JPH04154363A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the void caused by a drop of the potential by setting an edge part picture element of a linear latent image being vertical to the rotating direction of a photosensitive body to the potential between an image part and a non-image part. CONSTITUTION:In accordance with whether (x) coordinates of a start point and an end point of vector data are equal or not, whether image data is vertical or not is decided, and in the case it is vertical, the potential of an edge part picture element is set so as to become between an image part and a non-image part. Also, based on an area rate to be painted out, an output of the edge part picture element of the vector data is adjusted, and at the time of applying an anti-aliasing processing method for expressing smoothly notches of the edge part, an approximate area rate is set so that the potential of a latent image corresponding the edge part picture element becomes between the image part and the non-image part, and in the case the image data is not vertical, the approximate area rate is set by using the anti-aliasing processing. In such a way, the anti-aliasing processing which can prevent a void caused by a drop of the potential and can avoid it surely can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that avoids white spots in images and obtains high-quality images.

[Conventional technology]

In an image forming apparatus in which an electrostatic latent image on a photoreceptor is visualized by toner development via a developing device and an image is obtained through a transfer and fixing process, the developing sleeve of the developing device is generally twice as large as the photoreceptor. The developing sleeve rotates at a high speed, and a sliding force acts between the photoreceptor and the developing sleeve. When developing an electrostatic latent image on a photoreceptor, the reason why a speed difference is created between the photoreceptor and the developing sleeve is because sufficient density cannot be obtained with a speed ratio of 1=1. This is to increase the amount of developer that comes into contact with the latent image per unit area by increasing the number of rotations of the sleeve, thereby obtaining a sufficient developer concentration. Another purpose is to prevent scumming by utilizing the scraping effect of the sliding force caused by the speed difference.

On the other hand, in recent years, with the spread of publishing systems using personal computers, so-called DTP (desk top publishing), image forming systems that print vector images, such as those handled in computer graphics, have become widely used. There is. As a representative example,
For example, there is a system using Adobe's Post Script.

PostScript is a page description language (PageDe).
Scription Language: Hereafter, P
It belongs to a language genre called DL (described as DL), and describes the form of the contents of a single document, including the text (letter part), graphics, and their arrangement and appearance. It is a programming language for writing text, and in such systems, vector fonts are used as character fonts. Therefore, even if characters are changed, the printing quality can be significantly improved compared to systems using bitmap fonts (for example, conventional word processors). It has the advantage that it is possible to print a mixture of

However, the resolution of the multilevel laser printer used in the image forming apparatus used in these image forming systems is often 240 dpi to 400 dpi at most, and the problem is that jaggedness (aliasing) occurs due to the low resolution. be. Therefore, in order to improve the quality of the printed image when printing using a multilevel laser printer,
Anti-aliasing processing is now applied.

[Problem to be solved by the invention]

However, according to the conventional image forming apparatus, as described above, since the developing sleeve rotates at a faster speed than the photoreceptor, there is a problem in that abnormal images such as blank spots on solid surfaces occur.

Specifically, when attempting to develop a line latent image perpendicular to the rotational direction of the photoreceptor and developing sleeve, the electric field wraps around the boundary between the image area and the non-image area of the latent image, causing the potential to be emphasized. There is a phenomenon in which a drop in potential occurs in the non-image area, but if the developing sleeve is rotating at a faster speed than the photoreceptor, the developer that has passed through the drop in potential continues to be used for the next development. A phenomenon occurs. However, since the developer that has passed through the depressed area is affected by the reverse electric field of the depressed area, the next time the developing area is attempted to be developed, it will not be developed properly, resulting in white spots in the developed image. Ru.

Figure 15 shows the white area, and the diagonal line is the image area.
As shown in the figure, white areas occur in some areas. Here, it is assumed that the developer moves in the direction of the arrow with respect to the T-shaped latent image pattern.

On the other hand, in an image forming apparatus to which anti-aliasing processing is applied, for example, as shown in FIG. 16(a),
If the edge part covers only one part of the pixel,
Anti-aliasing processing sets data with an intermediate potential between the image area and the non-image area, which automatically prevents white spots in the image area. covers the entire edge pixel, and when the pixel boundary and the image area boundary match, anti-aliasing processing is not performed on the pixels that include this vertical line, so the image area and non-image area are separated. There was a problem in that the potential changed rapidly at the boundary, causing white spots on the solid cross, similar to when anti-aliasing processing is not applied.

The present invention has been made in view of the above, and a first object thereof is to prevent white spots due to drop in potential.

Further, the present invention has been made in view of the above, and a second object of the present invention is to perform anti-aliasing processing that can reliably avoid white spots due to drop in potential.

[Means to solve the problem]

In order to achieve the above-mentioned first object, the present invention provides an image forming apparatus in which an electrostatic latent image on a photoreceptor is visualized by toner development through a developing means, and an image is obtained through a transfer/fixing means. , an image forming apparatus is provided with a setting means for setting the potential of an edge portion pixel of image data forming a line latent image perpendicular to the rotational direction of a photoreceptor to an intermediate potential between an image portion and a non-image portion. This is what we provide.

In addition, in order to achieve the above-mentioned second object, the present invention adjusts the output of edge portion pixels of vector data based on the area ratio to be filled, and smoothes jaggedness (alias) at the edge portion of the output image. In an image forming apparatus that applies an anti-aliasing processing method expressed in The approximate area ratio of the pixels in the image area is set so that the potential is between that of the image area and the non-image area, and if a vertical line latent image is not formed, the approximate area ratio is set using anti-aliasing processing. An image forming apparatus including an area ratio setting means is provided.

[Effect]

In the image forming apparatus according to claim 1 of the present invention, the setting means sets the potentials of the pixels in the image area and the image area of the image data forming the line latent image perpendicular to the rotational direction of the photoreceptor. Set so that the potential is midway between the image area.

In the image forming apparatus according to claim 2 of the present invention, when the vector data forms a line latent image perpendicular to the rotational direction of the photoreceptor, the approximate area ratio setting means sets the approximate area ratio setting means to The approximate area ratio of the pixels in the image area is set so that the potential of the corresponding latent image is an intermediate potential between the image area and the non-image area, and if a vertical line latent image is not formed, anti-aliasing processing is applied. ) to set the approximate area ratio.

〔Example〕

Hereinafter, as an example of an image forming system to which the image forming apparatus of the present invention is applied, (1) setting of the approximate area ratio of pixels in the front and rear portions, (2) a block diagram of the image forming system, (2) configuration and operation of the PDL controller, A detailed explanation will be given in the following order: 1) the configuration of the image processing device, 2) the configuration and operation of the multi-valued color laser printer, and 2) the multi-valued drive of the driver.

■Setting the approximate area ratio of edge area pixels The image forming apparatus of the present invention sets the potential of edge area pixels of image data that forms a line latent image perpendicular to the rotational direction of the photoreceptor between image areas and non-image areas. The electric potential is set to be between the two.

More specifically, when the vector data forms a line latent image perpendicular to the rotational direction of the photoreceptor, the potential of the latent image corresponding to the edge area pixels becomes an intermediate potential between the image area and the non-image area. The approximate area ratio of the edge portion pixels is set in this way, and when a vertical line latent image is not formed, the approximate area ratio is set using anti-aliasing processing.

Hereinafter, setting of the approximate area ratio of the edge portion pixels will be specifically explained.

In advance, it is determined whether the vector data is vertical based on whether the X coordinates of the starting point and the ending point of the vector data are equal, and if the vector data is vertical, that information is stored as vector characteristic information.

Thereafter, during scan line processing, it is determined whether the vector data is perpendicular, and if it is not perpendicular, an approximate area ratio is calculated by normal anti-aliasing processing (eg, using a uniform averaging method). On the other hand, if it is vertical,
The approximate area ratio is calculated by the following processing without performing normal anti-aliasing processing on the pixel of the cut/edge portion.

First, referring to the approximate area ratio ko of the pixel immediately before the edge portion pixel through which the perpendicular hector data passes, and the approximate area ratio k of the pixel immediately after, the approximate area ratio k is calculated. 1 is calculated as the intermediate value between 2 and 2 using the following formula.

kl ”” (k6 +kZ) /2 Next, as shown in Figure 1(a), if the corresponding vector data exists between the two ends of the pixel (i.e., if it overlaps with the pixel boundary) (if not), kl is determined as the area ratio of the edge pixel.

On the other hand, if the corresponding vector data exists at both ends of the edge pixel (on the pixel boundary) as shown in FIG. As an edge pixel, the approximate area ratio of this edge pixel is determined as +. However, the reason why pixels in the image area are made thinner as edge pixels is to take into account that in laser printers, horizontal lines generally tend to be thinner than vertical lines due to process reasons. be.

In the case of the T-shaped figure shown in Figure 1 (C), the intermediate value kI
The portion where (approximate area ratio) is written is the position indicated by diagonal lines. The writing width is basically one pixel, but this varies depending on the type of antialiasing processing used and the characteristics of the image creation process.

Furthermore, diagrams of potential and electric field when the treatment of the present invention is not performed and when it is performed are shown in FIGS. 1(d) to (80).

Here, a indicates the image area and b indicates the non-image area, as shown in FIG.
is the potential when no treatment is performed, and (e) in the same figure shows the state of the electric field at that time. In addition, (f,) in the same figure shows the potential when processing is performed, and (6) in the same figure shows the electric field.The large drop in the electric field that occurs in (e) is as shown in (b) By processing the previous potential pattern into a potential pattern as shown in (8) of the same figure, the drop in the electric field is significantly reduced.

■Block diagram of the image forming system The image forming system of this embodiment uses the Page Description Language output from DTP (Desk Top Publishing).
e: hereinafter referred to as PDL language)) and image information read by an image reading device. The configuration of the image forming system of this embodiment will be described below with reference to FIG.

The image forming system includes a host computer 100 that creates a document written in PDL language (Postscript language is used in this embodiment);
The PDL controller 200, which applies anti-aliasing processing to the PDL language sent in page units from an image reading device 300 that reads image information via the PDL controller 20;
0. Alternatively, an image processing device 400 that inputs the image output from the WJ image reading device 300 and performs image processing (details will be described later), and a multi-value color printer that prints the multi-value image data output from the image processing device 400. - Laser printer 500 and PDL controller 200. Image reading device 300. Image processing device 400. and a system control section 600 that controls the multivalued color laser printer 500.

■Configuration and operation of PDL controller FIG. 3 shows the configuration of the PDL controller 200.
A receiving device 201 that receives the PDL language sent from the host computer 100, a CPU 202 that performs storage control and anti-aliasing processing for the PDL language received by the receiving device 201, and an internal system bus 203.
, a RAM 204 that stores the PDL language transferred from the receiving device 201 via the internal system hash 203, and a ROM 20 that stores anti-aliasing programs and the like.
5 and multivalued RGB with anti-aliasing processing
It is composed of a page memory 206 that stores image data, a transmitting device 207 that transfers the RGB image data stored in the page memory 206 to the image processing device 400, and an I10 device 208 that performs transmission and reception with the system control unit 600.

Here, the CPU 202 receives the P received by the receiving device 201.
The DL language is stored in the RAM 204 via the internal system bus 203 according to the program stored in the ROM 205. After that, you will receive one page of PDL language,
Once stored in the RAM 204, the graphic elements in the RAM 204 are subjected to anti-aliasing processing based on the flowchart described later, and the multivalued RGB image data is stored in the plain memory section of the page memory 206. , B's brain memory section and a feature information memory section).

The data in the page memory 206 is then transferred to the transmitter 2
07 to the image processing device 400.

The operation of the PDL controller 200 will be described below with reference to FIGS. 4(a) and 4(b).

FIG. 4(a) shows a flowchart of processing performed by the CPU 202. As described above, the PDL controller 200 performs anti-aliasing processing on the PDL language sent page by page from the host computer 100, and converts it to red (R).

Developed into three-color images: green (G) and blue (B).

In the PDL language, graphics and characters are all described using vector data, and as the name "page description language" indicates, image information is processed in units of pages. Furthermore, one page is made up of at least one path, with each path being made up of one or more elements (graphic elements and text elements).

First, when PDL language is input, it is determined whether the element is a curved vector, and if it is a curved vector, it is approximated to a straight line vector and registered as a straight line element (line) in the work area. This is performed for all graphic and character elements within one path, and linear elements are registered in the work area for each path (processing 1).

Then, the linear elements of the work area registered in this path unit are sorted by the starting X coordinate of the straight line (Processing 2
).

Next, in process 3, while updating the X coordinate one by one,
Performs filling processing using scanning lines. For example, in Figure 4 (
When performing the path filling process shown in b), the scanning line yc to be processed (in this embodiment, the above-mentioned Yo ・Y1
A scan line with a thickness of one pixel is described as a scan line, and a scan line that indicates a straight line with no thickness is described as a scan line), and the elements of the side that crosses that scan line. The real value of the X coordinate across yc (Xl Xz Xl
Active Edge Table: A table that records the X coordinate of an edge portion appearing on a scanning line). Here, the order of elements registered in the work area is
Since it is in the order registered in process 1, the X coordinates crossing the scanning line yc are not necessarily registered in ascending order. For example, in process 1, the scanning line y in FIG.
When a straight line element passing through c and x3 is processed first, x is the X coordinate of the edge portion appearing on the scanning line yc.
3 is first registered with AET. Therefore, after the AET is registered, the elements on each side within the AET are sorted in descending order of X coordinate. Then, pair the first two elements of AET and fill in the space between them. Anti-aliasing processing is achieved in this filling processing by adjusting the density and brightness of the pixels in the edge portion according to the approximate area ratio. Then, remove the processed edges from the AET,
The scanning line is updated (the X coordinate is updated), and the same process is repeated until all edges within the AET are processed, in other words, until all elements within one pass are processed.

Above processing 1. Processing 2. The work in process 3 is executed pass by pass and repeated until all passes for one page are completed.

Next, the anti-aliasing process executed during the scan line filling process of process 3 described above will be described in detail with reference to the flowchart of FIG. 4(C).

Here, for example, in process 1 of FIG. 4(a),
), this figure has the following elements.

(a) Five line vectors AB, BC, CD, DE, and EA (represented by real numbers) (b) Color and brightness values inside the figure As shown in Fig. 5 Φ), this figure is Seven straight line vectors extending in the main scanning direction (real number representation)
divided into At this time, in this embodiment, the following information is added to the starting points and ending points of the seven straight line vectors. That is, (c) Starting point coordinate values (real number expression) of vector elements ((a) above) that constitute the starting point and ending point of a straight line vector (d) Slope information (dip) of vector elements that constitute the starting point and ending point of a straight line vector Characteristic information of the starting point and ending point of a straight line vector (right edge, left edge, information that the vector data is vertical, etc.) When an edge pixel is detected in the scan line filling process, the flowchart in FIG. 4(C) Execute the anti-aliasing process shown below.

First, determine whether the vector data to be processed is vertical or not,
If it is not vertical, an approximate area ratio is calculated by normal anti-aliasing processing (uniform averaging method is used in this embodiment) (S401, 402).

On the other hand, if it is vertical, the approximate area ratio of the pixel immediately before the edge pixel through which the corresponding vertical hector data passes is 0.
And, refer to 2 for the approximate area ratio of the immediately following pixel 5403
), k+ = (ko +kz)/2 to calculate the approximate area ratio to a value intermediate between 0 and 2 (S404)
.

Next, it is determined whether the corresponding vector data overlaps with the pixel boundary line (5405), and if it does, the pixel containing the vector data and where the image part exists is set as the edge part pixel, and this edge part The approximate area ratio of the pixel is determined as 1 (S406). If they do not overlap, k is determined as the approximate area ratio of the edge pixels (S407).

The CPU 202 repeats the above process up to the last pixel of the scanning line (y coordinate).

(2) Configuration of Image Processing Apparatus The configuration of the image processing apparatus 400 will be explained with reference to FIG.

The image processing device 400 is a CC in the image reading device 300.
The three-color image signals read by D7r, 7g, and 7b are converted into black (BK), yellow (Y), magenta (M), and cyan (C) recording signals necessary for recording. Similarly, the RGB image data given from the PDL controller 200 described above is converted into black (BK).
, into yellow (Y), magenta (M), and cyan (C) recording signals. Here, the mode in which image signals are input from the image reading device 300 is called a copying machine mode, and the mode in which RGB image data is input from the PDL controller 200 is called a graphics mode.

The image processing device 400 includes CCDs 7r, 7g, and 7b.
The color gradation data obtained by A/D converting the output signal of
a shading correction circuit 401 that performs correction for sensitivity variations, etc. of internal terminal elements of 7r, 7g, and 7b;
a multiplexer 402 that selectively outputs either the color gradation data output from the shading correction circuit 401 or the color gradation data (ROB image data) output from the PDL controller 200 according to the aforementioned mode;
A γ correction circuit 40 receives the 8-bit data (color gradation data) output from the multiplexer 402, changes the gradation according to the characteristics of the photoreceptor, and outputs it as 6-bit data.
3, and red (R) and green (
G).

Complementary color generation circuit 405 converts 6-bit gradation data indicating the gradation of blue (B) into gradation data (6 bits) of cyan (C), magenta (M), and yellow (Y), which are respective complementary colors. and Y, M output from the complementary color generation circuit 405
, C, and a masking processing circuit 406 that performs predetermined masking processing on each gradation data of Y, M after the masking processing.
, an OCR processing/black generation circuit 407 that inputs each gradation data of C and executes UCR processing and black generation processing;
YM output from the CR processing/black generation circuit 407,
The 6-bit and 7-bit gradation data of C and BK are converted into 3-bit gradation data Yl, M1 . Convert to CI and BKI,
It is composed of a gradation processing circuit 408 that outputs output to the laser drive processing section 502 inside the multivalued color laser printer 500, and a synchronization control circuit 409 for synchronizing each circuit of the image processing apparatus 400.

Although details will be omitted, the γ correction circuit 403 has a configuration in which the gradation can be arbitrarily changed using an operation button on the console 700.

Further, as an algorithm used in the gradation processing circuit 408, a multi-value dither method or a multi-value error diffusion method can be applied. For example, a multi-value dither method dither matrix is
Then, the number of gradations of the multilevel color laser printer 500 is the product of 3×3 area gradations and 3 bits (that is, 8 levels) of multilevel hell, and is 3×3×8=72 (gradations).

Next, the processing of the masking processing circuit 406 and the UCR/black generation @path 407 will be explained.

Generally, the masking processing calculation formula of the masking processing circuit 406 is as follows: Y, , M, , C, , data before masking Yo, Mo
, Co: Data after masking processing In addition, the arithmetic expression of the UCF processing of the UCR processing/black generation circuit 407 is also generally expressed as follows.

Therefore, in this embodiment, new coefficients are obtained using the product of both coefficients.

Where? In this embodiment, a new coefficient (al+'', etc.) that performs the masking process and UCR process simultaneously is calculated in advance, and further, using this new coefficient, the scheduled input value Y of the masking process circuit 406, M.

Output value (y, °, etc.: UC) corresponding to C8 (6 bits each)
A value that is the calculation result of the R processing/black generation circuit 407 is obtained and stored in a predetermined memory in advance.

Therefore, in this embodiment, the masking processing circuit 406 and O
The CR processing/black generation circuit 407 is composed of a set of ROMs, and the data at the address specified by the manual input Y, M, and C of the masking processing circuit 406 is given as the output of the UCR processing/black generation circuit 407.

In addition, for boat fishing, the masking processing circuit 406 performs Y and M according to the characteristics of the spectral reflection wavelength of the toner for forming a recorded image.
, C signals, and the UCR processing/black generation circuit 407 performs correction for color balance in overlapping toners of each color. UCR processing/black generation circuit 4
07, black component data BK is generated by combining the input three color data of Y, M, and C, and the output Y,
The M and C color component data are corrected to values obtained by subtracting the black component data BK.

In the above configuration, the T correction circuit 403 executes processing based on the γ correction conversion graph shown in FIG. 7, and the complementary color generation circuit 405 executes processing as shown in FIGS. 8(a) and 8(b).

Processing is executed based on the conversion graph for complementary color generation shown in (C), and then the masking processing circuit 406 and the UCR processing/black generation circuit 407 execute processing based on the following equation.

Thereafter, the gradation processing circuit 40B performs gradation processing using a Heyer type 3×3 multivalued dither matrix shown in FIG.

■Multi-value color laser printer configuration First, the 10th
The schematic configuration of the multivalued color laser printer 500 will be described with reference to the control block diagram shown in the figure.

A photoreceptor development processing unit 501 uniformly charges the surface of a photoreceptor drum (described later), exposes the charged surface to a laser beam to form a latent image, develops the latent image with toner, and transfers it to recording paper. The details will be explained later, but the development and development of BK data is
A black development/transfer section 501bk that performs transfer, a cyan development/transfer section 501C that develops and transfers C data, and a magenta development/transfer section 5 that develops and transfers M data.
01m and a yellow developer that develops and transfers Y data.
The transfer unit 501y is provided with a transfer unit 501y.

The laser drive processing unit 502 includes the image processing device 4 described above.
The laser beam is output by inputting the 3-bit data of Y, M, C, and BK output from 00 (in this case, image density data). Input buffer memory 503y, 503m
, 503c, and a laser diode 504y that outputs laser beams corresponding to Y, M, C, and BK, respectively.
504m, 504c, and 504bk, and drivers 505y, 505m, and 505c that drive the laser diodes 504y, 504m, 504c, and 504bk, respectively.
505bk, and a photoreceptor development processing section 5.
01 black developing/transfer section 501bk, laser drive processing section 502 laser diode 504bk, and
The combination with the driver 505bk is called a blank recording unit BKU (see FIG. 11). Similarly, the cyan developing/transfer section 501C, the laser diode 504c,
The combination of the driver 505c and the buffer memory 503C is a cyan recording unit, 7 CUs (see Figure 11), a magenta developing/transfer section 501m, and a laser diode 50.
4m, driver 505m, and buffer memory 5
03m is called a magenta recording unit MU (see FIG. 11), a yellow developing/transfer section 501y, a laser diode 504y, a driver 505y, and a buffer memory 503y are called a yellow recording unit YU (see FIG. 11). . As shown in the figure, each of these recording units is connected to a conveyor belt 506 that conveys the recording paper.
Black recording unit B from the recording paper conveyance direction
KU, cyan recording unit CU, magenta recording unit MU, and yellow recording unit YU are arranged in this order.

Due to this arrangement of each recording unit, the laser diode 5 for black exposure starts exposure first.
04bk, and the laser diode 504y for yellow exposure starts exposure last. Therefore,
There is a time difference in the order of exposure start between each laser diode,
Data recorded during the time difference (output of the image processing device 400)
The laser drive processing unit 502 has the three sets of buffer memories 503)', 503m 50
3c is provided.

Next, the configuration of the multilevel color laser printer 500 will be specifically explained with reference to FIG.

The multilevel color laser printer 500 includes a conveyor belt 506 that conveys recording paper, and recording units YU, MU, and YU arranged around the conveyor belt 506 as described above.
Paper cassette 507 containing CU, BKU, and recording paper
a, 507b, and paper feed rollers 508a, 508b that feed recording paper from paper feed cassettes 507a, 507b, respectively.
The recording units 1-BKU, CU,
It is composed of a fixing roller 510 that sequentially transports MU and YU and fixes the transferred image on the recording paper, and a paper discharge roller 511 that discharges the recording paper to a predetermined discharge section (not shown). Here, each recording unit YU, MU, CU, BKU
are photosensitive drums 512y, 512m, 512c, 51
2bk, photoreceptor drum 512y, 512m5 respectively
a charger 513y that uniformly charges 12c and 512bk;
513m, 513c, 513bk and photosensitive drum 51
Polygon mirrors 514y, 514m, 5 for guiding laser beams to 2y, 512m, 512c, 512bk
14c, 514bk and motor 515y, 515m, 5
15c, 515bk, and photosensitive drums 512y, 512
toner developing devices 516y, 516m, 516c and 516bk that develop the electrostatic latent images formed on the respective surfaces of the electrostatic latent images formed on the toners of the respective toners of the respective toners of the corresponding colors;
Transfer charger 51 that transfers the developed toner image onto recording paper
7y, 517m, 517c, 517bk, and photosensitive drums 512y, 512m, 512c, 512bk after transfer.
Cleaning device 51s that removes toner remaining on the top
It consists of y, 518m, 518c, and 518bk.

Note that 519y, 519m, 519c, and 519bk are photosensitive drums 512y and 512m, respectively.

This shows a toner adhesion density measuring device for reading test patterns provided on 512c and 512bk, and is composed of a CCD line sensor and an LED light source arranged in the thrust direction.

In the above configuration, the operations of the yellow recording unit YU will be explained using exposure, development, and transfer as examples.

Figure 12 (a) and (b) are yellow recording unit YU.
The configuration of the exposure system is shown. In the figure, a laser beam emitted from a laser diode 504y is reflected by a polygon mirror 514y, passes through an f-theta lens 520y, is further reflected by a mirror 521y522y, and is irradiated onto a photoreceptor drum 512y through a dustproof glass 523y. Ru. At this time, the laser beam is
4y is driven to rotate at a constant speed by the motor 515y, so it moves in the direction along the axis of the photosensitive drum 512y (main scanning direction). Furthermore, in this embodiment, a photosensor 524y is provided to detect the base point for tracking the scanning position of the main scan, so that the laser beam at the non-exposed position is detected. Since the laser diode 504y is activated to emit light based on the recorded data (3-bit data from the image processing device 400), multivalue exposure corresponding to the recorded data is applied to the photoreceptor drum 504y.
performed on the surface of The surface of the photosensitive drum 504y is uniformly charged in advance by the charger 513y as described above, and an electrostatic latent image corresponding to the original image is formed by the exposure. The electrostatic latent image is developed by a yellow developing device 516y to become a yellow toner image. This toner image is
As shown in FIG. 11, the paper feed roller 508a (or 508
b), and is transferred by registration rollers 509 to the recording paper conveyed by conveyance belt 506 in synchronization with the toner image formation in black recording unit BKU.

The other recording units BKU, CU, and MU have similar configurations and perform similar operations, but the black recording unit BKU
is equipped with a blank toner developing device 516bk to form and transfer a blank toner image, the cyan recording unit CLI is equipped with a blank toner developing device 2516c to form and transfer a cyan toner image, and the magenta recording unit MU is configured to form and transfer a magenta toner image. A toner developing device 516m is provided to form and transfer a magenta toner image.

■The multi-value drive drivers 505y, 505m, 505c, and 505bk of the tricycle drive the Y, M, C, and B signals sent from the image processing device 400.
Based on the 3-bit data of K, control is performed to drive the corresponding laser diodes 504y, 504m, 504c, and 504bk in multiple values, and power modulation, pulse width modulation, etc. are common driving methods. It is used in

Hereinafter, the multi-level drive by power modulation that is used in this embodiment will be explained in detail with reference to FIGS. 13(a), (bl, (cl, and d).
505c, 505bk, and laser diode 50
4y, 504m, 504c, and 504bk each have the same configuration, so here, the driver 5Q5y and laser diode 504y will be explained as examples.

As shown in FIG. 13(a), the driver 505y includes a laser diode-on10ff circuit 550 that turns on and off the laser diode 504y based on a predetermined LD drive clock, and a 3-bit driver.

A D/A converter 551 converts the image density data (Y data in this case) into an analog signal, and an analog signal based on the image density value is input from the D/A converter 551, and a current is generated to drive the laser diode 504y. (
LD drive current) Icl and diode on10f
The constant current circuit 552 supplies the f circuit 550.

Here, the LD drive blocker is defined as "ON at 1" and off at O, as shown in FIG. 13(b).
The laser diode on10ff circuit 550 turns off the laser diode 504y accordingly.

Furthermore, since there is a proportional relationship between the LD drive current 1d and the laser beam power, by generating the LD drive current 1d based on the image density data value, the laser beam power output corresponding to the image density data value can be obtained. become. For example, as shown in FIG. 13(b), when the image density data value is "4" (data N to 1 in the figure), the corresponding LD drive current Id is supplied by the constant current circuit 552. , the laser beam power of the laser diode 504y is level 4. Also, the image density data value is 7" (
In the case of data N) in the figure, the corresponding LD drive current 1d is supplied by the constant current circuit 552, and the laser beam power of the laser diode 504y becomes level 7.

Next, referring to FIG. 13(C), laser diode on10ff circuit 550. A specific circuit configuration of the D/A converter 551 and the constant current circuit 552 is shown. The laser diode on10ff circuit 550 includes TTL inverters 553 and 554, differential switching circuits 555 and 556 that perform an onloff toggle operation, and a VGI
> When VO2 (7), the differential switching circuit 555 is o
n, differential switching circuit 556 is off, VG
When I<VO2, the differential switching circuit 555 is turned off.
f.

Resistors R2 and R form a voltage dividing circuit that generates VO2 that satisfies the conditions for the differential switching circuit 556 to be turned on.
It consists of 3. Therefore, when the LD drive clock is 1'', the output of the inverter 554 generates VGI,
The above condition (VGI>VO2) is satisfied, the differential switching circuit 555 is turned on, and the differential switching circuit 556 is turned on.
is turned off, and the laser diode 504y is turned on.

Conversely, when the LD drive clock is "0", there is no output from the inverter 554, so the above condition (VGI<
vc2) and the differential switching circuit 555 is
ff, the differential switching circuit 556 turns on and turns off the laser diode 504y.

The D/A converter 551 includes a latch 557 that launches the input image density data while the LD drive clock is "1'°," and a latch 557 that launches the input image density data while the LD drive clock is "1'°," and a latch 557 that launches the input image density data while the LD drive clock is "1'°."
t-emitting HE device 558, image density data and maximum output value V
and a 3-bit D/A converter 559 that outputs analog data Vd based on ret. Here, Vd, image density data, and maximum output value V ret
The relationship with is expressed by the following equation.

The constant current circuit 552 includes the laser diode 504 in the laser diode ON10ff circuit 550 as described above.
y current, and the transistor 560
and resistors R4 and R5. The output Vd from D/A converter 551 is applied to the base of transistor 560 to determine the voltage applied to resistor R4.

In other words, the current flowing through the resistor R4 is the current flowing through the transistor 5.
60, the current 1d flowing through the laser diode 504y is controlled by Vd.

FIG. 13(d) shows the output VG of the U.7chi 557 mentioned above.
5 is a timing chart showing the relationship between I, Vd, and Id. Here, Vd is based on the image density data (8 gradation data of 3 binoto data 20 to 7): ■1°+X
Values are taken in 8 steps from O/7 to 7/7, and Id is this Vd.
Based on the value of Io-1, eight levels are shown.

The laser diode 504y forms a latent image as shown in FIG. 14 on the photoreceptor drum 512y according to the eight levels of Id (I.-level OI, = levelt...7-level7).

In this embodiment, as described above, since white areas are prevented at the same time as anti-aliasing processing, beautiful images without white areas can always be obtained. This is especially effective for line drawings, and beautiful images can be obtained no matter what kind of anti-aliasing processing is applied.

In the above-mentioned embodiment, an image forming apparatus that applies anti-aliasing processing was used as an example, but in the case of an image forming apparatus that does not perform anti-aliasing processing, edge pixels of vertical line latent image image data may be A similar effect can be obtained by unconditionally setting the potential to be an intermediate potential between the image area and the non-image area.

〔Effect of the invention〕

As explained above, the image forming apparatus of the present invention is an image forming apparatus in which an electrostatic latent image on a photoreceptor is visualized by toner development through a developing means, and an image is obtained through a transfer/fixing means. Equipped with a setting means that sets the potential of the edge area pixels of image data that form a line latent image perpendicular to the rotational direction of the photoreceptor to a potential between the image area and the non-image area, thereby reducing potential drop. It is possible to prevent white spots due to

Further, the image forming apparatus of the present invention uses an anti-aliasing processing method that adjusts the output of edge portion pixels of vector data based on the area ratio to be filled, and smoothly expresses jaggedness (alias) at the edge portion of the output image. In a commonly used image forming apparatus, when vector data forms a line latent image perpendicular to the rotation direction of the photoreceptor, the potential of the latent image corresponding to the edge area pixels is the intermediate potential between the image area and the non-image area. The approximation area ratio of edge pixels is set so that a vertical line latent image is not formed. It is possible to perform anti-aliasing processing that can reliably avoid white spots due to depression.

[Brief explanation of drawings]

FIGS. 1(a) to (g) are explanatory diagrams showing the setting of the approximate area ratio of the edge portion pixels of the present invention, FIG. 2 is an explanatory diagram showing the configuration of the image forming system of this embodiment, and FIG. An explanatory diagram showing the configuration of the PDL controller, FIG. 4(a) is a flowchart showing the operation of the PDL controller, FIG. 4(b) is an explanatory diagram showing the path filling process, and FIG. 4(C) is the antialiasing process. Flowchart showing Fig. 4 (
d) is a flowchart of halftone darkness value correction processing, FIG.
a), l) are explanatory diagrams showing linear vector division of a figure,
FIG. 6 is an explanatory diagram showing the configuration of the image processing device, and FIG. 7 is a T
An explanatory diagram showing a conversion graph for T correction of the correction circuit, Fig. 8 (
a), (b), and (C) are explanatory diagrams showing conversion graphs for complementary color generation used in the complementary color generation circuit; FIG. 9 is an explanatory diagram showing a Heyer type 3×3 multivalued dither matrix; 10
The figure is a control block diagram showing a multi-value color laser printer, Fig. 11 is an explanatory diagram showing the configuration of a multi-value color laser printer, and Figs. 12 (a) and (b) are the exposure system of the yellow recording unit. An explanatory diagram showing the configuration of, Fig. 13 (
a), (b), (c), and (a) are explanatory diagrams showing multi-level driving using power modulation, Fig. 14 is an explanatory diagram showing the state of the latent image depending on the level of power modulation, and Fig. 15 is a white diagram. FIGS. 16(a) and 16(b) are explanatory diagrams showing the state of omission, and are explanatory diagrams showing the state of the boundary between the image area and the non-image area. Description of symbols 200, 203, 204, Host computer PDL controller Receiving device 202---CPU Internal system path RAM 205---ROM Page memory 207------Transmitting device I10 device Image reading device Image processing device Value color laser printer system control unit

Claims (2)

[Claims] (1) In an image forming apparatus in which an electrostatic latent image on a photoreceptor is visualized by toner development through a developing means and an image is obtained through a transfer/fixing means, the image forming apparatus is perpendicular to the rotational direction of the photoreceptor. 1. An image forming apparatus comprising: a setting means for setting a potential of an edge pixel of image data forming a line latent image to a potential intermediate between an image area and a non-image area. (2) In an image forming apparatus that applies an anti-aliasing processing method that adjusts the output of edge pixels of vector data based on the area ratio to be filled, and smoothly expresses jagged edges (aliases) of the output image. When the vector data forms a line latent image perpendicular to the rotational direction of the photoreceptor, the edge portion is adjusted so that the potential of the latent image corresponding to the edge portion pixels is an intermediate potential between the image portion and the non-image portion. The apparatus is characterized by comprising an approximate area ratio setting means for setting an approximate area ratio of pixels, and setting the approximate area ratio using anti-aliasing processing when the vector data does not form a vertical line latent image. Image forming device.