JPH06103382A - Image processor - Google Patents

Abstract

PURPOSE:To smoothly vary density of each picture element, and to prevent deterioration of a picture quality by deciding the propriety basing on density of an object picture element and the right picture elements thereof in accordance with a deciding condition set in advance, and determining the density of the object picture element. CONSTITUTION:In accordance with a program stored in advance in a ROM 25, respectively, while referring to a vector font stored in a font ROM 23 concerning a character code and decomposing image data stored in a RAM 24 into a linear component in the horizontal direction, a CPU 22 performs an anti-area thing processing and outputs it to a linear plotting device 28. The linear plotting device 28 plots an image of a linear component on a memory 26 by determining new density and writing in order in the page memory 26, from density of each picture element in the X axis direction inputted in order from a CPU 22, and density of a picture element read out of the page memory 26 in accordance with each picture element thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for performing anti-aliasing processing in order to form regions surrounded by edges of an image formed by edges displayed as vectors at specified densities. In particular, the present invention relates to an image processing apparatus that performs read-modify-write processing of anti-aliasing processing.

[0002]

2. Description of the Related Art An image described in a PDL language (page description language) such as Postscript which is input from a host machine such as a computer is printed by a printer such as a laser printer or a display such as a CRT. There is an image processing device that performs image processing in the middle of the image display for displaying.

In particular, when processing an image consisting of multiple gradations, areas surrounded by edges of an image formed by edges displayed as vectors (hereinafter referred to as "vector image") are respectively assigned with specified density. The filling process is frequently performed.

For example, when a character is printed, if a vector font is used, a beautiful character can be formed regardless of the size. However, the inside of the character cell formed by the edge displayed in vector is solidly black. The process of filling in is essential. An image having continuous gradations such as a photograph is also converted into an image having multiple gradations in order to perform digital processing, and image processing is performed as a vector image surrounding each area of the same gradation.

When an image processed in this way is output by a laser printer or a CRT, discontinuity at the next line is unavoidable no matter how high the pixel density or the resolution is. Very fine jaggedness (called jaggies or aliasing) appears in the shaded area near the horizontal. Therefore, visual smoothing is performed by anti-aliasing processing.

Anti-aliasing processing is roughly divided into methods for increasing the sample rate and one pixel.
With an averaging method that divides a pixel into sub-pixels and averages
There are types. Further, the averaging method includes a uniform averaging method in which each sub-pixel is treated as an equivalent value, and a weighted averaging method in which each sub-pixel is treated with a different weight.

Further, the read-modify-write processing of the anti-aliasing processing is performed on the continuous-tone image whose density changes continuously (multi-tone image converted for digital processing). . That is, when determining the density of a pixel on a page memory that stores multi-valued data, not only the density data of the area to which the pixel belongs, but also the density data of the pixel on the page memory is read out. The new density data is determined while referring to (modify) and written (write) on the page memory.

In this read-modify-write process, the density of a pixel on the edge portion, which is the boundary between two regions, is set to the density of one region by the area ratio K (0≤K) of the pixel in the region. ≤1) and the sum of the density on the page memory and (1-K) to determine the sum. To keep edge continuity and conspicuous edge aliasing, It is an effective method and is widely used.

[0009]

However, the conventional read-modify-write processing is performed in the case where the areas A, B, and C having the densities D = 64, 50, and 35 are arranged as shown in FIG. And the densities of the pixels PX1 and PX2 in the edge portions X1 and X2 that respectively divide the areas A and B and the areas B and C are D = 61 and D = 41 as shown in FIG. 7D. Is desirable, but D = 51 and D = 29, respectively, as shown in FIG.

The pixel PX1 of D = 51 is still inconspicuous because it is still between the densities D = 64, 50 of the areas A and B, but the pixel PX2 of D = 29 is each density D = of the areas B and C.
Since the concentration is lower than either 50 or 35, the area C
There is a problem that the image quality of the entire image is impaired because it is noticeable as a bright thin line even if the difference from the density is small.

Further, when a white background (D = 0) figure (D = 64) as shown in FIG. 9A is processed, the density of each pixel on the edge portion depends on each area ratio. The density as shown in FIG. 9B is stored in the page memory. In order to erase this figure, if the same figure is painted white (D = 0) and the conventional read-modify-write process is performed, a light outline remains, as shown in FIG. 10B. However, there was also a problem that the image quality was significantly impaired.

Conventionally, there is no way to accurately process the density of each pixel on the edge portion so as not to cause such a deterioration in image quality, but the processing time becomes complicated because of the complicated processing. It had the drawback of being long.

The present invention has been made in view of the above points, and has been achieved by the conventional anti-aliasing processing and read
An object of the present invention is to determine the pixel density without deteriorating the image quality in the processing time equivalent to the modification write processing.

[0014]

In order to achieve the above-mentioned object, the present invention is an image processing apparatus for performing anti-aliasing processing on an image formed by edges displayed by vectors, the density of each pixel A page memory for storing multi-valued data indicating, and image position information for each line and an area ratio of pixels forming the image for drawing the image on the page memory according to the input image data. And a straight line drawing for drawing a line on the page memory by determining a new density from the image information output by the data processing means and the density on the page memory beforehand. In the image processing apparatus including the means, a pair of target conditions for processing on the page memory is set in advance based on the density of the pixel, and a determination condition for enabling or disabling is set. An availability determination unit that determines availability of a pixel and respective densities of pixels on the left and right of the pixel based on a determination condition of the density, and a data determination unit that determines a new density of a target pixel according to a determination result of the availability determination unit are provided. .

In the above image processing apparatus, the propriety determination means determines the target pixel, and if not, the pixel next to the left or right side of the target pixel is determined. It may be a means for determining a pixel on the right or left of the pixel.

In addition, an anti
It is preferable to provide condition changing means for changing the judgment condition according to the processing mode of the aliasing processing.

[0017]

In the image processing apparatus configured as described above, the propriety determination means determines propriety based on the densities of the target pixel and the pixels on the left and right of the target pixel according to preset determination conditions, and according to the determination result. The data determination means determines the density of the target pixel. Therefore, the density of each pixel changes smoothly and the image quality is not deteriorated.

If the acceptability determination unit determines that the target pixel is negative, the pixel next to the left or right is next determined, and if the result is negative, the pixel to the right or left is further determined. If the determination is performed in the preset order in this way, the number of determinations as a whole can be reduced and the processing time can be shortened.

Further, if the condition changing means changes the judgment condition in accordance with the processing mode designated from the outside, the optimum image processing can be performed according to the purpose.

[0020]

FIG. 2 is a block diagram showing the relationship between the host machine 10 and the printer 15. A host machine 10 such as a computer is provided with a keyboard 11 which is an input device and a CRT display 12 which is a display device. The image information described in the PDL language input from the keyboard 11 is displayed on the CRT display 12 and edited. Output to the printer 15 for each page.

The printer 15 is composed of a controller 20 and an engine 30. The controller 20 performs anti-aliasing processing on image information written in the PDL language input from the host machine 10 and multivalued image data for each page. , And once stored in the page memory, it is output to the engine 30 as a video signal. The engine 30, which is an output device, converts each line into an image in accordance with an input video signal, prints the formed image of one page on a sheet, and outputs the image.

FIG. 3 is a circuit diagram showing the configuration of the controller 20 which is an embodiment of the image processing apparatus according to the present invention shown in FIG. The controller 20 includes a receiving device 21,
CPU 22, font ROM 23, RAM 24, ROM
25, a page memory 26, a transmission device 27 and a straight line drawing device 28, which are connected to each other by bus lines such as a data bus, an address bus, a control bus and the like.

The image data and the pixel density described in the PDL language which are respectively input from the host machine 10 via the receiving device 21, the multi-value level (indicating the pixel density), the page size, the enlargement or reduction ratio of the output image, etc. The image information for one page consisting of is temporarily stored in the RAM 24.

Next, the CPU (central processing unit) 22 which is the data processing means stores the character code in the RAM 24 while referring to the vector font stored in the font ROM 23 according to the program stored in the ROM 25 in advance. The stored image data is decomposed into straight line components in the horizontal direction (X-axis direction), subjected to anti-aliasing processing, and output to a straight line drawing device 28 which is a straight line drawing means.

The line drawing device 28 determines a new density from the density of each pixel in the X-axis direction which is sequentially input from the CPU 22 and the density of the pixel read from the page memory 26 corresponding to each pixel. By writing in the memory 26 in order, the image of the linear component is drawn on the page memory 26. That is, the read / modify / write processing is executed to obtain multi-gradation image data in the page memory 26.
Expand to the top.

In accordance with a command from the CPU 22 according to the designated pixel density, the transmitting device 27 sends multi-level image data for one page developed in the page memory 26 to a video signal synchronized line by line with an image clock. The image formed by the engine 30 is printed on a sheet by converting the image into a sheet and outputting it to the engine 30.

FIG. 4 is a circuit diagram showing an example of the structure of the straight line drawing device 28 shown in FIG. 3. FIG. 4A shows the entire structure of the straight line drawing device 28, and FIG. The configuration of a read-modify-write control unit (hereinafter referred to as "RMW control unit") 34, which is one of the constituent elements and executes read-modify-write processing, is shown.

The straight line drawing device 28 shown in FIG.
Is an FI including five FIFO memories 32a to 32e.
An FO memory unit 32, a memory synchronization control unit 33 that outputs a signal that controls the operation timing of each memory, an RMW control unit 34, an oscillation circuit (OSC) 35 that outputs a clock CLK that serves as a synchronization reference, and a clock. An X counter 36 that counts CLK and outputs coordinates in the X-axis direction;
It is composed of a comparator 37 which detects the match between the contents of the counter 36 and the data X2.

The RMW control section 34 shown in FIG.
Is a LUT (look-up table) circuit 42 and 3
Latch circuits 43a to 43c and latch circuits 43a to 43c
Comprising a comparator 44, which is an adequacy determining unit and a condition changing unit for determining the admissibility of the density held in the reference numeral 43c, and a selector 45 which is a data determining unit for determining the density of the target pixel in accordance with the result of the determination. There is.

The CPU 22 sends the write signal WR together with the FIF
The density value ZC of each pixel, the area ratio K, the ordinate Y of the drawing line, the drawing start position X1, and the drawing end position X2 are input to the respective FIFO memories 32a to 32e of the O memory unit 32, and the respective FIFO memories are input. When stored in 32a to 32e, the signal EM indicating the memory empty output from the FIFO memory unit 32 to the memory synchronization control unit 33 is negated to notify that the data is input.

When the read signal RD is input from the memory synchronization control unit 33, the FIFO memory unit 32 retains the density value ZC, the area ratio K, and the ordinate Y of the data stored in each of the FIFO memories 32a to 32e. It is output to the memory synchronization control unit 33 and latched. The start position X1 is loaded into the X counter 36, and the X counter 36 outputs the contents to the memory synchronization control unit 33 and the comparator 37.

The X counter 36 uses the loaded X1 as a start value to input a clock CL from the oscillation circuit 35.
Count up K. The comparator 37 is an X counter 36.
Contents and end position X input from the FIFO memory 32e
2 is compared, and when they are equal, an end signal is output to the memory synchronization control unit 33.

The memory synchronization control unit 33 includes an X counter 36.
While the content of is counting up from X1 to X2,
The density value ZC and the area ratio K are output to the RMW control unit 34, the contents of the X counter 36 are output to the page memory 26 as an address signal ADR, and a signal MWR for instructing writing and reading of the memory is output. .

The RMW control unit 34 reads the density value MD (readout data) of the pixel corresponding to the pixel of the coordinates Y and X to be processed on the page memory 26 and latches the circuits 43a to 43.
The LUT circuit 42 is latched by the latch circuit 43c.
Density value MD of the target pixel latched in, that is, density MC
And the density value ZC and the area ratio K that are input from the memory synchronization control unit 33, and the density value RM that is the calculation result of the read-modify-write processing from those data.
The WC is output to the selector 45.

Three latch circuits 4 connected in parallel with each other
Of the densities MD read from the page memory 26, 3a to 43c latch the densities ML, MR, and MC of the pixel on the left side, the pixel on the right side, and the target pixel, and output A,
It outputs to B and C to the comparator 44. The latch circuit 43c also outputs the output C (density MC) to the LUT circuit 42.

The comparator 44 inputs the outputs A, B and C and the density ZC input from the memory synchronization control unit 33,
The CPU 2 which is a condition changing means according to the processing mode of the read / modify / write processing designated from the outside in advance.
According to the determination condition instructed by the instruction 2, whether or not each concentration to be inputted is determined, and the signal SEL indicating the determination result is output to the selector 45.

The selector 45 receives the read-modify-write processed density RMW input from the LUT circuit 42 according to the signal SEL input from the comparator 44.
Either C or the density ZC input from the memory synchronization control unit 33 is selected and output as the density MD of the target pixel to be written in the page memory 26.

In FIG. 5, the CPU 22 shown in FIG.
Input vector image information for one page described in the language,
FIG. 9 is a flowchart showing an example of a routine for decomposing a graphic element into horizontal line components and accessing the line drawing device 28. In the following description, for example, “step 3” is abbreviated as “S3”.

When the routine shown in FIG. 5 starts,
In S1, the graphic element described in the PDL language is read and converted into a vector indicating an edge, and in S2 it is determined whether or not the converted vector is a curve. If so, the process proceeds to S3, the linear approximation is performed to decompose into a plurality of approximate straight lines, and then the process proceeds to S4.

In S4, data indicating the starting point, the ending point (each coordinate value) of each straight line vector, etc. is converted into an edge table (hereinafter referred to as "E").
(T)). For vector registration, one of the both ends of the straight line vector having the smaller Y coordinate value is the starting point, and if the Y coordinate values are the same, the one having the smaller X coordinate value is the starting point.
When all the registrations for one page are completed in S5, vector sorting is executed in order of increasing Y coordinate value of the starting point in S6, and the data in ET is sorted.

Next, in order to perform the anti-aliasing process for each line and output it to the line drawing device 28,
The address Y of the line is cleared in S7. Data for one line for each line to be processed in S8 is registered from the ET to the active edge table (hereinafter referred to as "AET"), and in S9, the data in the AET is sorted in ascending order of the X coordinate value to obtain the data. To organize.

Next, in order to calculate the area ratio K of the pixels of the edge portion, the pixels (pixels) are decomposed into subpixels vertically and horizontally subdivided in S10 to fill the subpixels in the edge region, and in S11. The area ratio K is calculated by dividing the number of filled subpixels by the number of all subpixels in the pixel.

When the area ratio K is calculated, in S12, the line drawing device 28 calculates the start position X1 (left end), end position X2 (right end), line address (coordinate value) Y, area ratio K, and density value ZC of the area. Information that has been processed in S13 after being transferred to
When it is removed from ET and all the information for one line is processed, the coordinate value Y is incremented in S14. In S15, it is determined whether or not all the lines are finished, and if not, S
Return to 8 and end when finished.

FIG. 6 is an explanatory view showing an example of an image in which the density continuously changes, and FIG. 7 shows a state in which the image shown in FIG. 6 is expanded in the page memory 26 as the density value of each pixel. FIG. The read / modify / write processing by the straight line drawing device 28 shown in FIG. 4 will be described below with reference to FIGS. 6 and 7.

As shown in FIG. 6, the areas A, B, and C having different densities are bounded by two edges X1 and X2 having X coordinate values X1 and X2, respectively, and the density is Da = 64, Db = 50, and Dc = 35. Since the edges are both vertical for convenience of explanation, the pixels PX1 and PX2 associated with the respective edges X1 and X2 are common to each line, and the area ratio of the area A in the pixel PX1 is Ka = 80%, The area ratio of B is Kb = (1-K
a) = 20%, the area ratio of the region B in the pixel PX2 is Kb = 40%, and the area ratio of the region C is Kc = (1-K
b) = 60%.

Originally, as shown in FIG. 7A, the density of each pixel is D = D for the pixel on the left side of the pixel PX1.
a = 64, the density of the pixel sandwiched between the pixels PX1 and PX2 is D = Db = 50, and the density of the pixel on the right side of the pixel PX2 is D
= Dc = 35 and the density D of the pixels PX1 and PX2
1, D2 is obtained as the sum of the products of the concentrations on both sides and the area ratio, so that D1 = 61,
It is desirable that D2 = 41.

[0047]

## EQU1 ## D1 = Da * Ka + Db * Kb = 64 × 0.8 + 50 × 0.2 = 61.2≈61 D2 = Db * Kb + Dc * Kc = 50 × 0.4 + 35 × 0.6 = 41

However, in order to calculate from the densities of the regions on both sides of the edge, it is necessary to input the densities ZC of the regions on both sides in addition to the densities ZC of the regions being processed from the CPU 22, which complicates the process. Therefore, in the conventional read-modify-write processing, the density data MD of the corresponding pixel on the page memory 26 is read and processed as the density outside the area being processed.

That is, the conventional read modify
In the write processing, if the density of the area being processed is ZC, the area ratio of the target pixel on the edge is K, and the density of the corresponding read pixel is MC, the new density MD to be written.
n was calculated and determined by the equation 2.

[0050]

(2) MDn = ZC × K + MC × (1-K)

According to the equation (2), the page memory 26 is initially cleared to Dm = 0, and the area A (Da = 6).
During the process of 4), the area ratio of the pixel on the left side of the pixel PX1 is K
= 1 and the area ratio K of the pixel PX1 is Ka = 0.8. Therefore, the respective densities MDa and MD1 are written in the page memory 26 as 64 and 51.2 as shown in Expression 3.

[0052]

## EQU00003 ## MDa = 64 × 1 + 0 × 0 = 64 MD1 = 64 × 0.8 + 0 × 0.2 = 51.2

Next, when the region B (Db = 50) is processed, the area ratio of the pixel PX1 is Kb = 0.2, the density MD is 51.2, and the pixel on the right side of the pixel PX1. Has an area ratio of K = 1 and Dm = 0, and the pixel PX2 has an area ratio of Kb = 0.4 and Dm = 0. Therefore, the respective densities MD1, MDb, MD2 are 51 as shown in Equation 4. , 50,20.

[0054]

MD1 = 50 × 0.2 + 51.2 × 0.8 = 50.96≈51 = D1 MDb = 50 × 1 + 0 × 0 = 50 MD2 = 50 × 0.4 + 0 × 0.6 = 20

When the area C (Dc = 35) is further processed, the area ratio of the pixel PX2 is Kc = 0.6 and the density MD = 20, and the area ratio of the pixel on the right side of the pixel PX2 is Since K = 1 and Dm = 0, the respective densities MD2 and MDc are 29 and 35 as shown in Expression 5, and are as shown in FIG. 7C.

[0056]

MD2 = 35 × 0.6 + 20 × 0.4 = 29 = D2 MDc = 35 × 1 + 0 × 0 = 35

As described above, in the example of the conventional processing shown in FIG. 7C, the densities MD1 and MD2 of the pixels PX1 and PX2 applied to the edge are compared with the example shown in FIG. 7A.
Both values are low. Even so, since the density MD1 = 51 of the pixel PX1 is in the relationship of MDa>MD1> MDb and even if there is a density error of 10, it is not noticeable, so there is no fear that the image quality will be degraded.

However, the density MD2 of the pixel PX2 =
Since 29 has a relationship of MDb> MD2 <MDc, the density error is not 12, and even if the density difference is only 6 lower than MDc, it stands out as a bright thin line that should not be there, so the image quality is improved. Remarkably damages.

Also in this embodiment, the read-modify-write processing described above is performed by the LUT circuit 42 of the RMW control section 34 shown in FIG. 4B. The LUT circuit 42 is an LU that stores the results calculated in advance.
Using the T (look-up table), the density ZC, the area ratio K, and the read density MC are input and the density RMWC after the read-modify-write processing is instantly selected by the selector 4
Output to 5.

The concentration RMWC is M of the calculation result in Equation 2.
Since it is Dn, the density ZC input from the CPU 22 when K = 1 and the density MC read out when K = 0 are the density RMW subjected to the read-modify-write processing.
It is apparent from the above description that the data is output as C.

The difference between the embodiment according to the present invention and the prior art is that the latch circuits 43a to 43a, as shown in FIG.
43c, the comparator 44, and the selector 45 are provided. Before the LUT circuit 42 calculates the density RMWC of the target pixel, the latch circuits 43a, 43b, 43c read the densities ML, MR, MC of the left adjacent pixel, the right adjacent pixel, and the target pixel read from the page memory 26. Of the comparator 44 and the LUT as outputs A, B and C, respectively.
It is output to the circuit 42.

When performing image processing, the operator first operates the keyboard 11 or printer 15 of the host machine 10.
From the operation panel (not shown), one of the normal mode (conventional process), the special mode A, and the special mode B among the anti-aliasing process modes is designated.

FIG. 1 is a flow chart showing the first embodiment of the processing algorithm according to the designated mode of the RMW control unit 34. When the flow shown in FIG. 1 starts, it is determined whether the area ratio K input in S20 is 1, and K = 1.
If so, the process jumps to S29, and if no, that is, if K <1, the process proceeds to S21, and the densities MC and M are read from the page memory 26.
Read L and MR and calculate RMWC.

Next, in S22, it is determined whether or not the designated mode is the normal mode. If the designated mode is the normal mode, the process jumps to S28. If not, that is, the special mode, the process proceeds to S23, and the read density MC is 0. Whether or not (condition), that is, whether to write for the first time or already written,
If MC = 0, jump to S28, and if MC> 0, proceed to S24.

At S24, it is determined whether the density MC is equal to or higher than the density ZC input from the memory synchronization control unit 33 (condition).
If NO, that is, if MC <ZC, the process jumps to S26, and if MC ≧ ZC, the process proceeds to S25 to determine whether the specified special mode is the mode A. If it is S29, that is, if it is mode B, then S
Jump to 28 respectively.

When jumping from S24 to S26, it is determined whether or not the density ML of the left adjacent pixel is less than or equal to the output RMWC of the LUT circuit 42 and greater than 0 (condition). If yes, that is, RMWC ≧ ML> 0, S28 Jump to
If not, that is, if ML is larger than RMWC or 0, S2
7, the same determination (condition) is made for the density MR of the pixel on the right, and if RMWC ≧ MR> 0, then S
28, and if not, jump to S29.

The processing mode designated in advance is the CPU 22.
Is transmitted to the comparator 44 via
4 includes a condition S in accordance with the designation of the processing mode S22
Through the determinations of S27 to S27, the signal output to the selector 45 is turned on / off. The selector 45 selects RMWC when the signal SEL is off and ZC when the signal SEL is on.
It is output to the page memory 26 as D.

That is, in S28, the comparator 44 turns off the output signal SEL, so that the read-modify-write processed density RMWC is stored in the page memory 26.
Since the signal SEL is turned on in S29, the density ZC input from the memory synchronization control unit 33 is written in the page memory 26, and the processing of one target pixel ends.

FIG. 8 is a flow chart showing a second embodiment of the processing algorithm of the RMW control section 34. The same parts as those of the first embodiment shown in FIG. To do. The flow chart shown in FIG. 8 is shown in FIG.
Except for the three latch circuits 43a to 43c shown in FIG. 3, the densities MC, ML, and MR are applied to the RMW control unit which is read out whenever necessary and input to the comparator 44 or the LUT circuit 42.

The second embodiment shown in FIG. 8 differs from the first embodiment in that S31 to S33 are provided instead of S21. That is, in S21 of the first embodiment, the latch circuit 4
Since there are 3a to 43c, MC, ML, and MR are read collectively, but in the second embodiment, S31 corresponding to S21.
Then, only MC is read, and S3 is performed immediately before S26 and S27.
2, S33 are provided to read out the required ML and MR respectively. The other parts are the same, so the operation is exactly the same.

Compared with the first embodiment, the second embodiment does not require three latch circuits, so that the structure of the RMW processing section is simple and the cost is reduced. Further, if it jumps to S28 or S29 in the determination of S22 to S25, it is not necessary to read ML and MR, and even if the process proceeds to the determination of S26, it is not necessary to read MR if possible, so MC and M in S21.
The entire processing time can be shortened as compared with reading L and MR.

However, the latch circuits 43a to 43c
If not provided, as a third embodiment, although not shown in the figure, when the selector 45 outputs the density MD at the end of the processing of one pixel in FIG. It is latched in the latch circuit 43a as ML, and the MR of the latch circuit 43b is used as MC of the next pixel.
By shifting to c, the MR of the next pixel need only be read from the page memory 26 in S21, so the processing time can be further shortened.

In the first and second embodiments, S26, S
The condition determined in step 27 is that the pixel density to be processed is M
Since the judgment conditions and the final jump destinations S28 and S29 are the same except for L and MR, the contents may be exchanged to judge the condition in S26 and the condition in S27. However, in the case of the second embodiment, S32 and S33
The contents of must also be exchanged.

Since the flow shown in FIGS. 1 and 8 is repeated for each pixel process, the number of image processes for one page is enormous. Therefore, if you can save even a little time, the total processing time will be greatly reduced. Since the designated processing mode is not changed during the execution of the processing, the comparator 44 (or the CPU 22), which is the condition changing means, may change the hardware of the comparator 44 before executing the image processing according to the input processing mode. Wear (preferably, but software may be used) is switched as follows, for example.

In the case of the normal mode, S22 of the flow chart
To an unconditional jump to S28. In the special mode, S22 is replaced with NOP (no operation), S25 is abolished, and the jump destination of Y in S24 is mode A.
It is set to S29 or S28 depending on whether the mode is mode B or not. By doing so, the determination time of S22 can be saved in the normal mode, and the determination times of S22 and S25 can be saved in the special mode.

An example of processing the image shown in FIG. 6 according to the first embodiment (the same applies to the second embodiment) will be described below. If the designated processing mode is the normal mode, it does not pass through S23 to S27, so that the image of the density shown in FIG. 7C is drawn on the page memory 26 as in the conventional example.

If the special mode is designated, the pixels in the area A are K = 1 and ZC = Da = 64, so S20,
MD = ZC = 64 through S29, the drawing of the area A is completed, that is, the processing of the target pixel PX1 (S20 to S23,
When S28) is completed, ML = MD as shown in Equation 3.
a = 64, MC = MD1 = 51, and MR = 0.

Next, when the area B having the density ZC = Db = 50 is drawn, the area ratio K of the target pixel PX1 is K = 0.2 <
When 1 = MC = 51> 0, the process proceeds to S20 to S24. Since MC (51)> ZC (50), the process proceeds to S25, and it is determined whether the designated mode is the special mode A.
If it is mode A, jump to S29 and set ZC = 50,
If it is mode B, jump to S28 and RMWC = 51
Page memory 2 with (MD1 of equation 4) as MD
Write to 6.

Since the pixels in the area B are K = 1 like the pixels in the area A, MD = Db = 50, and when the processing of the target pixel PX2 is completed, as shown in the equation (4). ML
= MDb = 50, MC = MD2 = 20, MR = 0. Next, when the area C having the density ZC = Dc = 35 is drawn, the target pixel PX2 is K = 0.6 similarly to the pixel PX1.
Since <1 and MC = 20, the process proceeds to S20 to S24. Since MC (20) <ZC (35) this time, the process jumps to S26.

At S26, RMWC = 29 (MD of equation 5)
2) and ML = 50, RMWC <ML and the process proceeds to S27. Since MR = 0, the process jumps to S29, and ZC = 35 is set as MD in the page memory 26 regardless of modes A and B. Write. Therefore, if the designated processing mode is the special mode A, the special mode B, or the normal mode, (A), (B) of FIG.
It is drawn as shown in FIG.

As described above, in the normal mode (conventional processing), the column (D) of the pixels PX2 forming an edge is formed.
= 29) is conspicuous as a thin line brighter than the low density region C (D = 35), the special mode A or B according to the present invention.
In any case, since the density of pixels forming an edge falls within the density range of the regions on both sides of the edge, there is no risk of image quality deterioration.

9 and 10 show the page memory 26 once.
FIG. 10 is an explanatory diagram showing an example of erasing a figure drawn above. FIG. 9A shows a relationship between an original figure and a pixel, and FIG. 9B shows a figure having a density D = 64 as a page memory. 26 shows the densities of the respective pixels when drawn, and FIGS. 10A and 10B show the densities of the respective pixels when the figure is erased by the embodiment and the conventional example.

When the figure with the density D = 64 shown in FIG. 9A is drawn on the page memory, the area ratio K of each pixel becomes complicated, so the description thereof is omitted. However, except for the white background (D = 0). Since there is no portion in contact with regions of different densities, each pixel is drawn with the densities shown in FIG. 9B in accordance with its area ratio in both the conventional example and the example. In order to cancel the figure once drawn, the figure whose density is corrected to D = 0 is drawn again.

In such a case, in the conventional example and the normal mode, the read-modify-write processing causes MD = 0 for the pixel having the area ratio K = 1, but the pixel having the area ratio K <1 is shown in FIG. As shown in B), MD = 0 does not hold, and there is a problem that the contour line remains with a light density even if the central portion of the figure is erased.

According to the first and second embodiments, if the special mode is designated, the pixels in the figure have area ratios K = 1, ZC =
Since it is 0, MD = 0 through S20 and S29. Pixels (outline) on the edge part are K <1, ZC =
At 0, MC ≠ 0, and at S24 through S20 to S23, MC> ZC (condition), so the routine proceeds to S25. If mode A is specified, MD = 0 in S29, but if mode B is specified, the process proceeds to S28 and becomes the same as the normal mode.

Therefore, if the special mode A is designated when erasing a figure formed on a white background, (A) in FIG.
As shown in, it can be completely erased without leaving a contour line. However, if special mode B is specified,
The contour line remains as in the conventional example.

FIG. 11 shows an example in which the same figure as in FIG. 9 is written on a black background (D = 64) with a white outline (D = 0), and FIG. 11A shows the original figure. 11B and 11C show the densities of the respective pixels when drawn in the special modes B and A, respectively.

When the drawing is performed in the mode A, as shown in FIG. 11C, the pixels on the edge portion also have MD = ZC = 0.
Therefore, jaggies remain and the result is exactly the same as when anti-aliasing processing is not performed. Mode B
If the drawing is carried out, the anti-aliasing process and the read-modify-write process are performed as described above, and an image of excellent image quality is formed as shown in FIG. 11B.

That is, even when a figure having a density D = 0 is similarly drawn, the special mode A is specified when erasing a figure formed on a white background, and the special mode is specified when a white figure is formed on a black background. If B is designated, excellent images can be formed respectively.

[0090]

As described above, the image processing apparatus according to the present invention determines the pixel density without deteriorating the image quality in the same processing time as the conventional anti-aliasing processing and read-modify-write processing. You can do it.

[Brief description of drawings]

FIG. 1 is a flowchart showing a first embodiment of a processing algorithm of an RMW control unit according to the present invention.

FIG. 2 is a block diagram showing a relationship between a host machine and a printer including an image processing apparatus.

3 is a circuit diagram showing a configuration of a controller which is an embodiment of the image processing apparatus shown in FIG.

4 is a circuit diagram showing an example of a configuration of the straight line drawing device shown in FIG.

5 is a flowchart showing an example of a routine of the CPU shown in FIG.

FIG. 6 is an explanatory diagram showing an example of an image whose density continuously changes.

FIG. 7 is an explanatory diagram showing an example of a state in which the image shown in FIG. 6 is drawn on a page memory.

FIG. 8 is a flowchart showing a second embodiment of the processing algorithm of the RMW control unit.

FIG. 9 is an explanatory diagram showing an example of a state in which a figure and its image are drawn.

FIG. 10 is an explanatory diagram showing an example of a state in which the image shown in FIG. 8 is erased.

FIG. 11 is an explanatory diagram showing another example of a state in which a figure and its image are drawn.

[Explanation of symbols]

10 host machine 15 printer 20 controller (image processing device) 22 CPU (data processing means, condition changing means) 26 page memory 28 straight line drawing device (straight line drawing means) 34 RMW (read-modify-write) control unit 44 comparator (possible / impossible) Judging means, condition changing means) 45 Selector (data deciding means)

Claims (3)

[Claims] 1. An image processing apparatus for performing anti-aliasing processing on an image formed by edges displayed by vectors, comprising: a page memory for storing multi-valued data indicating the density of each pixel; Data for calculating the position information of the image and the area ratio of the pixels forming the image for each line in order to draw the image on the page memory according to the image data, and outputting it as the image information together with the density data. An image processing apparatus comprising: a processing unit; and a straight line drawing unit that draws a line on the page memory by determining a new density from the image information output by the data processing unit and the density on the page memory in advance, A determination condition is set in advance based on the density of the pixel to determine whether it is acceptable or not, and each of the target pixel to be processed on the page memory and the pixels to the left and right of the target pixel are set. Every said and determination means for determining whether by determination condition, the image processing apparatus characterized in that a data determining means for determining a new concentration of the target pixel in accordance with the determination result of the movable determination means. 2. The image processing apparatus according to claim 1,
The availability determination unit determines the target pixel, and if not, then determines the pixel on the left or right side of the target pixel, and if the result is no, further on the right or left side of the target pixel. An image processing apparatus, which is a means for determining a pixel. 3. The image processing apparatus according to claim 1, further comprising condition changing means for changing the determination condition according to a processing mode of the anti-aliasing process designated from the outside in advance. Image processing device.