JPH10309812A - Image forming equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce pattern noise and improve image quality by making N indicating the number of columns of a matrix larger than M indicating the number of rows. SOLUTION: Pulse voltage corresponding to image data is applied to a piezoelectric element 306 from a head discharge driving section. However, as for image data, a dot pattern stored in ROM in advance is printed in either division of a matrix with its center aligned in accordance with a tone. In a dot pattern that is printed as one pixel corresponding to single pixel data, N, the number of dots in the transverse direction of a dot matrix corresponding to the transverse direction of an image to be printed is made larger than M, the number of dots in the vertical direction of a dot matrix corresponding to the vertical direction of the image to be printed. From visual characteristics, an image where one pixel is more divided in the vertical direction stands out as compared with an image where one pixel is more divided in the transverse direction, thus reducing pattern noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus for forming an image having a gradation based on printing dots arranged in a matrix corresponding to one pixel. Related to the device.

[0002]

2. Description of the Related Art An ink jet printer using a piezoelectric element (PZT) as a print head is conventionally known. In such a print head, a pulse voltage corresponding to the image data is applied to the piezoelectric element, and the ink in a predetermined container (ink channel) is pressurized by the distortion of the piezoelectric element caused by the application of the pulse voltage, and the ink is applied to the ink channel. The ink drop flies toward the recording sheet from the provided nozzle. An image based on the image data is formed on the recording sheet by the flight of these ink drops.

[0003] In the above-described ink jet printer, by varying the amplitude of the pulse voltage applied to the piezoelectric element, different-sized distortions are generated in the piezoelectric element, and the amount of the ink drop to be ejected is adjusted.
By adjusting the amount of the ink drop, ink dots having different diameters are printed on the recording sheet.

Further, a matrix in which dots of ink having different diameters are arranged on a plane is made to correspond to one pixel of an image to be printed, and the pattern of dots in the matrix is changed according to the gradation of the image. There is known a technique for expressing more gradations by causing the image to be displayed.

[0005]

However, the matrix used in such a manner is an N × N square matrix, and depending on the image, pattern noise may occur due to repetition of the dot pattern, especially in the highlight portion. ing. Such pattern noise significantly deteriorates image quality.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming apparatus capable of improving image quality.

[0007]

According to the first aspect of the present invention, M rows and N columns having a row corresponding to the horizontal direction of the image and a column corresponding to the vertical direction of the image for one pixel. Based on printing dots arranged in a matrix,
This is an image forming apparatus that forms an image having a density on a sheet.

The present image forming apparatus is characterized in that N indicating the number of columns in the matrix is larger than M indicating the number of rows in the matrix.

According to the first aspect of the present invention, dots arranged in a matrix of M rows and N columns, where N indicating the number of columns is larger than M indicating the number of rows, correspond to one pixel. Printed on the sheet. As a result, the pattern noise, which has conventionally been caused by printing dots by associating a matrix of N rows and N columns with one pixel, is reduced, and the image quality is improved.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an ink jet printer which is one of embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view for explaining a schematic configuration of an ink jet printer 1 according to a first embodiment of the present invention.

[0012] The ink jet printer 1 is provided with paper or OH.
An inkjet head 3 which is an inkjet type print head for printing on a recording sheet 2 which is a recording medium such as a P sheet, a carriage 4 holding the inkjet head 3, and the carriage 4 is arranged in parallel with the recording surface of the recording sheet 2. Oscillating shafts 5 and 6 for reciprocating movement, a driving motor 7 for reciprocatingly driving the carriage 4 along the oscillating shafts 5 and 6, and an idle pulley for changing the rotation of the driving motor 7 to reciprocating movement of the carriage 4 8, a timing belt 9.

The ink jet printer 1 has a platen 10 also serving as a guide plate for guiding the recording sheet 2 along the transport path, and a paper holding plate 11 for holding the recording sheet 2 between the platen 10 and preventing floating. , Recording sheet 2
Roller 12, spur roller 13 for discharging
The ink jet head 3 includes a recovery system 14 that cleans the nozzle surface of the inkjet head 3 that discharges ink and recovers poor ink discharge, and a paper feed knob 15 for manually transporting the recording sheet 2.

The recording sheet 2 is fed to a recording unit where the ink jet head 3 and the platen 10 face each other by a sheet feeding device such as a manual feed or a cut sheet feeder (not shown). At this time, the rotation amount of a paper feed roller (not shown) is controlled, and the conveyance to the recording unit is controlled.

The ink jet head 3 uses a piezoelectric element (PZT) as an energy source for flying ink. A voltage is applied to the piezoelectric element, causing distortion.
This distortion changes the volume of the channel filled with ink. Due to the change in the volume of the channel, ink is ejected from nozzles provided in the channel, and recording on the recording sheet 2 is performed.

The carriage 4 main scans the recording sheet 2 in the horizontal direction by a drive motor 7, an idle pulley 8, and a timing belt 9, and the inkjet head 3 mounted on the carriage 4 records an image for one line. 1
Each time the recording for the line is completed, the recording sheet 2 is fed in the vertical direction and sub-scanned, and the next line is recorded.

The image is recorded on the recording sheet 2 in this manner, and the recording sheet 2 that has passed through the recording section is connected to a discharge roller 12 disposed on the downstream side in the transport direction and a spur roller 13 that contacts the discharge roller 12 at a constant pressure. Is discharged by.

Next, the carriage 4 will be described with reference to FIGS.
The peripheral configuration and the configuration of the inkjet head 3 will be described.

FIG. 2 is a perspective view for explaining the configuration around the carriage 4. As shown in FIG. An ink cartridge 40 containing ink and having a vent 404 is provided around the carriage 4.
3, a casing 401 for accommodating the ink cartridge 403, a casing lid 405, and an ink cartridge 4
An ink receiving pin 402 for receiving the ink to the inkjet head 3 while making the ink jet head 03 detachable;
05 when the casing lid 405 is closed.
Clutch 406 and urging clutch stop 407 for fixing the ink cartridge 403 and the ink cartridge 403 together with the casing lid 406 while pushing the ink cartridge 403 in the direction opposite to the direction in which the ink cartridge 403 is stored (the direction of the arrow D3). And a leaf spring 408 for holding. As the carriage 4 moves in the direction of arrow D1 shown in the figure, the recording sheet is scanned in the main direction, and ink drops are ejected in the direction of arrow D2.

The ink in the ink cartridge 403 includes seven colors of normal inks of yellow, magenta, cyan, and black and photo inks of magenta, cyan, and black. Hereinafter, these compositions will be described.

The normal yellow ink contains 74.5% of water as a solvent, 11.0% of polyhydric alcohol / diethylene glycol (DEG), 6.5% of polyhydric alcohol ether / diethylene glycol monobutyl ether (TBG), and thickens. Agent / polyethylene glycol (PEG)
4.5% of # 400. In addition, dye / Ba is used as a coloring material.
yer Y-CA51092 2.5%, surfactant / Olfin E1010 0.8% as additive, p
H regulator / NaHCO ₃ 0.2%.

Normal magenta ink has 74.5% of water as a solvent, 11.0% of polyhydric alcohol / diethylene glycol (DEG), 6.5% of polyhydric alcohol ether / diethylene glycol monobutyl ether (TBG), and has a thickened viscosity. Agent / polyethylene glycol (PEG)
4.5% of # 400. In addition, dye / BA
2.5% SF Red FF-3282, 0.8% surfactant / Olfin E1010 as an additive,
Contains 0.2% of pH adjuster / NaHCO ₃ .

The normal cyan ink contains 74.0% of water as a solvent, 11.0% of polyhydric alcohol / diethylene glycol (DEG), 6.5% of polyhydric alcohol ether / diethylene glycol monobutyl ether (TBG), and increases viscosity. Agent / polyethylene glycol (PEG)
4.5% of # 400. In addition, dye / Ba is used as a coloring material.
It contains 3.0% of yer CY-BG, 0.8% of surfactant / Olfin E1010 and 0.2% of pH adjuster / NaHCO ₃ as additives.

The normal black ink has a solvent of 77.9% of water, 6.0% of polyhydric alcohol / diethylene glycol (DEG), and 6.0% of polyhydric alcohol ether / diethylene glycol monobutyl ether (TBG).
0%, thickener / polyethylene glycol (PEG) # 4
00 of 4.5%. Dye / Baye
r BK-SP, 4.6%, surfactant: Olfine E1010 0.8%, pH adjuster / N
Contains 0.2% of aHCO ₃ .

In the photomagenta ink, 76.3% of water was used as a solvent, 11.0% of polyhydric alcohol / diethylene glycol (DEG), 6.5% of polyhydric alcohol ether / diethylene glycol monobutyl ether (TBG), and the viscosity was increased. Agent / polyethylene glycol (PEG)
4.5% of # 400. In addition, dye / BA
0.7% SF RED FF-3282, 0.8% surfactant / Olfin E1010 as an additive,
Contains 0.2% of pH adjuster / NaHCO ₃ .

Photocyan ink has a water content of 7 as a solvent.
6.2%, polyhydric alcohol / diethylene glycol (D
EG) and 6.5% of polyhydric alcohol ether / diethylene glycol monobutyl ether (TBG).
%, Thickener / polyethylene glycol (PEG) # 40
0% is contained 4.5%. In addition, dye / Bayer is used as a coloring material.
0.8% of CY-BG, 0.8% of surfactant / Olfin E1010 as an additive, pH adjuster / Na
HCO ₃ and including 0.2%.

The photo black ink contains 81.3% of water, 6.0% of polyhydric alcohol / diethylene glycol (DEG), and 6.0% of polyhydric alcohol ether / diethylene glycol monobutyl ether (TBG) as a solvent.
0%, thickener / polyethylene glycol (PEG) # 4
00 of 4.5%. Dye / Baye
r BK-SP 1.2%, surfactant / Olfin E1010 0.8%, pH adjuster / N
Contains 0.2% of aHCO ₃ .

FIGS. 3 to 5 show the ink jet head 3.
FIG. 3 is a diagram for explaining a configuration (see FIG. 2). FIG. 3 is a perspective view showing the assembly of the inkjet head 3, FIG. 4 is a top view of the inkjet head 3, and FIG. 5 is a line XX of FIG. It is sectional drawing.

As shown in FIG. 4, the ink-jet head 3 includes a normal yellow ink head 31, a normal magenta ink head 32 for discharging yellow, magenta, and cyan normal inks, respectively.
A normal cyan ink head 33, a photo magenta ink head 34, and a photo cyan ink head 35 for ejecting magenta and cyan photo inks.
And a normal black ink head 36 and a photo black ink head 37 for discharging black normal ink and black photo ink.

The heads 31 to 37 corresponding to each color in the ink jet head 3 include a nozzle plate 301 having nozzles for discharging ink drops, a common ink chamber plate 302 for forming an ink flow path, an inlet plate 303, Channel plate 304, partition 30
5, a piezoelectric element 306 that generates a distortion by applying a voltage to fly an ink drop, and a ceramic substrate 307. Also,
The side portion is formed by a head holder 308, and lead frames 315 and 316 are connected to the piezoelectric element 306.

As shown in FIG. 5, each head 31-37 is provided with a common ink chamber 31 by each plate 301-305.
2, an ink flow path including an ink chamber 313 and a nozzle 314 is formed.
8, an ink introduction path 311 and a receiving pin 402
2 (see FIG. 2).
Is connected and ink is supplied.

The operation of the ink jet head 3 having such a configuration is controlled by the control unit of the ink jet printer 1. Head discharge drive unit 1 of control unit
05 (see FIG. 6), the lead frames 315, 31
A predetermined pulse voltage based on the image data is applied during 6, and the piezoelectric element 306 is deformed in a direction to push the partition 305. The deformation of the piezoelectric element 306 is transmitted to the partition 305, which pressurizes the ink in the ink chamber 313,
The ink drop 320 flies toward the recording sheet 2 (see FIG. 1) via.

Next, the control section of the ink jet printer 1 will be described. FIG. 6 is a block diagram for explaining the configuration of the control unit of the inkjet printer 1.

The control unit of the ink jet printer 1 is C
PU 101, RAM 102, ROM 103, data reception unit 104, head ejection drive unit 105, head movement drive unit 106, paper feed motor drive unit 107, recovery system motor drive unit 108, various sensor units 109 Contains.

The CPU 101 for controlling the whole executes a program stored in the ROM 103 by using the RAM 102 as necessary. The program includes a head ejection drive unit 105, a head movement drive unit 106, a paper feed motor drive unit based on image data read from the data reception unit 104, which is connected to a host computer or the like and receives image data to be recorded. 107, various sensor units 1
09 to control an image recording on the recording sheet 2 and, if necessary, the recovery system motor drive unit 108 and various sensor units 109 to recover the nozzle surface of the inkjet head 3 to a good state. And a part for.

Under the control of the CPU 101, the head ejection drive unit 105 applies a pulse voltage corresponding to the image data to
06, the head movement drive unit 106 drives the drive motor 7 that moves the carriage 4 holding the inkjet head 3, and the paper feed motor drive unit 107 drives the paper feed roller. Further, based on the control of the CPU 101, the recovery system motor drive unit 108 drives a motor or the like necessary to recover the nozzle surface of the inkjet head 3 to a good state.

As described above, the pulse voltage corresponding to the image data is applied to the piezoelectric element 306 from the head ejection drive unit 105, and the image data includes a dot stored in the ROM 103 in advance as described later. Processing is performed so that the pattern is printed in accordance with the density gradation.

Next, a procedure for processing the above image data will be described. FIG. 7 shows the CPU 10 for image data.
FIG. 2 is a block diagram for explaining a procedure of a process performed by the first embodiment;

The image data of 256 tones for each color corresponding to red (R), green (G), and blue (B) from the data receiving unit 104 (see FIG. 6) Will be corrected. The tone-corrected R, G, B image data is converted by the color conversion unit 1012 into image data corresponding to cyan (C), magenta (M), and yellow (Y). Next, in the black generation + UCR unit 1013, a gray component is separated from the converted C, M, and Y image data (under color removal, also referred to as UCR), and black (K) image data is generated. , Photo cyan (Cp),
Image data corresponding to photo magenta (Mp) and photo black (Kp) is generated.

Further, these image data are subjected to dither processing in a dither processing unit 1014, and image data of 256 gradations for each color is supplied from the head ejection drive unit 105 to the piezoelectric element 30.
C, M, K corresponding to the pulse voltage applied to 6
The data is converted into data of gradation (two gradations of normal ink, two gradations of photo ink and plain), and Y3 gradation (two gradations of normal ink and plain).

The following describes a dot pattern printed as one pixel corresponding to one piece of image data described above.

FIG. 8 is a diagram for explaining how a human eye perceives noise in an image composed of pixels of an M × N dot matrix. FIG. 8A shows that one pixel printed from the inkjet printer 1 is 2 × 3 (M <N).
FIG. 8B is a diagram showing an image when one pixel is composed of 3 × 2 (M> N), and FIG. 8C is a diagram showing an image from a conventional inkjet printer. FIG. 7 is a diagram illustrating an image in a case where one pixel to be printed is 3 × 3 (M = N).

When a person looks at a picture or a character printed on a recording sheet, his / her line of sight is scanned not in one point but in a two-dimensional direction at high speed, and the information is synthesized in the brain. In the visual field to which the line of sight is directed, since two human eyes are arranged side by side, scanning in the horizontal direction is greater than scanning in the vertical direction.

Therefore, in consideration of such characteristics of human vision, an image having more vertical divisions as shown in FIG. 8A than an image having more horizontal divisions as shown in FIG. 8B. Is more noticeable in the image. Such noise becomes noticeable in a highlight portion of the image.

When the number of dots in the vertical direction and the number of dots in the horizontal direction constituting the dot matrix are equal as shown in FIG. 8 (c), the eyes of a human are composed of pixels as shown in FIG. 8 (a). The image is captured as an image closer to an image composed of pixels as shown in FIG. 8B than an image.

Next, the types and sizes of dots printed by the ink jet printer 1 will be described with reference to FIG.
Using FIG. 10 to FIG. 17, printing is performed corresponding to one pixel.
3 shows a 2 × 3 dot matrix which is a dot pattern having 0 gradation.

FIG. 9 is a diagram for explaining the types and sizes of dots to be printed by the ink jet printer 1.

A dot 501 represents a small diameter dot made of photo ink, and a dot 502 represents a large diameter dot made of photo ink. A dot 503 indicates a small-diameter dot using normal ink, and a dot 504 indicates a large-diameter dot using normal ink. These dots 501 to 504 correspond to the colors of magenta, cyan, and black, respectively.
04 corresponds.

The size of the small diameter dot is about 50 μm for both the photo ink and the normal ink, and the size of the large diameter dot is 1 for both the photo ink and the normal ink.
It is about 00 μm.

FIGS. 10 to 17 are diagrams showing a 2 × 3 dot matrix printed in correspondence with one pixel and having 190 gradations. In the figures showing these dot matrices, one ink drop flying by driving the piezoelectric element corresponds to one dot forming the matrix, and the numerical value above the matrix is a numerical value for specifying the gradation. . The number of gradations of the density starts from 1, and increases as the density increases. The rows of these dot matrices correspond to the horizontal rows of the image to be printed, and the columns correspond to the vertical rows of the image to be printed.

As shown in these figures, the dots 501 to 504 (see FIG. 9) constituting the dot pattern have two levels according to the gradation of the density represented by the image data corresponding to the pixel.
Printing is performed so that the center of each section is aligned with one of the sections of the matrix partitioned into a × 3 grid. For example,
When the image data corresponding to a certain pixel is the gray scale 48, the gray scale 48 (see FIG. 11) is the first row of the matrix partitioned into a 2 × 3 grid corresponding to the pixel. Small-diameter dots 501 made of photo ink are printed in the first column, second row and second column, and large-diameter dots 502 made of photo ink are printed in the second row and third column. Large diameter dots 504 with normal ink in the section of the row
Is printed.

As described above, one pixel corresponds to the dot matrix, and the number of rows of the dot matrix corresponding to the horizontal direction of the image to be printed corresponds to the vertical direction of the image to be printed. By increasing the number of dot matrices to be arranged in the vertical direction, the pattern noise, which has conventionally been caused by printing dots by associating one pixel with a dot matrix of N rows and N columns, is reduced, and image quality is reduced. Is improved.

Hereinafter, dot patterns (dot matrices) corresponding to pixels constituting an image printed by the ink jet printer according to the second to sixth embodiments will be described. The overall configuration of the inkjet printer according to the second to sixth embodiments, the configuration of the print head, the configuration of the control unit, and the like are the same as those of the inkjet printer according to the first embodiment.

FIGS. 18 to 20 are views for explaining a 2 × 4 dot matrix by the ink jet printer according to the second embodiment.

As shown in these figures, in the ink jet printer according to the second embodiment, the dots 502 and 504 (see FIG. 9) forming the dot pattern have the gradation of the density represented by the image data corresponding to the pixel. 2 × 4, depending on
Is printed in any of the sections of the matrix partitioned into a lattice shape. For example, when the image data corresponding to a certain pixel is the gray scale 23, the gray scale 23 (see FIG. 19) is the second of the matrix partitioned into a 2 × 4 lattice shape corresponding to the pixel. Large-diameter dots 502 made of photo ink are printed in the section of the first row and the first column and the section of the first row and the second column,
1st row, 4th column, 2nd row, 1st column, 2nd row, 3rd
It is assumed that a large-diameter dot 504 is printed in a column section by normal ink.

FIGS. 21 to 23 are views for explaining a 2 × 4 dot matrix by the ink jet printer according to the third embodiment.

As shown in these figures, in the ink jet printer of the third embodiment, similarly to the ink jet printer of the second embodiment, the dots 502 and 504 (see FIG. 9) forming the dot pattern are formed. In accordance with the gradation of the density represented by the image data corresponding to the pixel, printing is performed in any of the sections of the matrix partitioned into a 2 × 4 grid. For example, the gradation 27 (see FIG. 22) is a certain 1
When the image data corresponding to one pixel is gradation 27,
A matrix of a first row and a first column, a first row and a second column of a matrix partitioned into a 2 × 4 grid corresponding to the pixel;
Large-diameter dots 5 of photo ink in the first row and third column
02 is printed, and large-diameter dots 504 of normal ink are printed in the first row and fourth column, the second row and first column, and the second row and second column.

Next, after explaining the dot matrix used in the conventional ink jet printer, an image printed by the conventional ink jet printer is compared with an image printed by the second and third ink jet printers.

FIG. 27 is a view for explaining a 2 × 2 dot matrix by a conventional ink jet printer.

As shown in these figures, in the conventional ink jet printer, the dots 502 and 504 (see FIG. 9) constituting the dot pattern are divided into two in accordance with the gradation of the density represented by the image data corresponding to the pixel. It is printed in any of the sections of the matrix partitioned into a × 2 grid.
For example, when the image data corresponding to a certain pixel is the gray level 8, the gray level 8 is the first row and the second column of the matrix partitioned into a 2 × 2 grid corresponding to the pixel. , The large-diameter dot 502 of the second row and the first column is printed with the photo ink, and the large-diameter dot 504 of the first row and the first example is printed with the normal ink. Further, when the image data corresponding to a certain pixel is the gradation 11, the gradation 11 is the second row and the first column of the matrix partitioned into a 2 × 2 lattice corresponding to the pixel. Are printed with large-diameter dots 502 using photo ink, and large-diameter dots 504 with normal ink are printed in the first row and first column and the first row and second column.

FIG. 28 is a diagram showing an example of printing by the ink jet printer of the second embodiment, and FIG. 29 is a diagram showing an example of printing by the ink jet printer of the third embodiment. FIG. 30 is a diagram showing a first example of printing by a conventional inkjet printer.
FIG. 1 is a view showing a second example of printing by a conventional ink jet printer.

An image composed of a group of dots shown in FIG. 28 is obtained by the ink jet printer of the second embodiment shown in FIG.
9 is printed by repeatedly printing the dot pattern 511 of the gradation 23 shown in FIG. 9, and an image composed of a set of dots shown in FIG. 29 is obtained by the inkjet printer of the third embodiment at the gradation 27 of FIG. Printing is performed by repeatedly printing the dot pattern 512. An image composed of a set of dots shown in FIG. 30 is printed by repeatedly printing the dot pattern 513 of gradation 8 shown in FIG. 27 by a conventional inkjet printer, and an image composed of a set of dots shown in FIG. FIG. 27 using a conventional inkjet printer
Are printed by repeatedly printing the dot pattern 514 of the gradation 11 shown in FIG.

In the image shown in FIG. 30, the repetition of the dot pattern is increased, so that the noise of the lattice pattern is particularly conspicuous. In the image shown in FIG. 31, the repetition of the dot pattern is increased, particularly in the horizontal direction. The noise of the line pattern becomes noticeable.

In the images shown in FIGS. 28 and 29, as compared with the images shown in FIGS. 30 and 31 described above, the repetition of the dot pattern especially in the horizontal direction is reduced.
As described using, the dot patterns are scattered to human eyes, and the pattern noise becomes less noticeable.

As described above, one pixel corresponds to the dot matrix, and the number of rows of the dot matrix corresponding to the horizontal direction of the image to be printed corresponds to the vertical direction of the image to be printed. By increasing the number of dot matrices to be arranged in the vertical direction, the pattern noise, which has conventionally been caused by printing dots by associating one pixel with a dot matrix of N rows and N columns, is reduced, and image quality is reduced. Is improved.

The present invention as described above can be similarly applied to a case where the number of gradations is even lower.

FIG. 24 is a view for explaining a 1 × 2 dot matrix by the ink jet printer according to the fourth embodiment.

In the ink jet printer of the fourth embodiment, the dots 502 and 504 forming the dot pattern
(See FIG. 9) is printed in any of the sections of the matrix divided into a 1 × 2 grid according to the gradation of the density represented by the image data corresponding to the pixel.

FIG. 25 is a diagram for explaining a 1 × 2 dot matrix by the ink jet printer according to the fifth embodiment.

In the ink jet printer of the fifth embodiment, the dots 501, 50 forming the dot pattern
2, 503 (see FIG. 9) is printed in any of the sections of the matrix divided into a 1 × 2 grid in accordance with the gradation of the density represented by the image data corresponding to the pixel.

FIG. 26 is a diagram for explaining a 1 × 2 dot matrix by the ink jet printer according to the sixth embodiment.

In the ink jet printer of the sixth embodiment, the dots 501, 50 forming the dot pattern
2, 503, and 504 (see FIG. 9) are printed in any of the sections of the matrix divided into a 1 × 2 grid according to the gradation of the density represented by the image data corresponding to the pixel.

As described above, even when the number of gradations is low, one pixel corresponds to the dot matrix, and the number of rows of the dot matrix corresponding to the horizontal direction of the image to be printed is printed. By increasing the number of dot matrices in the vertical direction corresponding to the vertical direction of the image, the pattern noise caused by printing dots in a manner in which one pixel corresponds to a dot matrix of N rows and N columns in the past. Is reduced and the image quality is improved.

[Brief description of the drawings]

FIG. 1 is a perspective view for explaining a schematic configuration of an inkjet printer 1 according to a first embodiment of the invention.

FIG. 2 is a perspective view for explaining a configuration around a carriage 4. FIG.

FIG. 3 is a diagram for explaining a configuration of an inkjet head 3.

4 is a top view of the inkjet head 3. FIG.

FIG. 5 is a sectional view taken along line XX of FIG. 4 for explaining the flow of ink in the inkjet head 3.

FIG. 6 is a block diagram for explaining a configuration of a control unit of the inkjet printer 1.

FIG. 7 is a block diagram for explaining a procedure of a process performed by a CPU 101 on image data.

FIG. 8 is a diagram for explaining how a human eye perceives noise in an image composed of pixels of an M × N dot matrix.

FIG. 9 is a diagram for explaining the types and sizes of dots printed by the inkjet printer 1.

FIG. 10 shows a print 190 printed by the inkjet printer 1;
It is a figure which shows the gradation 1-the gradation 24 of the dot pattern of a gradation.

FIG. 11 shows a print 190 printed by the inkjet printer 1;
It is a figure which shows the gradation 25-gradation 48 of a gradation dot pattern.

FIG. 12 shows a print 190 performed by the inkjet printer 1;
It is a figure which shows the gradation 49-gradation 72 of a gradation dot pattern.

FIG. 13 shows a print 190 performed by the inkjet printer 1;
It is a figure which shows the gradation 73-the gradation 96 of the dot pattern of a gradation.

FIG. 14 shows a print 190 printed by the inkjet printer 1;
It is a figure which shows the gradation 97-gradation 120 of the dot pattern of a gradation.

FIG. 15 shows a print 190 performed by the inkjet printer 1;
It is a figure which shows the gradation 121-gradation 144 of a gradation dot pattern.

FIG. 16 shows a print 190 performed by the inkjet printer 1;
It is a figure which shows the gradation 145-gradation 168 of the gradation dot pattern.

FIG. 17 shows a print 190 performed by the inkjet printer 1;
It is a figure which shows the gradation 169-gradation 190 of the gradation dot pattern.

FIG. 18 is a diagram illustrating gradations 1 to 16 of a dot pattern of 43 gradations printed by the inkjet printer according to the second embodiment.

FIG. 19 is a diagram illustrating gradations 17 to 32 of a 43-gradation dot pattern printed by the inkjet printer according to the second embodiment.

FIG. 20 is a diagram illustrating gradations 33 to 43 of a dot pattern of 43 gradations printed by the inkjet printer according to the second embodiment.

FIG. 21 is a diagram illustrating gradations 1 to 16 of a 43 gradation dot pattern printed by the ink jet printer according to the third embodiment.

FIG. 22 is a diagram illustrating gradations 17 to 32 of a dot pattern of 43 gradations printed by the inkjet printer according to the third embodiment.

FIG. 23 is a diagram illustrating gradations 33 to 43 of a dot pattern of 43 gradations printed by the inkjet printer according to the third embodiment.

FIG. 24 is a diagram for describing a 1 × 2 dot matrix by the inkjet printer according to the fourth embodiment.

FIG. 25 is a diagram for describing a 1 × 2 dot matrix by the inkjet printer according to the fifth embodiment.

FIG. 26 is a diagram for describing a 1 × 2 dot matrix by the inkjet printer according to the sixth embodiment.

FIG. 27 shows 2 × 2 by a conventional inkjet printer.
FIG. 3 is a diagram for explaining a dot matrix.

FIG. 28 is a diagram illustrating an example of printing by the inkjet printer according to the second embodiment.

FIG. 29 is a diagram illustrating an example of printing by the inkjet printer according to the third embodiment.

FIG. 30 is a diagram illustrating a first example of printing by a conventional inkjet printer.

FIG. 31 is a diagram showing a second example of printing by a conventional inkjet printer.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 ink jet printer 2 recording sheet 3 ink jet head 101 CPU 103 ROM 105 head ejection drive unit 306 piezoelectric element 307 ceramic base 314 nozzle 320 ink drop 511 dot pattern by ink jet printer of second embodiment 512 Third embodiment Dot pattern by inkjet printer 513, 514 Dot pattern by conventional inkjet printer

Claims (1)

[Claims] An M row N having a row corresponding to a horizontal direction of an image and a column corresponding to a vertical direction of the image for one pixel.
An image forming apparatus for forming an image having density on a sheet based on printing dots arranged in a matrix of columns, wherein N indicating the number of columns of the matrix is the number of rows of the matrix. An image forming apparatus, wherein M is larger than M.