JPH11115220A - Dot recording method for recording device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To sufficiently reduce the occurrence of streak-like density unevenness in recording in which intermediate gradation expression such as a natural image is frequently used. An ink jet recording head in which a plurality of ink ejection ports are arranged in a line is movably arranged in a main scanning direction which is a direction in which the ink ejection ports are arranged. Wound and moved in the sub-scanning direction, and dot printing is performed by synchronizing the rotation of the rotary drum and the movement of the recording head in the main scanning direction. Then, when the interval between the ink discharge ports is set to twice the minimum interval between the dots, and when printing a natural image that makes extensive use of the halftone expression, the recording head is moved in the main scanning direction during one rotation of the rotating drum. Move 2.5 times the minimum interval of
The dots are printed at a rate of one dot out of the dots, and the recording setting position of the even-numbered main scanning line is shifted by 1/2 dot with respect to the odd-numbered line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dot recording method for a recording apparatus provided with a recording head having a plurality of recording elements arranged in a line, such as an ink jet head having a plurality of ink ejection ports arranged in a line.

[0002]

2. Description of the Related Art In recent years, there has been known a recording apparatus which performs high-speed printing by providing a plurality of recording elements, as typified by an on-demand inkjet line printer. In such a recording apparatus, for example, an ink jet line printer, as shown in FIG. 8, the ink ejection volume and direction ejected from each ink ejection port 1 of a recording head 2 in which a plurality of ink ejection ports 1 as recording elements are arranged. Since there are variations among the individual ink ejection ports, variations occur in the size of the recording dots 3 and the dot positions.

When such a variation occurs, the density becomes high at a place where a dot is large or a place where a distance from an adjacent dot is short, and at a place where a dot is small or a place where a distance from an adjacent dot is long, the density becomes high. There is a problem that the density becomes low or white streaks occur, which causes uneven density and deteriorates image quality. It is conceivable to reduce the variation in the volume and direction of ink ejected from each ink ejection port 1 to a certain value or less. However, in order to achieve this, considerably high precision is required for the processing of each ink ejection port, and the manufacturing cost is reduced. Is very high and difficult to realize.

In order to solve this problem, there has been known a method of performing a checkered thinning-out printing by a recording head 12 having a plurality of ink ejection ports 11 as shown in FIG. In this method, the direction of arrangement of the ink ejection ports 11 of the recording head 12 is set as the main scanning direction, and dot recording is performed while the recording paper 13 is conveyed to the recording head 12 in the sub-scanning direction. In transporting the paper 13, the recording head 12
In this method, a checkered thinned-out printing is performed, and the printing is completed by transporting the recording paper 13 a plurality of times.

In FIG. 9, numerals 1 to 1 in the main scanning direction are used.
.. Indicate the print dot positions in the main scanning direction on the recording paper, and numerals 1 to 4,... Indicate the print dot positions in the sub scanning direction on the recording paper. One of the squares on the recording paper represents one dot. The numbers in the squares represent the numbers of the ink ejection ports for printing the dots and the printing order. For example, 1-1 is the number N
o. 1 indicates that dot printing is performed at the time of the first conveyance of the recording paper 13 by the ink discharge port 11, and 1-2 indicates the same number N.
o. This indicates that dot printing is performed at the time of the second transport of the recording paper 13 by one ink ejection port 11. Recording paper 13-2
At the time of the second transport, the recording head 12 is moved by one dot in the main scanning direction, that is, by the distance between the ink ejection ports.

In FIG. 8, one line is printed by one ink ejection port, but in FIG. 9, the first line in the sub-scanning direction and the third line in the sub-scanning direction are printed by the odd-numbered ink ejection port during the first conveyance of the recording paper 13. The second line, the fourth line, and the even line in the sub-scanning direction are printed at the even-numbered ink ejection ports.
Are moved by one dot in the main scanning direction, the first, third, and odd lines in the sub-scanning direction are printed by the odd-numbered ink ejection ports, and the second and third lines in the sub-scanning direction are printed by the even-numbered ink ejection ports. Print the 4th line and even line,
Printing is completed by carrying the recording paper 13 twice. As a result, one row is alternately printed by the two ink ejection ports, and the variation in printing by each ink ejection port can be dispersed into fine variations for each dot, so that stripe-like density unevenness can be reduced. It has become.

[0007]

The effect of reducing the density unevenness to some extent can be obtained by performing checkered thinning printing as described above, but a sufficient effect has not been obtained. That is, recently, a recording apparatus which can express one pixel in several gradations by modulating a printing area in one pixel using multi-valued image data is known. In the case of printing a flat-tone image on one surface with dots of an intermediate size, such as whether or not adjacent dots are in contact with each other, there is a problem that streak-like density unevenness is strongly noticeable visually. In particular, from the viewpoint of human visual characteristics, since the visual sensitivity in the horizontal and vertical directions is extremely high, it is highly likely that even a slight displacement will be recognized as streak-like density unevenness. Thus, the method of FIG. 9 did not provide a sufficient effect.

Accordingly, the present invention is directed to a dot recording method for a recording apparatus capable of sufficiently reducing the occurrence of streak-like density unevenness in recording in which halftone expression such as a natural image is frequently used. provide. The invention according to claim 2 is
Further, the present invention provides a dot recording method of a recording apparatus capable of maintaining a sufficient resolution for characters and line drawings. Further, the invention according to claim 3 further provides a dot recording method of a recording apparatus capable of maintaining a sufficient resolution for characters and line drawings and improving a recording speed.

[0009]

According to the first aspect of the present invention,
A recording head in which a plurality of recording elements are arranged in a line at predetermined intervals, and a recording medium is relatively moved with respect to the recording head in a direction orthogonal to a direction in which the recording elements of the recording head are arranged. In a printing apparatus that performs dot printing in the main scanning direction with each printing element of the printing head and moves dot printing in the main scanning direction in the sub-scanning direction by relative movement between the printing head and the printing medium, The recording head is arranged so as to be movable in the direction of the arrangement of the recording elements, and the interval between the recording elements of the recording head is set to N (an integer of N ≧ 2) times the minimum interval between dots to be recorded on the recording medium. While the recording medium passes through the recording head once, the recording head is moved in the main scanning direction by M times the minimum interval between dots (where M is an integer whose N / M is an irreducible fraction). Each recording element of the recording head performs dot recording in the sub-scanning direction at a rate of one dot out of R (an integer of R ≧ 2) dots, and the recording setting position with respect to the basic resolution of the dot in the odd and even lines in the main scanning line. It is possible to change.

According to a second aspect of the present invention, there is provided a recording head in which a plurality of recording elements are arranged in a line at predetermined intervals, and a recording medium is arranged on the recording head with respect to the recording head. Relative to the direction perpendicular to the main scanning direction, dot recording is performed in the main scanning direction by each recording element of the recording head, and dot recording in the main scanning direction is performed in the sub-scanning direction by relative movement between the recording head and the recording medium. In a printing apparatus, the printhead is movably arranged in the direction in which the print elements are arranged, and the interval between the print elements of the printhead is set to the minimum interval N (N ≧ N) between dots to be printed on a print medium. In the printing operation, the recording head is moved by the recording head once in the main scanning direction during the recording operation, and the minimum interval between dots in the main scanning direction is M (where M is N).
/ M is an integer that is an irreducible fraction) times and R (R ≧ 2) in the sub-scanning direction by each recording element of the recording head.
If the recording target is both a natural image such as a photograph and a character or a line image, and if the natural image is a natural image, the odd and even lines in the main scanning line are used for dot recording. Dot recording is performed with the recording setting position for the basic resolution shifted by half the minimum interval between dots, and for characters and line drawings, the recording setting positions for the odd and even lines of the main scanning line relative to the basic resolution are the same. It is to have done.

According to a third aspect of the present invention, in the dot recording method of the recording apparatus according to the second aspect, when a recording object on the same recording medium is both a natural image such as a photograph and a character or a line image, each recording is performed. For a line where the print setting position of the target odd-numbered line or even-numbered line coincides, dot printing is performed by each print element of the printhead while the print medium passes through the printhead once.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, an embodiment in which the present invention is applied to an inkjet line printer will be described. FIG. 1 is a view showing the overall configuration of a printer, in which a rotating drum 22 that rotates at a constant peripheral speed in a direction indicated by an arrow in the drawing is provided in a main body case 21. Is wound around the recording paper 25 conveyed.

That is, a paper feed cassette 26 is provided at the bottom of the main body case 21, and recording paper 25 is stacked and mounted on a mounting plate 27 of the paper feed cassette 26, and the recording paper 25 is fed to a feed roller 28. , One sheet at a time is taken out and fed to the paper feed rollers 23, 24. A manual feed tray 29 is mounted on the side of the main body case 21 so as to be openable and closable, and the manual feed tray 29 is opened and the recording paper 25 is manually fed from the manual feed tray 29 so that the feed roller 30 is used. The paper is fed to the paper feed rollers 23 and 24.
Switching between the feeding by the feeding roller 28 and the feeding by the feeding roller 30 is performed by a feeding switching unit 31.

A charging roller 32 for adsorbing and fixing the recording paper 25 fed by the feed rollers 23 and 24 to the drum surface is opposed to the rotary drum 22. Further, a printing mechanism having an ink jet recording head 33 in which a large number of ink ejection ports, which are recording elements, are arranged in a line at predetermined intervals is arranged opposite to the rotary drum 2. The printing mechanism includes the recording head 33.
, A linear motor 35 for controlling the reciprocating movement of the reciprocating mechanism 34 in the rotation axis direction of the rotary drum 22, and the reciprocating mechanism 34 in a direction perpendicular to the drum surface of the rotary drum 22. The apparatus includes a head moving device 37 including an advance / retreat moving means 36 for controlling the advance / retreat movement.

A recording paper peeling means having a peeling claw 38 which can be inserted between the drum surface and the recording paper 25 is disposed on the rotary drum 22. Is discharged to the recording paper discharging and conveying means 39. The recording paper discharging and conveying means 39
Is composed of a belt conveyor 40 in contact with the non-recording surface of the recording paper 25 and pressing means 41 for pressing the recording paper 25 against the surface of the belt conveyor 40.

At the end of the belt conveyor 40, the recording paper 25 conveyed by the belt conveyor 40 is discharged to an upper discharge tray 42 formed on the upper part of the main body case 21 or provided on a side surface of the main body case 21. Direction switching means 4 for switching between discharge and detachable discharge tray 43
4 are provided. Reference numeral 45 denotes an ink drying unit, 46 denotes an ink cassette, 47 denotes an ink buffer, and 48 denotes an ink supply tube.

FIG. 2 is a block diagram showing a hardware configuration. The control unit 51 includes a control unit 51. The control unit 51 controls the driving of the recording head 13 according to image data, and also controls the head moving device 37, A paper transport motor 52 for rotatingly driving the rollers 23 and 24, the feed roller 28, etc .; a drum motor 53 for rotatingly driving the rotary drum 22; and the charging for adsorbing and fixing the transported recording paper 25 to the rotary drum 22. The driving of the rollers 32 is controlled.

The head moving device 37 drives the linear motor 35 and synchronizes with the recording head 3 in synchronization with printing.
3 is moved in the rotation axis direction of the rotary drum 22 at a predetermined speed and timing. The paper transport motor 52 rotates the paper feed rollers 23 and 24 and the feed roller 28 to rotate the recording paper 2 fed from the paper feed cassette 26.
5 is conveyed to the rotating drum 22.

When the control unit 51 receives image data from the outside, it drives and controls the drum motor 53 and the paper transport motor 52, picks up the recording paper 25 from the paper supply cassette 26, and removes the recording paper 25 from the paper. Conveyed to the rotating drum 22 and wound around the rotating drum 22,
The sheet is fixed to the rotating drum 22 by the sheet fixing device 54. Then, the drum motor 53, the head moving device 37, and the recording head 33 are driven and controlled in synchronization with each other to perform dot printing on the recording paper 25.

FIG. 4 shows a dot recording method for the recording paper 25, that is, a printing method. The recording head 33 has a plurality of ink ejection ports 331 formed at predetermined intervals. Each ink ejection port 3 of the recording head 33
Numerals 1 to 15 in the main scanning direction, which is the direction in which 31 are arranged.
Indicates the print dot position in the main scanning direction on the recording paper 25, and numerals 1 to 1 in the sub-scanning direction which is the transport direction of the recording paper 25.
4,... Indicate print dot positions on the recording paper 25 in the sub-scanning direction. The transport of the recording paper 25 in the sub-scanning direction is performed by rotation of the rotary drum 22.

One of the squares on the recording paper 25 represents one dot. The numbers in the squares represent the numbers of the ink ejection ports 331 for printing the dots and the printing order. For example, 1-1 is a number No. A dot printed at the first transport of the recording paper 25 at the first ink ejection port 331, that is, a dot printed at the first rotation of the rotary drum 22.
4 is also the number No. Recording paper 2
5 shows dots to be printed at the time of the fourth transfer, that is, the fourth rotation of the rotating drum 22.

The recording head 33 is connected to the rotary drum 22
の of the interval between the ink ejection ports 331 during one rotation
In other words, the recording paper 25 is moved in the main scanning direction by the minimum interval between dots in the main scanning direction, and the rotation of the rotary drum 22 makes four rotations, whereby printing on the recording paper 25 is completed.
Is peeled off by the peeling claw 38 and is discharged by the recording paper discharging and conveying means 39.

In the recording head 33, one ink discharge port 331 can control ink discharge in eight stages including no ink discharge, and can reproduce an image of eight gradations per pixel. . That is, as shown in FIG. 3, seven types of variable dot sizes from one to seven gradations are used for one pixel, and a total of eight gradations including white can be expressed. Further, the dot size of each gradation is adjusted in advance so as to have a linear characteristic in density. The dot size of the seventh gradation, which is the maximum gradation value, is a size that forms a circle that completely covers a square pixel (dotted square in the figure) of a pure resolution possessed by the printer. . Therefore, this printer can handle 3-bit multivalued image data obtained by, for example, pseudo gradation processing.

When 3-bit multi-valued image data is input to the control unit 51, the control unit 51 converts the image data so that it can be transferred to the recording head 33 and stores it in a built-in storage unit. Then, the control unit 5
1 drives the drum motor 53 to rotate the rotating drum 22. The control unit 51 drives the paper transport motor 52 to drive the feed roller 30 and the paper feed roller 2.
One recording paper 25 is picked up from the paper feed cassette 26 by 3 and 24 and is conveyed to the rotating drum 22.

When the recording paper 25 reaches the rotating drum 22, the recording paper 25 is wound around the rotating drum 22, and the control section 51 drives and controls the charging roller 32. The recording paper 25 is charged by the charging roller 32 and
2 and is fixed by electrostatic attraction to the drum surface. Thus,
When the recording paper 25 is fixed to the rotary drum 22, the control unit 51 drives the recording head 33 and the head moving device 37 to start printing.

The printing operation is completed in four rotations with one rotation of the rotary drum 22 as one sub-scanning.
As shown in FIG. 4, each of the ink ejection port Nos. 1 to No. By the ink ejection from 8, ...
1,2-1,3-1,4-1,5-1,6-1,7-
The dots are printed at the positions of 1, 8-1,. That is, in the first rotation, printing is performed on odd-numbered rows every other dot in the main scanning direction and on odd-numbered lines in the sub-scanning direction. This can be realized by transferring image data thinned out in advance so as to print in this pattern to the recording head 33 in synchronization with the printing timing. The recording head 33 moves in the main scanning direction at a constant speed while the rotating drum 22 is rotating. This is performed by controlling the driving of the head moving device 37 by a control signal from the control unit 51. The moving speed of the recording head 33 is a speed at which the recording head 33 moves by の of the interval between the ink discharge ports during one rotation of the rotary drum 22.

In the second rotation of the rotary drum 22, each ink discharge port No. 1 to No. By the ink ejection from 8, ...
2,2-2,3-2,4-2,5-2,6-2,7-
Dots are printed at positions 2,. That is, printing is performed on even rows every other dot in the main scanning direction and on odd lines in the sub-scanning direction.

In the third rotation of the rotary drum 22, each ink ejection port No. 1 to No. By the ink ejection from 8, ...
3,2-3,3-3,4-3,5-3,6-3,7-
Dots are printed at positions 3,. That is, printing is performed on odd-numbered rows every other dot in the main scanning direction and on even-numbered lines in the sub-scanning direction.

In the fourth rotation of the rotary drum 22, each ink ejection port No. 1 to No. By the ink ejection from 8, ...
Dots are printed at positions 4, 2, 4, 3-4, 4-4, 5-4, 6-4,. That is, printing is performed on even rows every other dot in the main scanning direction and on even lines in the sub-scanning direction. And the rotating drum 22
Is rotated four times and printing is completed, the driving state of the charging roller 32 is released, the recording paper 25 is peeled off from the rotating drum 22 by the peeling claw 38, and the recording paper 25 is discharged to the upper discharge tray 42 by the recording paper discharge conveyance means 39. .

In this printing, the two rows on the left and right are in a state where dots are thinned out, and are not used for actual printing. This can be dealt with by setting blank data in an area of two dots each on the left and right when thinning out image data by the control unit 51.

The image data input to the control unit 51 includes a character object, a line drawing object,
Like a natural image object, each object is processed and input as a raster image that matches the printing architecture of the printer engine. From the viewpoint of image quality, these images can be classified into two types: objects of characters or line drawings / graphics whose resolution is important, and objects of natural images of photographs where gradation is important.

The characteristics of the image of a character or a line drawing object are as follows.
Basically, a pixel is formed at a level close to binary. That is, in most cases, a solid dot is formed except for the edge and outline of a character or a line drawing object. For example, when a smoothing process or the like is performed, a halftone dot is formed only at the edge. . The diameter of the largest solid dot is designed to cover the basic square lattice as shown in FIG. 3 as seven gradations. From compensation, density unevenness in the form of stripes hardly occurs.

On the other hand, the feature of the image of the natural image object is that dots of all sizes from 1 to 7 shown in FIG. 3 are used evenly. Therefore, there is a high possibility that an arbitrary gap always occurs between adjacent dots.
In particular, for a flat portion of an image in the vicinity of the halftone, since the halftone dots of the same size are arranged at regular intervals with a certain gap, the printing position of a series of pixels connected in the sub-scanning direction is determined. When the deviation occurs, stripe-shaped density unevenness is strongly recognized. In particular, from the viewpoint of human visual characteristics, since the visual sensitivity is extremely high for unevenness that continues in the horizontal or vertical direction, even a slight positional shift is recognized as streak-like unevenness in density.

Therefore, actually, the printing shown in FIG. 5A is performed for a character or a line drawing object, and the printing shown in FIG. 5B is performed for a natural image object. FIG.
(A) shows the case where normal checkered thinning printing is performed.The circles indicate the dots to be actually printed, the numbers in the dots indicate the numbers of the ink ejection ports for printing the dots, and the printing order. Squares indicate one dot area. Here, it is assumed that dots of approximately 3 to 5 gradations are actually printed. The moving speed of the recording head 33 in the main scanning direction is set to be 3/2 of the interval between the ink discharge ports 331 during one rotation of the rotary drum 22, that is, the moving speed of three dots in the basic resolution. . Also, here, No. 5 shows an example in which the fifth ink ejection port 331 is slightly shifted to the left due to the influence of misdirection or the like.

In the first rotation of the rotary drum 22, each ink ejection port No. 1 to No. By the ink ejection from 8, ...
1,2-1,3-1,4-1,5-1,6-1,7-
The dots are printed at the positions of 1, 8-1,. That is, in the first rotation, printing is performed on odd-numbered rows every other dot in the main scanning direction and on odd-numbered lines in the sub-scanning direction.

In the second rotation of the rotary drum 22, each ink ejection port No. 1 to No. By the ink ejection from 8, ...
2,2-2,3-2,4-2,5-2,6-2,7-
Dots are printed at positions 2,. That is, in the even-numbered row every other dot from the fourth dot in the main scanning direction,
In addition, printing is performed on odd-numbered lines in the sub-scanning direction.

In the third rotation of the rotary drum 22, each ink discharge port No. 1 to No. By the ink ejection from 8, ...
The dots are printed at the positions of 3, 2-3, 3-3, 4-3, 5-3,. That is, printing is performed on odd-numbered rows every other dot from the seventh dot in the main scanning direction and on even-numbered lines in the sub-scanning direction.

In the fourth rotation of the rotary drum 22, each ink ejection port No. 1 to No. By the ink ejection from 8, ...
Dots are printed at positions 4, 2, 4, 3, 4, 4-4,.... That is, printing is performed on even-numbered rows every other dot from the tenth dot in the main scanning direction and on even-numbered lines in the sub-scanning direction.

In this printing, the right and left 8 dots are thinned out and are not used for actual printing. This can be done by setting blank data in an area of 8 dots each on the left and right when thinning out image data by the control unit 51.

In FIG. 5B, in the checkered thinned-out printing, the printing start positions of the dots recorded by the odd lines and the even lines in the sub-scanning direction are shifted by one half of the one dot of the basic resolution. That is, while the dots on the odd lines are printed at their original positions, the printing positions on the even lines are printed with a shift of half the minimum interval between dots of the basic resolution.

Also in this case, the circle indicates the dot to be actually printed, the number in the dot indicates the number of the ink ejection port for printing the dot and the printing order, and the dotted square indicates one dot area. . Also in this case, dots of about 3 to 5 gradations are assumed as dots to be actually printed. The moving speed of the recording head 33 in the main scanning direction is
5/4 of the interval between the ink ejection ports 331 during one rotation of 2
, Ie, the speed at which 2.5 dots of the basic resolution are moved. Also here, No. 5 shows an example in which the fifth ink ejection port 331 is slightly shifted to the left due to the influence of misdirection or the like.

In the first rotation of the rotary drum 22, each ink ejection port No. 1 to No. By the ink ejection from 8, ...
1,2-1,3-1,4-1,5-1,6-1,7-
The dots are printed at the positions of 1, 8-1,. That is, in the first rotation, printing is performed on odd-numbered rows every other dot in the main scanning direction and on odd-numbered lines in the sub-scanning direction. This is similar to the case of FIG.

In the second rotation of the rotary drum 22, each ink ejection port No. 1 to No. By the ink ejection from 8, ...
2,2-2,3-2,4-2,5-2,6-2,7-
Dots are printed at positions 2,. That is, printing is performed every other dot from the 3.5th dot in the main scanning direction and on even lines in the sub-scanning direction.

In the third rotation of the rotary drum 22, each ink ejection port No. 1 to No. By the ink ejection from 8, ...
The dots are printed at the positions of 3, 2-3, 3-3, 4-3, 5-3, 6-3,. That is, printing is performed on even lines every other dot from the sixth dot in the main scanning direction and on odd lines in the sub-scanning direction.

In the fourth rotation of the rotary drum 22, each ink discharge port No. 1 to No. By the ink ejection from 8, ...
Dots are printed at positions 4, 2, 4, 3-4, 4-4, 5-4,. That is, 8.5 with respect to the main scanning direction.
Printing is performed every other dot from the dot and on even lines in the sub-scanning direction. Also in this printing, the left and right 8 dots are not used for actual printing.

Here, paying attention to the arrows in the figure, FIG.
5A, the shortest row of pixels in the sub-scanning direction is vertical, and in FIG. 5B, the shortest row of pixels in the sub-scanning direction is oblique. This is shown in FIG.
When the printing method of (1) is adopted, even if stripe-shaped density unevenness occurs, the density unevenness is diffused in an oblique direction. From the viewpoint of human visual characteristics, streak-like density unevenness can be made inconspicuous by diffusing in a diagonal direction.

From these results, a checkered thinning-out printing as shown in FIG. 5 (b), in which density unevenness is scattered in an oblique direction, is performed on a natural image object that uses a lot of intermediate gradations, On the other hand, checkered thinning-out printing with a square lattice spacing shown in FIG. In the case of printing a character or a line drawing object, in practice, printing is rarely performed using halftone dots as shown in FIG. is there. In addition, resolution is important for characters and line drawing objects, and images are often represented by combinations of horizontal and vertical lines. From this, the resolution can be sufficiently maintained and the image quality can be improved by adopting the printing method shown in FIG.

As described above, it is possible to sufficiently reduce the occurrence of streak-like density unevenness in recording in which half-tone expression such as a natural image is frequently used, and to obtain sufficient resolution for character and line image. The image quality can be improved by maintaining the image quality. FIG.
The actual image data generation for compensating for the difference between the printing positions of the odd-numbered lines and the even-numbered lines when printing (b) above is performed, for example, by performing simple line-to-line interpolation on the printer engine side or on the controller side. For example, there are various methods such as creation beforehand when a bitmap is generated, and any method may be adopted.

In some cases, characters, line drawings or graphics and natural images such as photographs are mixed and printed on one recording paper 25. In the case where the checkered thinning-out printing is not performed, when the recording head 33 is used to print an image in which a character or line drawing object and a natural image object are mixed, as shown in FIG. If the rotary drum 22 is rotated four times,
There is no problem because printing can be performed at each of the positions 1-4, but when performing checkered thinning-out printing, the relationship between the print moving position of the recording head in printing a character or line drawing object and a natural image object is described. Therefore, the printing on the recording paper 25 is not completed unless the rotating drum 22 is rotated eight times. This results in a decrease in printing speed.

Therefore, when printing on a single sheet of recording paper 25 a mixture of characters, line drawings, or graphics and natural images such as photographs, the odd-numbered lines or even-numbered lines whose printing positions are not shifted by 1/2 dot are printed. Can be completed, the printing on the recording paper 25 can be completed by six rotations of the rotating drum 22, and the printing speed can be improved.

That is, in the case of a character or a line drawing object, the recording head 33 applies the recording paper 25 to the recording paper 25 in FIG.
In the case of a natural image object, a checkerboard which disperses density unevenness in a diagonal direction as shown in FIG. Performs thinned-out printing. 7 (a) corresponds to FIG. 5 (a), and FIG. 7 (b) corresponds to FIG.
(b) is supported.

When printing these two types of objects on the same recording paper 25, if the rotary drum 22 is rotated four times for each object, a total of eight rotations must be performed. Therefore, the printing of the odd-numbered lines circled in FIG.
As shown in (d), printing on one recording paper 25 can be completed by six rotations. That is, No. The number of ink ejection ports of 1-1 is 1-1, 1-2, 1-3,1-
No. 4, 1-5 and 1-6 are printed. The two ink ejection ports are 2-1, 2-2, 2-3, 2-4, 2-
Perform printing of 5, 2-6. Other ink ejection ports perform the same printing.

By performing such printing, characters and line drawing objects and natural image objects can be mixed and printed on the same recording paper 25, and the resolution of the characters and line drawing objects can be sufficiently maintained. On the other hand, the natural image object has less stripe-like density unevenness, and the image quality can be improved as a whole. In addition, the printing speed can be improved.

In this embodiment, the case where the distance between the ink discharge ports of the ink jet recording head is set to twice the minimum distance between the dots has been described. However, the present invention is not limited to this. It should just be double. Further, in this embodiment, an example has been described in which the inkjet recording head is moved by 1, 2, 2.5 or 3 times the minimum dot interval in the main scanning direction while the rotary drum makes one rotation. The present invention is not limited to this. In short, M times the minimum interval between dots (where M is an integer whose N / M is an irreducible fraction when the interval between the ink ejection ports is N times the minimum interval between the dots). Or the M-folded one-half
What is necessary is just the thing which shifted the dot.

In this embodiment, the case where the ink jet recording head moves in the main scanning direction at a constant speed while the rotary drum is rotating has been described. However, the present invention is not limited to this. During recording, the movement of the recording head may be stopped, and the recording head may be moved to a predetermined position each time the recording head makes one rotation.

In this embodiment, a rotating drum is used as a means for transporting the recording paper in the sub-scanning direction with respect to the recording head. However, the present invention is not limited to this. Alternatively, the recording paper may be fixed and the recording head may be moved in the sub-scanning direction.

In this embodiment, a monochrome line printer using one ink jet recording head has been described. However, the present invention is not limited to this, and three color ink jet recording heads of yellow, magenta, and cyan or a black The present invention can also be applied to a color line printer using a four-color ink jet recording head to which is added. In this case, control of each ink jet print head is the same as control of one ink jet print head described in the embodiment.

In this embodiment, the present invention is applied to an ink jet line printer. However, the present invention is not necessarily limited to this.
The present invention can be applied to a line printer using another recording element such as D.

[0059]

According to the first to third aspects of the present invention, it is possible to sufficiently reduce the occurrence of streak-like density unevenness in recording in which intermediate gradation expression such as a natural image is frequently used. According to the second aspect of the present invention, a sufficient resolution can be maintained for characters and line drawings. According to the third aspect of the present invention, a sufficient resolution can be maintained for characters and line drawings, and the recording speed can be improved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a printer showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a hardware configuration in the embodiment.

FIG. 3 is a diagram showing a pixel size of each gradation in the embodiment. FIG.

FIG. 4 is a view for explaining a dot recording method for recording paper in the embodiment.

FIG. 5 is a diagram illustrating an example in which a character, a line drawing object, and a natural image object are printed at a pixel size of an intermediate gradation in the embodiment.

FIG. 6 is a diagram for explaining the positional relationship of print dots when an image in which a character or line drawing object and a natural image object are mixed is printed without performing checkered thinning;

FIG. 7 is an exemplary view for explaining a printing method in the case where an image in which a character or a line drawing object and a natural image object are mixed is printed in a checkered thinning pattern in the embodiment;

FIG. 8 is a diagram for explaining a problem of printing by a conventional inkjet printer.

FIG. 9 is a view for explaining checkered thinning printing by a conventional ink jet recording head.

[Explanation of symbols]

 Reference numeral 22: rotating drum 25: recording paper (recording medium) 33: ink jet recording head 331: ink discharge port (recording element) 37: head moving device 51: control unit

Claims (3)

[Claims] 1. A recording head having a plurality of recording elements arranged in a line at predetermined intervals, wherein a recording medium is directed to the recording head in a direction perpendicular to the direction in which the recording elements of the recording head are arranged. Relative to the recording head to perform dot recording in the main scanning direction with each recording element of the recording head, and to perform dot recording in the main scanning direction in the sub-scanning direction by relative movement between the recording head and a recording medium. In the apparatus, the recording head is movably disposed in a direction in which the recording elements are arranged, and an interval between the recording elements of the recording head is set to a minimum interval N (N ≧ 2) between dots to be recorded on the recording medium. In the recording operation, the recording head is moved by the recording head once in the main scanning direction during the recording operation, where M is the minimum interval between dots (where M is N / N).
M is moved by an integral number that is an irreducible fraction, and R (R ≧ R) in the sub-scanning direction by each recording element of the recording head.
Dot recording method, wherein dot recording is performed at a rate of 1 dot in 2) dots, and a recording setting position with respect to a basic resolution of a dot can be changed between an odd line and an even line in a main scanning line. . 2. A recording head having a plurality of recording elements arranged in a line at predetermined intervals, and a recording medium having a direction perpendicular to the direction of arrangement of the recording elements of the recording head with respect to the recording head. Relative to the recording head to perform dot recording in the main scanning direction with each recording element of the recording head, and to perform dot recording in the main scanning direction in the sub-scanning direction by relative movement between the recording head and a recording medium. In the apparatus, the recording head is movably disposed in a direction in which the recording elements are arranged, and an interval between the recording elements of the recording head is set to a minimum interval N (N ≧ 2) between dots to be recorded on the recording medium. In the recording operation, the recording head is moved by the recording head once in the main scanning direction during the recording operation, where M is the minimum interval between dots (where M is N / N).
M is moved by an integral number that is an irreducible fraction, and R (R ≧ R) in the sub-scanning direction by each recording element of the recording head.
(Integer of 2) Dot recording is performed at a rate of 1 dot in the dot. When the recording target includes both a natural image such as a photograph and a character or a line image, when the natural image is a natural image, the odd and even lines in the main scanning line are dots. In the case of a character or a line drawing, the recording setting position with respect to the basic resolution of the odd and even lines in the main scanning line is set with respect to the basic resolution for the basic resolution. A dot recording method for a recording device, wherein the dot recording method is the same. 3. When a recording target on the same recording medium is both a natural image such as a photograph and a character or a line drawing, a line whose recording setting position in an odd-numbered line or an even-numbered line of each recording target coincides is recorded. 3. The dot recording method according to claim 2, wherein the dot recording is performed by each recording element of the recording head while the recording medium passes through the recording head once.