JPH04139589A - Graphic processor - Google Patents

Abstract

PURPOSE:To recognize, smoothly and easily, a straight line which is not wider than 1 dot by deciding as well as storing the width of the line formed by vector data and changing the gradation value found by area rate calculation under anti-aliasing processing on the basis of the stored information of the line width. CONSTITUTION:If the targeted vector data from a straight line or not is decided and in case they do, if the line is not wider than one dot is decided. For a scanned line paint-out processing, one picture element is divided into 4*4 subpixel in the paint-out processing and the area to be painted out of every subpixel is calculated. Then in a density deciding processing, the picture elements of the scanned line is filtrated from the first element in order in the prescribed anti-aliasing method and the area rate of each picture element is counted to calculate the gradation value. Thus, a straight line which is not wider than 1 dot is expressed to be recognized smoothly and easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a graphic processing device that performs anti-aliasing processing to remove jagged edges of an output image.
More specifically, the present invention relates to a graphic processing device capable of outputting thin straight lines of one dot or less in an easily recognizable manner.

[Conventional technology]

In the field of computer graphics, when displaying an image on a CRT, which is an output medium, a technique called anti-aliasing processing is used to make the displayed image more beautiful. This process applies brightness modulation to the jagged parts (called aliases) on the stairs as shown in Figure 7(a), visually making the displayed image smooth as shown in Figure 7(5). It is something.

In conventional graphic processing devices, (1) uniform averaging method, (2) averaging method for weighting, (2) convolution integral method, etc. are generally applied2 as methods for unaliasing processing.

■In the uniform averaging method, each pixel (iii! element) is NmM
After decomposing it into sub-pixels (N and M are natural numbers) and performing Rask calculation at high resolution, the 0 luminance of each pixel is calculated by taking the average of N*M sub-pixels and is 2.
Referring to a) and (b), anti-aliasing processing using the average cultural method will be specifically explained. If the edge of the image overlaps a certain pixel (here, it is assumed that the image is strongly located at the bottom right of the diagonal line), if anti-aliasing is not performed, As shown, the brightness kid of this C pixel is assigned the maximum brightness of the displayable gradations (for example, kid·255 for 256 gradations). When performing antialiasing processing on this pixel using the uniform averaging method with N=M=7, the pixel is decomposed into 7*7 subpixels, and the subpixels covered by the image are Count the numbers. The count number (28) is divided by the total number of sub-pixels in one pixel (49 in this case), normalized (averaged), and multiplied by the maximum brightness (255) 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.

■Weighting is an averaging method The weighting and averaging method is a partial modification of the uniform averaging method. In contrast, the weighted averaging method assigns a weight to each subpixel, and the brightness of that subpixel (kid) is determined depending on which subpixel the image covers. The effects are different. Note that the weight at this time is given using a filter.

Referring to Figures 9(a) and 9(b), an example is shown in which the same image data as in Figure 8(a) is weighted using the same dividing method (N=M=7) and the averaging method. show.

FIG. 9(a) shows a filter (here, conef
i ] ter ), and the corresponding sub-pixel is given the same weight as this property. 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. Figures 1 and 2) show different display patterns of images depending on the weights of 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 (in this case, 336) corresponding to uniform averaging, averaged, and multiplied by the maximum brightness to calculate the brightness of this pixel.As a filter, Figure 10(a),
The filters shown in ■), (C), and (Φ) are known.

■Convolution integral method The convolution integral method is a method that 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
It is assumed that the 'XN' pixels correspond to pixels of the equal-averaging method or the weighted averaging method. 11th
The figure shows a convolution method with 3x3 pixel references. In this figure, the pixel whose brightness is to be determined is 1101
Indicated by 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 filter of 12 * engineering 2 will be used. This method has the effect of removing high frequency components contained in a vector image.

On the other hand, a publishing system using a personal computer,
With the spread of so-called DTP (desk top publishing), systems for printing vector images, such as those used in computer graphics, have become widely used. A typical example is a system using Adobe's Post Script. PostScript is a page description language (Page Des
criptionLanguage: Hereafter, PDL
It belongs to a language genre called ``Japanese language'', and describes the form of the contents of a single document, including the text (letter part), graphics, and their arrangement and appearance. It is a programming language for systems such as this, and vector fonts are used as character fonts in such systems. Therefore, even if the characters are scaled, the print quality can be significantly improved compared to systems using bitmap fonts (for example, conventional word processors).
Another advantage is that character fonts, graphics, and images can be mixed and printed.

However, the resolution of the laser printers used in these systems is at most 240dpi to 400dp.
There are many i, computer graphics C
Similar to RT display, there is a problem in that aliasing occurs due to the low resolution. Therefore, even when printing using a laser printer, anti-aliasing processing is performed to improve the quality of the printed image. Anti-aliasing processing is applied to the vector image and the gradation value of each pixel ( In the case of a CRT, it indicates the brightness value, and in the case of a laser printer, it indicates the density value), and then calculates the gradation value as the beam level value of the laser printer (in other words, the value that specifies the size of the dot drawn by the laser printer).
Nowadays, graphic processing devices and the like are used that convert the data into images and output them to laser printers.

[Problem to be solved by the invention]

However, according to a graphic processing device that applies conventional anti-aliasing processing, since the anti-aliasing processing uniformly removes the jagged edges of the output image, straight lines with a thin line width of 1 dot or less have a low density. Therefore, there was a problem that it became difficult to obtain certification.

Specifically, for example, in the case of a straight line with a line width of one dot or less as shown in FIG. 12(a), when anti-aliasing processing is not performed, as shown in FIG. 12(b),
If a straight line even partially overlaps a pixel, that pixel is output at the highest gradation value (total density), which causes aliasing and thicker line width, making it easier to recognize.

However, in conventional graphic processing devices, thin lines of one dot or less are similarly processed using anti-aliasing processing to make them visually smooth.
), although the alias is eliminated, the gradation value becomes smaller and becomes difficult to recognize (in other words,
There was a problem that it was difficult to measure and recognize because the density was modulated thinly.

The present invention has been made in view of the above, and it is an object of the present invention to be able to express straight lines with a line width of one dot or less in a smooth and easily recognizable manner.

[Means to solve the problem]

In order to achieve the above object, the present invention adjusts the output of pixels at the edges of vector data based on the area ratio to be filled, and performs anti-aliasing processing to smoothly express jaggedness (alias) at the edges of the output image. In a graphic processing device that executes the above, the line width determining means determines whether the line width of a straight line formed by vector data is one dot or less, and the line width information storage means stores the line width of the straight line as line width information. and a gradation value correction means for changing the gradation value obtained by calculating the area ratio of anti-aliasing processing based on the line width information stored in the line width information storage means. It is something.

Further, the line width information storage means stores the line width information of the straight line as "1" when the line width of the straight line is larger than 1 dot, and stores the line width information of the straight line as "1" when the line width of the straight line is 1 dot or less. It is desirable to store it as width information.

[Effect]

In the graphic processing device of the present invention, the line width information storage means includes:
Based on the judgment of the line width determining means, if the line width of the straight line is larger than 1 dot, the line width information of the straight line is stored as "1", and if the line width of the straight line is 1 dot or less, the line width of the straight line is stored. Stored as line width information.

The gradation value correction means changes the gradation value obtained by calculating the area ratio of the anti-aliasing process based on the line width information stored in the line width information storage means.

〔Example〕

Hereinafter, an image forming system incorporating the graphic processing device of the present invention as a PDL controller will be described as an example. ■A block diagram of the image forming system, ■Configuration of the PDL controller (graphic processing device of the present invention), and ■Operation of the PDL controller. A detailed explanation will be given in order.

(2) Block diagram of image forming system FIG. 1 is a block diagram showing an image forming system (desk top publishing system) incorporating the graphic processing apparatus according to the present invention as a PDL controller 200.

The image forming system of this embodiment uses a page description language output from DTP (desk top publishing).
e: hereinafter referred to as PDL language)) and image information read by an image reading device.

As shown in FIG. 1, the image forming system includes a host computer 100 that creates a document written in the PDL language (Bost script language is used in this embodiment), and a document that is sent page by page from the host computer 100. P
A PDL controller (graphic processing device of the present invention) 2 that develops the DL language into three-color images of red (R), green (G), and blue (B) while performing anti-aliasing processing.
00, an image reading device 300 that reads image information via an optical system unit, and a PDL controller 200. Alternatively, an image processing device 400 that inputs the image output from the image reading device 300 and performs image processing, and a multi-value color laser printer 500 that prints the multi-value image data output from the image processing device 400. PDL
Controller 200. iii image reading device 300. ii
i image processing device 400. and a system control section 600 that controls the multivalued color laser printer 500. Note that the control unit 600 is connected to the image processing device 4000 Å.
It performs processing such as whether to use the image forming system as a digital copying machine or a printer.

■Configuration of PDL Controller FIG. 2 shows the configuration of the PDL controller 200, which includes a receiving device 201 that receives the PDL language sent from the host computer 100, and storage control and anti-aliasing of the PDL language received by the receiving device 201. A CPU 202 that executes processing, an internal system bus 203, a RAM 204 that stores PDL language to be transferred from the receiving device 201 via the internal system bus 203, and a ROM 205 that stores a predetermined control program such as an anti-aliasing program. The page memory 206 stores multivalued ROB image data that has been subjected to anti-aliasing processing. RG
It is composed of a transmitting device 207 that transfers B image data to the image processing device 400, and an I10 device 20B that performs transmission and reception with the system control unit 600.

Here, the CPU 202 receives the P received by the receiving device 201.
The DL language is transferred to the RAM 204 through the internal system bus 203 according to the program stored in the ROM 205.
Store in. After that, 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, expanded into multivalued RGB image data, and then stored in the page memory. 206 (Details are omitted, but the page memory 206 stores R, G,
B brain memory section and feature information memory section).

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

(2) Operation of PDL Controller Regarding the above configuration, refer to FIGS. 3(a) and (b).

The operation of the PDL controller 200 will be explained.

FIG. 3(a) shows a flowchart of the processing performed by the CPL 1202.As mentioned above, the PDL controller 200 performs anti-aliasing processing on the PDL language sent page by page from the host computer 100. ).

It is developed into three-color images: green (G) and blue (B).

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

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

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

Next, in process 3, while updating the X coordinate one by one,
Performs filling processing using scanning lines.

For example, when performing the filling process of the path shown in Figure 3 (see Figure 3), the element on the side that the scanning line yc to be processed crosses, and the real value of the X coordinate across the scanning line yc (χ shown in the same figure)
, X□X5X4) and AET (Active Edge
Table: registers the X coordinate of the edge portion appearing on the scanning line). Here, the order of the elements registered in the work area is the order in which they were registered in process 1, so they are not necessarily registered in order of decreasing X coordinate across the scanning line yc. For example, in process 1, if a straight line element passing through scanning lines yc and X in FIG. 3(b) is processed first, scanning line yc
x3 is first registered in AET as the X coordinate of the edge portion appearing above. Therefore, after the AET is registered, the elements on each side within the AET are sorted in descending order of X coordinate. Anti-aliasing processing, which pairs the first two elements of AET and fills in the space between them, is achieved by adjusting the density and brightness of pixels in the edge portion according to the area ratio in this filling process. Then, remove the processed edge from the AET, update the scanline (update the Repeat the process.

Above processing 1. Processing 2. The work in process 3 is executed for each bus, and is repeated until all buses for one page are completed.

Next, with reference to FIGS. 4 and 5, the storage of the line width (line width information) of a straight line formed by vector data, which is the main part of the present invention, and the anti- A method of changing the gradation value obtained by calculating the area ratio of aliasing processing will be specifically explained.

In this embodiment, the line width information is stored in the AE of process 3 described above.
T registration, and based on the line width information (and the correction of the gradation value obtained by calculating the area ratio of anti-aliasing processing,
Similarly, processing 3 is executed using scan line filling processing.

FIG. 4 shows the AET registration process. First, it is determined whether or not the target vector data forms a straight line. If it does not form a straight line (that is, in the case of a graphic element other than a straight line),
Set line width information as "1" (5401, 5402
), when forming a straight line, it is determined whether the line width m of the straight line is 1 dot or less, and if it is 1 dot or less, the line width m of the straight line is set as line width information (S403, 5404).
), on the other hand, if it is not 1 dot or less, the process advances to 5402 and the line width information is set as "rl". After that, line width information is registered in the ART along with vector data start point/end point information, slope information, edge information (information indicating whether the vector data is at the right end or left end of the figure), etc. (3405 ), here, if all vector data has not been completed, the process returns to 5401, and if it has been completed, evening smoke is performed (5406).

As shown in the Q flowchart in Figure 5, the scanning line filling process first divides the IN element into 4*4 cube pixels and calculates the filling area for each subpixel. (S5
01). This process is repeated for all vectors that cross the scanning line (sso2+Next, in the density determination process (anti-aliasing process), the filter of the predetermined anti-aliasing method (main In the embodiment, a uniform averaging filter is used), and the area ratio of each pixel is calculated to calculate the gradation value (that is, the density) (S503).

Subsequently, in step 5504, straight line gradation value correction of one dot or less, which is the essential part of the present invention, is performed. Specifically, input the line width information m registered in AET, and calculate all the gradation values (i
1 degree) is multiplied by 1/m. As mentioned above, line width information is set to m = 1 for lines other than straight lines with a line width of 1 dot or less, so by multiplying the gradation value by 1/m, straight lines with a line width of 1 dot or less (ill, m ≦1) is corrected so that it has a gradation value of a straight line with a width of one dot.

After that, the details are omitted, but each color of the shape (
The gradation # value (21 degrees) of the four colors (BK, R, G, and B) is calculated (5505), and the gradation value of each color is written to the page memory in the page memory drawing process (S506).

Furthermore, the processes from 5503 to 5506 described above are repeatedly executed for all pixels of one line (S507).

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

Figure 6 (a) shows 0, the Fin value corrected in this way,
6 dot line 1'! An example of outputting a straight line (that is, a line width of 1 dot or less) is shown below.

If anti-aliasing processing is not performed on the straight line in figure (a), as shown in figure (bl), the straight line will not be sharp but jagged.On the other hand, if anti-aliasing processing is not performed If applied, the same figure (C)
As shown in , the jagged edges become less noticeable, but the straight lines become thinner and cut off.

In comparison, when the gradation value correction is performed according to the present invention, the jagged edges are less noticeable and appear at a density that is easy to recognize, as shown in FIG. 2(d). In other words, it is possible to output a straight line with a line width smaller than a dot, which is difficult to recognize due to thin density modulation due to anti-aliasing processing, with a recognizable density.

(Effects of the Invention) As described above, the graphic processing device of the present invention adjusts the output of pixels at the edge portion of vector data based on the area ratio to be filled, and eliminates jaggedness (aliasing) at the edge portion of the output image. In a graphic processing device that performs anti-aliasing processing to smoothly express a line, there is a line width determination means for determining whether the line width of a straight line formed by vector data is one dot or less, and a line width determination means for determining whether the line width of a straight line formed by vector data is one dot or less. A line width information storage means for storing information as information; and a gradation value correction means for changing the gradation value obtained by calculating the area ratio of anti-aliasing processing based on the line width information stored in the line width information storage means. As a result, a straight line with a line width of one dot or less can be expressed smoothly and easily recognizable.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the configuration of the image forming system of this embodiment, FIG. 2 is an explanatory diagram showing the configuration of the PDL controller (graphic processing device of the present invention), and FIG. 3 is an explanatory diagram showing the operation of the PDL controller. 4 is a flowchart showing AET registration processing, FIG. 5 is a flowchart showing scan line filling processing, and FIG. 6 is a flowchart showing 0.
An explanatory diagram showing an example of outputting a straight line with a line width of 6 dots (i.e., a line width of 1 dot or less); FIGS. 7(a) and 7(b) are explanatory diagrams showing conventional anti-aliasing processing; FIG. 8(a) ),
(b) is an explanatory diagram showing anti-aliasing processing using the uniform averaging method, FIG. 9(a), (b) is an explanatory diagram showing anti-aliasing processing using the weighting averaging method,
Figures 10 (a), (b), (C), and (d) are explanatory diagrams showing examples of filters used in the weighted averaging method;
FIG. 1 is an explanatory diagram showing a convolution integral method with reference to 3×3 pixels, and FIG. 12 is an explanatory diagram showing problems with a conventional straight line having a line width of one dot or less. Explanation of symbols 100 --- Host computer 200 --- PDL controller 201 ---
・-Receiver! 202-・-CP U203-------・
・-Internal system bus 204---RAM 20
5------ROM2O6----Page memory
207--------- Transmitting device 208------
-I10 device 300--Image reading device 400--Image processing device 500--Multiple laser printer 60 (1-m-
...-System control section

Claims (2)

[Claims] (1) In a graphic processing device that adjusts the output of pixels at the edge of vector data based on the area ratio to be filled, and executes anti-aliasing processing to smoothly express jaggedness (alias) at the edge of the output image, The line width of the straight line formed by the vector data is 1
line width determination means for determining whether the line width is equal to or smaller than a dot; line width information storage means for storing the line width of the straight line as line width information; A graphic processing apparatus comprising: gradation value correction means for changing the gradation value obtained by calculating the area ratio of the anti-aliasing process. (2) In claim 1, the line width information storage means stores the line width information of the straight line as "1" when the line width of the straight line is larger than 1 dot;
A graphic processing apparatus characterized in that when the line width of the straight line is one dot or less, the line width of the straight line is stored as line width information.