JP2002019179A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the edge part of a line extending across a plurality of pixels or 1 dot line of black from becoming too thick even for multivalued image data containing only density data, and to prevent the thickness of longitudinal and lateral lines from differentiating. SOLUTION: Image data Da of a plurality of bits indicative only density information inputted from a reading section 10 is processed at an image processing section 20 to produce image data Db which is then inputted to the code converting section of a writing section 30 where it is compared with a plurality of patterns preset depending on the density information and converted into code data Dd corresponding to a matched pattern. A density correction data generating means, i.e., a code switching section 60, generates density correction data De from the code data Dd and a density data generating means, i.e., an OR gate 70, generates density data Df through logical sum with image data Dc. Emission time and/or emission power of a laser diode is modulated at an image writing section depending on the density data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus equipped with a writing optical system using a laser, and more particularly to an image forming apparatus using multi-valued data that does not include phase data for controlling light emission timing by pattern matching. The present invention relates to a technique for detecting a specific pattern (edge portion of an image, one dot line) and adding phase data for controlling thinning and emission timing of the portion.

[0002]

2. Description of the Related Art There is a digital copying machine as one form of an image forming apparatus equipped with a writing optical system using a laser. As the image forming method, a negative / positive (N / P) process in which an image is formed by irradiating a laser beam on a portion corresponding to a black portion of the original data and applying toner on the portion is generally used. is there. Since the beam diameter of laser light is usually larger than one theoretical dot, in the N / P process of irradiating the image part with laser light to form that part as an image, the black line of one dot is usually reproduced thick and firmly. It will be stronger against broken lines.

However, since one black dot line is reproduced thicker than the black line of the original, and one white dot line becomes thinner, the reproducibility deteriorates. In particular, in a so-called grandchild copy in which the copied paper is used again as a document, the phenomenon appears greatly.

[0004] In addition, there is a difference in reproducibility between a vertical line and a horizontal line as a drawback of an electrophotographic image forming method. In general, a vertical line is reproduced thicker and firmer than a horizontal line. Therefore, when determining the image forming conditions, if the vertical line is set, the horizontal line tends to be thinner than the original, and if the horizontal line is set, the vertical line tends to be thicker than the original. This has contributed to the difficulty in determining the image conditions.

To solve such a problem, for example, Japanese Unexamined Patent Publication No. Hei 5-75816 discloses a method of detecting the density of a pixel of interest by referring to a pixel of interest and two or more pixels before and after the pixel of interest. Is determined to prevent the non-image portion from being crushed and to improve the reproducibility of one dot line.

[0006] Also, Japanese Patent Application Laid-Open No. 6-89338 discloses that
By determining the printing start position of the pixel of interest from the relationship between the pixel of interest and its neighboring pixels in the multi-valued image, the pixel of interest is printed with the pixel adjacent to the pixel, and the reproducibility of the thin line and the edge of the image is improved. Techniques for improving have been proposed.

[0007]

However, in the technique disclosed in Japanese Patent Laid-Open No. 5-75816, it is possible to improve the reproducibility of one dot line by correcting the density of only binary image data. Yes, but no consideration is given to multi-valued images. In the technique disclosed in Japanese Patent Application Laid-Open No. 6-89338, the reproducibility of a thin line divided into two or more pixels and an edge portion of an image is obtained by printing a pixel of interest of a multi-valued image at an adjacent pixel. However, no consideration has been given to the correction of the line width when the fine line of one pixel or the vertical line and the horizontal line have different thicknesses.

The present invention has been made in view of such a situation, and in an image forming apparatus equipped with a writing optical system using a laser, multi-valued image data containing only density information can be used. It is an object of the present invention to prevent an edge portion of a line extending over a plurality of pixels or a single black dot line from becoming too thick, and to prevent a vertical line and a horizontal line from being different in thickness.

[0009]

In order to achieve the above object, an image forming apparatus according to the present invention converts a plurality of bits of image data indicating only density information input from a scanner or an external device in advance in accordance with the density information. A code conversion unit that compares the image data with code data corresponding to the matched pattern when detecting a match with any of the plurality of set patterns, and a code output by the code conversion unit; Density correction data generating means for generating density correction data from the data; density data generating means for generating density data from the image data and the density correction data; and a light emitting time of a laser diode in an image writing unit according to the density data. Or a modulating means for modulating the light emission power or both.

When the code conversion means detects that the input image data matches a specific pattern such as a one-dot line, the density correction data generation is performed from the code data output from the code conversion means. The means may generate density correction data for correcting the light emission amount of the laser diode to be smaller than usual.

In the above image forming apparatus, further, when the black pixel is deviated to the left or right with respect to the center of the full pixel from the input image data, a means for detecting the black pixel is generated. In accordance with the phase data, the emission timing of the laser diode when writing the corresponding black pixel by the modulation means may be shifted so as to be shifted to the left or right from the original pixel center.

[0012]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 2 is an external view of a digital copying machine which is an embodiment of the image forming apparatus according to the present invention.

The digital copying machine 1 has a platen (platen glass) 2 for placing and reading an original and a pressure plate 3 for holding down the original, and an operation unit 4 on the near side of the upper part. I have. The operation unit 4 includes a group of keys for setting a reading mode, a copy magnification, the number of copies, and the like, and giving an instruction to start copying, and a display for displaying information to an operator. Further, a multi-stage paper feed unit 5 is shown on the lower side in FIG.
Is provided with a paper discharge unit 6 on the left side.

Inside the digital copying machine 1, known mechanisms of the digital copying machine such as an illumination system, an image forming optical system, a writing system, a paper feeding and conveying system, a developing system, a fixing system, a paper discharging system, and the like. Is realized, and the function as a copying machine is realized. That is, after the original is placed on the original platen 2 and the original is brought into close contact with the original platen 2 by the pressure plate 3, the image of the original is illuminated by an illumination system and an image forming optical system (not shown) according to an instruction from the operation unit 4. Perform a read.

After performing various corrections on the read image data, the writing system irradiates a laser beam from a laser diode (hereinafter also referred to as “LD”) based on the image data, and the laser beam is not shown. An electrostatic latent image is formed on the surface of the photoconductor. Thereafter, a copy image is formed on a sheet fed from the sheet feeding unit 5 through a so-called electrophotographic process.

FIG. 1 is a block diagram showing a configuration of an image data processing portion in the digital copying machine 1. As shown in FIG. The reading processing unit 10 performs various corrections such as shading correction on image data read at 600 dpi by a CCD line sensor (not shown), and converts the image data into 8-bit (256 gradation) image data Da for each pixel. 20.

The image processing section 20 receives the input image data D
After a is subjected to image quality correction by performing MTF correction and scaling processing, it is converted to 2-bit (four gradation) multi-valued image data Db and output to the write processing unit 30.

The write processing unit 30 converts the input multi-valued image data Db into a code corresponding to the density information by the code conversion unit 40, and outputs 6-bit image data (code data) Dc to the OR gate 70. The 64-bit code data Dd is output to the code switching unit 60. In addition, the phase data detection unit 50 calculates, based on the input image data,
When the black pixel is deviated to the left or right with respect to the center of the full pixel, this is detected, and phase data Dg for controlling the writing position is also generated.

The code switching section 60 receives from the control section 80 density correction data De corresponding to the 64-bit code data Dd input from the code conversion section 40. The OR gate 70 performs an OR operation on the acquired density correction data De and the image data Dc to generate density data Df whose density has been corrected.

Based on the density data Df and the phase data Dg generated by the phase data detection unit 50, the light emission time and / or the light emission power of the laser diode in the writing system are modulated, so that the edge in the image data is modulated. The writing density and the writing start position for the portion and the thin line portion are changed, and 256 gradations, 600 d
At pi, an image is written on a photoconductor (not shown).

The control unit 80 is connected to the operation unit 3, and based on the mode for reading the original set by the operation unit 4, the reading processing unit 10 and the image processing unit 20.
And the write processing unit 30. Read processing unit 1
0 and the image processing unit 20 are known technologies,
In the present invention, since it is not a characteristic part, detailed description is omitted.

Next, an image control signal according to the present invention will be described with reference to FIG. The image control signals include XLSYNC, which is a synchronization signal in the main scanning direction of the image, XLGATE, which indicates an image valid period in the main scanning direction, XFGATE, which indicates an image valid period in the sub-scanning direction, and CLK which synchronizes image data. There is. The image data Db is XLSY
Each line is synchronized by NC, and XFGATE and X
While LGATE is at the “L” level, the signal is output from the image processing unit 20 shown in FIG. 1 in synchronization with the pixel clock CLK.

Next, the configuration and operation of the code conversion unit 40 shown in FIG. 1 will be described with reference to FIGS. FIG. 4 is a block diagram showing the configuration of the code conversion section 40, FIG. 5 is a block diagram showing the configuration of the data delay section 140, and FIG. 6 is a timing chart for explaining the operation. FIG. 7 is an explanatory diagram showing the relationship between image data Db and print dots, and FIG.
It is explanatory drawing which shows the content of 41.

The code conversion unit 40 shown in FIG. 1 includes a data delay unit 140 and a pattern table 1 as shown in FIG.
41. The data delay unit 140
As shown in FIG. 5, three flip-flops 240, 2
41, 242.

The data delay section 140 converts the multivalued image data Db processed by the image processing section 20 of FIG.
, A data array of three pixels in the main scanning direction is generated. Each flip-flop 240, 24
1 and 242 are configured to have a function of delaying the input data by one clock and outputting the data. After various processes are performed by the image processing unit 20, the multi-valued image data Db converted into a 2-bit (quaternary) signal is transmitted to the data delay unit 1
It is input to 40 flip-flops 240.

The output Dc1 of the flip-flop 240
Is data obtained by delaying the multilevel image data Db by one clock, and this data is further input to the flip-flop 241 and is delayed in synchronization with the clock CLK. Similarly, the output of the flip-flops 241 and 242 is output as the image data Dc delayed by one clock.
2, Dc3 are obtained.

Each of the image data Dc1, Dc2, Dc3
Is output at the timing shown in FIG. Here, the image data Dn for each clock is data corresponding to the image data n shown in FIG. These image data Dc1, Dc2, and Dc3 are output to the pattern table 141 shown in FIG. 4, and the data after the part shown by the arrow in FIG. use.

Since the multi-valued image data Db processed by the image processing unit 20 is 2-bit data, the density is 4 bits.
Steps can be taken, and the relationship with the actual image is as shown in FIG. That is, when the combination of two bits is (0,0), white is at (0,1), halftone 1 is at (0,1), at (1,0) is halftone 2, which is higher in density than halftone 1, and ( 1,1)
Black at the time.

Therefore, as a combination of the image data Dc1 to Dc3, each dot can take four states, and it is 4 × 4 × 4, and has 64 states as shown in FIG. In the pattern table 141, as shown in FIG. 8, the code data Dd1 to Dd64 correspond to all possible value patterns of the image data Dc1, Dc2, and Dc3.
Is allocated.

{Dc1, Dc2, Dc3} = (0, 0,
0,0,0,0), (0,1,0,0,0,0), ...
The pattern of... Indicates one dot line, and one of them is selected. "1" is set in one of the code data Dd1 to Dd64 according to the selected pattern.
Therefore, the pattern table 141 reads the values of the input image data Dc1, Dc2, Dc3, and
1 bit (“0” or “1”) code data Dd1 to Dd64 indicating which pattern
Is output.

Next, referring to FIG.
Will be described. Phase data detector 50 in FIG.
Detects, when the black pixel is deviated to the left or right from the center of the full pixel, from the input image data, and generates the phase data Dg.

That is, the phase data Dg shown in FIG. 9 depends on whether the black pixel of the multi-valued image data Db is rightward, leftward, or centered with respect to the center of the full pixel.
(0, 1, 2) is generated. Normally left justified (data 0)
In this case, when the black pixel is on the right side, by shifting it to the right (data 1), an image with good print quality can be obtained at the leading end and the trailing end of the image.

Although not used in this embodiment, if the center can be selected by light emission timing control, the center (data 2) is generated when one dot line is detected, so that an image with good print quality can be obtained. Can be FIG. 9 shows the relationship between the phase data and the printing position.

Next, the configuration and operation of the code switching section 60 will be described with reference to FIG. FIG. 10 is a block diagram showing a configuration example of the code switching unit 60 shown in FIG.
In the code switching section 60, the density correction signal D corresponding to the pattern detected in the pattern table 141 shown in FIG.
e is output.

For this purpose, the code switching section 60 comprises 64 three-state buffers 161-1 to 161-64. Then, each of the three-state buffers 161-
The input terminals 1 to 161 to 64 are connected to the control unit 80, and are fixed to 8-bit density correction data corresponding to each pattern.

Then, the detection signal 1 bit Dd1 to Dd64 of each pattern detected in the pattern table 141 is
By inputting as an output enable signal of each 3-state buffer, one of the outputs of the 3-state buffers 161-1 to 161-64 corresponding to the matched pattern becomes valid, and the corresponding data is output as density correction data De. Is done.

That is, by using the code data Dd1 to Dd64 output from the pattern table 141 as output enable signals for the three-state buffers, the density correction data De of the pattern corresponding to the input data to the pattern table 141 is obtained. From the control unit 80.

FIG. 11 is a timing chart showing an operation example of the OR gate 70 shown in FIG. The 6-bit image data Dc output from the code conversion unit 40 and the density correction data De output from the code switching unit 60 are ORed.
The OR is taken by the gate 70 to generate 8-bit density data Df. The OR gate 70 adds the density correction data De to the original density data Df, and sends the density data Df to a light emission generation unit (not shown).

Next, an example of the operation of the digital copying machine will be described with reference to FIGS. FIG. 12 is a diagram for explaining the effect of the present invention, and shows an example in which a vertical line and a horizontal line of one dot are image-formed. In the case of one dot line, the result of processing the input image as shown in FIG. 12A by the image processing unit 20 is as shown in FIG.
If the emission data is set to the 8-bit maximum value 255 when the data is black (1, 1: 11 in the figure), the beam diameter is usually larger than one pixel so that the solid black portion is firmly filled.

Therefore, originally, the copy line tends to be thicker than the line on the original, but even if the emission data is the same, the vertical line and the horizontal line are the characteristics of the electrophotograph when actually output as a copy. Is likely to be thicker, so that the output image is as shown in FIG.

However, according to the pattern table 141, 1
When a pixel corresponding to the dot line pattern (0, 0, 1, 1, 0, 0) or (0, 0, 1, 0, 0, 0) is detected, the density correction output from the code switching unit 60 is performed. The data De is correction data for reducing the light emission amount of the laser diode to lower the density than usual. This density correction signal data is ORed with the image data Dc by the OR gate 70 to generate corrected density data Df.
Includes the density correction data De.

When density data Df including the density correction data De drives the laser diode (not shown) by the modulating means of the image writing section to write data on the photosensitive drum, the light emission intensity for the pixel is set to 200 to 200. 2
The laser diode is made to emit light by pulse width modulation by reducing it to about 20. Accordingly, the beam diameter due to the emission of the laser diode can be made longer than usual, so that each pixel of one dot line can be formed vertically, and the vertical line can be made thin. As a result, the image output as a copy becomes almost the same as the actual document as shown in FIG. 12D, and the reproducibility is improved. In addition, the portion other than the vertical line is not affected.

In the case of the leading edge and the trailing edge of the image, in addition to the same problems as the one dot line, FIG.
As shown in (c), when two data that should be originally attached and reproduced as one line are converted into data having no phase information and written, the light emission timing is fixed to the right or left (or the center). Because
In the case of fixed to the left, the line is divided at the front end of the image, and in the case of the fixed right, the line is divided at the rear end of the image.

If the density of the halftone portion is low and the interval is wide, the divided portion is output in a divided form. If the density of the halftone portion is high and the interval is narrow, the portion is filled and becomes a thick line. In any case, the reproducibility may be impaired.

However, here, the pattern (1, 1, 1, 1) indicating the leading or trailing edge of the image in the pattern table 141 is shown.
1,0,0), (0,0,1,1,1,1), (1,
(1,1,0,0,0), (0,0,1,0,1,1), the code switching unit 6
The density correction data De output by 0 is used as correction data for lowering the density than normal. The density data Df output from the OR gate 70 includes the density correction data De.
Is added, whereby the light emission data generation unit generates light emission data. As a result, it is possible to lower the writing density as compared with the normal case, and to correct the tendency that the line of the copy tends to be thicker than the original and the difference in the thickness between the vertical line and the horizontal line.

Further, in accordance with the phase data Dg generated by the phase data detecting section 50, the modulation means shifts the light emission timing of the laser diode when writing the corresponding black pixel from the original pixel center to the left or right. To make it move. Therefore, the reproducibility can be further improved by printing the pixel corresponding to the front end in the main scanning direction with respect to the vertical line to the right, and printing the pixel corresponding to the rear end to the left with respect to the vertical line.

As described above, according to the image forming apparatus of the present invention, the multi-value data of only the density information which does not include the phase data for controlling the light emission timing input from the scanner or the outside is coded according to the density information. It has been detected that the pattern of the pixel of interest of the multivalued data indicating only the data and the density information and the pattern of a plurality of pixels surrounding the pixel coincide with any one of a plurality of specific patterns indicating the edge portion of the image or one dot line. Sometimes coding is done according to the specific pattern that matched.

Then, for a pattern that needs to be corrected, corresponding density correction data is added. Then, density data including the density correction data is generated, and the light emission time and / or the light emission power of the laser diode are modulated based on the density data to change the density of the pixel, thereby changing the edge of the line or the black. Can be prevented from becoming too thick, and the vertical line and the horizontal line can be prevented from being different in thickness, so that an image with good reproducibility can be obtained.

For a code that matches a specific pattern, correction is made so that the amount of emitted light is smaller than usual, thereby preventing the edge portion of the line and one black dot line from becoming too thick. Further, since it is possible to prevent the vertical line and the horizontal line from being different in thickness, it is possible to obtain an image with good reproducibility.

Further, the method of generating density data detects that the pattern of the pixel not including the phase data for controlling the light emission timing coincides with either the edge portion of the line or the specific pattern of one dot line. At this time, phase data for controlling the light emission timing according to the specific pattern that matches is also generated. The phase data is used to modulate the emission time and / or emission power of the laser diode for the pixel located at the edge of the line and one dot line, and also to control the emission timing. Can be shifted left or center.

As a result, it is possible to prevent an edge portion of a line extending over a plurality of pixels or a black one-dot line from becoming too thick, and prevent a vertical line and a horizontal line from being different in thickness. Good images can be obtained. Although the above embodiment has been described with reference to the case where the present invention is applied to a digital copying machine, the present invention can be similarly applied to other image forming apparatuses such as a printer and a facsimile machine.

[0052]

As described above, according to the present invention, in an image forming apparatus equipped with a writing optical system using a laser, an edge portion of a line on which an image is formed and a black one-dot line become thicker. It is possible to obtain an image with good reproducibility by preventing the vertical line and the horizontal line from having different thicknesses.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an image data processing portion in the digital copying machine shown in FIG.

FIG. 2 is a diagram showing an appearance of a digital copying machine which is an embodiment of the image forming apparatus according to the present invention.

FIG. 3 is an explanatory diagram of a method for reading image data in the embodiment shown in FIGS. 1 and 2;

FIG. 4 is a block diagram illustrating a configuration example of a code conversion unit 40 illustrated in FIG. 1;

FIG. 5 is a block diagram showing a configuration example of a data delay unit 140 shown in FIG.

FIG. 6 is a timing chart for explaining an operation of data delay section 140 shown in FIG.

FIG. 7 is an explanatory diagram showing a relationship between image data Db and print dots.

8 is an explanatory diagram showing the contents of a pattern table 141 shown in FIG.

FIG. 9 is an explanatory diagram showing a relationship between phase data Dg and print dots.

FIG. 10 is a block diagram showing a configuration example of a code switching unit 60 shown in FIG.

11 is a timing chart showing an operation example of the OR gate 70 shown in FIG.

FIG. 12 is an explanatory diagram showing a conventional example of an input image of vertical and horizontal crosshairs, an output of an image processing unit, and a copy image, and an example according to the present invention.

FIG. 13 is an explanatory diagram showing a conventional example of a vertical line input image having a width of one and a half dots, an output of an image processing unit, and a copy image, and an example according to the present invention.

[Explanation of symbols]

 1: Digital copier 2: Original platen 3: Press plate 4: Operation unit 5: Paper supply unit 6: Paper discharge unit 10: Read processing unit 20: Image processing unit 30: Write processing unit 40: Code conversion unit 50: Phase data Detecting unit 60: code switching unit 70: OR gate 80: control unit 140: data delay unit 141: pattern table 240 to 242: flip-flop 161: 3-state buffer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA05 AA24 AA26 AA27 AB13 AC04 BB01 BB15 BB20 BB49 DA01 DA03 EA04 EA06 2C362 AA22 AA32 AA33 CA09 CA10 CA11 CA14 CB23 CB24 CB28 CB29 5C074 AA05 DD01 DD03 DD26 DD DD DD DD FF11 HH02 5C077 LL19 MP04 MP07 NN05 NN17 PP15 PP55 PP68 PQ04 PQ08 PQ23 RR10 TT03 TT06

Claims (4)

[Claims] 1. A method of comparing a plurality of bits of image data indicating only density information input from a scanner or an external device with a plurality of patterns set in advance according to the density information and detecting a match with any of the patterns. Code conversion means for converting the image data into code data corresponding to the matched pattern; density correction data generation means for generating density correction data from the code data output by the code conversion means; Density data generating means for generating density data from the correction data; and modulation means for modulating the light emission time and / or the light emission power of the laser diode in the image writing unit according to the density data. Image forming device. 2. When the code conversion means detects that input image data matches a specific pattern, the density correction data generation means uses the laser diode from the code data output from the code conversion means. 2. The image forming apparatus according to claim 1, wherein density correction data for correcting the amount of emitted light to be smaller than usual is generated. 3. The image forming apparatus according to claim 2, wherein the specific pattern is a pattern of one dot line. 4. The image forming apparatus according to claim 1, wherein, based on the input image data, when a black pixel is deviated left or right with respect to a center of a full pixel. A means for detecting the phase data and generating phase data is provided, and in accordance with the phase data, the light emission timing of the laser diode when the modulation means writes a corresponding black pixel is shifted to the left or right from the original pixel center. An image forming apparatus characterized in that the image forming apparatus is shifted so as to be shifted.