increase in a saturated area are attained, then stability of an image especially at its highlight part is secured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital copying machine,
The present invention relates to an image forming apparatus applied to a digital image forming apparatus such as a laser printer, a facsimile apparatus, and a display device, and more specifically, to stably reproduce an image highlight portion from a low density portion and from an intermediate density portion. The high-density portion relates to a color image forming apparatus such as an electrophotographic color copying machine and a printer which achieves resolution and stability.

[0002]

2. Description of the Related Art Conventionally, there has been known an electrophotographic image forming apparatus which forms a latent image on a photosensitive medium by scanning a light beam, develops the latent image with toner, and forms an image. , Laser printers, facsimile machines and the like. In recent years, a light beam is scanned according to a color-separated image signal to form a latent image of each color on a photosensitive medium, and the latent image is formed of yellow (Y), magenta (M), and cyan (C). ) And black (Bk) toner images, and color image forming apparatuses such as electrophotographic color copiers and printers that form a full-color image by transferring the toner images of each color onto a transfer material in a superimposed manner. Has been In such a color image forming apparatus, it is important to improve the reproducibility of dots and lines in low-density portions and to improve the stability of gradation and color reproduction in an environment. There are the following techniques relating to halftone processing in a color image forming apparatus.

[0003] For example, Japanese Patent Application Laid-Open No. 7-254985,
JP-A-7-254986, JP-A-7-28394
No. 1, JP-A-8-114965, JP-A-8-114965
Japanese Patent No. 125863 discloses a halftone processing technique called HIEST as a halftone processing technique in an electrophotographic color copying machine, and mainly improves the reproducibility of a highlight portion of an image. The purpose is. Specifically, pulse width modulation is used for writing, and dither processing weighted by two dots in the main scanning direction is performed to stabilize the image highlight portion with a low number of lines. Further, the writing beam diameter and the pixel interval in the main scanning direction for that purpose are defined.

However, the above-mentioned halftone processing technique has a drawback that since dither is used, there is no fidelity of density in a minute area, image information is lost such as disappearance of a line, and color moire occurs. .

By the way, the present inventor (the present applicant) firstly
An image that realizes high-quality image formation by reducing banding and image noise, stabilizing the image density, and adopting a two-dot multi-value method that combines a multi-level writing by dot modulation and a micro matrix with little reduction in resolution. A forming method and an image forming apparatus are proposed (Japanese Patent Laid-Open No. Hei 4-20007).
5, JP-A-4-200076, JP-A-4-2000
No. 77, JP-A-4-200078, JP-A-5-284
339, JP-A-5-292302, JP-A-6-62
248). These prior applications are inventions applied to digital copiers and the like and are characterized by adding and distributing density data of two adjacent dots, and 256 gradations per dot by pulse width modulation and power modulation of a semiconductor laser. By combining the output with a matrix of two dots in the main scanning and / or sub-scanning directions, the reproducibility of the halftone density region is further improved.

FIG. 38 (a) shows an example of a 1 × 2 matrix optical writing system, and FIG. 38 (b) shows an example of a 2 × 1 matrix optical writing system. Is shown). In the optical writing method shown in FIG. 38, in the low density portion, when the exposure power is increased from one dot and reaches a maximum value, the exposure power of the next dot is increased. Then, the image is reproduced while maintaining the density with two dots as one pixel. This stabilizes the concentration,
Banding is also reduced.

The chart of the formed halftone density region is generated as shown in FIG. In the figure, the density is filled from the EVEN dots. The 1 × 2 matrix shown in FIGS. 39A and 39C in which the area gray scale is executed in the sub-scanning direction is a horizontal line tone in a continuous intermediate density area, and the area gray scale in the main scan direction is shown in FIGS. The (2 × 1) matrix of (d) has a vertical line tone in a continuous intermediate density area. FIG. 39 (c),
(D) shows an example of addition + phase, each of which is shown in FIG.
The writing phases of (a) and (b) are alternately changed. In this case, two dots are formed in the main scanning or sub-scanning direction because the EVEN dots are adjacent to each other.

Next, FIG. 40 shows an example of a circuit which is added to the image processing section of the image forming apparatus and controls addition (addition of density data of adjacent pixels). FIG. 40 is a block diagram showing the configuration of a two-dot multi-valued circuit, in which line memories 1101 and 1102 connected in series to input an 8-bit signal input from an image scanner for reading an original image;
Latches 1103 and 1104 and the line memory 110
1, 1102 and the adders 11 connected to the latches 1103, 1104 via switches SW1 to SW4, respectively.
05 and the ROM 11 connected to the adder 1105
06. The output from the ROM 1106 is output to a laser printer as an 8-bit digital image data signal. Hereinafter, a 1 × 2 matrix,
The operation of the 2-dot multi-valued circuit will be described for a 2 × 1 matrix and dot concentration.

1 × 2 matrix. When performing area gradation with two dots in the sub-scanning direction (1 × 2 matrix),
Using two line memories 1101 and 1102, read data for two main scanning lines is delayed. Thereafter, the two 8-bit data are added by the adder 1105, and the 9-bit data is input to the ROM 1106 for γ conversion. In the ROM 1106, one table is composed of 256 bytes, the first 128 bytes of which are EVEN, and the latter 128 bytes are ODD data.

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

In the block diagram of the two-dot multi-valued circuit shown in FIG. 40, the switch SW1 and EVEN / ODD are switched for each main scanning line, and the switches SW3 and SW4 are switched.
Is set to the upper side so that data from the line memories 1101 and 1102 is selected. FIG. 41A is an explanatory diagram showing a combination (1 × 2 matrix) with the area gradation in the sub-scanning direction. Two dots in the sub-scanning for reading correspond to two dots in the sub-scanning for writing.

2 × 1 matrix. When performing area gradation with two dots in the main scanning direction (2 × 1 matrix),
Using two latches 1103 and 1104, read data for two dots in the main scanning direction is delayed. Below, 1 ×
As in the case of the two matrices, addition processing and γ conversion processing are executed to output write data, and switching between EVEN and ODD is executed in synchronization with the write clock signal WCLOCK. Thereafter, the process proceeds to the next two dots and the processing is sequentially repeated.

In the block diagram of the two-dot multi-valued circuit shown in FIG. 40, the switch SW2 and the switch EVEN / ODD are switched every clock for writing, and the switches SW3 and S
W4 is set on the lower side so that data from the latches 1103 and 1104 is selected. 41B shows a combination with the area gradation in the main scanning direction (2 × 1 matrix).
FIG. The two main scanning dots for reading correspond to the two main scanning dots for writing.

Dot concentration. When image formation is performed by adding and phase conversion in FIGS. 39 (c) and (d) in which the dots are concentrated by converting the phase in writing, EVEN / O
This is performed by dividing the DD switching cycle by two.
As described above, there is no loss of gradation information in all modes.
The reproducibility of the halftone density region can be improved.

[0015]

In contrast to the above-mentioned prior application filed by the present inventor (the present applicant), the present invention is a further development of this technology, and the purpose of the present invention is to reduce the image highlight area. The halftone processing in an image forming apparatus such as an electrophotographic color copying machine and a printer is realized in which the density is reproduced stably from the density range and the density range from the middle density range to the high density range is high in resolution and stability.

More specifically, according to the first aspect of the present invention, in an image forming apparatus for forming an image by modulating a multi-tone image signal, image data of a plurality of dots are added to generate a density from a specific pixel. In particular, it is an object of the present invention to make dots connected in the sub-scanning direction in a highlight portion, reduce banding and image noise, and secure image stability.

According to a second aspect of the present invention, in an image forming apparatus for forming an image by modulating a multi-tone image signal, in particular, after the minimum dot density data of a specific pixel for generating density is saturated, the next specific pixel The purpose of the present invention is to generate a concentration of, maintain saturation and ensure stability.

A third object of the present invention is to reduce the number of necessary line buffers (line memories) and reduce the cost in an image forming apparatus for forming an image by modulating a multi-tone image signal. .

According to a fourth aspect of the present invention, there is provided an image forming apparatus for forming an image by modulating a multi-tone image signal. The purpose is to be more faithful to the center of gravity of the concentration.

[0020]

According to a first aspect of the present invention, there is provided an image forming apparatus, comprising: means for adding image data of adjacent pixels; and means for generating density from a specific pixel based on the added data. And means for changing the density generation pixel in the sub-scanning direction. The means for changing the density generation pixel in the sub-scanning direction connects adjacent pixels in the sub-scanning direction.

According to a second aspect of the present invention, there is provided an image forming apparatus, comprising: means for adding image data of adjacent pixels; means for generating a density from a first specific pixel based on the added data; and density of a minimum dot of the specific pixel. When the data is saturated, the second
Means for generating the density of the specific pixel.

According to a third aspect of the present invention, there is provided an image forming apparatus, comprising: a light writing unit including at least pulse width modulation in light modulation; a unit for adding image data of an adjacent pixel in the main scanning direction; Means for generating a concentration from a specific position.

According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: an optical writing unit that includes at least pulse width modulation in optical modulation; a unit that adds image data of adjacent pixels in the sub-scanning direction; Means for generating a concentration from a specific position.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. (1) Image formation of a color copier, (2) image processing of a color copier, (3) LD multi-level modulation, (4) Addition control and phase control circuit, (5) Addition and distribution, and description of dot forming method by phase control method will be described in detail in this order.

(1) Image formation of a color copying machine. FIG. 1 is a schematic configuration diagram of a digital color copying machine showing one configuration example of an image forming apparatus according to the present invention. In FIG. 1, reference numeral 100 denotes a laser printer as an image forming unit, 200 denotes an automatic document feeder (ADF), 300 denotes an operation board, 400 denotes an image scanner as an image reading unit, and 500 denotes an external sensor.

An image scanner 400 mechanically moves a moving body on which an illumination lamp 402 disposed below a contact glass 401 is mounted at a constant speed in the left-right direction (sub-scanning direction) in FIG. This is an image reading unit to read. Light emitted from the illumination lamp 402 is reflected on the surface of the document placed on the contact glass 401 according to the density of the document image. This reflected light, that is, the light image of the document, passes through a number of mirrors and lenses and enters the dichroic prism 410. Dichroic prism 410
Separates incident light into three colors of red (R), green (G), and blue (B) according to the wavelength. 3 split
The two lights enter a different one-dimensional charge-coupled device (CCD) image sensor 410. Thus, the three one-dimensional image sensors 410 provided in the image scanner 400 can simultaneously read the R, G, and B color components of one line in the main scanning direction on the document image. The two-dimensional image of the document is sequentially read by the sub-scan of the moving body.

The external sensor 500 includes the image scanner 4
As in the case of 00, it is built in a handy type scanner composed of a CCD that can simultaneously detect the R, G, B color components of the original image.

The ADF 200 is an image scanner 400
, And a large number of originals can be held on the original platen 210 in a stacked state. When performing the document feeding operation, the rotating call roller 212 comes into contact with the uppermost document upper surface, and the contacted document is fed out. Reference numeral 213 denotes a separation roller for avoiding double feeding of originals. The document fed out to the predetermined position is further conveyed on the contact glass 401 of the image scanner 400 by driving the pull-out roller 217 and the conveying belt 216, and when the document advances to the predetermined reading position, that is,
The operation stops when the leading edge of the document reaches the left end position of the contact glass 401. When the reading of the document is completed, the conveyor belt 216 is driven again to contact the contact glass 40.
The original on top 1 is discharged, and the next original is sent to the reading position. A document presence / absence sensor 211, which is an optical sensor for detecting whether or not a document is loaded, is provided in front of the call roller 212. The leading end of the document and the separation roller 213 are provided between the separation roller 213 and the pull-out roller 217. A document leading edge sensor 214 which is an optical sensor for detecting a size is provided.

The document leading edge sensor 214 is composed of a plurality of sensors arranged at different positions in the main scanning direction (perpendicular to the paper surface). The original size, that is, the original width can be detected. Further, a pulse generator for outputting a pulse corresponding to the rotation amount is provided in a paper feed motor (not shown). The control device of the ADF 200 measures the time until the document passes the document leading edge sensor 214, thereby The original size in the scanning direction, that is, the original length is detected.

The calling roller 212 and the separation roller 21
Reference numeral 3 is driven by a paper feed motor (not shown), and the pull-out roller 217 and the transport belt 216 are driven by a transport motor (not shown). Further, a registration sensor 215 composed of an optical sensor is disposed downstream of the pull-out roller 217.

Next, the schematic structure and operation of the laser printer 100 will be described. Image reproduction is performed on the photosensitive drum 1. Around the photosensitive drum 1, a series of electrophotographic process units, that is, a charger 5, a writing unit 3, a developing unit 4, a transfer drum 2, a cleaning unit 6, and the like are provided. The writing unit 3 includes a semiconductor laser (not shown) (laser diode: L
D) is provided, and the laser light emitted by the laser beam is irradiated on the surface of the photosensitive drum 1 via the rotary polygon mirror 3b, the lens 3c, the mirror 3d, and the lens 3e. Rotating polygon mirror 3b
Is driven to rotate at a high speed at a constant speed by the polygon motor 3a.

An image control unit (not shown) controls the light emission timing of a semiconductor laser driven by a multi-tone image signal in pixel units corresponding to the density of an image to be recorded, by using a rotary polygon mirror that sequentially scans each pixel position. The driving signal of the semiconductor laser is controlled so as to synchronize with the rotation / deflection operation of 3b. That is, the emission of the semiconductor laser is controlled so that a laser beam corresponding to the density of the pixel is irradiated at each scanning position of the image on the surface of the photosensitive drum 1.

The surface of the photosensitive drum 1 is uniformly charged to a high potential in advance by corona discharge by the charging charger 5. When this surface is irradiated with the laser light emitted from the writing unit 3, the charging potential changes according to the intensity of the light. That is, a potential distribution is formed on the photosensitive drum 1 in accordance with the presence or absence of the laser light emitted from the semiconductor laser included in the writing unit 3. Thus, a potential distribution corresponding to the density of the original image, that is, an electrostatic latent image is formed on the photosensitive drum 1. This electrostatic latent image is visualized by a developing unit 4 disposed downstream of the writing unit 3.

In this embodiment, the developing unit 4 is provided with four sets of developing units 4M, 4C, 4Y, and 4Bk.
M (magenta), C (cyan), Y (yellow), and Bk (black) toners having different colors are stored in the respective developing devices. Laser printer 100
Is configured such that any one of the above four developing devices is selectively energized, so that the electrostatic latent images are M, C,
A visible image is formed with any one of the Y or Bk toners. On the other hand, the transfer paper stored in the paper feed cassette 11 is fed out by the paper feed roller 12, sent to the surface of the transfer drum 2 at a timing by the registration roller 13, and
It moves with the rotation of the transfer drum 2 while being attracted to the surface. Then, at a position close to the surface of the photosensitive drum 1, the toner image formed on the photosensitive drum 1 is transferred to the surface of the transfer paper by charging by the transfer charger 7.

In the case of the single-color copy mode, the transfer of the toner image is completed, and the transfer paper separated from the transfer drum 2 is fixed and discharged to the discharge tray 10. In the case of the full-color mode, the transfer paper is discharged. It is necessary to form images of four colors of Bk, M, C and Y on a single sheet of transfer paper. in this case,
First, a Bk color toner image is formed on the photosensitive drum 1 and transferred to a transfer sheet. Then, the next M color toner image is formed on the photosensitive drum 1 without separating the transfer sheet from the transfer drum 2. The toner image is formed, and the toner image is transferred to the transfer paper again. Further, for the C color and the Y color, a toner image is formed on the photosensitive drum 1 and transferred to a transfer sheet. That is, one color image is formed on the transfer paper by repeating the process of forming and transferring the toner image.

When the transfer of all the toner images is completed, the transfer paper is separated from the transfer drum 2 by charging by the separation charger 8, is subjected to the fixing process of the toner image by the fixing device 9, and is discharged to the discharge tray 10. You.

Although the configuration and the image forming operation of the digital color copying machine have been described above, the image forming apparatus according to the present invention is not limited to the illustrated configuration. A method may be used in which a toner image of four colors Bk, M, C, and Y is formed on a photosensitive drum for each color, is sequentially superimposed on an intermediate transfer body, and is transferred onto a transfer sheet. .

(2) Image processing of a color copying machine. FIG.
FIG. 2 is a circuit block diagram illustrating a configuration example of an image processing unit of the digital color copying machine illustrated in FIG. 1. The operation control of the entire copying machine is controlled by a system controller 50 composed of a microcomputer.

The synchronization control circuit 60 generates a clock pulse as a reference for control timing, and inputs and outputs various synchronization signals for synchronizing signals between the control units.
The main scanning synchronization signal based on the scanning timing in this configuration example is synchronized with the scanning start timing of the laser beam by the rotation of the rotary polygon mirror 3b of the laser printer 100.

The image signals of R, G, and B colors read by the image scanner 400 are A / D converted,
It is output as bit color image information. This image information is output to the laser printer 100 after undergoing various processes in the image processing unit. The image processing unit
Scanner gamma correction 71, RGB smoothing filter 72, color correction 73, under color removal (UCR) / UCA 74, selector 75, edge enhancement filter 76, printer gamma 77 as a density curve, gradation processing 78, image area separation 79, and A
Each circuit of CS80 is provided.

In the scanner gamma correction 71, the linear RGB data read by the image scanner 400 is converted into linear RGB data. The RGB smoothing filter 72 performs a smoothing process for suppressing moire caused by a halftone dot document.

The color correction circuit 73 converts the image information of each color of R, G and B into image information of each color of Y, M and C which are complementary colors thereof. The UCR / UCA circuit 74 extracts a black component included in the color of the image signal obtained by synthesizing all of the input image information of the Y, M, and C colors, outputs it as a Bk signal, and outputs the remaining color image. The black component is removed from the signal, and the YMC component is added.

The selector 75 is connected to the system controller 5
In response to an instruction of 0, any one of the input Y, M, C, and Bk color signals is selected and output to the next block.

The edge emphasis filter circuit 76 emphasizes edge information of a character portion or a picture portion. Also.
In the printer gamma 77, a curve is set according to the printer characteristics so that the density becomes linear including gradation processing.

The gradation processing circuit 78 is a circuit for binarizing the inputted 8-bit density information or converting it into multi-valued data.
Generally, dither processing or the like is often performed, and a binary or multilevel image signal is output to the laser printer 100. The later-described halftone processing of the present invention is executed by the gradation processing circuit 78 and outputs multi-value data.

The output of the scanner gamma 71 is sent to the image area separating circuit 79 and the ACS circuit 80 on the one hand. The image area separation circuit 79 has a circuit for determining whether the input image is a character part or a picture part, and a circuit for determining whether the image is chromatic or achromatic. The data is sent to each processing block in units of one pixel. In each processing block, processing is switched according to the result of the image area separation circuit 79.

The ACS circuit 80 determines whether the original set on the scanner 200 is a black-and-white original or a color original, and sends the result to the system controller 50 at the end of scanning the Bk plate. If the original is a color original, the remaining three scans are performed, and if the original is a black and white original, the operation is terminated by the Bk scan.

The image processing units 71 to 80 shown in FIG.
All the parameters of each image processing block are set by the CPU of the system controller 50. The system controller 50 controls the image forming operation of the laser printer 100 including the LD multi-value writing operation.

(3) LD multi-level modulation. Next, the multi-level modulation method of the semiconductor laser (LD) constituting the optical writing means will be described. There are a pulse width modulation (PWM) system and a light intensity modulation (PM) system as a semiconductor laser multi-level modulation system for performing one-dot multi-level output. FIGS. 3A and 3B are diagrams illustrating an example of a light intensity modulation method and a pulse width modulation method.
Hereinafter, these modulation methods will be described.

Light intensity modulation method. Since halftone recording is realized by using the intermediate exposure area, stabilization of the printing process is an important requirement, and the requirements for the printing process are strict. However, semiconductor laser control modulation is simplified. That is, as shown in FIG. 3A, the light intensity modulation method is a method in which recording is performed by changing the light output level itself, and each dot pattern is output in a pattern as shown in the upper part of the figure. In this method, the control modulation section of the semiconductor laser can be configured simply and compactly.However, since the halftone is reproduced using the intermediate exposure area, it is necessary to stabilize the printing process such as stabilizing the developing bias. Requirements become stricter.

Pulse width modulation method. As shown in FIG. 3B, the pulse width modulation method has a light output level of two.
Although the value is a value, the light emission time, that is, the pulse width is changed so that recording is performed, and each dot pattern is output in a pattern as shown in the upper part of the figure. Since this method is basically binary recording, the intermediate exposure area is less used than the light intensity modulation method, and the intermediate exposure area can be further reduced by combining adjacent dots. , The requirements for the printing process can be reduced. However, in order to set the pulse width to 8 bits per dot, several tens of nsec. Must be divided into 256, and high-speed and high-precision semiconductor control is required, which complicates the control portion of the semiconductor laser. That is, in the light intensity modulation method, the requirement for stabilizing the printing process becomes strict, and in the pulse width modulation method, the configuration of the control modulation unit of the semiconductor laser becomes complicated. Therefore, in consideration of the above points, the image forming apparatus of the present invention employs a pulse width modulation (PWM) system and a light intensity modulation (PM) system in combination.

Pulse width intensity mixing method. FIG. 4 shows an example of the pulse width intensity mixing method. This pulse width intensity mixing method is based on pulse width modulation, and a pulse width and a transition portion of the pulse width are interpolated by light intensity modulation as shown in FIGS. 4 (a) and 4 (b). A modulation degree equivalent to 8 bits (2 ⁸ = 256 gradations) can be obtained by setting 8 values and 32 light intensity modulation setting values. In this scheme,
Since the number of pulse width modulation stages is small, the pulse width can be digitally set, the pulse width can be easily set, and the pulse position control can be easily realized. That is, FIG.
(B) shows a right mode in which an optical writing pulse is generated from the right end of one dot, and a left mode in which an optical writing pulse is generated from the left end of one dot. These control the phase so that the exposure pulse is generated from the rear end and the front end, respectively, and as a result, the dot generation position can be controlled. Further, as shown in FIG. 5C, a medium mode in which optical writing pulses are generated in both directions from the center position of one dot can be selected.

Next, an example of a method of driving a semiconductor laser (LD) of a multi-level writing system combining pulse width modulation (PWM) and light intensity modulation (PM) will be described. In this semiconductor laser driving method, the light emission pattern of the semiconductor laser for one pixel is temporally set to 1/2 ＾ m (2 ＾ m
Is divided into 2 m steps with a resolution of a pixel clock width of 2 m, and the light emission power is divided into 2 m steps with a light emission power resolution of 1/2 (nm). Since division is performed and 2 ＾ n gradations are expressed by a combination of the two, the division accuracy of the light emission time and the light emission power is alleviated, and multiple gradations can be easily realized.

In the case of an 8-bit digital image signal according to the embodiment of the present invention, m = 3, pulse width modulation (PWM) is performed in 8 (= 2 ＾ m = 2 ³ ) steps, and light intensity modulation (PM) is 32. If (= 2 ＾ (nm) = 2 ⁵ ) stages, 2 ＾ n = 2 ⁸ = 256 kinds of light emitting patterns can be formed by a combination of the two, and 256-level LD multi-level modulation can be performed. Become. Also, an arbitrary light emission pattern can be obtained by changing a signal generated and output by a timing generation circuit or a power setting circuit of the semiconductor laser. The configuration of the semiconductor laser drive circuit and device of the multi-level writing system is described in the prior application by the present applicant, for example, in Japanese Patent Laid-Open No. 24336/1990.
No. 3, JP-A-3-1656, JP-A-6-34
It can be configured by utilizing those described in, for example, US Pat.

Next, phase control of pulse width modulation (position control)
5 according to the mode (right mode / left mode / middle mode) set by the phase (position) control logic.
As shown in (a) to (c), the dot position is controlled to the right, middle, and left by controlling the phase of the pulse width of the pulse width modulation. In addition to this function, it also has a fraction processing function as shown in FIGS.

In the fraction processing function, when two pixels consecutive in the main scanning direction are output collectively (added), two times of light intensity modulation usually occur as shown by the hatched portion in FIG. 6B. Performs an operation to combine them into one place. This is realized basically by adding data of a small fraction to a large fraction. As long as the fractional part does not reach the maximum, the data of the fractional part is all added to the fractional part, and the remainder when the fractional part becomes the maximum is distributed to the fractional part and the intensity modulation is performed. Do. By having the fraction processing function as described above, the pulse width setting step is made sufficiently smaller than the writing beam diameter. That is, FIGS. 6A to 6C are schematic diagrams in the case where the above operation is a dot image and an optical waveform. FIG. 6A shows a dot image before correction, and FIG. 6B shows an optical waveform before and after correction. , (C) are dot images after correction. In the data of two adjacent pixels (pixels), the portion of Δt where the light intensity does not reach the maximum is compared between adjacent pixels, and the smaller one is added to the larger one, and the remainder is made smaller.

(4) Addition control and phase control circuit Next, a configuration example of a control circuit that performs addition of adjacent pixel data of an image, determination and distribution of the added data, and dot phase control will be described with reference to FIG.
Shown in Here, a description will be given of a later-described method 6 in which two dots in the main scanning direction and two dots in the sub-scanning direction are added at maximum. In FIG. 7, input image data of each color converted into Y, M, C, and Bk is input with 256 gradations of 8 bits.
The 8-bit data A and B of two adjacent dots in the main scanning direction are input to the addition circuit 604 by the DF / F latch circuit 602. The line memory 601 delays the data of the previous line, and the latch circuit 603 inputs 8-bit data C and D of two adjacent dots at the same address in the main scanning direction of the previous line to the addition circuit 604. Then, after adding data of a total of 4 dots by the addition circuit 604, the comparison / distribution / phase control circuit 605 compares the data with the threshold value 1 of the data at which the dot becomes saturated. Switch between addition and addition. The added value is distributed so as to concentrate data according to an algorithm described later. Further, the writing phase signal is switched to toggle by the frequency-divided signal of the pixel clock. In the present embodiment, the control circuit for adding the adjacent pixel data of the image, determining and distributing the added data, and controlling the dot phase is shown by hardware as shown in FIG. But you can.

FIG. 8 shows a state of data transition by the addition of four dots and the addition of two dots by the above processing. FIG.
The low density portion of the image as in (a), the sum of the input data d ₄ from d ₁ in the main scanning direction 2 dots and the sub-scanning direction 2 dots, and D ₁ of the data. In the middle and high density portions of the image as shown in FIG. 8B, d ₁ and d _{2 of} two dots in the main scanning direction are used.
Of the input data of D ₁ , the saturation value of the data of D ₁ and the rest are D ₂
Data.

According to the present invention, in contrast to the above-mentioned prior application filed by the present inventor, the highlight portion of the image is reproduced more stably from a lower density, and the resolution and stability are improved from the middle density portion to the high density portion. It is intended. More specifically, The image data of a plurality of dots are added to generate a density from a specific pixel. In particular, dots are connected in the sub-scanning direction in a highlight portion, banding and image noise are reduced, and image stability is secured. That, 2. 2. In particular, after the minimum dot density data of the specific pixel for which the density is to be generated is saturated, the density of the next specific pixel is generated to secure the saturation and the stability. 3. In particular, reduce the number of necessary line buffers (line memories) to reduce costs. In particular, the result of density generation from a specific pixel is more faithful to the center of gravity of the density of the original data.

(5) Description of dot forming method by addition, distribution, and phase control method. In order to realize the above 1 to 4, in the present invention, two adjacent pixels in the main scanning direction or the sub-scanning direction are used.
Dot or 4 adjacent in the main scanning direction and sub-scanning direction
The image data of the dots are added, and the dots are reproduced in order from a predetermined specific pixel based on the calculation result. At this time, the right and left phases of the specific pixel are used to combine with the adjacent specific pixel.
Hereinafter, the six methods will be described in detail as specific examples.

(A) Method of adding image data of two dots in the sub-scanning direction (1/2 pulse division): methods 1, 2, 3,.
In the methods 1 to 3, one dot size is set to (a) in FIG.
FIG. 9B shows one pixel size (minimum density unit), and FIG.
A dot formation matrix such as 0 is set, and pulses are generated sequentially from the place where the numerical value of the dot formation matrix is small. At this time, one dot is divided into half pulses by pulse width modulation (PWM), and full dots (50%
When y) is reached, move to the next higher number and generate the next pulse. At this time, EVEN / O in the main scanning direction
The right phase / left phase of the PWM is switched by DD (hereinafter abbreviated as E / O), and the write pulses are combined in the same numerical direction. The algorithm for writing density generation is expressed as follows.

When 0 ≦ d ₁ + d ₂ ≦ 127, D ₁ =
d ₁ + d ₂ , D ₂ = 0 When 128 ≦ d ₁ + d ₂ ≦ 254 D ₁ = 127, D ₂
= D ₁ + d ₂ -127 When 255 ≦ d ₁ + d ₂ ≦ 382 D ₁ = d ₁ + d ₂ −1
27, D ₂ = 127 When 383 ≦ d ₁ + d ₂ ≦ 510 D ₁ = 255, D ₂
= D ₁ + d ₂ -255

In the above equation, d ₁ and d ₂ are input image data (8-bit data) before processing of adjacent dots, and D ₁ and D ₂
Is image data (8-bit data) after processing adjacent dots
It is. The 8-bit data after this processing is used as a write signal of the semiconductor laser (LD) of the laser printer. Hereinafter, specific examples of the methods 1 to 3 will be described.

(Method 1) Dot formation algorithm. 1) Add the density of two dots in the sub-scanning direction. 2) Generate pulses sequentially from the dot matrix 1. 3) The right / left phase of the PWM is switched in the main scanning direction E / O, and the write pulses are combined in the same numerical value direction. 4) One dot is divided into half pulses, and full (50% du)
ty), the next numbered PWM is generated.

[0065] In this manner is as shown in FIG. 11 is expressed by the minimum density unit dot formation matrix of FIG 10, D ₁
In FIG. 12, a pulse is generated in the right phase, and in D ₁ ′, a pulse is generated in the left phase, and a pulse combined with the portion 1 in FIG. 10 is generated (FIG. 12A). In the same manner, pulses are generated in the second and subsequent portions of FIG. 10 according to the density.

Next, details of dot formation by this method will be described with reference to FIGS. Density-1/8 (2 isolated dots). When the density is up to 1/8, as shown in FIG. 12 (A), the odd-numbered pixels in the main scanning direction are right-aligned, and the even-numbered pixels are left-aligned to generate a pulse combined with one portion of the dot forming matrix. . Density-1/4 (isolated 2 dots). The concentration is 1/8 to 1 /
In FIG. 4, as shown in FIG. 12B, the pulse coupled to one portion of the dot formation matrix is 50% of FULL.
Increase pulse width until duty. Concentration ３/8 (300 lines per line). The concentration is 1/4 to 3 /
At 8, as shown in FIG. 12C, a pulse combined with the 2 portion is generated in phase with the 1 portion of the dot formation matrix. Concentration １ ／ (300 lines per line). The concentration is 3/8 to 1 /
In FIG. 12, as shown in FIG. 12 (D), the pulse coupled to the second portion of the dot formation matrix is 50% of FULL.
Increase pulse width until duty. Concentration ５5/8. When the concentration is 1/2 to 5/8, FIG.
As shown in (A), a pulse combined with three parts is generated so as to increase the pulse width of one part of the dot formation matrix. Concentration ~ 3/4. When the concentration is 5/8 to 3/4, FIG.
As shown in (B), the pulse width is increased until the pulse coupled to the portion 3 of the dot formation matrix becomes 50% duty of FULL. Concentration ７7/8. When the concentration is 3/4 to 7/8, FIG.
As shown in (C), a pulse combined with the portion 4 is generated so as to increase the pulse width of the portion 2 of the dot forming matrix. Concentration ~ 1/1. When the density is 7/8 to 1/1, the pulse combined with the portion 4 of the dot formation matrix is FULL
The pulse width is increased until the duty becomes 50%.

In the above-described method 1, a growth type of isolated dots and vertical lines which can be regularly reproduced by isolated dots in a highlight portion, provides 300 lines and 600 lines (600 dpi) in a medium density portion, and has a gradation Features such as being linear, increasing the potential concentration and saturation region, ensuring stability, and being resistant to banding are obtained.

(Method 2) Dot formation algorithm. 1) Add the density of two dots in the sub-scanning direction. 2) Generate pulses sequentially from the dot matrix 1. 3) The right / left phase of the PWM is switched in the main scanning direction E / O, and the write pulses are combined in the same numerical value direction. 4) One dot is divided into half pulses, and full (50% du)
ty), the next numbered PWM is generated.

In this system, the spatial frequency of the highlight and high-density portions is increased by setting the dot forming matrix to have the same phase in the sub-scanning direction as in system 1. FIG. 14 shows a dot formation matrix. When the dot formation matrix 14 is expressed in the minimum density unit is shown in Figure 15, in the right phase in D _1, generates pulses in the left phase in D ₁ ', attached to one portion of the FIG. 14 Pulses are generated (FIG. 16A). In the same manner, FIG.
A pulse is generated in the part after 2 of 4.

Next, details of dot formation by this method will be described with reference to FIGS. Density-1/8 (isolated one dot). When the density is up to 1/8, as shown in FIG. 16 (A), odd-numbered pixels in the main scanning direction are right-aligned, and even-numbered pixels are left-aligned to generate a pulse combined with one portion of the dot forming matrix. . Density １ ／ (isolated one dot). The concentration is 1/8 to 1 /
In FIG. 4, as shown in FIG. 16B, the pulse coupled to one portion of the dot formation matrix is 50% of FULL.
Increase pulse width until duty. Concentration ３/8 (300 lines per line). The concentration is 1/4 to 3 /
At 8, as shown in FIG. 16C, a pulse combined with the 2 portion is generated in phase with the 1 portion of the dot formation matrix. Concentration １ ／ (300 lines per line). The concentration is 3/8 to 1 /
In FIG. 16, as shown in FIG. 16D, the pulse coupled to the second portion of the dot formation matrix is 50% of FULL.
Increase pulse width until duty. Concentration ５5/8. When the concentration is 1/2 to 5/8, FIG.
As shown in (A), a pulse combined with three parts is generated so as to increase the pulse width of one part of the dot formation matrix. Concentration ~ 3/4. When the concentration is 5/8 to 3/4, FIG.
As shown in (B), the pulse width is increased until the pulse coupled to the portion 3 of the dot formation matrix becomes 50% duty of FULL. Concentration ７7/8. When the concentration is 3/4 to 7/8, FIG.
As shown in (C), a pulse combined with the portion 4 is generated so as to increase the pulse width of the portion 2 of the dot forming matrix. Concentration ~ 1/1. When the density is 7/8 to 1/1, the pulse combined with the portion 4 of the dot formation matrix is FULL
The pulse width is increased until the duty becomes 50%.

In the above method 2, as compared with the method 1, the highlight portion is dispersed into one isolated dot and is hardly visible, and the dot size of a missing portion (white background) in the high density portion is small, and the character crack is less noticeable. Is obtained.

(Method 3) Dot formation algorithm. 1) Add the density of two dots in the sub-scanning direction. 2) Generate pulses sequentially from the dot matrix 1. 3) The right / left phase of the PWM is switched in the main scanning direction E / O, and the write pulses are combined in the same numerical value direction. 4) One dot is divided into half pulses, and full (50% du)
ty), the next numbered PWM is generated.

In this system, in contrast to system 2, high-density reproduction dots of the dot formation matrix are dispersed, and the spatial frequency of the high-density portion is increased (character cracks are not noticeable). FIG.
Shows a dot formation matrix. When the dot formation matrix 18 is expressed in the minimum density unit is as shown in FIG. 19, the right phase in D _1, 1 a D ₁ generates pulses in the left phase in ", similar to scheme 2 Figure 18 Pulses are generated in the same manner as described above, and pulses are generated in the same manner as in FIG.

Next, details of dot formation by this method will be described with reference to FIG. Density-1/8 (isolated one dot) to density-1/2
In the density range up to (300 lines per line), FIG.
A dot pattern similar to that shown in FIGS. Concentration ５5/8. When the concentration is 1/2 to 5/8, FIG.
As shown in FIG.
A pulse combined with the part 3 is generated so as to increase the pulse width of the part. Concentration ~ 3/4. When the concentration is 5/8 to 3/4, FIG.
As shown in (B), the pulse width is increased until the pulse coupled to the portion 3 of the dot formation matrix becomes 50% duty of FULL. Concentration ７7/8. When the density is 3/4 to 7/8, a pulse combined with the portion 4 is generated so as to increase the pulse width of the portions 1 and 2 of the dot forming matrix. Concentration ~ 1/1. When the density is 7/8 to 1/1, the pulse combined with the portion 4 of the dot formation matrix is FULL
The pulse width is increased until the duty becomes 50%.

In the above-mentioned method 3, since the voids (white background) are dispersed in a high-density portion in a staggered manner as compared with the method 2, it is possible to obtain a feature that character cracks are less noticeable.

(B) Method of adding image data of two dots in the sub-scanning direction (1/4 pulse division): Method 4. In the method 4, similarly to the method 3, pulses are sequentially generated from the place where the numerical value of the dot formation matrix is small as shown in FIG. At this time, one dot is divided into ま た は or パ ル ス pulses, and when the duty reaches 50% duty or 25% duty, the number is shifted to the next larger number and the next pulse is generated. At this time, the right phase / left phase of the PWM is switched in the main scanning direction E / O, and the write pulses are combined in the same numerical value direction.
The algorithm for writing density generation is expressed as follows.

When 0 ≦ d ₁ + d ₂ ≦ 127, D ₁ =
d ₁ + d ₂ , D ₂ = 0 When 128 ≦ d ₁ + d ₂ ≦ 190 D ₁ = 127, D ₂
= D ₁ + d ₂ -127 When 191 ≦ d ₁ + d ₂ ≦ 254 D ₁ = d ₁ + d ₂ -6
3, when D ₂ = 63 255 ≦ d ₁ + d ₂ ≦ 318 D ₁ = 191, D ₂
= D ₁ + d ₂ −191 When 319 ≦ d ₁ + d ₂ ≦ 382 D ₁ = d ₁ + d ₂ −1
27, D ₂ = 127 When 383 ≦ d ₁ + d ₂ ≦ 510 D ₁ = 255, D ₂
= D ₁ + d ₂ -255

In the above equation, d ₁ and d ₂ are input image data (8-bit data) before processing of adjacent dots, and D ₁ and D ₂
Is image data (8-bit data) after processing adjacent dots
It is. The 8-bit data after this processing is used as a write signal of the semiconductor laser (LD) of the laser printer. Hereinafter, a specific example of the method 4 will be described.

(Method 4) Dot formation algorithm. 1) Add the density of two dots in the sub-scanning direction. 2) Generate pulses sequentially from the dot matrix 1. 3) The right / left phase of the PWM is switched in the main scanning direction E / O, and the write pulses are combined in the same numerical value direction. 4) Divide one dot into half or 1/4 pulse;
When the duty becomes 0% duty or 25% duty, the PWM of the next number is generated.

In this method, compared to the method 3, a duty 25% of 2 is used in the same dot formation matrix (FIG. 21) as in FIG.
Then, the processing shifts to writing 3 to make the character crack in the middle density portion inconspicuous. When the dot formation matrix 21 is expressed in the minimum density unit is shown in Figure 22, in the right phase in D _1, it generates pulses in the left phase in D ₁ ",
Similar to the method 3, a pulse combined with a portion 1 in FIG. 21 is generated. Hereinafter, similarly, according to the density, 2 in FIG.
Pulses are generated in the subsequent portions.

Next, details of dot formation by this method will be described with reference to FIG. Density ~ 1/8 (isolated one dot) to density ~ 3/8
In the density range up to (300 lines), a dot pattern is formed in the same manner as in method 3. Concentration-1/2. When the concentration is 3/8 to 1/2, FIG.
As shown in (A), the pulse coupled to the portion 2 of the dot formation matrix shifts to 3 at 25% duty, and the pulse coupled to the portion 3 changes to 7 at 25% duty when coupled to 1.
Increase to 5%. If the arrangement of the matrix of the highlights is arranged in a staggered manner (1 and 2 are interchanged), the arrangement of 3 and 4 is alternately exchanged, so that the arrangement can be made less noticeable as in the method 3. Concentration ５5/8. When the concentration is 1/2 to 5/8, FIG.
As shown in (B), the number of combined pulses is increased until the portion 2 of the dot formation matrix becomes 50% duty of FULL. After the concentration of 〜 to ／, the same operation as in method 3 is performed.

In the above-described method 4, character cracks of medium density can be made less conspicuous than in method 3, and omissions (white background) in high-density portions are dispersed as in method 3, so that character cracks Is obtained, which is less noticeable.

(C) Method of adding image data of two dots in the main scanning direction (1/2 pulse division): Method 5. In method 5, one dot size is set to (a) in FIG. 24, one pixel size (minimum density unit) is set to (b) in FIG. 24, and a dot formation matrix as shown in FIG. Pulses are generated sequentially from the place where the value of the matrix is small. At this time, one dot is divided into half pulses by pulse width modulation (PWM), and when it becomes full (50% duty), the next number is increased and the next pulse is generated. At this time, the right phase / left phase of the PWM is switched by E / O in the main scanning direction, and the write pulses are combined in the same numerical value direction. The algorithm for writing density generation is expressed as follows.

When 0 ≦ d ₁ + d ₂ ≦ 127, D ₁ =
d ₁ + d ₂ , D ₂ = 0 When 128 ≦ d ₁ + d ₂ ≦ 254 D ₁ = 127, D ₂
= D ₁ + d ₂ -127 When 255 ≦ d ₁ + d ₂ ≦ 382 D ₁ = d ₁ + d ₂ −1
27, D ₂ = 127 When 383 ≦ d ₁ + d ₂ ≦ 510 D ₁ = 255, D ₂
= D ₁ + d ₂ -255

In the above equation, d ₁ and d ₂ are input image data (8-bit data) before processing of adjacent dots, and D ₁ and D ₂
Is image data (8-bit data) after processing adjacent dots
It is. The 8-bit data after this processing is used as a write signal of the semiconductor laser (LD) of the laser printer. Hereinafter, a specific example of the method 5 will be described.

(Method 5) Dot formation algorithm. 1) Add the density of 2 dots in the main scanning direction. 2) Generate pulses sequentially from the dot matrix 1. 3) The right / left PWM phase is switched, formed from outside each pixel, and the write pulse is combined. 4) One dot is divided into half pulses, and full (50% du)
ty), the next numbered PWM is generated.

In this method, 2 × 1 continuous pixels in the main scanning direction
The matrix is the minimum pixel, and the highlight portion is reproduced with staggered dots. When the dot formation matrix 25 is expressed in the minimum density unit is shown in Figure 26, in the right phase in D _1, generates pulses in the left phase in D ₁ ', attached to one portion of the FIG. 25 Pulses are generated (FIG. 27A). In the same manner, pulses are generated in the second and subsequent portions of FIG. 25 according to the density.

Next, details of dot formation by this method will be described with reference to FIGS. Density-1/8 (isolated one dot). When the density is up to 1/8, as shown in FIG. 27 (A), the odd-numbered pixels in the main scanning direction are right-aligned, and the even-numbered pixels are left-aligned to generate a pulse combined with one portion of the dot forming matrix. . Density １ ／ (isolated one dot). The concentration is 1/8 to 1 /
In FIG. 4, as shown in FIG. 27B, the pulse coupled to one portion of the dot formation matrix is 50% of FULL.
Increase pulse width until duty. Concentration ３/8 (300 lines per line). The concentration is 1/4 to 3 /
In FIG. 27, as shown in FIG. 27C, a pulse combined with two portions from the outside of the pixel of the dot formation matrix is generated. Concentration １ ／ (300 lines per line). The concentration is 3/8 to 1 /
In FIG. 27, as shown in FIG. 27 (D), the pulse coupled to the portion 2 of the dot formation matrix is 50% of FULL.
Increase pulse width until duty. Concentration ５5/8. When the concentration is 1/2 to 5/8, FIG.
As shown in (A), a pulse combined with three parts is generated so as to increase the pulse width of one part of the dot formation matrix. Concentration ~ 3/4. When the concentration is 5/8 to 3/4, FIG.
As shown in (B), the pulse width is increased until the pulse coupled to the portion 3 of the dot formation matrix becomes 50% duty of FULL. Concentration ７7/8. When the concentration is 3/4 to 7/8, FIG.
As shown in (C), a pulse combined with the portion 4 is generated so as to increase the pulse width of the portion 2 of the dot forming matrix. Concentration ~ 1/1. When the density is 7/8 to 1/1, the pulse combined with the portion 4 of the dot formation matrix is FULL
The pulse width is increased until the duty becomes 50%.

In the method 5 described above, a staggered isolated dot can be regularly reproduced in the highlight portion, and 3 in the middle density portion.
An isolated dot, which can provide 00 lines per line (600 dpi)
Features such as a vertical line growth type with linear gradation, increased potential concentration and saturation region to ensure stability, and strong banding are obtained.

(D) Method of adding image data of 4 dots in the main scanning direction (1/2 pulse division): Method 6. In method 6, image data for 4 dots is added in a highlight portion having a density of 1/4 or less, and image data of 2 dots in the main scanning direction is added in subsequent highlight, middle, and shadow portions. Hereinafter, each method will be described.

(A) When the density is 1/4 or less. One dot size is shown in FIG. 29A, and one pixel size (minimum density unit) is shown in FIG. 29B. Pulses are sequentially generated from a dot forming matrix having a small numerical value as shown in FIG. At this time, one dot is divided into half pulses by pulse width modulation (PWM), and when it becomes full (50% duty), the next number is shifted to the same number or a larger number, and the next pulse is generated. In this case, P / P in E / O in the main scanning direction
The WM is switched between the right phase and the left phase, and the write pulses are combined in the same numerical direction. When the dot formation matrix of FIG. 30 is expressed in the minimum density unit, it becomes as shown in FIG.
_A pulse is generated in the left phase in _{1 and} in the right phase in D ₁ ′, and a pulse combined with the portion 1 in FIG. 30 is generated (FIG. 34A). In the same manner, a pulse is generated in another portion of FIG. 30 according to the density. The algorithm for writing density generation is expressed as follows.

When 0 ≦ d ₁ + d ₂ + d ₃ + d ₄ ≦ 127
D ₁ = d ₁ + d ₂ + d ₃ + d ₄ , D ₂ = D ₃ = D ₄ = 0 When 128 ≦ d ₁ + d ₂ + d ₃ + d ₄ ≦ 254 D ₁ = 1
_{27, D 2 = d 1 +} d 2 + d 3 + d 4 -127, D 3 = D 4 =
0

In the above equation, d ₁ , d ₂ , d ₃ , and d ₄ are input image data (8-bit data) before processing adjacent dots, and D ₁ , D ₂ , D ₃ , and D ₄ are adjacent dot dots. Is the image data (8-bit data) after the processing. The 8-bit data after this processing is used as a write signal of the semiconductor laser (LD) of the laser printer.

(A) When the density is 1/4 or more. FIG. 29A shows one dot size, and FIG. 32 shows one pixel size (minimum density unit). When the dot formation matrix 30 is expressed in the minimum density unit is shown in Figure 33, in the D ₁ in the left phase, generates pulses in the right phase in D ₁ ', attached to the second portion of Figure 30 Pulses are generated (FIG. 35A). In the same manner, a pulse is generated at a portion 3 in FIG. 30 according to the density. The algorithm for writing density generation is expressed as follows.

When d ₁ + d ₂ + d ₃ + d ₄ = 254 in the representation of one pixel size shown in FIG. 29B, D ₁ = D ₂ = 127
Therefore, if it is replaced with the expression of one pixel size in FIG. 33, when d ₁ + d ₂ = 127, D ₁ = 127 and D ₂ = 0, and thereafter, when 128 ≦ d ₁ + d ₂ ≦ 382 D ₁ = d ₁ + d ₂ -1
27, D ₂ = 127 When 383 ≦ d ₁ + d ₂ ≦ 510 D ₁ = 255, D ₂ =
d ₁ + d ₂ -255. Hereinafter, a specific example of the method 6 will be described.

(Method 6) Dot formation algorithm. 1) Add the density of 4 dots in the main / sub scanning direction or 2 dots in the main scanning direction. 2) Generate pulses sequentially from the dot matrix 1. 3) The right / left PWM phase is switched, formed from outside each pixel, and the write pulse is combined. 4) One dot is divided into half pulses, and full (50% du)
ty), the same or the next number of PWM
Generate.

Next, details of dot formation by this method will be described with reference to FIGS. (A) Concentration 1/4 or less. -1: density １ ／ 1/16 (isolated one dot). The concentration is 1 /
In the case of 16 or less, as shown in FIG. 34A, the density data of the surrounding four dots are added, and an isolated dot is generated from the upper part of the pixel. -2: Density-1/8 (isolated one dot). Concentration is 1/1
In 6 to 1/8, as shown in FIG. 34B, the density data of the surrounding four dots are added, and the pulse width is increased until the upper part of the pixel is saturated (full 50% duty). -1: density ~ 3/16 (isolated 2 dots). The concentration is 1 /
In 8 to 3/16, as shown in FIG.
The dot density data is added, and after the upper portion of the pixel is saturated, the remaining dot is generated in the lower portion of the pixel. -2: density ~ 2/8 (isolated 2 dots). The concentration is 3/1
In 6 to 2/8, as shown in FIG. 34 (D), the density data of the surrounding four dots are added, and the pulse width is increased until the portion 1 below the pixel is saturated (full 50% duty).

(A) Concentration of 1/4 or more. Concentration ３/8 (300 lines per line). The concentration is 1/4 to 3 /
In FIG. 35, as shown in FIG. 35A, a pulse combined with two portions from the outside of the pixel of the dot formation matrix is generated. Concentration １ ／ (300 lines per line). The concentration is 3/8 to 1 /
In FIG. 35, as shown in FIG. 35 (B), the pulse coupled to the portion 2 of the dot formation matrix is 50% of FULL.
Increase pulse width until duty. Concentration ５5/8. When the concentration is 1/2 to 5/8, FIG.
As shown in (C), a pulse combined with three parts is generated so as to increase the pulse width of one part of the dot formation matrix. Concentration ~ 3/4. When the concentration is 5/8 to 3/4, FIG.
As shown in (D), the pulse width is increased until the pulse combined with the portion 3 of the dot formation matrix becomes 50% duty of FULL. Concentration ７7/8. When the density is 3/4 to 7/8, as shown in FIG. 36, a pulse combined with the portion 4 is generated so as to increase the pulse width of the portion 2 of the dot formation matrix. Concentration ~ 1/1. When the density is 7/8 to 1/1, the pulse combined with the portion 4 of the dot formation matrix is FULL
The pulse width is increased until the duty becomes 50%.

In the above method 6, compared with method 5, the density 1
In a highlight portion of ４ or less, the density of 4 dots is added, and isolated dots are arranged in a staggered manner. In a highlight portion to a shadow portion of 濃度 or more of density, image data of 2 dots in the main scanning direction is added. And since 2 dots are arranged in a staggered pattern,
The reproducibility of the highlight portion can be improved from a lower density.

[0100]

As described above, in the image forming apparatus according to the first aspect, means for adding image data of adjacent pixels, means for generating density from a specific pixel by the added data, and generation of the density Means for changing the pixel in the sub-scanning direction, and means for changing the density generation pixel in the sub-scanning direction by combining adjacent pixels in the sub-scanning direction. ), When image data of a plurality of dots are added in the sub-scanning direction and density is generated from specific pixels, dots connected in the sub-scanning direction can be reproduced by appropriately arranging specific pixels of density generation,
Since the potential concentration and the increase of the saturation region can be achieved, the stability of the image can be ensured particularly in the highlight portion. This is because the potential distribution of the photoconductor exposed with isolated dots is generally
The periphery of the dot is mountain-shaped, and its foot is an unstable area. On the other hand, by combining the exposure dots, the potential of the connection is saturated and becomes a stable area.

According to a second aspect of the present invention, there is provided an image forming apparatus, comprising: means for adding image data of adjacent pixels; means for generating a density from a first specific pixel based on the added data; and density of a minimum dot of the specific pixel. When the data is saturated, the second
Means for generating the density of the specific pixel (corresponding to the methods 1, 2, 3, 5, and 6). Since the density of the specific pixel is generated, the saturation can be secured and the stability can be secured.

According to a third aspect of the present invention, there is provided an image forming apparatus, comprising: a light writing unit including at least pulse width modulation in light modulation; a unit for adding image data of adjacent pixels in the main scanning direction; Means for generating a density from a specific position.
), Since the addition of adjacent dots and the generation of density from a specific pixel are all performed on the same main scan, it can be realized without using a line buffer memory as compared with the case of adding adjacent dots in the sub-scanning direction. Therefore, cost can be reduced.

According to a fourth aspect of the present invention, there is provided an image forming apparatus, comprising: an optical writing unit including at least pulse width modulation in optical modulation; a unit for adding image data of an adjacent pixel in the sub-scanning direction; Means for generating a concentration from a specific position.
2, 3, and 4), the addition of adjacent dots in the sub-scanning direction makes the result of density generation from a specific pixel smaller than the method of adding adjacent dots in the main scanning direction. The result can be more faithful to the center of gravity. More specifically, as shown in FIG. 37, when the adjacent pixel data in the sub-scanning direction of (a) is added, dots are generated from diagonal (oblique) positions with respect to the center of gravity of two dots of the original data. When the distance is 1 / √2 dots, when adding the adjacent pixel data in the main scanning direction of (b), a dot is generated from the end position with respect to the center of gravity of 2 dots of the original data, The distance is one dot.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a digital color copying machine showing one configuration example of an image forming apparatus according to the present invention.

FIG. 2 is a circuit block diagram showing a configuration example of an image processing unit of the digital color copying machine shown in FIG.

FIG. 3 is an explanatory diagram of a multi-level modulation method of a semiconductor laser.

FIG. 4 is an explanatory diagram of a multilevel modulation method of a semiconductor laser in which a pulse width modulation method and a power modulation method are combined.

FIG. 5 is an explanatory diagram of pulse position control during multilevel modulation of a semiconductor laser.

FIG. 6 is an explanatory diagram of an addition mode of adjacent pixels.

FIG. 7 is a block diagram illustrating a configuration example of a control circuit that performs addition of adjacent pixel data of an image, determination and distribution of added data, and dot phase control.

FIGS. 8A and 8B are diagrams showing the transition of data when adding adjacent pixel data of an image, and discriminating and distributing the added data, and performing dot phase control. FIG. (B) is a diagram illustrating an example of a medium-high density portion (addition of two dots).

FIG. 9 is an explanatory diagram of one dot size and one pixel size (minimum density unit) in schemes 1 to 4 according to the present invention.

FIG. 10 is a diagram showing a dot formation matrix in the method 1 according to the present invention.

FIG. 11 is a diagram showing a dot formation matrix in a minimum density unit in the method 1 according to the present invention.

FIG. 12 is an explanatory diagram of dot formation in method 1 according to the present invention.

FIG. 13 is an explanatory diagram of dot formation in method 1 according to the present invention.

FIG. 14 is a diagram showing a dot formation matrix in a method 2 according to the present invention.

FIG. 15 is a diagram showing a dot formation matrix in the minimum density unit in the method 2 according to the present invention.

FIG. 16 is an explanatory diagram of dot formation in method 2 according to the present invention.

FIG. 17 is an explanatory diagram of dot formation in method 2 according to the present invention.

FIG. 18 is a diagram showing a dot formation matrix in a method 3 according to the present invention.

FIG. 19 is a diagram illustrating a dot formation matrix in the minimum density unit in the method 3 according to the present invention.

FIG. 20 is an explanatory diagram of dot formation in method 3 according to the present invention.

FIG. 21 is a diagram showing a dot formation matrix in a method 4 according to the present invention.

FIG. 22 is a diagram expressing a dot formation matrix in a minimum density unit in the method 4 according to the present invention.

FIG. 23 is an explanatory diagram of dot formation in Method 4 according to the present invention.

FIG. 24 is an explanatory diagram of one dot size and one pixel size (minimum density unit) in method 5 according to the present invention.

FIG. 25 is a diagram showing a dot formation matrix in Method 5 according to the present invention.

FIG. 26 is a diagram expressing a dot formation matrix in a minimum density unit in the method 5 according to the present invention.

FIG. 27 is an explanatory diagram of dot formation in Method 5 according to the present invention.

FIG. 28 is an explanatory diagram of dot formation in Method 5 according to the present invention.

FIG. 29 is an explanatory diagram of one dot size and one pixel size (minimum density unit) in a highlight having a density of 1/4 or less in method 6 according to the present invention.

FIG. 30 is a diagram showing a dot formation matrix in a method 6 according to the present invention.

FIG. 31 is a diagram showing a dot formation matrix in a density of 1/4 or less of the system 6 according to the present invention in a minimum density unit.

FIG. 32 is an explanatory diagram of one pixel size (minimum density unit) at a density of 1/4 or more in the method 6 according to the present invention.

FIG. 33 is a diagram expressing a dot formation matrix in a minimum density unit in a density of 1/4 or more in the method 6 according to the present invention.

FIG. 34 is an explanatory diagram of dot formation at a density of 1/4 or less in the method 6 according to the present invention.

FIG. 35 is an explanatory diagram of dot formation at a density of 1/4 or more in method 6 according to the present invention.

FIG. 36 is an explanatory diagram of dot formation at a density of 7/8 in method 6 according to the present invention.

FIG. 37 shows the center of gravity of the density of the original data and the output when adding the adjacent dots in the sub-scanning direction and when adding the adjacent dots in the main scanning direction when calculating the image data of the adjacent pixels. FIG. 4 is an explanatory diagram showing a center of gravity of data density generation.

FIG. 38 is an explanatory diagram showing an optical writing method for pixels of a 1 × 2 matrix and a 2 × 1 matrix.

FIG. 39 is a chart showing halftone areas in pixels of a 1 × 2 matrix and a 2 × 1 matrix.

FIG. 40 is a block diagram illustrating a configuration example of a two-dot multilevel circuit that performs addition + phase control.

FIG. 41 is an explanatory diagram showing a combination of a 2-dot addition pixel and an area gradation in the main scanning / sub-scanning direction.

[Explanation of symbols]

 1: Photoconductor drum 2: Transfer drum 3: Writing unit 4: Developing unit 9: Fixing unit 11: Paper cassette 50: System controller 60: Synchronous control circuit 71: Scanner gamma circuit 72: Smoothing filter 73: Color correction circuit 74 : UCR / UCA circuit 75: Selector 76: Edge emphasis filter 77: Printer gamma circuit 78: Gradation processing circuit 100: Laser printer 400: Image scanner 601: Line memory 602, 603: Latch circuit 604: Addition circuit 603: Comparison / Distribution / phase control circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA05 AA24 AA26 AA27 AB13 AC11 BB09 BB20 BB44 DA09 2C362 CA11 5B057 AA11 BA28 CA01 CA08 CA12 CA16 CB01 CB07 CB12 CB16 CC02 CE08 CE13 5C077 LL19 MP08 PN12 NN02NN

Claims (4)

[Claims] 1. An image forming apparatus for forming an image by modulating a multi-tone image signal, means for adding image data of adjacent pixels, means for generating density from a specific pixel by the added data, Means for changing the density generation pixels in the sub-scanning direction, and connecting the adjacent pixels in the sub-scanning direction by the means for changing the density generation pixels in the sub-scanning direction. 2. An image forming apparatus which forms an image by modulating a multi-tone image signal, means for adding image data of adjacent pixels, and means for generating density from a first specific pixel based on the added data. And a means for generating the density of the second specific pixel when the density data of the minimum dot of the specific pixel is saturated. 3. An image forming apparatus for forming an image by modulating a multi-tone image signal, wherein light writing means including at least pulse width modulation in light modulation and image data of an adjacent pixel in the main scanning direction are added. An image forming apparatus comprising: means for generating density from a specific position of a specific pixel based on the operation data. 4. An image forming apparatus for forming an image by modulating a multi-gradation image signal, wherein light writing means including at least pulse width modulation in light modulation and image data of an adjacent pixel in the sub-scanning direction are added. An image forming apparatus comprising: means for generating density from a specific position of a specific pixel based on the operation data.