JP2790707B2 - 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 executing an anti-aliasing process for removing jagged edges of an output image, and more particularly, to a high-speed anti-aliasing process. The present invention relates to a graphic processing device that can be executed on a computer.

[Conventional technology]

In the field of computer graphics, when an image is displayed on a CRT as an output medium, a technique called anti-aliasing is used to make the displayed image more beautiful. In this processing, the jagged portion (called an alias) on the stage as shown in FIG. 25 (a) is subjected to luminance modulation to visually smooth the displayed image as shown in FIG. 25 (b). It is.

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 an anti-aliasing processing method.

In the uniform averaging method, each pixel (pixel) is decomposed into N * M (N, M are natural numbers) sub-pixels, and a high-resolution raster calculation is performed. Then, the luminance of each pixel is averaged over N * M sub-pixels. It is what you want. FIG. 26 (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. 27 (a) and (b), an example is shown in which the same image data as in FIG. 26 (a) is subjected to a weighted averaging method using the same division method (N = M = 7).

FIG. 27 (a) shows a filter (here, cone filte
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. 28 (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 by referring to the surrounding pixels. That is, N ′ × N ′ pixels around one pixel whose luminance is to be determined are considered to correspond to pixels of the uniform averaging method or the weighted averaging method. Figure 29 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. It is a programming language for describing forms, and in such a system, a vector font is adopted as a character want. 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. For this reason, even in printing using a laser printer, anti-aliasing processing needs to be performed to improve the quality of a printed image.

[Problems to be solved by the invention]

However, according to the graphic processing apparatus to which the conventional anti-aliasing processing method is applied, one pixel is divided into a plurality of sub-pixels (for example, 49 sub-pixels), and the number of sub-pixels to be filled is counted. Since the area ratio (luminance) is calculated, it takes time to calculate the area ratio, which hinders an improvement in display speed or printing speed. In particular, in a graphic processing apparatus to which the convolution integration method is applied, there is a problem that it is difficult to improve the processing speed because a large amount of calculation is performed and a plurality of pixels are affected.

Even when the vector data (image) crosses a very small part of the sub-pixel, the sub-pixel is filled and counted, so that the area ratio of the actual image part tends to be larger. Is smaller, in other words, the smaller the number of gradations of the approximate area ratio is, the more noticeable the error with the actual area ratio is.
There was also a problem that an appropriate area ratio could not always be obtained.

The present invention has been made in view of the above, and it is an object of the present invention to obtain an area ratio at high speed without performing sub-pixel division and counting of the number of painted areas.

It is another object of the present invention to be able to approximate the area ratio of the closest gradation even when the number of gradations of the approximate area ratio is small.

[Means for solving the problem]

In order to achieve the above object, the present invention adjusts the output of pixels at the edge of vector data based on the area ratio to be filled, and performs anti-aliasing processing for smoothly expressing jaggies (alias) at the edges of the output image. In a graphic processing apparatus that executes the above, a storage unit that stores a reference area ratio that is set based on a plurality of divided straight lines that pass through a predetermined end point on a pixel and that have different slopes, A reference area ratio input unit that selects a division line having an inclination close to the inclination of the vector data and reads a corresponding reference area ratio from the storage unit based on the selected division line, and input / output coordinates of vector data with respect to pixels at the edge portion. A decimal part detecting means for detecting a decimal part of
Decimal part of input / output coordinates detected by decimal part detection means,
And correcting the reference area ratio read by the reference area ratio input means based on the edge information of the vector data,
An object of the present invention is to provide a graphic processing apparatus provided with an area ratio calculating means for calculating an area ratio.

[Action]

The graphic processing device of the present invention passes through a predetermined end point on a pixel, and stores a reference area ratio set based on a plurality of divided straight lines each having a different slope in a storage unit in advance, and performs an anti-aliasing process. The reference area ratio input means selects a division line having a slope close to the inclination of the vector data from the plurality of division lines, and reads the corresponding reference area ratio from the storage means based on the selected division line. Further, the decimal part detecting means detects a pixel at the edge part. Then, the reference area ratio is corrected by the area ratio calculating means based on the edge information of the decimal part and the vector data, and the area ratio of the edge portion pixel is determined.

〔Example〕

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

Outline of Anti-Aliasing Processing The graphic processing apparatus of the present invention (hereinafter, referred to as a PDL controller) registers an area ratio determined by a predetermined dividing line in advance in a LUT (Look Up Table) as a reference area ratio. During the anti-aliasing process, the reference area ratio of the divided straight line having the closest slope is read as the approximate area ratio of the edge part pixel based on the slope information of the straight line (vector data) constituting the edge of the figure. By correcting the rough area ratio using the value of the decimal part of the input / output coordinates of the vector data with respect to the edge pixel as a parameter, the area ratio of the edge pixel can be obtained quickly and easily. is there. Hereinafter, a PD which will be described later with reference to FIGS. 1 (a), (b), (c) and (d) will be described.
The anti-aliasing processing by the L controller 200 will be described in detail.

FIG. 1 (a) shows a state passing through a predetermined end point on a pixel and
Shows a plurality of divided straight l ₁ to l ₁₄ having different slopes, respectively. In the present embodiment, when setting a dividing line, as shown in the figure, a pixel is divided into 3 * 3 sub-pixels, and the inclination of the dividing line is set with reference to an end point of a predetermined sub-pixel. Specifically, as divided straight line passing through the upper right end point P ₀ of the pixel, the gradient is 1 ° (through the vicinity of the end points P _1, the angle may if 0 ° value close 0 ° or more) a division line l _1, and the divided linear l ₂ passing through the end point P _2, and the divided linear l ₃ passing through the end point P _3, divided line l passing through the end point P _4
4, a divided linear l ₅ passing through the end points P _5, a divided linear l ₆ passing through the end point P _6, and passes through the vicinity of the slope 89 ° (the end point P _7, the angle is 90 ° or less 90 ° a divided linear l ₇ of long if good) a value close to, as divided straight line passing through the upper left end point P ₀₀ of pixels, and passes near the slope -1 ° (the end point P _8, the angle is 0 ° or less in division straight line l ₈ of 0 ° may be a close value)
When a divided linear l ₉ passing through the end point P _9, the divided linear l ₁₀ passing through the end point P _10, and the divided linear l ₁₁ passing through the end point P _11,
And dividing the straight line l ₁₂ passing through the end point P _12, and the divided linear l ₁₃ passing through the end point P _13, and passes near the slope -89 ° (the end point P _14, -90 ° in angle -90 ° or more Should be close to)
Consisting of divided straight l ₁₄ Prefecture. Although the details will be described later, the vector data is approximated to a division straight line having a close slope among the division lines l _{1 to} l ₁₄ when calculating the area ratio. In other words, all the vector data are replaced with 14 straight lines.

In the present embodiment, the pixel is divided into 3 * 3 sub-pixels, and the inclination of the division straight line is set with reference to the end point of the predetermined sub-pixel. However, the present invention is not limited to this. Alternatively, a dividing line may be provided for each inclination (for example, every 10 °), or the number of dividing pixels may be increased to increase the dividing lines.

FIG. 1B shows the contents of the LUT according to the present embodiment, and the division straight lines l _{1 to} l ₁₄ are left edges (or right edges).
Is obtained and stored as a reference area ratio.

For example, the reference area ratio when divided linear l ₁ is the left edge, as shown in FIG. 1 (a), since the most covers the entire surface of the pixel, to 1 (and 1 the area of one pixel) Can be approximated. Conversely, the reference area ratio when divided linear l ₁ is the right edge (here, 0) value from the area 1 of the pixel minus the area ratio of the left edge becomes.

The reference area ratio when divided linear l ₂ is the left edge,
As shown in FIG. 1A, the number of sub-pixels is 7.5, and if the area of one pixel is 1, 7.5 / 9 ≒ 0.83.
Conversely, when the division straight line l ₂ is the right edge, the reference area ratio is 1
-0.83 = 0.17. Hereinafter, it is possible to determine the reference area ratio of divided straight l ₃ to l ₁₄ similarly.

Next, referring to the pixels A, B, C, D, and E in FIG.
A method of obtaining the area ratio of the edge portion pixel based on the reference area ratio and the value of the decimal part of the input / output coordinates of the vector data will be described.

Reference area ratio of the LUT is to pass the end point vector data configuring the edge portion is always P ₀ or P ₀₀ (integer coordinates) as described above. Therefore, in the case shown by the pixels A, B, C, D and E in FIG. 1C, the reference area ratio cannot be used as it is. Therefore, the decimal part of the input / output coordinates of the vector data constituting the edge part (Xa, Xb,
Ya, Yb) is detected, and based on the decimal part, the area ratio is corrected in five cases of pixels A, B, C, D, and E shown in the following table. Therefore, here, the inclination is 0
Limited to the range of ゜ to 90 ゜).

The correction of the area ratio of the pixel A is a value obtained by removing the space portion from the area 1 of one pixel. First, based on the inclination of the vector data, a division straight line having the closest inclination is selected from the above-described division straight lines l _{1 to} l ₁₄ (here, it is assumed that the division straight line l ₃ has been selected). Then, based on the divided linear l ₃ selected, reads the reference area ratio [0.66] from LUT.

In the case of the pixel A, the area of the square (specifically, Xa ² ) having the decimal part Xa as one side is obtained, and the area and the area ratio of the LUT [0.
66], calculate the blank space Space that does not cover the image,
It is determined by removing from the entire pixel area 1. Specifically, the following equation is used.

S _PACE = Xa ² × (1−reference area ratio) Area of pixel A = 1−Space Area ratio of pixel B is always corrected based on the inclination of the vector data for the above-described divided straight lines l _{1 to} l ₁₄ . Select the closest dividing straight line from among them. Next, the reference area ratio is read from the LUT based on the selected dividing straight line.

In the case of the pixel B, the division straight lines l ₁ to l ₁ shown in FIG.
Assuming that the end point P ₀ of the l ₇ has moved 1-Xa min to D _X direction in FIG. (c), the area Add the 1-Xa portion reference area ratio was added,
It is determined by excluding a portion protruding into an area other than the pixel B. Specifically, the following equation is used.

Add = 1−Xa Over = Yb ² × reference area ratio Area of pixel B = reference area ratio + Add−Over In the case of pixel C, the division straight lines l ₁ to l shown in FIG.
Assuming that the end point P ₀ of the l ₇ has moved 1-Xa min in D _X direction in FIG (c), the reference area ratio determined by adding the area Add parts of 1-Xa. Specifically, the following equation is used.

Add = 1−Xa Area of pixel C = reference area ratio + Add In the case of pixel D, the division straight lines l ₁ to l shown in FIG.
Assuming that the end point P ₀ of the l ₇ has moved Ya min in D _Y direction in FIG. (c), determined by subtracting the area Sub the Ya portions from the reference area ratio. Specifically, the following equation is used.

In the case of Sub = Ya pixel D area = reference area ratio−Sub pixel E, the division straight lines l ₁ to l shown in FIG.
the end point P ₀ of the l ₇ is assumed to have moved Ya min in D _Y direction in FIG. (c), subtracting the area Sub the Ya portions from the reference area ratio, adds the portion indicated by OverSub in FIG Ask by
Specifically, the following equation is used.

Sub = Ya OverSub = Xb ² × (1−reference area ratio) Area of pixel E = reference area ratio−Sub + OverSub FIG. 1 (d) calculates the reference area ratio of the edge portion pixel by the above method, and corrects the correction. The added area ratio is shown. Here the vector data, has an intermediate degree of slope of the divided linear l ₃ and l ₄ of FIG. 1 (a), (in other words those of the state away from the most divided straight, and the actual reference area ratio (Where the error of the area ratio is large). For comparison, the area ratio was similarly obtained by 3 * 3 sub-pixel division (uniform averaging method).
As is apparent from this result, even when the error is the largest, a value closer to the actual area ratio can be obtained as compared with the conventional sub-pixel division.

Accuracy can be improved by further increasing the number of dividing straight lines described above. Further, by simplifying the correction of the reference area ratio by the decimal part, the accuracy is reduced, but the speed of the area ratio calculation can be improved.

The correction by the decimal part has been described with the edge part pixel as an example of the proportion of the left edge. However, in the case of the right edge, the area ratio of the left edge is obtained, and then subtracted from the entire pixel (1-area ratio of the left edge). Is more easily sought.

Although the description is omitted, the inclination of the vector data is −0.
In the case of the range from ゜ to -90 ゜
The reference area ratio is corrected.

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).
And the image information read from the image data read by the image reading device. Hereinafter, the configuration of the image forming system of the present 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 (an anti-aliasing processing device of the present invention) 200 for developing three color image images of red (R), green (G), and blue (B), and an image for reading image information via an optical system unit Reader 300
And an image processing device 400 that inputs an image image output from the PDL controller 200 or the image reading device 300 and performs image processing (details will be described later), and an image processing device 400
Prints multi-valued image data output by
It comprises a laser printer 500, a PDL controller 200, an image reading device 300, an image processing device 400, and a system controller 600 for controlling the multi-valued color laser printer 500.

Configuration and Operation of PDL Controller FIG. 3 shows the configuration of the PDL controller 200. The receiving device 201 receives the PDL language sent from the host computer 100, and the storage control and anti-storage of the PDL language received by the receiving device 201. CPU 202 that performs aliasing processing
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 multi-valued RGB with anti-aliasing processing
A page memory 206 for storing image data, and an RGB image data stored in the page memory 206.
The transmission device 207 includes a transmission device 207 for transferring data to the system controller 400 and an I / O device 208 for transmitting and receiving data to and from the system controller 600.

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 an anti-aliasing method based on a flowchart described later, and the multi-valued RGB image data is stored in the plane memory of the page memory 206. (The page memory 206 includes an R, G, B plane memory unit and a feature information memory unit.)

The data in the page memory 206 is
Is sent to the image processing apparatus 400 via the.

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

FIG. 4A shows a flowchart of the processing performed by the CPU 202. The PDL controller 200 performs the anti-aliasing processing on the PDL language sent from the host computer 100 in page units as described above,
The image is developed into three color image images of green (G) and blue (B).

In the PDL language, both graphics and characters are described in vector data, and as indicated by the term “page description 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 straight line elements of the work area registered for each pass are sorted by the start 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, the fourth
When performing the path filling process shown in FIG.
The element of the side crossing the scanning line yc to be processed and the real value of the x coordinate crossing the scanning line yc (x ₁ x ₂ x ₃ shown in FIG. 5B)
x ₄ ) are registered in AET (Active Edge Table: a table for recording the x-coordinate of the edge appearing on the scanning line). Here, the order of the elements registered in the work area is the processing 1
, The order is not necessarily registered in ascending order of the x-coordinate across the scanning line yc. For example, in processing 1, the scanning line yc shown in FIG.
And when the linear element which passes through the x ₃ is processed first, it x ₃ as the x-coordinate of the edge portions appearing on the scanning line yc AE
First registered with T. Therefore, after the registration of the AET, the elements on each side in the AET are sorted in ascending order of the x coordinate. Then, the two elements from the first element of the AET are paired, and the space between them is painted (painting processing using scanning lines). The anti-aliasing process is realized by adjusting the density and brightness of the pixel at the edge portion in accordance with the area ratio in the filling process. After that, the processed side is removed from the AET, the scanning line is updated (y coordinate is updated), and the processing is performed until all the sides in the AET are processed, in other words, all the elements in one pass are processed. Is repeated.

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 process (calculation of the area ratio of the edge portion pixels) performed during the scan line filling process of the above-described process 3 will be described in detail with reference to the flowchart of FIG.

Here, for example, assuming that a pentagon ABCDE as shown in FIG. 5A is input in the processing 1 of FIG. 4A, this figure has the following elements.

(B) Five line vectors of AB, BC, CD, DE, and EA (representation of real numbers) (b) Color and luminance values inside the figure This figure is obtained by the above-described operation as shown in FIG. , 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.) The anti-aliasing process shown in the flowchart of FIG. First,
It is determined whether there is a plurality of vector data (linear vectors) in one pixel of the edge part pixel (S401). If there is a plurality of vector data, the process proceeds to S405, where sub-pixel division (conventional uniform averaging method) ) To determine the area ratio. In the case of _one piece of vector data, based on the inclination of the vector data, a division straight line having an inclination close to the inclination of the vector data is selected from the division straight lines l _{1 to} l ₁₄ , and further based on the selected division straight line. The corresponding reference area ratio is read from the LUT (S402). Next, the decimal part of the input / output coordinates of the vector data for the pixel at the edge is detected (S403). Thereafter, based on the decimal part of the input / output coordinates and the edge information (left edge or right edge), the reference area ratio is corrected by the method shown in FIG. 1C to obtain the area ratio k (S405). ).

The area ratio k of the figure in FIG. 5 (a) obtained by the anti-aliasing processing in this manner has a value as shown in FIG.

Here, assuming that the graphic in FIG. 5A is drawn with a background color of white (maximum luminance: 255) and a graphic color of red (maximum luminance: 255), for example, the area ratio k ( From FIG. 6), the luminance values _Kr (red), _Kg (green), _Kb (blue) for each color of the figure can be obtained.
Is calculated based on the following equation.

K _r = K _R1 × k + K _R2 × (1-k) K _g = K _G1 × k + K _G2 × (1-k) K _b = _{KB 1} × k + KB ₂ × (1-k) where K _R1 , K _G1 , K _B1 indicates the luminance value of the color (red, green, and blue, respectively) of the figure given in (b) above.
_R2, K _G2, K _B2 denotes the brightness value of each painted previously colors. still,
K _R2 , K _G2 , and K _B2 refer to the data of each plane memory corresponding to RGB of the page memory 206.

The luminance values of the luminance values K _r , K _g , and K _b obtained in this manner are stored in the corresponding plane memory section of the page memory 206 as shown in FIGS. 7 (a), (b) and (c). Is stored as RGB image data. Here, for comparison, RGB image data without anti-aliasing is shown in FIGS. 8 (a), (b) and (c).

Configuration of Image Processing Apparatus The configuration of the image processing apparatus 400 will be described with reference to FIG.

The image processing device 400 includes the CCDs 7r and 7 in the image reading device 300.
The three color image signals read by g and 7b are converted into black (BK), yellow (Y), magenta (M), and cyan (C) recording signals required for recording. The RGB image data supplied from the PDL controller 200 is similarly converted into black (BK), yellow (Y), magenta (M), and cyan (C) recording signals. Here, the mode for inputting an image signal from the image reading device 300 is a copying machine mode, and the RGB
The mode for inputting image data is called a graphics mode.

The image processing device 400 inputs color gradation data obtained by A / D-converting the output signals of the CCDs 7r, 7g, and 7b to 8 bits, and performs optical illuminance unevenness of the color gradation data and the CCDs 7r, 7g, 7b, a shading correction circuit 401 that performs correction for sensitivity variations and the like of the internal terminal elements, and color gradation data output from the shading correction circuit 401 or color gradation data (RGB image data) output from the PDL controller 200. A multiplexer 402 for selectively outputting one according to the above-described mode, and 8-bit data (color gradation data) output from the multiplexer 402 are input, and the gradation is changed according to the characteristics of the photosensitive member to change the 6-bit data. And a 6-bit gradation data indicating the gradations of (R), green (G), and blue (B) output from the gamma correction circuit 403 as cyan (C) ), Magenta (M) ,
A complementary color generation circuit 405 for converting to yellow (Y) gradation data (6 bits), and Y, M,
A masking processing circuit 406 that performs a predetermined masking process on each gradation data of C; and a UCR that inputs each gradation data of Y, M, and C after the masking process and performs a UCR process and a black generation process
The processing / black generation circuit 407 and the 6-bit gradation data of Y, M, C, and BK output from the UCR processing / black generation circuit 407 are converted into 3-bit gradation data Y1, M1, C1, and , BK1 and a gradation processing circuit 408 for outputting to the laser drive processing unit 502 inside the multi-valued color laser printer 500, and an image processing device
And a synchronization control circuit 409 for synchronizing each of the 400 circuits.

Although the details are omitted, the gamma correction circuit 403 is connected to the console 7
In this configuration, the gradation can be arbitrarily changed using the operation button 00.

As an algorithm used in the gradation processing circuit 408, a multi-value dither method, a multi-value error diffusion method, or the like can be applied.
If the value is × 3, the number of gradations of the multi-valued color laser printer 500 is the product of the area gradation of 3 × 3 and the multi-valued level of 3 bits (that is, 8 steps), and 3 × 3 × 8 = 72. (Gradation).

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

Generally, the arithmetic expression of the masking processing of the masking processing circuit 406 is as follows. Y _i , M _i , C _i : pre-masking data Y ₀ , M ₀ , C ₀ : post-masking data It is represented by

Therefore, in this embodiment, a new coefficient is obtained from these equations using the product of both coefficients.

In the present embodiment, a new coefficient (a ₁₁ ″, etc.) for simultaneously performing this masking process and the UCR process is calculated and found in advance, and further, using the new coefficient, the scheduled input value Y _{i of the} masking process 406 is performed. , M _i , and C _i (6 bits each) (output values such as Y ₀ ′: values to be calculated by the UCR processing / black generation circuit 407) are obtained and stored in a predetermined memory in advance. In this embodiment, the masking processing circuit 406 and the UCR processing
The black generation circuit 407 is constituted by a set of ROMs, and data of an address specified by the inputs Y, M, and C of the masking processing circuit 406 is given as an output of the UCR processing / black generation circuit 407.

Incidentally, generally speaking, the masking processing circuit 406 adjusts the Y, M, and C according to the spectral reflection wavelength characteristics of the recording image forming toner.
The signal is corrected, and the UCR processing / black generation circuit 407 performs correction for color balance in superimposing toner of each color. After passing through the UCR processing / black generation circuit 407, the black component data BK is generated by combining the input three-color data of Y, M, and C, and the output Y, M, and C color component data is black. It is corrected to a value obtained by subtracting the component data BK.

In the above configuration, the gamma correction circuit 403 executes the processing based on the gamma correction conversion graph shown in FIG. 10, and the complementary color generation circuit 405 generates the complementary colors shown in FIGS. 11 (a), (b) and (c). The processing is executed based on the conversion graph for generation, and thereafter, the masking processing circuit 406 and the UCR processing / black generation circuit 407 become Assuming that the processing is executed on the basis of FIG.
The RGB image data shown in (b) and (c) passes through a gamma correction circuit 403, a complementary color generation circuit 405, a masking processing circuit 406, and a UCR processing / black generation circuit 407, and FIG.
The conversion is performed as shown in (b), (c), and (d).

Further, assuming that the Bayer type 3 × 3 multivalued dither matrix shown in FIG.
The data of Y, M, C, and BK in FIGS. (A), (b), (c), and (d) are the data shown in FIGS. 14 (a), (b), (c), and (d), respectively. Is converted.

For comparison, when data that has not been subjected to anti-aliasing processing (data in FIGS. 8A, 8B, and 8C) is processed by the image processing device 400, FIGS. The conversion is performed as shown in (b), (c), and (d).

Configuration of Multilevel Color Laser Printer (Configuration and Operation of Developing Unit of Multilevel Color Laser Printer) First, referring to the control block diagram shown in FIG. 16, the schematic configuration of the multilevel color laser printer 500 will be described. explain.

The photoreceptor development processing unit 501 uniformly charges the surface of the 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 501bk for developing / transferring BK data, a cyan developing / transferring unit 501c for developing / transferring C data, and a cyan developing / transferring unit for developing / transferring M data. A development / transfer unit 501m and a cyan development / transfer unit 501y for developing / transferring Y data are provided.

The laser drive processing unit 502 includes the image processing device 400 described above.
Y, M, C, BK 3-bit data output from
(To be image density data) and output a laser beam. Buffer memories 503y, 503m, and 503c for inputting 3-bit data of Y, M, and C, and Y, M, C, and BK, respectively. Laser diodes 504y, 504m, 504c, 504bk that output corresponding laser beams, and laser diodes 504y, 5
Drivers 505y, 505m, which drive 04m, 504c, 504bk, respectively
505c and 505b.

The black developing / transfer unit 501 of the photoreceptor developing unit 501
bk and laser drive processing unit 502 laser diode 504b
The combination with k and the driver 505bk is called a black recording unit BKU (see FIG. 17). Similarly, cyan development
Transfer unit 501c, laser diode 504c, driver 505c, and buffer memory 503c are combined in a cyan recording unit.
CU (see Fig. 17), magenta development / transfer unit 501m, laser diode 504m, driver 505m, and buffer memory
The combination of 503m is used for the magenta recording unit MU (see Fig. 17), yellow development / transfer unit 501y, laser diode 5
The combination of 04y, driver 505y, and buffer memory 503y is called a yellow recording unit YU (see FIG. 17). As shown in the figure, these recording units are arranged in the order of a black recording unit BKU, a cyan recording unit CU, a magenta recording unit MU, and a yellow recording unit YU around a transport belt 506 that transports the recording paper from the transport 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.
504bk, laser diode 504 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 502 stores the above-mentioned three sets of buffer memories 503y and 503m in order to hold the recording data (output of the image processing device 400) during the time difference. , 503c.

Next, the configuration of the multi-level color laser printer 500 will be specifically described with reference to FIG.

The multi-level color laser printer 500 includes a transport belt 506 for transporting the recording paper and a transport belt 506 as described above.
, Recording units YU, MU, CU, and BKU, paper cassettes 507a and 507b that store recording paper, and paper feed rollers 508 that feed recording paper from the paper cassettes 507a and 507b, respectively.
a, 508b, a registration roller 509 for aligning the recording paper sent from the paper cassettes 507a, 507b, and an image transferred by being sequentially conveyed through the recording units BKU, CU, MU, and YU by the conveyance belt 506. Fixing roller for fixing on recording paper
510 and a discharge roller 511 for discharging the recording paper to a predetermined discharge unit (not shown). Here, each of the recording units YU, MU, CU, BKU is a photoconductor drum 512y, 512m, 512c, 512bk.
And a charger 513y, 513m, 513c, 513bk for uniformly charging the photosensitive drums 512y, 512m, 512c, 512bk, respectively, and a polygon mirror 514y for guiding a laser beam to the photosensitive drums 512y, 512m, 512c, 512bk. , 514m, 514c, 514bk and motor 515y, 5
15m, 515c, 515bk and photosensitive drums 512y, 512m, 512c, 512bk
Toner developing devices 516y, 516m, 516c, 516bk for developing the electrostatic latent images formed thereon using toners of respective colors
And a transfer charger 51 for transferring the developed toner image to recording paper.
7y, 517m, 517c, 517bk, and photoreceptor drums 512y, 512 after transfer
m, 512c, and 512bk, and cleaning devices 518y, 518m, 518c, and 518bk that remove toner remaining on them. In addition, 51
9y, 519m, 519c, and 519bk are photosensitive drums 512y and 512, respectively.
m, 512c, shows a CCD line sensor for reading a predetermined pattern provided on 512bk, the details are omitted,
Thus, the process state of the multi-level color laser printer 500 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 504y is reflected by a polygon mirror 514y, passes through an f-θ lens 502y, and is further reflected by a mirror 521.
The light is reflected by y and 522y, and is irradiated on the photosensitive drum 512y through the dustproof glass 523y. At this time, the polygon mirror 514y is driven at low speed by the motor 515y to rotate the laser beam.
It moves in the direction (main scanning direction) along the axis of the photosensitive drum 512y. In this embodiment, the photo sensor 524y is provided with a laser beam at a non-exposure position in order to detect a base point for tracking the scanning position of the main scanning. Since the laser diode 504y is energized to emit light based on recording data (3-bit data from the image processing device 400), multi-level exposure corresponding to the recording data is performed on the surface of the photosensitive drum 504y. The surface of the photosensitive drum 504y is uniformly charged in advance by the charger 513y as described above, and the exposure forms an electrostatic latent image corresponding to the original image. The electrostatic latent image is developed by the yellow developing device 516y to become a yellow toner image. As shown in FIG. 17, the toner image is fed from the cassette 507a (or 507b) to the sheet feed roller 508a (or 50).
The sheet is fed out at 8b), and is transferred onto the recording paper conveyed by the conveyance belt 506 in synchronization with the formation of the toner image of the black recording unit BKU by the registration roller 509.

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 516bk to form and transfer a black toner image, and the cyan recording unit CU. Is provided with a cyan toner developing device 516c, and forms and transfers a cyan toner image. The magenta recording unit MU is provided with a magenta toner developing device 516m, and forms and transfers a magenta toner image.

The driver 505y, 505m, 505c, and 505b are based on 3-bit data of Y, M, C, and BK sent from the image processing apparatus 400.
The laser diodes 504y, 504m, 504c, and 504bk are controlled to perform multi-level driving. As a driving method, power modulation, pulse width modulation, and the like are generally used.

Hereinafter, multi-level driving by power modulation applied in this embodiment will be described in detail with reference to FIGS. 19 (a), (b), (c) and (d). Note that the drivers 505y, 505m, 505c, 505b and the laser diodes 504y, 504m, 504c, 504bk have the same configuration, and therefore, here, the driver 505y and the laser diode 504y will be described as an example.

As shown in FIG. 19 (a), the driver 505y
Laser diode 50 based on LD drive clock
4y on / off laser diode on / off circuit 550,
A D / A converter 551 that converts 3-bit image density data (here, Y data) into an analog signal, and an analog signal based on the image density value are input from the D / A converter 551,
Current for driving laser diode 504y (LD drive current)
And a constant current circuit 552 for supplying Id to the laser diode on / off circuit 550.

Here, the LD drive clock is defined as “1”, on “0”, and off, and as shown in FIG. 19 (b), the laser diode on / off circuit 550 turns on / off the laser diode 504y accordingly. I do. Also, since the LD drive current Id and the laser beam power are in a proportional relationship, by generating the LD drive current Id based on the image density data value, a laser beam power output corresponding to the image density data value can be obtained. . For example, as shown in FIG. 19B, when the image density data value is “4” (data N−1 in FIG. 19), the corresponding LD drive current Id is supplied by the constant current circuit 552, The laser beam power of the laser diode 504y becomes level 4. When the image density data value is “7” (data N in the same figure), the corresponding LD drive current Id is supplied by the constant current circuit 552, and the laser diode 504y
Is at the level 7.

Next, referring to FIG. 19 (c), a laser diode
On / off circuit 550, D / A converter 551, and constant current circuit 552
Is shown below. Laser diode on / off
The circuit 550 includes TTL inverters 553 and 554, a differential switching circuit 555 and 556 that performs on / off toggle operation, and VG1> VG
When 2, the differential switching circuit 555 is on, the differential switching circuit 556 is off, and when GV1 <VG2, the differential switching circuit 555 is off and the differential switching circuit 556 is on. Resistors R ₂ and R ₃ that form a voltage divider that generates VG2
It is composed of Therefore, LD drive clock is “1”
At this time, the output of the inverter 554 generates VG1 and satisfies the above condition (VG1> VG2), and the differential switching circuit 555
n, the differential switching circuit 556 is turned off, and the laser diode 504y is turned on. Conversely, when the LD drive clock is “0”, there is no output of the inverter 554, so that the above condition (VG1 <VG2) is satisfied and the differential switching circuit
555 is off, the differential switching circuit 556 is on, and the laser diode 504y is off.

The D / A converter 551 includes a latch 557 for latching input image density data while the LD drive clock is “1”, a _Vref generator 558 for providing a maximum output value _Vref , an image density data and a maximum output value V. and a 3-bit D / A converter 559 that outputs analog data Vd based on _ref .
Here, the relationship between Vd and the image density data and the maximum output value _Vref is represented by the following equation.

Constant current circuit 552 is for supplying the current of the laser diode 504y to the laser diode on / off circuit 550 as described above, and has a transistor 560, resistors R _4, R ₅ Prefecture. The output Vd of the D / A converter 551 is applied to the base of the transistor 560, it determines the voltage applied to the resistor R _4. In other words, since the current flowing through the resistor R ₄ is approximately equal to the collector current of the transistor 560, V
The current Id flowing through the laser diode 504y is controlled by d.

FIG. 19D shows the output of the latch 557, VG1, Vd,
6 is a timing chart showing a relationship between Id and Id. Here, Vd takes eight values of _Vref × 0/7 to 7/7 based on image density data (3-bit data: 8 gradation data of 0 to 7), and Id is the value of Vd. based on, it indicates the level of eight levels of I ₀ ~I _7. The laser diode 504y forms a latent image as shown in FIG. 20 on the photosensitive drum 512y in accordance with the eight levels of Id (I ₀ = level 0, I ₁ = level 1 ‥‥, I ₇ = level 7). Form.

In the image forming system to which the anti-aliasing method and the apparatus of the present invention are applied, the pentagonal ABCDE shown in FIG. 5A is finally replaced with the toner image shown in FIG. Is formed on the recording paper. Generally, the resolution of the laser printer is 240-400
In consideration of the dpi, the density of the edge portion of the figure is visually reduced by the anti-aliasing process.
FIG. 22 shows a pentagonal ABCDE toner image in the case where the anti-aliasing processing is not performed. As is apparent from a comparison between FIG. 21 (the toner image of the present invention) and FIG. The jagged part (alias) on the stairs that appears in the shaded area becomes visually smooth.

Further, in the present embodiment, the multi-level drive by the power modulation is applied, but the same effect can be naturally obtained by using the multi-level drive by the pulse width modulation. Here, for reference, the change of the latent image form depending on the level of the pulse width modulation is shown in FIG. 23. Further, the toner image obtained when pulse width modulation is applied to the pentagonal ABCDE shown in FIG. As shown in FIG.

〔The invention's effect〕

As described above, the graphic processing apparatus of the present invention adjusts the output of the pixel at the edge of the vector data based on the area ratio to be filled, and smoothly expresses the jaggies (alias) at the edge of the output image. A graphic processing device for executing an anti-aliasing process, wherein a storage means for storing a reference area ratio set based on a plurality of divided straight lines passing through a predetermined end point on a pixel and having different slopes, and a plurality of divided straight lines A reference area ratio input unit that reads a corresponding reference area ratio from the storage unit based on the selected division line, and a vector data for the pixel of the edge portion. A decimal part detecting means for detecting a decimal part of the input / output coordinates; a decimal part of the input / output coordinates detected by the decimal part detecting means; Based on the edge information of the file data, the reference area ratio read by the reference area ratio input unit is corrected, and the area ratio calculation unit for calculating the area ratio is provided. In addition, the area ratio can be obtained at high speed. Further, even when the number of gradations of the approximated area ratio is small, the area ratio of the closest gradation can be approximated, and the accuracy can be improved.

[Brief description of the drawings]

1 (a) to 1 (d) are explanatory diagrams showing the principle of anti-aliasing processing in the graphic processing apparatus of the present invention, FIG. 2 is an explanatory diagram showing the configuration of an image forming system of the present invention, and FIG.
FIG. 4 is an explanatory diagram showing the configuration of a PDL controller (graphic processing device of the present invention). FIG. 4A is a flowchart showing the operation of the PDL controller. FIG. 4B is an explanatory diagram showing a path filling process. FIG. 4C is a flowchart showing the anti-aliasing process, and FIGS. 5A and 5B.
Is an explanatory diagram showing a linear vector division of a figure, FIG. 6 is an explanatory diagram showing an area ratio after performing an anti-aliasing process,
7 (a), (b) and (c) are explanatory diagrams showing RGB image data stored in the plane memory section of the page memory, and FIGS. 8 (a), (b) and (c) are anti-aliasing. FIG. 9 is an explanatory diagram showing the RGB image data stored in the plane memory section of the page memory when no processing is performed, FIG. 9 is an explanatory diagram showing the configuration of the image processing device, and FIG. Explanatory diagram showing a conversion graph, eleventh
FIGS. 12A, 12B and 12C are explanatory views showing a conversion graph for complementary color generation used in a complementary color generation circuit, and FIGS.
(B), (c), and (d) show FIGS. 7 (a), (b),
FIG. 13 (c) is an explanatory diagram showing a state where the RGB image data is output from the UCR processing / black generation circuit. FIG. 13 is an explanatory diagram showing a Bayer type 3 × 3 multi-valued dither matrix.
FIGS. 12 (a), 12 (b), 12 (c) and 12 (d) show FIGS.
FIGS. 15 (a), (b), (c), and (d) are explanatory diagrams showing a state in which Y, M, C, and BK data of (b), (c), and (d) are converted by a gradation processing circuit. FIG. 8 (a)
FIG. 16 is an explanatory view showing a state in which the data of (b) and (c) are processed by the image processing apparatus. FIG.
FIG. 17 is a control block diagram showing a printer.
FIGS. 18 (a) and (b) are explanatory diagrams showing the configuration of an exposure system of a yellow recording unit, and FIGS. 19 (a), (b), (c) and (c). d)
Is an explanatory diagram showing multi-level driving by power modulation, FIG. 20 is an explanatory diagram showing the state of a latent image according to the level of power modulation, and FIG.
The figure is an explanatory view showing the final toner image of the pentagonal ABCDE shown in FIG. 5 (a), FIG. 22 is an explanatory view showing the toner image of the pentagonal ABCDE when the anti-aliasing processing is not performed, and FIG. FIG. 24 is an explanatory diagram showing the state of a latent image according to the level of pulse width modulation. FIG. 24 is a pentagonal ABCD shown in FIG.
FIGS. 25 (a) and 25 (b) are explanatory diagrams showing a conventional anti-aliasing process when pulse width modulation is applied to E, and FIGS. 26 (a) and 26 (b) are uniform diagrams. Explanatory diagram showing anti-aliasing processing by the averaging method, FIG.
FIGS. 27 (a) and 27 (b) are explanatory diagrams showing the anti-aliasing processing by the weighted averaging method, and FIGS.
(B), (c), and (d) are explanatory diagrams showing examples of filters used in the weighted averaging method, and FIG. 29 is an explanatory diagram showing a convolution integration method with reference to 3 × 3 pixels. 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 300 …… Image reading device 400 …… Image processing device 500 …… Multi-level color laser printer 600 …… System controller

Claims (2)

(57) [Claims] 1. A graphic processing apparatus for adjusting an output of a pixel at an edge of vector data based on an area ratio to be filled and executing an anti-aliasing process for smoothly expressing a jagged (alias) at an edge of an output image. A storage means for storing a reference area ratio which is set based on a plurality of divided straight lines passing through a predetermined end point on a pixel and having respectively different inclinations; A reference area ratio input unit that reads a corresponding reference area ratio from the storage unit, based on the selected division line, and an input / output coordinate of the vector data with respect to the pixel of the edge portion. A decimal part detecting means for detecting a decimal part; a decimal part of the input / output coordinates detected by the decimal part detecting means; A graphic processing apparatus comprising: an area ratio calculating unit that corrects a reference area ratio read by the reference area ratio input unit based on edge information of vector data and calculates an area ratio. 2. The graphic processing apparatus according to claim 1, wherein when a pixel at the edge portion intersects a plurality of vector data, an area ratio is determined by a filling process for each sub-pixel.