JPH0818788A - Image processing method and apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an image processing method and apparatus in which cost performance is improved by performing smoothing processing with a minimum required memory capacity. [Configuration] For example, when the output paper size is A3,
4 bit × 4 kword and 5 bit × 4 kword SRAM are used, and the density of the input image signal is 600.
When it is dpi, it is a conventional 9bit × 4kword SRAM
However, the number of lines of pixels to be referred to is controlled so that the smoothing process is performed with the same memory capacity (b) as in the case of 300 dpi.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and apparatus for performing a smoothing process by selecting a pixel line to be referred to in accordance with the density of an input image signal.

[0002]

2. Description of the Related Art Conventionally, in a laser beam printer having a resolution of 600 dpi, which is composed of a printer controller and a printer engine, an image signal of 300 dpi or 600 dpi output from the printer controller has a density of 2400 dpi in the main scanning direction and sub scanning. It is configured to be converted into a smoothed image signal having a directional density of 600 dpi and output to the printer engine.

[0003]

However, in the above-mentioned conventional example, when the smoothing process is performed when the resolution is 600 dpi, the memory capacity is required to be about twice as large as that of the smoothing process when the resolution is 300 dpi, and the cost performance is improved. There was a drawback that it went down.

The present invention has been made to solve the above-mentioned problems, and provides an image processing method and apparatus in which cost performance is improved by performing smoothing processing with a minimum required memory capacity. With the goal.

[0005]

In order to achieve the above object, the image processing apparatus of the present invention has the following configuration.

That is, control means for controlling the number of lines of pixels to be referred to in the smoothing processing according to the density of the input image signal, and smoothing for performing the smoothing processing by referring to the pixels of the lines controlled by the control means. And means.

The image processing method according to the present invention has the following steps.

That is, a control process of controlling the number of lines of pixels to be referred to in the smoothing process according to the density of the input image signal, and a smoothing process of performing the smoothing process by referring to the pixels of the lines controlled by the control process. And the process.

[0009]

In such a configuration, the number of lines of pixels to be referred to in the smoothing process is controlled according to the density of the input image signal, and the smoothing process is performed by referring to the pixels stored in the plurality of controlled lines. To work.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing the arrangement of a laser beam printer according to this embodiment. As shown in the figure, a signal processing circuit 103 and a crystal oscillator 104 are provided between the printer controller 101 and the laser beam printer 102. In the signal processing circuit 103,
A printer controller 101 to 300 dpi including a host interface (I / F) 110, an image data generator 111, a CPU 112, an operation panel 113, an image memory 114, an address generator 115, an output buffer register 116, and an interface (I / F) circuit 117. Alternatively, the image signal VDO of 600 dpi is transferred to the transfer clock VCLK.
And the density in the main scanning direction is 2400.
The printer engine 10 converts the smoothed image signal SVDO of which the density in the sub-scanning direction is 600 dpi.
2 is performed.

Further, the CPU 112 is configured such that the printer controller 101 is currently in the above 600 dpi mode and 300 dpi.
The RESO signal is output as a signal indicating which of the pi modes is operating. This RES0 signal is a signal input to the signal processing circuit 103, and
The operation mode is 600 dpi when O = “H” and 300 dpi when RESO = “L”.

FIG. 2 shows a signal processing circuit 10 according to this embodiment.
3 is a block diagram showing the configuration of FIG. In the figure, 10
Is a memory control circuit for controlling writing and reading of the memory unit 30 described later. A selector 11 selects one of the two inputs A and B and outputs it to the terminal Y. 12 is a 9 × 9 bit shift register,
Image data is output while being shifted each time a clock is input. Reference numerals 13 to 15 are selectors similar to the selector 11, 16 and 23 are AND circuits, and 17 is a toggle flip-flop (T-FF). 18 is an interpolation logic circuit A
When the image signal from the printer controller 101 is 600 dpi, it has a function of converting the image signal into a signal of main scanning 2400 × sub scanning 600 dpi, and at the time of conversion, as shown in FIG. The number of lines is reduced from 9 to 5 and processing is performed.

On the other hand, 19 is an interpolation logic circuit B, which receives an image signal from the printer controller 101 at 300 dpi.
If this is the case, the main scanning is 2400 × the sub scanning 600d.
It has a function of converting into a signal of pi or main scanning 600 × sub scanning 600 dpi. Reference numeral 20 denotes a parallel-serial conversion circuit, which converts the parallel 4-bit output from the interpolation logic circuit A18 into a serial signal and outputs it. Reference numeral 21 denotes a parallel-serial conversion circuit, which is an interpolation logic circuit B19.
The parallel 8-bit output from is converted into a serial signal and output. Reference numeral 22 is a frequency dividing circuit, which is a crystal oscillator 104.
The clock signal CLK is divided in frequency for each main scan in synchronization with the horizontal synchronizing signal EBD from the printer engine 102, and clock signals having a division ratio of 1/2, 1/8, 1/16 are output. A memory unit 30 stores the image signal from the printer controller 101. The detailed configuration will be described below.

FIG. 4 shows a memory unit 3 according to this embodiment.
It is a block diagram which shows the detailed structure of 0. In the figure, reference numeral 410 is half the depth of the conventional line memories 1 to 9 shown in FIG. 5 (a memory constituted by the line memories 401 to 404. Capacity 1/2) For example, the output paper size is A3. In case of size, 4bit × 4kword
SRAM can be used. Reference numeral 411 is a similar memory composed of line memories 405 to 409, and it is possible to use an SRAM of 5 bits × 4 kword. Reference numeral 412 is a selector, which selects the input A when it is 600 dpi and selects the input B when it is 300 dpi. 413 is a selector, 300 dpi and 600 d
Select input A up to 4096 dots of pi, 600 dpi
Input B is selected after 4097 dots of i.

The memory control circuit 10 includes a selector 41.
3 and 600 dpi, the main scanning direction is 409.
Read and write to the memory 410 up to the 6th dot, and
Control is performed so that the 97th dot and thereafter are read and written to the memory 411.

Here, the configuration of the above-mentioned memory unit 30 will be briefly described in comparison with the conventional one, taking as an example the case where the output paper size is A3 (the printer engine is compatible with A3).
It becomes like FIG. As shown in the figure, it is clear that the memory capacity is half in the case of (b) as compared with the conventional configuration of (a).

In the above arrangement, the printer controller 101 has a resolution of 60 with respect to the signal processing circuit 103.
The image signal VDO of 0 dpi or 300 dpi is transmitted. The resolution of the image signal VDO is the signal R as described above.
Determined by ESO. That is, RESO = "H"
When the density is 600 dpi, the density is 600 dpi, and when RESO = “L”, the density is 300 dpi. . Next, the operation of the signal processing circuit 103 according to this embodiment will be described. Here, a case where the density of the image signal VDO is 600 dpi will be described. In this case, the selectors 11 and 13-1
5 is a state in which the input A is all selected by the RESO signal. Further, the horizontal synchronization signal EBD from the printer engine 102 is directly input as the horizontal synchronization signal BD to the printer controller 101. The printer controller 101 synchronizes with the image clock signal VCLK sent from the signal processing circuit 103 every time the horizontal synchronizing signal BD is input, and the image signal VDO for one line of main scanning.
Is sent. The VCLK signal is a signal obtained by dividing the output CLK of the crystal oscillator 104 by ⅛ in synchronization with the EBD signal in the frequency dividing circuit 22. The image signal VDO of the first line input to the signal processing circuit 103 is input to the first bit of the shift register 12 and also written to the line memories 401 and 405 of FIG. And
The selector 413 reads out up to the 4096th dot in the main scanning direction from the line memory 40 and thereafter reads from the line memory 405, and in the next main scanning, simultaneously with the input of the image signal VDO of the second line, the line memory 4 is read.
The image signals VDO at the same position on the first line, which are stored in 05, are read and input to the corresponding shift registers 12.

On the other hand, the input second-line image signal VDO is written in the same positions in the line memories 402 and 406. Thus, the image signal VDO input for each line is stored in the line memories 401, 405 → 402, 4
Writing and reading are performed while being shifted in the order of 06 → ... → 404 and 408. Therefore, the memories 410 and 411 store image signals VDO for four consecutive lines. Then, the outputs of the memories 410 and 411 and the image signal VDO from the printer controller 101 are input to the shift register 12, and the image signal for the main scanning 9 dots × the sub scanning 5 lines, a total of 45 dots, is the VCLK signal. Is output while being shifted by. Then, the image signals for these 45 dots are input to the interpolation logic circuit A18.

In the interpolation logic circuit A18, as shown in FIGS. 7 and 8, the image signals of the peripheral pixels of the target pixel M are referred to, and the density of the image signal with respect to the target pixel M in the main scanning direction is quadrupled and smoothed. Signal Ma, Mb, Mc and M
Convert to d. This conversion is performed by comparing the output data of the shift register 12 with a plurality of predetermined dot patterns. This dot pattern is for extracting the feature of the target pixel M. For example, in the case shown in FIG. 9A, the target pixel M is regarded as a part of the diagonal line close to the vertical direction (sub-scanning direction). , Is converted into the illustrated data. Further, in the case as shown in (b), it is considered that the target pixel M is a part of a diagonal line which is close to the horizontal direction (main sub-scanning direction),
Converted to the data shown.

However, in FIG. 9, “●” is a black dot,
“O” indicates a white dot, and other portions in the reference area may be either black or white.

The data of the target pixel M is determined by comparing it with a large number of dot patterns as shown in FIG. The algorithm for converting the image signal is different between the diagonal line close to the vertical and the diagonal line close to the horizontal as described above.
Conversion is performed such that dots are added or deleted in units of 0 dpi. In addition, in a diagonal line that is close to the horizontal, small dots of 2400 dpi unit are added as density in the vicinity of pixels that form a step. By adding the small dots as the density, the printed image becomes smooth due to the step portion being blurred due to the characteristics of electrophotography, and the smoothing effect can be obtained.

The pixel signal Ma determined as described above
To Md are converted into serial signals by the parallel-serial conversion circuit 20, and the image signals SV are transmitted through the selector 15.
It is sent to the printer engine 102 as DO. Therefore, this image signal SVDO is used for main scanning 2400 × sub scanning 6
The signal has a density of 00 dpi. However, the smoothing process designation signal SON from the printer controller 101
When "No smoothing processing" is specified by,
The image signal VDO of 600 dpi is directly sent to the printer engine 102 as SVDO in both main scanning and sub-scanning.

Since the above-described processing is performed, the image signal VDO from the printer controller 101 is delayed by 5 dots in the main scanning direction and 4 lines in the sub scanning direction before the actual printing. Therefore, the printer controller 101
Then, at the timing when this delay is taken into consideration, the image signal VD
Output O. The image signal VDO output from the printer controller 101 is L1, L in order from the first line of the main scan.
FIG. 10 shows the timings of the image signals when 2, ... In the figure, signals read out from the line memories 405 to 408 are shown. The printer engine 102 modulates the laser based on the above-mentioned image signal SVDO to perform an image forming operation.

An example of an image printed by the above processing results is schematically shown in FIGS. 11 and 12. 11 and 1
In FIG. 2, (a) is the actual data of 600 dpi sent from the printer controller 101, (b) is the data converted by the signal processing circuit 103, and (c) is actually printed by the data shown in (b). The image is shown. One grid of each grid is a unit of 600 dpi. In this way, the density of the image signal in the main scanning direction is set to 4
By doubling, it becomes possible to obtain a high quality image.

Next, the density of the image signal VDO is 300 dp.
The operation of the case i will be described with reference to the related drawings. In this case, the selectors 13 to 1 shown in FIG.
5, the B input is all selected by the RESO signal, and the selector 412 shown in FIG.
13, the A input is in the selected state. The printer controller 101 has the above-mentioned image signal VDO density of 600 dpi.
In the same manner as in the above case, the image signal VDO for one main scanning line is sent in synchronization with the image clock signal VCLK from the signal processing circuit 103 every time the horizontal synchronizing signal BD is input.
However, the BD signal in this case is the printer engine 102.
The EBD signal from is extracted every other line to 300 dp
The BD signal is equivalent to that of the printer engine of i. The VCLK signal is obtained by dividing the oscillation clock of the crystal oscillator 104 by 1/16 in the frequency dividing circuit 22. Here, since the data amount of one line of the image signal VDO of 300 dpi is 1/2 of that in the case of 600 dpi, by configuring as described above, the image signal VDO of one line is sent from the printer controller 101. The time becomes equal to that when the density of the image signal VDO is 600 dpi.

The image signal VDOL of the first line input to the signal processing circuit 103 is input to the first bit of the shift register 12 via the selector 11 and is also written to the line memory 401. Selector 11
When the density of the image signal VDO is 300 dpi, is switched alternately by the EBD signal from the printer engine 102. That is, the printer engines 102 to 600
When viewed in units of dpi, the A input is selected on the odd line and the B input is selected on the even line. Therefore, in the next main scan, the first read from the line memory 401
The image signal VDOL of the line is again supplied to the shift register 12
Is written to the line memory 401 while being input to the first bit of the. At this time, the printer controller 101
Since no BD signal is transmitted to the controller 101, the controller 101 suspends the transmission of the image signal VDO on the even lines.

Further, in the next main scanning, the image signal VDO of the second line to the controller 101 is input, and at the same time, the image signal VDO of the same position of the first line stored in the line memory 401 is received. It is read and input to each shift register 12. Then, the input second-line image signal VDO is written in the line memory 401, and the signal read from the line memory 401 is written in the same address in the line memory 402. In this way, each line memory 401-409
Is input to the shift register 12 while writing and reading of the image signal VDO of the same line are performed twice. Therefore, the same image signals for 9 lines are continuously output from the shift register 12 for two main scanning lines. These image signals are input to the interpolation logic circuit B19.

The interpolation logic circuit B19 is shown in FIGS.
As shown in FIG. 4, the density of the image signal for the target pixel N is converted by referring to the image signals of the peripheral pixels of the target pixel N.
The logic of this conversion can be selected by the smoothing processing designation signal SMTH and the dither processing designation signal DITH from the printer or controller 101. Further, the SMTH signal can be designated on the operation panel 113 or the application software according to the preference of the user.

The smoothing processing designation signal SMTH designates the density of the converted image signal in the main scanning direction. In the interpolation logic circuit B19, when SMTH = “H”, the density of the image signal for the target pixel N is increased by 8 times in the main scanning direction and doubled in the sub scanning direction as shown in (a) of FIG. Smoothed signal, ie, main scanning 2400 x sub scanning 600
Convert to a signal having a density of dpi. On the other hand, SMTH =
In the case of "L", the image signal for the target pixel N is converted into a signal having a double density in both the main scanning direction and the sub scanning direction, that is, a signal of 600 dpi in both the main scanning direction and the sub scanning direction as shown in (b).
This conversion is performed by comparing the output data of the shift register 12 with a predetermined plurality of dot patterns, as in the case of 600 dpi described above. However, the dot pattern in this case is a unit of 300 dpi.

FIG. 15 shows an example of a dot pattern in the case of SMTH = “H”, and the order of conversion is that of odd-numbered lines in FIG.
4 N1a, N1b, N1c, N1d, N1e, N1
8 data of f and N1h are generated, and N is generated on the even line.
2a, N2b, N2c, N2d, N2e, N2f, N2
Generate eight data of h. 16 shows SMTH =
This is an example of a dot pattern in the case of "L", and the conversion order is to generate two data N1a and N1b in the odd line and two data N2a and N2b in the even line.

The dither processing designating signal DITH is a signal for designating whether or not the conversion processing is performed on the dither image. The conversion process for the dither image is performed on the dither image having a predetermined growth pattern, for example, as shown in FIG.
(A) is converted into the 300 dpi, 4 × 4 dither pattern into the 600 dpi, 4 × 4 dither pattern shown in (b) of FIG. 17, whereby the image quality of the dither image can be improved.

The signal thus generated by the interpolation logic circuit B19 is converted into a serial signal by the parallel-serial conversion circuit 21 and sent to the printer engine 102 as the image signal SVDO via the selector 15.
However, when "no smoothing process" is designated by the smoothing process designation signal SON from the printer controller 101, the image signal VDO of 300 dpi is doubled in both the main scanning direction and the sub scanning direction in both the main scanning direction and the sub scanning direction. And is sent to the printer engine 102 as an image signal SVDO at a density of 600 dpi. The timing of the above signals is shown in FIG. In the figure, the line memory 4
The signals to be read are shown for 01 to 409. The printer engine 102 modulates the laser based on the image signal SVDO to perform an image forming operation.

Based on the results of the above processing, SMTH
19 and 20 show an example of an image printed when = "H".
Is schematically shown in. In the figure, (a) shows the controller 1
The original data of 600 dpi sent from 01, (b) is the data converted by the signal processing circuit 103, and
(C) shows an image actually printed by the data shown in (b). One grid of each grid is 300dp
It is a unit of i.

Further, in the above-mentioned processing, as described above, in the diagonal line near the horizontal, 2400 dp is generated in the vicinity of the pixel forming the step.
Smoothness is obtained by adding small dots of i units as density and blurring the boundary. However, if you dislike this processing, set SMTH = “L” to obtain 600 × 600.
Since the mode is the dpi mode, the smoothness is somewhat inferior, but a sharp image of 600 dpi can be obtained.
In this way, by converting the density of the image signal,
Even with a small memory of 300 dpi, it is possible to obtain high-quality images that make the most of the performance of the 600 dpi engine.

If there is an edge with a 1-dot width in each of 4 lines before and after the current line, smoothing processing is performed over 9 lines, but at 600 dpi, 2 lines before and after the current line are included. If there is no 1-dot width edge in each line, it is regarded as a straight line, and smoothing processing can be performed only over 5 lines. Therefore,
When the angle is close to vertical (about 78.5 ° or more) only at 600 dpi, the image quality is slightly inferior to the conventional one, but 300 dpi
When i, the same image quality as the conventional one can be obtained.

As described above, according to this embodiment, the number of pixel lines to be referred to during smoothing is changed (30).
By reducing to about half of that at 0 dpi), 300d
When pi, smoothing processing can be performed exactly as in the conventional case. In addition, even at 600 dpi, smoothing processing (image quality that is almost comparable to the conventional one) is possible, the memory capacity can be saved in half (the memory capacity required at 300 dpi is enough), and the cost performance improves. effective.

<Modification> In the embodiment, the reference to 9 lines is made to be 5 lines, but the present invention is not limited to this, and may be 7 lines, for example, in consideration of image quality. Also, the method of dividing the memory is not limited.

Furthermore, in the embodiment, the case where the density of the image signal from the printer controller is 300 dpi and 600 dpi has been described, but the present invention is not limited to this, and for example, 2400 dpi, 480 dpi or 4 dpi.
Of course, the case of 00 dpi and 800 dpi is also acceptable. If the printer engine can switch the resolution by a command from the controller, the signal processing circuit is
Each of the resolutions of 0, 300, 480, 600, and 800 dpi is supported. For example, when the density of the image signal from the controller is 240, 300, and 400 dpi, the density in the main scanning direction is 8 times the density in the sub scanning direction. It is also possible to adopt a configuration in which when the image signal density is doubled and the image signal density is 480, 600, or 800 dpi, only the density in the main scanning direction is doubled and printed. Further, in the embodiment, when the density of the image signal from the controller is 300 dpi, the example in which the scanning line density is converted into the data of 600 dpi which is doubled and printed is described, but the present invention is not limited to this and, for example, 900 dpi. Of course, it is also possible to convert the data into 900 dpi data having a scanning line density three times higher and print it by using the printer engine of.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can also be applied to the case of being achieved by supplying a program to a system or an apparatus.

[0041]

As described above, the cost performance can be improved by performing the smoothing process with the minimum required memory capacity.

[0042]

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a laser beam printer according to this embodiment.

FIG. 2 is a block diagram showing a detailed configuration of a signal processing circuit shown in FIG.

FIG. 3 is a diagram illustrating reference pixels in the case of 600 dpi according to the present embodiment.

FIG. 4 is a diagram showing a detailed configuration of the memory unit shown in FIG.

FIG. 5 is a diagram showing a configuration of a conventional signal processing circuit, particularly a memory unit.

FIG. 6 is a diagram showing a configuration example of a memory unit according to the related art and the present embodiment.

FIG. 7 is a diagram showing a target pixel and its peripheral pixels in the case of 600 dpi.

FIG. 8 is a diagram showing a process of quadrupling the density of a pixel of interest in the main scanning direction.

FIG. 9 is a diagram showing an example of a dot pattern for extracting diagonal lines close to the vertical in the case of 600 dpi.

FIG. 10 is a diagram showing an example of a dot pattern for extracting a diagonal line close to the side in the case of 600 dpi. It is a figure which shows the timing of each signal in case of 600 dpi.

FIG. 11 is a schematic diagram showing an example of a printed image in the case of 600 dpi.

FIG. 12 is a schematic diagram showing an example of a printed image in the case of 600 dpi.

FIG. 13 is a diagram showing a target pixel and its peripheral pixels in the case of 300 dpi.

FIG. 14 is a diagram showing a process of converting the density of a pixel of interest in the case of 300 dpi.

FIG. 15 is a diagram showing an example of a dot pattern in the case of performing the smoothing process of FIG.

16 is a diagram showing an example of a dot pattern when the smoothing process of FIG. 14 is not performed.

FIG. 17 is a diagram showing a 300 dpi, 4 × 4 dither pattern and a dither image.

FIG. 18 is a diagram showing the timing of each signal in the case of 300 dpi.

FIG. 19 is a schematic diagram showing an example of a printed image in the case of 300 dpi.

FIG. 20 is a schematic diagram showing an example of a printed image in the case of 300 dpi.

[Explanation of symbols]

 10 memory control circuit 11 selector 12 shift register 18 interpolation logic circuit 19 interpolation logic circuit 20 parallel-serial conversion circuit 21 parallel-serial conversion circuit 22 frequency dividing circuit 30 memory unit 101 printer controller 102 printer engine 103 signal processing circuit 104 crystal oscillator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location G06T 5/20 G06F 15/66 355 P 15/68 410

Claims (4)

[Claims] 1. A control unit for controlling the number of lines of pixels to be referred to in the smoothing process according to the density of an input image signal, and a smoothing process for performing the smoothing process by referring to the pixels of the line controlled by the control unit. An image processing apparatus comprising: 2. The image processing apparatus according to claim 1, wherein the control unit controls to reduce the number of lines of pixels to be referred to when the density of the input image signal is high. 3. A control means for controlling the number of lines of pixels to be referred to in the smoothing processing according to the density of an input image signal, and a smoothing for performing the smoothing processing by referring to the pixels of the lines controlled by the control means. An image processing apparatus, comprising: a recording unit configured to record an image smoothed by the smoothing unit. 4. A control step of controlling the number of lines of pixels to be referred to in the smoothing processing according to the density of an input image signal, and a smoothing process of performing the smoothing processing by referring to the pixels of the lines controlled by the control step. An image processing method comprising the steps of: