JP2002103652A - Recorder, recording method and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out high-quality recording having superior gradation characteristics without greatly increasing an image processing load even when an ink density changes. SOLUTION: In a recorder which carries out multi-gradation recording by changing kinds of ink used for recording and the number of ink drops, inputted data are converted to density data of each pixel in a recording region, and a target pixel is selected from the recording region (12). The ink density when the target pixel is to be recorded is estimated, and a range of a standard ink distribution table 4c which is required to be corrected is calculated from the estimated ink density (18). A corrected ink distribution table 4e after a density change correction is formed for only the subject range (13). The ink kind to be used and the number of ink drops are selected from the table (14).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording apparatus, a recording method, and a storage medium.
A recording apparatus, a recording method, and a multi-gradation recording method using a plurality of ink jet recording heads that discharge inks having different densities and changing the type of ink and the number of ink droplets discharged to each pixel on a recording medium. It relates to a related storage medium.

[0002]

2. Description of the Related Art Recording devices such as printers, copiers, and facsimile machines record an image composed of a dot pattern on a recording material (recording medium) such as paper or a thin plastic plate based on image information. It is configured. Such recording apparatuses can be classified into an ink jet system, a wire dot system, a thermal system, a laser beam system, and the like according to the recording system.

[0003] Of the above-mentioned systems, an ink-jet type recording apparatus is configured to eject ink (recording liquid) droplets from an ejection port of a recording head and fly the ink droplets onto a recording material to perform recording. The configuration is relatively simple.

[0004] 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 have been required for these recording apparatuses. The ink jet recording apparatus is used for a relatively small recording apparatus as a recording apparatus meeting such a demand, and is rapidly spreading.

[0005] An ink jet recording apparatus uses a recording head in which a plurality of ink discharge ports (nozzles) are integrated and arranged to improve the recording speed and the like. Are often used.

In order to satisfy the demand for high resolution and high quality, halftone processing methods such as a dither method and an error diffusion method have been used as a method for faithfully reproducing the gradation of image information in these ink jet recording apparatuses. I have.

In these methods of reproducing the gradation, the resolution of the recording apparatus is sufficiently high (about 1000 dots / inch or more).
In this case, excellent gradation recording is possible. However, when the resolution of the recording apparatus is low (about 360 to 720 dots / inch), the recording dots in the highlight portion are conspicuous,
The roughness of the image is likely to occur due to the discontinuity of the pixels.

Therefore, in order to further increase the number of gradations, a method of making the recording dots themselves multi-valued has been performed.

For example, there is known a method of controlling a voltage or a pulse width applied to a recording head to modulate the diameter of a recording dot attached to a recording material to obtain a gradation. However, this method has a high environmental dependency, the diameter of the recording dot is not stable, and the size of the minimum recording dot that can be recorded is limited, so that it is difficult to reproduce the gradation stably.

There is a density modulation method for changing the density of dots in a matrix while keeping the dot size constant. However, in order to increase the number of gradations, a considerable area is required and the resolution is deteriorated.

In order to improve the gradation characteristics and obtain a high-density and high-gradation image using an ink-jet recording apparatus, a method of landing a plurality of droplets on substantially the same location on a recording material is proposed. A so-called multi-droplet method in which one dot (pixel) is formed and gradation is represented by changing the number of droplets to be landed, or at least two types of densities of similar colors using a plurality of inks having different densities A recording method that reproduces gradation by using different recording dots, a method that combines the two, and the like have been proposed and put to practical use.

On the other hand, an error diffusion method has been proposed as one means of pseudo tone reproduction, which is described in the literature: Earl Floyd & L. Steinberg, "An Adaptive Algorithm for Special Gray Scale", S Day 7
5 digests (R.FLOYD & L.STEINBERG, “An Adaptive
Algorithm for Spatial Gray Scale ”SI D75DIGEST),
pp. 36-37.

As an image recording method to which the error diffusion method is applied, for example, “Multi-level error diffusion method” by Katoh, Y. Arai, and Y. Yasuda (National Conference of Communicatio)
n, Department in Showa 53 Year, Society of Electroni
c Communication in Japan (1973), pp504 (Japanese)) realizes an error diffusion method in which a plurality of thresholds are provided, in contrast to the conventional error diffusion method in which one fixed threshold is provided. For example, if the range of image data is 0 to 255, error diffusion is conventionally performed using 128 as a threshold,
Although binary data is obtained, according to the “multi-valued error diffusion method” by Katoh, Y. Arai, and Y. Yasuda, when gray-scale printing is performed with two types of ink densities, 85 and 175 are set as thresholds,
Three-valued data is obtained with two types of recording densities.

In recent years, attempts have been made to obtain multivalued data with three or more types of recording densities and express high-quality images.

In the ink jet recording apparatus, as a recovery operation performed when the recording quality is deteriorated, ink is discharged from nozzles of the recording head by a suction means or a pressure means to remove foreign matters and bubbles in a liquid path, or to discharge ink. A process of removing the ink fixed matter near the ejection port by cleaning the surface with a wiper or the like is performed.

In addition, even during the recording operation, the ink gradually adheres to the discharge port surface of the recording head due to the discharge of the ink, which causes a discharge failure. Therefore, the discharge port surface of the recording head is wiped at a predetermined timing. Processing is performed.

Further, from the unused nozzles during the printing operation,
In order to discharge the ink thickened by the evaporation of the solvent, a pre-discharge, which is different from the recording, is performed at a predetermined timing, and fresh ink is always retained in the recording head to perform stable recording. Have been done.

[0018]

However, when the above-described recovery operation is performed, fresh ink is supplied into the ink flow path. Immediately after the recovery operation, the solvent forming the ink flows from the nozzle tip. A phenomenon is observed in which the ink gradually evaporates and the ink concentration at the nozzle tip rises with time.

In particular, in a multi-droplet system or a system in which gradation is expressed using inks of similar colors and different densities, the balance of the gradation is lost due to an increase in the ink density, and the smoothness of the gradation is lost, resulting in a false contour. And the image quality may be impaired.

On the other hand, it is conceivable to appropriately change the combination of inks to be used in accordance with the increase in the density of the ink. In this case, however, the load of calculation and rearrangement in image processing increases, and the processing time increases. Is another problem. This is especially true for many types of ink used,
That is, it becomes remarkable when the number of gradations is large.

The present invention has been made in view of the above circumstances. For example, a plurality of ink jet recording heads that eject inks having different densities are used, and the ink ejected to each pixel on a recording medium is controlled. When performing multi-gradation printing by changing the type and the number of ink droplets, even if the recording characteristics such as the ink density change, the load of image processing is not increased so much, and the gradation is excellent. It is an object of the present invention to provide a recording apparatus, a recording method, and a storage medium that can perform high-quality recording.

[0022]

In order to achieve the above object, a recording apparatus according to the present invention uses a plurality of ink jet recording heads for discharging inks having different densities, and ink discharged to each pixel on a recording medium. A multi-gradation printing device that changes the type of ink droplets and the number of ink droplets, comprising: a conversion unit that converts input data into density data of each pixel in a printing area; An ink distribution table for associating a combination of the type of ink and the number of ink droplets to be used, a selecting unit for selecting a target pixel from the recording area, and predicting the density of the ink when the target pixel is recorded Calculating a correction range that needs to be corrected in the ink distribution table from an ink density prediction unit and the ink density predicted by the ink density prediction unit; A positive range calculating unit, and a correction ink distribution table for associating a value of density data within the correction range in the ink distribution table with a combination of the type of ink used for recording and the number of ink droplets. A correction ink distribution table creating means for creating based on the ink density predicted in the above, and a combination of the type of ink and the number of ink droplets used when recording the target pixel, An ink distributing means for selecting based on the density data of the target pixel; and a driving means for generating a driving signal to be transmitted to the recording head according to a combination of the type of ink and the number of ink droplets selected by the ink distributing means. It has.

The recording method of the present invention for achieving the above object uses a plurality of ink jet recording heads for discharging inks having different densities, and uses a plurality of ink jet recording heads for each type of ink on a recording medium. A printing method for performing multi-tone printing by changing the number, wherein a conversion step of converting input data into density data of each pixel in a printing area, a value of density data and a type of ink used for printing Creating an ink distribution table for associating a combination of the number of ink drops and the number of ink droplets; selecting a pixel of interest from the recording area; and ink density for predicting the density of the ink when recording the pixel of interest. A correction range that needs to be corrected in the ink distribution table is calculated from the prediction step and the ink density predicted in the ink density prediction step. A positive range calculating step, and a correction ink distribution table for associating a value of density data within the correction range in the ink distribution table with a combination of the type of ink used for recording and the number of ink droplets. And a combination of a type of ink and the number of ink droplets used when recording the target pixel, and a correction ink distribution table generating step of generating based on the ink density predicted in An ink distribution step of selecting based on the density data of the pixel of interest, and a driving step of generating a drive signal to be transmitted to the recording head according to a combination of the type of ink and the number of ink droplets selected in the ink distribution step. It has.

Further, the object of the present invention is also attained by a storage medium storing a program including each step of the recording method.

That is, a plurality of ink jet recording heads for ejecting inks having different densities are used, and the recording which performs the multi-gradation recording by changing the kind of ink ejected to each pixel on the recording medium and the number of ink droplets. In the apparatus, the input data is converted into density data of each pixel in the printing area, and an ink distribution table is created which associates the value of the density data with a combination of the type of ink used for printing and the number of ink droplets. The target pixel is selected from the recording area, the density of the ink at the time of printing the target pixel is predicted, the correction range that needs to be corrected in the ink distribution table is calculated from the predicted density of the ink, and the correction range in the ink distribution table is calculated. A correction ink distribution table that associates the value of the density data within the correction range with a combination of the type of ink used for recording and the number of ink droplets. And a combination of the type of ink and the number of ink droplets to be used when recording the pixel of interest based on the density data of the pixel of interest from the corrected ink distribution table. A drive signal to be transmitted to the recording head is generated in accordance with a combination of the type of ink selected and the number of ink droplets selected in the ink distribution step.

According to this, even when the recording characteristics such as the ink density change with time, a corrected ink distribution table is created based on the ink density predicted for the correction range that needs to be corrected. By selecting a combination of the type of ink and the number of ink droplets used when recording each target pixel from the correction ink distribution table,
It is possible to reduce the rewriting / updating process of the ink distribution table in the image processing when the ink throat changes.

Therefore, even when the ink density changes, high-quality printing with excellent gradation can be performed without increasing the load of image processing so much.

[0028]

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 following embodiments, for simplicity of description, an ink jet recording apparatus that records a transmission image using an additive ink / film system will be described as an example.

In this specification, the term “record” (also referred to as “print”) refers not only to the formation of significant information such as characters and figures, but also to the meaning of human beings, whether significant or insignificant. Regardless of whether or not the image has been exposed so as to be perceivable, a case where an image, a pattern, a pattern, or the like is widely formed on a recording medium or a medium is processed is also referred to.

Here, the "recording medium" is not limited to paper used in a general recording apparatus, but is widely used for cloth, plastic film, metal plate, glass, ceramics, wood,
A material that can accept ink, such as leather, is also referred to.

Further, “ink” (sometimes referred to as “liquid”) is to be interpreted widely as in the definition of “recording (printing)”, and by being applied on a recording medium, It refers to a liquid that can be used for forming an image, a pattern, a pattern, or the like, processing a recording medium, or processing ink (for example, solidifying or insolubilizing a colorant in ink applied to the recording medium).

First, the additivity and the concentration of the ink used in the following embodiments will be described.

<Additivity> When an ink jet recording apparatus performs recording on a recording medium such as a film for transmission image recording, the ink is ejected a plurality of times onto the same portion when the ink / film system has an additivity. (Overlapping) means that the transmission density increases in accordance with the total ejection amount of the ink.

An example where the additivity holds will be described. As a recording medium, Canon BJ Transparency Film CF-301 was used, and a dye-based C.I. I.
When a 2% solution of Direct Black 19 is uniformly recorded using an inkjet recording apparatus, an image having a transmission density of 0.8D is obtained. I. When a 1% solution of Direct Black 19 is uniformly recorded, an image having a transmission density of 0.4 D is obtained. When the two types of inks are superimposed and recorded, a transmission density of 1.2D can be obtained. 0 to 2.5 for this ink / film system
It has been experimentally confirmed that the additive property is substantially satisfied in the range of D.

In such an ink / film system in which additivity is satisfied, the number of gradations that can be expressed can be significantly increased by over-printing a plurality of inks having different densities on the same pixel.

<Ink Density> Next, in the ink jet recording apparatus according to the present embodiment, six types of inks having different densities satisfying additivity are used, and four inks are applied to the same location on the recording medium.
The overprinting is performed up to the number of times, and the ink density used in such an inkjet recording apparatus will be described below.

In the ink jet recording apparatus as described above, six ink densities D1, D2, D3, D4, D
5, the maximum ratio of D6 is 1: 2: 4: 8: 16: 32, and the maximum number of gradations is 64 by changing the combination of the types of inks that are overprinted on the same location on the recording medium. Can be.

FIG. 3 shows an example of an ink distribution table representing driving data of a recording head for ejecting each ink with respect to density data. This will be described below with reference to FIG.

D1 to d6 are signals (recording data) indicating the presence or absence of ink ejection for the inks D1 to D6 having different ink densities. When the signal is 1, the ink is ejected.
This is a binary signal that means non-ejection that does not eject when it is 0.

For example, if the image density value is 10, it indicates that the inks D2 and D4 are ejected so as to overlap the same location on the recording medium. Here, since the ink density ratio is set to 1: 2: 4: 8: 16: 32, density data from 0 to 63 can be expressed at equal intervals depending on the combination of the presence or absence of ejection of each ink. It is.

That is, as described above, when there are n kinds of ink densities and the recording medium can absorb the ink amount of the n times of overprinting, the density ratio of each ink for expressing the maximum number of gradations is 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 represented as Ds = (1 + 2 +... +2 ^i-1 +... +2 ^n-1 ) + 1 = 2 ⁿ Understand.

In other words, holding n types of inks
, The concentration ratio is 1: 2:. ^i-1:…: 2^n-1In table
Per pixel by combining inks
The maximum number of tones of 2ⁿCan be

[First Embodiment] <Structure of Printing Apparatus> FIG. 1 is a block diagram showing a first embodiment of an ink jet printing apparatus according to the present invention.

In FIG. 1, reference numeral 1 denotes an image input unit such as a scanner, 2 denotes an operation unit having various keys for instructing setting of various parameters and start of recording, and 3 denotes the entire recording apparatus according to various programs in a storage medium. CPU that controls
It is.

Reference numeral 4 denotes a storage medium which stores a program for operating the recording apparatus according to a control program and an error processing program. All the embodiments operate according to this program. As the recording medium 4 for storing the program, ROM, FD, CD-RO
M, HD, memory card, magneto-optical disk, and the like can be used.

In the storage medium 4, reference numeral 4a denotes a gamma correction conversion table referred to in the gamma conversion process, and reference numeral 4b denotes an ink density rise table indicating the increase in the ink density with respect to the non-ejection time, referred to in the process of the density increase correction process. Is a standard ink distribution table referred to in an ink distribution process described later, 4e is an ink distribution table after density change correction for reference in an ink distribution process described later, and 4d is a program group storing various programs. Is shown.

Reference numeral 5 denotes a RAM used as a work area for various programs in the storage medium 4, a temporary save area for error processing, and a work area for image processing. In the present embodiment, it is also possible to copy various tables in the recording medium 4 to the RAM 5, change the contents of the tables, and proceed with image processing while referring to the changed tables.

Reference numeral 6 denotes an image processing system for creating an ejection pattern for realizing multiple gradations using inks of various densities as described above, based on an input image.

Reference numeral 7 denotes a printer unit for forming a dot image based on the ejection pattern created by the image processing unit at the time of recording. Reference numeral 8 denotes a bus line for transmitting address signals, data, control signals, and the like in the apparatus. .

<Image Processing Unit> Next, the processing in the image processing unit 6 will be described with reference to the processing flow and the related configuration shown in FIG.

In the gamma correction processing 11, the image signal CV input to the image input unit 1 is converted into a gamma correction conversion table 4.
The signal is converted into a signal CD representing the density using a and stored in the page memory area of the image processing work area of the RAM 5.

In the target pixel selection 12, one pixel to be processed in the page memory area is selected, and density data CD is obtained.

In the calculation 18 of the density change correction range, the density CD of the target pixel is referred to with reference to the standard ink distribution table 4c.
(A) is obtained. next,
The non-use time of the nozzle is calculated, and by referring to the ink density increase table 4b which is linearly approximated by the least squares calculation, the ink of the darkest density and the ink of the density lower than the highest density which are ejected by the combination of the obtained inks. Determine the density change values and add them.

When the added value is 0, a setting is made so that the standard ink distribution table 4c is referred to in the next ink distribution processing.

When the added value is other than 0, the added value is subtracted from the ink density of the ink combination (A) obtained previously, and the ink combination (B) expressing the density is replaced with the standard ink. Determined by referring to the distribution table.
The combination (B) to (A) is defined as a density change correction range.

In the density change correction processing 13, the combinations of the inks selected in the ink distribution processing 14 are determined by referring to the ink density increase table 4b for the parts (B) to (A) of the ink distribution table 4e. It predicts how much the density will fluctuate with respect to the ideal density, changes and rearranges the threshold according to the combination of inks, and creates (rewrites) the ink distribution table 4e again.

In the ink distribution process 14, the CD of the pixel of interest is
With reference to the ink distribution table 4c rewritten based on the values, a combination of inks expressing the density CD of the target pixel, that is, the print head ejection / non-ejection binary signals d1 to d1 corresponding to the respective density inks. d6 is determined.

In the density error calculation 15, the difference between the density that can be expressed by the combination of inks determined in the density increase correction processing 14 according to the additivity and the CD value of the target pixel is calculated.

In the error diffusion processing 16, the density error calculation 15
The difference calculated in is spread to peripheral pixels on the page memory according to the distribution coefficient.

By performing the above processing, the processing for one pixel of interest ends. Based on the density data CD of the image, the above-described processing from 12 to 16 is repeated for all the pixels, so that the ejection / depth for each pixel is performed for each print head that ejects ink of different density.
Non-ejection binary signals d1 to d6 are formed.

In the printer section 7, ink is ejected from the corresponding ink ejection port array in accordance with the signals d1 to d6 from each ink jet unit to form a multi-tone image. Here, reference numerals 17-1 to 17-6 denote delay circuits, which have a function of setting a timing at which the same pixel is overprinted from each ink ejection row.

<Printer Unit> Next, the printer unit of this embodiment will be described with reference to the external top view of FIG.

On the carriage 20, there are a plurality of ink jet units 21-1 to 21-6. Each ink jet unit 21 has a discharge port array for discharging ink, and the discharge port rows of each ink jet unit 21 are installed at predetermined intervals. The ink to the corresponding nozzle row of each of the inkjet units 21-1 to 21-6 is supplied from the ink cartridge 22,
2-1 to 22-6 are inks D1 having different densities, respectively.
This is an ink cartridge that supplies D2, D3, D4, D5, and D6.

A control signal or the like to the ink jet unit 21 is sent via the flexible cable 23.
A recording medium 24 made of paper, a thin plastic plate, or the like is sandwiched between discharge rollers 25 via a transport roller (not shown), and is sent in the direction of the arrow as the transport motor 26 is driven. The carriage 20 is guided and supported by the guide shaft 27 and the linear encoder 28. The carriage 20 is reciprocated along the guide shaft 27 by driving of a carriage motor 30 via a drive belt 29.

A heating element (electric / thermal energy converter) for generating thermal energy for ink discharge is provided inside the ink discharge port (liquid path) of the ink jet unit 21 described above. In accordance with the read timing of the linear encoder 28, the heating element is driven based on the recording signal, and the inks D1, D2, D3, D4, D5, D6
An image can be formed by flying and adhering ink droplets on the recording sheet in the following order.

At the home position of the carriage 20 set outside the recording area, a recovery unit 32 having a cap portion 31 is installed. When not recording,
The carriage 20 is moved to the home position, and the cap 31-1 to 31-6 of the cap unit 31 seals the corresponding ink ejection port surface of the ink jet unit 21 to fix ink or dust due to evaporation of the ink solvent. To prevent clogging due to the adhesion of foreign substances such as.

The capping function of the cap portion 31 is to discharge ink to the cap portion that is apart from the ink ejection port in order to eliminate ejection failure and clogging of the ink ejection port with a low recording frequency. It is used for discharging or operates a pump (not shown) with the cap capped,
The ink is sucked from the ink discharge port, and is used for recovery of the discharge of the discharge port in which the discharge failure has occurred.

Reference numeral 33 denotes an ink receiver, which performs preliminary ejection toward the ink receiver 33 when each of the ink jet units 21-1 to 21-6 passes above the ink receiver 33 immediately before recording. By disposing a blade (not shown) and a wiping member (not shown) at a position adjacent to the cap portion, it is possible to clean the ink discharge port forming surface of the inkjet unit 21.

<Recording Head> The detailed configuration of the inside of the ink jet unit is disclosed in Japanese Patent Application Laid-Open No. Hei 7-125262, and will not be described. Here, the configuration of the ink discharge port array will be described with reference to FIG. explain.

FIG. 5 shows the ink jet units 21-1 to 21-1.
FIG. 6 is a diagram of an ink ejection port array 21-6 as viewed from a recording material side. In the ink jet unit, 40-1 to 40
Reference numeral -6 denotes an ejection port array for ejecting the inks D1 to D6. The ejection port array of each unit has 256 ejection ports arranged in the sub-scanning direction at a pitch of 600 dots per inch (600 dpi). The four types of inks D1 to D4 are configured to be ejected by being superimposed on the same pixel during one scan, and a high-gradation image can be recorded without increasing the recording time.

<Ink Distribution Table> FIG. 6 shows the inks D1, D2, D3, D4, D5 and D5 with respect to the image signal level.
A standard ink distribution table representing ejection / non-ejection of D6, standard transmission densities of inks D1, D2, D3, D4, D5, and D6, and standard transmission densities in the case of overprinting according to combinations of inks in the distribution table. Is represented.

The image signal level is 8 bits, and a smaller value indicates a lower density and a larger value indicates a higher density. For simplicity of description, the transmission density of a transparent film as a recording medium is set to 0D. Ink D1, D
The standard transmission densities of D2, D3, D4, D5, and D6 are 100% solid recording with each ink alone when there is no increase in the ink concentration at the nozzle tip due to drying of the ink in the ink jet recording apparatus of the present embodiment. Represents the transmission density when the ink D1, D2, D3, D4, D5, D
The concentration ratio of 6 is 1: 2: 4: 8: 16: 32 as described above.
It is.

As described above, in the present embodiment, an 8-bit image signal level is expressed in 64 gradations from the transmission density of 0D to 2.52D.

<Ink Density Rise> FIG. 7 is a graph showing an example of a change in the ink density with respect to the non-ejection time. This graph is a linear approximation of the representative concentration 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 transmission density (OD) of the ink. Here, the non-ejection time refers to the time from the time when one nozzle of the inkjet unit ejects ink to the time when the next ejection is performed.

In this embodiment, the ejection frequency (drive frequency) of the nozzle row of the ink jet unit of the printing apparatus is 1
The case of 0 kHz will be described. In the case of solid recording, 10,000 ink droplets are ejected at a pitch of 600 dpi from the nozzle row of the inkjet unit per second.
The scanning speed of the carriage 20 at that time is about 423.3 mm
/ Sec, and scans the short side of A3 paper in about 0.7 seconds.

As shown in FIG. 7, the short side (297
It has been experimentally confirmed that the ink density used in the present embodiment increases in proportion to the non-ejection time while the carriage 20 scans (mm).

The increase in the ink density during the printing scan is due to the evaporation of the ink solvent at the nozzle tip, but the ink at the nozzle tip whose density has increased after ejection once is ejected again as droplets. Then, since the fresh ink is filled, the 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 converted into the number of non-ejection dots when the ejection frequency is 10 kHz. In the present embodiment, in the ink distribution process for forming a discharge / non-discharge binary signal, an increase in the ink concentration is predicted based on the non-discharge history by referring to the density change graph. Then, by correcting the predicted increase, it is possible to record an image that is not affected by the increase in density.

Specifically, an ink density increase table is created based on FIG. 8 so that the ink density increase can be easily referred to when performing image processing.

For example, as shown in FIG. 8, when the non-ejection period is 5000 dots, the ink density is 150%. Hereinafter, this case will be described as an example.

<Ink Density Increase Table> FIG.
9 is an example of an ink density increase table showing the calculation result of the density increase rate dD shown in FIG.

The contents of FIG. 9 are stored in the area of the ink density increase table 4b in the storage medium 4 shown in FIG. By writing the calculation result in advance in this way, the amount of calculation in image processing can be reduced, and the processing can be speeded up. In this example, the density increase rate dD is 4-byte data, and the address offset of the ink density increase table is every four addresses.

The number of non-ejection dots corresponds to the address offset, and the number of non-ejection dots may be multiplied by four in order to correspond to the address. This value is added to the base address of the ink density increase table, and the address is read to determine the density increase rate. By multiplying the increase rate by the basic density of the ink to be obtained, the ink density at that time can be predicted.

<Details of Image Processing> The configuration example of the image processing unit has been described above with reference to FIG. 2, but here, FIG.
The process up to the generation of the binarized signal indicating the discharge / non-discharge by performing the image processing shown in (1) will be described in more detail with a specific example.

FIG. 10 is a diagram schematically showing the main scanning section of the printer section shown in FIG. (A) is a diagram of the printer unit viewed from above, and (b) is a diagram of the recording medium 24 of (a) viewed from the front.

When the recording start signal is sent to the printer unit,
The carriage 20 on which the inkjet units 21-1 to 21-6 are mounted starts moving in the direction of arrow S from a home position (not shown), and
However, at the time when the carriage passes through the ink receiver 33, the carriage is moving at a constant speed. Each of the ink jet units 21-1, 21-2, 21-3,
It passes in the order of 21-4, 21-5, and 21-6, and performs preliminary ejection to the ink receiver 33 at the position A.

A recordable area is between B and C of the recording medium 24. In this case, recording is started from a position D. Also,
In one scan, the width EF shown in (b) is recorded, the recording medium 24 is fed by the recording width in the direction of arrow F, and the width FG is recorded in the next scan.

The frequency at which the ink jet unit 21 of the recording apparatus discharges ink from the nozzle row is 10 kHz, and the recording density in the main scanning direction is 600 dpi. Than this,
The main scanning speed of the carriage 20 is about 423.3 mm / sec.
c.

It is assumed that the distance from the preliminary ejection position A to the recording start position D is 211.7 mm. In this case, from the main scanning speed, each inkjet unit reaches the recording start position D 0.5 second after the preliminary ejection, and starts recording according to the ejection pattern.

As described above, when the ink is ejected, the ink whose density has increased at the nozzle tip of the ink jet unit jumps out as droplets, so that the ink density at the nozzle tip returns to a normal value.

Here, using the ink distribution table, the ink density, and the overprint density with respect to the density data shown in FIG. 6, the density change of each ink D1, D2, D3, D4, D5, and D6 is shown in FIG. Assuming the characteristics shown in FIG. 8, immediately after the preliminary ejection at the ink receiving position A in FIG. 10, the ink density at the nozzle tip becomes a normal value, that is, the standard transmission density. The concentration at the tip of the nozzle is increased by 50%.

FIG. 11 shows an example of the density signal level of an image stored in the page memory area of the image processing work area of the RAM 5 to be recorded on the recording medium 24 of FIG.

Each symbol corresponds to the symbol in FIG. 10, and one cell corresponds to one pixel of a 600 dpi image to be recorded. The image shown here has a density level of 100 followed by 3 pixels,
This is a pattern in which the density level of 0 is 6 pixels, and thereafter the density level of 100 is continuous. A similar pattern follows below.

Next, in the present embodiment, the relationship between the OD value and the signal level is represented by OD = (2.4 / 255) × image density signal level.

As described above, since the image density signal and the OD value are in a proportional relationship, in actually generating the ejection data for each ink, the ink density is determined not by the OD value but by the digital value of the image density signal level. Perform processing while predicting. That is, a 50% increase in the OD value is defined as a 50% increase in the image density signal level.

On the other hand, as shown in FIG. 8, the density of the ink in the non-ejected nozzles increases by 0.01% every one pixel movement, so that about 10 pixels in the x direction as shown in FIG. In the case of movement, the density increase rate is 0.1%, but is ignored here for the sake of simplicity.

As shown in FIG. 6, D1, D2, D
The standard transmission densities of the inks of D3, D4, D5, and D6 are 4, 8, 16, and 3 at the image density signal level, respectively.
2, 64, 128. Based on this, FIG. 12 shows the table of FIG. 6 in which a threshold value for multi-level error diffusion and a value corresponding to the image density signal level of the standard transmission density of ink are added.

FIG. 13 shows an example of weighting of the distribution of the error of the target pixel to the peripheral pixels in the error diffusion processing 16 performed in this embodiment. In the figure, * (asterisk) indicates a pixel of interest. In the error diffusion processing of the present embodiment, a difference error between the density that can be expressed by a combination of inks and the image density signal level is distributed to peripheral pixels using the error distribution coefficient shown in FIG.

In FIG. 11, the numbers starting from 0 indicated by x and y are the addresses of the pixels.
Indicates the vertical direction, and an arbitrary pixel is represented by (x, y). That is, the pixel (0, 0) indicates the upper left pixel in FIG.
Since the ink jet unit moves in the main scanning direction S, pixels arranged in the same row in the main scanning direction are recorded by the same nozzle in the ink jet unit for each ink density.

Based on the above-described various settings and conditions, specific processing from the target pixel selection 12 to the error diffusion processing 16 in FIG. 2 for each pixel will be described.

First, in the target pixel selection processing 12,
The pixel (0, 0) is selected as the target pixel. Pixel (0,
The density signal level of 0) is 100. Considering the combination of inks based on the ink distribution table including the threshold values of FIG. 12 created based on the standard transmission density of the ink, N
o. A combination of 25 inks D1, D4 and D5 is selected as a candidate.

However, as described above, the inks D1, D2,
D3, D4, D5, and D6 all increase in concentration by 50%, and D1
From 4 to 6, D2 from 8 to 12, D3 from 16 to 2
4, D4 from 32 to 48, D5 from 64 to 96,
D6 is predicted to increase in concentration from 128 to 192,
In the combination of D1, D4 and D5, the target density 10
It becomes 150 which is 50% darker than 0.

For this reason, the ink distribution table is rewritten in the range in which the density increase needs to be corrected in consideration of the ink density increase, and the ink distribution table 4e after the density change correction is created. In the present embodiment, the value of the density change due to the temperature rise of the ink that may be used is calculated as a reference for obtaining the correction range.

Specifically, first, in a density change correction range calculation process 18, a range that needs to be corrected due to an increase in density is calculated. In the ink combination (No. 25) obtained from the ink distribution table of the standard transmission density shown in FIG. 12, the density increase of the ink D5 having the highest density and the inks D4, D3, D2, and D1 having the lower density than the ink D5. Is calculated as a value of the correction range. In this case,
32 + 16 + 8 + 4 + 2 = 62.

If the added value is 0, the standard ink distribution table shown in FIG. 12 is used in the ink distribution processing 13 without performing the density change correction processing 13. Here, since the added value is 62, the temperature change correction processing 13 is performed.

In the temperature change correction process 13, first, in the ink distribution table for the standard transmission density shown in FIG. From the standard transmission density 100 of the ink combination selected from the standard ink distribution table, the value of the correction range 6 calculated above
A combination having the transmission density closest to the value 38 obtained by subtracting 2 is selected from the standard ink distribution table. At this time, when there are two sets, a combination having a low density is selected.

In this case, with respect to the obtained value 38, the standard transmission density 40 becomes No. 4. No. 10 and a standard transmission density of 36 No. 9 was selected, and No. 9 having a low concentration was selected. Nine combinations are selected. This No. No. 9 first selected from the combination of No. 9 Up to 25 combinations are defined as the range in which the correction of the density increase is required.

Then, this No. 9 to No. 9 The ink distribution table 4e after the density change correction is created by adding the increase in the ink density to each combination in the range up to 25. Specifically, the transmission density obtained by adding the increase in density is converted into a density signal conversion value, and the image density signal level for each ink combination is obtained based on the density signal conversion value.
Then, rearrangement is performed in the order of the image density signal levels. After rearranging, the threshold is calculated again.

The ink D obtained by the above processing
FIG. 16 shows the ink distribution table 4e after the density change correction when the ink density of each of D1, D2, D3, D4, D5, and D6 increases by 50%.

In the ink distribution process 14, a combination of inks is selected and determined based on the table shown in FIG. In this case, the combination No. The 17 combinations of the inks D1 and D5 are selected and determined because the density signal level 102 is suitable for expressing the density signal level 100 of the pixel (0, 0).

The ink combination determined at this time is as follows:
The memory Md1, Md2, Md3, Md4, Md5, Md6 are used as binary signal patterns of ejection / non-ejection of each ink.
Is stored at the address corresponding to the pixel of.

In the density error calculation processing 15, a difference error at this time is obtained. Here, the difference is −2 obtained by subtracting the predictable density 102 that can be expressed from the image density signal level 100 of the pixel (0, 0).

In the error diffusion process 16, this value is distributed to surrounding pixels by the error distribution coefficient shown in FIG. That is, -1 for pixel (1,0) and-for pixel (0,1).
0.75 is allocated. An error is added to each target peripheral pixel, and the density signal level of the pixel (1, 0) is 99 and the density signal level of the pixel (0, 1) is 99.
25 is rewritten.

Thus, the processing of the pixel (0, 0) of interest is completed, and the discharge / non-discharge binary signal d1, with respect to the pixel (0, 0) of the inks D1, D2, D3, D4, D5, and D6.
d2, d3, d4, d5, and d6 are determined.

In the next pixel of interest selection process 12, pixel (1, 0) is selected as the pixel of interest. The density signal level of the pixel (1, 0) is 99 due to error diffusion of the pixel (0, 0).

Considering the combination of inks from the ink distribution table including the threshold values at the standard transmission density shown in FIG. A combination of 25 inks D1, D4 and D5 is selected as a candidate.

At this time, the inks D1 and D1 are applied to the pixel (0, 0).
Since No. 5 was used, the ink densities of the inks D1 and D5 are the standard transmission densities of 4 and 64, respectively. Unused inks D2, D3, D4, D6 have a 50% increase in density, D2 from 8 to 12, and D3 from 16 to 2.
4, D4 from 32 to 48, D6 from 128 to 192
The concentration is expected to increase.

In the same manner as described above, in the density change correction range calculation processing 18, a range that needs to be corrected due to an increase in density is calculated. Combination of ink obtained from ink distribution table of standard transmission density shown in FIG. 12 (No. 25)
In step (1), the value of the correction range is calculated by adding the inks D5 having the highest density and the inks D4, D3, D2, and D1 having the lower density. In this case, 0 + 16 + 8 + 4 + 0 = 28.

In the temperature change correction process 13, first, in the ink distribution table for the standard transmission density shown in FIG. From the standard transmission density 100 of the ink combination selected from the standard ink distribution table, the value of the correction range 2 calculated above
The combination whose transmission density is closest to the value 72 obtained by subtracting 8 is selected from the standard ink distribution table. Here, the combination No. 18 is selected.

Then, this No. 18 to No. For each combination in the range up to 25, the transmission density obtained by adding the increase in density is converted into a density signal conversion value, and the image density signal level for each ink combination is obtained based on the density signal conversion value. Then, rearrangement is performed in the order of the image density signal levels. After the rearrangement, the threshold is calculated again to create the ink distribution table 4e after the density change correction.

The ink D obtained by the above processing
FIG. 17 shows the ink distribution table 4e after the density change correction when the densities of 2, D3, D4, and D6 are increased by 50%.

In the ink distribution process 14, a combination of inks is selected and determined based on the table shown in FIG. In this case, the combination No. 22 inks D2,
The combination of D3 and D5 is the density signal level 100
Is selected and determined because it is suitable for expressing the density signal level 99 of the pixel (1, 0).

The ink combination determined at this time is as follows:
The memory Md1, Md2, Md3, Md4, Md5, Md6 are used as binary signal patterns of ejection / non-ejection of each ink.
Is stored at the address corresponding to the pixel of.

In the density error calculation processing 15, a difference error at this time is obtained. Here, the difference is -1 obtained by subtracting the representable predicted density 100 from the image density signal level 99 of the pixel (1, 0).

In the error diffusion processing 16, this value is distributed to surrounding pixels by the error distribution coefficient shown in FIG. That is, −0, 5 is assigned to the pixel (2, 0), −0.375 is assigned to the pixel (1, 1), and −0.125 is assigned to the pixel (0, 1). Surrounding pixels (2,
(0), (1, 1), and (0, 1).

In the next pixel of interest selection processing 12, pixel (2, 0) is selected as the pixel of interest. The density signal level of the pixel (2, 0) is 99.5 due to error diffusion of the pixel (1, 0).

At this time, pixels (0,0) and (1,0)
Since the inks D1, D2, D3, and D5 were used, the ink densities of the inks D1, D2, D3, and D5 were the standard transmission densities. The concentration of inks D4 and D6 is increased by 50%, D4 is increased from 32 to 48, and D6 is increased by 12
The concentration is expected to increase from 8 to 192.

In the same manner as described above, in the density change correction range calculation processing 18, a range that needs to be corrected due to an increase in density is calculated. Combination of ink obtained from ink distribution table of standard transmission density shown in FIG. 12 (No. 25)
In step (1), the value of the correction range is calculated by adding the inks D5 having the highest density and the inks D4, D3, D2, and D1 having the lower density. In this case, 0 + 16 + 0 + 0 + 0 = 16.

In the temperature change correction process 13, first, a range in which the density increase needs to be corrected is obtained in the ink distribution table for the standard transmission density shown in FIG. From the standard transmission density 100 of the ink combination selected from the standard ink distribution table, the value of the correction range 1 calculated above
A combination having the transmission density closest to the value 84 obtained by subtracting 6 is selected from the standard ink distribution table. Here, the combination No. 21 is selected.

Then, this No. 21 to No. 21. For each combination in the range up to 25, the transmission density obtained by adding the increase in density is converted into a density signal conversion value, and the image density signal level for each ink combination is obtained based on the density signal conversion value. Then, rearrangement is performed in the order of the image density signal levels. After the rearrangement, the threshold is calculated again to create the ink distribution table 4e after the density change correction.

The ink D obtained by the above processing
FIG. 18 shows the ink distribution table 4e after the density change correction when the density of D4 and D6 is increased by 50%.

In the ink distribution processing 14, an ink combination is selected and determined based on the table shown in FIG. In this case, the combination No. 23 inks D1,
The combination of D2, D3 and D5 is the density signal level 9
2 is selected and determined because it is suitable for expressing the density signal level 99.5 of the pixel (2, 0).

The ink combination determined at this time is as follows:
The memory Md1, Md2, Md3, Md4, Md5, Md6 are used as binary signal patterns of ejection / non-ejection of each ink.
Is stored at the address corresponding to the pixel of.

In the density error calculation processing 15, a difference error at this time is obtained. Here, a difference 7.5 is obtained by subtracting the representable predicted density 92 from the image density signal level 99.5 of the pixel (2, 0).

In the error diffusion processing 16, this value is distributed to surrounding pixels by the error distribution coefficient shown in FIG. That is, 3.75 is assigned to the pixel (3, 0), 2.8125 is assigned to the pixel (2, 1), and 0.9375 is assigned to the pixel (1, 1). , 0),
An error is added to (2,1) and (1,1). Based on the density signal level of the image, the above-described processing is sequentially repeated in the main scanning direction S to select a pixel of interest, so that a binary signal for each pixel for each pixel with respect to each inkjet unit having a different density. d1, d2, d3, d
4, d5 and d6 are formed, and they are discharge and non-discharge 2
The memory Md1, Md2, Md
3, Md4, Md5, and Md6 are stored at addresses corresponding to the pixels.

As described above, based on the density signal level of the image, the target pixel selection 12 to the error diffusion processing 1
6 are sequentially repeated in the main scanning direction S to select the pixel of interest, so that binary signals d1, d2, d3, and d4 for ejection / non-ejection for each pixel with respect to each inkjet unit having a different density are obtained. These are formed as binary signal patterns of ejection / non-ejection in the memory M
It is stored at an address corresponding to the pixels of d1, Md2, Md3, and Md4.

When the processing of one line in the main scanning direction is completed, the pixel of interest is moved to (0, 1), and the processing is similarly started in the main scanning direction S. At this time, as in the case where the target pixel is (0, 0), the process starts under the expectation that the density of each ink has increased by 50% at the target pixel (0, 1). Hereinafter, the same process is repeated for each line,
An ink ejection / non-ejection pattern is created.

FIG. 14 shows a discharge / non-discharge binary signal pattern (bit plane) Md1 of the inks D1, D2, D3, D4, D5, and D6 created on the memory in this embodiment.
(A), Md2 (b), Md3 (c), Md4 (d),
Md5 (e) and Md6 (f) are shown for two lines in the main scanning direction.

FIG. 15 shows an example in which the combination described above is changed in the basic ink distribution table in consideration of an increase in ink density by the processing described in the above embodiment.
1 shows an input image density signal as density data actually recorded.

As can be seen from the data in this table, an extreme increase in the density especially at the start of writing an image is suppressed as compared with the case where the increase in the density of each ink is not considered.

The storage medium 4 storing the program according to the present invention is supplied to another system or apparatus, and the computer of the system or apparatus reads out and executes the program code stored in the storage medium to execute the present invention. Is achieved.

[Second Embodiment] In the first embodiment, the same density increase table is referred to for four types of inks having different densities, but in the present embodiment, the characteristics and the like of each ink are referred to. , The rate of increase in the density of the plurality of inks is different.

The basic configuration and processing of this embodiment are the same as those of the first embodiment, and only the differences will be described here.

In this embodiment, a plurality of ink density increase tables 4b are prepared. That is, a density change curve as shown in FIG. 7 in the first embodiment is obtained for a plurality of inks having different density increase rates, and an ink density rise table as shown in FIG. It is created for each of the inks having different rise rates and stored in the storage medium 4 as the ink density rise table 4b.

Then, in the density increase correction processing 13,
The ink distribution table 4c is created (rewritten) again with reference to the plurality of ink density increase tables.

The subsequent processing is the same as in the first embodiment.

In the case where the rate of density increase differs for each ink, a separate density increase table may be prepared for each ink.

Further, 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 and saturates, etc. Thus, a density increase curve as shown in FIG. 7 may be obtained, and the relationship may be reflected in the density increase table shown in FIG.

[Modification] In the above embodiment, an example has been described in which an ink density increase table is used to deal with an increase in the ink density. However, the change in the recording characteristics of ink is limited to an increase in the density. is not. In other words, if the recording data indicates a change in the recording characteristics of the ink, it is possible to perform the correction process in the same manner and reproduce the recording data more faithfully.

In the above embodiment, the ink density increasing table 4b and the ink distribution table 4c are stored in the storage medium 4. However, these tables are provided in a rewritable storage medium such as the RAM 5. Then, it is possible to rewrite the characteristic as required.

Further, in this embodiment, the case where the present invention is applied to the ink jet recording apparatus has been described.
The present invention can be applied to other recording apparatuses. For example, even in a thermal sublimation printer and the like, in the case of a printer using a heat generating head, the temperature of the head increases when recording is continued, and the density of a recorded image increases. If the density change table described in the present embodiment is replaced with the relationship between the recording duty and the density increase, an increase in the recording density can be predicted and a correction corresponding thereto can be made.

By correcting the recording parameter table by estimating the change of the recording characteristics of the thermal paper, the ink ribbon, the cartridge film of the thermal sublimation printer, etc. due to the aging, these corrections can be made.

[Other Embodiments] In the above-described embodiments, the means (for example, an electrothermal converter, a laser beam, or the like) for generating thermal energy as energy used for causing ink to be ejected, particularly in an ink jet recording system, is used. ), And by using a method in which a change in the state of the ink is caused by the thermal energy, it is possible to achieve higher density and higher definition of recording.

The typical configuration and principle are described in, for example, US Pat. Nos. 4,723,129 and 4,740.
It is preferable to use the basic principle disclosed in the specification of Japanese Patent No. 796. This method is applicable to both on-demand type and continuous type. In particular, in the case of the on-demand type, liquid (ink)
By applying at least one drive signal corresponding to the recorded information and providing a rapid temperature rise exceeding the nucleate boiling to the electrothermal transducer arranged corresponding to the sheet or the liquid path in which Since thermal energy is generated in the electrothermal transducer and film boiling occurs on the heat-acting surface of the recording head, bubbles in the liquid (ink) corresponding to this drive signal on a one-to-one basis can be formed. It is valid.

The liquid (ink) is ejected through the ejection opening by the growth and contraction of the bubble to form at least one droplet. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of a liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable.

As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further, if the conditions described in US Pat. No. 4,313,124 relating to the temperature rise rate of the heat acting surface are adopted, more excellent recording can be performed.

As the configuration of the recording head, in addition to the combination of a discharge port, a liquid path, and an electrothermal converter (a linear liquid flow path or a right-angled liquid flow path) as disclosed in the above-mentioned respective specifications, The configurations described in U.S. Pat. No. 4,558,333 and U.S. Pat. No. 4,459,600, which disclose the configuration in which the heat acting surface is arranged in the bending region, are also included in the present invention. In addition, Japanese Unexamined Patent Application Publication No. 59-123670 discloses a configuration in which a common slot is used as a discharge portion of an electrothermal transducer for a plurality of electrothermal transducers, or an opening for absorbing a pressure wave of thermal energy is discharged. A configuration based on JP-A-59-138461, which discloses a configuration corresponding to each unit, may be adopted.

Further, as a full-line type recording head having a length corresponding to the width of the maximum recording medium that can be recorded by the recording apparatus, the length is determined by combining a plurality of recording heads as disclosed in the above specification. This may be either a configuration satisfying the above requirements or a configuration as a single recording head formed integrally.

In addition to the cartridge type recording head in which the ink tank is provided integrally with the recording head itself described in the above embodiment, the recording head is electrically connected to the apparatus main body by being mounted on the apparatus main body. A replaceable chip-type recording head, which enables a simple connection and supply of ink from the apparatus main body, may be used.

It is preferable to add recovery means for the printhead, preliminary auxiliary means, and the like to the configuration of the printing apparatus described above, since the printing operation can be further stabilized. Specific examples thereof include capping means for the recording head, cleaning means, pressurizing or suction means, preheating means using an electrothermal transducer or another heating element or a combination thereof. It is also effective to provide a preliminary ejection mode for performing ejection that is different from printing, in order to perform stable printing.

Further, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but may be a single recording head or a combination of plural recording heads. Alternatively, the apparatus may be provided with at least one of full colors by color mixture.

Even if the present invention is applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine, a facsimile, etc.) Device).

An object of the present invention is to supply a storage medium (or a recording 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 a computer (a computer) of the system or the apparatus. It is needless to say that the present invention can also 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. Also,
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also the operating system (OS) running on the computer based on the instructions of the program code.
It goes without saying that a case where the functions of the above-described embodiments are implemented by performing some or all of the actual processing, and the processing performs the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the program code is read based on the instruction of the program code. Needless to say, the CPU included 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.

When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the above-described processing procedures (shown in FIG. 2).

[0166]

As described above, according to the present invention, even when the ink concentration changes with time, each of the ink concentrations can be adjusted based on the predicted ink concentration without increasing the load of image processing so much. By selecting a combination of the type of ink and the number of ink droplets used when printing the target pixel, it becomes possible to perform high-quality printing with excellent gradation.

This is particularly effective when the type of ink used is large and the number of gradations is large, since the process of rewriting the ink distribution table is significantly reduced.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a flow of image processing in the embodiment of FIG.

FIG. 3 is a diagram illustrating an example of an ink distribution table in the embodiment of FIG. 1;

FIG. 4 is a diagram illustrating a main configuration of a printer unit in the embodiment of FIG.

FIG. 5 is a diagram illustrating an arrangement of ink ejection port arrays in the embodiment of FIG. 1;

FIG. 6 is a diagram showing an example of a table in which ink density and overprinted density data are added to the ink distribution table of FIG. 3;

FIG. 7 is a graph showing the relationship between non-ejection time and ink density.

FIG. 8 is a graph showing the relationship between the number of non-ejection dots and ink density.

FIG. 9 is a diagram illustrating an example of an ink density increase table in the embodiment of FIG. 1;

FIG. 10 is a diagram illustrating a recording example by the printer unit of the embodiment of FIG. 1;

11 is a diagram showing an example of a density signal level of an image stored in a work area of a RAM 5 in the embodiment of FIG.

12 is a diagram illustrating an example in which a threshold value of multi-level error diffusion and image density signal level data of ink transmission crush degree are added to the ink distribution table of FIG. 6;

FIG. 13 is a diagram illustrating an example of weighting of distribution of an error of a target pixel to peripheral pixels in the embodiment of FIG. 1;

14 is a diagram showing a binary signal pattern of ejection / non-ejection of each ink created on the memory of the embodiment of FIG. 1;

15 is a diagram illustrating an example of density data in which the image density signal of FIG. 11 is actually recorded in the embodiment of FIG. 1;

FIG. 16 is a diagram illustrating an example in which each ink density is increased by 50% with respect to the table of FIG. 12;

FIG. 17 shows D2, D3, D
FIG. 4 is a diagram illustrating an example when the ink density of D4 and D6 increases by 50%.

18 is a diagram illustrating an example in which the ink densities of D4 and D6 are increased by 50% with respect to the table of FIG.

[Explanation of symbols]

 Reference Signs List 1 image input unit 2 operation unit 3 CPU 4 storage medium 4a gamma correction conversion table 4b ink density rise table 4c standard ink distribution table 4d control program group 4e ink distribution table after density change correction 5 RAM 6 image processing unit 7 printer unit 11 Gamma correction processing 12 Target pixel selection 13 Density increase correction processing 14 Ink distribution processing 15 Error calculation 16 Error diffusion processing 17-1 to 17-4 Delay circuit 18 Calculation of density change correction range 20 Carriage 21-1 to 21-4 Inkjet Units 22-1 to 22-4 Ink cartridge 23 Flexible cable 24 Recording medium 25 Discharge roller 26 Transport motor 27 Guide shaft 28 Linear encoder 29 Drive belt 30 Carriage motor 31-1 to 31-4 Cap 32 Recovery unit Tsu door 33 ink received 40 outlet row

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C056 EA04 EB38 EB41 EB59 EC28 EC76 ED03 ED07 FA03 FA10 2C057 AF39 AG12 AG46 AH13 AL37 AL40 AM40 AN01 CA04 CA07

Claims (15)

[Claims] 2. Description of the Related Art A plurality of ink jet recording heads for discharging inks having different densities are used to perform multi-tone recording by changing the type of ink and the number of ink droplets discharged to each pixel on a recording medium. A conversion unit for converting input data into density data of each pixel in a printing area; and an ink for associating a value of the density data with a combination of the type of ink used for printing and the number of ink droplets. A distribution table; selecting means for selecting a pixel of interest from the recording area; ink density estimating means for estimating the density of the ink at the time of printing the pixel of interest; and an ink density estimating means for estimating the ink density. Correction range calculating means for calculating a correction range that requires correction in the ink distribution table from the density; A correction ink distribution table is created based on the density of the ink predicted by the ink density prediction means, in which the density data within the positive range is associated with a combination of the type of ink used for recording and the number of ink droplets. Correction ink distribution table creating means; and ink distribution for selecting a combination of the type of ink and the number of ink droplets used when recording the target pixel based on the density data of the target pixel from the correction ink distribution table. And a drive unit for generating a drive signal to be transmitted to the printhead in accordance with a combination of the type of ink and the number of ink droplets selected by the ink distribution unit. 2. The recording apparatus according to claim 1, wherein said ink density estimating means estimates the density of each ink based on the time elapsed since each recording head ejected ink. 3. The recording apparatus according to claim 1, wherein the ink density estimating unit estimates the density of the ink based on a density change characteristic table stored in a predetermined area. 4. The recording apparatus according to claim 3, further comprising the density change characteristic table for each of the inks having different densities. 5. The density change characteristic table stored in a rewritable area.
The recording device according to claim 1. 6. A density difference calculating means for calculating a difference between density data of the pixel of interest and a density recorded according to the type of ink and the number of ink droplets selected by the ink distributing means; 6. An apparatus according to claim 1, further comprising error diffusion means for diffusing the difference in density calculated by the means into density data of pixels surrounding the pixel of interest based on a predetermined error diffusion method. The recording device according to claim 1. 7. The correction range calculation means selects a first combination corresponding to the density data of the pixel of interest in the ink distribution table, and selects the ink having the highest density in the first combination and the plurality of inks. In the ink of the above, the value of the density change of each ink whose density is lower than that of the ink is obtained and added, and a value obtained by subtracting the added value from the density by the combination is obtained. 7. The recording according to claim 1, wherein a second combination to be performed is obtained, and a range from the first combination to the second combination is set as the correction range. 8. apparatus. 8. When the added value is 0, the correction ink distribution table creation means does not create the correction ink distribution table, and the ink distribution means sets the ink used for recording the pixel of interest. 8. The recording apparatus according to claim 1, wherein a combination of the type and the number of ink drops is selected from the ink distribution table. 9. The recording head according to claim 1, wherein the recording head ejects ink by using thermal energy, and includes a thermal energy converter for generating thermal energy to be applied to the ink. Item 9. The recording device according to any one of Items 1 to 8. 10. A printing method in which a plurality of ink jet printing heads for discharging inks having different densities are used, and the type of ink and the number of ink droplets discharged to each pixel on a printing medium are changed to perform multi-tone printing. A method of converting input data into density data of each pixel in a printing area, and an ink for associating a value of the density data with a combination of the type of ink used for printing and the number of ink droplets. A step of creating a distribution table; a selecting step of selecting a target pixel from the recording area; an ink density predicting step of predicting the density of the ink when the target pixel is printed; and an ink density predicting step. A correction range calculating step of calculating a correction range that needs to be corrected in the ink distribution table from the density of the ink, A correction ink distribution table that associates the value of the density data within the correction range with the combination of the type of ink and the number of ink droplets used for recording based on the ink density predicted in the ink density prediction step. And selecting a combination of the type of ink and the number of ink droplets to be used when recording the target pixel based on the density data of the target pixel from the correction ink distribution table. And a driving step of generating a driving signal to be transmitted to the recording head in accordance with a combination of the type of ink and the number of ink droplets selected in the ink distributing step. Method. 11. The recording method according to claim 10, wherein in the ink density prediction step, the density of each ink is predicted based on an elapsed time after each recording head discharges ink. 12. A density difference calculating step of calculating a difference between density data of the pixel of interest and a density recorded according to the type of ink and the number of ink droplets selected in the ink distribution step; 12. An error diffusion step of diffusing the density difference calculated in the step to density data of pixels around the target pixel based on a predetermined error diffusion method. Recording method. 13. The correction range calculating step includes selecting a first combination corresponding to the density data of the pixel of interest in the ink distribution table, and selecting the ink having the highest density in the first combination and the plurality of inks. In the ink of the above, the value of the density change of each ink whose density is lower than that of the ink is obtained and added, and a value obtained by subtracting the added value from the density by the combination is obtained. 13. A second combination to be determined, and a range from the first combination to the second combination is set as the correction range.
The recording method according to any one of the above items. 14. When the value added is 0,
The correction ink distribution table is not created in the correction ink distribution table creation step. In the ink distribution step, a combination of the type of ink and the number of ink droplets used when recording the target pixel is determined from the ink distribution table. 14. The recording method according to claim 10, wherein the recording method is selected. 15. A method of performing multi-tone printing by using a plurality of ink jet print heads that discharge inks having different densities and changing the type of ink and the number of ink droplets discharged to each pixel on a print medium. A storage medium storing a program of an apparatus, the program comprising: a conversion step of converting input data into density data of each pixel in a printing area; and a density data value and a type of ink used for printing. A step of creating an ink distribution table that associates a combination of the number of ink droplets; a step of selecting a target pixel from the recording area; and an ink density prediction for predicting the density of the ink when the target pixel is recorded. And a correction range that needs to be corrected in the ink distribution table from the ink density predicted in the ink density prediction step. A correction range calculating step of calculating the density distribution data within the correction range in the ink distribution table and a combination of the type of ink used for recording and the number of ink droplets. A correction ink distribution table creation step for creating based on the ink density predicted in the density prediction step, and a combination of the type of ink and the number of ink droplets used when recording the target pixel, An ink distribution step of selecting from the table based on the density data of the target pixel; and a drive signal to be transmitted to the recording head in accordance with a combination of the type of ink and the number of ink droplets selected in the ink distribution step. And a driving step.