JP2798496B2 - Graphic processing unit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphic processing apparatus for removing jagged edges of vector data, and more particularly, to a sub-pixel division method for dividing a pixel of an edge part of vector data into pixels. The present invention relates to a graphic processing apparatus for obtaining a tone value (density value) and outputting the tone value to an output device capable of dot modulation.

[Conventional technology]

In the field of computer graphics, when an image is displayed on a CRT as an output medium, a method called an anti-aliasing process is used to make the displayed image more beautiful. This processing is performed by a jagged portion (called an alias) on a stair as shown in FIG. 39 (a).
Is subjected to luminance modulation to visually smooth the displayed image as shown in FIG. 39 (b).

In a conventional graphic processing apparatus, a uniform averaging method, a weighted averaging method, a convolution integration method, and the like are generally applied as anti-aliasing processing methods.

In the uniform averaging method, each pixel (pixel) is N * M (N, M
Is a natural number), is subjected to raster calculation at high resolution, and then the luminance of each pixel is obtained by averaging N * M sub-pixels. FIG. 40 (a),
The anti-aliasing processing by the uniform averaging method will be specifically described with reference to FIG. When the edge of the image is over a certain pixel (here, the image is connected to the lower right of the diagonal line), and when the anti-aliasing process is not performed, as shown in FIG. To the luminance kid of this pixel, the highest luminance of a displayable gradation (for example, kid = 255 at 256 gradations) is assigned. When anti-aliasing processing is performed on this pixel by the uniform averaging method of N = M = 7, the pixel is decomposed into 7 * 7 sub-pixels and covered with an image as shown in FIG. Count the number of sub-pixels. The count (28) is divided by the total number of sub-pixels in one pixel (49 in this case) and normalized (averaged) is multiplied by the maximum luminance (255) to calculate the luminance of the pixel. As described above, in the uniform averaging method, the brightness of each pixel is determined in consideration of how the image is applied to each pixel.

Weighted Averaging Method The weighted averaging method is a partial modification of the uniform averaging method. In the uniform averaging method, all the subpixels in one pixel have the same weight (that is, the subpixels on which the image is applied are simply weighted). In contrast, the weighted averaging method weights each sub-pixel so that the effect on the luminance kid of that sub-pixel depends on which sub-pixel the image covers. . The weight at this time is given using a filter.

Referring to FIGS. 41 (a) and (b), an example is shown in which the same image data as in FIG. 40 (a) is subjected to the weighted averaging method by the same division method (N = M = 7).

FIG. 41 (a) shows a filter (here, conefille
r), and the corresponding sub-pixel is given the same weight as this characteristic. For example, the weight of the sub-pixel at the upper right corner is 2. When an image is applied to each sub-pixel, the value of the weight given by the filter characteristic becomes the count value of the sub-pixel. FIG. 7B shows a different display pattern of the image depending on the difference in the weight of the sub-pixel. In this case, if the weighted sub-pixels of the image are counted, 199 is obtained. This value is averaged by dividing by the sum of the filter values (in this case, 336) corresponding to the uniform averaging, and multiplying by the highest luminance to calculate the luminance of this pixel. The filters are shown in FIGS. 42 (a), (b), (c),
The filter shown in (d) is known.

Convolution Integral Method The convolution integral method is a method of determining the luminance of one pixel and also referring to the surrounding pixels. That is, it is considered that N ′ × N ′ pixels around one pixel for which anger is to be determined correspond to pixels of the uniform averaging method or the weighted averaging method. Figure 43 is 3
3 shows a convolution integration method with reference to a × 3 pixel. In this figure,
The pixel whose luminance is to be determined is denoted by 2901. The image continues to the lower right of the diagonal line, and the subpixels painted black are the subpixels to be counted. Each pixel is divided into 4 * 4. Therefore, in this case, a 12 * 12 filter is used. This method has the effect of removing high frequency components contained in the vector image.

On the other hand, with the spread of a publishing system using a personal computer, so-called DTP (desktop publishing), a system for printing vector images as handled by computer graphics has been widely used. A typical example is a system using Adobe Post Script. Post Script is a Page Description Language
Language: hereinafter referred to as PDL), which belongs to a language genre called “PDL”, and includes the text (character part), graphics, and their layout and appearance that are included in the contents of one document. This is a programming language for describing a form. In such a system, a vector font is used as a character font. Therefore, even if the character is scaled, the print quality can be remarkably improved as compared with a system using a bitmap font (for example, a conventional word processor or the like). There is an advantage that printing can be performed in a mixed manner.

However, the resolution of laser printers used in these systems is often at most 240 dpi to 400 dpi, and there is a problem that aliasing occurs due to the low resolution as in the case of computer graphics CRT display. Therefore, there is a need to improve the quality of a printed image by performing an anti-aliasing process even in printing using a laser printer.

[Problems to be solved by the invention]

However, in the conventional graphic processing device, N × N
When introducing an anti-aliasing processing method by sub-pixel division, for example, if N is increased, the calculation takes time. On the other hand, if it is too small, the effect cannot be expected much, and the processing time and the subjective image quality evaluation specifications Since an appropriate N is determined and used, there is a problem that a sufficient effect cannot always be obtained.

Further, according to the graphic processing apparatus to which the conventional uniform averaging method is applied, one type of subpixel shape (for example, a pixel is used as a subpixel shape used when calculating a gradation value (luminance value and density value)). (Shape divided into N * M), the gradation value obtained from the actual area and the gradation value obtained using the sub-pixel shape may be different depending on the inclination of the vector data. There is also a problem that the anti-aliasing processing is not sufficiently performed.

That is, when the sub-pixel shape decomposed into N * M is used, when the inclination of the vector data is an inclination close to vertical or horizontal, there is a high possibility that a gradation value different from the actual area ratio is calculated. For example, assuming that a sub-matrix (sub-pixel shape) divided into 3 * 3 is used, as shown in FIGS. 44 (a) and 44 (b), vector data passes with a nearly vertical gradient. In the case of the edge part pixel, the probability that the gradation value 1 and the gradation value 2 are calculated out of the ten gradations from the gradation value 0 to the gradation value 9 is small. on the other hand,
Since the probability that the gradation value 3, the gradation value 6, and the gradation value 9 are calculated becomes higher, the gradation value (the gradation value 4 in FIG. 4B) calculated from the actual area is calculated. There is a large difference from the gradation value calculated by the sub-pixel division (gradation value 6 in FIG. 3A), and the intended final output cannot be obtained.
The effect of the anti-aliasing process cannot be sufficiently exhibited.

Further, in the graphic processing apparatus to which the weighted averaging method and the convolution integration method are applied, compared with the uniform averaging method, a gradation value calculated from an actual area and a gradation value calculated by sub-pixel division are compared. Although the difference is small and the effect of the anti-aliasing processing is high, there is a problem that it takes time to calculate the area ratio and the processing speed is reduced.

In addition, according to the graphics processing apparatus to which the conventional anti-aliasing processing method is applied, even though the output device has been replaced by a laser printer that outputs an image from a CRT by an electrophotographic process, the brightness value of the CRT is simply changed to a value of the laser printer. Since the density value is diverted, there is a problem that the effect of the anti-aliasing process is not always sufficiently exhibited depending on the characteristics of the electrophotographic process.

For example, an anti-aliasing process is performed on a vector image as shown in FIG. 45 (a) to obtain a gradation value (expressed here as 10 gradations 0 to 9) shown in FIG. 45 (b). When this gradation value is displayed as a luminance value on a CRT, a smooth image close to a vector image can be obtained by the effect of the anti-aliasing process as shown in FIG. However, the tone value in FIG.
When the output of the laser beam is adjusted by the pulse width modulation method to form a latent image, the density is reduced at the left end (left edge) of the latent image, and conversely, at the right end ( A phenomenon occurs in which the density increases at the right edge), which causes a disadvantage that the effect of the anti-aliasing processing is impaired. This is because when a latent image is formed by the pulse width modulation method, a dot is formed by outputting a laser beam by a predetermined amount (predetermined pulse width) based on the gradation value with the left end of the pixel as a base point. Therefore, in the pulse width modulation method, at the left end of the latent image, a dot having a smaller gradation value is formed at a position farther from the position of the actual image portion, so that the gradation value obtained by the anti-aliasing process is obtained. Not only cannot the image of FIG. 1B be faithfully reproduced (see FIG. 1B), but also, on the contrary, the jaggedness is noticeable.

The present invention has been made in view of the above, and has as its first object to improve the effect of anti-aliasing processing.

A second object of the present invention is to obtain a gradation value that does not greatly differ from a gradation value obtained from an actual area ratio without lowering the processing speed.

A third object of the present invention is to prevent the effect of the anti-aliasing process from being impaired in consideration of the characteristics of the electrophotographic process.

Further, the present invention is intended to prevent the low-density dots from deteriorating the effect of the anti-aliasing process and causing aliasing without reducing the processing speed and by the characteristics of the pulse width modulation method. The purpose of.

Furthermore, a fifth object of the present invention is to prevent the occurrence of aliasing due to low-density dots without lowering the accuracy of the anti-aliasing processing.

[Means for solving the problem]

In order to achieve the first object, the present invention obtains a gradation value (density value) of an edge portion pixel of vector data by sub-pixel division, and outputs the gradation value to an output device capable of dot modulation. It is an object of the present invention to provide a graphic processing device provided with a sub-pixel changing means for changing a divided shape of a sub-pixel.

According to the present invention, in order to achieve the first object, a gradation value (density value) of an edge pixel of vector data is obtained by sub-pixel division, and the gradation value is output to an output device capable of dot modulation. The present invention provides a graphic processing apparatus having a sub-pixel varying unit that approximates vector data to a linear vector and varies a sub-pixel division size of an edge part pixel in accordance with an inclination of the linear vector. is there.

According to the present invention, in order to achieve the second object, a gradation value (density value) of an edge portion pixel of vector data is obtained by sub-pixel division, and the gradation value is output to an output device capable of dot modulation. In the output graphic processing device, an appropriate sub-pixel shape is selected from a plurality of sub-pixel shapes based on the inclination of the vector data and the presence / absence of an end point in the edge portion pixel, and sub-pixel division is performed. An object of the present invention is to provide a graphic processing device provided with pixel dividing means.

In order to achieve the third object, according to the present invention, a gradation value (density value) of an edge pixel of vector data is obtained by sub-pixel division, and the gradation value is converted to a pulse width modulation laser printer. Graphic processing apparatus comprising: a gradation value determining means for converting an area of a right portion when an edge portion pixel is divided into left and right into a gradation value with a higher contribution ratio than an area of a left portion. Is provided.

In order to achieve the fourth object, according to the present invention, a gradation value (density value) of a pixel at an edge portion of vector data is obtained by sub-pixel division, and the gradation value is converted into a pulse width modulated laser printer. In the graphic processing apparatus for outputting to a sub-pixel division area, a pixel is divided into a sub-pixel division area where sub-pixel division is performed and a sub-pixel division area where sub-pixel division is not performed. It is an object of the present invention to provide a graphic processing apparatus provided with a tone value determining means for determining a tone value based on the number of pixels.

In order to achieve the fifth object, the present invention obtains a gradation value (density value) of an edge portion pixel of vector data by sub-pixel division, and converts the gradation value to a pulse width modulation laser printer. The image processing unit which outputs the image data to the image unit which determines which of the upper, lower, left and right portions of the edge pixel is based on the inclination of the vector data crossing the edge pixel and the type of edge Determining means, an upper filter used when the image part to be filled is located above the edge part pixel, a lower filter used when the image part to be filled is located below the edge part pixel, the image to be filled The right filter used when the part is located to the right of the edge pixel, and the image part to be filled is located to the left of the edge pixel. Storage means storing the four weighting filters of the left filter used in the case of performing the processing, and the corresponding weighting filter is selected from the storage means based on the determination result of the image part determination means, and the gradation value of the edge part pixel is determined. It is intended to provide a graphic processing device provided with a gradation value determining means for determining.

[Action]

The graphic processing device according to the present invention changes the shape of the sub-pixel in the sub-pixel division to make the gradation value of each pixel an appropriate value.

In addition, the graphic processing device of the present invention uses filters having different weights in sub-pixel division to set the gradation value of each pixel to an appropriate value.

〔Example〕

Hereinafter, a graphic processing apparatus of the present invention will be described in detail in the order of Embodiment 1, Embodiment 2, Embodiment 3, Embodiment 4, and Embodiment 5 with reference to the drawings.

First Embodiment An image forming system in which the graphic processing apparatus of the present invention is incorporated as a PDL controller will be described as a first embodiment.

The image forming system according to the present embodiment uses a page description language (hereinafter, referred to as a PDL language) output from DTP (Desktop Publishing).
Is converted into an image through a PDL controller to form an image of image information.

As shown in FIG. 1, the image forming system receives a host computer 100 that creates a document described in a PDL language (a PostScript language is used in this embodiment), and is sent from the host computer 100 in page units. Black (BK), yellow (Y), magenta (M),
And PD to expand to cyan (C) multi-valued image data
L controller (graphic processing device of the present invention) 200, multi-valued color laser printer 300 for printing multi-valued image data output from PDL controller 200, PDL controller 200, and multi-valued color laser printer 300 And a system control unit 400 that controls the

FIG. 2 shows a configuration of the PDL controller 200. The PDL controller 200 receives the PDL language sent from the host computer 100, and performs storage control of the PDL language received by the receiving device 201 and execution of anti-aliasing processing and the like. CPU202 to do
And an internal system bus 203 and a RAM 2 for storing a PDL language to be transferred from the receiving device 201 via the internal system bus 203.
04 and RO containing anti-aliasing program etc.
M205 and anti-aliasing multi-valued YMC
And a page memory 206 for storing BK image data,
A transmitting device 207 for transferring the YMC and BK image data stored in the page memory 206 to the multi-valued color laser printer 300, and an I / O device 2 for transmitting and receiving to and from the system control unit 400
08 and a sub-pixel changing unit 209.

Here, the CPU 202 converts the PDL language received by the receiving device 201
According to the program stored in the ROM 205, the data is stored in the RAM 204 through the internal system bus 203. Thereafter, when the PDL language for one page is received and 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 multi-valued YMC and BK image data are stored in the plane of the page memory 206. The data is stored in the memory unit (the page memory 206 includes a Y, M, C, and BK plane memory unit and a feature information memory unit).

The data in the page memory 206 is
To the multi-valued color laser printer 300 via

3 (a) and 3 (b) show a part of the image information stored in the page memory 206 extracted by one pixel G. FIG. FIG. 7A shows a case where the pixel G is divided into 4 * 4 sub-pixels S1, and four out of the 16 sub-pixels S1 are painted out. FIG. 2B shows a case where the pixel G is divided into eight vertical pixels and two horizontal subpixels S2.
Three of the sixteen sub-pixels S2 are filled. At this time, the luminance of the pixel in FIG. 3A is 25%, and the luminance of the pixel in FIG. 3B is 18.75%. Further, since the actual area of the shaded portion is 12.5%, there is a case where even if the same number of sub-pixels is set to be different vertically and horizontally, the accuracy is higher. Therefore, as shown in FIG. 4, the straight line is divided into regions A, B, and C in accordance with the inclination with respect to the x-axis and the y-axis, and for each region, for example, as shown in FIG. A has 4 * 4 sub-pixels S1 ((a) in the figure), area B has 2 * 8 sub-pixels S3 ((b) in the figure), and area C has
Is associated with 8 * 2 sub-pixels S2 (FIG. 3 (c)). In this way, the accuracy of the anti-aliasing processing is improved.

Next, the operation of the PDL controller 200 configured as described above will be described in detail with reference to the flowchart of FIG.

First, as shown in FIG. 4 and FIG.
The coordinates of the end point and the data of the inclination that can be calculated from both points are stored in the RAM 204 as table data.

Then, the page memory 206, when the graphic data D ₀₀ as shown in Figure 7 is stored, and the position of the start line L = 0 graphic data D _00, the end line L = E position each graphic data D ₀₀ It is equal to the Y coordinate of point e ₀ (X ₀ , Y ₀ ) and point e ₂ (X ₂ , Y ₂ ). Therefore, it reads the Y coordinate of the starting L = 0 graphic data D ₀₀ (S601), performs a linear approximation of the curve-shape edge portion (S602). Straight line approximation refers to a process for allowing a curve RL to be represented by a set of straight lines such as a straight line DL, as shown in FIG. In this way, the coordinates of the start point and end point of the approximated straight line and the data of the inclination that can be calculated from both points are stored as table data (S603). When the processing of each line L is performed by the sub-pixel varying unit 209, the inclination of the approximate straight line is obtained from the table data and the table data stored in the RAM 204 in advance. Next, the area to which the obtained inclination belongs is determined (S60
4), the corresponding sub-pixel is determined, and the sub-pixel s1,
The sizes of s2 and s3 are determined (S605). Then, scan line conversion processing is performed on each of the sub-pixels s1, s2, and s3 according to the inclination of the approximate straight line (S606). After that, the luminance is calculated from the number of the filled sub-pixels s1, s2, and s3 (S6
07), and write as pixel luminance data (S608). This process is continued from L = 0 to L = E, and the process ends. (S609, S610).

As described above, in the present embodiment, the division size of the sub-pixel that divides each pixel of the approximation line is changed according to the inclination of the straight line approximation of the straight line of the image. , The sub-pixel size used for calculating the luminance of one pixel can be changed, and the anti-aliasing process can be performed more effectively than in the case of a fixed size.
In addition, it can be performed with high accuracy. Therefore, the quality of the formed image can be improved.

Embodiment 2 Hereinafter, an image forming system in which the graphic processing apparatus of the present invention is incorporated as a PDL controller will be described as Embodiment 2, and an outline of anti-aliasing processing, a block diagram of the image forming system, and a PDL controller (graphic processing apparatus of the present invention) ), The configuration and operation of the multi-level color laser printer, and the multi-level driving of the driver will be described in detail.

Overview of Anti-Aliasing Processing The graphic processing apparatus (hereinafter, referred to as a PDL controller) according to the second embodiment uses a sub-pixel shape when performing sub-pixel division based on the inclination of vector data crossing an edge pixel and the presence or absence of an end point. Is changed so that the gradation value obtained by the sub-pixel division does not largely deviate from the gradation value calculated from the actual area.

Hereinafter, the outline of the anti-aliasing processing in the graphic processing apparatus of the present embodiment will be described in detail with reference to FIGS. 9 (a) to 9 (f).

9A, 9B, and 9C show three sub-pixel shapes (hereinafter, referred to as sub-matrices) used in this embodiment, and FIG. 9A shows the inclination θ of the vector data.
Is a 1 * 9 sub-matrix used when tan θ> 9/2 (that is, 77.47 ° <θ <102.53 °). FIG. 3B shows that the inclination θ of the vector data is 2/9> tan θ <−2/9. (Ie 12.53
{>Θ> -12.53}), a 9 * 1 sub-matrix used when the inclination of vector data is other than the above-mentioned 3 * 3 sub-matrix.
In the case where the end point (the start point or the end point of the vector data) is present in the edge portion pixel, the gradient θ of the vector data cannot be determined unconditionally, and in this embodiment, the sub-matrix of FIG. .

For example, when the inclination θ of the vector data is tan θ> 9/2, in other words, when the inclination is close to vertical, as shown in FIG.
When the sub-matrix is divided, a gradation value of 4 is obtained. On the other hand, for the same edge portion pixel, the conventional method (3)
(* 3 sub-matrix), the gradation value is 6, as shown in FIG. 9 (e). Therefore, 1 * 9
The gradation value obtained using the sub-matrix is a value close to the actual gradation value (or the same value).

If there is an end point in the edge portion pixel, a gradation value is obtained using a 3 * 3 sub-matrix as shown in FIG. 9 (f).

These processes make a judgment using the value of the slope θ easily obtained from the vector data of the edge part pixel and the presence or absence of an end point, and the vector data determines which subpixel in the pixel the edge part passes through. Performs the same determination processing as in the prior art, so the processing speed is almost the same as in the conventional uniform averaging method. In other words, the processing speed is several steps faster than the weighted averaging method or the convolution integration method.

Block Diagram of Image Forming System The image forming system according to the present embodiment has a page description language (hereinafter referred to as a PDL language) output from DTP (Desktop Publishing).
Is converted into an image through a PDL controller to form an image of image information. Hereinafter, the configuration of the image forming system of this embodiment will be described with reference to FIG.

The image forming system performs an anti-aliasing process on a host computer 100 that creates a document described in a PDL language (a postscript language is used in this embodiment) and a PDL language sent from the host computer 100 in page units. Meanwhile, a PDL controller (graphic processing apparatus of the present invention) 200 for developing into multi-valued image data of black (BK), yellow (Y), magenta (M), and cyan (C) necessary for recording, and a PDL controller It comprises a multi-valued color laser printer 300 for printing multi-valued image data output by 200, a PDL controller 200, and a system control unit 400 for controlling the multi-valued color laser printer 300.

Configuration and Operation of PDL Controller (Graphic Processing Apparatus of the Present Invention) FIG. 11 shows the configuration of a PDL controller 200, and a receiving apparatus 201 for receiving a PDL language sent from the host computer 100 and a receiving apparatus 201 for receiving the PDL language. CPU 202 that performs storage control of the selected PDL language and execution of anti-aliasing processing, etc.
And an internal system bus 203 and a RAM 2 for storing a PDL language to be transferred from the receiving device 201 via the internal system bus 203.
04 and RO containing anti-aliasing program etc.
M205 and anti-aliasing multi-valued YMC
And a page memory 206 for storing BK image data,
A receiving device 207 for transferring the YMC and BK image data stored in the page memory 206 to the multi-valued color laser printer 300, and an I / O device 2 for transmitting and receiving to and from the system control unit 400
08.

Here, the CPU 202 converts the PDL language received by the receiving device 201
According to the program stored in the ROM 205, the data is stored in the RAM 204 through the internal system bus 203. Thereafter, when the PDL language for one page is received and 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 multi-valued YMC and BK image data are stored in the plane of the page memory 206. The data is stored in the memory unit (the page memory 206 includes a Y, M, C, and BK plane memory unit and a feature information memory unit).

The data in the page memory 206 is
To the multi-valued color laser printer 300 via

Hereinafter, the operation of the PDL controller 200 will be described with reference to FIGS. 12 (a) and 12 (b).

FIG. 12A shows a flowchart of a process performed by the CPU 202. As described above, the PDL controller 200 performs black (BK), yellow (Y), magenta (M), and cyan (C) while performing anti-aliasing processing on the PDL language sent from the host computer 100 in page units. ) To four color image images.

In the PDL language, both graphics and characters are described in vector data, and as indicated by the term "page language", the processing unit of image information is handled in page units. Further, one page is composed of at least one path in units of a path composed of one or a plurality of elements (graphic elements and character elements).

First, when the PDL language is input, it is determined whether or not the element is a curve vector. If the element is a curve vector, this is approximated to a straight line vector and registered in the work area as a straight line element (line). This is performed for all figures and character elements in one pass, and the registration of linear elements in the work area is performed for each pass (Process 1).

Then, the linear elements of the work area registered in the path unit are sorted by the starting y-coordinate of the straight line (process 2).

Next, in the process 3, while the y-coordinate is updated one by one, the filling process by the scanning line is performed. For example, twelfth
When performing the path filling process shown in FIG.
The elements of the sides crossing the scanning line yc to be processed (in this embodiment, a line having a thickness of one pixel is described as a scanning line, and a straight line having no thickness is described as a scanning line), real values of x coordinates across the scanning line yc (x ₁ shown in Figure 12 _{(b), x 2, x} 3, x 4) and AET (Active Edge Table:
Table for recording the x-coordinate of the edge part appearing on the scanning line). Here, since the order of the elements registered in the work area is the order registered in the process 1, the elements are not necessarily registered in the order of smaller x-coordinates crossing the scanning line yc. For example, in process 1,
If the linear elements passing through the scanning line yc and x ₃ of 12 Figure (b) it is processed first is, x ₃ is registered initially in AET as x-coordinate of the edge portions appearing on the scanning line yc . So, AET
After the registration, the elements on each side in the AET are sorted in ascending order of the x coordinate. Then, the first two elements of the AET are paired and the space between them is painted (specifically, for example, a painting process using a scan line formed by the scan line yc and the scan line yc + 1). The anti-aliasing process is realized by adjusting the density of the edge portion pixels according to the area ratio in the filling process. After that, the processed edge is removed from the AET, and the scan line is updated (y
The same processing is repeated until all the sides in the AET are processed, in other words, all the elements in one pass are processed.

The above-mentioned processing 1, processing 2, and processing 3 are executed for each path,
Repeat until all the passes for one page are completed.

Next, the anti-aliasing processing executed during the scan line filling processing in the above-described processing 3 will be described in detail with reference to the flowchart in FIG. 12 (c).

Here, for example, assuming that a rectangular ABCD as shown in FIG. 13 (a) is input in the processing 1 of FIG. 12 (a),
This figure has the following elements:

(A) Four line vectors of AB, BC, CD, and DA (represented by real numbers) (b) Color and luminance values inside the figure This figure is obtained by the above-described operation, as shown in FIG. It is divided into five linear vectors (real numbers) extending in the scanning direction. At this time, in the present embodiment, the following information is added to the start point and the end point of the five linear vectors.
(C) Starting point coordinate values (expressed as real numbers) of vector elements (starting point and end point of the linear vector) ((a) above) (d) Slope information of vector elements forming the starting point and end point of the linear vector (e) ) Characteristic information of the start point and end point of a straight line vector (right edge, left edge, vertex of figure, line of 1 dot or less, intersection of straight line, etc.) In the process of filling a scan line, when an edge pixel is detected, 12 The anti-aliasing process shown in the flowchart of FIG.

First, in the sub-pixel filling process, it is determined whether or not the end point of the vector data exists in the edge portion pixel. If the end point exists, the 3 * 3 sub-point shown in FIG. Using a matrix, one pixel is divided into sub-pixels, and a filled area is calculated for each sub-pixel. If there is no end point, the inclination θ of the vector data is determined. If θ is tan θ> 9/2, the 1 * 9 sub-matrix (see FIG. 9A) is used, and θ is 2/9> t
If anθ> −2/9, use a 9 * 1 sub-matrix (see FIG. 9 (b)); otherwise, use a 3 * 3 matrix to divide one pixel into sub-pixels, and Is calculated (S1201). This process is repeated for all vectors crossing the scanning line (S1202).

Next, in the density determination processing, the gradation value (density) of each pixel is calculated in order from the first pixel of the scanning line (S120).
3).

Subsequently, although not described in detail, the gradation value (density) of each color (four colors of BK, R, G, B) of the figure is calculated by the overwriting process (S120).
Four).

After that, the gradation value of each color is written to the page memory by the page memory drawing process (S1205).

Further, the processing from S1203 to S1205 is repeatedly executed for all pixels of one line (S1206).

The CPU 202 repeats the above processing up to the last pixel of the scanning line (y coordinate), and at the same time, updates the content of (c) with the information of (d). The gradation value k of the graphic in FIG. 13A obtained by the anti-aliasing processing in this manner becomes a value as shown in FIG.

The tone value k thus obtained is subjected to a predetermined YMC and BK conversion process (details are omitted, but in this embodiment, a YMC and BK conversion program is provided as software).
Thus, black (BK), yellow (Y), and black (BK),
The image data is developed into image images of four colors of magenta (M) and cyan (C) and stored as image data in the corresponding plane memory section of the page memory 206. FIGS. 15 (a), (b), (c) and (d) show the case where the information of the color and the luminance value is C: M: Y = 1: 0.5: 0.3 and the UCR is multiplied by 100%. Indicates the status.

First, the schematic configuration of the multi-value color laser printer 300 will be described with reference to the control block diagram shown in FIG.

The photoreceptor development processing unit 301 uniformly charges the surface of a photoreceptor drum described later, forms a latent image by exposing the charged surface with a laser beam, develops the latent image with toner, and transfers the latent image to recording paper. As will be described in detail later, a black developing / transferring unit 301bk for developing / transferring BK data, a cyan developing / transferring unit 301c for developing / transferring C data, and a cyan developing / transferring unit for developing / transferring M data. The image forming apparatus includes a developing / transferring unit 301m and a cyan developing / transferring unit 301y that develops and transfers Y data.

The laser drive processing unit 302 is the PDL controller described above.
A 5-bit data of Y, M, C, and BK (here, image density data) output from 200 is inputted, and a laser beam is output. Buffer memories 303y, 303m, 303c to be input, laser diodes 304y, 304m, 304c, 304bk to output laser beams corresponding to Y, M, C, BK, and laser diode 30
Drivers 305y, 3 that drive 4y, 304m, 304c, 304bk, respectively
05m, 305c, and 305bk.

The block development / transfer unit 301 of the photoconductor development processing unit 301
bk and laser drive processing unit 302 laser diode 304b
The combination with k and the driver 305bk is called a black recording unit BKU (see FIG. 17). Similarly, the cyan phenomenon
The combination of the transfer unit 301c, the laser diode 304c, the driver 305c, and the buffer memory 303c is used as a cyan recording unit.
CU (see Fig. 17), magenta phenomenon / transfer section 301m, laser diode 304m, driver 305m, and buffer memory
The magenta recording unit MU (see Fig. 17), yellow development / transfer unit 301y, laser diode 3
The combination of 04y, driver 305y, and buffer memory 303y is called a yellow recording unit YU (see FIG. 17). As shown in the drawing, these recording units are arranged in the order of the black recording unit BKU, the cyan recording unit CU, the magenta recording unit MU, and the yellow recording unit YU around the conveyance belt 306 for conveying the recording paper from the conveyance direction of the recording paper. Has been established.

According to the arrangement of each recording unit, the first exposure starts with the laser diode for black exposure.
304bk, laser diode 304 for yellow exposure
y will start the exposure last. Therefore, there is a time difference between the laser diodes in the order of the exposure start, and the laser drive processing unit 302 stores the above-mentioned three sets of buffer memories 303y, 303m, and so on in order to hold the recording data (output of the PDL controller 200) during the time difference. 303c is provided.

Next, the configuration of the multi-level color laser printer 300 will be specifically described with reference to FIG.

The multi-valued color laser printer 300 includes a transport belt 306 for transporting the recording paper, and a transport belt 306 as described above.
The recording units YU, MU, CU, and BKU conveyed around the paper, paper feed cassettes 307a and 307b containing recording paper, and paper feed rollers 308 that feed recording paper from the paper feed cassettes 307a and 307b, respectively.
a, 308b, a registration roller 309 for aligning the recording paper sent from the paper cassettes 307a, 307b, and a transfer belt 306 sequentially transporting the recording units BKU, CU, MU, and YU to transfer the transferred image. Fixing roller for fixing on recording paper
310, and a discharge roller 311 for discharging the recording paper to a predetermined discharge unit (not shown). Here, each of the recording units YU, MU, CU, and BKU is a photoconductor drum 312y, 312m, 312c, 312bk.
And chargers 313y, 313m, 313c, 313bk for uniformly charging the photosensitive drums 312y, 312m, 312c, 312bk, respectively, and a polygon mirror 314y for guiding a laser beam to the photosensitive drums 312y, 312m, 312c, 312bk. , 314m, 314c, 314bk and motor 315y, 3
15m, 315c, 315bk and photosensitive drums 312y, 312m, 312c, 312bk
Toner developing devices 316y, 316m, 316c, 316bk for developing the electrostatic latent images formed thereon using toners of respective colors
And a transfer charger 31 for transferring the developed toner image to recording paper.
7y, 317m, 317c, 317bk, and photoreceptor drums 312y, 312 after transfer
m, 312c, 312bk, and cleaning devices 318y, 318m, 318c, 318bk for removing toner remaining on the surfaces. Incidentally, 31
9y, 319m, 319c, and 319bk are photosensitive drums 312y and 312, respectively.
m, 312c, shows a CCD line sensor for reading a predetermined pattern provided on 312bk, the details are omitted,
Thus, the process state of the multi-level color laser printer 300 is detected.

The operation of the above configuration will be described by taking exposure, development, and transfer of the yellow recording unit YU as an example. FIGS. 18A and 18B show the configuration of the exposure system of the yellow recording unit YU. In the figure, a laser beam emitted from a laser diode 304y is reflected by a polygon mirror 314y, passes through an f-θ lens 302y, and further passes through a mirror 321.
The light is reflected by y and 322y, and is irradiated on the photosensitive drum 312y through the dustproof glass 323y. At this time, the laser beam is driven at a constant speed by the polygon mirror 314y by the motor 315y.
It moves in the direction (main scanning direction) along the axis of the photosensitive drum 312y. In this embodiment, the photo sensor 324y is provided with the laser beam at the non-exposure position in order to detect the base point for tracking the scanning position of the main scanning. Since the laser diode 304y is energized to emit light based on the recording data (5-bit data from the PDL controller 200), multi-level exposure corresponding to the recording data is performed on the surface of the photosensitive drum 304y. As described above, the surface of the photosensitive drum 304y is uniformly charged by the charger 313y in advance, and a corresponding electrostatic latent image of a document image is formed by the above exposure. The electrostatic latent image is developed by the yellow developing device 316y to become a yellow toner image. This toner image, as shown in FIG. 17,
The recording paper fed from the cassette 307a (or 307b) by the paper feed roller 308a (or 308b) is synchronized with the toner image formation of the black recording unit BKU by the registration roller 309, and is conveyed by the conveyance belt 306. Transcribed.

The other recording units BKU, CU, and MU perform the same operation with the same configuration, but the black recording unit BKU includes a black toner developing device 316bk to form and transfer a black toner image, and the cyan recording unit CU. Is provided with a cyan toner developing device 316c and forms and transfers a cyan toner image. The magenta recording unit MU is provided with a magenta toner developing device 316m and forms and transfers a magenta toner image.

The driver 305y, 305m, 305c, 305bk is a multi-value driver of the image processing apparatus 400.
Corresponding laser diodes 304y, 304m, 304c, 304bk based on 5-bit data of Y, M, C, BK sent from
Is controlled to perform multi-value driving, and a pulse width modulation method is used as the driving method.

Hereinafter, the multi-value driving by the pulse width modulation method applied in this embodiment will be described in detail with reference to FIGS. 19 (a), (b), (c) and (d). Drivers 305y, 305m, 305c, 305
bk and the laser diodes 304y, 304m, 304c, and 304bk have the same configuration, so that the driver 30
A description will be given using 5y and the laser diode 304y as examples.

The driver 305y turns on / off the laser diode 304y as shown in FIG.
ff Circuit 350 and 5-bit image density data (here, Y
A pulse width modulation circuit 351 for modulating the pulse width of the LD driver clock based on the data
A constant current circuit 352 for supplying a current (LD drive current) Id for driving 04y to the laser diode on / off circuit 350.

FIG. 19 (b) shows a configuration of the pulse width modulation circuit 351.
FIG. 19 (c) shows the timing chart. In this circuit, 5-bit data D0, D1, D2, D3, and D4 are input as image density data, and 10 levels including 0 (off) are selected by the D latch 351a. D0 indicates on / off of the laser beam, and when 0, the laser beam is off, 1
It is on when

Furthermore, only when the laser beam is on, D1, D2, D3, D4
A bit is used to select nine pulse widths. Hereinafter, nine adjustments of the pulse width will be described.

First, the LD drive clock is supplied to the delay elements 351b, 351c,
Four kinds of signals of C1, C2, C3 and C4 are generated through 351d and 351e. Next, A1 is calculated by the LD drive clock and NAND 351i of C1.
And the LD drive clock is passed through the AND351m to obtain P1 of about 1/9 duty. Similarly, about 2/9, about LD drive clock and C2, C3, C4 signals
Signals P2, P3, P4 of 3/9, about 4/9 duty are obtained. Further, the signal P6 of about 11/18 duty is obtained by the OR drive 351q of the LD drive clock and C1. LD drive clock and C in the same way
Signals P7, P8 and P9 of about 13/18, about 15/18 and about 17/18 duty are obtained from the signals of 2, C3 and C4. On the other hand, LD drive clock and C2
OR351f gives about 90% duty P3. On the other hand, LD
The drive clock itself is about 50% duty P5.
P1, P2, P3, P4, P5, P6, P7, P8, and P9 are input to the data selector 351g, and one of them is selected based on the image density data D1, D2, D3, and D4. Then, D0 is set to o by AND351h.
Pn (n is 0 to 3) only when n is LD after pulse width modulation
Output as drive clock V.

Next, referring to FIG. 19 (d), a laser diode
The specific circuit configuration of the on / off circuit 350 and the constant current circuit 352 is shown. Laser diode on / off circuit 350 has TTL inverters 353 and 354, differential switching circuits 355 and 356 that perform on / off torque operation, and when VG1> VG2, differential switching circuit 355 is on and differential switching circuit 356 is o
ff, when VG1 <VG2, the differential switching circuit 355 is turned off,
V that satisfies the condition that the differential switching circuit 356 turns on
It comprises resistors R ₂ and R ₃ forming a voltage dividing circuit for generating G2. Therefore, when the LD drive clock is on, the output of the inverter 354 generates VG1 and satisfies the condition (VG1> VG2), the differential switching circuit 355 is on, the differential switching circuit 356 is off, and the laser O diode 304
n. Conversely, when the LD drive clock is off,
Since there is no output of the inverter 354, the above condition (VG1 <VG
2) is satisfied, the differential switching circuit 355 is off, the differential switching circuit 356 is on, and the laser diode 3
Turn off 04y.

Constant current circuit 352 is for supplying the current of the laser diode 304y to the laser diode on / off circuit 350 as described above, and has a transistor 360, resistors R _4, R ₅ Prefecture.

The laser beam from the laser diode 304y forms a latent image as shown in FIG. 20 on the photosensitive drum 312y based on levels 0 to 9 (corresponding to gradation values 0 to 9) (however, Level 0 is not shown to indicate no dot).

In the graphic processing device according to the second embodiment, the above-described configuration and operation allow the rectangular ABCD shown in FIG.
Finally, the toner image shown in FIG. 21 is formed on the recording paper.

Third Embodiment Hereinafter, an outline of an anti-aliasing process will be described using an image forming system in which a graphic processing apparatus of the present invention is incorporated as a PDL controller as a third embodiment. The other configuration is the same as that of the second embodiment, and the description of the configuration and operation is omitted.

In the graphic processing device (hereinafter, referred to as a PDL controller) according to the third embodiment, in the edge portion pixels of the final image output from the laser printer, the left edge pixels are formed thin and the right edge pixels are formed dark. When the gradation value (density value) is determined in advance in consideration of the characteristics of the electrophotographic process, the area of the right part when the edge part pixel is divided into the left and right is higher than the area of the left part. Is used to convert to a gradation value.

Hereinafter, the outline of the anti-aliasing processing in the graphic processing device of the third embodiment will be described in detail with reference to FIGS. 22 (a) to 22 (c).

In the third embodiment, in order to convert the area of the right part when the edge part pixel is divided into left and right into a gray scale value with a higher contribution ratio than the area of the left part, when comparing adjacent sub-pixels, the area of the right part is always A sub-pixel divided by a predetermined sub-pixel division ratio set so as to reduce the sub-pixel is used. Specifically, as shown in FIG. 22 (a), the horizontal division ratio when dividing a pixel into sub-pixels is
The pixels are divided so as to have a 3: 2: 1 relationship from the left side of the pixel.
In this embodiment, 3 * 3 sub-pixel division will be described as an example. However, the present invention is not particularly limited to this and can be applied to all sub-pixel divisions. Also,
The horizontal division ratio of the rust pixel is not particularly limited.

FIG. 22 (a) shows a case where 3 * 3 sub-pixel division is performed, in other words, the output device (here, a laser printer) should be filled when the number of gradations is 10 (0 to 9). The case where the area (the area of the image portion) is converted into a gradation value is shown. The weights of these sub-pixels are uniform, and all "1" s are assigned irrespective of the size of the sub-pixel, as shown in FIG. Therefore, when the left portion of the vector image is drawn (that is, when the edge pixel is the left edge portion), the possibility that the subpixel intersects with the image portion on the right portion of the pixel increases, so that the left edge There is a tendency for the density of the partial pixels to increase. On the other hand, when the right portion of the vector image is drawn (that is, when the edge pixel is the right edge), the possibility that the subpixels intersect the image portion on the left portion of the pixel is reduced. The density of the pixel tends to decrease.

For example, as shown in FIG. 22 (b), when the vector image covers the edge part pixel, the number of sub-pixels intersecting the image part is three, so that 3/9 gradation (gradation value 3) Becomes On the other hand, conventional 3 * 3 with horizontal split ratio of 1: 1: 1
Similarly, using the sub-pixel division to obtain the gradation of the edge portion pixel on which the vector image is applied, the number of sub-pixels intersecting the image portion is two, so that the 2/9 gradation (gradation value 2) is obtained. Become.

Although the description is omitted, when the image portion is on the left side of the edge part pixel, the gradation value is smaller in the sub-pixel division of FIG. It tends to fall.

Therefore, by using the sub-pixel division shown in FIG. 22 (a), the area of the right side when the edge part pixel is divided into left and right is converted into a gradation value with a higher contribution ratio than the area of the left side. be able to.

In addition, by performing sub-pixel division with a different horizontal division ratio, weighting is performed to convert the area of the right part into a gradation value with a higher contribution ratio than the area of the left part when the edge part pixel is divided into left and right. Instead, the gradation value can be determined at the same high speed as the conventional uniform averaging method.

As a method of converting the area of the right part when the edge part pixel is divided into right and left into a gradation value with a higher contribution ratio than the area of the left part, a weighting filter in which the weight of the subpixel on the right side of the edge part pixel is increased is used. It is also possible to determine the gradation value by using the weighted averaging method. For example, as shown in FIG. 22 (d), a pixel is divided into sub-pixels with a horizontal division number of 6 and a vertical division number of 3, and a tone value is obtained using a weighted filter as shown. The same effect (3/9 gradation (gradation value 3)) as in FIG. However, in this case, since the weighting multiplication processing is performed, the processing speed becomes slower than the method of performing subpixel division in which the horizontal division ratio is changed as shown in FIG.

Here, for example, a pentagon AB as shown in FIG.
Assuming a CDE is entered, this figure has the following elements:

(A) Five line vectors of AB, BC, CD, DE, and EA (representation of real numbers) (b) Color and luminance value inside the figure This figure is obtained by the above-described operation as shown in FIG. 23 (b). , Are divided into seven linear vectors (real numbers) extending in the main scanning direction. At this time, in the present embodiment, the following information is added to the start and end points of the seven linear vectors.
(C) Starting point coordinate values (expressed as real numbers) of vector elements (starting point and end point of the linear vector) ((a) above) (d) Slope information of vector elements forming the starting point and end point of the linear vector (e) ) Characteristic information of the start point and end point of the straight line vector (right edge, left edge, vertex of figure, line of 1 dot or less, intersection of straight line, etc.) Next, referring to the flowchart of FIG. The anti-aliasing processing in the processing will be described. As shown in FIGS. 22 (a) to 22 (c), in the present invention, the area of the right part when the edge part pixel is divided into left and right is converted into a gradation value with a higher contribution ratio than the area of the left part. .

First, in the sub-pixel filling process, one pixel is divided into 3 * 3 sub-pixels at the horizontal division ratio shown in FIG. 22A, and a filling region is calculated for each sub-pixel (S2401). This process is repeated for all vectors crossing the scanning line (S2402).

Next, the gradation value (density) of each pixel is calculated using a filter of the uniform averaging method (anti-aliasing method) in order from the first pixel of the target scanning line (S2).
403).

Subsequently, as described in detail, the gradation value (density) of each color (four colors of BK, R, G, B) of the figure is calculated by the overwriting process (S240).
Four).

After that, the gradation value of each color is written to the page memory by the page memory drawing process (S2405).

Further, the processing from S2403 to S2405 is repeatedly executed for all pixels of one line (S2406).

The CPU 202 repeats the above processing up to the last pixel of the scanning line (y coordinate), and at the same time, updates the content of (c) with the information of (d). The tone value k of the graphic in FIG. 23 (a) obtained by the anti-aliasing processing in this manner is a value as shown in FIG.

The tone value k thus obtained is subjected to a predetermined YMC and BK conversion process (details are omitted, but in this embodiment, a YMC and BK conversion program is provided as software).
Thus, black (BK), yellow (Y), and black (BK),
The image data is developed into image images of four colors of magenta (M) and cyan (C) and stored as image data in the corresponding plane memory section of the page memory 206. FIGS. 26 (a), (b), (c) and (d) show the case where the information of the color and the luminance value is C: M: Y = 1: 0.5: 0.3 and the UCR is multiplied by 100%. Indicates the status.

In the graphic processing apparatus according to the third embodiment, the toner image shown in FIG. 27 is finally formed on the recording paper for the pentagon ABCDE shown in FIG. FIG. 28 shows a pentagonal ABCDE toner image when subpixel division is performed with a horizontal division ratio of 1: 1: 1.
As is clear from the comparison between FIG. 28 (toner image according to the present invention) and FIG. 28, a toner image can be formed without impairing the effect of the anti-aliasing processing. In practice, the low density edge portion of the toner image is not reliably reproduced due to the characteristics (defects) of the electrophotographic process.
In the image after the transfer, the effect of the third embodiment becomes more apparent.

In the third embodiment, the area of the right part when the edge pixel is divided into the left and right parts by the sub-pixel division with the horizontal division ratio of 3: 2: 1 is converted into the gradation value with a higher contribution ratio than the area of the left part. Although the conversion is performed, it goes without saying that the same effect can be obtained by using a weighting filter as shown in FIG. 22 (d).

Embodiment 4 Hereinafter, an outline of an anti-aliasing process will be described using an image forming system in which the graphic processing apparatus of the present invention is incorporated as a PDL controller as Embodiment 4. The other configuration is the same as that of the second embodiment, and the description of the configuration and operation is omitted.

The graphic processing apparatus (hereinafter, referred to as a PDL controller) according to the fourth embodiment divides one pixel into a sub-pixel divided area in which sub-pixel division is performed and an area outside the sub-pixel divided area in which sub-pixel division is not performed. By determining the gradation value based on the number of sub-pixels in the image portion of the sub-pixel division region, the effect of the anti-aliasing process may be impaired due to the characteristics of the pulse width modulation method, which may cause aliasing. It is possible to set the gradation value of the edge portion pixel having the color "0" to "0".

Hereinafter, the outline of the anti-aliasing processing in the graphic processing device of the fourth embodiment will be described in detail with reference to FIGS. 29 (a) to 29 (e).

In the fourth embodiment, as shown in FIG. 29 (a), the left part of a pixel (pixel to be subjected to anti-aliasing processing) is set as a sub-pixel division area, and the right part is set as outside the sub-pixel division area. Further, the sub-pixel division region is divided into 3 * 3 sub-pixels.

Next, referring to FIGS. 29 (b) to 29 (e), a method of obtaining a gradation value according to the present invention will be described in comparison with a conventional method (method by 3 * 3 sub-pixel division). As shown in FIG. 7B, when the image portion covers only the sub-pixel divided region of the pixel, in other words, when the image portion does not cover the sub-pixel, the number of sub-pixels to be filled is 0. / 9, the gradation value is “0”. On the other hand, in the conventional 3 * 3 sub-pixel division, the number of sub-pixels to be filled is 1/9, as shown in FIG. In this case, since the image portion is almost at the edge of the pixel, if the dot is formed by the pulse width modulation method, the effect of the anti-aliasing process will be impaired apart from the image portion.

Also, as shown in FIG. 3D, when the image portion covers the sub-pixel division area, the number of sub-pixels to be filled is 2/9, and the gradation value is “2”. . On the other hand, in the conventional 3 * 3 subpixel division, the number of subpixels to be filled is 3/9 as shown in FIG. in this case,
Although the gradation value is determined to be smaller than the conventional method, when the pixel at the left edge is viewed in the sub-scanning direction,
Since all pixels are similarly assigned smaller gradation values, the effect of the anti-aliasing process is not impaired.

Furthermore, as is clear from the above description, since a weighting filter is not used, there is no need to perform a weighting multiplication process, and the gradation value can be obtained at a processing speed similar to that of a normal uniform averaging method.

Next, the anti-aliasing process in the scan line filling process will be described with reference to the flowchart in FIG. As shown in FIGS. 29 (a) to 29 (e), in the present invention, the area of the right side when the edge part pixel is divided into left and right is converted into a gradation value with a higher contribution ratio than the area of the left side. .

First, in the sub-pixel filling process, as shown in FIG. 29A, one pixel is divided into a sub-pixel divided region and a sub-pixel divided region, and further, the sub-pixel divided region is divided into 3 * 3 sub-pixels. Then, a painted area is calculated for each sub-pixel (S3001). This process is repeated for all vectors crossing the scanning line (S3002).

Next, the gradation value (density) of each pixel is calculated using a filter of the uniform averaging method (anti-aliasing processing method) in order from the first pixel of the target scanning line (S3).
003).

Subsequently, although not described in detail, the gradation value (density) of each color (four colors of BK, R, G, and B) of the figure is calculated by the overwriting process (S300).
Four).

After that, the gradation value of each color is written in the page memory by the page memory drawing process (S3005).

Further, the processing from S3003 to S3005 is repeatedly executed for all pixels of one line (S3006).

The CPU 202 repeats the above processing up to the last pixel of the scanning line (y coordinate), and updates the contents of (c) (see Example 3) with the information of (d) (see Example 3) in FIG. . By the anti-aliasing processing in this way, for example, the gradation value k of the figure in FIG. 23 (a) becomes a value as shown in FIG.

The tone value k thus obtained is subjected to a predetermined YMC and BK conversion process (details are omitted, but in this embodiment, a YMC and BK conversion program is provided as software).
Thus, black (BK), yellow (Y), and black (BK),
The image data is developed into image images of four colors of magenta (M) and cyan (C) and stored as image data in the corresponding plane memory section of the page memory 206. FIGS. 32 (a), (b), (c) and (d) show the case where the information of the color and the luminance value is C: M: Y = 1: 0.5: 0.3 and the UCR is multiplied by 100%. Indicates the status.

In the graphic processing apparatus according to the fourth embodiment, the toner image shown in FIG. 33 is finally formed on the recording paper with respect to the pentagon ABCDE shown in FIG. As is apparent from comparison with the conventional 3 * 3 sub-pixel division shown in FIG. 28, a toner image can be formed without impairing the effect of the anti-aliasing processing.

In the fourth embodiment, the sub-pixel division area is set to 3 * 3
Although the image is divided into sub-pixels, the present invention is not limited to this. Further, the ratio outside the sub-pixel division region may be increased.

Embodiment 5 Hereinafter, an outline of an anti-aliasing process will be described with an image forming system in which the graphic processing apparatus of the present invention is incorporated as a PDL controller as a fifth embodiment. The other configuration is the same as that of the second embodiment, and the description of the configuration and operation is omitted.

The graphic processing apparatus (hereinafter referred to as a PDL controller) according to the fifth embodiment is configured such that an image portion to be filled is positioned above, below, left, and right of the edge pixel based on the inclination of the vector data crossing the edge pixel and the type of edge. Which part is determined, based on the determination result, select a corresponding weighting filter from a predetermined weighting filter,
The tone value of the edge part pixel is determined. In other words, by selecting the weighting filter to be used from the inclination of the vector data and the direction of the filled area, and determining the gradation value using the most appropriate weighting filter for the upper, lower, left and right edge pixels, A print image having an appropriate density is obtained at the time of final output. In particular, a pixel generated at the left edge (an edge portion pixel in which an image portion to be filled is located on the right side of the pixel) due to the characteristics of the pulse width modulation method. This is to prevent the occurrence of aliases due to low density dots.

Hereinafter, the outline of the anti-aliasing processing in the graphic processing device of the fifth embodiment will be described in detail with reference to FIGS. 34 (a) to (f).

In the fifth embodiment, the tone value of the edge part pixel is obtained by using four weighting filters having different weight values of the weighted averaging method in a 4 * 4 filter shape.
Multilevel color laser with pulse width modulation method with gradation
In order to output to the printer 300, it is converted into 10 gradations to obtain a final gradation value.

FIGS. 34 (a), (b), (c) and (d) show four weighting filters used in the present embodiment.
A right edge filter used when the image portion to be filled is located on the left side of the edge portion pixel, and FIG. 3B shows a left edge filter used when the image portion to be filled is located on the right side of the edge portion pixel. FIG. 3C is an upper edge filter used when the image portion to be filled is located below the edge portion pixels, and FIG. 4D is a filter for the upper edge portion where the image portion to be filled is an edge portion pixel. If it is located above the lower edge, it is the lower edge filter to be used. Note that the weighting values of these filters are not particularly limited to this, and the final printed image is less jagged in consideration of the number of gradations and dot shapes of a laser printer serving as an output device. It should be set as follows.

FIG. 34 (e) shows an image portion which determines which of the upper, lower, left and right portions of the edge pixel is to be filled based on the inclination of the vector data crossing the edge pixel and the type of edge. 9 shows an example of determination.
Here, for example, an edge pixel having a slope α of vector data of π / 2 and an edge type of a right edge portion is determined to be filled on the left side of the edge pixel, and a right edge filter is applied as shown in the drawing. Selected as filter to use.

In the fifth embodiment, the image portion to be filled is determined vertically or horizontally based on whether the gradient α of the vector data is equal to or larger than π / 4 (or −π / 4). Π / 4 (or −π /
It is not limited to 4).

Next, a specific example of using a filter will be described with reference to FIG. 34 (f).

Pixel G _1, as is clear from the illustration, the inclination alpha is 0 ≦ alpha
If <π / 4, the edge type is the left edge, so it can be determined that the lower side of the edge part pixel is to be painted. Therefore, when the tone value is obtained using the upper edge filter, the tone value is 4 (4/19).

Pixel G ₂ is the inclination α is greater than [pi / 4, since the type of edge is a left edge, it can be determined that fill the right edge pixel. Accordingly, when the tone value is obtained using the left edge filter, the tone value is 0 (0/19).

Pixel G ₃ are, the inclination α is less than - [pi] / 4, since the type of edge is a right edge, it can be determined that fill the left edge pixel. Therefore, when the tone value is obtained using the right edge filter, the tone value is 6 (6/16).

Pixel G ₄ are in the inclination alpha is 0 ≦ α <π / 4, since the type of edge is a right edge, it can be determined that fill the upper edge portion pixel. Therefore, when the gradation value is obtained using the lower edge filter, the gradation value is 0 (0/20).

Next, the anti-aliasing processing in the scan line filling processing will be described with reference to the flowchart in FIG.

First, in the sub-pixel filling process, one pixel is divided into 4 * 4 sub-pixels, and a filling region is calculated for each sub-pixel (S3501). This process is repeated for all vectors crossing the scanning line (S350
2).

Next, in the density determination processing, as shown in FIG. 34 (e), the inclination of the vector data crossing the edge portion pixel,
Further, based on the type of the edge, it is determined whether the image portion to be filled is located above, below, left or right of the edge portion pixel, a corresponding filter is selected, and a target scanning line is determined by the weighted averaging method. The tone value (density) of each pixel is calculated in order from the first pixel (S3503).

Next, although not described in detail, the gradation value (density) of each color (four colors of BK, R, G, and B) of the figure is calculated by the overwriting process (S350).
Four).

After that, the gradation value of each color in the page memory drawing process is written to the page memory (S3505).

Further, the processing from S3503 to S3505 is repeatedly executed for all pixels for one line (S3506).

The CPU 202 repeats the above processing up to the last pixel of the scanning line (y coordinate), and at the same time, updates the contents of (c) (see Embodiment 3) with the information of (d) (see Embodiment 3). The tone value k of the graphic in FIG. 23 (a) obtained by the anti-aliasing processing in this manner is a value as shown in FIG.

The tone value k thus obtained is subjected to a predetermined YMC and BK conversion process (details are omitted, but in this embodiment, a YMC and BK conversion program is provided as software).
Thus, black (BK), yellow (Y), and black (BK),
The image data is developed into image images of four colors of magenta (M) and cyan (C) and stored as image data in the corresponding plane memory section of the page memory 206. FIGS. 37 (a), (b), (c) and (d) show the case where the information of the color and the luminance value is C: M: Y = 1: 0.5: 0.3 and the UCR is multiplied by 100%. Indicates the status.

In the graphic processing apparatus according to the fifth embodiment, the toner image shown in FIG. 38 is finally formed on the recording paper with respect to the pentagon ABCDE shown in FIG. As shown, a toner image can be formed without impairing the effect of the anti-aliasing process.

〔The invention's effect〕

As described above, the graphic processing apparatus of the present invention obtains a gradation value (density value) of an edge portion pixel of vector data by sub-pixel division, and outputs the gradation value to an output device capable of dot modulation. Since the graphic processing apparatus includes the sub-pixel changing unit that changes the divided shape of the sub-pixel, the effect of the anti-aliasing processing can be improved.

Further, the graphic processing apparatus of the present invention obtains a gradation value (density value) of an edge pixel of vector data by sub-pixel division, and outputs the gradation value to an output device capable of dot modulation. The sub-pixel changing means for approximating the vector data to a linear vector and changing the sub-pixel division size of the edge part pixel according to the inclination of the linear vector is provided, so that the effect of the anti-aliasing process can be improved.

Further, the graphic processing apparatus of the present invention obtains a gradation value (density value) of an edge pixel of vector data by sub-pixel division, and outputs the gradation value to an output device capable of dot modulation. , The slope of the vector data,
And a sub-pixel dividing unit that selects an appropriate sub-pixel shape from a plurality of sub-pixel shapes based on the presence or absence of an end point in the edge portion pixel and performs sub-pixel division, thereby reducing the processing speed. Without this, it is possible to obtain a gradation value having a value that does not greatly differ from the gradation value obtained from the actual area ratio.

Further, the graphic processing apparatus of the present invention obtains a gradation value (density value) of an edge pixel of vector data by sub-pixel division, and outputs the gradation value to a pulse width modulation type laser printer. In the above, since there is provided a gradation value determining means for converting the area of the right part when the edge part pixel is divided into right and left into a gradation value with a higher contribution ratio than the area of the left part, the characteristics of the electrophotographic process are taken into consideration. Thus, the effect of the anti-aliasing processing can be prevented from being impaired.

Further, the graphic processing apparatus of the present invention obtains a gradation value (density value) of a pixel at an edge portion of vector data by sub-pixel division, and outputs the gradation value to a pulse width modulation type laser printer. In the device, the pixels are divided into a sub-pixel division region where sub-pixel division is performed and a sub-pixel division region where sub-pixel division is not performed, and based on the number of sub-pixels covered by the image portion of the sub-pixel division region. , Because of the provision of the tone value determining means for determining the tone value, the low-density dots impair the effect of the anti-aliasing process due to the characteristics of the pulse width modulation method without lowering the processing speed and causing aliasing. Can be avoided.

Further, the graphic processing apparatus of the present invention obtains a gradation value (density value) of an edge pixel of vector data by sub-pixel division, and outputs the gradation value to a pulse width modulation type laser printer. In the above, based on the inclination of the vector data traversing the edge portion pixel and the type of edge, an image portion determining means for determining whether the image portion to be filled is located above, below, left or right of the edge portion pixel, and to be filled The upper filter used when the image part is located above the edge pixel, the lower filter used when the image part to be filled is located below the edge pixel, and the image part to be filled is the edge pixel Right filter used when located on the right,
And a storage means for storing four weighting filters of a left filter used when the image portion to be filled is located on the left side of the edge portion pixel, and a corresponding weighting from the storage means based on the determination result of the image portion determination means. Since a tone value determining means for selecting a filter and determining a tone value of an edge portion pixel is provided, it is possible to avoid the occurrence of aliasing due to low-density dots without lowering the accuracy of anti-aliasing processing.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the configuration of an image forming system according to the first embodiment, FIG. 2 is an explanatory diagram showing the configuration of a PDL controller according to the first embodiment, and FIG. 3 (a), (b), FIG. 5 (a), 5 (b) and 5 (c) are explanatory diagrams each showing the principle of the first embodiment, FIG. 6 is a flowchart showing the operation of the first embodiment,
7 and 8 are explanatory diagrams each showing the operation of the first embodiment,
9 (a) to 9 (f) are explanatory diagrams showing an outline of an anti-aliasing process in the graphic processing device according to the second embodiment.
FIG. 3 is an explanatory diagram illustrating a configuration of an image forming system according to a second embodiment.
FIG. 11 shows a PDL controller (graphic processing device of the second embodiment).
FIG. 12 (a) is a flowchart showing the operation of the PDL controller, FIG. 12 (b) is an explanatory diagram showing a path filling process, and FIG. 12 (c) shows an anti-aliasing process. Flow chart, FIG. 13 (a),
(B) is an explanatory view showing a linear vector division of a figure, FIG. 14 is an explanatory view showing a gradation value after performing anti-aliasing processing, and FIGS. 15 (a), (b), (c) and (d). ) Is an explanatory diagram showing YMC and BK image data stored in the plane memory section of the page memory, FIG. 16 is a control block diagram showing a multi-valued color laser printer, and FIG. 17 is a multi-valued color laser printer FIGS. 18 (a) and (b) are explanatory diagrams showing the configuration of the exposure system of the yellow recording unit, and FIGS. 19 (a), (b), (c) and (d).
Is an explanatory diagram showing multi-level driving by pulse width modulation, FIG. 20 is an explanatory diagram showing the state of a latent image according to the level of pulse width modulation,
FIG. 21 is an explanatory view showing the final toner image of the square ABCD shown in FIG. 13 (a), and FIGS. 22 (a), (b), (c),
FIG. 23D is an explanatory diagram showing an outline of the anti-aliasing process in the graphic processing device according to the third embodiment.
FIG. 24 (b) is an explanatory diagram showing a linear vector division of a figure, FIG. 24 is a flowchart showing an anti-aliasing process according to the third embodiment, and FIG. 25 is a description showing gradation values after the anti-aliasing process in the third embodiment is performed. Fig. 26 (a),
(B), (c), and (d) are explanatory diagrams showing YMC and BK image data stored in the plane memory unit of the page memory according to the third embodiment. FIG. 27 is a pentagon shown in FIG. FIG. 28 is an explanatory diagram showing a final toner image of ABCDE, FIG. 28 is an explanatory diagram showing a conventional pentagonal ABCDE toner image by sub-pixel division, and FIGS. 29 (a), (b), (c), and FIG.
(D) and (e) are explanatory diagrams showing an outline of the anti-aliasing processing in the graphic processing apparatus of the fourth embodiment, FIG. 30 is a flowchart showing the anti-aliasing processing of the fourth embodiment, and FIG. FIG. 32 (a) is an explanatory diagram showing the gradation values after the aliasing process is performed.
(B), (c), and (d) are explanatory diagrams showing YMC and BK image data stored in the plane memory unit of the page memory in the fourth embodiment, and FIG. 33 is a pentagon shown in FIG. FIG. 34 (a), (b), (c), (d), (e), and (f) show the final toner image of ABCDE. FIG. 35 is a flowchart showing the anti-aliasing processing of the fifth embodiment, FIG. 36 is an explanatory view showing the gradation values after the anti-aliasing processing is performed in the fifth embodiment, and FIG. ), (B), (c), (d)
FIG. 9 is an explanatory diagram showing YMC and BK image data stored in the plane memory unit of the page memory in the fifth embodiment.
FIG. 8 is an explanatory view showing a final toner image of the pentagonal ABCDE shown in FIG. 23 (a), FIGS. 39 (a) and (b) are explanatory views showing a conventional anti-aliasing process, and FIG. 40 ( a),
(B) is an explanatory diagram showing an anti-aliasing process by a uniform averaging method, and FIGS. 41 (a) and (b) are explanatory diagrams showing an anti-aliasing process by a weighted averaging method;
Figures (a), (b), (c), and (d) are explanatory diagrams showing examples of filters used for the weighted averaging method.
FIG. 44 (a), (b), and FIG. 45 (a), (b),
(C), (d) is an explanatory view showing a problem of the conventional anti-aliasing processing. EXPLANATION OF SYMBOLS 100: Host computer 200: PDL controller 201: Receiving device, 202: CPU 203: Internal system bus 204: RAM, 205: ROM 206: Page memory, 207: Transmitting device 208 …… I / O device 209 …… Sub-pixel variable unit 300 …… Multi-valued color laser printer 400 …… System control

 ──────────────────────────────────────────────────続 き Continuation of the front page (31) Priority claim number Japanese Patent Application No. 2-202190 (32) Priority date Hei 2 (1990) July 30 (33) Priority claim country Japan (JP) (31) Priority Claim number Japanese Patent Application No. 2-202191 (32) Priority date Hei 2 (1990) July 30 (33) Priority claiming country Japan (JP)

Claims (9)

(57) [Claims] 1. A graphic processing apparatus which obtains a gradation value (density value) of an edge portion pixel of vector data by sub-pixel division and outputs the gradation value to an output device capable of dot modulation. A graphic processing apparatus comprising a sub-pixel variable unit for changing a division shape. 2. A graphic processing apparatus for obtaining a gradation value (density value) of an edge portion pixel of vector data by sub-pixel division and outputting the gradation value to an output device capable of dot modulation. A graphic processing apparatus, comprising: a sub-pixel changing unit that approximates a straight line vector and changes a sub-pixel division size of the edge portion pixel according to an inclination of the straight line vector. 3. A graphic processing apparatus for obtaining a tone value (density value) of an edge portion pixel of vector data by sub-pixel division and outputting the tone value to an output device capable of dot modulation. Sub-pixel dividing means for selecting an appropriate sub-pixel shape from a plurality of sub-pixel shapes based on the inclination and the presence or absence of an end point in the edge portion pixel, and performing sub-pixel division. Graphic processing device. 4. The method according to claim 3, wherein the shape of the plurality of sub-pixels is such that an edge portion pixel is 1 * N.
A graphic processing device comprising three types of subpixel shapes: a divided quadrilateral, a quadrilateral obtained by dividing an edge pixel by N * 1, and a quadrilateral obtained by dividing an edge pixel by N * M. 5. A graphic processing apparatus which obtains a tone value (density value) of an edge pixel of vector data by sub-pixel division and outputs the tone value to a pulse width modulation type laser printer. A graphic processing apparatus comprising: tone value determining means for converting an area of a right portion when a pixel is divided into right and left into a tone value with a higher contribution ratio than an area of a left portion. 6. The gradation value determination unit according to claim 5, wherein the gradation value determination unit uses a predetermined subpixel division ratio set such that, when adjacent subpixels are compared, the right subpixel is always smaller. A graphic processing apparatus for determining a gradation value by a uniform averaging method. 7. The tone value determining unit according to claim 5, wherein the tone value determining means determines a tone value by a weighted averaging method using a weighting filter in which the weight of a subpixel on the right side of the edge portion pixel is increased. A graphic processing device characterized by the above-mentioned. 8. A graphic processing apparatus which obtains a gradation value (density value) of a pixel at an edge portion of vector data by sub-pixel division and outputs the gradation value to a pulse width modulation type laser printer. Is divided into a sub-pixel division region where sub-pixel division is performed and a sub-pixel division region where sub-pixel division is not performed, and the gradation is determined based on the number of sub-pixels in the image portion of the sub-pixel division region. A graphic processing apparatus comprising a tone value determining means for determining a value. 9. A graphic processing apparatus for obtaining a gradation value (density value) of an edge pixel of vector data by sub-pixel division and outputting the gradation value to a pulse width modulation type laser printer. An image portion determining means for determining whether an image portion to be filled is located above, below, left or right of the edge portion pixel based on a gradient of vector data traversing the pixel and a type of edge; and the image portion to be filled. An upper filter used when is located above the edge pixel, a lower filter used when the image part to be filled is located below the edge pixel, and the image part to be filled is the edge. A right filter used when located on the right side of the edge pixel, and the image portion to be filled is the edge portion pixel. Storage means for storing four weighting filters of a left filter to be used when located on the side, and a corresponding weighting filter is selected from the storage means based on the determination result of the image part determination means, and the edge part is selected. A graphic processing apparatus comprising: a tone value determining unit that determines a tone value of a pixel.