JP2001145999A - Method for inkjet recording and its apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record an image with high quality by predicting change in concentration of ink and determining a more optimum combination of the inks and recording the image. SOLUTION: A printer part 7 has a plurality of inkjet head units respectively having a different kind of ink and a plurality of test patterns respectively having a different continuous non-jetting time are recorded based on test pattern image data 4c and based on concentration of the recording of a plurality of the recorded test patterns, either of a plurality of characteristic tables 4e of change in concentration for predicting the change in concentration of the ink in accordance with the continuous non-jetting time is selected and based on the continuous non-jetting time during actual recording, change in concentration of the ink is predicted by the selected characteristic table of change in concentration and based on the predicted concentration of the ink, kind of the ink to be used for recording in accordance with the image data is determined and the image is recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ink jet recording method and apparatus for recording an image by discharging ink onto a recording medium.

[0002]

2. Description of the Related Art A recording apparatus employed in a printer, a copying machine, a facsimile or the like is configured to record an image composed of a dot pattern on a recording material such as paper or a thin plastic plate based on image information. ing. Such recording apparatuses can be classified into an ink jet type, a wire dot type, a thermal type, a laser beam type, and the like according to the recording method. Among them, an ink jet type (ink jet recording apparatus) discharges ink (recording liquid) droplets from a discharge port of a recording head by a simple device configuration,
The recording is performed by attaching this to a recording material.

In recent years, a large number of recording apparatuses have been used, and high-speed recording, high resolution, high image quality, low noise, and the like are required for these recording apparatuses. As a recording apparatus that meets such demands, an ink jet recording apparatus is used for a relatively small-sized recording apparatus, and has been rapidly spreading in recent years.

In such an ink jet recording apparatus,
In order to further improve the recording speed, a recording head using a plurality of ink ejection ports in an integrated arrangement and a recording head having a plurality of recording heads for color recording are often used. In addition, due to demands for high resolution and high image quality, a halftone processing method such as a dither method or an error diffusion method is used as a method for faithfully reproducing the gradation of image information in these inkjet recording apparatuses. .

[0005] Reproduction of these gradations enables excellent gradation recording when the resolution of the recording apparatus is sufficiently high (for example, 1000 dots / inch or more). However, when the resolution of the recording apparatus is low (for example, about 360 / inch to 720 dots / inch), the recording dots in the high-luminance portion become conspicuous, causing discontinuity of pixels, and the image tends to be rough. Therefore, in order to further increase the number of reproducible gradations, a method of making the recording dots themselves multi-valued has been performed. For example, the voltage applied to the recording head or
There is known a method of reproducing a gradation by controlling a pulse width or the like of an applied signal to modulate a diameter of a recording dot attached to a recording material. However, such a method is highly dependent on the environment, and the recorded dot diameter is not stable, and there is a limit to the size of the minimum dot that can be recorded, so that it is possible to reproduce gradation stably. There are problems such as difficulty.

In addition, there is a density modulation method for expressing gradation by changing the density of dots in a pixel matrix while keeping the dot size constant. However, in order to increase the number of reproducible gradations, However, there is a problem that the dot matrix size needs to be increased, and the resolution of an image to be reproduced deteriorates.

Therefore, an ink jet recording apparatus uses:
As a method of improving the gradation reproduction characteristic and obtaining a high-density and high-gradation image, one pixel is formed by landing a plurality of droplets on substantially the same location on a recording medium, A so-called multi-droplet method for expressing gradation by changing the number of droplets to be landed, or using a plurality of inks having different densities, at least two colors for similar colors are used.
A recording method for reproducing gradation by using different kinds of recording dots with different densities, a method combining these two methods, and the like have been proposed and put to practical use.

On the other hand, an error diffusion method (literature: Earl Floyd & L. Steinberg, "Adaptive Algorithm for Spatial Grayscale", S.I. Day 75 Digest (R. FLOYD &
L.STEINBERG, “An Adaptive Algorithm for Spatial Gr
ey Scale ”SI D75 DIGEST), pp36-37).

As an image recording method to which the error diffusion method is applied, for example, Katoh, Y. Arai, Y. Yasuda, "Multi-level error diffusion method" (National Conference of Communication,
Department in Showa53Year, Society of Electronic Co
mmunication in Japan (1973), pp504 (Japanese))
An error diffusion method in which a plurality of threshold values are provided is realized in contrast to the conventional error diffusion method in which one fixed threshold value is provided. For example, assuming that the range of image data is 0 to 255, binary data is obtained by error diffusion using “128” as a threshold value in the past, but “multi-valued error” by Katoh, Y. Arai, and Y. Yasuda was obtained. In the “diffusion method”, when performing grayscale printing with two types of ink densities, two values “85” and “175” are set as thresholds, and ternary data is obtained with two types of recording densities.

Further, in recent years, there has been attempted a method of obtaining multi-valued data at three or more types of recording densities and expressing a high-quality image.

[0011] As recovery means when the recording quality of the ink jet recording apparatus deteriorates, ink is discharged from the nozzles of the recording head by a suction means or a pressure means to remove foreign matter or bubbles in the liquid path, or the ink discharge surface. Is cleaned with a wiper or the like to remove the ink adhered matter near the ejection port.

Further, even during the printing operation, the ink is gradually attached to the ejection opening surface of the recording head due to the ejection of the ink, which causes an ejection failure. Therefore, the wiping (wiping) of the ink ejection port surface of the recording head is performed at predetermined timings. Furthermore, in order to expel the ink thickened by the evaporation of the solvent from the nozzles not used during the recording operation, the preliminary ejection for performing the ink ejection different from the recording is performed at a predetermined timing, so that fresh ink is always discharged. It is also performed to perform stable recording by supplying the ink into a nozzle.

[0013]

However, fresh ink is supplied into the nozzle by the recovery operation by the above-described recovery means. Immediately after this recovery operation, the solvent forming the ink is discharged from the nozzle tip. A phenomenon is seen in which the ink is more gradually evaporated and the ink concentration at the nozzle tip rises with time. Further, there is a phenomenon in which the degree of increase in the density of ink changes depending on the environmental temperature, humidity, and the like in which the recording apparatus is placed.

In particular, in a multi-droplet system or a system in which gradation is expressed by using a plurality of inks of similar colors and different densities, the balance of reproduced gradation is lost due to an increase in ink density, and the gradation is smooth. In some cases, false contours were lost and the quality of the recorded image was impaired.

The present invention has been made in view of the above-mentioned conventional example, and records a high-quality image by predicting a change in ink density, determining a more optimal ink combination, and recording an image. It is an object to provide a method and an apparatus thereof.

Another object of the present invention is to provide:

In order to achieve the above object, an ink jet recording apparatus according to the present invention has the following arrangement. That is, a recording unit capable of recording with a plurality of types of inks having different densities, and an ink type determination for determining which of the plurality of types of ink is to be used for recording by the recording unit in correspondence with multi-valued image data Means, a plurality of types of density change characteristic tables for estimating ink density changes corresponding to continuous non-ejection times, and test patterns for recording a plurality of test patterns having different continuous non-ejection times by the recording means. Recording means, selecting one of the plurality of types of density change characteristic tables based on the recording densities of the plurality of test patterns recorded by the test pattern recording means, and selecting the density change characteristic table based on the selected density change characteristic table. Control means for controlling to record an image corresponding to the multi-valued image data with the ink determined by the ink type determining means; Characterized in that it has.

To achieve the above object, the ink jet recording method of the present invention comprises the following steps. That is,
A recording method in an ink jet recording apparatus having a recording unit capable of recording with a plurality of types of inks having different densities, wherein recording is performed by the recording unit using any of the plurality of types of inks corresponding to multi-valued image data. An ink type determining step of determining whether or not to perform, a test pattern recording step of recording a plurality of test patterns having different continuous non-discharge times by the recording unit, and a plurality of test patterns recorded in the test pattern recording step. Based on the recording density, select one of a plurality of types of density change characteristic tables for estimating the density change of the ink corresponding to the continuous non-ejection time, and select the ink based on the selected density change characteristic table. A control step of controlling to record an image corresponding to the multi-valued image data with the ink determined in the type determining step. And having a, the.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the first embodiment, for simplicity of explanation, a case where a transmitted image is recorded using an additive ink / film system will be described.

[Additivity] First, an ink / film system having additivity means that, when recording on a film used for recording a transmission image by an ink jet method, ink is overprinted at the same pixel position a plurality of times. Then, it means that transmission densities are added (density is increased). An example where such additivity holds is given.

As a recording sheet, a dye-based C.I. on a BJ transparency film CF-301 (manufactured by Canon Inc.). I. When a 2% solution of Direct Black 19 is uniformly printed using an inkjet printer, an image having a transmission density of “0.8 D” is obtained. Similarly, C.I. I. When a 1% solution of direct black 19 is uniformly printed, an image having a transmission density of “0.4D” is obtained. Furthermore, when these two types of inks are overlaid and printed, a transmission density of “1.2D” can be obtained. In such an ink / film system, it has been experimentally confirmed that the above-described additivity is substantially satisfied in the range of the transmission density from "0" to "2.5D".

Therefore, in such an ink / film system in which additivity is satisfied, the number of gradations that can be expressed can be significantly increased by overprinting a plurality of inks having different densities at the same pixel position.

[Regarding Ink Density] Next, the ink density of the ink jet head unit used in the ink jet recording apparatus will be described.

First, consider the case where an image is formed using four types of inks. Now, when the ink can be ejected four times to one pixel position without overflowing and the ink can be overprinted, and the above-described additivity is satisfied, the inks D1, D2,
By setting the ratio of the densities of D3 and D4 to "1: 2: 4: 8" and changing the combination of the ejections of the respective inks, the number of gradations of the recorded image can be maximized.

FIG. 3 is a view for explaining an ink type distribution table showing combinations of ink ejection with respect to image data (density data).

In the drawing, each of d1 to d4 is the ink D
This signal indicates the presence or absence of ink ejection corresponding to each of 1 to D4. If "1", the ink is ejected;
If so, it is binary data meaning no ejection. As an example, when the image data value (density value) is “10”, 2
Since the value data d2 = d4 = 1 and d1 = d3 = 0,
The inks D2 and D4 are ejected onto the same pixel in an overlapping manner.

As described above, since the density ratio of the inks D1 to D4 is set to "1: 2: 4: 8", the density data " From "0" to "15" can be reproduced without skipping the density.

That is, when there are n types of inks and the recording medium (recording sheet) used for recording can absorb the amount of ink that has been repeatedly struck n times, the maximum number of gradations is expressed. The density ratios of the respective inks are as follows: D1: D2: ...: Di: ...: Dn = 1: 2: ...: 2 ^ (i-
1):...: 2 ^ (n-1), and the maximum number of gradations Ds at that time is: Ds = (1 + 2 + ... + 2 ^ (i-1) + ... + 2 ^ (n-1) + 1 = 2
You can see that it is represented as ^ n. Here, "^" indicates a power, for example, "2 ^ n" indicates 2 to the power of n.

In other words, when the ink has n kinds of concentrations, the concentration ratio of these inks is set to “1: 2:.
2 ^ (i-1):...: 2 ^ (n-1) ", the combination of these inks allows the number of gradations per pixel to be up to 2
^ n.

[First Embodiment] [Explanation of Overall Structure] FIG. 1 is a block diagram showing a structure of an ink jet recording system according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an image input unit such as a scanner for inputting an image signal. This image input unit 1
May be, for example, an interface unit with a host computer. Reference numeral 2 denotes an operation unit including various keys for instructing setting of various parameters and recording start, and 3 denotes a CPU that controls the operation of the entire system according to the present embodiment in accordance with a control program stored in a storage medium 4. 4
Is a storage medium that stores a program for operating the system of the present embodiment according to a control program and an error processing program. The operations of the first embodiment are all operations based on this program. As the storage medium 4 for storing this program, for example, a ROM,
FD, CD-ROM, HD, memory card, magneto-optical disk, and the like.

The configuration of the storage medium 4 will be described. Reference numeral 4a denotes a gamma correction conversion table for reference in gamma conversion processing, 4b denotes an ink type distribution table for reference in ink type distribution processing described later, and 4c denotes an ink type distribution table. The image data 4d of the test pattern used when selecting the density change characteristic table is a plurality of densities, which are referred to in the process of multi-tone processing and ink type distribution processing, and indicate the ink density increase characteristics with respect to non-ejection time. The change characteristic tables and 4e indicate programs each storing various programs.

Reference numeral 5 denotes a RAM, which is used as a work area used for temporarily storing various data, a temporary save area for error processing, and a work area for image processing when the CPU 3 executes processing. Also, this RAM
5, after copying various tables stored in the storage medium 4, the contents of the tables can be changed, and the image processing can be performed while referring to the changed tables. Further, a plurality of density increase characteristic tables can be directly created in the RAM 5 based on the density fluctuation data. 5a is a record history counter for counting the record history,
The recording history (particularly the number of continuous non-ejection dots) for each ink jet head (ink type) is counted and stored by the CPU 3. Reference numeral 6 denotes an image processing unit which creates head drive data for realizing multiple gradations by inkjet based on the image data input from the image input unit 1. A printer unit 7 forms an image based on the head drive data created by the image processing unit 6. Reference numeral 8 denotes a bus line for transmitting address signals, data, control signals, and the like in the present system.

[Image Processing Unit 6] FIGS. 2A and 2B are diagrams for explaining the flow of processing in the image processing unit 6 of the ink jet recording system according to the first embodiment.

FIG. 2A shows the printer unit 7 based on the test pattern image data 4c stored in the storage medium 4.
To print a test pattern (18). Reference numeral 19 denotes processing for selecting an optimum table from the density change characteristic tables 1 to 14 (4d). Here, the non-use time of the nozzle under various conditions is calculated, and an optimal table is selected from a plurality of density change characteristic tables 4d linearly approximated by the least squares method calculation based on the print result of the test pattern. ing. Details of this processing will be described later.

FIG. 2B shows the flow of processing for generating head drive data for input image data.

The gamma correction processing 11 converts the image data CV input from the image input unit 1 into a signal CD representing the density using the gamma correction conversion table 4a, and stores the signal CD in the page memory area of the image processing work area of the RAM 5. Store.
The target pixel selection 12 selects one pixel to be processed in the page memory area of the RAM 5 and obtains density data CD of the pixel. Ink type distribution processing 13
Refers to the ink type distribution table 4b based on the CD value of the target pixel and determines an ink combination candidate (binary data) expressing the density CD of the target pixel. In the density increase correction processing 14, the density change characteristic table 9 selected based on the print result of the test pattern described above is referred to,
It predicts how much the combination of the inks selected in the ink type distribution processing 13 fluctuates with respect to the ideal density, and changes the head drive data (binary data) for discharging the ink as necessary. Thus, binary data (d1, d2, d3, d3) indicating the optimum combination of densities, that is, ink ejection and non-ejection from the head corresponding to each ink density
…).

By performing the above processing, the processing of one pixel of interest ends. Then, the image density data CD
By repeatedly performing the processing shown in the above 12 to 14 on all the pixels based on the above, a binary value indicating the ink discharge or non-discharge for each pixel with respect to each head having inks of different densities Data (d1, d2,
d3, d4) are formed.

[Printer Unit 7] In the printer unit 7, the ink jet head units 21-1 to 21-4 (FIG. 4)
The ink is ejected from the corresponding ink ejection port array in accordance with the binary data (d1, d2, d3,...) To form a multi-tone image. 17-1 and 17-2 in FIG.
, 17-4 are delay circuits, which function to set the timing of superimposing the same pixel position from each ink discharge port (nozzle) row.

Next, the printer unit 7 of the first embodiment will be described with reference to FIG.

A plurality of ink jet head units 21-1 to 21-4 are arranged on the carriage 20. Inkjet head units 21-1 to 21-4
Are provided with an ejection port array (40-1) for ejecting ink.
To 40-4: FIG. 5), and the inkjet head units 21-1 to 21-4 are arranged at predetermined intervals. The ink to the ejection port array corresponding to each of the inkjet head units 21-1 to 21-4 is supplied to the corresponding ink cartridge 22.
-1 to 22-4, and the ink cartridges 22-1 to 22-4 respectively have inks D1, D2,
This is an ink cartridge that supplies D3 and D4. still,
Each ink density will be described later. Here, control signals and the like supplied to the inkjet head units 21-1 to 21-4 are sent via the flexible cable 23.

The recording medium 24 composed of a sheet or a thin plastic plate is nipped by a discharge roller 25 via a conveying roller (not shown), and is sent in the direction of the arrow as the conveying motor 26 rotates. The carriage 20 is guided and supported by a guide shaft 27 and a linear encoder 28. The carriage 20 is reciprocated along the guide shaft 27 by driving a carriage motor 30 via a drive belt 29.

The above-described ink jet head unit 21
Heating elements (electric / thermal energy converters) for generating thermal energy for ink ejection are provided inside (liquid paths) of the respective ink ejection ports -1 to 21-4. In accordance with the movement timing of the carriage 20 detected by the linear encoder 28, these heating elements are driven based on the above-described binary data, so that ink droplets are formed on the recording sheet in the order of the inks D1, D2, D3, and D4. Is flying and attached on the recording medium 24. Thus, an image can be recorded on the recording medium 24.

These ink jet head units 21
At the home position of the carriage 20 set outside the recording area by -1 to 21-4, cap units 31-1 to 31-1 are provided.
A recovery unit 32 comprising 31-4 is installed.
Here, when recording is not performed, the carriage 20 is moved to the home position, and the ink ejection port surfaces of the corresponding inkjet head units 21-1 to 21-4 are moved by the caps 31-1 to 31-4 of the caps. It is possible to prevent the ink discharge port from being clogged due to adhesion of the ink due to evaporation of the ink solvent or adhesion of foreign matter such as dust due to evaporation of the ink solvent.

The capping functions of the cap portions 31-1 to 31-4 are provided in order to eliminate the ejection failure and clogging of the ink ejection ports having a low recording frequency. The ink is forcibly sucked from the ink ejection port by being used for idle ejection for ejecting ink to 1-31-4, or by operating a pump (not shown) with each inkjet head unit capped. It is used to recover the ejection of the ejection port that has caused the ejection failure.

Reference numeral 33 denotes an ink receiver. When each of the ink jet head units 21-1 to 21-4 passes above the ink receiver 33 immediately before recording, the ink receiver 3 is used.
It is used to perform a predischarge toward 3. In each scan of the carriage 20, preliminary discharge is performed by each ink jet head by the ink receiver 33 so that the ink at the nozzle tip whose ink density has increased is idle-discharged, and fresh ink is supplied to the nozzle tip. Records can be made.

As a result, since the preliminary ejection position of each ink jet head unit is set to the determined position each time, the time from the position of the ink receiver 33 to the recording start position of the image is always substantially constant. That is, at the beginning of the processing for each line of the image, the initial value set in the history counter 5a may be the same value for any head unit. In addition, cap parts 31-1 to 31-31
By disposing a blade (not shown) and a wiping member at a position adjacent to the ink jet head 4, the inkjet head units 21-1 to 21-1 are arranged.
It is possible to clean the respective ink ejection port forming surfaces 21-4 just before the start of the recording operation.

[Regarding the Head] The detailed configuration of the inside of the ink jet head unit according to the present embodiment is disclosed in Japanese Patent Application Laid-Open No. Hei 7-125262, and a description thereof will be omitted.

Next, with reference to FIG. 5, the configuration of the ink ejection port array in the ink jet head unit of the present embodiment will be described.

FIG. 5 shows the ink jet head unit 21.
FIG. 4 is a diagram of the ink ejection port arrays -1 to 21-4 as viewed from the recording medium 24 side.

Inkjet head units 21-1 to 21-1
21-4, each of 40-1 to 40-4 is an ink ejection port array for ejecting each of the inks D1 to D4, and the ejection port array of each unit has a pitch of 600 dots per inch (600 dpi). And has 256 ink ejection ports. In addition, since four inks D1 to D4 can be ejected in one scanning in the sub-scanning direction, a high-gradation image can be generated without increasing the recording time.

[Ink Type Distribution Table] FIG. 6 shows inks D1 and D for 8-bit density data (image data).
2, binary data representing ejection and non-ejection of D3 and D4,
It shows the transmission densities of the inks D1, D2, D3, and D4 and the transmission densities of the overprinting by combining the inks based on the determined binary data.

Here, it is assumed that the density data is represented by 8 bits, and that the smaller the value of the density data is, the lower the density (lighter) and the larger the density data, the higher the density (dark). To simplify the description, the transmission density of the transparent film as the recording medium is set to “0”.
D ". The transmission densities of the inks D1, D2, D3, and D4 represent the transmission densities when 100% solid printing is performed using only the respective inks in the inkjet recording system according to the first embodiment.
The concentration ratio of 1, D2, D3, and D4 is “1: 2: 4: 8”. Here, the 8-bit density data is converted to the transmission density “0”.
Consider a case in which the image is expressed by 16 gradations from “D” to “2.4D”.

[Ink Density Increase Graph] FIG. 7 (A)
FIG. 4B is a diagram illustrating an example of a graph representing a density increase rate with respect to a continuous non-ejection time of ink. These values are obtained by linearly approximating the representative concentrations by the least square method based on the experimental results. The horizontal axis indicates the non-ejection time of the ink, and the vertical axis indicates the rate of increase of the transmission density (OD) of the ink.

FIG. 7A is a graph showing the rate of increase in ink density when the humidity is changed from 10% to 70% in units of 10% with the temperature kept constant at 30 ° C. FIG. Is at a constant humidity of 40%, and the temperature is 15 ° C to 35 ° C
FIG. 9 is a graph showing the rate of increase in ink density when the temperature is changed in 5 ° C. units. Here, the non-ejection time refers to a time from when ink is ejected from one nozzle of the ink jet head unit to when ink is ejected from the next nozzle.

In the present embodiment, the case where the frequency at which ink is ejected from the nozzle row in the ink jet head unit of the printer unit 7 is 10 kHz will be described. In the case of solid printing, 10000 ink droplets are ejected from each nozzle row of each inkjet head unit at 600 dpi per second. The moving speed of the carriage 20 at that time is about 42
Since the speed is 3.33 mm / sec, the short side of the A3 sheet is scanned in about 0.7 seconds.

As shown in FIG. 7, while the carriage 20 scans the short side (297 mm) of the A3 sheet, the rate of increase in the ink density used in the present embodiment is proportional to the non-ejection time. Experiments have confirmed that the inclination changes with the environmental temperature and humidity. The increase in the ink density during head scanning during printing is caused by the evaporation of the ink solvent at the nozzle tip. However, if the ink at the nozzle tip at the increased density is ejected as droplets by ink ejection, Next, since the nozzle is filled with fresh ink, the ink density at the nozzle tip returns to the specified density before the density increase.

FIG. 8 shows the non-ejection time on the horizontal axis in FIG. 7 in terms of the number of non-ejection dots based on an ejection frequency of 10 kHz. Here, the state at a temperature of 30 ° C. and a humidity of 40% is shown. In the above-described processing for determining the binary data of ink ejection and non-ejection, by referring to the characteristics of this density increase graph, an increase in the ink density is predicted based on the history of ink non-ejection, and the increase in the ink density is estimated. By changing the amount of ink by changing the combination of inks or by performing image processing, it is possible to print an image that is not affected by an increase in ink density.

In the first embodiment, the image processing unit 6 for performing the image processing is made easy to refer to the increase in the ink density as shown in FIG.
A density change characteristic table is created based on.

In the example of FIG. 8, the continuous non-ejection period is 5000
At the time corresponding to the dot, the ink density increase rate is 150
%. The density change characteristic table will be described based on this. The horizontal axis in FIG. 8 is set to the number of non-ejection dots in order to obtain a change in ink density corresponding to the count value of the above-described recording history counter 5a.

[Description of Ink Density Change Characteristic Table]
FIG. 9 is a diagram showing a density change characteristic table according to the present embodiment. In the inkjet recording system according to the first embodiment, a total of 14 types of density change characteristic tables including the density change characteristic table shown in FIG. 9 are stored in the area of the density change characteristic table 4 d of the storage medium 4.
The number of non-ejection dots (N) in FIG. 9 can be obtained based on the value of the recording history counter 5a provided for each head unit.

The calculation result of the density increase rate dD shown in FIG. 8 is written in the density change characteristic table of FIG. 9 corresponding to the number of non-ejection dots. By writing the calculation result in advance in this way, the amount of calculation in the image processing unit 5 can be reduced, and the processing can be speeded up. Assuming now that the density increase rate dD is 4-byte data, the address offset of the density change characteristic table is every four addresses.

The number of non-ejection dots indicated by the recording history counter 5a corresponds to the offset of this address. To correspond to that address, the content of the recording history counter 5a may be quadrupled. This value is added to the base address of the density change characteristic table, and the ink density rise rate can be obtained by reading the address. By multiplying the increase rate by the basic density of the ink to be obtained, the ink density at that time can be predicted.

[Description of Image Processing in Image Processing Unit 6]
FIG. 2 shows the processing of the image processing unit 6 according to the first embodiment.
Although described with reference to FIGS. 2A and 2B, FIG.
A method of selecting a density change characteristic table using a test pattern shown in FIG.

FIGS. 10A and 10B schematically show the main scanning section of the printer section 7 shown in FIG. 4. FIG. 10A shows the recording section viewed from the side, and FIG. ) Is the one shown in FIG.
FIG. 3 is a diagram of the recording medium 24 of the recording unit viewed from above.

When the recording start signal is sent to the printer section 7, the ink jet head units 21-1 to 21-
4 starts moving from the home position (not shown) in the direction of arrow S, and when the ink jet head unit 21-1 passes through the ink receiver 33, the carriage 20 moves at a speed corresponding to the recording speed. They are moving at the same constant speed. Each of the ink jet head units is arranged above the ink receiver 33 by the head units 21-1 and 21-1.
21-2, 21-3, and 21-4, and 101
The preliminary ejection is performed on the ink receiver 33 at the position indicated by. An area surrounded by 102 to 103 is a recordable area of the recording medium 24. In this example, recording is started from a position indicated by 104 in the recordable area.

In FIG. 10B, an area corresponding to the width EF in the sub-scanning direction is recorded (test pattern "1") in one main scan, and the width F in the sub-scanning direction is recorded in the next main scan. -G
The process of recording (test pattern "2") in an area corresponding to is repeated in the same manner as described above.

Here, the ink jet head unit 21
The frequency at which each of -1 to 21-4 ejects ink from the nozzle row is 10 kHz, and the recording density in the main scanning direction is 600 dpi. Therefore, the main scanning speed of the carriage 20 is about 423.33 mm / sec. The distance from the preliminary ejection position 101 to the recording start position 104 is 42.3.
If it is 3 mm, the main scanning speed (approximately 423.33 m
m / sec), each inkjet head unit reaches the recording start position 104 in about 0.1 second after the preliminary ejection, and ejects ink according to the input binary data while moving at a constant speed. Make a record.

When the ink is ejected from the nozzles of each ink jet head unit in this manner, the ink whose density has increased at the nozzle tip jumps out as droplets, and the ink density at the nozzle tip returns to a normal value.

Using the ink type distribution table shown in FIG. 6, the ink density, and the overprint density for the density data, the density rise rates of the inks D1, D2, D3, and D4 are all 30 ° C. and 40% humidity in FIG. % Characteristic, that is, FIG.
It is assumed that the characteristics are shown. Based on these assumptions, FIG.
At 0, immediately after the preliminary ejection at the ink receiving position 101, the ink density at the nozzle tip becomes a normal value, and at the recording start position 104, the density at the nozzle tip of each inkjet head unit increases by 1%. .

As described above, a certain test pattern is stored in the test pattern image table 4c of FIG. 2A, and based on this test pattern, printing of the test pattern by the printer unit 7 (FIG. 2: 18), the image data corresponding to the test pattern is called from the test pattern image table 4c, and for example, the test patterns "1" to "1" as shown in FIG.
4 "is recorded.

The test patterns “1” to “14” are
In the first main scan, after the ink is continuously ejected between the position 104 and the position H in the main scanning direction and recording is performed, an area between the position H and the position I (50-2) ), Non-discharge is continuously performed, and the region 50 between the position I and the position J is further discharged.
At -3, the ink is continuously ejected. In the region between the preliminary ejection position 101 and the rightmost end 103, the inkjet head units 21-1 to 21-4 are driven at a constant speed.
Further, it is driven at a discharge frequency of 10 kHz.

FIG. 11 is a graph showing an increase in ink density in a nozzle when a test pattern as shown in FIG. 10B is printed.

As shown in FIG. 11, the ink receiving position 10
After the preliminary ejection is performed at 1 and the ink temperature returns to the initial value, the ink non-ejection state continues to the position 104, the ink temperature increases, and the ink temperature continuously increases from the position 104 to the position H. Ink ejection (50-1) is performed.
The ink density has returned to the normal value. Subsequently, the ink temperature increases from position H to position I due to continuous non-ejection,
From the position I to the position J, the ink discharge 50
Since -3 is performed, the ink temperature has returned to the initial value. Here, since the carriage 20 moves between the position H and the position I in about 0.3 seconds, it can be seen that the distance between the positions is converted to about 3000 dots in terms of the number of recording dots.

Next, in the second main scan (FIG. 10B), the interval 50-2 between continuous non-discharge between the position H and the next recording start position (I) increases. Here, since the carriage 20 moves between the position H and the position I in about 0.35 seconds, it can be understood that when this is converted into the number of recording dots, it becomes about 3500 dots.

That is, there is a continuous non-discharge 50-2 between the first continuous discharge 50-1 and the next continuous discharge 50-3, and the interval between the continuous non-discharge 50-2 is the first main scan. Then 30
At 00 dots, the number of dots is increased by 500 for each main scan (test pattern), and is repeatedly recorded until finally 9500 dots (the 14th main scan: test pattern “14”).

FIG. 12 shows the density change characteristic tables “1” to “1”.
It is a graph explaining the data of "14".

This graph shows fourteen types of inks showing the rate of increase in ink density corresponding to the number of continuous non-ejection dots, which was measured in advance under conditions related to the increase in ink density, such as various temperatures and humidity. 5 shows a density rise graph, and stores a density change characteristic table corresponding to each characteristic graph. The numbers given to the lines indicating the respective characteristics in FIG. 12 are the test pattern numbers 50-4 (the numbers of the test patterns “1” to “14”), that is, the intervals between the continuous non-ejection areas 50-2. Yes, it is.

Here, the sheet on which these test patterns are recorded is placed at a distance of 25 cm, and the increase in ink density is visually observed in the continuous ejection area 50-3 after the continuous non-ejection area 50-2. I confirmed whether or not. This is because, in general, a density difference of 0.3 or more in OD value can be visually confirmed under a standard light source at a distance of 25 cm. In this manner, when an increase in the ink density is recognized in the test pattern having the continuous non-ejection area 50-2 having a certain length or more, the test pattern corresponding to the interval of the non-ejection area 50-2 described in the test pattern The user selects the number 50-4 and inputs the number from the operation unit 2.
Thus, the optimum density change characteristic table is selected from the plurality of ink density change characteristic tables 4d stored in the storage medium 4.

Now, under the conditions of a temperature of 30 ° C. and a humidity of 40%,
The test patterns "1" to "14" described above are shown in FIG.
As a result of visually inspecting whether or not an increase in the ink density has occurred in the continuous ejection area 50-3, in the test pattern “5”, the area 50-
In No. 3, an increase in the ink density was observed. In this case, the operator inputs the number “5” from the operation unit 2.
As a result, the density change characteristic table corresponding to the number “5” is selected from the density change characteristic table 4d.

When the recording result of test pattern "5" is measured using a densitometer, the OD value in area 50-3 changes from "0.75" to "1.05". Was. This corresponds to a density increase rate of 140%. Therefore, it has been confirmed that the increase in density can be visually determined.

FIG. 20 is a flowchart for explaining a process of selecting a density change characteristic table based on such a test pattern.

First, in step S11, test patterns "1" to "14" are recorded as shown in FIG. Next, in step S12, the density of the test pattern on the sheet on which these test patterns are recorded is measured, for example, visually or using a densitometer. Here, it is checked whether or not there is a test pattern in which the density of the print area 50-3 after the continuous non-ejection area 50-2 is higher than the print density of the area 50-1 by a predetermined amount or more. If there is a test pattern in which such a change in density is recognized, a number corresponding to the test pattern having the smallest continuous non-ejection area 50-2 is input from the operation unit 2 (step S13). . Thereby, the CPU 3 stores the density change characteristic table corresponding to the input number
It is selected from the density change characteristic table group 4d, and is used as an ink density change characteristic table to be used for subsequent image processing (step S14).

Next, a specific example of performing the image processing shown in FIG. 2B using the density change characteristic table 9 (FIG. 2) selected as described above will be described. Note that the density change characteristic table of “5” is a value under the same conditions (temperature of 30 ° C., humidity of 40%) as the example of the ink density increase characteristic shown in FIG. This embodiment will be described using a table.

FIG. 13 is a diagram for explaining an example of the main scanning and printing operation of the carriage 20 in the printer unit 7 of the ink jet printing system according to the present embodiment.

As in the case of FIG. 10, the area between the position 102 and the position 103 of the recording medium 24 is the recording area. In the example of FIG. 13, the recording is started from the position D. Here, the distance from the preliminary ejection position 101 to the recording start position D is 21
1.7 mm, and based on the above-described main scanning speed of the carriage 20, the inkjet head units 21-1 to 21-1
Each of the prints 21-4 reaches the print start position D 0.5 second after the preliminary discharge, and thereafter performs printing by discharging ink according to print data (binary data) while moving at a constant speed.

FIG. 14 shows the images 130 and 13 shown in FIG.
2 shows an example of image data (density data) stored in a page memory area of the RAM 5 in order to record 1 on the recording medium 24. Each code shown in FIG. 13 corresponds to the code shown in FIG. 13, and one cell corresponds to one pixel (600 dpi) of a recorded image. These images 130, 1
At 31, in the image 130, an image 131 in which pixels of density data “100” continue for three pixels, density “0” (space) continues for six pixels, and thereafter, pixels of density data “100” continue is stored. ing.

The relationship between the OD value and the density data in the present embodiment is represented by the following equation.

OD = (2.4 / 255) × Density Data As described above, since the density data and the OD value are in a proportional relationship, when generating the binary data for determining whether or not to eject each ink. Performs processing while estimating the ink density based on the image data, that is, the value of the density data, instead of the OD value of the actually recorded image. For example, if the density data increases by 50%, the OD value is predicted to increase by 50%.

As shown in FIG. 8, every time the carriage 20 moves by one pixel, the density of the undischarged ink becomes about 0.01%.
It is thought to rise. However, if there is no ink ejection of about 10 pixels continuously in the x direction of FIG. 14, the ink density increase rate at that time is 0.1%. The rate of concentration increase shall be ignored.

The inks D1, D2, D in FIG.
3 and D4 (0.16D, 0.32D, 0.
64D and 1.28D) are the density data “1” respectively.
7 "," 34 "," 68 ", and" 136 ".

FIG. 15 shows the table of FIG. 6 in which a threshold value for multi-value error diffusion and a conversion value obtained by converting the transmission density of each ink into density data are added.

An operation example will be described below.

In FIG. 14, numbers starting from “0” assigned to the upper side and the left side indicate pixel addresses, the horizontal direction is x, the vertical direction is y, and an arbitrary pixel is represented by coordinates (x, y). . That is, the pixel (0,0) indicates the upper left pixel in FIG. Further, the inkjet head unit 2
Since 1-1 to 21-4 (carriage 20) move in the main scanning direction S, rows of pixels arranged in the main scanning direction correspond to one of the inkjet head units having inks of different densities. It corresponds to the nozzle.

First, the processing is performed focusing on the pixel (0, 0). The density data of the pixel (0, 0) is “100”. Considering the combination of inks from the table of FIG.
Combination No. The combination (“102”) of the inks D2 and D3 corresponding to = 6 is selected as a candidate closest to the density data “100”. However, at the recording start position D shown in FIG.
In both cases, since the ink density has increased by about 50%, the ink D
It is predicted that the density of No. 2 will increase from “34” to “51”, and the density of ink D3 will increase from “68” to “102”. On the other hand, the concentration "15
3 ". Therefore, the pixel of interest (0, 0)
Considering that the density data “100” is expressed, since the density of the ink D2 has increased by about 51, the ink D2 is removed and only the ink D3 is ejected. Thus, the predicted density at that time becomes “102”. The combination of the inks determined in this way is determined by the ejection of each ink,
As the non-ejection binary data, the memory Md shown in FIG.
It is stored at the address corresponding to the pixel in 1, Md2, Md3, and Md4. In FIG. 18, the memory M
Each of d1, Md2, Md3, and Md4 is the ink D
1, D2, D3, and D4.

Thus, the processing of the pixel of interest (0, 0) is completed, and the pixels (0, 0, 1) of the inks D1, D2, D3, D4
0) binary data d1, which determines whether to discharge or not discharge
d2, d3, and d4 are determined.

Next, the position of the target pixel is moved to pixel (1, 0). The density data of this pixel (1, 0) is “100”. Here, in the same manner as described above, based on the table threshold value shown in FIG. =
A combination of six inks D2 and D3 is selected as a candidate. In this case, since only the ink D3 is ejected at the pixel (0, 0), the density of the ink D3 is about 0.01 from the recording history counter 5a and the density change characteristic table of FIG.
%, And since the other inks D1, D2, and D4 have not been ejected since the preliminary ejection, the ink density is considered to have increased by about 50.01%.

Therefore, in the ink density prediction at this time, the density of the ink D2 is “51.0034”,
The density of No. 3 is "68.0068", and the density of the combination of the inks D2 and D3 is "119.0102".
At this time, the density of the ink D1 is increased by 50.01% to “25.5017”. Therefore, the ink D1
The density of the combination of D1 and D3 is “93.5085”, and the combination of the inks D1 and D3 expresses the density data “100” of the pixel (1, 0) as compared with the combination of the inks D2 and D3. Would be suitable for Thus, the pixel (1, 0) is recorded by discharging the inks D1 and D3. The binary data indicating the determined ink combination is stored in the memory Md as shown in FIG.
1, Md2, Md3, and Md4 are stored at addresses corresponding to the pixel (1, 0).

In the same manner, a target pixel is sequentially selected in the main scanning direction S based on the density data of each pixel of the image.
By repeating the above-described processing, binary data (d) for instructing ink ejection and non-ejection for each pixel with respect to each inkjet head unit having a different density.
1, d2, d3, d4) are generated, and the memories Md1, Md
The data is stored at addresses d2, Md3, and Md4 corresponding to each pixel.

The contents of each recording history counter 5a are also updated in accordance with such processing. When the processing for the pixels on one main scanning line is completed in this way, the position of the target pixel is moved to (0, 1) on the second line, and the processing for each pixel is sequentially performed in the main scanning direction S in the same manner as described above. I do. At this time, similarly to the case where the target pixel is (0, 0), the process starts on the basis of the expectation that the ink density of the target pixel (0, 1) has increased by 50%.

[Second Embodiment] Next, a second embodiment of the present invention will be described. In the second embodiment, the printing is performed by combining the inks having the densities corresponding to the values of the image data in the above-described FIG. 2B, but here, the printing is performed by using the error diffusion method. Predicted density of the pixel to be
An example will be described in which an error from the density value of actual image data is diffused to peripheral pixels of a target pixel. In addition, this Embodiment 2
Is the same as the above-described configuration, and a description thereof will be omitted.

FIG. 16 shows a second embodiment according to the present invention.
The flow of processing for generating head drive data for input image data is shown.

The gamma correction processing 11 converts the image data CV input from the image input unit 1 into a signal CD representing density using the gamma correction conversion table 4a, and stores the signal CD in the page memory area of the image processing work area of the RAM 5. Store.
The target pixel selection 12 selects one pixel to be processed in the page memory area of the RAM 5 and obtains density data CD of the pixel. Ink type distribution processing 13
Refers to the ink type distribution table 4b based on the CD value of the target pixel and determines an ink combination candidate (binary data) expressing the density CD of the target pixel. In the density increase correction processing 14, the density change characteristic table 9 selected based on the print result of the test pattern described above is referred to,
It predicts how much the combination of inks selected in the ink type distribution processing 13 fluctuates with respect to the ideal density, and changes the head drive data (binary data) for ejecting ink as necessary. Thus, binary data (d1, d2, d3, d3) indicating the optimum combination of densities, that is, ink ejection and non-ejection from the head corresponding to each ink density
…).

In the density error calculation 15, the difference between the density that can be expressed by the combination of the inks determined in the density increase correction processing 14 and the CD value of the target pixel is calculated in accordance with the additivity described above. In the error diffusion processing 16, the difference calculated in the density error calculation 15 is diffused to pixels around the pixel of interest in the page memory area according to the distribution coefficient. After performing the error diffusion in this way, the process shifts to the twelve target pixel selection process, and the above-described process is executed.

FIG. 17 shows an example of weighting when distributing an error of a target pixel to its surrounding pixels in the multi-level error diffusion process performed in the second embodiment. In FIG. 17, “*” indicates a target pixel. The difference error between the density that can be expressed by the combination of ink and the density data,
The pixels are distributed to peripheral pixels according to the error distribution coefficient shown in FIG.

In FIG. 14, numbers starting from “0” assigned to the upper side and the left side indicate the address of a pixel, the horizontal direction is x, the vertical direction is y, and an arbitrary pixel is represented by coordinates (x, y). . That is, the pixel (0,0) indicates the upper left pixel in FIG. Further, the inkjet head unit 2
Since 1-1 to 21-4 (carriage 20) move in the main scanning direction S, rows of pixels arranged in the main scanning direction correspond to one of the inkjet head units having inks of different densities. It corresponds to the nozzle.

First, processing is performed focusing on the pixel (0, 0). The density data of the pixel (0, 0) is “100”. Considering the combination of inks from the table of FIG.
Combination No. The combination (“102”) of the inks D2 and D3 corresponding to = 6 is selected as a candidate closest to the density data “100”. However, at the recording start position D shown in FIG.
In both cases, since the ink density has increased by about 50%, the ink D
It is predicted that the density of No. 2 will increase from “34” to “51”, and the density of ink D3 will increase from “68” to “102”. On the other hand, the concentration "15
3 ". Therefore, the pixel of interest (0, 0)
Considering that the density data “100” is expressed, since the density of the ink D2 has increased by about 51, the ink D2 is removed and only the ink D3 is ejected. Thus, the predicted density at that time becomes “102”. The combination of the inks determined in this way is determined by the ejection of each ink,
As the non-ejection binary data, the memory Md shown in FIG.
It is stored at the address corresponding to the pixel in 1, Md2, Md3, and Md4. In FIG. 18, the memory M
Each of d1, Md2, Md3, and Md4 is the ink D
1, D2, D3, and D4.

The difference error at this time is a difference “−2” obtained by subtracting the density value “102” of the ink D3 whose 50% ink density has increased from the density data “100” of the pixel (0, 0). When this error is distributed to pixels around the pixel according to the error distribution coefficient shown in FIG.
0) is “−1”, and pixel (0, 1) is “−0.75”.
Is sorted. These allocated pixel values are added to the values of the corresponding peripheral pixels. As a result, the density data of the pixel (1, 0) becomes “99” and the pixel (0, 1)
Is changed to “99.25”.

Thus, the processing of the pixel of interest (0, 0) is completed, and the pixels of the inks D1, D2, D3, and D4 (0, 0)
0) binary data d1, which determines whether to discharge or not discharge
d2, d3, and d4 are determined.

Next, the position of the target pixel is moved to the pixel (1, 0). The density data of the pixel (1, 0) has been changed to “99” by the error diffusion associated with the pixel (0, 0) described above. Here, in the same manner as described above, based on the table threshold value shown in FIG.
= 6 inks D2 and D3 are selected as candidates. In this case, since only the ink D3 is ejected at the pixel (0, 0), the density of the ink D3 is about 0.0 from the recording history counter 5a and the density change characteristic table of FIG.
Since the other inks D1, D2, and D4 have not been ejected since the preliminary ejection, the ink density is about 50.01%.
It is thought to be rising.

Therefore, in the ink density prediction at this time, the density of the ink D2 is "51.0034" and the density of the ink D2 is "51.0034".
The density of No. 3 is "68.0068", and the density of the combination of the inks D2 and D3 is "119.0102".
At this time, the density of the ink D1 is increased by 50.01% to “25.5017”. Therefore, the ink D1
The density of the combination of D1 and D3 is “93.5085”, and the combination of the inks D1 and D3 expresses the density data “99” of this pixel (1, 0) as compared with the combination of the inks D2 and D3. Would be suitable for Thus, the pixel (1, 0) is recorded by discharging the inks D1 and D3. The binary data indicating the determined ink combination is stored in the memory Md as shown in FIG.
1, Md2, Md3, and Md4 are stored at addresses corresponding to the pixel (1, 0).

The difference error at this time is the pixel (1, 0)
The difference “5.491” obtained by subtracting the predicted density “93.5085” of the inks D1 and D3 from the density data “99” of
5 ". If this error is distributed to the peripheral pixels of the pixel (1, 0) according to the error distribution coefficient shown in FIG. 17, the pixel (2, 0) has" 21.966 / 8 "and the pixel (1 ,
“16.4745 / 8” is assigned to 1), and “5.4915 / 8” is assigned to pixel (0, 1). As a result, each of the peripheral pixels (2, 0), (1, 1),
The error is added to (0,1), the value of pixel (2,0) is “102.74575”, and the value of pixel (1,1) is “1.
02.0593 ”, and the value of the pixel (0, 1) is“ 100.
6864 ".

Next, the target pixel is moved to the pixel (2, 0).
The density data of the pixel (2, 0) has been changed to “102.74575” by error diffusion of the pixel (1, 0). Also in this case, from FIG. = 6
Of inks D2 and D3 are selected as candidates. In this case, since the inks D1 and D3 are ejected at the pixel (1, 0), the density of the inks D1 and D3 is increased by 0.01%, and the inks (D2, D4)
Has not been ejected at all since the preliminary ejection, so the density has increased by 50.02%. Accordingly, the ink densities at this point are predicted to be “51.0068” for the ink D2 and “68.0068” for the ink D3,
The density by the combination of 3 is “119.0136”. Incidentally, the density of the combination of the inks D1 and D3 is “85.0085”, and the density data of the pixel (2, 0) is “102.85” for the combination of the inks D2 and D3.
Thus, this pixel (1, 0) is recorded by the inks D2 and D3. The binary data thus determined is stored in the memory as shown in FIG. Md1, Md2, Md3, Md4
At the address corresponding to the pixel (2, 0).

The difference error at this time is based on the density data “102.74575” of the pixel (2, 0),
3, the difference is “−16.26785” obtained by subtracting the predicted density “119.0136”. This error is distributed to the peripheral pixels of the pixel (2, 0) according to the error distribution coefficient shown in FIG. 17, and these peripheral pixels (3, 0), (2, 1),
An error is added to each of (1, 1).

As described above, the target pixel is sequentially selected in the main scanning direction S based on the image density data, and the above-described processing is repeated. Binary data (d1, d) for instructing ink ejection and non-ejection for each pixel
2, d3, d4) are generated, and the memories Md1, Md2,
Md3 and Md4 are stored at addresses corresponding to each pixel.

Further, the contents of each recording history counter 5a are updated in accordance with such processing. When the processing on the pixels on one main scanning line is completed in this way, the target pixel is moved to the pixel (0, 1) on the second line, and the processing on each pixel is sequentially performed in the main scanning direction S in the same manner as described above. I do. At this time, similarly to the case where the target pixel is (0, 0), the process starts on the basis of the expectation that the ink density of the target pixel (0, 1) has increased by 50%.

FIG. 18 shows the inks D1, D2, D3, and D3 created on the memory (RAM5) in this embodiment.
Md1 and Md for storing binary data (bit plane) indicating ink ejection and non-ejection corresponding to each of D4
FIG. 2 is a diagram for explaining Md2, Md3, and Md4.

FIG. 19 shows the density at which the image data (density data) shown in FIG. 14 is actually drawn by changing the ink combination based on the ink type distribution table 4b in the second embodiment. It is a figure explaining a value. As described above, the writing start portion of the image (pixel (0, 0)
And the pixel (0, 1), etc.), it can be seen that an extreme increase in the recording density due to an increase in the ink density due to the fact that the ink has not been continuously ejected until then is suppressed.

The present invention can also be realized by supplying the storage medium 4 storing the program according to the present invention to another system or apparatus and causing a computer of the system or apparatus to read and execute the program code stored in the storage medium. Achieved.

In the first embodiment, a common density change characteristic table is referred to for each ink density. However, when the density increase rate is different due to the difference in the ink density, the density change characteristic is different for each ink density. A table may be prepared, or an individual density change characteristic table may be prepared for each ink.

When the relationship between the ink density increase rate and the non-ejection time is not proportional, for example, when the density increase reaches a plateau after a certain period of time, the relationship is shown in FIG. It should be reflected on the table.

In the first embodiment, the density increase table has been described. However, the density change characteristic table is not limited to the density increase. That is, any curve may be used as long as it shows the ink density change characteristic.

Further, if the above-mentioned density change characteristic table is provided in a rewritable storage medium such as the RAM 5, for example, it is possible to rewrite an arbitrary characteristic.

In the above-described embodiment, the test pattern is provided with an ejection area for setting the ink density at the nozzle tip to a normal value. However, this ejection area is not provided, and preliminary ejection is performed for each row. A test pattern that selects the density change characteristic table based on the distance from the preliminary ejection position to the ejection area may be used.

In the above-described embodiment, whether or not an increase in the ink density has occurred is visually confirmed. However, the density may be measured using a density measuring device if the accuracy is to be further improved.

The test pattern used in the present embodiment may be any pattern as long as the non-ejection time can be quantitatively determined.

The present invention can be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but can be applied to a single device (for example, a copying machine, a facsimile machine, etc.). ) May be applied.

An object of the present invention is to supply a storage medium (or a storage medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and to provide a computer (a computer) of the system or the apparatus. Alternatively, this can be achieved by a CPU or an MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. By executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. This also includes a case where some or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.

Further, after the program code read from the storage medium is written into the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. This also includes the case where the CPU provided in the function expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

As described above, according to the present embodiment, a plurality of types of test patterns are recorded in order to select an optimum density change characteristic table from a plurality of density conversion characteristic tables, and the recorded test patterns are recorded. It has become possible to select an optimal density change characteristic table based on the density. Further, by predicting the change in the ink density at the continuous non-ejection nozzles based on the selected density change characteristic table, it is possible to predict the density of the recorded image in consideration of the surrounding environment.

As a result, it has become possible to optimally correct gradation disturbance at the time of recording due to a change in the surrounding environment, which has been a problem before.

[0131]

As described above, according to the present invention, it is possible to record a high-quality image by predicting a change in ink density, determining a more optimal combination of inks and recording an image. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an inkjet recording system according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a flow of a process performed by the image processing unit according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of an ink type distribution table according to the present embodiment.

FIG. 4 is a perspective view showing a configuration of a main part of a printing unit according to the embodiment.

FIG. 5 is a diagram showing an arrangement of an ink ejection port array of the inkjet head unit according to the embodiment.

FIG. 6 is an ink type distribution table according to the embodiment;
FIG. 4 is a diagram illustrating the density of overprinting with respect to ink density and density data.

FIG. 7 is a diagram illustrating an example of an increase in ink density with respect to a continuous ink non-ejection time.

FIG. 8 is a diagram showing an example in which the continuous ink non-ejection time is converted into the number of continuous non-ejection dots, and an increase in ink density with respect to the number of continuous non-ejection dots.

FIG. 9 is a diagram illustrating an example of an ink density change characteristic table according to the present embodiment.

FIG. 10 is a diagram illustrating an example of recording a test pattern by the printer unit according to the present embodiment.

FIG. 11 is a diagram illustrating a temperature rise of a head when a test pattern according to the present embodiment is printed.

FIG. 12 is a diagram showing an example in which an example of a change in the number of continuous non-ejection dots and an ink density according to the present embodiment is set corresponding to a test pattern.

FIG. 13 is a diagram illustrating image recording by the printer unit according to the present embodiment.

FIG. 14 is a diagram showing an example of image data recorded in FIG.

15 is a diagram illustrating a table in which a threshold value of multi-value error diffusion and a density data conversion value of ink transmission density are added to the ink type distribution table of FIG. 6 according to the present embodiment.

FIG. 16 is a diagram illustrating a flow of a process performed by the image processing unit according to the second embodiment of the present invention.

FIG. 17 is a diagram illustrating a distribution coefficient for distributing a density error to peripheral pixels according to the second embodiment.

FIG. 18 is a diagram illustrating a memory configuration of binary data corresponding to each inkjet head unit (each ink D1 to D4) in the present embodiment.

FIG. 19 shows a result of error diffusion according to the second embodiment.
FIG. 3 is a diagram for explaining predicted density values (stored in a RAM) of pixels actually recorded.

FIG. 20 is a flowchart illustrating a process of selecting a density change characteristic table based on a test pattern according to the present embodiment.

Claims (18)

[Claims] A recording unit capable of recording with a plurality of types of inks having different densities; and determining which one of the plurality of types of ink is to be used for recording by the recording unit in accordance with multi-valued image data. An ink type determining unit, a plurality of types of density change characteristic tables for predicting an ink density change corresponding to the continuous non-ejection time, and a plurality of test patterns having different continuous non-ejection times recorded by the recording unit A test pattern recording means for causing the test pattern recording means to select one of the plurality of density change characteristic tables based on the recording densities of the plurality of test patterns recorded by the test pattern recording means, Control to record an image corresponding to the multi-valued image data with the ink determined by the ink type determining means based on the image data. An ink jet recording apparatus characterized by having a control means. 2. An ink jet recording apparatus according to claim 1, wherein said recording means has an ink jet head corresponding to each of said plurality of types of inks having different densities. 3. The ink jet recording apparatus according to claim 1, wherein said recording means discharges ink of different types at substantially the same pixel position on the recording medium to perform recording. 4. The plurality of density change characteristic tables,
The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is provided for each ink of similar colors and different densities. 5. The apparatus according to claim 1, further comprising pseudo halftone processing means for performing pseudo halftone processing to represent a density value represented by said multi-valued image data. Inkjet recording device. 6. The ink jet recording apparatus according to claim 5, wherein the pseudo halftone processing means uses an error diffusion method as the intermediate processing. 7. The ink jet recording apparatus according to claim 2, wherein the plurality of ink jet heads are recording heads that perform recording by scanning in a main scanning direction. 8. The printing apparatus according to claim 7, wherein the printing unit performs preliminary ejection at a predetermined position before the plurality of inkjet heads start printing scan and enter a printable area.
3. The ink jet recording apparatus according to claim 1. 9. The ink type determining means predicts a change in each ink density by the selected density change characteristic table based on each continuous non-ejection time of the plurality of inks, and 9. The ink jet recording apparatus according to claim 1, wherein an ink corresponding to the image data is determined according to a density. 10. A recording method in an ink jet recording apparatus having a recording unit capable of recording with a plurality of types of inks having different densities, wherein the method uses any one of the plurality of types of inks corresponding to multi-valued image data. An ink type determining step of determining whether to perform printing by a printing unit; a test pattern printing step of printing a plurality of test patterns having different continuous non-discharge times by the printing unit; Based on the recording densities of the plurality of test patterns, select one of a plurality of types of density change characteristic tables for estimating the density change of the ink corresponding to the continuous non-ejection time, and select the selected density change characteristic table. An image corresponding to the multi-valued image data is recorded with the ink determined in the ink type determining step based on And a control step of controlling the ink jet recording method. 11. An ink jet recording method according to claim 10, wherein said recording means has a plurality of ink jet heads for each of said plurality of types of inks having different densities. 12. The ink jet recording method according to claim 10, wherein said recording means discharges and records a plurality of types of inks having different densities at substantially the same pixel position on a recording medium. 13. The ink jet recording apparatus according to claim 10, wherein the plurality of types of density change characteristic tables are provided for inks of similar colors and different densities. 14. The method according to claim 10, further comprising a pseudo halftone processing step of performing pseudo halftone processing to represent a density value represented by the multi-valued image data. Inkjet recording method. 15. The ink jet recording method according to claim 14, wherein an error diffusion method is used as the pseudo halftone processing. 16. The plurality of inkjet heads,
12. The ink jet recording method according to claim 11, wherein the recording head is configured to perform recording by scanning in a main scanning direction. 17. The ink jet recording method according to claim 16, wherein said recording means performs preliminary ejection at a predetermined position before the plurality of ink jet heads start recording scan and enter a recordable area. . 18. The method according to claim 18, further comprising: measuring a continuous non-ejection time of each of the plurality of types of ink. In the ink type determining step, based on each of the continuous non-ejection times of the plurality of types of ink, Predict the change of each ink density by the selected density change characteristic table,
18. The ink jet recording method according to claim 10, wherein an ink corresponding to the image data is determined according to the predicted ink density.