JPH1110954A - Printing apparatus and print method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve gradation reproducibility at a low-density range in an apparatus and a method for printing with using laser beams. SOLUTION: When a distributed dither matrix screen is selected from a plurality of kinds of dither matrix screens (S802), values to microdots are output with the use of a table storing values obtained by substituting values at a low- density range of the selected distributed dither matrix screen with larger values of a different dither matrix screen at the low-density range (S803, S804, S805).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a printing apparatus and a printing method thereof, and more particularly, to a printing apparatus using a laser beam and a printing method thereof.

[0002]

2. Description of the Related Art Conventionally, when multi-valued image input data is processed using a dither method by pseudo gradation processing, it has been processed using a predetermined multi-valued output value table. For example, even when the dither matrix screen has a dither matrix screen having two different output patterns of a distributed dither matrix screen and a centralized dither matrix screen, a common multi-valued output value is used. Output was performed using a table.

[0003]

However, the above-mentioned 2)
In the prior art using different types of output patterns, the form of output dots in the low density region by the distributed dither matrix screen is smaller (low density) than in the case of the centralized dither matrix screen. It is easy to become dots, and the reproducibility of minute output dots on a medium that is actually output tends to deteriorate. For this reason, there is a problem that low-density output dots reproduced on the display of the host computer device are difficult to reproduce on a medium on which recording is actually performed, and appear faint or almost disappear. As described above, in the low-density region, there is a problem that the number of tones reproduced by the distributed dither matrix screen is smaller than that in the case of the centralized dither matrix screen, and the gradation reproducibility is poor. Was.

Accordingly, the present invention has been made in view of the above-mentioned points, and a printing apparatus and a printing method for solving the above-mentioned problems when performing processing for printing and recording image data with high definition and high gradation. The purpose is to provide.

[0005]

In order to achieve the above object, in the apparatus according to the present invention, dither processing is performed on an input image using a plurality of types of dither matrix screens having different patterns. A printing device that emits a laser beam based on the dither-processed image data and prints out the data, wherein a selecting unit that selects a distributed dither matrix screen from the plurality of types of dither matrix screens; Using a table storing values obtained by replacing values in the low-density region of the dispersed dither matrix screen with values that are darker than the values in the low-density region of the other dither matrix screen, Output means for outputting the image data, and performing gradation correction of the image data in the low density region. And wherein the door.

Here, in the apparatus according to the present invention, the other dither matrix screen is a centralized dither matrix screen, and the user can arbitrarily select one of the dither matrix screens by the selecting means. -It is also possible to select a matrix screen and use the replaced table according to the selection.

Here, in the apparatus according to the third aspect of the present invention, the selecting means is a host device connected to the outside, the host device includes display means for displaying an output image, and It is also possible to select a value in the low density region of the type dither matrix screen.

In this case, in the apparatus according to the present invention, the host apparatus recognizes the use frequency and type of the low density area in the output image, and according to the recognition result, the distributed dithering. The value in the low density region of the matrix screen can be selected automatically.

Here, in the device of the present invention described in claim 5, the host device can be connected via a network.

Here, in the apparatus according to the present invention, the output means uses the value of m (m ≦ n−1) bits stored in the table in which the input image of n bits is replaced. Can also be output.

In order to achieve the above object, in the method according to the present invention, the input image is subjected to dither processing using a plurality of types of dither matrix screens having different patterns, and the dither processing is performed. In a printing method of a printing apparatus for emitting a laser beam based on image data to print out, a distributed dither matrix screen is formed from the plurality of types of dither matrix screens.
A selecting step of selecting a screen, and storing a value obtained by replacing the selected value in the low-density area of the distributed dither matrix screen with a value darker than the value in the low-density area of another dither matrix screen. Outputting a value for a minute dot using a table, and performing gradation correction of the image data in the low density range.

Here, in the method according to the present invention, the other dither matrix screen is a centralized dither matrix screen, and in the selecting step, the user can arbitrarily select any one of the dither matrix screens. -It is also possible to select a matrix screen and use the replaced table according to the selection.

Here, in the method according to the ninth aspect of the present invention, in the selecting step, an output image is displayed by display means provided in an externally connected host device,
It is also possible to select a value in the low density region of the distributed dither matrix screen.

Here, in the method according to the present invention, in the selecting step, the use frequency and type of the low-density region in the output image are recognized by the host device, and according to the recognition result. The distributed dither
The values in the low density range of the matrix screen can be automatically selected.

Here, in the method according to the present invention, in the output step, m (m ≦ n−m) stored in the table in which the input image of n bits is replaced is stored.
1) It is also possible to output using a bit value.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) First, the overall configuration of the apparatus of the present invention will be described.

FIG. 1 is a block diagram showing a first embodiment of a printing apparatus to which the present invention is applied, and includes a work station (WS) 1 as a host computer. The work station 1 creates image data such as character information using an application, and stores the corresponding data in PDL.
The information is converted into (PDL) format page description input information and transmitted to the printer controller 14. The sent PDL data is stored in the input buffer 2 in the printer controller 14.
Is stored in A font ROM 3 stores character bit patterns or outline information, character baselines and character metric information, and is used for printing characters. Work station 1 is a CAD,
It is used in CG, design, and DTP fields in business.

Reference numeral 4 denotes a program ROM in which controller software such as a PDL command analysis program is stored in advance, and the CPU 12 loads the PDL command analysis program and executes processing to scan input data. Reference numeral 5 denotes a management RAM for software, which stores intermediate data obtained by analyzing input PDL data, global information, and the like.

The hardware renderer 8 executes the rendering process by ASIC hardware,
The rendering process is performed in real time in synchronization with the image data transfer of the printer interface (IF) 10. As a result, banding processing with a small memory capacity is realized. The data subjected to the rendering processing is temporarily stored in the page buffer 9. The object buffer 6 is a buffer for storing a page object in which drawing data is converted into bitmap data. Pseudo gradation processing is performed by the dither processing unit 11 to reproduce color accuracy with a small bit depth.

The CPU 12 is a central processing unit, and controls overall processing inside the printer controller 14. Reference numeral 13 denotes a well-known laser beam printer, which irradiates a rotary photosensitive member with laser light based on image data sent from a printer controller 14 to perform printing and the like.

By using the work station 1, the printer controller 14, and the printer 13, the printer 13 prints an image or the like based on the data generated by the work station 1 under the control of the printer controller 14. The device can be configured.
Image data is input to a printer engine of the printer 13, and a semiconductor laser is driven based on a signal obtained by pulse-modulating the image data to execute printing. In the above configuration, when the page description input information (PDL) is analyzed and multi-value halftone image information for recording is created, dither processing of pseudo gradation processing is used.

Here, pulse width modulation (Pulse Wi-Fi)
dth Modulation (PWM) will be described with reference to FIG. In FIG. 2A, reference numeral 20 denotes
A hatched portion indicates 256-gradation image data output from the printer IF 10 and input to the printer engine of the printer 13. In pulse width modulation,
For the density value of each pixel of the image data 20, a triangular wave 21
Is used as a comparison reference signal to compare the input density values. Then, when the density value of the image data 20 is larger than the level of the triangular wave 21 as in the period indicated by the thick line, the printer engine outputs a laser beam having a constant intensity as shown in FIG. By this pulse width modulation, gradation can be expressed by controlling the laser output time without changing the laser output intensity.

Here, the number of lines of the triangular wave 21 per inch for the print output image is counted as the number of lines. For example, in FIG. 2A, the number of lines of the triangular wave 21 is 200 (100 cycles per inch), and the resolution of the output image is 600 dp.
If i, 3 pixels (3 dots) in one cycle of the triangular wave 21
As a result of the comparison of the density values, the result is as shown in FIG.

Therefore, the on-time of the laser output shown in FIG. 2B differs depending on the frequency (period) of the triangular wave used as the comparison reference signal even when the density value of the pixel is the same. Also affect. In particular, when a low-density image is printed out, the higher the frequency of the triangular wave, the shorter the laser output time, which tends to make it difficult to express the density. Also, when dots are concentrated when outputting low-density dots, the characteristics of the electrophotography are similar to the case where the frequency is low compared to the case of outputting isolated dots as a whole, so that the expression of density is Easy to do. Therefore,
It is necessary to correct the density value of the pixel of the image data input to the printer engine according to the number of lines of the triangular wave, which is the PWM comparison reference signal, that is, the cycle (frequency).

Here, in order to explain the dither processing, first, the principle of simple multi-valued conversion will be described by using 8 bits (25 bits).
FIG. 3 shows an example in which the input (6 values) is converted into 2 bits (4 values).
The algorithm will be described with reference to FIG.

The 8-bit data that can take 256 values is divided into three areas AREA0 to AREA2 as shown in FIG. 3, and the following processing is performed on the input value of the target pixel. Where ARE
64 for A0, 128 for AREA1, AREA2
Is set as a threshold value in each area. The bold vertical lines in the figure corresponding to the 256 values 85 and 170 indicate the break between AREA 0,1 and the break between AREA 1,2. The thick line corresponding to 0 indicates the minimum value of 8-bit data, and the thick line corresponding to 255 indicates the maximum value.

First, in a region to which an input value belongs, a binarization process is performed so that an output value takes one of values at both ends of the region using a threshold value in the region. Therefore, AREA
0 or 85, AREA1 for inputs belonging to 0
85 or 170, AREA for inputs belonging to
For inputs belonging to 2, 170 or 255 are obtained according to each threshold value. These values are 2-bit data (0
0), (01), (10), and (11), and finally these 2-bit data are output.

FIG. 4 is an explanatory diagram showing an example in which the above processing is applied to multi-valued dither.

A threshold value suitable for the area is calculated from the target pixel data of the 8-bit input data shown in FIG. 4A and the dither matrix value corresponding to the target pixel, and the data of the target pixel is calculated by using the threshold value as 2 Value. The input data is
If the enlargement / reduction processing is performed, it is already converted to the resolution of the page buffer.

The dither matrix (D) shown in FIG.
other Matrix) is a 4 × 4 pattern,
The same pattern is repeatedly used on the page buffer 9. The maximum value of the elements of the dither matrix is 255 / (bit level-1), which does not exceed 255/3. Here, the bit level is the number of possible values of the data obtained by the above-described multi-level coding.

Hereinafter, the actual dither algorithm will be described with reference to FIG.

1. The value of the target pixel 400 in the input data is read, and it is determined to which region in FIG. 3 the pixel belongs. The value of the target pixel 400 is 180, and it is determined that the pixel 400 belongs to AREA2.

2. The value (74) of the element 410 of the dither matrix corresponding to the pixel of interest 400 is read and converted into a matching threshold value in the determined area AREA2. This threshold is obtained from 74 + 85 × 2 = 244.

3. If the value of the target pixel 400 is equal to or greater than the threshold value in AREA2, the maximum value of AREA2 is set as the output value, and if the value is less than the threshold value, the minimum value of AREA2 is set as the output value. Attention pixel value (1
80) <threshold (244), so the minimum value (170) of AREA2 is output.

4. The same process is repeated for the next pixel.

The above processing can be performed at high speed using a look-up table (LUT) in terms of hardware. In other words, for each of the input density values from 0 to 255, a 2-bit output density value that has been dithered at each position of the (4 × 4) size dither matrix is stored in advance in a look-up table. it can. The table size at this time is 2 for each YMCK color.
56 × (4 × 4) × 2 = 8192 bits are required.
That is, 1024 bytes are required.

The pointer indicating this table is shown in FIG.
This pointer has two bits each for row address data and column address data for 8-bit input data. The two bits indicated by this pointer are accessed from the dither matrix screen table shown in FIG.

In the present invention, after the input PDL data is expanded in accordance with the drawing information, dither processing is performed in accordance with the above-described dither algorithm.

FIG. 6 is a view showing a model of a state in which the result of dither processing is actually printed on a medium.

As shown in FIG. 6A, a distributed dither
In the output in the low density region of the dither processing by the matrix screen, there are many isolated dots (611, 612,...).
618), the output time of the laser by the PWM of the printer engine is shortened. As a result, in the low-density output portions 611... 618, the toner adhesion amount is small, so that the reproducibility is deteriorated.

As shown in FIG. 6 (B), in the small dot output in the low density region of the dither processing by the centralized dither matrix screen, the minute dots are concentrated at one place. Therefore, even if the reproducibility of one dot is low, it can be considered as one large dot as a whole. As a result, the output time of the laser modulated by the PWM of the printer engine is relatively long, so that the reproducibility of the dots as a whole is better as compared with the case of the distributed dither matrix screen.

FIG. 7 is a diagram showing the optimum output value according to the type of the dither matrix screen.

In order to improve the output reproducibility of isolated minute dots by the distributed dither matrix screen in the example of FIG. 6A, the optimum output value corrected as shown in FIG. 7 is used. . That is, when the output bit is a value (01) in the low density range, the centralized dither matrix
The output density value of the minute output dots of the screen (centralized DMS) is 85, while the output density of the isolated minute output dots of the distributed dither matrix screen (distributed DMS) is 100, which is higher than that of the centralized DMS. It is a dark value. When the dispersion type DMS dither is selected in the low density region, this value corrected by replacing it with a dark value is adopted as the output result of the dither processing.

FIG. 8 is a flowchart showing an outline of the algorithm of the present embodiment.

First, in step S 801, PDL data is input from the work station 1. In step S802, it is determined whether a distributed dither matrix screen has been selected as the dither matrix screen used for dither processing. The selection and switching of the dither matrix screen can be performed by the host device or the user.

If the centralized dither matrix screen is selected instead of the distributed dither matrix screen, the flow advances to step S807. On the other hand, if the distributed dither matrix screen has been selected, the processing after step S803 is performed.

In step S803, the output value look-up table (LUT) of the dither matrix screen in the printer controller 14 is selected or shared with the centralized dither matrix screen. Determine whether an output value LUT optimized for the type dither matrix screen has been selected. If a common item has been selected, the process proceeds to step S807.

In step S807, the corresponding output value of the output value LUT (standard output value table) for the centralized dither matrix screen is output in the dither processing, and the dither processing is performed, and the flow advances to step S810.

Also, a distributed dither as shown in FIG.
Optimized output value L for matrix screen
If a UT has been selected, the process advances to step S804 to read the LUT optimized by replacement and perform dither processing. In step S805, in the dither processing, the distributed dither
The value (01) of the output bit of the minute dot for the matrix screen is converted and output.

In the following step S810, step S8
The result of the dither processing in step 07 or S805 is transferred to the printer engine of the printer 13. The printer engine performs PWM modulation on the transferred data to control the emission of the laser output, and executes printing.

By the above processing, as shown in FIG. 9, low density output portions 911, 912,.
Also in 918, since the output time of the laser by the PWM modulation of the printer engine becomes longer, the reproducibility in the low density range is improved, and more reliable gradation expression can be realized.

As described above, according to the present embodiment, in a printer capable of multi-valued color reproduction, a dispersion type small dot output value of an output value table corresponding to an output of a centralized dither matrix screen is used. Dither matrix
In order to improve the reproducibility of minute output dots in the low-density region by the distributed dither matrix screen corresponding to the screen, the values of the low-density (small dots) output values in the multi-value output value table are centralized. Dither matrix
It is used by switching to a value replaced with a value darker than the minute dot output value of the screen. By using this table, low-density minute output dots due to the distributed dither matrix screen are difficult to reproduce on the medium where they are actually recorded, and look faint or almost disappear and disappear. On the other hand, since the density of the low-density output dot itself increases, the effect that the reproducibility of the output dot is improved even in the case of an isolated dot is obtained.

(Second Embodiment) In addition, the first embodiment
In the embodiment, a printing apparatus is connected to a stand-alone type work station 1 via a predetermined interface, but a plurality of computers are connected via a predetermined network or an integrated network such as ISDN. The present invention is also applicable to a printing device that receives print information between devices.

(Third Embodiment) In addition, the first embodiment
Has described an example in which pseudo gradation processing is performed on data of n = 8 bits to reduce the gradation to 2-bit data. However, the output value table of the dither matrix has multiple values other than 2 bits. Needless to say, the present invention can be applied to data in which output value data is stored and m (m ≦ n−1) bits other than 2 bits are reduced to multi-value gray scale.

(Fourth Embodiment) The first embodiment
In the embodiment, the value is converted for a minimum output value other than 0, and the converted output value LUT is used for dither processing. However, for a plurality of halftone values other than the 0 output value and the maximum output value, Therefore, the present invention can be applied to a case where a value is converted.

(Fifth Embodiment) When the user selects a distributed dither matrix for input image data in the host computer, the host computer automatically generates the output density table. It may be configured to set a minute output density value.

(Sixth Embodiment) The present invention recognizes the use frequency of low-density, that is, light to medium-density colors and the type of image in an image output from a host computer, and automatically controls the host computer. The present invention can also be applied to a printing apparatus capable of switching and selecting the density of output dots in this density area of the distributed dither matrix on the computer device side.

The method of the present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Needless to say, the method of the present invention can also be applied to a case where the method is achieved by supplying a program to a system or an apparatus. In this case, by reading out a storage medium storing a program represented by software for achieving the method of the present invention into a system or an apparatus, the system or apparatus can enjoy the effects of the method of the present invention. .

[0060]

As described above, according to the present invention, when printing using two types of dither matrix screens having different output patterns of a centralized dither matrix screen and a distributed matrix screen, The value of the fine dot output of the output table by dither processing is dispersed by using the fine dot output value of the distributed dither matrix screen replaced with a darker value than the output value of the centralized dither matrix screen. -Type dither matrix screen improves the output reproducibility of minute dots that tend to be isolated in low-density areas, avoids degradation of reproducibility of minute output dots, and reduces the number of output gradations of a distributed dither matrix screen. By avoiding the reduction, the floor by the distributed dither matrix screen The effect of the output of the corrected optimum image becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a printing / recording apparatus according to a first embodiment of the present invention.

FIG. 2 shows pulse width modulation (P
It is explanatory drawing which shows the principle of (WM).

FIG. 3 is an explanatory diagram illustrating an input / output relationship of dither processing to be used;

FIG. 4 is an explanatory diagram showing an example in which the processing of FIG. 3 is applied to multi-value dither.

FIG. 5 is a diagram illustrating a principle for realizing dither processing by hardware.

FIG. 6 is a diagram schematically showing an output image when the present invention is not applied.

FIG. 7 is a diagram illustrating optimal output values according to the type of dither matrix screen.

FIG. 8 is a flowchart showing an outline of an algorithm of the method of the present invention.
It is a chart.

FIG. 9 is a diagram schematically showing an output image when the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 work station 2 input buffer 3 font ROM 4 program ROM 5 management RAM 6 object buffer 7 color conversion hardware 8 hardware renderer 9 page buffer 10 printer interface 11 dither processing unit 12 CPU 13 printer 14 printer controller

Claims (11)

[Claims] 1. A printing apparatus that performs dither processing on an input image using a plurality of types of dither matrix screens having different patterns, emits a laser beam based on the dither-processed image data, and prints out. Selecting means for selecting a distributed dither matrix screen from the plurality of types of dither matrix screens, and selecting a value in the low density range of the selected distributed dither matrix screen from another dither matrix screen. Output means for outputting a value for a minute dot using a table storing a value replaced with a value darker than the value in the low density range, and performing tone correction of the image data in the low density range. A printing device characterized by the above-mentioned. 2. The other dither matrix screen is a centralized dither matrix screen, and the selection means allows a user to arbitrarily select any one of the dither matrix screens and display the replaced table. The printing apparatus according to claim 1, wherein the printing apparatus is configured to be used according to the selection. 3. The selection device is a host device connected to the outside, the host device includes a display device for displaying an output image, and a value in the low density region of the distributed dither matrix screen. The printing apparatus according to claim 1, wherein the user can select a printing apparatus. 4. The host device recognizes the use frequency and type of the low-density region in the output image, and automatically changes the value of the distributed dither matrix screen in the low-density region according to the recognition result. The printing apparatus according to claim 1, wherein the printing apparatus is selectively selected. 5. The printing apparatus according to claim 1, wherein the host device is connected via a network. 6. The output unit stores m (m ≦ n−1) stored in the table in which the input image of n bits is replaced.
2. An output using a bit value.
6. The printing apparatus according to any one of claims 5 to 5. 7. A printing apparatus which performs dither processing on an input image using a plurality of types of dither matrix screens having different patterns, emits a laser beam based on the dither-processed image data, and prints out. In the printing method, a selection step of selecting a distributed dither matrix screen from the plurality of types of dither matrix screens, and a value in a low density range of the selected distributed dither matrix screen is converted to another dither matrix. An output step of outputting a value for a minute dot using a table in which a value replaced with a value darker than the value in the low-density area of the screen is included, and the gradation correction of the image data is performed in the low-density area. A printing method for a printing apparatus. 8. The other dither matrix screen is a centralized dither matrix screen, and in the selecting step, a user arbitrarily selects any one of the dither matrix screens and displays the replaced table. The printing method of a printing apparatus according to claim 7, wherein the printing method is used according to the selection. 9. In the selecting step, an output image is displayed by display means provided in an externally connected host device, and the distributed dither matrix
9. The printing method according to claim 7, wherein a value in the low density area of the screen is selected. 10. In the selecting step, the host device recognizes a use frequency and a type of the low-density region in the output image, and according to the recognition result, the low-density region of the distributed dither matrix screen. 10. The printing method according to claim 7, wherein a value in the area is automatically selected. 11. In the output step, m is stored in the table in which the input image of n bits is replaced.
The printing method of a printing apparatus according to claim 7, wherein the output is performed using a value of (m ≦ n−1) bits.