JPH0937076A - Printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printer capable of developing the original picture of gradation picture data to be picture data which visually looks gradating smoothly from low density to high density. SOLUTION: Based on original picture data inputted from an external device such as a host computer, a recording matrix selection means selects a matrix to use for the reproduction of the original picture from among plural recording matrixes corresponding to each density level of an output dot stored in a recording matrix storing means. Based on the selected recording matrix, CPU 101 executes print processing through the use of a printing data developing program 106. At this time, the recording matrix selection means selects the recording matrix of a dot distributed type to the low density part of the original picture and selects the matrix of a dot concentrated type to a high density part.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention is capable of printing output dots in a plurality of density steps, and by appropriately arranging the output dots in a predetermined recording matrix, halftone expression is performed to reproduce a grayscale image. The present invention relates to a printing apparatus using a halftone image reproduction method using a tissue dither method.

[0002]

2. Description of the Related Art Conventionally, a tissue dither method has been known as a method for reproducing a halftone image by a hard copy device or the like.

This tissue dither method assumes a recording matrix composed of a plurality of pixels, compares a threshold value determined for each pixel with the density level of an original image to be reproduced, and determines the density level as a threshold. The output dot is displayed for pixels exceeding the value, and is widely used because high-speed processing can be performed by a simple control system.

Further, in this tissue dither method, when the threshold value is set for the pixels in the recording matrix, a smaller threshold value is set for the pixels in the central portion of the recording matrix so that the output dots are centrally arranged. In many cases, the dot concentrated type is used.

[0005]

However, in order to increase the number of gradations in the tissue dither method, it is necessary to increase the number of pixels in the recording matrix. In that case, in the dot-concentrated arrangement, the output dots are arranged in the recording matrix. Since the halftone dots are concentrated in the center to reduce the apparent resolution, the reproduced halftone image has a large coarse halftone dot.

Further, in the printing with this arrangement, the output dots placed on a white background are very conspicuous in the low density region, and the output dots placed in the high density region are hardly conspicuous. Therefore, when a halftone image with a gradation that changes linearly from white to black is reproduced, it looks as if it suddenly becomes dark in the low-density area and changes little in the high-density area. It will not look beautiful.

On the contrary, in the dot dispersion type arrangement in which the output dots are placed as far apart as possible, conversely, the output dots placed on a white background are less noticeable in the low density region, but the output at the time of printing in the high density region. The gradation does not look neat after all, because it seems to be suddenly darkened due to the influence of dot bleeding.

The present invention has been made to solve the above-mentioned problems, and it is possible to visually see a smooth density change from a low density to a high density of an image, which is necessary for reproducing an original image. It is an object of the present invention to provide a printing apparatus capable of reproducing an original image of grayscale image data into image data in which halftone is expressed at high speed without making halftone dots conspicuous with the number of gradations.

[0009]

In order to achieve this object, a printing device according to a first aspect of the present invention is capable of printing an output dot in a plurality of density steps, and is a two-dimensional image composed of a plurality of pixels. Assuming a recording matrix having a wide range, a halftone image reproduction method is used that reproduces the original image by determining the output dots of the pixels of the recording matrix according to the density level of the multi-gradation original image to be reproduced. Furthermore, a recording matrix storage unit that stores a plurality of recording matrices corresponding to the respective density levels of the output dots, and an original image is reproduced from the plurality of recording matrices stored in the recording matrix storage unit. A recording matrix selecting means for selecting a recording matrix to be used and a control means for executing printing using the recording matrix selected by the recording matrix selecting means. There. Further, in the printing apparatus according to claim 2, the recording matrix storage means stores at least a dot concentration type recording matrix and a dot dispersion type recording matrix, and the recording matrix selecting means,
A dot dispersion type recording matrix is selected for the low density portion of the original image, and a dot concentration type matrix is selected for the high density portion.

[0010]

According to the printing apparatus of the present invention having the above-mentioned structure, the recording matrix selecting means selects the output dots stored in the recording matrix storing means on the basis of the original image data inputted from an external device such as a host computer. The one used for reproducing the original image is selected from a plurality of recording matrices corresponding to the respective density steps, and the control means executes printing based on the selected recording matrix.

According to another aspect of the printing apparatus of the present invention, the recording matrix selecting means selects a dot dispersion type recording matrix for a low density portion of an original image from the recording matrix storing means, and a high density is selected. A dot-concentrated matrix is selected for the part.

[0012]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the arrangement of a printing apparatus according to an embodiment of the present invention. An interface 102 that receives print data from an external device such as a host computer to a CPU 101 that controls the entire printing apparatus.
And 50% density of black and 10 for each point of the output dot
A print engine 103 capable of printing in two levels of 0% density, and a volatile memory for storing data that needs to be temporarily stored during operation of the printing apparatus. The RAM 104 is connected to the ROM 105, which is a non-volatile memory that stores various programs read and executed by the CPU 101.

Inside the RAM 104, a work memory 110 for temporarily storing data necessary for developing print data, and one page of image image data created by developing the print data are stored. A page memory 111 and a recording matrix corresponding to the output level used by the organization dither method when expanding the print data.
A 0% density recording matrix 112, a 100% density recording matrix 113, and a halftone pattern 114 used for expansion are prepared.

The recording matrix 112 for 50% density is also used.
7 is a dot dispersion type threshold value such as 701 shown in FIG. 7 at which output dots are dispersed as much as possible, and dot concentration like 704 shown in FIG. 7 at which output dots are concentrated as much as possible in the recording matrix 113 for 100% density. The type threshold is set.

Reference numerals 702 and 703 shown in FIG.
It is an example of 25% and 50% density halftone patterns created by using the tissue dither method for a print engine that can output one recording matrix for one output dot at a single density level. The dots are dispersed throughout the matrix. On the other hand, 705 and 706 are 704
Is a 25% and 50% density halftone pattern created by using the tissue dither method for the same print engine, and the output dots are concentrated in the center of the matrix. The ROM 105 has a print data expansion program 106 for expanding the print data received by the interface 102 into image image data by the organization dither method, and a recording matrix selection for selecting an output level corresponding recording matrix used by the print data expansion program 106. A recording matrix selection program 107, which is a means, is prepared.

The image image data is bitmap data having data of 2 bits per pixel corresponding to a print pixel, and the page memory 111 has a capacity capable of storing image image data corresponding to one print sheet. There is. Here, in the bitmap data 201 of FIG. 2, 0 is no printing, 1 is printing at 50% density, and 3 is 100%.
Shown is printing at a density, which results in a printed output 202 when printed. The filled squares of the printout 202 are printed in black at 100% density, and the shaded squares are 50.
Gray print at% density.

Next, the operation of the printing apparatus will be described, focusing on the operation of the print data expansion program 106. When print data, which is grayscale image data, is sent from an external device such as a host computer through the interface 102, the CPU 101 activates the print data expansion program 106 in the ROM 105 to display an image from the print data as shown in the flowchart of FIG. Performs expansion processing to image data.

First, when the CPU 101 receives data from the interface 102 (S301), it is checked whether the received data is a print instruction command (S).
302), if it is a print instruction command, page memory 11
Printing is performed according to the image image data in 1 (S3
03).

If it is not a print instruction command, the received data is sent to the print data expansion program 106 and expanded into image image data (S304). S304
Then, the print data expansion program 106 expands the grayscale image data, which is the print data, into image image data by using the following tissue dither method.

The print processing executed by the CPU 101 based on the print data expansion program 106 corresponds to the control means.

When outputting an image of grayscale data with a device in which the density level of the color that can be output to one dot is limited, it is necessary to convert the original image of the grayscale data into image image data of the density level that can be output. At this time, if a plurality of pixels are collectively treated as one pixel, many density levels can be expressed according to the number of constituent dots as shown in FIG. At this time, a group of a plurality of pixels is called a recording matrix. In the example of FIG. 4, the recording matrix is composed of vertical 2 pixels × horizontal 2 pixels. If this recording matrix is regarded as one pixel, one dot has two density levels of 50% density and 100% density. In the print engine of the present embodiment capable of outputting the above, this pixel can express the density in 9 steps as shown in FIG. The shaded cells represent the output at a density of 50% and the filled cells represent the output at a density of 100%. The numbers below indicate the density levels when the recording matrix is regarded as one pixel. Then, the density level close to the print data is shown in FIG.
If a halftone pattern such as the above is created and the pattern is spread over the shape of the print data, even a print engine that can output only two density levels can perform pseudo 9-gradation printing.

Next, a method of expanding the print data in the page memory 111 by the print data expanding program 106 will be described with reference to the flowchart shown in FIG. When the original image data is input, the print data expansion program 106 first determines the recording matrix to be used by the recording matrix selection program 107 (S501, S502, S).
503).

The recording matrix selection program 107 checks whether or not the original image data has a density of 50% or less (S50).
1) 100 when the original image data exceeds 50% density
Select the recording matrix 113 for% density (S502),
When the density is 50% or less, the recording matrix 112 for 50% density is selected (S503).

If the original image data exceeds 50% density, the print data expansion program 106 follows S502.
Creates a 100% density halftone pattern (S
504). In S504, the halftone pattern 114 is first set to 1 so that the background is filled with the output level of 50% density. Then, in order to set the amount exceeding 50% density, F = (L-50) × 2 × 0.01 × M + 1 (Equation 1) F: density boundary value of the original image M: pixels forming the recording matrix Number L: The density boundary value F of the original image is calculated with the density level of the original image. The F calculated by this is compared with the threshold value in the 100% density recording matrix 113, and if F exceeds the threshold value, 3 is set at a position corresponding to the pixel of the halftone pattern 114.
Is set so that the pixel is filled with the output level of 100% density.

If the original image data is 50% or less, S5
50% of the print data expansion program 106 following 03
A density halftone pattern is created (S505).
In S505, the halftone pattern 114 is initially set to 0.
Set so that the background is not painted. Then, F = L × 2 × 0.01 × M + 1 (Equation 2) F: density boundary value of original image M: number of pixels forming recording matrix L: density boundary value F of original image at density level of original image The F calculated by this is compared with the threshold value in the recording matrix 112 for 50% density, and when F exceeds the threshold value, 1 is set to the position corresponding to the pixel of the halftone pattern 114. , So that the pixel is filled with the output level of 50% density.

By S504 and S505, an image image having a density close to the density level of the original image data is created in the halftone pattern 114. Next, the halftone pattern 114 is laid out within the outline of the original image data, and the image is paged. The shape data is combined by setting in the memory 111 (S506), and the expansion of the print data is completed. When this operation is performed on all print data for one page, image image data capable of reproducing a grayscale original image with a density close to the specified density level is generated in the page memory 111.
Is created.

Halftone pattern 1 created below
14 will be described with an example in which print data of 75% and 25% density levels is developed. In the printing apparatus of this embodiment, the recording matrix 112 for 50% density is as shown in FIG.
As shown in 701, a dot dispersion type threshold value is set so that the output dots are separated as much as possible, and in the 100% density recording matrix 113, the output dots are concentrated around a certain point in the matrix as 704. Dot concentration type threshold value is set.

When the print data of the density level of 75% is input, the density level exceeds 50%, so that 1 is set to all the halftone patterns 114. Then, the calculation is performed by the equation 1 to calculate F = (75-50) × 2 × 0.01 × 16 + 1 = 9. And the recording matrix 11 for 100% density
At 704, which is 3, 3 is set at a position on the halftone pattern 114 corresponding to a pixel having a threshold value smaller than 9, and a halftone pattern 601 is created. Then, the halftone pattern 602 is written on the page memory 111 at a position corresponding to the inside of the contour of the print data.

On the other hand, when print data with a density level of 25% is input, the density level is 50% or less, so 0 is set in all halftone patterns 114. Then, the calculation is performed by the equation 2 to calculate F = 25 × 2 × 0.01 × 16 + 1 = 9. And the recording matrix 112 for 50% density
In step 701, 1 is set at a position on the halftone pattern 114 corresponding to a pixel having a threshold value smaller than 9, and a halftone pattern 603 is created. Then, the halftone pattern 603 is written on the page memory 111 at a position corresponding to the inside of the contour of the print data.

When the development of the original image data for one page is completed and the print start data is sent, the CPU 101 transfers the image image data in the page memory 111 to the print engine 1.
03 to print. The dots in which 0 is set in the image data are not printed, the dots in which 1 is set are printed in gray with 50% density, the dots in which 3 is set are printed with black with 100% density, and the halftone pattern 601 is printed as 602, and the halftone pattern 603 is printed as 604. The filled squares of the printouts 602 and 603 are black prints at 100% density, and the shaded squares are gray prints at 50% density.

In the 50% density recording matrix 112, the threshold values are set so that the dots are separated as much as possible, so that the output dots that are placed apart are not conspicuous, and the total circumference of all the output dots is smaller. Since the length is long, the outline of the output dot is blurred due to the influence of bleeding at the time of printing, and the fact that the color is gray with 50% density also adds dots in the low density area up to 50% density. It is possible to avoid becoming conspicuous.

The recording matrix 11 for 100% density is also provided.
In 3, the thresholds are set so that the dots are concentrated, and the part where the background can be seen and the part where the output dots are placed are clearly separated, so that the background should not be hidden too much. In addition, since the total circumference of all output dots is short, the influence of bleeding during printing is small, and it is possible to suppress the appearance of dark black in a high density area up to 100% density. .

The present invention is not limited to the embodiment described in detail above, and various modifications can be made without departing from the spirit of the invention.

For example, although the print engine of this embodiment can print at two different density levels for one pixel,
It may be capable of printing at three or more density levels. In that case, two kinds of output level corresponding recording matrixes may be allocated to three or more kinds of density levels for low density and high density, or different output level corresponding recording matrices may be provided for each density level. You may prepare.

Although the threshold value of the recording matrix corresponding to the output level is set in advance, the number of pixels forming the recording matrix and the set threshold value can be changed according to the original image data to be reproduced. Good.

[0037]

As described above, according to the printing apparatus of the present invention, the recording matrix used in the tissue dither method can be switched according to the density of the grayscale image data. At this time, since the dots are arranged as far apart as possible by using the recording matrix in which the dots are not conspicuous in the low density region, the output dots that are arranged inconspicuously are not conspicuous. In addition, since the total circumference of all output dots is long, it is possible to prevent the outline of the output dots from being blurred due to the influence of bleeding at the time of printing so that the dots are concentrated and conspicuous.

On the other hand, in the high density region, the recording matrix is used so that the dots are conspicuous, so that the dots are arranged in a concentrated manner, so that the part where the background can be seen and the part where the output dots are placed. Is clearly separated, and makes you feel not to hide the background too much. Moreover, since the total circumference of all output dots is short, the influence of bleeding during printing is small, and it is possible to suppress the appearance of dark colors in the high density region.

Therefore, in the normal tissue dither method, the dots are suppressed from being conspicuous in a low density region where the dots are easily conspicuous. On the contrary, when the dots are dispersed, the color becomes too dark and the density change becomes inconspicuous. By concentrating the dots in the high density area to prevent it, it is possible to visually see the density change smoothly from low density to high density, which is necessary for reproducing the original image. Image data in which the original image of grayscale image data is expressed in halftone can be reproduced at high speed without making the halftone dots stand out by the number of gradations.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a printing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing image image data in one embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of the printing apparatus according to the embodiment of the present invention.

FIG. 4 is a diagram showing an example of density expression by a tissue dither method in one embodiment of the present invention.

FIG. 5 is a flowchart showing a print data rasterization process according to an embodiment of the present invention.

FIG. 6 is a diagram showing a difference in halftone pattern depending on a density according to an embodiment of the present invention.

FIG. 7 is a diagram showing a difference in dot arrangement according to a recording matrix in an embodiment of the present invention.

[Explanation of symbols]

 101 CPU 106 Print Data Development Program 107 Recording Matrix Selection Program 112 50% Density Recording Matrix 113 100% Density Recording Matrix

Claims (2)

[Claims] 1. A density level of a multi-gradation original image to be reproduced, assuming a recording matrix capable of printing output dots in a plurality of density steps and having a two-dimensional spread composed of a plurality of pixels. In accordance with the above, in a printing apparatus using a halftone image reproduction method of determining an output dot of the pixels of the recording matrix and reproducing an original image, a plurality of recording matrices corresponding to respective density steps of the output dot are provided. The recording matrix storage means to be stored, and the recording matrix selection means for selecting the one used for reproducing the original image from the plurality of recording matrices stored in the recording matrix storage means, and the recording matrix selection means. A printing apparatus comprising: a control unit that executes printing using a recording matrix. 2. The recording matrix storage means stores at least a dot concentration type recording matrix and a dot dispersion type recording matrix, and the recording matrix selecting means disperses dots in a low density portion of an original image. 2. The printing apparatus according to claim 1, wherein a type recording matrix is selected and a dot concentration type matrix is selected for a high density portion.