JPH04260981A - Graphic processor - Google Patents

Abstract

PURPOSE:To unnecessitate image developing processing or image reading processing with high resolution and to obtain an output image with visually high picture quality at high speed without an anti-aliasing procedure. CONSTITUTION:This graphic processor is provided with a multi-level color laser printer 500 capable of outputting an image whose resolution in a main scanning direction is twice of a subscanning direction and outputting white, black and half tone picture elements and a high resolution circuit 403 for detecting a slash part and adding a half tone (gray) to the detected part.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a graphic processing device that removes jaggies from the outline of an output image and outputs the image, and more specifically, the present invention relates to a graphic processing device that improves visual resolution and enables high-speed output. Regarding equipment.

0002

2. Description of the Related Art In the field of computer graphics, when displaying images on a CRT, which is an output medium, a technique called anti-aliasing processing is used to make the displayed images more beautiful. This process is shown in Figure 31.
By applying brightness modulation to the jagged portions (called aliases) on the stairs as shown in (a), the displayed image is visually smoothed as shown in FIG. 31(b).

[0003] As an anti-aliasing processing method,
■Uniform averaging method, ■weighted averaging method, ■convolution integral method, etc. are known.

■Uniform averaging method The uniform averaging method calculates each pixel by N*M (N, M
is a natural number), performs raster calculation at high resolution, and then calculates the brightness of each pixel by taking the average of N*M subpixels. Figure 32(a), (
Anti-aliasing processing using the uniform averaging method will be specifically explained with reference to b). If the edge of the image overlaps a certain pixel (here, it is assumed that the image is connected to the bottom right of the diagonal line), and when anti-aliasing processing is not performed, as shown in Figure (a), The brightness kid of this pixel is the maximum brightness of the gray scale that can be displayed (
For example, for 256 gradations, kid=255) is assigned. When performing anti-aliasing processing on this pixel using the uniform averaging method with N=M=7,
), the pixel is divided into 7*7 subpixels and the number of subpixels covered by the image is counted. The count number (28) is divided by the total number of subpixels in one pixel (49 in this case) and normalized (averaged)
The maximum brightness (255) is multiplied by this value to calculate the brightness of that pixel. In this way, in the uniform averaging method, the brightness of each pixel is determined by taking into consideration how the image covers each pixel.

■ Weighted averaging method The weighted averaging method is a partial modification of the uniform averaging method. In contrast to the weighted averaging method, which simply counts subpixels, each subpixel is given a weight, and the influence on the brightness of that subpixel differs depending on which subpixel the image covers. That's what I do. still,
At this time, weights are assigned using a filter.

Referring to FIGS. 33(a) and 33(b), FIG.
Same image data as (a), same division method (N=M=7)
An example of implementing the weighted averaging method is shown below. Figure 33(a)
denotes the characteristic of the filter (here conefilter), and the corresponding sub-pixel is given the same weight as this characteristic. For example, the weight of the upper right corner subpixel is 2. When an image is applied to each subpixel, the weight value given by the filter characteristics becomes the count value of that subpixel. FIG. 6B shows the display pattern of the image changed depending on the weight of the sub-pixels. In this case, the number of weighted subpixels in the image is 199. This value is divided by the sum of the filter values (336 in this case) corresponding to uniform averaging, averaged, and multiplied by the maximum brightness to calculate the brightness of this pixel. In addition, as a filter, FIGS. 34(a), (b), (c), (d
) is known.

■Convolutional Integral Method The convolutional integral method is a method that also refers to the appearance of surrounding pixels when determining the brightness of one pixel. That is, the area around one pixel whose brightness is to be determined is N
Consider '×N' pixels to correspond to pixels in the uniform averaging method or weighted averaging method. Figure 35 shows 3×
A 3-pixel reference convolution method is shown. In this figure, the pixel whose brightness is to be determined is indicated by 3501. The image continues below and to the right of the diagonal line, and the subpixels painted black are the subpixels that are counted. Each pixel is divided into 4*4. Therefore, in this case, a 12*12 filter will be used. This method has the effect of removing high frequency components contained in a vector image.

On the other hand, with the spread of publishing systems using personal computers, so-called DTP (desk top publishing), systems for printing vector images, such as those handled in computer graphics, have become widely used. . A typical example is a system using Adobe's Post Script. PostScript is a page description language (Pag).
It belongs to a language genre called e-Description Language (hereinafter referred to as PDL), and describes the contents of a single document, including the text (letter part), graphics, and their arrangement and appearance. It is a programming language for describing forms including .In such systems, vector fonts are used as character fonts. Therefore, even when characters are scaled, printing quality can be significantly improved compared to systems that use bitmap fonts (for example, conventional word processors), and character fonts, graphics, and images can be There is an advantage that printing can be performed in a mixed manner.

However, the resolution of the laser printers used in these systems is no more than 240 dpi.
Many of them have a resolution of ~400 dpi, and similar to CRT display of computer graphics, there is a problem that aliasing occurs due to the low resolution. For this reason, even when printing using a laser printer, there is a need to perform anti-aliasing processing to improve the quality of the printed image.

0010

[Problems to be Solved by the Invention] However, since the brightness modulation processing in the anti-aliasing method uses the filling processing result for each sub-pixel, for example, even if 2*2 sub-pixels are used, the vector The problem was that the expansion process took twice as long as normal.

[0011] Furthermore, when applying the above anti-aliasing method to a digital copying machine, there is a problem in that a high-resolution scanner is required because it is necessary to read image information with sub-pixel level detail. .

Furthermore, as a method for achieving high image quality without using an anti-aliasing method, there is a method of making the resolution in the main scanning direction higher than that in the sub-scanning direction. This method takes advantage of the fact that it is easier to improve resolution in the main scanning direction than in the sub-scanning direction, but since it requires high-resolution source data, when using the anti-aliasing method described above, A similar problem was occurring.

[0013] The present invention has been made in view of the above, and provides high-speed visually high-quality output without requiring high-resolution image development processing or image reading processing, and without using anti-aliasing techniques. The purpose is to obtain an image.

[0014]

[Means for Solving the Problems] In order to achieve the above-mentioned objects, the present invention provides an image that can be outputted at a resolution that is twice as high in the main scanning direction as that in the sub-scanning direction, and that can output white, black, and halftones. In the coordinate system where the main scanning direction is the horizontal direction and the sub-scanning direction is the vertical direction, and the main scanning direction is from left to right, the first output data is the corresponding source data. Black when the corresponding source data is white, and the source data immediately above and to the left of the source data are both black, or when the source data immediately below and to the left are both black , otherwise it is white, and the second output data is black when the corresponding source data is black, and the corresponding source data is white and the source data directly above and to the right of the source data is black. and high-resolution means for outputting an intermediate tone when both are black, or when the source data directly below and to the right are both black, and otherwise outputs white at a resolution twice that of the source data in the main scanning direction. The present invention provides a graphics processing device that has the following features.

[0015] In order to achieve the above object, the present invention also provides an image output means that is capable of outputting at a resolution in the main scanning direction that is twice as high as that in the sub-scanning direction, and is capable of outputting white, black, and halftones; In the coordinate system where the main scanning direction is the horizontal direction, the sub-scanning direction is the vertical direction, and the main scanning direction is from right to left, the first output data is
Black when the data is black; when the corresponding source data is white and the source data immediately above and to the right of the source data are both black, or when the source data directly below and to the right are both black The second output data is black when the corresponding source data is black, and the second output data is white when the corresponding source data is white and the source data immediately above and to the left of the source data is white. High-resolution means for outputting halftone data when both data are black or when source data immediately below and to the left are both black, and otherwise outputting white at a resolution twice that of the source data in the main scanning direction; The present invention provides a graphic processing device equipped with the following.

In order to achieve the above object, the present invention also provides an image output means capable of outputting at least white, black, and halftones, and an image output unit capable of outputting at least white, black, and halftones, and an image outputting means that outputs a target pixel whose source data is black based on binary source data. black when the source data of the pixel of interest is white, and white when there is no combination in which the source data of the four neighboring pixels among the source data of the four neighboring pixels of the pixel of interest are both black; The present invention provides a graphic processing device including a multi-value processing means that outputs each halftone at other times.

Further, in order to achieve the above object, the present invention inputs black and white binary source data, and when the pixel of interest is at the black level, the pixel of interest is set to the first density value, and the pixel of interest is set to the first density value. When the pixel is at the white level and two diagonally adjacent pixels among the four neighboring pixels adjacent to the pixel of interest are at the black level, the pixel of interest is set to the second density value, and the first and second density values are set. Pixels other than the second density value are set to the third density value, and further, the third density value is set to the third density value.
Among the four neighboring pixels adjacent to the pixel of interest set to the density value, if there is a combination in which one of the two diagonally adjacent pixels has the second density value and the other has the first density value,
The present invention provides a graphic processing device including density value setting means for changing the third density value to the fourth density value.

[0018]

[Operation] In the graphic processing device of the present invention (claim 1), in a coordinate system in which the main scanning direction is the horizontal direction and the sub-scanning direction is the vertical direction, the scanning direction of the main scanning is from left to right. The output data of the eye is black when the corresponding source data is black, and the corresponding source data is white and the source data directly above and to the left of the source data are both black, or if the source data directly below and to the left are both black. The second output data is black when the corresponding source data is black, and the second output data is white when the corresponding source data is white. If the source data directly above and to the right of the data are both black, or if the source data directly below and to the right are both black, it is a halftone, otherwise it is white and the main scanning direction is twice that of the source data. Output at resolution.

[0019] Also, a graphic processing device of the present invention (claim 2)
In the coordinate system where the main scanning direction is horizontal, the sub-scanning direction is vertical, and the main scanning direction is from right to left, the first output data is the corresponding source data that is black. If the corresponding source data is white and the source data immediately above and to the right of the source data are both black, or if the source data immediately below and to the right are both black, then the corresponding source data is white. The second output data is black when the corresponding source data is black, and the second output data is black when the corresponding source data is black.
If the corresponding source data is white and the source data immediately above and to the left of the source data are both black, or if the source data directly below and to the left are both black, it is a halftone, otherwise Output as white in the main scanning direction at twice the resolution of the source data.

[0020] Also, a graphic processing device of the present invention (claim 3)
Based on binary source data, when the source data of the pixel of interest is black, the source data of the pixel of interest is black.
If the data is white and there is no combination in which the source data of the four neighboring pixels of the pixel of interest are both black, then white is used, otherwise each halftone is Output.

Furthermore, in the graphic processing apparatus of the present invention (claims 4 and 5), the density value setting means outputs the second density value (dark halftone) to the stepped change portion of the source data. Furthermore, in this state, a fourth density value (light halftone) is output to the stepped portion.

[0022]

[Example] Hereinafter, the graphic processing device of the present invention will be explained. [Example 1]
], [Embodiment 2], and [Embodiment 3] will be described in detail with reference to the drawings.

[Embodiment 1] An image forming system to which the graphic processing device of the present invention (claims 1 and 2) is applied will be described as embodiment 1. The image forming system of Example 1 is as follows:
Page description language output from DTP (desk top publishing)
This configuration allows image formation of both image information, including vector data written in PDL language (hereinafter referred to as PDL language) and an image 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 the PDL language (postscript language is used in this embodiment), and an output device that outputs the PDL language sent page by page from the host computer 100. A PDL controller 200 that develops an image at a resolution in the lower resolution direction and stores it in an internal page memory, an image reading device 300 that reads image information via an optical system unit, and a PDL controller 2
00, or an image processing device 400 that inputs a binary image output from the image reading device 300 and performs various image processing (details will be described later), and prints multivalued image data output from the image processing device 400. Multilevel color laser printer 500 and PDL controller 200
, an image reading device 300, an image processing device 400, and a system control section 600 that controls a multivalued color laser printer 500.

Next, the configuration and operation of the PDL controller 200 will be explained. FIG. 2 shows the configuration of the PDL controller 200, which includes a receiving device 201 that receives PDL language sent from the host computer 100,
A CPU 202 that controls storage of the PDL language received by the receiving device 201 and executes anti-aliasing processing, an internal system bus 203, and an internal system bus 203.
A RAM 204 that stores the PDL language transferred from the receiving device 201 via the ROM 205 that stores predetermined programs, etc., and a page memory 20 that stores multi-level RGB image data that has been subjected to anti-aliasing processing.
6, a transmitting device 207 that transfers RGB image data stored in the page memory 206 to the image processing device 400, and an I/O device 2 that performs transmission and reception with the system control unit 600.
08.

[0026] Here, the CPU 202
The received PDL language is sent to the RA via the internal system bus 203 according to the program stored in the ROM 205.
Store in M204. After that, when one page of PDL language is received and stored in the RAM 204, multilevel RGB image data is stored in the plain memory section of the page memory 206 based on the program in the RAM 204 (the page memory 206 is , B, and a feature information memory section).

The data in the page memory 206 is then sent to the image processing device 400 via the sending device 207. Further, transmission and reception with the system control unit 600 is performed via the I/O device 208.

The system control unit 600 includes a PDL controller 200, a multivalued color laser printer 500,
It controls the image processing device 400 and the image reading device 300, and for example, switches the input of the image processing device 400, selects the output image data of the image reading device 300 to operate as a digital copying machine, and controls the PDL controller 200. Select the output image data of PDL
Executes processing such as outputting images.

FIG. 3 is an internal block diagram of image processing device 400. The image processing device 400 includes a system control unit 6
By the control process of 00, the input data is transferred to the image reading device 3.
A multiplexer 401 switches the output from the multiplexer 401 to an external interface circuit 404 that connects the PDL controller 200 or the PDL controller 200, and converts the output from the multiplexer 401 into black and white.
A high-resolution circuit 403 that converts value data into monochrome and intermediate level binary data with twice the resolution in the main scanning direction, and then outputs the data to a multi-value color laser printer 500 for data printing, and a system control unit. The synchronization control circuit 402 receives control signals from the synchronization control circuit 600 and manages synchronization clock signals supplied to each circuit.

FIG. 4 shows the high resolution circuit 40 shown in FIG.
3 is a circuit diagram showing the configuration of line memories 452 to 455 each holding data for one line, and writing or writing to line memories 452 to 455 by counting the CLK signal and clearing the count by the LSYNC signal. A counter 451 that generates a read address, a line memory control circuit 456 that controls the line memories 452 to 455, and a D flip-flop 457 that receives the output from the line memory control circuit 456 and delays it by 1 to 3 clocks. Shift register 470 composed of ~463 and shift register 4
The necessary arithmetic processing is performed on the signal output from the printer 70, and the ternary data is sent to the multi-value color laser printer 500.
It is composed of an arithmetic circuit 464 that outputs an output to.

The high resolution circuit 403 of the image processing device 400 performs an operation of converting the main scanning direction into ternary level data with double the resolution. In this conversion method, when the main scanning direction is horizontal, the sub-scanning direction is vertical, and the main scanning direction is from left to right, the first output data is
If the corresponding source data is black, it is black; if the corresponding source data is white and the source data directly above and to the left of the source data are both black, or if the source data directly below and to the left is black,
When both data are black, it is gray, otherwise it is white.The second output data is black when the corresponding source data is black, and the corresponding source data is white and is directly above the source data. If both the source data and the source data to the right are black, or if the source data immediately below and to the right are both black, the color is gray, otherwise it is white, and the resolution in the main scanning direction is set to twice that of the source data. (Also, when the main scanning direction is horizontal, the sub-scanning direction is vertical, and the main scanning direction is from right to left, the first output data is black when the corresponding source data is black, When the corresponding source data is white and the source data immediately above and to the right of the source data are both black, or when the source data directly below and to the right are both black, it is gray; otherwise, it is white. The second output data is black when the corresponding source data is black, and the corresponding source data is white and the source data directly above and to the left of the source data are both black, or When the source data immediately below and to the left are both black, the color is gray, otherwise it is white, and the resolution in the main scanning direction may be set to twice that of the source data.)

The arithmetic circuit 464 in the high resolution circuit 403 realizes the above operation. FIG. 7 is a timing chart showing the operation of the high resolution circuit 403, in which the CLK signal is a clock signal that is the basis of all operations, the LSYNC signal is a synchronization signal for each line,
The DATA signal is an image data signal and is synchronized with the CLK signal. Furthermore, the data near the part where the LSYNC signal is active is invalid data, and AD is the output data of the counter 451 in FIG. 4, and is the address of the line memories 452 to 455.

The counter 451 counts the CLK signal, and since the LSYNC signal is connected to the clear (CLR) of the counter 451, it is cleared for each line and supplies the necessary address to the line memory. . Further, the W signal is a write signal, and is given only to the line memories 452 to 455 that perform writing.

FIG. 5 shows the configuration of the arithmetic circuit 464, in which a plurality of AND circuits 480 to 485 (AND circuit 480
The output of the AND circuit 481 is AB, AND
The output of the circuit 482 is AC, and the output of the AND circuit 483 is A.
D), OR circuit 486 (output of OR circuit 486 is BA)
, 487 (the output of the OR circuit 487 is BB) and an inverter circuit 488 (the output of the inverter circuit 488 is C).

FIG. 6 shows input data, which is structured as shown in Table 1 below, corresponding to source data (i, j) corresponding to the pixel of interest.

[0036]

[Table 1]

Furthermore, in FIG. 5, the outputs are FL and FR, with FL being the first data and FR being the second data. Further, FL0 means bit 0 of FL, FL1 means bit 1, and both FL and FR output 2-bit data. Further, 0 indicates white, 1 indicates gray, and 2 indicates black. This output data is sent to the multilevel color laser printer 500 by the synchronization control circuit 402, and a corresponding image is output.

Next, the operation of the arithmetic circuit 464 will be explained in detail using FIG. Let black be H(1), white be L(0),
When (i, j) is the pixel of interest, the pixel of interest D(i, j
) is black, FL1 and FR1 become 1. on the other hand,
The output C of the inverter 488 becomes L because FL0,
FR0 becomes 0.

When the pixel of interest D(i,j) is white, the output C
is H because FL0 and FR0 are respectively output BA,
The state of BB is output as is.

Output AA is D(i-1,j) and D(i,j
-1) are both H, the result is H. Therefore, the pixel of interest D(
i, j)'s left neighbor D(i-1, j) and directly above D(i, j+1
) is H only when both are black. Similarly, the output AB is the left neighbor D(i-1,j) of the pixel of interest D(i,j) and the directly above D(
It becomes H only when both i, j+1) are black.

Output BA is the sum of output AA and output AB, and the left neighbor D(i-1
, j) and directly below D(i, j-1) are both black, or when the left neighbor D(i-1, j) and directly above D(i, j+1) are both black.

Similarly, the output AC is the pixel of interest D(i,j)
It becomes H only when the directly above D(i, j+1) and the right neighbor D(i+1, j) are both black. Similarly, the output AD is the pixel of interest D
The right neighbor D(i+1,j) of (i,j) and the one directly below D(i,j-
1) is H only when both are black.

Output BB is the sum of output AC and output AD, and is located directly above D(i,j) of the pixel of interest D(i,j).
+1) and the right neighbor D(i+1,j) are both black, or the right neighbor D(i+1,j) and the right neighbor D(i+1,j) of the pixel of interest D(i,j) are black.
, j-1) are both black, it becomes H only.

The schematic configuration of multi-valued color laser printer 500 will be explained with reference to the control block diagram shown in FIG. 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. Although the details will be described later, a black development/transfer section 501bk that develops and transfers BK data;
Cyan development/transfer section 501 that develops/transfers C data
c, a cyan developing/transfer section 501m that develops and transfers M data, and a cyan developing/transfer section 501m that develops and transfers Y data.
The transfer unit 501y is also provided with a transfer unit 501y.

The laser drive processing unit 502 processes three Y, M, C, and BK signals output from the image processing device 400 described above.
It inputs bit data (in this case, image density data) and outputs a laser beam.
, a buffer memory 503 into which 3-bit data of C is input.
y, 503m, 503c, laser diodes 504y, 504m, 504c, 504bk that output laser beams corresponding to Y, M, C, BK, respectively, and laser diodes 504y, 504m, 504c, 504.
Drivers 505y, 505m, which drive bk, respectively.
505c and 505b.

Furthermore, the black developing/transfer section 501bk of the photoreceptor development processing section 501, the laser drive processing section 502, the laser diode 504bk, and the driver 505b
The combination with k is called a black recording unit BKU (see FIG. 9). Similarly, the combination of cyan developing/transfer section 501c, laser diode 504c, driver 505c, and buffer memory 503c is connected to cyan recording unit C.
U (see FIG. 9), magenta developing/transfer section 501m, laser diode 504m, driver 505m, and buffer memory 503m are combined into magenta recording unit MU (see FIG. 9), yellow developing/transfer section 501y, laser diode 504y, driver 505y, and
The combination of buffer memories 503y is called a yellow recording unit YU (see FIG. 9). As shown in the figure, each of these recording units includes a black recording unit BKU located around a conveyor belt 506 that conveys the recording paper from the conveyance direction of the recording paper.
, cyan recording unit CU, magenta recording unit MU
, yellow recording unit YU.

With this arrangement of each recording unit, the laser diode 504bk for black exposure starts exposure first, 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, and during this time difference, the recorded data (image processing device 4
00 output), the laser drive processing unit 50
2 includes the three sets of buffer memories 503y and 503 described above.
m, 503c is provided.

Next, the configuration of the multivalued 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 a conveyor belt 506 as described above.
Each recording unit YU, MU, CU, arranged around
BKU and paper feed cassettes 507a, 5 containing recording paper
07b, paper feed rollers 508a and 508b that feed the recording paper from the paper feed cassettes 507a and 507b, registration rollers 509 that aligns the recording paper fed from the paper feed cassettes 507a and 507b, and a conveyor belt 506. Unit BKU, CU, MU, Y
It is composed of a fixing roller 510 that fixes the transferred image on the recording paper after being sequentially conveyed through U, 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 has a photoreceptor drum 512y, 512m, 512c, 512bk, and a photoreceptor drum 512y, 512m, 512c, respectively.
, 512bk uniformly charging chargers 513y, 513
m, 513c, 513bk, and photosensitive drum 512y,
Polygon mirrors 514y, 514m, 514c for guiding laser beams to 512m, 512c, 512bk
, 514bk and motor 515y, 515m, 515c
, 515bk and photosensitive drums 512y, 512m, 5
A toner developing device 5 that develops the electrostatic latent images formed on 12c and 512bk using toner of a corresponding color.
16y, 516m, 516c, 516bk, and transfer chargers 517y, 51 that transfer the developed toner image to recording paper.
7m, 517c, 517bk, and cleaning devices 518y, 518 that remove toner remaining on the photosensitive drums 512y, 512m, 512c, 512bk after transfer.
It consists of m, 518c, and 518bk. In addition, 51
9y, 519m, 519c, and 519bk are photosensitive drums 512y, 512m, 512c, and 512bk, respectively.
CCD for reading a predetermined pattern provided on the top
A line sensor is shown, and although its details are omitted, it detects the process status of the multivalued color laser printer 500.

In the above configuration, the operations of the yellow recording unit YU will be explained using exposure, development, and transfer as examples. FIGS. 10A and 10B show the configuration of the exposure system of the yellow recording unit YU. 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 502y, is further reflected by mirrors 521y and 522y, passes through a dustproof glass 523y, and hits a photosensitive drum 512y. irradiated. At this time, the laser beam is transmitted to the polygon mirror 514.
Since y is rotationally driven at a constant speed by the motor 515y, 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 recording data (3-bit data from the image processing device 400), multilevel exposure corresponding to the recording data is performed on the surface of the photoreceptor drum 504y. 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 stored in the cassette 507a (or 507a) as shown in FIG.
b), the toner is fed out by paper feed rollers 508a (or 508b), and is transferred by registration rollers 509 onto recording paper conveyed by conveyor belt 506 in synchronization with toner image formation in black recording unit BKU.

Other recording units BKU, CU, and MU have similar configurations and perform similar operations, but black recording unit BKU is equipped with a black toner developing device 516bk, forms and transfers a black toner image, and performs cyan toner image formation and transfer. The recording unit CU includes a cyan toner developing device 516c to form and transfer a cyan toner image, and the magenta recording unit MU includes a magenta toner developing device 516m to form and transfer a magenta toner image.

Next, multi-value driving of the driver will be explained. Driver 505y, 505m, 505c, 505b
are Y, M, C, sent from the image processing device 400.
Based on the 3-bit data of BK, 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

The multivalue drive by power modulation applied in this embodiment will be explained in detail below with reference to FIGS. 11, 12, 13, and 14. In addition, the drivers 505y, 50
5m, 505c, 505b and laser diodes 504y, 504m, 504c, and 504bk have the same configuration, so here, the driver 505y and laser diode 504y will be explained as an example.

As shown in FIG. 11, the driver 505y includes a laser diode on/off circuit 550 that turns on and off the laser diode 504y based on a predetermined LD drive clock, and 3-bit image density data (here, D to convert Y data) into an analog signal
/A converter 551 and a current (LD drive current) I that drives the laser diode 504y by inputting an analog signal based on the image density value from the D/A converter 551.
d to a laser diode on/off circuit 550.

Here, the LD drive clock is defined as "1" to be on and "0" to be off, and as shown in FIG. 12, the laser diode on/off circuit 550 turns on/off the laser diode 504y accordingly. . Furthermore, since there is a proportional relationship between the LD drive current Id and the laser beam power, by generating the LD drive current Id based on the image density data value, a laser beam power output corresponding to the image density data value can be obtained. . For example, as shown in FIG. 12, the image density data value is "4".
” (data N-1 in the figure), the constant current circuit 55
2, the corresponding LD drive current Id is supplied, and the laser beam power of the laser diode 504y becomes level 4. Further, when the image density data value is "7" (data N in the figure), the corresponding LD drive current Id 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, laser diode on/off circuit 550 and D/A converter 551
, and the specific circuit configuration of the constant current circuit 552. The laser diode on/off circuit 550 is TTL
Inverters 553 and 554, differential switching circuits 555 and 556 that perform on/off toggle operation, and V
When G1>VG2, the differential switching circuit 555
n, differential switching circuit 556 is off, VG1<
When VG2, the differential switching circuit 555 is off,
a resistor R2 forming a voltage dividing circuit that generates VG2 that satisfies the conditions for the differential switching circuit 556 to be turned on;
It is composed of R3. Therefore, when the LD drive clock is "1", the output of the inverter 554 generates VG1, the above condition (VG1>VG2) is satisfied, the differential switching circuit 555 is turned on, and the differential switching circuit 556 is turned off. and turn on the laser diode 504y.
Do n. Conversely, when the LD drive clock is "0", there is no output from the inverter 554, so the above condition (
VG1<VG2), and the differential switching circuit 5
55 is turned off, the differential switching circuit 556 is turned on, and the laser diode 504y is turned off.

The D/A converter 551 includes a latch 557 that latches the input image density data while the LD drive clock is "1", and a latch 557 that latches the input image density data while the LD drive clock is "1", and a latch 557 that latches the input image density data while the LD drive clock is "1", and a
It consists of a ref generator 558 and a 3-bit D/A converter 559 that outputs analog data Vd based on image density data and maximum output value Vref. Here, Vd, image density data, and maximum output value Vref
The relationship with is expressed by Equation 1 below.

[0057]

[Math 1]

The constant current circuit 552 supplies the current of the laser diode 504y to the laser diode on/off circuit 550 as described above, and is composed of a 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, since the current flowing through the resistor R4 is approximately equal to the collector current of the transistor 560, the current Id flowing through the laser diode 504y is controlled by Vd.

FIG. 14 shows the output of the latch 557 described above,
3 is a timing chart showing the relationship between VG1, Vd, and Id. Here, Vd is Vref based on image density data (3 bit data: 8 gradation data from 0 to 7).
It takes a value in 8 steps from ×0/7 to 7/7, and Id is this V
Based on the value of d, eight levels from I0 to I7 are shown. The laser diode 504y has eight levels of this Id (I0 = level 0, I1 = level 1..., I
7 = level 7), a latent image as shown in FIG. 15 is formed on the photosensitive drum 512y.

When the graphic processing apparatus of the first embodiment is used, an output as shown in FIG. 17 is obtained for the input data of FIG. 16. In FIG. 17, diagonal lines in both directions indicate black, and diagonal lines in one direction indicate intermediate tones. As shown in Figure 17,
Since halftone dots are added to the stepped portions, jaggies in the diagonal line portions become less noticeable. Furthermore, since no intermediate tone dots are added to horizontal or vertical lines, blurring of the image is less likely to occur.

In this way, in the first embodiment, a predetermined digital filter (high-resolution circuit) is used to detect diagonal line portions, without executing the time-consuming anti-aliasing process, and the halftone portion is added thereto. (gray) to suppress jaggedness. Furthermore, since the present invention uses an image output device (printer) that has twice the resolution in the main scanning direction as in the sub-scanning direction, the addition of halftones (gray) can be finely adjusted, further improving the visual resolution. . Therefore, an output image with high visual resolution can be obtained at high speed.

[Embodiment 2] The graphic processing device (claim 3) of the embodiment 2 creates a document written in the PDL language (postscript language is used in this embodiment) as shown in FIG. A host computer 100, a PDL controller 200 that develops the PDL language sent page by page from the host computer 100 into an image at a lower resolution of the output device and stores it in an internal page memory, and an optical system unit. an image reading device 300 that reads image information via a PDL controller 2;
00, or an image processing device 400 that inputs a binary image output from the image reading device 300 and performs various image processing (details will be described later), and prints multivalued image data output from the image processing device 400. 3-value laser
It is composed of a printer 700 and a system control unit 600 that controls the PDL controller 200, image reading device 300, image processing device 400, and ternary laser printer 700. Note that components common to those in the first embodiment are indicated by the same reference numerals.

FIG. 19 is an internal block diagram of the image processing apparatus. The image processing apparatus 400 sends input data to an external interface circuit 404 that connects the image reading apparatus 300 or the PDL controller 200 under the control processing of the system control unit 600. Switching multiplexer 401
, a ternarization circuit 405 that converts the output from the multiplexer 401 from black and white binary data to black and white and intermediate level ternary data, and then outputs it to the ternary laser printer 700 for data printing; and a system control circuit. The synchronization control circuit 402 receives the control signal from the section 600 and manages the synchronization clock signals supplied to each circuit.

FIG. 20 shows the ternarization circuit 40 shown in FIG.
5 is a circuit diagram showing the configuration of line memories 452 to 455 each holding data for one line, and writing or writing to line memories 452 to 455 by counting the CLK signal and clearing the count by the LSYNC signal. The counter 451 that generates the read address and one of the line memories 452 to 455 execute the write process of the input data Din, and write the data of the previous line for which the write process is being executed as D(j+1). , there is a line memory control circuit 456 that outputs the data of the two previous lines to D(j) and the data of the three previous lines to D(j-1), and the output from the line memory control circuit 456. A shift register 470 composed of D flip-flops 457 to 463 that inputs and delays by 1 to 3 clocks, and a shift register 470
Perform the necessary arithmetic processing on the signal output from 3.
It consists of an arithmetic circuit 465 that outputs value data to the ternary laser printer 700.

The ternarization circuit 405 converts the output from the multiplexer 401 from black and white binary data to black and white and intermediate level ternary data, and then sends the output to a ternary laser printer 700 to print the data. Perform the action to output.

This conversion method is based on binary source data. When the source data of the pixel of interest is black, it is black, and when the source data of the pixel of interest is white, the sources of the four neighboring pixels of the pixel of interest are black.・If there is no combination of data in which the source data of four adjacent neighbors are both black, white,
At other times, each intermediate tone is output.

The ternarization circuit 40 realizes the above operation.
This is the arithmetic circuit 465 in No. 5. FIG. 23 is a timing chart showing the operation of the ternarization circuit 405.
The K signal is a clock signal that is the basis of all operations,
The LSYNC signal is a synchronization signal for each line, and the DAT
The A signal is an image data signal and is synchronized with the CLK signal.

Furthermore, the data near the part where the LSYNC signal is active is invalid data, and the AD is as shown in FIG.
This is the output data of the 0 counter 451, and is the address of the line memories 452 to 455.

The counter 451 counts the CLK signal, and since the LSYNC signal is connected to the clear (CLR) of the counter 451, it is cleared for each line and supplies the necessary address to the line memory. .

Further, the W signal is a write signal, and is applied only to line memories 452 to 455 that execute write processing.

FIG. 21 shows the configuration of the arithmetic circuit 465, in which a plurality of AND circuits 490 to 494 (AND circuit 49
0 output is A1, AND circuit 491 output is A2, AN
The output of the D circuit 492 is A3, the output of the AND circuit 493 is A4), the OR circuit 495 (the output of the OR circuit 495 is B)
and an inverter circuit 496 (the output of the inverter circuit 496 is C).

FIG. 22 shows input data, which is structured as shown in Table 2 below, corresponding to source data (i, j) corresponding to the pixel of interest.

[0073]

[Table 2]

Further, the operation of this arithmetic circuit 465 is as follows: When black is H(1), white is L(0), and (i, j) is the pixel of interest, if the pixel of interest is black, 2(D1 = 1,D0
= 0), and if there is a combination in which the pixel of interest (i, j) is white and the source data of the four neighboring pixels among the four neighboring pixels of the pixel of interest are both black data, It outputs 1, and 0 in other cases.

Further, the operation of the arithmetic circuit 465 will be explained in detail using FIG. When the pixel of interest D(i,j) is black, D1 is 1 and the output C is L, so D0 is the output B
is L(0) regardless of the value of , and therefore 2 is output.

Next, when the pixel of interest D(i,j) is white,
D1 is 0 and the output C becomes H. Therefore, regardless of the value of output B, it is L(0), and therefore the state of output B is output as is to D0.

Output A1 is D(i,j-1) and D(i+1
, j), which is the AND output of the pixel of interest D(i, j
) if the source data immediately above and to the right are both black, the value is H; otherwise, the value is L.

Similarly, the output A2 is the pixel of interest D(i,j)
Output A3 becomes H only when the source data immediately below and to the right are both black, output A3 becomes H only when the source data immediately below and directly below are both black, and output A4 becomes H only when the source data immediately below and directly above are black.
When both data are black, it becomes H.

Output B is the sum of outputs A1 to A4, and output B becomes H because the source data of the four neighboring pixels of the pixel of interest D(i,j) is This is true only when there is a combination in which both are black data, otherwise it is L.

When the graphic processing apparatus of the second embodiment is used, an output as shown in FIG. 25 is obtained for the input data of FIG. 24. In FIG. 25, diagonal lines in both directions indicate black, and diagonal lines in one direction indicate intermediate tones. As shown in Figure 25,
Since halftone dots are added to the stepped portions, jaggies in the diagonal line portions become less noticeable. Furthermore, since no intermediate tone dots are added to horizontal or vertical lines, blurring of the image is less likely to occur.

In this way, in the second embodiment, the time-consuming anti-aliasing process is not performed, but the diagonal line portion is detected using a predetermined digital filter (ternarization circuit), and the halftone (gray) portion is added thereto. ) to suppress jaggedness, it is possible to quickly obtain output images with high visual resolution.

[Embodiment 3] Hereinafter, a graphic processing device (claims 4 and 5) of embodiment 3 will be explained in detail with reference to the drawings. FIG. 26 shows an example of an image forming system to which the graphic processing device of Example 3 is applied.

An image reading device 300 that converts image data read through the CCD 301a into a binary level of black and white in a binarization circuit 301b, an external interface 200 for inputting data from a source other than the image reading device 300,
A multiplexer 401 that switches whether input data is input from the image reading device 300 or from the external interface 200 side, and a multi-value conversion circuit 800 that converts binary image data input via the multiplexer 401 into multi-value data. , a multi-value laser printer 900 that outputs image data multi-valued by a multi-value conversion circuit 800, and a system control section 600 that controls the entire system.

Referring to FIG. 27, the internal configuration of multi-value quantization circuit 800 will be described. The multi-level conversion circuit 800 includes RAMs 801 to 810, each of which stores one line of data, and an R
A line memory control circuit 811 that controls AM801-810, D flip-flops 812-818 that temporarily stores the output of the line memory control circuit 811, and D flip-flops 812-818. Data is input from the line memory control circuit 811 and the calculation results of the calculation circuit 819 which performs predetermined calculations and stored in the RAMs 807 to 810 are input via the line memory control circuit 811. , D flip-flops 820 to 831 for temporary storage, and an arithmetic circuit 832 that performs predetermined calculations based on data input via the D flip-flops 820 to 831.

FIG. 28(a) shows the internal configuration of the arithmetic circuit 819. In the third embodiment, the black level pixels are set to High,
A pixel with a white level is expressed as Low. Here, select the pixel of interest (
i, j), centering on the pixel of interest (i, j),
The four neighboring pixels adjacent to the pixel of interest are (i, j-1), (i-1, j), (i+1,
j), (i, j+1). Arithmetic circuit 8
19 is the data D(i, j-1), D(
i-1,j), D(i+1,j), D(i,j+1), and two diagonally adjacent pixels are set to black level (High
), outputs High.

FIG. 29(a) shows the internal configuration of the arithmetic circuit 432. The arithmetic circuit 432 converts the pixel of interest into (i, j+2
), centering on the pixel of interest (i, j+2), the four neighboring pixels adjacent to the pixel of interest are (i, j+1), (i+1, j+2), (i
−1, j+2), (i, j+3), and when the source data D(i, j+2) of the pixel of interest is black level,
Dout=3(out1=High, out0=Low
), and the source data D(i, j+2
) is the white level, the processed data H(i, j+2) is H
If igh, output Dout = 2, H(i, j+2)
is Low, and among the four neighboring pixels of the pixel of interest, the source data is High and the processed data are High, for example, D (i, j + 1) = High
If gh, H (i+1, j+2) = High, Dou
Output t = 1. Otherwise Dout = 0
This is a configuration that outputs .

The operation of the above configuration will be explained. The image reading device 300 converts the image data read through the CCD 301a into black and white binary levels using the binarization circuit 301b, and outputs the converted data to the multi-value conversion circuit 800 through the multiplexer 401.

The line memory control circuit 811 of the multilevel conversion circuit 800 controls the RAMs 801 to 806 to hold five lines of binary source data Din, and stores the line immediately before the current line. data of D
Output from (j-1) and convert the previous line to D(j)
, the line before that is D(j+1), the line before that is D(j+2), the line before that is D(j+3)
). Also, Hin data is stored in RAM807.
~810 is used to hold 3 lines, output the data of the previous line from H(j+1), output the previous line from H(j+2), and output the previous line from H(j+3).
).

D flip-flops 812-818 are
D(j-1 of line memory control circuit 811
), D(j), and D(j+1) are temporarily stored,
Centering on D(i,j), data of four neighboring pixels are supplied to an arithmetic circuit 819.

As described above, the arithmetic circuit 819 calculates the data D(i,j-1) of the four neighboring pixels of the pixel of interest D(i,j).
), D(i-1,j), D(i+1,j), D(i,j
+1) so that the two diagonally adjacent pixels are at the black level (
High is output when there is a combination that results in High). The output of this arithmetic circuit 819 is input to the line memory control circuit 811, and the output is sent to the RAM 807.
~810.

Line memory control circuit 811
The outputs of D(j+2) and D(j+3) of 418 are temporarily stored in D flip-flops 820 to 824, and
It is supplied to an arithmetic circuit 832 along with the output of the flip-flop. On the other hand, line memory control circuit 8
The outputs of H(j+1), H(j+2), and H(j+3) of No. 11 are temporarily stored in D flip-flops 825 to 831 and supplied to an arithmetic circuit 832.

The arithmetic circuit 832 converts the pixel of interest into (i, j+
2), centering on the pixel of interest (i, j+2), the four neighboring pixels adjacent to the pixel of interest are (i, j+1)
, (i+1, j+2), (i-1, j+2), (i, j
+3), and the source data D(i,
j+2) is the black level, Dout = 3(out1
=High, out0=Low), if the source data D(i, j+2) of the pixel of interest is a white level, and if the processed data H(i, j+2) is High, Dout=
2, H(i, j+2) is Low, and among the four neighboring pixels of the pixel of interest, the source data is High and the processed data is High, for example, D(i, j+1) =High, H(i+1,j+
2) If =High, output Dout =1. Otherwise, Dout=0 is output. This output data is sent to the multilevel laser printer 900 and
When ut is 3, it is the darkest black, and when Dout is 0,
White, light midtone when Dout is 1, and D
When out is 2, it is output in deep intermediate tones.

FIG. 30 shows the processing results of this example. The jagged part of the step-like part of the source data shown on the left side is changed to the processed data shown on the right side by adding intermediate level pixels. Visually smooth. In addition, the processing results are processed using the uniform averaging method to obtain 2*2 size sub-
This was equivalent to using a matrix, and the processing speed was almost real-time.

[0094]

As explained above, according to the graphic output device according to the present invention (claims 1 and 2), it is possible to output in the main scanning direction at twice the resolution in the sub-scanning direction, and,
Equipped with an image output means capable of outputting white, black, and halftones, and a predetermined digital filter (high resolution circuit) that detects diagonal lines and adds halftones (gray) there, it is possible to achieve high resolution. It is possible to obtain visually high-quality output images at high speed without requiring image development processing or image reading processing, and without using anti-aliasing techniques.

Further, according to the graphic processing device according to the present invention (claim 3), the image output means capable of outputting white, black and halftones, and the source image of the pixel of interest based on the binary source data. Black when the data is black, and when the source data of the pixel of interest is white and there is no combination in which the source data of the four neighboring pixels among the source data of the four neighboring pixels of the pixel of interest are both black. Since it is equipped with a multi-value processing means that outputs white and halftones in other cases, high-resolution image development processing or image reading processing is not required, and high-speed processing is possible without using anti-aliasing methods. It is possible to obtain visually high-quality output images.

Further, according to the graphic processing apparatus according to the present invention (claims 4 and 5), when black and white binary source data is input and the pixel of interest is at the black level, the pixel of interest is When the pixel of interest is at the white level and two diagonally adjacent pixels among the four neighboring pixels adjacent to the pixel of interest are at the black level, the pixel of interest is set to the second density value. , pixels other than the first density value and the second density value are set to the third density value, and further, among the four neighboring pixels adjacent to the pixel of interest set to the third density value, two diagonally adjacent pixels are set to the third density value. If there is a combination in which one of the two pixels has the second density value and the other has the first density value, the density value setting means is provided for changing the third density value to the fourth density value. Smoothing of step-like jagged parts can be performed at high speed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a graphic output device according to the present invention.

FIG. 2 is a block diagram showing the configuration of the PDL controller shown in FIG. 1.

FIG. 3 is a block diagram showing the configuration of the image processing device shown in FIG. 1.

FIG. 4 is a block diagram showing the configuration of the high resolution circuit shown in FIG. 3;

FIG. 5 is a circuit diagram showing the configuration of the arithmetic circuit shown in FIG. 4;

FIG. 6 is an explanatory diagram showing input data;

[Figure 7] Figure 7
5 is a timing chart showing the operation of the high-resolution circuit shown in FIG. 4. FIG.

FIG. 8 is a control block diagram showing a multilevel color laser printer.

FIG. 9 is an explanatory diagram showing the configuration of a multivalued color laser printer.

FIGS. 10(a) and 10(b) are explanatory diagrams showing the configuration of an exposure system of a yellow recording unit.

FIG. 11 is an explanatory diagram showing multi-value drive using power modulation.

FIG. 12 is an explanatory diagram showing multivalue drive using power modulation.

FIG. 13 is an explanatory diagram showing multivalue drive using power modulation.

FIG. 14 is an explanatory diagram showing multi-value drive using power modulation.

FIG. 15 is an explanatory diagram showing the state of a latent image depending on the level of power modulation.

FIG. 16 is an explanatory diagram showing an example of graphic data input to this embodiment.

FIG. 17 is an explanatory diagram showing an example of graphic data output from this embodiment.

FIG. 18 is a block diagram showing the configuration of a graphic processing device according to the present invention.

FIG. 19 is a block diagram showing the configuration of the image processing device shown in FIG. 18.

20 is a block diagram showing the configuration of the ternarization circuit shown in FIG. 19. FIG.

FIG. 21 is a circuit diagram showing the configuration of the arithmetic circuit shown in FIG. 20;

FIG. 22 is an explanatory diagram showing input data.

FIG. 23 is a timing chart showing the operation of the ternarization circuit shown in FIG. 20;

FIG. 24 is an explanatory diagram showing an example of graphic data input to this embodiment.

FIG. 25 is an explanatory diagram showing an example of graphic data output from this embodiment.

FIG. 26 is a configuration diagram of an embodiment of an image forming system to which the graphic processing device of the present invention is applied.

FIG. 27 is an explanatory diagram showing the internal configuration of a multi-value quantization circuit.

FIGS. 28(a) and 28(b) are explanatory diagrams showing the internal configuration of an arithmetic circuit.

FIGS. 29(a) and 29(b) are explanatory diagrams showing the internal configuration of an arithmetic circuit.

FIG. 30 is an explanatory diagram showing processing results of the example.

FIGS. 31A and 31B are explanatory diagrams showing conventional antialiasing processing.

FIGS. 32A and 32B are explanatory diagrams showing antialiasing processing using a uniform averaging method.

FIGS. 33A and 33B are explanatory diagrams showing antialiasing processing using a weighted averaging method.

FIGS. 34A, 34B, 34C, and 34D are explanatory diagrams showing examples of filters used in the weighted averaging method.

FIG. 35 is an explanatory diagram showing a convolution method with 3×3 pixel reference.

[Explanation of symbols]

100 host computer 200 PDL controller 300 image reading device 301a CCD 301b binarization circuit 400 image processing device 403 high resolution circuit 405 ternarization circuit 451 counter 452 453 454 455 line memory 456 line memory control circuit 4
64 465 Arithmetic circuit 470 Shift register 500 Multi-value color laser printer 600
System control unit 700 Three-level laser printer 800
Multivalue circuit 819 Arithmetic circuit

Claims (5)

[Claims] 1. Image output means capable of outputting in the main scanning direction at twice the resolution of the sub-scanning direction and capable of outputting white, black, and halftones, the main scanning direction being horizontal and the sub-scanning direction In a coordinate system in which the main scanning direction is from left to right, where is the vertical direction, the first output data is black when the corresponding source data is black;
The data is white and the sources directly above and to the left of the source data are
If the data are both black, or if the source data immediately below and to the left are both black, it will be halftone, otherwise it will be white, and the second output data will be black if the corresponding source data is black. , when the corresponding source data is white and the source data immediately above and to the right of the source data are both black, or when the source data immediately below and to the right are both black, it is a halftone; 1. A graphics processing device comprising: high resolution means for outputting white in the main scanning direction at twice the resolution of source data. 2. Image output means capable of outputting in the main scanning direction at twice the resolution of the sub-scanning direction, and capable of outputting white, black, and halftones, the main scanning direction being horizontal and the sub-scanning direction In a coordinate system in which the main scanning direction is from right to left, where is the vertical direction, the first output data is black when the corresponding source data is black;
The data is white and the sources directly above and to the right of the source data are
When the data are both black or when the source data immediately below and to the right are both black, it is halftone, otherwise it is white, and the second output data is black when the corresponding source data is black. , when the corresponding source data is white and the source data immediately above and to the left of the source data are both black, or when the source data immediately below and to the left are both black, it is a halftone; 1. A graphics processing device comprising: high resolution means for outputting white in the main scanning direction at twice the resolution of source data. 3. An image output means capable of outputting at least white, black, and halftone; and an image output means that outputs black when the source data of the pixel of interest is black, based on binary source data; If the pixel is white and there is no combination in which the source data of the four neighboring pixels of the pixel of interest are both black, white is output; otherwise, a half tone is output. 1. A graphic processing device comprising: multi-value processing means. 4. Inputting black and white binary source data, setting the pixel of interest to a first density value when the pixel of interest is at the black level, and setting the pixel of interest to the first density value when the pixel of interest is at the white level and the pixel of interest is at the black level. When two diagonally adjacent pixels among the four neighboring pixels adjacent to the pixel of interest are at the black level, the pixel of interest is set to a second density value, and a density value other than the first density value and the second density value is set to the pixel of interest. A pixel is set to a third density value, and among four neighboring pixels adjacent to the pixel of interest set to the third density value, one of two diagonally adjacent pixels is set to the second density value, and the other is set to the second density value. 1. A graphic processing apparatus comprising density value setting means for changing the third density value to a fourth density value when there is a combination in which the third density value is a first density value. 5. The first density is the deepest black level;
5. The graphic processing apparatus according to claim 4, wherein the second density is a deep halftone, the third density is white, and the fourth density is a light halftone.