JPH10315507A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet printer in which the quality of an image to be printed can be enhanced. SOLUTION: The ink jet printer prints normal color dots of yellow, magenta, cyan and black (hereinafter, referred to Y, M, C and K) and photocolor dots of magenta and cyan (hereinafter, referred to Mp and Cp) depending on an image data thus printing an image having density on a recording sheet. In such an ink jet printer, dots of C, M and K corresponding to a relatively light color are printed on the recording sheet preferentially to dots of Cp, Mp and Y corresponding to a relatively light color.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus using inks having different densities according to image data.

[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 image data transmitted from a personal computer or the like is formed on the recording sheet by these ink drops flying.

Further, a technique for printing an image having a color using the above-described ink jet printer is known. In such an ink jet printer, yellow, magenta, cyan, and black (hereinafter, referred to as Y,
M, C, and K) may be used to print a full-color image. further,
In addition to these normal colors with normal density,
There is known a technique for reproducing a smooth image having more gradations by using a photo color having a lower density (lighter color) than a normal color. As the photo colors, magenta of normal color, photo magenta having lower density than cyan, and photo cyan (hereinafter sometimes referred to as Mp and Cp, respectively) are used, and a total of six types of normal color and photo color are used. Are printed on the recording sheet in a predetermined order.

FIGS. 16 and 17 are diagrams for explaining the order of printing normal color and photo color dots by an ink jet printer according to a first conventional example. FIGS. 18 and 19 are diagrams illustrating a second conventional example. FIG. 7 is a diagram for explaining the order of printing normal color and photo color dots by the inkjet printer. 16 and 18, the pitch in the main scanning direction (the direction of arrow D4 in FIG. 16) is set to 3
The pitch in the sub-scanning direction (the direction of the arrow D5 in FIG. 16) is set to 180 dpi. Hereinafter, the same pitch is assumed to be the same in similar drawings.

As shown in FIG. 16, in the first conventional ink jet printer, dots having the same diameter are printed in the order of Cp → C → Mp → M → Y → K. These are shown in FIG.
As shown in FIG. 1, the first conventional ink jet printer means that relatively light dots 551 and relatively dark dots 552 are printed in an alternate order.

Further, as shown in FIG. 18, in the second conventional ink jet printer, Cp and Mp having a small diameter are used.
Are printed before the C and M dots having a large diameter and the K dots having a small diameter. This means that, as shown in FIG. 19, in the ink jet printer of the second conventional example, relatively light dots 553 are printed before relatively dark dots 554.

[0007]

However, a total of six types of color dots, normal color and photo color, are printed on the recording sheet in the above-described order. Dots due to color are conspicuous, and the image may be rough. Images printed in this way are not sufficiently smooth and color-balanced, nor are they closer to photographs, and although the image quality is sufficiently high. Absent.

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 the quality of a printed image.

[0009]

According to the first aspect of the present invention, a first ink having a certain density and a second ink having a lower density than the first ink are used in accordance with image data. This is an image forming apparatus that forms an image having a density on a sheet based on printing a dot on a sheet.

The present image forming apparatus is characterized in that after printing dots on a sheet with a first ink, the dots are printed with a second ink.

According to the first aspect of the present invention, after dots are printed with ink having a certain density, dots are printed with ink having a lower density than this ink. As a result, the roughness of the image as in the related art can be eliminated, and the color balance can be maintained as compared with the related art, so that the quality of the printed image can be improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an ink jet printer according to an embodiment 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.

[0014] The ink jet printer 1 uses 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 horizontally scans the recording sheet 2 in a 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 has a discharge roller 12 disposed downstream of the recording sheet and a spur roller 13 contacting 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 is composed of six colors: normal inks of yellow, magenta, cyan, and black, and photo inks of magenta and cyan. Hereinafter, these compositions will be described.

The normal yellow ink contains 76.0% of water as a solvent, 11.0% of polyhydric alcohol / diethylene glycol (DEG), 6.5% of polyhydric alcohol ether / triethylene glycol monobutyl ether (TGB), Thickener / polyethylene glycol (PEG)
# 400 is included in 3.0%. 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 contains 75.8% of water as a solvent, 11.0% of polyhydric alcohol / diethylene glycol (DEG), 6.5% of polyhydric alcohol ether / triethylene glycol monobutyl ether (TGB), Thickener / polyethylene glycol (PEG)
3.2% 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 75.5% of water as a solvent, 11.0% of polyhydric alcohol / diethylene glycol (DEG), 6.5% of polyhydric alcohol ether / triethylene glycol monobutyl ether (TGB), Thickener / polyethylene glycol (PEG)
# 400 is included in 3.0%. 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 contains 79.1% of water as a solvent, 6.0% of polyhydric alcohol / diethylene glycol (DEG), 6.0% of polyhydric alcohol ether / triethylene glycol monobutyl ether (TGB), Thickener / polyethylene glycol (PEG)
4.5% of # 400. In addition, dye / Ba is used as a coloring material.
include yer BK-SP 3.4%, including surfactant / OLFINE E1010 0.8%, pH adjusting agents / NaHCO ₃ 0.2% as an additive.

The photo magenta ink used as a solvent was 76.3% of water, 11.0% of polyhydric alcohol / diethylene glycol (DEG), 6.5% of polyhydric alcohol ether / triethylene glycol monobutyl ether (TGB), Thickener / 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 .

The photocyan ink uses water as a solvent.
6.2%, polyhydric alcohol / diethylene glycol (D
EG) and polyhydric alcohol ether / triethylene glycol monobutyl ether (TGB) at 11.0%.
5%, thickener / polyethylene glycol (PEG) # 4
00 of 4.5%. Dye / Baye
r CY-BG 0.8%, surfactant: Olfine E1010 0.8%, pH adjuster / N
Contains 0.2% of aHCO ₃ .

FIG. 3 to FIG.
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 for discharging black normal ink.

The heads 31 to 36 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 a flow path of ink, 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 of the heads 31 to 36 is provided with a common ink chamber 31 by each of the plates 301 to 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 these image data are stored in the ROM 1 in advance.
A process is performed so that the dot pattern stored in 03 is printed in accordance with the density gradation.

Next, the procedure for processing the above image data will be described. FIG. 7 shows the CPU 1 for image data.
FIG. 2 is a block diagram for explaining a procedure of a process performed by a first embodiment.

The image data of 256 gradations for each color corresponding to red, green, and blue (hereinafter, sometimes referred to as R, G, and B, respectively) from the data receiving unit 104 (see FIG. 6)
The gradation is corrected by the gradation correction unit 1101. The R, G, and B image data subjected to the gradation correction is supplied to a color conversion unit 1012.
Is converted into image data corresponding to C, M, and Y. Next, in the black generation + UCR unit 1013, the converted C,
A gray component is separated from the M and Y image data (under color removal, also called UCR), K image data is generated, and image data corresponding to Cp and Mp is generated.

Further, these image data are subjected to dither processing by 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.
The data is converted into data of eight gradations for each color corresponding to the pulse voltage applied to 6.

The order of printing each color on a recording sheet in an image printed based on the above image data will be described below.

FIGS. 8 and 9 show the ink jet printer 1.
FIG. 6 is a diagram for explaining the order of printing of each color in an image according to FIG.

As shown in FIG. 8, in the ink jet printer 1, C, M, and K dots having a small diameter (about 50 μm) are replaced with Cp, M having a large diameter (about 100 μm).
Printing is performed before the p and Y dots. This means that, as shown in FIG. 9, in the ink jet printer 1, the relatively dark dots 502 having a small diameter are printed before the relatively light dots 501 having a large diameter. .

Hereinafter, the second and third embodiments will be described with reference to FIGS.
13 and 14 after describing the printing order of dots of each color by the ink jet printer according to the embodiment.
The effect of an image printed by the inkjet printer according to the first embodiment will be described with reference to FIG.
The effect of the image printed by the ink jet printer according to the first to third embodiments using FIG.
A description will be given in comparison with images printed by ink jet printers of the first and second conventional examples shown in FIG. The overall configuration of the inkjet printer according to the second and third 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. 10 and 11 are diagrams for explaining the order of printing of each color in an image by the ink jet printer according to the second embodiment.

As shown in FIG. 10, the ink jet printer according to the second embodiment has a large diameter (about 100 μm).
Are printed before the C and M dots having a small diameter (about 50 μm) and the K dots having a small diameter and the Y dots having a large diameter. As shown in FIG. 11, in the ink jet printer according to the second embodiment, relatively dark dots 504 are printed before relatively light dots 503, regardless of the diameter. Means that.

FIG. 12 is a diagram for explaining the order of printing of each color on an image by the ink jet printer according to the third embodiment.

As shown in FIG. 12, the ink jet printer according to the third embodiment has a large diameter (about 100 μm).
Are printed before the relatively light-colored dots 505 of Cp, Mp, and Y having a small diameter (about 50 μm).

FIGS. 13 and 14 show reflections of the image shown in FIG. 8 printed by the ink jet printer of the first embodiment and the image shown in FIG. 18 printed by the first conventional ink jet printer. It is a figure showing the result of measurement of optical density (Optical Density). FIG. 13 shows the measurement result of the reflection optical density at a resolution higher than that of the human eye, and FIG. 14 shows the measurement result of the reflection optical density at the same resolution as that of the human eye.

In measuring these reflection optical densities, a recording sheet "KJHA4100 IJ printer / word processor paper high grade color KJHA4100" was used as a recording sheet, an ink having the composition shown in FIG. Sa from Sakura (now Konica Corporation)
kura Densitometer (PDA65) is used.

These measurements were performed on the recording sheet on which the images shown in FIGS. 8 and 18 were printed using the above-described ink at a speed of 10 sec.
It is performed by scanning while moving at c / mm. The detect head has a light source that irradiates light onto the recording sheet, a slit that splits the reflected light from the recording sheet, and a photoelectric tube that measures the reflection optical density from the light passing through the slit.

In FIG. 13 and FIG. 14, the horizontal axis represents FIG.
The measurement results are shown by taking the scanning distance from left to right toward the image 8 and the reflection optical density of the image corresponding to this scanning distance on the vertical axis.

As described above, in this measurement, the reflection optical density is measured at two levels of resolution, and this resolution is performed by adjusting the slit width of the slit of the detect head. The resolution higher than the human eye shown in FIG. 13 is obtained by setting the slit width to 20 μm, and the same resolution as the human eye shown in FIG. 14 is obtained by setting the slit width to 40 μm.

FIGS. 13 and 14 show curves 601 and 603 showing the relationship of the reflection optical density with respect to the scanning distance in the ink jet printer of the first embodiment at such two-stage resolution, and the first and second curves, respectively. And curves 602 and 604 showing the relationship between the scanning optical distance and the scanning optical density in the conventional inkjet printer of FIG. As shown in FIG. 14, a value at which the reflection optical density is maximum in a relatively dark color dot is ODmax, and a value ODmin at which the reflection optical density is minimum in a relatively light color dot.

Referring to the measurement result of the reflection optical density shown in FIG. 13, the reflection optical density of the dot corresponding to the relatively dark color of C, M, and K in FIGS.
It can be seen that the reflection optical density of the dots corresponding to the relatively light colors of p, Mp, and Y is about 0.5, and the reflection optical density corresponding to the white background of the recording sheet is about 0.1. In the curve 601 obtained by the ink jet printer of the first embodiment, the width of the scan distance at which the reflection optical density becomes the maximum of about 0.7 is the curve 602 obtained by the first conventional ink jet printer. It can be seen that it is narrower.

Further, the measurement result of the reflection optical density shown in FIG. 14 shows the portion where the reflection optical density is highest as described above.
In the image of FIG. 18 by the first conventional inkjet printer, it is shown that the eyes of a person are clearly recognizable, while in the image of FIG. The eye shows that the difference in density can be recognized, but the density cannot be clearly recognized.

As described above, the image printed by the ink jet printer according to the first embodiment has a relatively high density dot printed before a relatively low density dot, thereby providing a human image. Shading is not clearly recognized by the eyes but appears blurred, and such shading is recognized as a smooth halftone.

FIG. 15 shows an image printed on a recording sheet by the ink jet printers of the first to third embodiments, and an image printed on a recording sheet by the first and second conventional ink jet printers. It is a figure for showing evaluation with.

The evaluation items are the smoothness of the image and whether or not a tone jump has occurred. Here, for the smoothness of the image, the reflection optical density measured to obtain the graph in FIG. 14 was measured for five ink jet printers, and from these, the reflection optical density was maximized within relatively dark dots. Is evaluated by the difference ΔOD (= ODmax−ODmin) between the value ODmax that yields the value and the value ODmin that minimizes the reflection optical density within the relatively light colored dots. Here, when ΔOD <0.1, the smoothness is ○, when 0.1 ≦ ΔOD <0.2, the smoothness is 、,
When ΔOD ≧ 0.2, the smoothness is indicated by x.

Referring to the results, in the images printed by the first and second prior art ink jet printers, the smoothness, which was x and 、, respectively, indicates that the dark ink dots were earlier than the light ink dots. 1st to 3rd printed on
In the image printed by the ink jet printer according to the embodiment, the mark is ○, indicating that the image has been improved to be smooth. The tone jump that has occurred in the images printed by the first and second conventional inkjet printers has not occurred in the inkjet printers of the first to third embodiments. By improving smoothness and tone jump in this way,
The roughness of the image is eliminated and the color balance is improved.

As described above, the relatively dark C, M, and K ink dots are formed on the recording sheet by the relatively light color C dots.
By printing before the p, Mp, and Y ink dots, the roughness of the image printed by the conventional ink jet printer can be eliminated, and the color balance can be improved as compared with the conventional one. Quality can be 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 perspective view showing the assembly of the 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 first diagram for explaining a printing order of each color.

FIG. 9 is a second diagram for explaining the printing order of each color.

FIG. 10 is a first diagram for explaining a printing order of each color in an image by the inkjet printer according to the second embodiment.

FIG. 11 is a second diagram for describing the order of printing of each color in an image by the inkjet printer according to the second embodiment.

FIG. 12 is a diagram for explaining a printing order of each color in an image by the inkjet printer according to the third embodiment.

FIG. 13 shows the result of measuring the reflection optical density of the image shown in FIG. 8 printed by the inkjet printer of the first embodiment and the image shown in FIG. 18 printed by the inkjet printer of the first conventional example. It is the 1st figure which shows.

FIG. 14 shows the results of measuring the reflection optical density of the image shown in FIG. 8 printed by the ink jet printer of the first embodiment and the image shown in FIG. 18 printed by the ink jet printer of the first conventional example. It is the 2nd figure which shows.

FIG. 15 illustrates an image printed on a recording sheet by the inkjet printer according to the first to third embodiments,
FIG. 9 is a diagram illustrating evaluation with an image printed on a recording sheet by first and second conventional inkjet printers.

FIG. 16 is a first diagram for explaining the order of printing normal color and photo color dots by an ink jet printer as a first conventional example.

FIG. 17 is a second diagram for explaining the order of printing normal color and photo color dots by the inkjet printer according to the first conventional example.

FIG. 18 is a first diagram illustrating a printing order of normal color and photo color dots by an ink jet printer according to a second conventional example.

FIG. 19 is a second diagram for explaining the order of printing normal color and photo color dots by an ink jet printer according to a second conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Ink-jet printer 2 Recording sheet 3 Ink-jet head 101 CPU 103 ROM 105 Head ejection drive part 306 Piezoelectric element 307 Ceramic base 314 Nozzle 320 Ink drop 501, 503, 505 Dots 502 corresponding to relatively light colors of Cp, Mp, Y, 504, 506 Dots corresponding to relatively dark colors of C, M, K

Claims (1)

[Claims] 1. A method for printing dots on a sheet based on printing dots using a first ink having a certain density and a second ink having a lower density than the first ink in accordance with image data. An image forming apparatus for forming an image having a high density, comprising: printing dots on the sheet using the first ink, and then printing dots using the second ink. apparatus.